# The Influence of Bit Edge Shape Parameters on Bone Drilling Force Based on Finite Element Analysis
## 6 Conclusions  
Most researchers studied the drilling parameters or one or two parameters of the cutting edge. To obtain the best drilling parameters and drill bit edge shape parameters, this work further studies the influence of point angle, helix angle and edge radius on drilling forces in detail and draws the following conclusions:  
When the rotary speed is 1100 r/min and the diameter of the drill is 5 mm, the drilling force at the feed speeds of 0.03 mm/r, 0.07 mm/r, 0.11 mm/r and 0.15 mm/r is analyzed, respectively. It is found that the drilling force is the lowest at the feed speed of 0.03 mm/r, and its value is about 40 N.  
This work found that the variation trend of drilling force is consistent with the experiment, and the relative error is 13-21%, which is slightly larger. However, the similar variation trend illustrates that the simulation model can basically reflect the drilling process in the experiments.  
Through the analysis of drill bit shape parameters, it is found that edge radius has the most significant influence on drilling force, followed by point angle and then helix angle. The prediction model of the relationship between the bit shape parameters and drilling force is established through regression analysis. The model can fit 95% of the experimental data, and the fitting effect is significant. The model is optimized by adopting particle swarm optimization algorithm, and the minimum drilling force is 30.31 N. The optimum drill bit shape parameter combination is 95\({}^{\circ}\) in point angle, 35\({}^{\circ}\) in helix angle, and 0.02 mm in edge radius.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Authors** & **Material** & **Research Content** & **Conclusion** \\ \hline \multirow{6}{*}{[PERSON] et al. [42]} & \multirow{6}{*}{Skull} & The effects of bur material & \multirow{6}{*}{The results of maximum and duration of temperature, axial force, and surface defect evaluation show CO\({}_{2}\) coolants (especially internal CO\({}_{2}\) coolant) are the best options to decrease thermal damage.} \\  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \hline \multirow{6}{*}{[PERSON] et al. [43]} & \multirow{6}{*}{Pork rib} & \multirow{6}{*}{Temperature distribution and drilling quality observation using the medical twist drill in the physiological conditions (salt solution cooling) and without external cooling.} \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \hline \multirow{6}{*}{This work} & \multirow{6}{*}{Porcine femur} & \multirow{6}{*}{\(\Phi\)5 mm drill, on the premise of the predetermined rotation speed and feed rate, the influence of drill bit shape parameters including point angle, helix angle and edge radius on drilling force; and optimum matching of drill bit shape parameters.} \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \cline{1-1}  & & & \\ \hline \hline \end{tabular}
\end{table}
Table 9: Comparison between previous mostly related studies and this work.  
**Author Contributions:** Conceptualization, X.C.; methodology, T.H. and X.C.; software, T.H.; validation, T.H.; formal analysis, T.H.; investigation, T.H.; resources, T.H; data curation, T.H. and X.G.; writing--original draft preparation, T.H.; writing--review and editing, M.D.; visualization, T.H.; supervision, M.D.; project administration, M.D.; funding acquisition, M.D. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was supported by the National Natural Science Foundation of China (grant Number 61562055).  
**Institutional Review Board Statement:** Attachment view.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data sharing not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.