Impact Innovations, Rattenkirchen, Germany, has developed a Cold Spray Additive Manufacturing method for Ti6Al4V which is said to exceed the requirements of ASTM F3001, ISO 5832-3 and AMS 4930. This alloy is of particular use in marine and defence applications, for manufacturing aerospace structural parts, gas turbine components and biomedical implants and prostheses.
Up to now, Ti6Al4V was a challenging material for use in Cold Spray Additive Manufacturing, due to its high critical velocity, which must be overcome during the deposition process and resulted in porosities in the cold spray deposits of 3% and higher. By using a combination of cold spray hardware, process parameters and post-process procedure, Impact Innovations’ recently developed Cold Spray Additive Manufacturing process achieved porosity levels < 0.5%.
Cold Spray Additive Manufacturing technology is said to be particularly attractive for the manufacturing of large parts, which can be challenging for other Additive Manufacturing processes due to equipment size limitations or the need for a protective atmosphere, especially when depositing reactive materials such as Ti6Al4V.
In contrast to other Additive Manufacturing technologies, powder particles are not melted during the Cold Spray process; the bonding, instead, occurs due to plastic deformation. Since Cold Spray does not require high temperatures, it enables the manufacture of large components without the necessity for any protective atmosphere, with almost no dimensional limitation and without creating any thermal residual stresses. For Ti6Al4V, the material efficiency from powder to deposit is reported to be over 98%.
Impact Innovations demonstrated its Cold Spray Additive Manufacturing process by building a Ti6Al4V freestanding turbojet aircraft engine fan shaft which measures 380 mm long and has a diameter of 223 mm at its widest point. It was built in about two hours, at deposition rate of 2.7 kg/h, and the net weight of the fan shaft after final machining is 3.2 kg.
The fan shaft was deposited onto a pre-machined Al alloy mandrel, which was chemically dissolved after the build. The fan shaft demonstrator underwent further post-treatment processes to achieve desired mechanical properties, followed by turning to achieve the final outer dimension and the creation of additional features via conventional subtractive processes.
In addition to Additive Manufacturing with its Cold Spray process, Impact Innovations uses the technology to add wear protection coatings to components such as brake discs. In tests, the cold gas sprayed composite coating of a cast iron brake disc showed a 95% reduction in wear.
The technology is also applied to cookware, coating aluminium pans with a thin layer of ferritic steel to enable their use on induction stoves. This removes the need for brazed steel induction plates, thermal coatings or pressed perforated plates used currently to provide the necessary ferromagnetic base. With an effective coating of under 1 mm, there is hardly any change in weight to the aluminium pan.