# Numerical Study of Coolant Flow Phenomena and Heat Transfer at the Cutting-Edge of Twist Drill
## 1 Introduction  
In the realm of mechanical manufacturing processes, drilling stands out as a pivotal metal shaping operation. However, the involvement of various secondary phenomena in drilling operations renders the entire process costly, particularly when aiming for high-quality outcomes and process reliability [1, 2]. During drilling operation, both tool and workpiece are exposed to a very high temperature, resulting from evolving friction and shear force at the tool and workpiece interface [3, 4, 5]. This extreme thermal load reduces the strength of the tool material and accelerates tool abrasive and adhesive wear, which affects machining accuracy and productivity, and diminishes tool life and the surface quality ofthe workpiece [6; 7]. In this context, the supply of internal coolant plays the most important role in improving the process efficiency and extending tool life. However, the intricacies of drilling, where the cutting operation occurs inside the workpiece, pose a significant challenge in ensuring an adequate supply of coolant at the tip of the tool [8; 9; 10]. This is particularly crucial for efficient heat dissipation at the cutting-edge area. Additionally, the removal of chips increases the complexity of the drilling operation, subjecting the tool to high torsional loads because of the spiral flutes and less favourable cooling conditions [2]. Thus, a comprehensive understanding of the mechanisms contributing to tool wear and surface integrity in the drilling process is really important. In analysing the tribological stress on the drill, comprehensive thermodynamic properties of the tool and cutting fluid, body of the tool, counter-body of the chip, optimizing the ideal coolant, location and structure of the coolant channel, corresponding exit position on the flank face, and coolant flow rate and pressure must be meticulously taken into account [11]. The implementation of appropriate cooling technology can reduce tool wear, prolong tool life, and improve surface quality as well as overall sustainability of the production system [12; 13]. During the cutting process with a twist drill, the supply of cutting fluid to the cutting zone is facilitated through internal cooling channels. However, complexity arises as the exit points of these cooling channels are situated on the flank face, creating a challenge in delivering adequate coolant to the cutting zone and leading to an indirect cooling process [7]. Moreover, the complex behaviours of centrifugal and Coriolis forces come about due to increased angular velocities and the curvature of the spiral channels, thereby influencing the turbulent flow of the coolant. In addition to that, the gap between the tool and workpiece is very small, requiring the velocity of the coolant to be twice as large as the maximum cutting speed to effectively fill this confined space [14]. To ensure the proper cooling effect and decrease the thermal load, various design modifications can be applied. By changing the location, diameter, and geometry of the cooling channels, a higher lubricant flow rate and thermal convection can be obtained. However, it is noteworthy that experimental investigations into tribological stress analysis are often constrained and, at times, rendered impossible due to the inaccessibility of the complex cutting zone. [PERSON] et al. [15] provided a comprehensive overview of the state-of-the-art complex machining operations within metal cutting processes, highlighting research gaps that require immediate attention for improved outcomes. While numerous investigations have been conducted on metal cutting operations, with a predominant focus on milling and turning, the attention dedicated to the drilling process is notably limited, despite it being one of the most prevalent machining operations [16]. This is possibly due to the difficulties in accessing and analysing the complex cutting zone [17]. Among all drilling operations, almost 75% of jobs are performed using twist drills [18].