Analytical and experimental study of effective parameters on process temperature during cortical bone drilling.

Bone drilling process is a prominent step of internal fixation in orthopedic surgeries. Process forces, leading to chip production, produce heat in the vicinity of the drilled bore and increase the probability of necrosis phenomenon. In this article, an analytical model to predict process temperature is presented based on Sui and Sugita model. This heat transfer model is the combination of a heat equilibrium equation for tool-chip system and a heat distribution equation for the bone itself where heat generation in tool's tip is due to cutting frictional forces. In an analytical model, it is possible to use material properties of the bone and geometry of the tool; therefore, the calibration test is not necessary. In order to validate analytical model, experiments were done using bovine bone. Using response surface method, a second-order linear regression mathematical model is derived using experimental results. The effect of each individual parameter as well as their interactions on the output of the process was investigated. Within the range of the parameters studied in this article, with an increase in rotational speed, process temperature boosts up. Effect of feed rate is complicated due to the tool-bone contact time issue. While higher temperature is achieved in lower feed rates because of higher tool-bone contact time but higher temperature is observed with high feed rates due to an increase in force and friction. Optimized combination of the parameters to minimize temperature of 35.6 °C is tool diameter of 2.5 mm, rotational speed of 500 r/min and feed rate of 30 mm/min. Good correlation was observed between analytical and experimental results.