A machining strategy to fulfil geometrical quality requirements in cryogenic turning of acetabular cups made of Additive Manufactured Ti6Al4V

Additive Manufacturing (AM) techniques are more and more employed in the biomedical industry to produce surgical implants made of Ti6Al4V alloy. After the AM process, some finishing machining operations are still required to obtain the final product geometry. In recent years, cryogenic cooling has been adopted to improve the Ti6Al4V poor machinability, but mainly in rough machining operations. The adoption of cryogenic cooling can cut down the cleaning and sterilizing costs of biomedical components due to the drastic reduction of residual pollutants on the parts. This paper investigates the feasibility of cryogenic cooling using LN2 when finishing turning AM acetabular cups made of Electron Beam Melted (EBM) Ti6Al4V, focusing on geometrical accuracy. A preliminary study conducted on a test specimen, showed that the most critical thermal induced dimensional errors are caused by the progressive tool holder contraction and that they can be limited by acting on the cutting length. On the basis of these findings a temperature-dependent correction of the tool trajectory can be implemented to achieve the required dimensional accuracy of the acetabular cup when machined under cryogenic cooling.