# Influence of Coolant Properties and Chip Former Geometry on Tool Life in Deep Drilling
## 2 State of the Art  
Deep drilling is currently used in various industries, such as mechanical engineering, construction, geological surveying, etc. The main task of this technology of drilling is to correctly determine the drilling process parameters and the correct selection of the tool [1; 2]. The most important parameters are rotational speed, torque, and contact force. The correct choice of parameters depends on the strength of the drilled material, the diameter of the drilled hole, and the force exerted in the process of the hole-drilling [3; 4; 5]. The correct selection of parameters with optimal settings can be monitored in real time by a suitably selected sensor involved in the drilling process [6; 7]. The paper by [PERSON] et al. presents an overview of several methods applied to the creation of holes with a large length-to-diameter ratio of the tool. The authors focused on the description of the basic principles of hole formation using deep drilling technology with regard to the quality of the drilled hole when using different types of workpiece materials. In conclusion, they summarized the results of the development of the deep drilling process and the production of tools around the world [8]. Deep holes are formed by conventional or unconventional methods. The article by [PERSON] et al. compares the methods of this drilling process based on the results achieved in research by several authors from around the world who investigate this area. These are conventional methods of drilling deep holes, such as, e.g., Gun Drilling (GD), Boring and Trepanning Association (BTA) deep-hole drilling, and Single Lip Drilling (SLD), and unconventional methods such as Electro-Chemical Machining (ECM), Laser Beam Machining (LBM), Electro Discharge Machining (EDM), and Abrasive Water Jet Machining (AWJM). They elaborated and described in detail the parameters entering the drilling process under individual methods and the direction of the research activity in this area of hole formation technology [9]. In their paper, the authors of [PERSON] et al. focused on the description of a new lubrication method in the process of deep drilling stainless steel AISI SUS 304. The new lubrication method consisted of creating a \"nanofluid\" by adding a graphene nanolayer to the soluble emulsion and then mixing the two substances with water. The results showed that the created nanofluid provides a 4.4-fold reduction in drilling torque, resulting in a 20-fold increase in the life of the cutting tool compared with the use of a conventional emulsion lubricant. Furthermore, the authors dealt with the optimal setting of cutting parameters using the Taguchi L9 experiments, the results of which they presented and which are suitable for further exploration of this hole production technology [10]. The authors, [PERSON] et al., used combined simulation methods to analyze the behavior of cutting fluids for tool cooling and chip removal. The analysis pointed to the need to adjust the cross-sectional area of the internal cooling channel as well as the internal and external angles of the cutting edge. As a result, the drilling process was optimized by 40% by adjusting the cutting fluid speed and by 60% in terms of chip removal [11]. Authors [PERSON] et al. studied the reduction in deviations emerging in deep hole drilling through the proposed hydrodynamic lubrication. They designed a centering device with Archimedes spirals that was fastened between the drill tool and the drill pipe to create three wedge oil films to prevent the drilling system from deflecting [12]. A study by [PERSON] et al. looked at the distribution of cutting fluid and chip removal during microcurvature drilling of deep holes using 3D multi-physical simulation methods [13]. The authors, [PERSON] et al., dealt with the mechanical load and the formation of chips when drilling deep holes using various cooling agents. In the experiments, they drew on changes in the settings of the feed force, torque, quality of the hole created, and tool wear.