Machining of a functional hip prosthesis cone in TI-6AL-4V ELI titanium alloy produced by electron beam melting

Abstract

Digital manufacturing using 3D models and innovative fabrication methods present challenges for functional areas of medical devices. The advantages arising from 3D manufacturing processes like electron beam melting (EBM) play a major role in producing medical devices as, for example, orthopaedic implants. However, surfaces with functional demands for surface roughness and dimensional accuracy require machining operations to achieve the necessary standards. This study aimed to manufacture a functional cone of the modular component of the hip prosthesis through turning and to assess if an EBM-obtained component could offer better machinability as compared to wrought titanium and ensure functionality. To achieve this, the variances in cutting forces and surface roughness of the resulting surface were analysed during the turning tests. The results show that the EBM test samples had higher roughness (Ra) values, yet it was possible to achieve Ra = 0.4 μm for f = 0.1 mm/rev. and approximately 20% lower resulting cutting forces, for example, for f = 0.1 mm/rev, 122N compared to 101N. Using the Kienzle-Victor model, the specific cutting force of titanium EBM was determined to be 1775 N/mm2. The impact of the shell geometry of the EBM test samples had no significant effect on the results. This allows for the exploration of its potential in component design, as it provides an economic advantage in manufacturing. In conclusion, the cutting forces and surface roughness showed similar or superior machinability compared to that of wrought titanium. The EBM technology enables the production of intricate forms and facilitates finishing operations in functional zones.