Master thesis : Multi-material die pressing, an innovative approach to printing near net shape titanium alloy medical implants at reduced cost

Abstract

Conventional die pressing involves filling a die with powder and compacting the powder once the die is filled. This conventional process is used to manufacture parts with simple geometry as the geometry of the die defines the geometry of the part. Aerosint is engaged in a research project with Amnovis, the Bel-SME project, which intends to produce near net shape titanium alloy parts for medical industry at reduced cost. The conventional process can then be replaced by an innovative process, aiming at compacting the powder layers at regular intervals, allowing to achieve higher and more homogeneous densities. The selective powder deposition approach invented by Aerosint results in multi-material, binderless printing, allowing the production of parts with more complex geometry.

The objectives of this thesis were to determine the layer thickness that allows to obtain green compacts that do not show delamination effects; to determine the compaction pressure to be applied to obtain a self-supporting green compact that has the desired relative density after sintering; to characterise virgin and modified Ti-6Al-4V powders, and to quantify the thickness of the ceramic material layer around the modified powders.

Compaction tests on AlSi10Mg and nitrided CuCr1Zr powders proved the value of compacting thin layers at regular intervals, demonstrating that compaction after deposition of 500 µm layers provided green compacts without delamination effects. Analysis of the density variation along the thickness of the green compacts did not reveal statistical significance, suggesting a homogeneous density. A self-supporting Ti-6Al-4V green compact was obtained by gradually compacting 500 µm layers to 305 MPa. The thickness of the ceramic layer on the surface of the modified Ti-6Al-4V powder is in the range 1-2 µm.

The Bel-SME project proposes a unique binder-free powder solidification process that produces parts that are both complex, thanks to the possibility of using a support powder that is different from the part powder and that dictates the geometry of the part, and dense, thanks to the compaction of the powder at regular intervals. This Master thesis contributed to this project, which in the near future will print near net shape medical devices in titanium alloy at reduced prices.