Experimental investigation, sensitivity analysis and optimization on the effect of drill bit’s point angle and helix angle on cortical bone drilling process temperature

In this study, considering the point angle and helix angle as the most prominent geometrical parameters associated with the tool, using design of experiment based on Response Surface Method, evolution of process temperature and possibility of thermal necrosis were investigated. For this purpose, performing experimental tests on fresh bovine cortical bone, second order linear regression equation reflecting the process temperature was derived and validated. Using the Sobel sensitivity analysis, the exact influence of each point angle and helix angle on temperature was specified. Also, using derringer optimization method, the minimum process temperature, coincided with the optimum point angle and helix angles, was obtained. Results showed that minimal temperature could be obtained with vortex angle of 90 and helix angle of 27. Moreover, with higher point angles and lower helix angles drilling temperature in bone tissue increased. Finally, drilling temperature was more sensitive to the variation of helix angle rather than point angle.