Precision turning for robust optimization in the manufacture of femoral heads for hip arthroplasty

The large elderly population has naturally led to an increase in the number of orthopedic surgeries, such as hip replacement, highlighting the need to develop machining manufacturing technologies that meet the quality requirements of the prosthesis. ABNT 316L austenitic stainless steel is used in the manufacture of joint prostheses and, although it is considered a material with low machinability, it is an economical alternative to the application of other biomaterials such as titanium alloys and ceramics. This work presents the optimization of the turning of femoral heads for a total hip prosthesis. To this end, it has used the response surface methodology and the robust parameters design to model and optimize the main process responses: roughness and sphericity. The experiments were carried out based on a combined array considering three control variables: cutting speed, feed rate and depth of cut, and two noise variables: fixed length of the workpiece and cutting fluid flow. As quality characteristics, the surface finish and the sphericity of the femoral heads were analyzed using the mean roughness and total circularity deviation, respectively. Robust optimization was performed by combining mean square error and normal boundary intersection techniques. Therefore, the formulation of the optimization problem was to minimize the roughness in the turning process of ABNT 316L, limiting the sphericity to 10 µm. From the results obtained in this investigation, it was possible to generate components with surface and shape quality simultaneously. The noise variables had significant effects on the evaluated responses leading to their robustness.