A reliable clean process for five-axis milling of knee prostheses

Prosthesis production for hips, knees, and other human body elements, including dental implants and spine screws, requires eliminating any risk of material damage or contamination. Five-axis milling is the most suitable technique to manufacture tailor-made prostheses for different personalized sizes with affordable costs. Human life expectancy is growing, so the demand of a higher prosthesis lifecycle and manufacturing optimization is a current necessity. In this work, a robust five-axis milling process using cryogenic CO2 as coolant fluid is presented and applied to a Ti6Al4V knee implant. Ti6Al4V (grade 5 and grade 23) alloys are very difficult to cut without lubri-cooling using oil emulsion coolant; however, this emulsion implies risks from introducing little oil drops entrapped in surface roughness valleys, hampering the cleaning process before patient's surgery. CO2 reduces this risk uncertainty, making machining operations more feasible and suitable regarding environmental sustainability. In terms of feasibility, the surface finishing, roughness, and residual stresses was analysed, obtaining a standard of IT4-IT5, N4 and compressive stresses, respectively. Virtual simulation of machining is also a key in five-axis to make a more robust industrial process.