a speech by Daniela Corsini

Abstract

In 2020, the Covid-19 epidemic disrupted global supply chains and boosted demand for safe-haven assets. In 2021, the global gold market should benefit from a rebound in jewelry demand and a supportive macroeconomic environment amid expansionary monetary policies, low interest rates and a pick-up in inflation expectations.

Commodities: hit by Omicron and monetary policies

The negative impact of the Omicron variant and the threat of more restrictive monetary policies now represent the worst headwinds for commodity markets and could trigger deeper corrections in market prices in the near term. However, temporarily weaker commodity prices would clearly benefit the global economy, contributing to an acceleration in growth rates, and simplify the task of the main central banks, which could continue supporting the global recovery instead of fighting commodity-driven inflationary pressures.

The macroeconomic outlook remains weaker than earlier expected due to persistently high inflation pressures, and concerns about a quicker than earlier expected pace of tightening from the Federal Reserve. In addition, the unexpected spread of the Omicron variant forced downward revisions to estimates about global commodity demand, further delaying the recovery in some sectors, like the aviation industry, or worsening the prospects of global supply chains due to the persistent threat of logistic bottlenecks and lockdowns.

In our opinion, the negative impact of the Omicron variant and the threat of more restrictive monetary policies now represent the worst headwinds for commodity markets and could trigger deeper corrections in market prices in the near term.

However, temporarily weaker commodity prices would clearly benefit the global economy, contributing to an acceleration in growth rates, and simplify the task of the main central banks, which could continue supporting the global recovery instead of fighting commodity-driven inflationary pressures.

According to our baseline scenario, after a probable, deeper correction in early 2022, most commodities could resume a path of modest price increases. In fact, market prices of crude oil and non-ferrous metals could recover part of the lost ground as soon as central banks reassure markets and global economic growth consolidates.

In 2022, specific supply and demand fundamentals should come back as core drivers of commodity prices, prevailing over macroeconomic factors, and volatility should be mainly fuelled by news flows about supply disruptions, delays across the logistic chains and forecasts about future consumption patterns, especially in China.

In the medium- and long-term, we still forecast a bullish trend for industrial metals, while natural gas and energy prices should gradually decrease, maintaining their usual seasonal swings.

Forecasts for the commodities universe

Crude oil. Given the recent weakening in crude oil supply and demand fundamentals and concerns about a quicker pace toward restrictive monetary policies, we revised downwards our estimates for crude prices in 2022. In our opinion, a temporary correction could push Brent near an average of USD 65 in 1Q22. Then, upward pressures on crude prices could resume strength driven by more optimistic forecasts about global crude demand, thanks to a seasonal increase in fuel consumption and, hopefully, easing concerns about the development of the epidemic. Thus, we envisage a rising trend in crude prices from the 2Q22 onwards. In our baseline scenario, we now forecast that on average Brent should record a level of USD 67.5 in 2022 and USD 70 in 2023. Volatility should remain an important market feature and will often contribute to amplify intra-day market movements.

Energy. Although the extreme conditions faced by global gas and power markets ahead of the 2021/22 winter are unlikely to repeat every year, we can expect further moments of market stress and more volatility on energy prices, as the necessary and ineluctable transition toward cleaner energy sources proceeds and the penetration of renewable energies progresses.

Precious metals. In 2021, all the main precious metals have fallen in price. We maintain a negative view on both gold and silver, as we think that the headwinds of more restrictive monetary policies will continue to weaken appetite for both metals on financial markets. On the contrary, we now expect that platinum and palladium could recover part of their recent losses, as demand from the automotive sector should pick up thanks to the easing semiconductor shortage.

Industrial metals. After the unexpected spread of the Omicron variant and talks about a quicker pace of tightening from the Federal Reserve, the risk of a deeper correction in most industrial metals’ prices intensified and now we see lower prices in 1Q22. However, later in 2022 specific supply and demand fundamentals should come back as core drivers of metals’ prices, and non-ferrous metals’ prices should recover ground. In the medium- and long-term, we still forecast a bullish trend for industrial metals.

Agricultural products. Agriculture is the most supply-elastic commodity sector. Thus, the high prices recorded in 2021 should contribute to expand supplies in 2022, when possible, and could trigger widespread price declines in anticipation of the next harvest season. However, unusual weather patterns remain the most worrying threat and could fuel volatility due to deeper and less predictable impacts of climate change and global warming on the sector.

Precious metals: we favour palladium vs. gold

In 2021, all the main precious metals have fallen in price. We maintain a negative view on both gold and silver, as we think that the headwinds of more restrictive monetary policies will continue to weaken appetite for both metals on financial markets. On the contrary, we now expect that platinum and palladium could recover part of their recent losses, as demand from the automotive sector should pick up thanks to the easing semiconductor shortage. Thus, in a medium-term strategic asset allocation we would favour palladium vs. gold.

In 2021, all the main precious metals have fallen in price. Gold and silver suffered downward pressures due to a stronger U.S. dollar and announcements from the main central banks anticipating tighter monetary policies. In fact, expectations of higher rates discourage investments in gold and other non-interest-bearing assets as they increase their opportunity cost. We maintain a negative view on both metals, as we think that the headwinds of more restrictive monetary policies will continue to weaken appetite for gold on financial markets. Currently, silver isn’t strong enough to decouple from gold despite the promising fundamentals in the long term.

In the second half, platinum and palladium prices also dropped, as the global shortage of semiconductors had a deeper than expected negative impact on global vehicle production and thus on consumption of both metals. Prices probably bottomed and we now expect that platinum and palladium could recover part of their recent losses, as demand from the automotive sector should pick up thanks to the easing semiconductor shortage.

In our baseline scenario, we envisage a consolidation in global growth and a gradual easing of bottlenecks and semiconductor shortage. Monetary policies should tighten, but remain supportive of the global economic recovery as long as necessary. Thus, in a medium-term strategic asset allocation we would favour palladium vs. gold.

Gold

The latest data published by the World Gold Council (WGC) show that appetite for gold on financial markets further deteriorated during 3Q21 as monetary policies were tightening and the Fed progressed toward the planned tapering.

Considering ETFs’ holdings as a proxy for gold appetite on financial markets, at the end of September global holdings were close to 3,600 tons, as the sector had recorded outflows worth about 156 tons since January 2021, the largest decline since 2013. In 3Q21, ETFs’ gold holdings decreased by about 27 tons, thus ETFs’ contribution to gold demand turned negative during the quarter, representing a net loss worth about 2% of global demand. It is a remarkable change in market sentiment, when considering that ETFs’ flows were a positive contributor worth about 4% of global consumption in 2Q21 and covered a stunning 40% of demand in 2Q20.

Given the relevance of ETFs’ flows, in 3Q21 global gold demand contracted by 7% y/y, although all non-financial components of gold demand rose. In fact, a recovery in global economic growth boosted gold consumption in the jewellery (+33% y/y) and technology sectors (+7% y/y), while higher saving rates, concerns about inflation risks and uncertainty about epidemiological developments fuelled demand for bars and coins (+18% y/y). In the official sector, a renewed appetite in diversifying official reserves supported gold demand. In fact, central banks turned from net sellers of gold in 3Q20 to net buyers of the precious metal in 3Q21.

Given the current expectations of tighter monetary policies and still robust global growth, over the next quarters the non-financial components of gold demand may extend their recovery, and we envisage higher purchases from the jewellery, technology and official sectors. On the contrary, gold-backed ETFs could suffer from more outflows due to an increase in the opportunity cost of holding gold, amid expectations of higher yields and threats of higher benchmark interest rates.

According to our baseline model, we forecast that gold could average about USD 1,770 in 1Q22 and could decline toward a USD 1,720 average in 2022. Despite the unfavourable monetary framework, we envisage only moderate downside pressures on gold prices thanks to the important support of the ongoing recovery in the jewellery sector, which should gain support from global growth, and of the official sector, as central banks could take advantage of lower gold prices to diversify their reserves. In addition, inflation concerns could limit the volumes of ETFs’ outflows.

Given the exceptionally high level of uncertainty that clouds the macroeconomic framework due to unpredictable development in epidemiological risks, record high energy prices and persistent bottlenecks negatively affecting logistic chains and manufacturing activities, our forecasts remain subject to significant risks.

The worst-case scenario for gold would be a macroeconomic environment characterized by a further acceleration in global growth, thanks to fading epidemiologic concerns, easing bottlenecks and a strong commitment from central banks to intervene and prevent the economy from overheating. In fact, under this scenario investors would favour cyclical assets against safe haven assets, while higher interest rates would also discourage gold holdings. Under such worst-case scenario, gold could quickly drop toward a USD 1,450 support.

On the contrary, the best-case scenario for gold would be a macroeconomic environment characterized by a deterioration in the prospects for global growth, possibly driven by a spreading epidemic coupled with scarcely effective vaccines. Central banks would be forced to postpone a planned tightening of monetary conditions in an effort to support their economies, while bottlenecks to logistic and supply chains would persist, fuelling inflation pressures. Under such extreme scenario of stagflation, gold could retest its peaks above USD 2,000.

Silver

According to our baseline model, silver should trade close to an average price of USD 24 an ounce both in 1Q22 and in 2022. We expect that the metal could remain most of the time in a trading range between USD 21 and USD 27 an ounce.

Relative to gold, silver should maintain higher volatility, but it will not probably be strong enough to decouple from the yellow metal. Thus, silver will probably follow gold’s downward trajectory over the next years despite positive fundamentals and expectations of expanding global demand, especially in green technologies.

We expect that the gold/silver ratio could remain slightly above its long-term average over the next years, as the long-term positive correlation between silver and gold should remain significant, despite the support granted to silver by the green transition.

Platinum and palladium

Our forecasts for platinum-group metals (PGM) are strictly connected with expectations about a possible recovery in the automotive sector and thus with developments in the semiconductor crisis. In fact, according to estimates from Johnson Matthey, about 85% of palladium demand comes from autocatalysis mainly used in vehicles mounting gasoline-powered engines, while more than 30% of platinum demand comes from autocatalysis mainly used in vehicles mounting diesel-powered engines.

In 2021, PGM have gone through a boom and bust cycle. In fact, in the first half platinum and palladium overperformed other precious metals because car manufacturers quickly expanded their purchases to restock their warehouses and satisfy new vehicle orders, despite the first signs of disruptions to global supply chains due to semiconductors’ shortage.

Then, as time passed, and the global recovery consolidated, semiconductor scarcity deepened and forced car manufacturers to scale down their output plans and even halt some production facilities. As a consequence, PGM demand faded. Several car producers revised downwards their output guidance, fuelling pessimism on financial markets and raising doubts about future consumption growth for platinum and palladium in the sector.

Now, car producers are probably adequately supplied to meet their medium-term needs of PGM. Thus, so far low prices have failed to attract consumers due to still uncertain estimates about future vehicle production. In the longer term, although we still see ample room for a recovery in prices, probably the upward potential for PGM prices has been structurally lowered by the semiconductor crisis, as the current delays in PGM consumption patterns imply more time for global PGM supply to satisfy demand and more time for secondary supply to flow back in the market thanks to a pick-up in recycling activities.

Our baseline scenario now assumes an average platinum price of USD 1,025 an ounce and an average palladium price of USD 2,000 an ounce in 1Q22. We forecast that in 2022 platinum could trade near a USD 1,075 average and palladium near a USD 2,050 average.

In our opinion, palladium probably bottomed in late November, as USD 1,700 should represent a strong support for the metal. On the contrary, the USD 950 low reached in November is a weaker support for platinum, and we see the level of USD 900 as a more solid floor.

We maintain a bullish view in the long term (albeit forecast numbers have been revised downward from previous forecasts due to longer and deeper than expected disruptions along the supply chain) because we expect that the semiconductor crisis could ease in 2022, following plans to expand the global output of microchip, and both vehicle production and global demand for PGM should pick up.

Appendix

Analyst Certification

The financial analysts who prepared this report, and whose names and roles appear on the first page, certify that:
(1) The views expressed on companies mentioned herein accurately reflect independent, fair and balanced personal views;
(2) No direct or indirect compensation has been or will be received in exchange for any views expressed.

Specific disclosures

The analysts who prepared this report do not receive bonuses, salaries, or any other form of compensation that is based upon specific investment banking transactions.

Important Disclosures

This research has been prepared by Intesa Sanpaolo S.p.A. and distributed by Intesa Sanpaolo SpA-London Branch (a member of the London Stock Exchange) and Intesa Sanpaolo IMI Securities Corp (a member of the NYSE and FINRA). Intesa Sanpaolo S.p.A. accepts full responsibility for the contents of this report. Please also note that Intesa Sanpaolo S.p.A. reserves the right to issue this document to its own clients. Intesa Sanpaolo S.p.A. is authorised by the Banca d’Italia and is regulated by the Financial Conduct Authority in the conduct of designated investment business in the UK and by the SEC for the conduct of US business.
Opinions and estimates in this research are as at the date of this material and are subject to change without notice to the recipient. Information and opinions have been obtained from sources believed to be reliable, but no representation or warranty is made as to their accuracy or correctness.
Past performance is not a guarantee of future results.
This report has been prepared solely for information purposes and is not intended as an offer or solicitation with respect to the purchase or sale of any financial products. It should not be regarded as a substitute for the exercise of the recipient’s own judgement.
No Intesa Sanpaolo S.p.A. entity accepts any liability whatsoever for any direct, consequential or indirect loss arising from any use of material contained in this report.
This document may only be reproduced or published with the name of Intesa Sanpaolo S.p.A..
This document has been prepared and issued for, and thereof is intended for use by, Companies which have suitable knowledge of financial markets, which are exposed to the volatility of interest rates, exchange rates and commodity prices and which are capable of evaluating risks independently.
Therefore, such materials may not be suitable for all investors and recipients are urged to seek the advice of their relationship manager/independent financial advisor for any necessary explanation of the contents thereof.
Person and residents in the UK: this document is not for distribution in the United Kingdom to persons who would be defined as private customers under rules of the FCA.
US persons: this document is intended for distribution in the United States only to Major US Institutional Investors as defined in SEC Rule 15a-6. US Customers wishing to effect a transaction should do so only by contacting a representative at Intesa Sanpaolo IMI Securities Corp. in the US (see contact details below).
Intesa Sanpaolo S.p.A. issues and circulates research to Major Institutional Investors in the USA only through Intesa Sanpaolo IMI Securities Corp., 1 William Street, New York, NY 10004, USA, Tel: (1) 212 326 1199.

Inducements in relation to research

Pursuant to the provisions of Delegated Directive (EU) 2017/593, this document can be qualified as an acceptable minor non-monetary benefit as it is:
– macro-economic analysis or Fixed Income, Currencies and Commodities material made openly available to the general public on the Bank’s website – Q&A on Investor Protection topics – ESMA 35-43-349, Question 8 & 9.

Method of distribution

This document is for the exclusive use of the recipient with whom it is shared by Intesa Sanpaolo and may not be reproduced, redistributed, directly or indirectly, to third parties or published, in whole or in part, for any reason, without prior consent expressed by Intesa Sanpaolo.
The copyright and all other intellectual property rights on the data, information, opinions and assessments referred to in this information document are the exclusive domain of the Intesa Sanpaolo banking group, unless otherwise indicated. Such data, information, opinions and assessments cannot be the subject of further distribution or reproduction in any form and using any technique, even partially, except with express written consent by Intesa Sanpaolo.
Persons who receive this document are obliged to comply with the above indications.

Valuation Methodology

This document has been prepared in accordance with the following method.

Macroeconomic Data
Comments on macroeconomic data are prepared based on macroeconomic and market news and data available via information providers such as Bloomberg and Refinitiv-Datastream. Macroeconomic and interest rate forecasts are prepared by the Intesa Sanpaolo Research Department, using dedicated econometric models. Forecasts are obtained using analyses of historical-statistical data series made available by the leading data providers and also on the basis of consensus data, taking account of appropriate connections between them.

Forecasts in the Energy Sector
Comments on the Energy Sector are prepared based on macroeconomic and market news and data available via information providers such as Bloomberg and Refinitiv-Datastream. Unless otherwise stated, consensus estimates come from the leading international energy Agencies, primarily the IEA (International Energy Agency – which deals with this sector on a global scale), the EIA (Energy Information Administration – an institute that deals specifically with the US energy sector) and OPEC. Forecasts are prepared by the Intesa Sanpaolo Research Department, using dedicated models.

Forecasts in the Metals Sector
Comments on the Metals Sector are prepared based on macroeconomic and market news and data available via information providers such as Bloomberg and Refinitiv-Datastream.
Unless otherwise specified consensus estimates on precious metals come mainly from GFMS, the long-established forecasting agency based in London. The forecasts cover gold, silver, platinum and palladium. Forecasts are prepared by the Intesa Sanpaolo Research Department, using dedicated models.
Unless otherwise stated, consensus estimates for industrial metals come mainly from Brook Hunt, an independent forecasting agency which has prepared statistics and predictions on metals and minerals since 1975, and from the World Bureau of Metal Statistics (WBMS), an independent research body on the global market of industrial metals which publishes a series of monthly, quarterly and annual statistical analyses. Forecasts are prepared by the Intesa Sanpaolo Research Department, using dedicated models.

Forecasts in the Agricultural Sector
Comments on the Agricultural Sector are prepared based on macroeconomic and market news and data available via information providers such as Bloomberg and Refinitiv-Datastream.
There are several consensus estimates on agricultural products. Each individual country has its own internal statistics agency that estimates and forecasts crops, production capacity, the product supply quantities and, above all, the amount of land available for cultivating a particular product, in both absolute and percentage terms.
At an international level, the main agencies are: the USDA (United States Department of Agriculture) which, in addition to providing data on the US territory, also deals in general with the grain industry worldwide through the FAS (Foreign Agricultural Service); the Economist Intelligence Unit of the Economist Group which deals with all agricultural products on a global scale; and CONAB (Companhia Nacional de Abastecimento), the Brazilian Government agency that deals with agriculture (with a particular focus on coffee) and which also provides some insight into the entire South America.
Forecasts are prepared by the Intesa Sanpaolo Research Department, using dedicated models.

Technical levels
Comments on technical levels are based on market news and data available via information providers such as Bloomberg and Refinitiv-Datastream. Interest rate technical level forecasts are prepared by the Intesa Sanpaolo Research Department, using dedicated technical models. Forecasts are obtained using analyses of historical-statistical data series made available by the leading data providers and also on the basis of consensus data, taking account of appropriate connections between them. There is also a further in-depth study linked to the choice of appropriate derivatives that best represent the sector or the specific commodities on which one intends to invest.

Recommendations
Negative Outlook: a Negative Outlook recommendation for a sector is a wide-ranging indication. It not only indicates deteriorating price conditions of the indices or futures that best represent the commodity in question (thus the reduction of a price performance), but it also implies the deterioration in the forecasts on production, weather and input supplies (like water or energy) that characterize these sectors more than other financial instruments.
Neutral Outlook: a Neutral Outlook recommendation for a sector is an indication that includes a multitude of aspects. It indicates that the combination of price forecasts of indices and futures and all the conditions of production, weather and input supplies (like water or energy) will lead to a sideways movement in prices or inventories or production capacity, recording, therefore, void or minimum performances for the sector under examination.
Positive Outlook: a Positive Outlook recommendation for a sector is an indication covering a wide range of areas. It not only indicates net improvements in price conditions of the indices or futures that best represent the commodity in question (thus a positive price performance), but it also implies the improvement in the forecasts on production, weather and input supplies (like water or energy) that characterize these sectors more than other financial instruments.

Frequency and validity of forecasts

Market indications refer to a short period of time (the same day or the following days, unless stated otherwise in the text). Forecasts are developed over a time span of between one week and 5 years (unless specified otherwise in the text) and have a maximum validity of three months.

Disclosure of potential conflicts of interest

Intesa Sanpaolo S.p.A. and the other companies belonging to the Intesa Sanpaolo Banking Group (jointly also the “Intesa Sanpaolo Banking Group”) have adopted written guidelines “Organisational, management and control model” pursuant to Legislative Decree 8 June, 2001 no. 231 (available at the Intesa Sanpaolo website, webpage https://group.intesasanpaolo.com/en/governance/leg-decree-231-2001) setting forth practices and procedures, in accordance with applicable regulations by the competent Italian authorities and best international practice, including those known as Information Barriers, to restrict the flow of information, namely inside and/or confidential information, to prevent the misuse of such information and to prevent any conflicts of interest arising from the many activities of the Intesa Sanpaolo Banking Group which may adversely affect the interests of the customer in accordance with current regulations.
In particular, the description of the measures taken to manage interest and conflicts of interest – related to Articles 5 and 6 of the Commission Delegated Regulation (EU) 2016/958 of 9 March 2016 supplementing Regulation (EU) No. 596/2014 of the European Parliament and of the Council with regard to regulatory technical standards for the technical arrangements for objective presentation of investment recommendations or other information recommending or suggesting an investment strategy and for disclosure of particular interests or indications of conflicts of interest as subsequently amended and supplemented, the FINRA Rule 2241, as well as the FCA Conduct of Business Sourcebook rules COBS 12.4 – between the Intesa Sanpaolo Banking Group and issuers of financial instruments, and their group companies, and referred to in research products produced by analysts at Intesa Sanpaolo S.p.A. is available in the “Rules for Research ” and in the extract of the “Corporate model on the management of inside information and conflicts of interest” published on the website of Intesa Sanpaolo S.p.A., webpage https://group.intesasanpaolo.com/en/research/RegulatoryDisclosures. This documentation is available to the recipient of this research upon making a written request to the Compliance Department, Intesa Sanpaolo S.p.A., Via Hoepli, 10 – 20121 Milan – Italy.
Furthermore, in accordance with the aforesaid regulations, the disclosures of the Intesa Sanpaolo Banking Group’s interests and conflicts of interest are available through webpage https://group.intesasanpaolo.com/en/research/RegulatoryDisclosures/archive-of-intesa-sanpaolo-group-s-conflicts-of-interest. The conflicts of interest published on the internet site are updated to at least the day before the publishing date of this report.
We highlight that disclosures are also available to the recipient of this report upon making a written request to Intesa Sanpaolo S.p.A. – Macroeconomic Analysis, Via Romagnosi, 5 – 20121 Milan – Italy.
Intesa Sanpaolo Spa acts as market maker in the wholesale markets for the government securities of the main European countries and also acts as Government Bond Specialist, or in comparable roles, for the government securities issued by the Republic of Italy, by the Federal Republic of Germany, by the Hellenic Republic, by the European Stability Mechanism and by the European Financial Stability Facility.

a speech by Carlo Buckhardt

Abstract

In order to overcome existing restraints in the in-service behaviour of currently available additive manufacturing (AM) materials’ sets, an advanced production method for high performance technology metals was developed on the basis of a modified vat polymerisation-based (VP) printing for metal powders. The new lithography-based metal manufacturing (LMM) process is able to photoharden highly filled innovative metal-photopolymeric binder.
After debinding and sintering, the fully dense metal AM parts will provide various advantages such as superior properties with respect to cracks or internal stress when compared to laser-based powder bed fusion (L-PBF) AM parts. LMM is suitable to build very detailed, complex structures with a minimum of after-treatments without need for support structures, exhibiting superior surface quality, having less demanding requests with respect to powder particle size/morphology and allowing effective re-use of the feedstock materials.
In the paper, the LMM process will be explained in detail, its suitability for the production of jewellery and watch pieces will be demonstrated for stainless steel type materials and titanium alloys on various samples, an outlook for precious metal powders will be given

Pforzheim University

• founded 1899
• one of the biggest Universities for Applied Sciences in Germany (~6.000 students)
• threefaculties:
  Business, Economics & Law
  Engineering
  Design
• 29 Bachelor-and 17 Master-Courses
• one of 7 fully certified universities in Germany

Institute for Precious and Technology Metals

Partner oftheregional precision engineering industry

• contract research, serial inspections, damage analyses, expert opinions, production optimisations, etc.
• fully equipped materials lab; incl. 2 SEM, FIB, EDX/XRD, Laserscan, DTA, mechanical testing, corrosionetc. (DAkkSakkredited)
  National and international research partner
• recycling of rare earth metals/permanent magnets
• additive manufacturing of metals
  Head: Prof. Dr.Carlo Burkhardt
• 4 national projects, 3 international multilateral (EU) projects (>30 M€ overall budget)

LMM Additive Manufacturing

Lithography-based Metal Manufacturing

• basedon theVat-PolymerizationPrinciple
• verygoodsurfacecharacteristics
• verygoodgeometricalprecision
• nothermal distortions
• materials: stainlesssteel, toolsteel, titanium, […]
• suitable also for non-weldable materials
• printing speed: max. 16 cm³/h
• suitable for:
• smalland very small parts(<30g)
• smalltomoderate quantities

LMM-Process

How it works

LMM-Process

Sintering

LMM-Process

Shrinkage

LMM-Process

Precision

• finished part tolerances up to ±0.5% of nominal dimension possible
• stair-step effect due to layer-by-layer production

LMM-Process

Surfaces

LMM-Process

Some parts

MetShape GmbH

• Start-up and spin-off of Pforzheim University as of 01.04.2019
• funded by the program “Young Innovators” of the Ministry of Science, Research and the Arts Baden-Württemberg
• specialized in additive component manufacturing using the Lithography-based Metal Manufacturing process (LMM) and related development services
• main focus:
  • conducting feasibility studies for components and materials
  • small scale productions
  • installationof process chains for in-house production

a speech by Christopher W Corti

Abstract

Platinum has only been known to Europe since the 16^th century. This was impure platinum which is found as grains of native metal in alluvial deposits, often associated with native gold. Such grains are mainly platinum alloyed with the other 5 platinum group metals and were exploited by pre-Colombian Indians of Ecuador and Colombia in NW South America.

In more recent times, the popular use of platinum in jewellery dates from the early 20^th century, often as a basis for diamond (and other precious gemstone) jewellery.  Its use in jewellery was restricted in the Second World War as it was considered a strategic industrial metal with limited availability. Thus, early jewellery alloys tended to be based on the existing industrial alloys and comparatively little development of specific jewellery alloys was carried out.  Its acceptance as a hallmarkable jewellery metal came much later in 1975 when, with a wider availability of the metal, platinum was promoted as a high value jewellery metal and platinum jewellery started to grow in popularity, mainly at 950 and 900 fineness qualities. Since that time there has been alloy development specifically for jewellery application and tailored to the requirements of different manufacturing technologies.

This presentation reviews the evolution of platinum alloys over the last century against the challenges – physical and metallurgical – presented in developing improved alloys for jewellery application.

INTRODUCTION

Platinum has only been known to Europe since the 16^th century with rumours of the existence of a white metal, platina, in central and south America that cannot be melted¹. This was impure platinum which is found as grains of native metal in alluvial deposits, often associated with native gold. Such grains are mainly platinum alloyed with the other 5 platinum group metals (PGMs – palladium, rhodium, ruthenium, osmium and iridium) – and were exploited by pre-Colombian Indians of Ecuador and Colombia in NW South America. Analysis of ancient trinkets indicates that iron and copper were also present as impurities¹.

JEWELLERY ALLOYS: 1920s to 1999

In more recent times, the popular use of platinum in jewellery dates from the late 19^th– early 20^th century, often as a basis for diamond (and other precious gems) jewellery. Smith, in his book published in 1933², notes its use in jewellery at 99.5% fineness with small additions of alloying metals to harden it, including Ir, Rh, Ru, Au, Ag and Cu. He also notes that the platinum standard (in the UK) is 950 fineness and is finding general acceptance.  The term ‘platinum’ is deemed to include iridium.  He further notes that much of the platinum in use in jewellery is alloyed with copper to improve hardness and colour. The use of platinum in jewellery was restricted in the Second World War as it was considered a strategic industrial metal with limited availability, which led to the development of white gold alloys as an alternative for jewellery. Thus, early jewellery alloys tended to be based on the existing industrial alloys and comparatively little development of specific jewellery alloys was carried out. These tended to be 90-95% platinum alloyed with other PGMs, usually iridium. These alloys have high melting temperatures, making manufacturing of jewellery, particularly investment (lost wax) casting, difficult and challenging for the jeweller used to gold and silver.

A further issue had been the lack of accurate analysis techniques. All this meant that its acceptance as a hallmarkable jewellery metal in the UK came much later in 1975³.  From this time, with its now much wider availability, platinum was promoted by the platinum producers as a rare, high value jewellery metal and platinum jewellery grew in popularity, mainly at 950 and 900 fineness qualities, in Japan, Europe and the USA, although some growth in demand began earlier in Japan in the 1960s for historical reasons linked to the ban on the import of gold until 1973.  This marketing and growth led to some alloy development such as the platinum-cobalt alloy for investment casting⁴ and the use of gallium additions to produce heat treatable alloys with higher strength and hardness⁵ as Normandeau has reported⁶. For example, one European platinum producer lists only 4 alloys for jewellery application in their catalogue dating to the late 1980s, all at 950 fineness, namely platinum – copper, platinum – cobalt, platinum -ruthenium and platinum-gallium-indium. The copper alloy is listed as a general purpose alloy and the cobalt alloy is listed as suitable for investment casting. Another European producer lists only 3 alloys at 950 fineness:  Pt-5Cu, Pt-5Co/Ni and Pt-5Ru.

Huckle of Johnson Matthey reported on the development of platinum alloys to overcome production problems at the 1996 Santa Fe Symposium⁷. He noted that platinum and its alloys had some different characteristics compared to gold and silver, notably weight, hardness and thermal conductivity and that its alloys have a high density, as well as high melting points. Its high surface resistance leads to clogging (galling) and high wear of saw blades, files and machine tools. He notes that, in Japan, Pt-Pd alloys are in common use, particularly Pt-10%Pd, whereas in Europe Pt-5% Cu is preferred but that it is not a good casting alloy whereas for casting application Pt-5%Co is finding success. In the USA, he notes Pt-10%Ir is commonly in use as an all-purpose alloy and that Pt-5%Ru is used where a hard, good machining alloy is needed. He also notes Pt-5% Co is finding growing use for casting applications in the USA.

Maerz (Platinum Guild International) also reviewed platinum jewellery alloys at the 1999 Santa Fe Symposium⁸ and this built on the information provided by Huckle. It sums up the alloys widely available and their application in jewellery at that time with some comment on the new alloys being introduced, Table2.

In this context, Maerz and Huckle noted that it is important to recognise the different marking standards of various countries at that time. Maerz noted that European countries generally allowed only 950 fineness alloys, with some allowing no negative tolerance (Austria, Ireland, Sweden, Norway, Finland, United Kingdom and Switzerland), some allowing a small negative tolerance (Denmark, Portugal and Italy) and others allowing iridium content to be counted as platinum within the 950 standard (Belgium, France, Italy, Greece, Netherlands and Spain). In Germany, he noted that several fineness standards and alloys were allowed, Table 1.

In the USA, he noted that the standard for jewellery to be marked as platinum was 950 fineness but that the minimum amount of platinum allowed was 500 parts per thousand with the rest of the alloy comprising 950 parts per thousand total platinum group metals (PGMs) with a zero tolerance. He also notes that 950,900 and 850 fineness standards are allowed in Japan.

With regard to actual alloy compositions, he notes that each alloy is made for specific manufacturing functions. Some alloys are preferred for tubing or machining and others for casting, for example, and there are differences in preference in different countries. Table 2 lists the alloys in common (or growing) usage around the world with their function and countries of major use.  He also lists separately a number of alloys that are specific to Japan

Maerz’s list did not record the platinum-5% copper alloy (except its use in Japan) which has been mentioned above as an alloy commonly used in Europe. Maerz does note that, in the USA, the most common alloys in use are 950 platinum with 5% cobalt or ruthenium and 900 platinum – 10% iridium alloy. However, in an updated later version of this paper⁹, the Pt-5Cu alloy is included.

In his book published in 1984, Savitskii¹⁰ notes only two 950 fineness alloys are in use in the old USSR – Pt-5 Ir in Russia and Pt-4.5 Pd – 0.5 Ir in East Germany (GDR).

TECHNICAL ASPECTS OF ALLOYS: 1920s to 1999

From the list of alloys summarised in Table 2, it is evident that at 950 and 900 fineness qualities, there is a broad range of alloys available to the jeweller, each suited to various manufacturing techniques. All have a good white colour, although some may benefit from rhodium plating, e.g. Pt-10% Pd alloy, to give a brighter, whiter colour. The main differences lie in their hardness (or strength) and melting ranges.

Battaini has examined the microstructure of several platinum alloys¹¹ and notes many alloys are single phase, as one might expect from examination of their phase diagrams, particularly at 950 and 900 fineness qualities.  Some alloy systems, however, show large areas of miscibility gaps at low temperatures, for example Pt-Au and Pt-Cu systems and this raises the possibility of age-hardening alloys by heat treatment.  Platinum-5% gold is an example here, Fig 1(a), where an aged hardness of HV300 can be attained, leading to better scratch and wear resistance, but I have not observed its use in as-cast Pt-Au rings^12,13, suggesting it is a treatment not in common use. Platinum- cobalt, Fig 1(b), forms an ordered intermetallic compound, Pt₃Co, that could also enable some hardening at 950 fineness.  The use of gallium also allows age hardening, as is evident from the phase diagram, Fig 2, as well as lowering melting ranges and its use forms the basis of several heat treatable alloys as noted earlier.

Clearly, some alloys are quite soft (hardness lies in range HV50-100), some have a moderate hardness (HV100-150) and others are quite hard (HV 150 – 350), the higher values usually when in the age-hardened condition. In a recent study by the author of customer complaints^12,13, it has been noted that use of soft alloys is a significant factor in platinum jewellery becoming deformed in shape and badly scratched when worn by consumers, particularly in as-cast gem-set rings and wedding bands.

Work around the turn of the 21^st century and summarised in recent reviews^14,15 has demonstrated that microalloying of pure platinum and its alloys with small additions of calcium and/or rare earth metals such as cerium, samarium and gadolinium, typically up to about 0.3%, can increase hardness substantially but such micro-alloys do not appear to have been commercialised by the jewellery industry, probably because they are not easily cast or recyclable.

The melting point of pure platinum is 1769°C, considerably higher than gold (1064°C) and silver (961°C). Its alloys tend to have similarly high melting ranges, as shown in Table 3, although the gallium-containing alloys do have a significantly reduced melting range. Thus, melting and casting platinum alloys requires good furnace equipment capable of attaining melt temperatures some 100°C above the liquidus temperature of the alloy for investment casting. Induction melting is preferred. Melting by gas torch is not easy, although a propane or hydrogen-oxygen torch can be used by bench jewellers.  However, in general, working of platinum alloys is not a problem, although polishing requires skill and effort to obtain a good quality polish. Machining of platinum also requires skill to obtain a good smooth finish, requiring special tool materials and different tool geometries¹⁶, as platinum tends to gall (adhere) on the tool. The low thermal diffusivity of platinum alloys makes welding easier, particularly laser welding¹⁸ compared to gold and silver alloys.

The major manufacturing problem has been with investment casting.  The high melting and casting temperatures require use of special phosphate bonded investment mould materials¹⁹ and the poor melt fluidity requires use of centrifugal casting machines²⁰ to obtain good mould fill rather than the modern gravity machines commonly used for gold and silver. The new generation of tilt casting machines are also suitable. The chief problem with platinum casting is getting defect-free castings^7,20,21 and there have been several investigations on the relative merits of different alloys^4,22-24, looking particularly at surface quality, form-filling and gas and shrinkage porosity. The general findings from these studies show the Pt-5%Co alloy to be the best of current alloys but still not ideal.

JEWELLERY ALLOYS: 2000 to the Present

There have been several studies to develop improved platinum jewellery alloys in the last two decades. These have focussed on either stronger (harder) alloys or improved investment casting

alloys, although alloys suitable for additive manufacturing (3D printing) technology have also been of interest.

A] Stronger, harder alloys

The resistance of jewellery to abrasion and knocks – wear and scratch resistance – depends to a large extent on the hardness of the alloy. As noted earlier, a study of customer complaints showed platinum rings and wedding bands to be particularly prone to deformation of shape (misshapen) and to heavy wear (scratches and dents) during customer service (i.e. whilst being worn), when made in soft – moderately hard alloys. Hard alloys tend to be difficult to work in manufacture, especially to set gems in mounts, and so it is advantageous if an alloy is relatively soft whilst being manufactured into a piece of jewellery but can be subsequently hardened to improve its durability whilst being worn by the customer. This can be achieved by age hardening of suitable alloys after manufacture, a treatment involving the precipitation of a dense dispersion of fine particles of a second phase within the matrix grains.

For platinum, it has been noted that some current alloys are age-hardenable and alloys containing gallium have been developed specifically for this purpose. The first was the Pt-3% Ga-1.5% In alloy developed by Johnson Matthey⁵ and others have also followed such as the HTA alloy⁶ developed by Imperial Smelting and the ‘S’ alloys developed by S Kretchmer and discussed by Maerz⁸. Weisner, in a paper²⁵ presented in 1999, discusses heat treatable alloys and notes earlier work at Degussa, C Hafner, Johnson Matthey (Pt-Ga-In) and S Kretchmer (Pt-Ga-Pd) to develop heat treatable 950 platinum alloys. He notes that all are ternary alloys, many with melting ranges much lower than the conventional binary alloys, suggesting they all contain gallium and/or indium additions. Such alloys are useful for their spring properties in springs and clasps, for example.

Research²⁶ carried out at Mintek, South Africa in 2005 has examined potential platinum alloy systems with additions of 7% or less to identify suitable binary alloy systems that can be substantially age-hardened. Over 20 alloying metals were studied in the preliminary trials at levels of addition of 2 & 4 % and those showing promise were also studied at the 3% addition level. From this work, alloys with additions of Ti, Zr, Sn, Ga, Ge, Mg, In and V were studied in more depth. From this, along with consideration of other aspects, it was concluded that the best alloy was a Pt-2% Ti alloy which had as cast and annealed hardnesses sufficiently low to be easily worked and formed but with subsequent heat treatment, the hardness value could be increased by about HV90. Interestingly, there are parallels here with the development of 990Gold (Au-1%Ti) alloy²⁷. The Mintek work does not appear to have been further developed into a commercial alloy, possibly because it does not show much advantage over the existing commercial gallium-containing alloys.

More recently, a harder general purpose alloy, TruPlat™, has been introduced to the market in the USA by Hoover & Strong. It is a 950Pt-Ru-Ga alloy that is not age-hardenable. It has a higher work hardening rate compared to 950Pt-Ru, with an annealed hardness of HV180.

B] Improved casting alloys

The motivation here is to develop alloys less prone to casting defects, particularly casting porosity.  Use of alloys with lower melting ranges to inhibit mould reaction is desirable too. Work carried out by Fryé at Techform and Klotz and co-workers at FEM ^{23,24 28-30, 32} on platinum cast in shell and conventional moulds has focussed on which alloys are best in terms of casting porosity formation, form-filling and surface quality and establishing the mechanical properties of cast alloys. The use of computer simulation of the casting process has also assisted in optimising process parameters in casting. Fryé has also shown the benefits of a Hot Isostatic Pressing (HIP) treatment post casting in removing porosity from castings and improving mechanical properties. What is particularly noticeable is the growing number of new platinum casting alloys that feature in these studies.  This alloy development started a little earlier in 1997.

In a paper³⁴ presented at the 1997 Platinum Day symposium in New York, Lanam, Pozarnik and Volpe reported on a new investment casting alloy, 950 Pt-Cu-Co, developed at Engelhard, that combines the good properties of Pt-5Co and Pt-5Cu and reduces the issue of magnetism in Pt-Co alloy. It’s as-cast hardness is about HV119, somewhat lower than Pt-5Co. Porosity was still present and it had a tendency to form a surface oxide on heating.

Another alloy development was presented by Normandeau in 2000³⁵ in which he reported on a new 950 platinum Hard Casting Alloy (HCA) with an as-cast hardness of HV 160-170, much higher than Pt-5Co alloy. Little detail is given on the composition but the discussion in the paper points to it being a 950Pt-Ga-Ir alloy, since he provides data on the Ga:Ir ratio and it’s effect on hardness.

A further alloy development was presented by Grice & Cart in 2002³⁶ where the development of a 950 Pt-Au-X alloy, PlatOro™, is reported as an alternative to Pt-5Co. This has an as-cast hardness of HV125, a little softer than Pt-5Co alloy but is non-magnetic and has lower melting range of 1590° – 1629°C. This does not appear to be the Pt-Au-In alloy examined by Fryé & Klotz³⁰ and Maerz and Laag³³, Table 4, since the melting ranges and hardness values are different.  Grice has since reported³⁷ that the PlatOro™ alloy is actually a Pt-Au-Cu alloy but is no longer commercially produced.

Fryé and Fischer-Buehner in their study reported in 2011²⁴ recognised the inadequacies of the existing commercial casting alloys and widened their search to include 3 newer versions that contained undisclosed elements, which they designated as hard alloys (HV175 or greater). These are included in the table of alloys reported in Table 4. The platinum-cobalt- X hard alloy with unknown additions appeared to show some promise. The Pt-Ru-X alloy is now known to be the Pt-Ru-Ga alloy from Hoover & Strong³⁷ and the Pt-Co-X alloy is a Pt-Co-In alloy from Legor³⁸ and is harder and non-magnetic compared to Pt-Co.

In 2014, Klotz et al at FEM utilised computer simulation of casting and thermodynamic calculations to optimise the process parameters of casting Pt-5Ru and Pt-5Co alloys²⁹ and was significant in that ternary alloys of 950 platinum-cobalt-ruthenium alloys were explored. Improved form-filling and surface quality resulted from additions of Co to Pt-Ru alloys, the optimum amount depending on casting technique – centrifugal or tilt casting.

Maerz and Laag³³ studied six alloys in their 2016 study, Table 4, which used tilt casting (as opposed to centrifugal casting) in their trials. Two contained gallium or indium and these alloys showed higher as-cast hardness and were rated high in terms of castability. Each alloy had different strengths and weaknesses and the authors concluded that no alloy was perfect but that progress was being made. It is noted that C Hafner patented an alloy, 950 Pt-Au-In in 2013, with the use of Ir or Ru as grain refiners³⁹, which is probably the alloy referred to in Table 4

The largest range of alloys was studied by Fryé and Klotz, Table 4, who also measured mechanical properties and wear resistance of castings³⁰. They warned against use of soft alloys in cast jewellery and noted pronounced micro-segregation in Ga- and In-containing alloys which increased micro shrinkage porosity. Hot isostatic pressing treatment (HIPing) after casting eliminated porosity and restored ductility. They also noted wear was related to hardness, harder alloys wearing less.

It is clear from the foregoing that no new alloy completely met the desired casting requirements, although a database of mechanical properties of many of the casting alloys was established by Klotz and Fryé for alloys in the as-cast and in the HIPed condition³². This database has data on 13 compositions at 950 fineness and 2 at 900 fineness. As well as the conventional compositions described in Tables 2 and 4, it also includes some newer ternary/quaternary compositions, as shown in Table 5, which only lists the hardness values; perhaps, it also clarifies some of the unknown compositions documented in Table 4.

A more fundamental approach to improved casting alloy design³⁹ has been undertaken recently by Professor Glatzel and his co-workers at the University of Bayreuth and Richemont International.  They looked to develop an improved casting alloy of 950 fineness with the following requirements:

• Low casting temperature
• Small melting range
• Microstructure that is homogenous, fine-grained (100 – 150 µm) and with low porosity
• Hardness in range Hv 155-170 for wear resistance and good ductility (>30%)
• Good reflectance with a bright surface
• Alloying elements that are biocompatible and recyclable

Their benchmark alloy was the 95Pt-1.8Cu-2.9Ga which is a recent alloy development (see Tables 4 & 5). Excluding allergenic, radioactive and toxic elements, 25 possible alloying elements were selected and ranked according to a Suitability Index which comprised 4 characteristics: maximum solubility in platinum (C_max), hardness Index (H_i), melting interval index (M_ii) and liquidus temperature change index (T_lci). From these, a first iteration of 5 alloys were selected for testing and following this, a second set of 5 alloys were selected for testing. Casting was performed in a tilt casting machine. These alloys contained up to 5 alloying elements from a list including Al, Au, Cu, Cr, Fe, Ir, Mn, Pd, Rh and V. From these 10 alloys, two in the second iteration were found to be the most promising, Table 6. It is very evident that these compositions are radically different from those listed in Tables 4 and 5.  They have a hardness of HV 164 (A2) & 165 (B2) respectively compared to HV 225 for the benchmark Pt-Cu-Ga alloy. It will be interesting to see if these or similar alloys are developed to commercial status and find a niche amongst the current alloys. With the base metal alloying elements including iron and manganese, it is possible there may be tarnishing issues with such alloys, if we compare the experiences in developing alternative white gold compositions.

C] Alloys for Additive Manufacturing (3D Printing)

The development of Additive Manufacturing (3D printing) of jewellery has attracted much interest in the industry in recent years and considerable R & D has been carried out on developing machine technology, build techniques and suitable alloys. The technology involves selective laser melting (SLM) of successive layers of alloy powders, and it has become evident that such powders need to be tailored in composition to suit the process. Alloying additions of high vapour pressure metals are not desirable, for example.  In the field of carat golds, it is also important to reduce reflectivity and thermal conductivity/diffusivity to better absorb energy and inhibit heat loss through the metal, thus enhancing consolidation of the powders during laser melting. Examples of modifying carat gold alloy compositions have been discussed⁴⁰.  Regarding platinum alloys, these tend to have considerably lower thermal conductivities as has been discussed by Wright in terms of laser welding¹⁸ and Zito in terms of 3D printing of jewellery⁴¹ Work at Progold Spa on laser selective melting of 950 fineness platinum jewellery has been reported by Zito and his co-workers^41-44. In his 2014 paper⁴¹, Zito used an unspecified 950 Pt alloy powder whilst in his 2015 paper⁴³, Zito used a 950 platinum alloy powder ‘with alloying additions slightly different from the cobalt-containing alloy used in the preceding work’ but gives no further details other than to say it was not doped with semiconductor elements to reduce thermal conductivity (as was done with the carat gold alloys in his work). In the 2018 paper, in which jewellery made by SLM is compared to the same pieces made by investment casting⁴⁴, Zito notes the items produced by casting and by SLM were made in the same 950 Pt-Cu-Ga-In alloy but gives no details on actual composition. This is different from the casting alloys discussed in the earlier section, in that it contains indium as well as copper and gallium.

Thus, it appears that there is little need to develop special alloy compositions suited to 3D printing technology; the conventional alloys are acceptable and do not appear to pose any major problems.

D] Other Alloys

To conclude this paper, I note there are other recent alloy developments that appear in the patent and other literature that do not fit into the 3 preceding categories. For example, European Patent applications from Heimerle and Meule⁴⁵ describe alloys that have optimised processing properties at 950 and lower finenesses based on Pt-W-Cu –(Ru/Rh/Ir) and described as having high hardness and abrasion resistance. The Ru/Rh/Ir additions act as grain refiners.

Another patent from the watchmaker, Omega SA⁴⁶, concerns 950 platinum alloys that are cobalt- and nickel-free, based on Pt-Ir-Au-Ge- (Ru/Rh/ Pd/Sn/Ga/Re) that have mechanical properties that meet the criteria for watchmaking whilst having the colour and luminosity of Pt-Ir alloys.

CONCLUSIONS

1. There has been an evolution of – and growth in – platinum alloy compositions for jewellery application since the 1920s, with a focus on developing alloys suited to the manufacturing technologies in current use. Until the advent of the 21^st century, most platinum alloys for jewellery were based on the existing industrial alloys with the platinum -iridium alloys favoured in the early part of the 20^th century.
2. There is now a wide range of alloys available at 950 and 900 fineness levels with a spectrum of properties. Of note has been the development of heat treatable alloys containing gallium.
3. The investment casting of platinum alloys remains a major issue in terms of surface quality and defect formation, particularly gas and shrinkage porosity. The use of hot isostatic pressing post casting removes porosity and improves mechanical properties. As yet, there is no ideal casting alloy to replace the universally accepted Pt-5Co alloy..
4. There has been a major evolution in platinum alloys, particularly for investment (lost wax) casting application, in the last two decades (21^st century). A recent substantial, structured alloy development approach has produced some significantly different casting alloys containing up to 5 alloying metals It remains to be seen if these prove to be superior.
5. The new manufacturing technology of additive manufacturing (3D printing) does not appear to require special alloy compositions.

ACKNOWLEDGEMENTS

I would like to thank Massimo Poliero and his staff at Legor Srl for inviting me to present at the Jewellery Technology Forum once again.  It is always a pleasure to present at this important international technology conference.

Thanks are also due to many friends and companies in the industry for information and allowing use of pictures and tables; these include Johnson Matthey, Legor,FEM, Progold, Platinum Guild International, Hoover and Strong and Techform.

REFERENCES

1. D McDonald & L B Hunt, “A History of Platinum and its allied metals”, 1982, Johnson Matthey, Chapter 1. ISBN 0 905118 83 9
2. E A Smith, “Working in Precious Metals”, 1933. Reprinted 1978, N.A.G. Press Ltd. Chapter 15. ISBN 7198 0032 3
3. J S Forbes, “Hallmark – A history of the London Assay Office”, 1998, Unicorn Press/The Goldsmiths’ Company, Chapter 12. ISBN 0 906290 26 0
4. G Ainsley, A A Bourne & R W E Rushforth, “Platinum Investment Casting Alloys”, Platinum Metals Review, 1978, vol 22(3), 78-87
5. A A Bourne and A Knapton, US patent US4165983A, 1979/ UK patent GB58258A, 1981
6. G Normandeau & D Euno, “Understanding Heat Treatable Platinum Alloys”, 1999, Santa Fe Symposium, ed D Schneller, Met-Chem Research Inc, 73-103. See also ibid,1998, Platinum Day symposium, Platinum Guild International, vol 5, 35-41
7. J Huckle, “The Development of Platinum Alloys to overcome Production Problems”, 1996, Proc Santa Fe Symposium, ed D Schneller, Met-Chem Research Inc, 301-325. See also: J Huckle, “Choosing platinum alloys to maximise production efficiency”, Platinum Day symposium, 1995, Platinum Guild International, vol 1, 2-6,
8. J Maerz, “Platinum Alloy Applications for Jewelry”, 1999, Proc. Santa Fe Symposium, ed D Schneller, Met-Chem Research Inc, 55-71 ,
9. Maerz, “Platinum Alloys – Features and Benefits”,2004, Platinum Guild international. Download from the Ganoksin website: www.ganoksin.com/article/platinumalloys-features-benefits )
10. E M Savitskii, “Handbook of Precious Metals”, English edition ed. A Prince, 1989, Hemisphere Publishing Corp., Chapter 6. ISBN0 89116 709 9
11. P Battaini, “Metallography of Platinum and Platinum Alloys”, 2010, Proc. Santa Fe Symposium, ed E Bell, Met-Chem Research Inc, 27-49. Also: ibid, Platinum Metals Review, 2011, vol 55(2),74-83
12. C W Corti, “Jewellery – Is it fit for Purpose?: An Analysis based on examination of customer complaints”, Presented at the Jewellery Technology Forum, Held at Vicenza, Italy, January 2018 (download from Legor/JTF website)
13. C W Corti, “Jewelry – Is it fit for purpose? An analysis based on customer complaints”, 2018, Proc. Santa Fe Symposium, Ed E Bell, Met-Chem Research Inc, p163-175
14. C W Corti, “Microalloying of High Carat Gold, Platinum and Silver”,, presented at the Jewellery Technology Forum, Vicenza, Italy, 17-18^th June 2005. Publ. in conference proceedings.
15. C W Corti, “Jewellery Alloys – Past, Present and Future”, Keynote lecture presented at the 1^st Jewellery Materials Congress, Goldsmiths Hall, London, July 2019 (download from website https://www.assayofficelondon.co.uk/events/the-goldsmiths-company-jewellery-materials-congress .
16. R W E Rushforth, “Machining Properties of Platinum”, Platinum Metals Review, 1978, vol 22 (1), p2-12
17. C W Corti, “Basic Metallurgy of the Precious Metals – Part 1”, 2017, Proc Santa Fe Symposium, Ed E Bell, Met-Chem Research Inc, 25-61
18. J C Wright, “Laser-welding platinum jewellery”, 2001, Proc Santa Fe Symposium, ed E bell, Met-Chem Research Inc, p455-468. See also J C Wright, “Jewellery-related properties of platinum”, Platinum Metals Review, 2002, vol 46(2) 66-72
19. P J Horton, “Investment Powder Technology – The Present and the Future”, 2001, Proc Santa Fe Symposium, Ed. E Bell, Met-Chem Research Inc, 213-239
20. J Maerz, “Platinum Casting Tree Design”, 2007, Proc Santa Fe Symposium, Ed E Bell, Met-Chem Research Inc, 305-322
21. R Atkin, “Trouble Shooting Platinum Casting Defects and Difficulties”, 1996, Proc Santa Fe Symposium, Ed D Schneller, Met-Chem Research Inc, 327-337.
22. P Lester, S Taylor & R Süss, “The Effect of different investment powders and flask temperatures on the casting of platinum alloys”, 2002, Proc Santa Fe Symposium, Ed E Bell, Met-Chem Research Inc, 321-334.
23. U Klotz & T Drago, “The role of process parameters in Platinum Casting”, 2010, Proc Santa Fe Symposium, ed E Bell, Met-Chem research Inc, 287-325 and references therein. Also, ibid, Platinum Metals Review, 2011, vol 55(1), 20-27
24. T Fryé & J Fischer-Buehner, “Platinum alloys in the 21^st Century: A Comparative Study”, 2011, Proc Santa Fe Symposium, Ed E Bell, Met-Chem Research Inc, 210-229 and references therein. Also ibid, Platinum Metals Review, 2012, vol 56(3),155-171. An updated version also presented at the Jewellery Materials Congress, London, July 2019 (download from https://www.assayofficelondon.co.uk/events/the-goldsmiths-company-jewellery-materials-congress )
25. K Weisner, “Heat treatable platinum for jewelry”, 1999, Platinum Day symposium, Platinum Guild International, vol 6, 25-30
26. T Biggs, S Taylor & E van de Lingen, “The hardening of platinum alloys for potential jewellery application”, Platinum Metals Review, 2005, vol 49(1), 2-15.
27. C W Corti, “Metallurgy of Microalloyed 24 carat Golds”, 1999, Proc Santa Fe Symposium, Ed E Bell, Met-Chem Research Inc, p379-402; also ibid, Gold Bulletin, vol 32(2), 39-47
28. T Fryé, J T Strauss, J Fischer-Buehner, U Klotz, “The effects of Hot Isostatic Pressing of platinum alloy castings on mechanical properties and microstructure”, 2014, Proc. Santa Fe Symposium, Ed E Bell & J Haldeman, Met-Chem Research Inc, 189-209
29. U Klotz, T Heiss, D Tilberto & F Held, “Platinum investment casting: Materials properties, casting simulation and optimum process parameters”, presented at Santa Fe Symposium, 2014 but published in Proc Santa Fe Symposium, 2015, ed E Bell et al, Met-Chem Research Inc, p143-180. Also, ibid, Johnson Matthey Technology Review, 2015, vol 59(2), 95-108 & 129-138
30. T Fryé & U Klotz, “Mechanical properties and wear resistance of platinum jewelry casting alloys: A comparative study”, 2018, Proc Santa Fe Symposium, ed E Bell et al, Met-Chem Research Inc, 235-273.
31. T Laag & H-G Schenzel, C Hafner GmbH, German patent application DE10212007299A1, 17.10.2013,
32. U Klotz & T Fryé, “Mechanical properties of platinum jewellery casting alloys”, 2019, Johnson Matthey Technology Review, vol 63(2), 89-99
33. J Maerz & T Laag, “Platinum Alloys, Features and benefits: comparing six platinum alloys”, 2016, Proc Santa Fe Symposium, ed E Bell et al, Met-Chem Research Inc, 335-353
34. R Lanam, F Pozarnik, T Volpe, “Platinum alloy characteristics: A comparison of existing platinum casting alloys with Pt-Cu-Co”, 1997, Platinum Day symposium, Platinum Guild International, vol 3, 2-12
35. G Normandeau & D Ueno,”Platinum alloy design for the investment casting process”, 2000, Platinum Day symposium, Platinum Guild International,, vol 8, 41-49
36. S Grice & C Cart, “PlatOro™: The perfect marriage”, 2002, Platinum Day symposium, Platinum Guild International, vol 10, 4-7
37. S Grice, Private communication, June 2021
38. R Bertoncello & J Fischer-Bühner, Legor patent application ITM120110750A1, 2011 “Platinum-cobalt alloys with improved hardness”.
39. T Trosch, F Lalire, S Pommier, R Völkl, U Glatzel, “Optimisation of a jewellery platinum alloy for precision casting: Evaluation of mechanical, microstructural and optical properties”, 2018, Johnson Matthey Technology Review, vol 62(4),364-382.
40. U Klotz, D Tilberto & F Held, “Additive manufacturing of 18 karat yellow gold alloys”, 2016, Proc Santa Fe Symposium, ed. E Bell et al, Met-Chem Research Inc, 255-272
41. D Zito, A Carlotto, P Sbornicchia et al, “Optimisation of SLM technology main parameters in the prodiction of gold and platinum jewellery”, 2014, Proc Santa Fe Symposium, ed E bell & J Haldeman, Met-Chem Research Inc, 439-469
42. D Zito, V Allodi,, P Sbornicchia & S Rappo, “Why should we direct 3D print jewelry? A comparison between two thoughts: Today and tomorrow”, 2017, Proc Santa Fe Symposium, ed E Bell et al, Met-Chem Research Inc, 515-556
43. D Zito, A Carlotto, A Loggi, P Sbornicchia, D Bruttomesso & S Rappo, “Definition and solidity of gold and platinum jewlry produced using selective laser melting (SLM™) technology, 2015, Proc Santa Fe Symposium, ed E Bell et al, Met-Chem Research Inc, 455-491
44. D Zito, “Potential and innovation of the selective laser melting technique in platinum jewelry”, 2018, Proc Santa Fe Symposium, ed E Bell et al, Met-Chem Research Inc, 625-684
45. G Steiner, “Platinum Alloy for Jewelry”, European patents EP 2260116B1, 2014 and EP 209994181, 2007, Heimerle & Meule GmbH,
46. E Leoni et al, “Platinum alloy” European Patent EP3502286 (A1), 2019, Omega SA.

Note: Papers published in Platinum Metals Review/Johnson Matthey Technology Review can be downloaded free from the archive at https://www.technology.matthey.com/ . Many papers from the various Santa Fe Symposia can be downloaded free from the Santa Fe Symposium website archive at www.santafesymposium.org . Papers from Gold Bulletin can be downloaded from the Springer/Gold Bulletin website at https://link.springer.com/journal/13404/volumes-and-issues

a speech by Florian Bulling

Introduction

Titanium alloys are known for their high mechanical strength, low density and high corrosion resistance. Therefore, their application is mainly in the field of aerospace industry, but also in medicine as implant material. The alloy Ti-6Al-4V, also known as Grade 5 titanium is the most widely used alloy. Other titanium-based alloys are the intermetallic compounds NiTi, known as Nitinol®, which is used for its superplasticity as stent material or as actuator. Another important alloy is the intermetallic compound TiAl, which is used in aircraft turbine engines.

The excellent and outstanding properties of these alloys are opposed by the difficulties in manufacturing titanium alloys. The high chemical reactivity of titanium melts allows only cold-walled crucible melting techniques such as vacuum arc melting.

Induction melting and casting was so far compromised by crucible reactions [1-4]. A very recent review on crucibles for induction melting of titanium alloys can be found in [4]. Conventional crucible materials such as alumina or quartz are not suitable due to the decomposition of the ceramic in contact with the titanium melt. Even high stability refractories such as zirconia or yttria, which are used as crucible coatings, are not stable enough [3].

A new ceramic material based on calcium zirconate (CaZrO₃) [1, 5-7] was recently introduced. Calcium zirconate is a synthetic ceramic material that is produced by melting a stoichiometric mixture of calcia and zirconia in an arc furnace (fused CaZrO₃). Alternatively, it can be produced by in-situ reactive sintering. Calcium zirconate shows very promising properties as crucible as well as shell mold material. The present paper provides a comparison of a standard investment with yttria front coat compared to the new, silica-free shell mold and crucibles based on calcium zirconate.

Experimental

Crucibles

The production of the crucibles was in line with the procedure described by Schafföner et al. [8]. The crucibles were manufactured by cold isostatic pressing with two types of molding material consisting of pure fused CaZrO₃ (Type A) or CaZrO₃ with amounts of ZrO₂ and CaO₃ (Type D) for an in situ reaction [9]. A mandrel of steel was used to obtain the inner shape of the crucible. After decompressing and drying of the green ceramic crucibles they were fired at 1650°C for 6 h. Typical crucibles are shown in Figure 1 (left).

To produce crucibles for centrifugal casting a CaZrO₃ slurry was used to prepare a functional coating on a commercial crucible of aluminum titanate (Porzellanfabrik Hermsdorf, Germany). The coating was fired at 1450°C to avoid cracks through different thermal expansion coefficients between the stucco and the coating of the crucible. Typical crucibles are shown in Figure 1 (right).

Shell molds

The shell molds were processed from standard wax trees according to the procedure described in [1]. The wax parts and the tree setup for centrifugal casting shown in Figure 2 and Figure 3, respectively. At wax trees for tilt casting the parts were mounted at two levels of four parts each (Figure 5).

Wax trees were dipped into a calcium zirconate slurry followed by the application of calcium zirconate stucco. Six layers were applied, three fine grained and 3 coarse grained. The dipping was practiced in 2 layers per day. Each layer was dried for at least 5 h before the following layer was applied. Careful drying of the final shells was performed under controlled atmosphere in a climatic chamber at 60% humidity, at 30°C and with an air movement of 1.3 m/s for seven days. After drying, the shells were fired at 1500°C for 4 h. Before casting the shells were preheated to casting temperature. A series of shell molds for centrifugal and tilt casting is shown in Figure 4.

For comparison a commercial silica-bonded shell system, which is commercially available from Ransom&Randolph, Dentsply, USA was used. The wax parts were coated with a front coat of yttria.

Casting trials

Before casting, the crucibles were preheated in a furnace at about 200°C in order to evaporate possible humidity absorbed in the crucible. This procedure was applied to avoid cracking of the crucibles in the casting machine due to water evaporation.

For casting trials a tilt casting machine (VTC200VTi, Indutherm, Germany) and a centrifugal casting machine (TCE10, Topcast, Italy) were used. The tilt-casting machine was equipped with two rotary vane pumps connected in series and achieved a pressure of about 8×10^-3 mbar and an oxygen partial pressure of 10^‑4 mbar immediately before casting. Such vacuum level was necessary in order to avoid reactions of the titanium melt with the gas atmosphere. The casting chamber was back-filled with argon to atmospheric pressure. A batch size of up to 300 g was used for casting. The series of casting trials was carried out with the crucibles type A and D.

The centrifugal casting machine had a maximum power of 10 kW. By the fact that this machine was not especially designed for casting titanium only a low vacuum of 40 mbar was achieved, which meant that a significantly higher oxygen partial pressure remained during casting. This caused a stronger reaction of the titanium melt due to residual oxygen in the casting atmosphere. Before casting, the casting chamber was refilled with argon to a pressure of 700 mbar. With the centrifugal machine laboratory-produced crucibles of Al₂TiO₅ with a CaZrO₃ coating and commercial crucibles with modified yttria coating were tested. The maximum batch size was 100 g titanium.

During inductive heating, the metal temperature was monitored using a thermal imaging camera (Pyroview 640N, DIAS, Germany). The camera allowed an integral determination of the temperature on the surface of the melt and the subsequent evaluation of the melting process. To investigate the influence of pre-casting evacuation, overheating and dwell time on the reaction between the titanium melt and the crucibles, different parameters were applied. The pre-cast evacuation was only necessary with the tilt-casting machine to achieve good form filling. Depending on the pumping duration, a low vacuum was obtained.

Starting with a low heating power, the metal charge was heated close to melting temperature. The slow heating led to a homogeneous temperature of the rod and thus kept the time of liquid phase in crucible (exposition time) short. As determined in several casting trials, the reactivity of the titanium melt was much higher than in the solid state. When the liquidus temperature was reached, the power was increased to melt the whole material and to overheat it before casting. The dwell time means the time while all of the material was liquid. During the dwell time, the melt was heated until the desired temperature was reached. After the dwell time the casting was manually triggered. In case of the tilt-casting machine, the tilt speed was set up to 47°/s until the final angle of 90° was reached to achieve a fast filling and a low heat loss.

Microstructure, hardness and composition measurement

After casting metallographic samples were prepared to investigate the interaction of alloy and shell mold. This employed electron scanning microscopy (Zeiss, Gemini SEM 300) and optical microscopy (Zeiss, Imager Z2M).

The chemical composition was analyzed in the center of sample cross sections by glow discharge optical emission spectroscopy (GDOES) (Spectruma, GDA750) and by EDS. In addition, X-ray diffraction (XRD) was carried out to examine the phase composition of the crucibles before and after the casting process. To detect possible cracks and defects, the crucibles were investigated by X-ray computed tomography (XCT).

Results and discussion

After casting and quenching, the different shell systems showed significantly different surface appearance (Figure 5). The trees with the yttria modified R&R shell showed large residues of the shell material sticking on the surface. Due to their hardness, it was impossible to remove them by water jetting. Instead, sand blasting was required to remove the remains of the shell. The new, CaZrO₃-based shell showed a golden colored metal surface with few shell residues on the surface. This is an indication of a very limited reaction of the melt with the new, CaZrO₃-based shell material as examined in [10].

The investigation by SEM showed the different nature of reaction of the two shell systems (Figure 6 and Figure 7). At the bottom of the pictures, the typical so-called Widmannstätten structure of the titanium alloy is visible. It consists of two phases (a, dark, and b, bright). The a-phase and the b-phase have different crystal structure that are hexagonal close packed and body centered cubic, respectively [11].

Due to the reaction with the melt the refractory from the shell decomposes [12]. Oxygen is dissolved in the alloy, which stabilizes the a-phase. Therefore, a layer of a-phase is formed at the metal surface in contact to the shell, the so-called a-case. Such a-case was found for the modified R&R shell (Figure 6, left). The a-case forms a very hard and brittle surface layer, which can be removed only with great difficulty.

The residues of the shell were surrounded by metal, which explains the difficulty in the removal of shell residues. The yttria front layer that was used to limit shell reactions was not effective. Similar effects were examined with yttria-coated crucibles. The yttria layer was dissolved into the titanium melt. During cooling yttria re-precipitated at the grain boundaries (Figure 6, right). Such ceramic inclusions resulted in embrittlement.

The calcium zirconate shell also showed certain reaction with the titanium alloy (Figure 7). However, such reaction was much weaker compared to the modified R&R shell. The porous shell was not infiltrated by the melt. For this reason, it could be removed much more easily compared to the modified R&R shell. At the interface of metal and shell, the calcium zirconate started to be dissolved by the melt.

The reaction of calcium zirconate with the melt follows a certain reaction scheme [13]. Calcium zirconate decomposes into zirconia and calcia. Both refractories further decompose to their chemical elements. Zirconium and oxygen dissolve in the titanium melt. Calcium is not soluble in titanium and evaporates. As a result, the content of zirconium and oxygen are increased. The zirconium content in the surface layer of the titanium part appears brighter in the backscattered electron image (Figure 7, indicated by arrows). However, the dissolution of oxygen and zirconium did not result in the formation of a hard a-case.

The hardness and the oxygen content in cast 10mm rods were investigated by hardness and composition profiles (Figure 8). The interface of alloy and shell is defined by the position zero. Positive and negative distance values are in the metal and in the shell, respectively. Figure 8 shows results for different combinations of crucible and shell mold. Samples melted in a copper crucible (“Cu”) were prepared by electric arc melting. Oxygen content and sample hardness were clearly correlated: The higher the oxygen content, the higher was the hardness. The samples from the yttria modified R&R shell (green and black curve) exhibited higher surface hardness and oxygen level compared to those from the calcium zirconate shell (red and blue curve). For both shells the bulk hardness was reached at a depth above 300-400µm.

The melt temperature and duration play an important role for the bulk hardness of the alloy. In order to compare different combinations of melting temperature and duration a parameter was introduced, which is based on the Larson-Miller parameter (LMP) [14]. This parameter is originally used to compare diffusion controlled processes in high temperature deformation (creep). The LMP is calculated from the temperature and the logarithm of melting duration. Figure 9 shows a plot of the bulk chemical composition and the hardness over the LMP value.

It appears that oxygen and zirconium content as well as the hardness remain constant up to an LMP value of 47. The oxygen level was between the values of the feedstock and the limit given by the ASTM standard B367-09. The ASTM standard specifies no special value for the zirconium content, but a maximum concentration of 0.1 % for all other elements. Even this limit could be met with appropriate casting parameters. The hardness of the as-cast material was ca. 360 HV1, which was higher than the hardness of the feedstock (312 HV1). Such hardness increase was due to the different microstructure of as-cast material and feedstock.

At LMP values > 47 the concentrations of oxygen and zirconium increased strongly, as well as the hardness. Therefore, both temperature and melting duration have to be controlled carefully to avoid contamination of the melt. The melting range of grade 5 titanium is 1605-1660°C. A certain superheating of at least 50 K will be required to achieve sufficient form filling. The maximum LMP value of 47 can be converted into a maximum holding time of the melt in the crucible at a certain temperature. For instance the LMP = 47 equals to a holding time of 440s at 1700°C, 72s at 1750°C and only 13s at 1800°C. This indicates the high sensitivity of the reaction to uncontrolled overheating. Therefore, we have chosen to use a slow heating process that provides a homogeneous melting of the feedstock.

Besides jewelry items, the process and materials were also tested for industrial parts such as turbine wheels or small parts of glasses frames. Figure 10 shows a turbine wheel directly after casting without further surface treatment. The defect visible on the part on the left side was already present on the wax part. The feasibility of such cast parts in grade 5 titanium proves the suitability of the new shell mold for successful investment casting of titanium parts.

Summary and Outlook

A new shell mold and crucible material based on calcium zirconate was successfully tested for the investment casting of grade 5 titanium alloy (Ti-6Al-4V). In comparison to a commercial shell with yttria front coat, the new shell resulted in less oxygen contamination, less surface hardening and prevented the formation of an a-case. However, the control of the melt temperature was crucial to keep the oxygen level low. Excessive superheating and prolonged melting durations resulted in significant oxygen contamination and hardness increase. Ideally, the melt temperature should not exceed 1700°C to avoid contamination.

Further work will focus on the heat treatment of as-cast parts and the determination of mechanical properties. Different titanium alloys and other high melting and highly reactive alloys such as CoCr, Pt and Zr will be tested with the new calcium zirconate crucible and shell molds.

Acknowledgements

This IGF Project was supported via AiF No. 18293BG within the program for promoting the Industrial Collective Research (IGF) of the German Ministry of Economic Affairs and Energy (BMWi), based on a decision of the German Bundestag.

References

1. Klotz, U.E., et al., Investment casting of titanium alloys with calcium zirconate moulds and crucibles. The International Journal of Advanced Manufacturing Technology, 2019. 103(1): p. 343-353.
2. Nastac, L., et al., Advances in investment casting of Ti–6Al–4V alloy: a review. International Journal of Cast Metals Research, 2006. 19(2): p. 73-93.
3. Klotz, U.E. and T. Heiss, Evaluation of crucible and investment materials for lost wax investment casting of Ti and NiTi alloys. International Journal of Cast Metals Research, 2014. 27(6): p. 341-348.
4. Fashu, S., et al., A review on crucibles for induction melting of titanium alloys. Materials and Design, 2020. 186: p. 108295.
5. Freitag, L., et al., Silica-free investment casting molds based on calcium zirconate. Ceramics International, 2017. 43(9): p. 6807-6814.
6. Schafföner, S., et al., Advanced refractories for titanium metallurgy based on calcium zirconate with improved thermomechanical properties. Journal of the European Ceramic Society, 2019. 39(14): p. 4394-4403.
7. Freitag, L., et al., Improved Precision Casting of Titanium Alloys Using Calcium Zirconate Moulds. refractories WORLDFORUM, 2019. 11(2): p. 76-82.
8. Schafföner, S., et al., Fused calcium zirconate for refractory applications. Journal of the European Ceramic Society, 2013. 33(15-16): p. 3411-3418.
9. Schafföner, S., et al., Influence of in situ phase formation on properties of calcium zirconate refractories. Journal of the European Ceramic Society, 2017. 37(1): p. 305-313.
10. Bulling, F., Einfluss der Gießparameter auf die Eigenschaften von Feingussteilen aus Titanlegierungen, 2017, Hochschule Aalen: Schwäbisch Gmünd.
11. Pederson, R., Microstructure and Phase transformation of Ti-6Al-4V, 2002, Luleå tekniska universitet.
12. Frye, H., D.H. Sturgis, and M. Yasrebi, Basic Ceramic Considerations for the Lost Wax Processing of High Melting Alloys, in The Santa Fe Symposium, E. Bell, Editor 2000: ABQ, NM, USA.
13. Bulling, F., et al. Investment casting of high reactive and high melting metals using calcium zirconate crucibles. in Proceedings of the liquid metal processing casting conference 2019. 2019. TMS.
14. Larson, F. and M. J., Time-Temperature Relationship for Rupture and Creep Stresses. Transaction of the ASME, 1952. 74: p. 765-771.

a speech by Marco Giuseppe Andreetta

Sisma, a growth journey of more than sixty years

Open systems and relevance for jewellery additive manufacturing

Open systems are a value for the jewellery manufacturer, enabling:

• freedom of choice

→ potentially every powder manufacturer could be validated

• possibility to adapt the building parameters to each geometry

→ different geometries have different requirements. In order to exploit all the benefits of additive manufacturing it is necessary to fine tune the building strategy

A harmonized approach to precious metal 3D printing

A harmonized approach to precious metal 3D printing:

to establish a SISTEMIC COMPENTENCE

– Density > 99,9%

– Digital microstructure

– Compliance with jewellery quality standards

– Building strategies adapted to the post processing

Compatibility with material manufacturers of precious metals

Having open parameters grants compatibility with multiple precious metal material supplier, leaving the customer free to evaluate existing suppliers or propose a new one for validation.

Currently available alloys for Jewelry additive manufacturing: 

Precious metals:

Au750 White Gold

Au750 Yellow Gold

Au750 Red Gold

Ag925

Non precious metals:

Bronze9010

Stainless Steel

Titanium alloys

Partnership with Application Specialists:

The application specialist works alongside with the final customer with the machine manufacturer support.

We chose to partner with one application experts for each strategic jewellery market, in order to accomodate requests from all over the world.

Advanced parameters:

Laser  (power, scanning speed)

Hatching (hatching distance, hatching strategies, order)

Contours (number, distance)

Beam spot (diameter, compensation) 

Layer thickness (multiple layer thickness)

Protective Gas (speed, gas mixture choice)

Powders (grain size, chemical composition)

Upskin & Downskin

Advanced parameters: before and after the building process

Geometry driven parameters

Small dimension part

• Part description: thin wall section (0.7mm)
• Validation criteria: surface quality, complex geometries compliance

• Small beam spot diameter
• Material choice with smaller than usual grain size
• Easy to remove support, only supportive function

Massive part

• Part description: wall thickness changes across the part
• Validation criteria: mechanical properties, density and geometry compliance, build speed

• Medium or variable beam spot
• Supports: heat exchange, supporting and anchoring function
• Benefits from pre-heating
• Skin/core laser parameters to increase build speed

Beam spot diameter: small beam spot for special applications

“Pixel” technical sample – Bronze 90-10

▪ No correlation with conventional technologies

▪ The part is made of interconnected pieces

▪ The complete part is made in a single Ø100mm print job

▪ Combination off additive manufacturing, polishing and surface treatment (gold plating)

▪ Small beam spot parameter choice (30µm) to make the geometry possible

▪ Parameter fine tuning of the beam compensation (on the file preparation) rather than tweaking the CAD geometry

Titanium: a growing trend in jewellery

Titanium popularity is increasing in the jewellery market.

Once considered a minor metal relegated to aviation and medical industry, is now gaining importance for many reasons:

– weights a quarter of gold → bigger items are worn without discomfort

– anti-allergenic (e.g. in watchmaking Titanium can be used by whom is allergic to Nickel contained in 904L)

– can be processed to show a wide range of bold colours

Titanium: traditional technologies drawbacks

Titanium has its drawbacks for traditional machining:

Traditional processing of Titanium is costly.

Dedicated machinery is used to safely and effectively work with this alloy.

Machining Titanium usually requires:

– high torque machine and low speeds, to reduce the heat generation

– higher speeds usually generate unwanted hardening of the metal, increasing tool wear

Casting Titanium is a difficult task as well.

Titanium: advantages of 3D printing

Titanium can be 3D printed easily and safely on a well tuned machine.

Indeed, is one of the easiest material to be 3D printed:

– highly self supporting → a small amount of supports leads to increased geometry freedom and reduction of post processing

– relatively low elastic modulus → controlled distorsion during 3D printing

And, moreover, a wide range of alloys are already developed for other demanding markets.

Commonly Available Titanium alloys

Ti6Al4V – gr.23 ELI

Industry standard for aerospace and medical applications. More than 350 HV5

Ti gr.1, Ti gr.2

This two Titanium grades shares corrosion resistance, weldability, and high ductility. Almost pure Titanium, other elements are less than 0,2%. Roughly 225 HV5

Ti6Al4V – gr.5

Widely available on the market, it shares the chemical composition of gr.23 but with higher amount of Oxygen.

Serial production of hollow Titanium chain. Titanium itself helps stacking easily complex geometry with small amout of supports.

Source: A 3D-Printed Ultra-Low Young’s Modulus β-Ti Alloy for Biomedical Applications by Massimo Pellizzari, Alireza Jam, Matilde Tschon, Milena Fini, Carlo Lora and Matteo Benedetti https://www.mdpi.com/1996-1944/13/12/2792

New Titanium alloy being researched

Requirements:

Lower elastic modulus

Great fatigue resistance

Optimal corrosion resistance

Optimal biocompatibility (alloy without Vanadium)

New Titanium alloy being researched

Findings:

Lower elastic modulus was also useful to control the deformations during the printing process

–> the  new material  has even higher buildability characteristics if compared with conventional Ti6Al4V

It may be possible to completely avoid the heat treatment or at least switch to a lower temperature aging and stress relieving process

–> Possibility of using cheaper furnaces and avoid vacuum heat treatment for Titanium

New Titanium alloy being researched

Flexible Titanium applications in the luxury market

Current developments in Sisma :

• Development of new alloys
• Fine tuning of existing alloys for the LMF process
• Fine tuning of the whole process (powders, LMF, heat treatment, inert gas mixture choice) to satisfy specific market requests.

a speech by Vera Benincasa

Simulating processes has been mandatory in many companies from the most diverse manufacturing sectors for years. One only need think of the aviation industry where companies must be absolutely certain that the components produced have no micro-structural defects whatsoever and where a rejected part cannot be re-processed. 
Casting process simulation identifies areas subject to defects and helps to design the casting system in the most efficient manner. It also allows the causes of any inefficiency to be analysed and to understand how to increase productivity.
This system has been used for over twenty years in smelting processes in the automotive and aerospace industries and for some years now, it has also been adopted by our sector. 
In the jewellery world, lost wax micro-casting has always been linked to operator experience or trial and error. Nowadays, simulation software can optimize the entire process starting from the very first prototype design to the mass production of jewellery items. 

The micro-casting process is one of the oldest methods for producing many types of article.
Different peoples and cultures used this process to produce tools, objects and statues in bronze. One very famous example is the Bronze Riace Warriors that were salvaged from the sea in 1907, 2500 years after they were made in Greece in the sixth century BC.
The process developed over the centuries, evolving from a simple artistic method and demonstrating exceptional versatility.
Micro-casting, or lost wax casting, has been used for many years in the automotive and aerospace technology sectors, however, this process, although highly reliable, still presents defects.  

In the jewellery world, the most common and problematic defects are:
– incomplete filling of the cast
– porosity by retraction.
While cases of the first type of defect are limited to specific kinds of production (filigree, particular alloys, complex geometries…), the second can be found in all micro-cast products because it is intrinsically linked to the solidification process of the metal alloy.

It is on this latter category of defect that we will be focusing our attention.
Up until a few decades ago, “Trial and Error” was the obligatory method of trying to solve the problem of porosity by retraction.
With practice and experience, the aim was to minimize and hide the defect.
In order to obtain a commendable result, modest amounts of time and metal needed to be invested.
Simulating the process in a virtual environment minimizes this investment and achieves a better result in less time.

Nowadays, simulation software has reached a high level of precision so that excellent results can be obtained in terms of product development times and the production process can be improved.
The use of casting process simulation software in the jewellery sector is relatively recent although it is constantly on the increase due to the growing request for quality on the part of the big jewellery companies.

Simulation software works when there is a deep knowledge of the entire process. For this reason, the more it is used, the more information will be available to configure the process and the more the results provided by the software will correspond to industrial needs.

The software used for this study is produced by the French ESI Group and is called ProCAST.
It is an advanced and complete tool and has been on the market for over 20 years. It is widely used in various industrial fields. The software is based on finite element technology and is able to simulate a long list of real processes. This study focuses on the module for simulating the lost wax casting process.

A knowledge of metallurgy and the production process is necessary to be able to use the software to its best advantage. With the help of the SW, the process technologist can work out the best conditions for a reliable and robust micro-casting process.

The software consists of the following environments:
– MESH
– CAST
– VISUAL

MESH is the environment in which our object, starting from the CAD model, is broken down into minor elements (mesh) that the then software uses to understand the points on which to calculate the thermal exchange and solidification equations. The operator decides on the size of the mesh in accordance with various factors. Besides the object of our study, the mould into which we will be casting the metal in order to accurately simulate our process must also be designed and “meshed”.

CAST is the environment where all the parameters to be taken into account in our process are inserted: type of alloy, process temperature, pressure of the metal as it goes into the mould, entry section, thermal exchange, radiation phenomena, etc…

VISUAL is the ideal environment for observing and measuring the simulation results and, depending on what is being analysed and measured, different physical measurements can be viewed (temperature range, solid fraction, voids, porosity, flow speed, etc…)
With the help of Procast, it is extremely easy to foresee where the defects of a particular micro-cast will be and how large these defects effectively are.

Thanks to the software, we can quickly and fully investigate the porosity by retraction defect.

The problem of porosity by retraction is strictly correlated to the solidification concept. In fact, porosity by retraction occurs when the metal status turns from liquid to solid: the metal undergoes a volumetric contraction and, where the volume retracts, dendritic structures, which can become larger as the alloy hardens, can emerge on the surfaces.

Dendrites are tree-like structures that form during metal alloy solidification. The metal forms crystals that grow and solidify in the most energetically favourable crystallographic directions. If cooling is fast, dendrite growth is limited. On the other hand, if cooling is slow, the dendrites will be larger and, in the worst scenarios, visible to the naked eye in the volumetric retraction zone.

Volumetric contraction is intrinsic to the solidification process and therefore, porosity by retraction is an inevitable defect in the casting process.
Porosity by retraction cannot be eliminated but it can be conveyed to strategic points by encouraging directional solidification.

When a metal alloy solidifies, the last volume to do so, that is, the one that stays “hot” the longest, will be the part that contains porosity by retraction.
In designing a casting system, it is therefore essential to study the thermo-dynamic factors that lead to controlled solidification: the casting channels, feeders and risers are to be designed and sized so as to be able to correctly feed the piece being produced and, at the same time, “keep” retraction out of the areas of interest.

To study the solidification of micro-cast objects, it is important to consider the cooling module.
The cooling module, or thermal module, is given by the ratio between mass and surface of an object M=V/S.
Starting with volume, if the surface of the object is greater, solidification time will drop drastically. Solidification time depends on M and also on the type of material and the object’s geometry.
Studying solidification time is essential for shifting the direction of solidification. 

Let’s take a very simple object, such as a wedding band, for example.
Being circular and symmetrical, the point in which we put the feeder is of no importance. What is important, however, is the feeder’s section and geometry.
Below is an example of the solidification simulations of the same ring with three different feeders in ascending section size.

As can be seen in the picture above, the feeder with the largest section tapered towards the metal entry section is the one that fills the cast and directs ring solidification correctly. 

As further evidence of the correctness of feeder 3’s design, we can see, again by simulation, a reduction in porosity (in purple) in the diagrams below.

Now let’s look at another simple ring geometry, but this time with a variable section.

In this case, since the geometry is not symmetrical, the point at which we feed the ring is of fundamental importance. Figure 7 below shows the progress of solidification based on the point chosen for positioning the cast feed.

Solidification observed in the previous figure leads to porosity in the areas highlighted in figure 8.

The results can be verified by observing the actual components cast. When using simulation software, it is extremely important to calibrate the reliability of the software with one’s own casting process.  
The photographs below show the surfaces of the ring analysed and cast with the two different feeder positionings:

Similarly, taking a larger object, we can see that the same directional solidification rules can be applied in this case too.
The figure being examined is a “C” which could be used to make half a bracelet.

In the first example, let’s consider the item with the same type of feed but cast with different parameters. The response variation to the change in temperature, both in the mould and in casting, is particularly notable.

As can be seen from the diagrams, as the temperature rises, the size of the porosities decreases. This happens because the metal is given more time to solidify in a directional manner. In this case, however, only modifying the process parameters does not solve the problem at the root.
It is therefore necessary to modify the feed. Let’s look at two different feeds.

The figure below shows the simulation of the solidification process in both cases.

Analysing the figure on the left, it can be noted that the six feed spokes are solidifying before the bracelet itself has solidified (as in the previous example), thus “blocking” the way for the metal to continue to feed the object correctly. In the figure on the right, however, we can see how the four spokes are feeding the piece well, resulting in a directional solidification towards the heart of the column.

Evidence of the efficiency of type B feeding position can be given by analysing the porosity.
In figure 16, it can be noted how, in case B, the object has no porosity, while in case A, there are six porosity nuclei exactly where the metal took longer to cool.

The accurateness of these simulations is shown in the photographs below.

The analysis of these simple geometries demonstrates the validity of simulation. The software can precisely predict which areas will be affected by defects and their size.
The micro-casting simulation process is a useful tool for the technologist who cannot totally eliminate the “Trial and Error” process but can limit it in the virtual simulation environment, thus reducing product industrialization times and costs.

The fundamental tool for using casting simulation software is CAD 3D modelling.
In fact, as already mentioned, in order to be able to simulate the casting process, it is absolutely necessary to start from a 3D model of both the casting system we want to simulate and the mould in which we will be casting the metal.
The more accurate the initial model is, the more accurate the simulation results will be.
Moreover, CAD modelling offers the advantage of being able to rapidly design and simulate various types of feeding points and casting systems.
By simulating different feeding points, we can find the best one for our item.
By carrying out casting simulation at the beginning of the design process, it would immediately be possible to identify errors in the design and intervene by modifying the model’s geometry.   
If modifying the item is not possible, then acting on the other parameters (feeding, process parameters, etc..) will become necessary.

Once the importance of simulating each individual detail has been understood, new possibilities for more complex casting systems can be explored. By simulating an entire casting tree, for example, it is possible to analyse the entire process and optimize it.

In conclusion, introducing this technology into the jewellery supply chain is undoubtedly helpful for moving towards better production performances and benefits companies that want to use additional forces and means in their production processes.

Resources and study are needed to take best advantage of this technology. Nevertheless, the benefits resulting from its usage (savings in time and means as well as the effectiveness of the results obtained) eliminate every uncertainty. In time, this will be the only way to proceed in jewellery industrialization, as has already happened in other production sectors.

una relazione di Vera Benincasa

Simulare i processi è da anni obbligo in molte realtà dei più disparati settori produttivi, basti pensare al settore aeronautico dove è necessario essere certi che i componenti prodotti siano esenti da difettosità microstrutturali anche minime e dove un pezzo di scarto non può essere rilavorato.
La simulazione dei processi di colata consente di identificare le aree soggette a difetti e aiuta a progettare il sistema di colata nel modo più efficiente, consente di analizzare le cause di inefficienza e di comprendere come aumentare la produttività.
Questo sistema è utilizzato da più di vent’ anni nei processi di fonderia legati al settore automotive e aerospace, ma da qualche anno si è avvicinata anche al nostro settore.
Nel mondo orafo la microfusione a cera persa è sempre stata legata all’esperienza degli operatori oppure ad operazioni di trial and error.
Oggi, con i software di simulazione, si può ottimizzare tutto il processo a partire dal primissimo disegno del prototipo fino alla produzione in massa dei gioielli.

Il processo di microfusione è uno dei più antichi metodi per la produzione di manufatti di svariato genere.
Popoli e culture diverse hanno impiegato questo processo per la produzione di strumenti, oggetti e statue in bronzo. Un esempio famosissimo sono i bronzi di Riace, ritrovati in mare nel 1907 dopo 2500 anni dalla loro produzione nella Grecia del VI secolo a.C.
Nel corso dei secoli, il processo si sviluppato, evolvendo da semplice metodo artistici e dimostrando una eccezionale versatilità.
La microfusione, o fusione a cera persa, viene utilizzata da tantissimi anni nei settori tecnologici dell’ automotive e dell’ aerospace tuttavia tale processo, benché molto affidabile, non è esente da difetti.

Nel mondo del gioiello i difetti più diffusi e più problematici sono sicuramente:
– mancato riempimento del getto
– porosità da ritiro
Mentre per la prima tipologia di difettosità le casistiche sono limitate a produzioni specifiche (filigrane, leghe particolari, geometrie complesse, ..) la seconda è riscontrabile sul 100% dei prodotti microfusi poiché intrinsecamente legato al processo di solidificazione delle leghe metalliche.

È su quest’ultima categoria di difettosità che focalizzeremo la nostra attenzione.
Fino a pochi decenni fa, per affrontare la problematica delle porosità da ritiro era obbligatorio passare attraverso processi di “Trial and Error”.
Con pratica ed esperienza si puntava a minimizzare ed occultare il difetto.
Per arrivare ad un risultato apprezzabile era necessario investire modeste quantità di tempo e metallo.
Simulare il processo in un ambiente virtuale, consente di minimizzare questo investimento, giungendo in tempi ridotti ad un risultato migliore.

Oggi i software di simulazione sono giunti ad un alto livello di precisione consentendo di ottenere ottimi risultati termini di tempo di sviluppo del prodotto e consentendo di migliorare il processo produttivo.
L’utilizzo del software di simulazione del processo di colata nel settore orafo è relativamente recente ma in costante espansione a causa di una crescente richiesta di qualità da parte delle grandi case orafe.

I software di simulazione funzionano grazie alla conoscenza approfondita dell’intero processo, per questo motivo maggiore è il loro utilizzo, maggiori informazioni si hanno a disposizione per configurare il processo, maggiore sarà la rispondenza dei riscontri forniti dal SW alla realtà industriale.

Il software utilizzato per questo studio è della casa francese ESI Group e si chiama ProCAST.
Si tratta di uno strumento avanzato e completo, sul mercato da oltre 20 anni ed ampiamente utilizzato in diversi campi industriali. Il software si basa sulla tecnologia agli elementi finiti ed è in grado di simulare un lungo elenco di processi reali. Nel caso in studio l’attenzione è focalizzata sul modulo per la simulazione del processo di colata a cera persa.

Per poter utilizzare al meglio il software è necessario avere delle conoscenze di metallurgia e del processo produttivo. Il tecnologo di processo può con l’ausilio del SW studiare le migliori condizioni affinché il processo di microfusione sia affidabile e robusto.

Il software consta dei seguenti ambienti:
– MESH
– CAST
– VISUAL

MESH è l’ambiente all’interno del quale il nostro oggetto, a partire dal modello CAD, viene scomposto in elementi minori (mesh) che il software usa per sapere i punti ove calcolare le equazioni di scambio termico e di solidificazione. La dimensione delle mesh è scelta dall’operatore in base a diversi fattori. Oltre all’oggetto del nostro studio, bisogna disegnare e “meshare” anche lo stampo all’interno del quale andremo a colare il metallo per poter simulare in maniera accurata il nostro processo.

CAST è l’ambiente dove inserire tutti i parametri di cui tener conto nel nostro processo: tipo di lega, tipo di stampo, temperature di processo, pressione di ingresso del metallo nello stampo, sezione di ingresso, scambio termico, fenomeni di irraggiamento, etc..

VISUAL è l’ambiente idoneo all’osservazione e alla misurazione dei risultati della simulazione e in base a ciò che si vuole analizzare e misurare si possono visualizzare grandezze fisiche differenti (range di temperature, frazione solida, vuoti, porosità, velocità di flusso, ecc..)

Con l’ausilio di Procast è molto semplice prevedere dove saranno i difetti sul particolare microfuso e quali sono le entità effettive di questi difetti.

Grazie al software possiamo sviscerare in poco tempo il difetto della porosità da ritiro.

Il problema della porosità da ritiro è strettamente correlato al concetto di solidificazione. La porosità da ritiro, infatti, viene a crearsi quando il metallo passa dallo stato liquido allo stato solido: il metallo subisce una contrazione volumetrica e nella zona del ritiro di volume possono affiorare in superficie le strutture dendritiche che si accrescono in fase di solidificazione della lega.

Le dendriti sono strutture ad albero che si formano durante la solidificazione delle leghe metalliche. Il metallo forma cristalli che si accrescono e solidificano nelle direzioni cristallografiche energeticamente più favorevoli. Con un raffreddamento rapido l’accrescimento delle dendriti è limitato. Mentre con un raffreddamento lento si ottengono delle dendriti di dimensioni maggiori, nei casi peggiori visibili a occhio nudo nella zona del ritiro volumetrico.

La contrazione volumetrica è intrinseca al processo di solidificazione e, quindi, la porosità da ritiro è una difettosità inevitabile nel processo di fusione.
La porosità da ritiro non può essere eliminata, ma può essere veicolata in punti strategici promuovendo la solidificazione direzionale.

Nella solidificazione di una lega metallica, l’ultimo volume a solidificare, ovvero quello che rimane “caldo” per più tempo, sarà quello che conterrà le porosità da ritiro.
Nella progettazione di un sistema di colata è fondamentale, quindi, lo studio dei fattori termodinamici che portano ad una solidificazione controllata: i canali di colata, gli alimentatori e le materozze vanno studiati e dimensionati in maniera tale da riuscire ad alimentare correttamente il pezzo da realizzare e allo stesso tempo “trattenere” il ritiro fuori dalle zone di interesse.

Per studiare la solidificazione degli oggetti microfusi è importante considerare il modulo di raffreddamento.
Il modulo di raffreddamento, o modulo termico, è dato da rapporto tra massa e superficie di un oggetto M=V/S. A parità di volume, se la superficie dell’oggetto è maggiore, il tempo di solidificazione diminuisce drasticamente. Il tempo di solidificazione è una funzione di M, e dipende anche dal tipo di materiale e dalla geometria dell’oggetto. Studiare il tempo di solidificazione è fondamentale per veicolare la direzione di solidificazione.

Prendiamo ad esempio un oggetto molto semplice, come può essere una fede.
Avendo una geometria circolare e simmetrica il punto in cui andremo a mettere l’alimentatore non ha importanza. Ha importanza, però, la sezione e la geometria di quest’ultimo. Di seguito sono riportati come esempio le simulazioni della solidificazione della stessa fede ma con tre alimentatori a sezione crescente.

Come si può vedere nell’ultima immagine, l’alimentatore con sezione maggiore e rastremato verso la sezione di imbocco del metallo è quello che consente il corretto riempimento del getto e la solidificazione direzionale della fede.

A riprova della correttezza della progettazione dell’alimentatore 3 possiamo vedere, sempre dalla simulazione, la riduzione di porosità (in viola) nell’ultima immagine.

Prendiamo ora ad esempio un’altra geometria semplice di un anello, ma stavolta con sezione variabile.

In questo caso, essendo la geometria non simmetrica, il punto in cui andremo ad alimentare l’anello è di fondamentale importanza. Di seguito vediamo nella fig 5 l’andamento della solidificazione a seconda del punto dove si è scelto di mettere l’alimentazione del getto.

La solidificazione osservata nella figura precedente, conduce alla presenza di porosità nelle zone evidenziate nella figura 6.

I risultati possono essere verificati osservando i componenti fusi. E’ molto importante, nell’utilizzo dei software di simulazione, tarare l’affidabilità del software con il proprio processo di fusione.
Di seguito sono riportate le immagini delle superfici dell’anello analizzato e fuso con i due diversi posizionamenti dell’alimentatore:

Allo stesso modo prendendo in esame un oggetto di dimensioni maggiori, possiamo vedere che le stesse regole della solidificazione direzionale sono applicabili anche in questo caso.
La figura in esame è una “C” che potrebbe essere utilizzata per realizzare la metà di un bracciale.

Nel primo esempio prendiamo in considerazione il pezzo con la stessa tipologia di alimentazione ma fuso con parametri diversi. In particolare si può notare la variazione di risposta al variare della temperatura, sia di stampo che di fusione.

Come si può notare dalle immagini, al crescere della temperatura le dimensioni delle porosità decrescono. Questo avviene perché si da più tempo al metallo per solidificare in maniera direzionale. In questo caso, tuttavia, il solo variare dei parametri di processo non riesce a risolvere il problema alla radice.
È necessario, quindi, modificare l’alimentazione. Prendiamo in esame due tipologie di alimentazioni.

Di seguito possiamo vedere la simulazione del processo di solidificazione in entrambi casi.

Analizzando la figura a sinistra si può notare che i sei raggi di alimentazione stanno solidificando prima che il bracciale sia esso stesso solidificato (come nell’esempio precedente), “chiudendo” le strade al metallo per continuare ad alimentare correttamente il pezzo. Nella figura a destra, invece, si nota come i quattro raggi vadano ad alimentare bene il pazzo consentendo una solidificazione direzionale verso il cuore del piantone.

La riprova dell’efficienza dell’alimentazione tipo B è data dall’analisi delle porosità.
In figura 16 si può notare come nel caso B il pezzo sia esente da porosità, mentre nel caso A si riscontrino sei nuclei di porosità da ritiro esattamente dove il metallo ha raffreddato per ultimo sul pezzo.

Le evidenze di queste simulazioni sono riportate nelle immagini seguenti.

L’analisi di queste geometrie semplici dimostra la validità della simulazione. Il software è in grado di prevedere con precisione quali saranno le zone affette da difetti e l’entità di questi ultimi.
La simulazione del processo di microfusione è uno strumento utile al tecnologo che non elimina del tutto il processo di “Trial and Error” ma lo limita all’ambiente virtuale della simulazione abbattendo i tempi e i costi dell’industrializzazione del prodotto.

Lo strumento fondamentale per l’utilizzo del software di simulazione di colata è la modellazione CAD 3D.
Come si è già detto, infatti, per poter simulare il processo di colata è indispensabile partire da un modello 3D, sia del sistema di colata che vogliamo simulare sia dello stampo all’interno del quale andremo a colare il metallo.
Quanto più è accurato il modello di partenza, tanto più saranno accurati i risultati della simulazione.
La modellazione CAD offre anche il vantaggio di poter disegnare e simulare in tempi rapidi diverse tipologie di alimentazioni e di sistemi di colata.
Simulando diverse alimentazioni potremmo stabilire la più idonea al nostro particolare.
Prevedendo la simulazione di colata all’inizio del processo di progettazione, sarebbe possibile individuare da subito eventuali errori di design e intervenire modificando la geometria del modello.
Laddove non è possibile modificare il design del pezzo, si dovrà forzatamente andare ad agire su altri parametri (alimentazioni, parametri di processo, etc..) 

Una volta capita l’importanza della simulazione sul singolo particolare, è possibile esplorare nuove possibilità per sistemi di colata complessi.
Simulare un intero albero di fusione consente, ad esempio, di analizzare il processo nel suo insieme e di ottimizzarlo.

Concludendo l’introduzione di questa tecnologia nella filiera della creazione orafa è senza dubbio di aiuto alla transizione verso una produzione più performante e mette il “turbo” alle aziende che vogliono impiegare forze e mezzi per implementarla nei loro processi produttivi.

Per poter sfruttare al meglio questa tecnologia occorrono mezzi e studio, tuttavia i vantaggi risultanti dal suo utilizzo (il risparmio di tempo, mezzi e l’efficacia dei risultati ottenuti) abbattono tutte le incertezze. Nel tempo questo diventerà l’unico modo di procedere per industrializzare un manufatto orafo, così come già avviene in tutti gli altri settori di produzione.

una relazione di Antonello Donini

Stiamo parlando di DIAMANTE SINTETICO.
Carbonio (C)  cristallizzato nel sistema cubico disposto nel reticolo secondo la configurazione spaziale tetraedrica.
Come accade nel diamante naturale tale configurazione conferisce a  questo materiale proprietà che lo rendono unico nel suo genere.

Non parliamo quindi di una imitazione ma di vero e proprio diamante prodotto con metodi artificiali di sintesi fatti dall’uomo e non dalla natura.

I primi tentativi di  realizzare in laboratorio l’esatta controparte sintetica del diamante sono databili intorno alla fine del 19° secolo, ma  il primo successo storicamente documentato risale alla prima metà degli anni ’50 del 20° secolo, quando i ricercatori dell’americana General Electric hanno sintetizzato i primi piccoli cristalli di diamante.

Sempre la General Electric, circa 20 anni dopo, ha realizzato i primi diamanti sintetici aventi dimensioni sufficienti per poter avere un utilizzo come gemma, seguita negli  anni ’80 dalla giapponese Sumitomo, dalla De Beers e verso l’inizio degli anni ’90, da laboratori  russi.

Metodi di sintesi

Metodo di produzione HPHT

Il metodo si basa sulle condizioni che hanno permesso in natura la formazione del diamante ovvero alte pressioni ed alte temperature.

All’interno delle celle di reazione contenenti  cristalli-seme, una lega/soluzione metallica (ad esempio nickel e ferro) che funge da fondente/catalizzatore, il nutriente (solitamente grafite) viene esposto a condizioni di alte pressioni ed alte temperature (tra 1400 e 1600°C e tra 50 e 60 kbar) grazie a elementi riscaldanti e presse.
Il carbonio si dissolve nel fondente e si deposita quindi sui cristalli seme posti solitamente in una zona della cella con temperatura inferiore sotto forma di diamante.

Metodo HPHT  BARS

Metodo HPHT  TOROID

Metodo HPHT  CUBOID

Una importante problematica da affrontare per questo metodo di sintesi è quello di tenere lontana la presenza di azoto responsabile di una colorazione verde giallo alla bruna dei cristalli sintetizzati.
L’utilizzo di nuove leghe metalliche utilizzate come fondenti, con l’aggiunta di particolari elementi (come alluminio, cobalto o rame) che permettono di fissare l’azoto facendo in modo che non rientri nel reticolo del diamante.

Si ottengono così diamanti incolori (tipo Iia) o con lieve colorazione  bluastra per la presenza di lievissime quantità di boro (tipo IIb).

DIAMANTE SINTETICO CVD

Ha il grosso vantaggio di avvenire a basse pressioni, nell’ordine di 10-200 torr.

Nella camera viene creato un plasma che rompe la molecola di metano o altro gas contenente C.

Il carbonio si va quindi poi a depositare sotto forma di diamante su un substrato solitamente costituito da sottili semi di diamante.

Elementi utili alla identificazione

I diamanti sintetici incolori CVD sono in generale del tipo IIa ovvero composti da solo carbonio.

Per eliminare una possibile componente bruna presente nei diamanti cristallizzati con questo metodo dovuta a dislocazioni, vengono sottoposti a un post trattamento HPHT in grado di eliminarla.

Al microscopio i diamanti sintetici HPHT mostrano spesso caratteristiche figure di crescita, correlate ai settori di crescita cubici e ottaedrici.

È possibile rilevarle in corrispondenza di zonature di diversa fluorescenza o nella distribuzione del colore all’interno della pietra che segue questi settori di crescita.
Le inclusioni  caratteristiche, ma non sempre presenti, sono residui di fondente che si presentano come inclusioni nere e opache con lustro metallico.

Le inclusioni  caratteristiche, ma non sempre presenti, sono residui di fondente che si presentano come inclusioni nere e opache con lustro metallico o estesi gruppi di inclusioni puntiformi (probabilmente minute particelle di fondente disperso).

I diamanti sintetici CVD potrebbero avere minute inclusioni scure (residui carboniosi) con aloni di tensione probabilmente generati da un post trattamento termico utilizzato per migliorare il colore delle gemme.

Molti diamanti sintetici HPHT mostrano una caratteristica fluorescenza da gialla a verde giallastra agli UVL (365 nm) e agli UVC (254 nm).

Le impurità che vengono assorbite nella struttura del diamante sintetico durante la sua crescita tendono a concentrarsi ciascuna in determinati settori di crescita, ciò origina caratteristiche figure di fluorescenza, a forma di croce o ottagonali, mai viste in diamanti naturali.

Spesso, a differenza di quanto accade nei naturali, la reazione è più intensa all’onda corta che a quella lunga.

I diamanti naturali generalmente mostrano una fluorescenza più o meno marcata di colore blu (più raramente gialla e, meno comunemente ancora, verde o rosa), abbastanza uniforme e, comunque,  più marcata all’onda lunga che all’onda corta.

La presenza di fosforescenza solitamente persistente (rarissima in natura e atipica nelle pietre incolori) è un buon segno identificativo.
Sono infatti i diamanti di tipo IIb estremamente rari in natura (contenenti boro) che presentano questo effetto solitamente di breve durata.

Una caratteristica particolare dei diamanti prodotti con il metodo HPHT è quello di mostrare poche o lievi birifrangenze anomale al contrario dei diamanti naturali. Nei sintetici CVD le birifrangenze anomale sono generalmente simili a quelle dei diamanti di tipo IIa naturali ovvero con una specie  di graticcio, spesso orientato secondo la direzione di deposizione dei cristalli.

Esistono però cristalli sintetici CVD di qualità “ottica” (QUINDI OTTICAMENTE PERFETTI ED OMOGENEI) privi di birifrangenze anomale.

Identificazione certa solo attraverso tecniche analitiche avanzate

La spettrofotometria IR (infrarosso) è un ottimo aiuto per riconoscere la tipologia del diamante ovvero per verificare la presenza o assenza di tracce di alcuni elementi fondamentali. SI hanno così potenziali informazioni per isolare tipologie di diamante che potrebbero essere compatibili con una produzione sintetica.

I Diamanti sintetici incolori sono di tipo IIa (azoto presente in quantità talmente piccola da non poter essere rilevato strumentalmente con IR), mentre quelli blu, come i loro analoghi naturali, sono di tipo IIb (presenza di boro). La presenza del tipo IIb ovvero di tracce di boro è riscontrabile spesso in moltissimi diamanti sintetici incolori. Sono stati anche visti in commercio diamanti sintetici di colore rosa dovuto ad un post trattamento per irraggiamento e successivo riscaldamento a bassa temperatura. E’ bene ricordare che le prime produzioni, proprio per la presenza di azoto prevedevano colorazioni nel giallo con diverse sfumature di bruno o bruno verdastro. Alcuni diamanti di questo tipo trattati per irraggiamento hanno assunto un vivacissimo colore rosso.

Allo spettrofotomentro UV-VIS-NIR la componente Ib presente nei diamanti sintetici giallo verdi genera un assorbimento a partire dai 500 nm verso l’ultravioletto.
Molti diamanti mostrano, una serie di assorbimenti tra 470 nm e 700 nm, dei quali il più evidente è a  658 nm. Questi picchi sono dovuti alla presenza di nickel all’interno della struttura cristallina presente nel catalizzatore.
I diamanti incolori sintetici di tipo IIa sono trasparenti sino a 270 nm.

Presenza di elementi come nickel, ferro, alluminio, cobalto, rame o gli altri metalli impiegati nella crescita, possono essere identificati mediante un’analisi chimica con fluorescenza ai raggi X (EDXRF).

Attraverso la Fotoluminescenza è possibile rilevare centri di colore diagnostici grazie alle tracce di impurità presenti   quindi riconoscere la natura sintetica.

La osservazione degli effetti di luminescenza ad uv molto corti può essere molto utile per riconoscere i diamanti sintetici.  

Quadro della situazione commerciale

I produttori di diamanti sintetico sostengono che:

I diamanti prodotti artificialmente in laboratorio hanno essenzialmente la stessa composizione chimica, struttura cristallina, proprietà ottiche e fisiche dei diamanti estratti dalle miniere: sono quindi diamanti al 100%. L’unica differenza tra i diamanti sintetici e quelli estratti è che uno è stato creato all’interno ed estratto dalla Terra e l’altro è stato creato in un laboratorio all’avanguardia.

Sono numerosi i produttori che sintetizzano diamante soprattutto per scopi industriali.

In gioielleria la dimensione delle gemme sfaccettate ha raggiunto dimensioni decisamente importanti: sono state viste gemme di oltre 10 ct. Ma la maggiore diffusione di questo prodotto si ha su gemme fino ad un max di 2,00 ct e nei lotti melèe (da meno di un punto fino a 0,25 ct).

Costante crescita e diffusione nel settore orafo dell’utilizzo di questo materiale gemmologico, trascinato dall’intensivo e sempre maggiore impiego industriale di questo materiale.
Ampiamente utilizzato negli strumenti come superabrasivi, mole, utensili da taglio, strumenti di perforazione e lucidatura, prodotti dell’industria automobilistica, medica, aerospaziale ed elettronica.

Per i costi di manifattura e per importanza di mercato fanno la parte del leone i paesi asiatici, seguiti dal nord America.

Commercialmente stanno avendo un forte spunto e diffusione soprattutto negli USA e in Giappone.

A fornire un forte discapito per chi tratta il naturale, la FTC statunitense (Federal Trade Commission, organo legislativo commerciale) ha permesso che queste sintesi potessero essere chiamate come “grown diamonds”.
Ha inoltre stabilito che il “diamante sintetico” è da considerarsi come vero e proprio “diamante” permettendo ai produttori di sintetici di commercializzare i loro prodotti come «reali» / «veri» (real diamonds).

Il resto del mondo e le norme ISO internazionali prevedono che questo materiale gemmologico debba essere chiamato, ai fini della chiarezza nei confronti del consumatore solo come  “diamante sintetico” al pari di qualsiasi altra sintesi.
Nessuna altra definizione o semplificazione è ammessa.
ISO 18323:2015

Il costo di questo materiale è attualmente inferiore al naturale di circa il 30-40% ma sono previste ulteriori diminuzioni dovute ad una sempre maggiore diffusione e alla riduzione dei costi di produzione.

I diamanti sintetici rappresentano attualmente circa Il 2% del mercato globale.
Ci si aspetta che entro il 2030 tale quota possa salire al 10%.
Per pietre con peso attorno al 0,50-1,50 ct, adatte ad un impiego come solitario ovvero per un anello da fidanzamento la quota del 7,5% potrebbero essere raggiunta già nel 2020.

Per il «melèe» si potrebbe arrivare ad una quota del 15% nei prossimi due anni.

La diffusione di questo materiale nel melèe potrebbe essere intensificata da una progressiva  scarsità di diamanti estratti in natura in quanto è attesa la chiusura della miniera di Argyle (ormai quasi esausta) che attualmente fornisce la maggior parte dei diamanti piccoli del mondo.

Difficile quindi fare oggi delle previsioni su quale sarà il reale impatto di questo materiale sul mercato dei preziosi.

Le nuove generazioni sembrano, dagli studi di marketing, positivamente favorevoli all’utilizzo di questo nuovo materiale in ornamentazione.

Il diamante sta perdendo quel fascino di pietra simbolo di rarità e amore eterno per raggiungere sempre più lo status di gemma a larga diffusione.
I consumatori iniziano  a percepire i diamanti sintetici come allettanti: è possibile avere gemme più grandi a prezzi più bassi e, soprattutto, fare un investimento «privo di sensi di colpa».
È attiva una importante operazione mediatica per pubblicizzare queste gemme come maggiormente “etiche” rispetto le naturali.
I giovani, essendo giustamente orientati all’ambiente e al non sfruttamento di risorse naturali e soprattutto umane, mostrano maggiore interesse per questo tipo di gemme, rispetto le generazioni precedenti coinvolte maggiormente sulla unicità e rarità del singolo gioiello.

Grossi nomi dello spettacolo e del mondo web come Di Caprio, Lady Gaga, Penelope Cruz o i possessori di Facebook, Twitter e eBay hanno pubblicizzato o persino finanziato strutture per la produzione di diamanti sintetici, credendo nel loro futuro.
La Diamond Foundry uno degli ultimi produttori statunitensi comparsi sul mercato ha dichiarato di essere attualmente l’unico produttore di diamanti certificato “carbon neutral”, in quanto i suoi diamanti sono fabbricati in un reattore al plasma ad energia idroelettrica.
Sostiene inoltre che: “l’estrazione mineraria ha un impatto ambientale maggiore rispetto a qualsiasi altra attività umana. Per un singolo carato di diamante, devono essere scavate circa 250 tonnellate di terra, e vengono rilasciati notevoli quantità di inquinamento atmosferico con l’emissione pesante di anidride carbonica”.

De Beers attraverso il marchio LIGHTBOX ha iniziato la commercializzazione on-line di linee di gioielleria con diamanti sintetici incolori, azzurri e rosa ad un costo molto basso cercando di accaparrarsi una importante fetta di mercato mondiale. (1.00 ct 800,00 US$ – 0.50 ct 400.00 US$ – 0.25 ct 250.00 US$).

Dagli studi più del 60% degli intervistati sarebbero disposti, interessati all’acquisto di un diamante sintetico su un anello di fidanzamento, per il costo inferiore del materiale permettendo così di avere gemme di dimensione maggiore ad un costo inferiore.

I consumatori con disponibilità economica solitamente più legati al fascino, al mistico all’unico  e all’irripetibile…sembrano invece mostrare molto interesse per questo materiale.

I produttori di diamanti sintetici sono stati in grado di interessare i cosiddetti «millennials» promuovendo il Lab Grown Diamond  come high-tech, innovativo e pulito.

In tutti gli aspetti della loro vita cercano marchi, aziende e prodotti che ritengono trasparenti, socialmente e rispettosi dell’ambiente.

Il consumatore non crede ormai più nel valore dei diamanti o del gioiello in generale.

Ci sono infatti stati nel tempo diversi fattori che hanno diffuso sfiducia nel settore.

• Operatori commerciali poco trasparenti
• Scarsa conoscenza dei materiali e del mercato da parte degli operatori
• Scarsa resa dei diamanti da investimento
• Poche certezze

Occorre però tener conto che: un diamante naturale anche se di brutta qualità avrà sempre un possibile acquirente.
Non esiste invece un mercato secondario per i diamanti sintetici, soprattutto perché i commercianti di diamanti attuali tendenzialmente non li trattano.
Il «buon affare», il risparmio che si può avere acquistando un diamante sintetico, sfuma quando si pensa al fatto che sarà impossibile rivenderlo.

Al momento il quadro è decisamente confuso, poco chiaro. Gli operatori del mondo, dati gli interessi economici che ruotano attorno al materiale naturale, sono decisamente preoccupati e spaventati dalla improvvisa diffusione e dal numero delle operazioni mediatiche che stanno ruotando attorno al diamante sintetico.

Ma se guardiamo al passato quello che sta accadendo ora è stato promosso nello stesso ed identico modo in passato quando DeBeers all’inizio del secolo scorso attraverso operazioni mediatiche mirate e personaggi dello spettacolo (pensiamo a Marylin Monroe e alla frasi «i diamanti sono i migliori amici delle ragazze» e «li diamante è per sempre») ha diffuso l’uso del diamante in gioielleria in modo che potesse diventare per tutti «simbolo di vero amore eterno».

Quindi difficile dare una risposta al quesito iniziale anzi, possiamo aggiungere ora un altro quesito: “il diamante sintetico potrebbe essere una opportunità?”