# Numerical Study of Coolant Flow Phenomena and Heat Transfer at the Cutting-Edge of Twist Drill
## 4 Results and Discussion
This performance can be attributed to the velocity profile of the model. As shown in Figure 7, the coolant flow successfully reaches the cutting-edge area for this specific drill model, resulting in improved heat dissipation. As previously explained, fluid flow and heat transfer depend on the shape of coolant channels and their exit, among other factors. Comparing the temperature distribution for 40- and 60-bar pressures, there is a slight decrease in temperature as the pressure increases. Remarkably, at 60-bar pressure, the temperature range is relatively lower in the standard-with-notch model,  
Figure 8: Fluid temperature distribution at the cutting-edge for three modified drill models for varying inlet pressures. Note: the colour legend is in \({}^{\circ}\)C.  
including the outer corner of the cutting-edge, where fluid flow is limited. However, at 40-bar pressure at the inlet, the very edge of the outer corner exhibits a higher temperature. Given the higher fluid flow rate near the cutting-edge area of the standard-with-notch model (Figures 6 and 7), it can be assumed that the coolant is relatively mobile at the cutting-edge area of this specific model, leading to sufficient heat transfer. The removal of chips is a critical factor in the design and performance of drilling tools. Effective chip evacuation is essential to maintain a clear cutting zone, reduce friction, and prevent the re-cutting of chips, which can lead to increased tool wear and thermal load. In our study, the different coolant channel designs not only aimed at improving coolant flow and heat dissipation but also at facilitating efficient chip removal. The presence of notches in the modified drill models, such as the standard model drill with a notch and the profile model drill with a notch, enhanced the escape path for both coolant and chips. This design modification proved beneficial in reducing the formation of dead zones where chips could accumulate, thereby minimizing the risk of clogging and improving overall tool performance. High-pressure coolant supply further aided in flushing out chips from the cutting zone, maintaining optimal cutting conditions and extending tool life. Future designs should continue to integrate considerations for both coolant delivery and chip evacuation to enhance machining efficiency and tool durability. In addition to the coolant channel design and pressure conditions, the rotational speed of the drill is another critical parameter that can significantly impact the flow and heat transfer characteristics. Higher rotational speeds can enhance coolant circulation due to increased centrifugal forces, potentially improving heat dissipation at the cutting-edge. However, excessive speeds might lead to turbulence and unstable flow patterns, which could negatively affect the efficiency of coolant delivery and chip evacuation. While this study did not include a parametric analysis of rotational speed, future research should investigate its effects to provide a more comprehensive understanding of coolant flow dynamics and thermal management during drilling operations. Lastly, the typical tool material for twist drill bits is high-speed steel (HSS), known for its excellent thermal stability, hardness, and wear resistance. HSS can withstand extremely high pressures of up to 150 bar and high temperatures of up to 650 \({}^{\circ}\)C [30], making it ideal for demanding machining operations. In this study, the coolant channels were tested under simulations using a maximum fluid pressure of 60 bar and it was observed that the maximum temperature experienced by the tool cutting-edge was 450 \({}^{\circ}\)C for the profile with a notch channel design (shown in Figure 5). The combination of HSS's thermal properties and the controlled conditions used in this study ensures that the material will not degrade or lose its performance capabilities. The choice of HSS ensures the reliability and effectiveness of the tool even under the specified high-pressure and high-temperature conditions.