Geometry driven parameters and relevance of open material system for jewelry additive manufacturing.

a speech by Marco Giuseppe Andreetta

Sisma, a growth journey of more than sixty years

More than 40 years in jewellery making machines, more than 60 years in micromechanics

More than 20 years in laser manufacturing and laser based process expertise

More than 10 years in manufacturing of metal 3D printing machines designed for small and complex geometries

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.

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