Study on 4-axial precision milling of spatial freeform surface for individualized hip prosthesis stem

Abstract

The fabrication of individualized hip prosthesis stem requires high machining freedom to dovetail precisely with the bond cavity of the patient. Hence, a 3-axial linkage motion is proposed in 4-axial milling along with a 1-axial differential drive and a cutter offset angle. Its advantage is to prevent from the accumulated errors of multi-axial motions. First, the centerline of spatial stem with the length of 200 mm was installed to a rotating axis; then, the transfer model of non-closed polar coordinate points was constructed to design 2D closed tool paths for the control of 3D cutting contact points; finally, the form error and the surface roughness of milled stem surface were investigated in connection with cutter posture angle. Theoretical analysis shows that the cutter offset angle contributes to an increase in cutter posture angle for high cutting velocity and the predication of the interference between cutter bar and workpiece. Experimental results show that the milled surface roughness and the milled form error are decreased by about 50 % and reach 0.26 and 126 μm when the cutter posture angle decreases to 20–40 °, respectively. It is confirmed that the 3-axial linkage milling along with 1-axial differential drive is likely to realize the precision machining of spatial hip prosthesis stem by controlling the cutter offset angle.