Development of a surface roughness model in end milling of nHAP using PCD insert

Similar physical properties with human bone make hydroxyapatite (HAP) a suitable bioceramic material for hard tissue replacement in the fields of orthopedics and dentistry. Before being used in the human body, HAP needs to be machined to the required shape and dimensions with minimal surface roughness. This study investigates the machinability of fully dense nano-crystalline hydroxyapatite (nHAP) bioceramic in milling operations using polycrystalline diamond insert (PCD). The focus is on the effects of various machining conditions on surface roughness. The first order and second order surface roughness models for the end milling of nHAP is developed using response surface methodology (RSM), relating surface roughness to the cutting parameters: cutting speed, feed, and depth of cut. Based on the experimental results, it is found that cutting parameters have significant effect on surface roughness. For the ranges used in this study, a low feed (0.002 mm/rev) results in a smooth surface, and the middle depth of cut (0.5 mm) should be avoided. The final results show that the combination of cutting speed v=92 m/min, feed f=0.002 mm/rev, and depth of cut ap=1.6 mm gives a minimum surface roughness of 0.64 μm. In addition, it is proven that milling of nHAP is feasible for the fabrication of implants.