Linde, a global industrial gas specialist headquartered in Guildford, Surrey, UK, is exhibiting a number of gas technologies at Formnext 2022, including its bespoke gas mixture developed specifically to optimise Laser Beam Powder Bed Fusion (PBF-LB) Additive Manufacturing, gas atomisation solutions for metal powder production, and the acceleration of the use special alloy nitinol (NiTi). The company will also have people on its stand to discuss countering counterfeit Additive Manufacturing.
“Linde has long been a pioneer in the development of innovative gas technologies to optimise manufacturing processes,” stated Pierre Forêt, Associate Director, Additive Manufacturing, Linde. “In this rapidly developing world of Additive Manufacturing, we are delighted to be showcasing some of our most groundbreaking solutions at Formnext.”
Nitinol (NiTi) is a metal alloy of 50/50 nickel and titanium with unique properties, including superelasticity and ’shape memory effect’, meaning it can change its shape when heated and return to its original shape when cooled. Increasingly used in the medical and dental industries for orthopaedic implants, stents and orthodontic parts, and in aerospace for solar panels, manufacturers of NiTi products face challenges as the parts are difficult to machine, and product design is limited to simple structures. Additionally, traditional machining results in excessive tool wear, high cutting forces and surface degradation.
While PBF-LB offers greater design freedom and production efficiency, there are still issues to overcome when additively manufacturing with nitinol. Vapourisation of the nickel during the process can lead to a shift in the nickel:titanium ratio, thus increasing the transformation temperature. Additionally, oxygen contamination inside the material can also affect the transformation temperature, while surface oxidation can require significant post-production cleaning. To avoid these latter issues, it is important to reduce the amount of oxygen in the build chamber. To provide control of O levels, Linde an 3D Medlab have collaborated to optimise the build atmosphere using Linde’s ADDvance O2 precision oxygen monitoring system and ADDvance® Laser230 process gas mixture.
The ADDvance O2 precision provides continuous analysis of the gas atmosphere and is able to recognise O2 concentrations as low as 10 ppm and initiate an automatic purging process to maintain optimal atmospheric conditions. The ADDvance Laser230 process gas combines argon with helium to reduce particle redeposition, porosity and powder loss by up to 20%. It is also said to increase the lifecycle of the Additive Manufacturing machine, as well as mitigate fume formation and accelerate cycle times, making the AM process safer and cheaper. It is alloy agnostic and well suited for additively manufacturing lattice structures.
The ADDvance Sinter250 is a gas-enabled solution for Binder Jetting which optimises sintering atmospheres to avoid oxidation in metal Fused Deposition Modelling (FDM). Linde has developed a range of tailored gases (e.g., pure argon, pure hydrogen, and a special argon/hydrogen mixture). ADDvance Sinter250 is said to be suited for ensuring the integrity and strength of parts manufactured from stainless steel powders. Linde also offers turnkey solutions including heater, control panel and gas supply to enable the creation of finer powders or reduce gas consumption.
Linde’s test bench laboratory – expected to be operational in March 2023 – will enable the testing of industrial-scale gas parameters in an effort to advance the understanding of gas behaviour when used in a typical metal powder atomiser.
As innovative Additive Manufacturing technologies have made significant advances to the process itself, the demand for novel metal powders has grown significantly. While vast in size and requiring multi-million-dollar investments, standard metal powder atomisers are unsuitable for the observation and analysis of gas behaviour, as parameters are adapted. Linde’s new laboratory is a much smaller scale version (1.60 m high) of a typical atomiser, but has specially adapted windows, lighting, high-speed cameras and schlieren imaging allowing for surveillance and data capture of each change of gas parameter.
The laboratory does not rely on the introduction of molten metal, instead using data from the simulated process to provide evidence of gas behaviour under certain conditions. The different parameters to be assessed include gas type, volume of gas, pressure and temperature, with the miniature atomiser able to rapidly switch over to analyse hundreds of combinations within minutes. The laboratory is expected to enable Linde to develop new technologies to improve the atomisation process – particularly increasing yield and process stability. Linde will also collaborate with powder manufacturers and OEMs to help them test specific gas behaviours on the test bench, allowing them to then scale up the results on their large atomisers.