# The Influence of Bit Edge Shape Parameters on Bone Drilling Force Based on Finite Element Analysis
## 1 Introduction  
A standard twist drill is one of the most common tools in orthopedic surgery. The cutting-edge structure of standard twist drills often leads to high drilling force or temperature. Therefore, it is necessary to fully understand drilling performance and optimize drill structure parameters to reduce drilling force, thermal damage, and bone recovery time. Larger drilling forces can lead to cracks in bone around the borehole [1], poor quality of the borehole [2], and even permanent necrosis of bone [3], which can easily lead to pathological fractures [4]. According to reports, shank implants fail between 2.1% and 7.1% due to large drilling force [5, 6]. Therefore, the bone drilling process needs to minimize drilling force. The effects [7] of various parameters on the process in drilling of the bone, such as bit diameter, feed rate, depth of the borehole, bit geometry, bit material, and drilling method, are described. In the past period, the study of the bone drilling process on the drilling force and drilling temperature is limited, and the research on the drill bit is summarized as follows. Technological parameters are studied by researchers have shown that the drilling force and temperature are affected. Still, the cutting-edge structure affects not only the drilling force and temperature but also the bit location and drilling quality. [PERSON] et al. [8] discussed the influence of cutting-edge shape and depth on the cutting law of femur drilling and concluded that a small rake angle could help reduce cutting force. [PERSON] et al. [9] studied the effects of bit diameter, point angle, drilling speed, feed rate, and external cooling on bone thermal necrosis in drilling of the porcine femur. Theresults show that the increase in bit diameter and rotation speed will lead to the increase in drilling temperature, the change in point angle has little effect on the temperature, and the temperature decreases when the feed rate increases. [PERSON] et al. [10] studied the effects of rotational speed, feed rate, point angle, and bit geometry on drilling force and temperature. The results show that rotary speed has little effect on drilling force and is proportional to the maximum temperature. The feed rate is proportional to drilling force and inversely related to the drilling temperature. [PERSON] et al. [11] studied heat transfer models in drilling of bovine femur. They proposed a new thermal model for orthopedic drilling, in which the maximum temperature increases with spindle speed, feed rate, and point angle and decreases with bit diameter and helix angle. The influence of spindle speed, feed speed, point angle, bit diameter, and helix angle on the maximum drilling temperature is discussed. Often, a much bigger point angle weakens the tool's ability to center itself, resulting in a rounded vertex. However, the point angle of the drill is greater than 90\({}^{\circ}\), resulting in less heat generated and, therefore, could be the suitable angle [12]. The point angle of less than 90\({}^{\circ}\) facilitates cartilage and chip flow penetration, reduces deviation from drilling target, increases radial force, and reduces axial force. It is generally believed that increasing the point angle increases drilling force when the bit enters the cortex [13]. [PERSON] et al. [14] concluded that larger point angles and drilling speeds were unsuitable for achieving minimum temperatures. A helix angle, also known as groove angle, can be defined as the angle between the groove edge and the bit spindle. A notch is a groove in the bit that provides a path for cutting debris from the hole. Its value usually ranges from 13\({}^{\circ}\) to 35\({}^{\circ}\)[15]. Most researchers have concluded, respectively, that helix angles of 28\({}^{\circ}\)[13; 16], 30\({}^{\circ}\)[17], and 27\({}^{\circ}\)-28\({}^{\circ}\)[18] have minimum temperatures, drilling forces, and torque. [PERSON] and [PERSON] [19] optimized bit geometry using high-speed steel bits with a helix angle of 23\({}^{\circ}\). [PERSON] et al.