# Influence of Coolant Properties and Chip Former Geometry on Tool Life in Deep Drilling
## 4 Testing the Impact of Changing the Coolant Parameters on the Service Life of the Gun Drill
### Applied Coolant  
The main function of the cutting fluid is efficient heat dissipation from the site of cutting by perfect cooling or lubrication to reduce internal and external friction through consistent means such as powder lubricants, which reduce friction but do not allow for intensive heat dissipation from the site of the cut. These means are rarely used, for example, in thread cutting or in some special machining operations. In addition to the cooling and lubrication effects, the cooling fluids also have a cleaning function, but they must not corrode the machine or pose a hazard to health. The choice of coolant is assessed according to  
* The quality requirements for the component machining;
* Chip-forming mechanism;
* The characteristics of the material being machined;
* The characteristics of the tool material used.  
The Quaker 3755 BIO KS coolant was used in the testing, representing a versatile, polysynthetic, cutting, and abrasive fluid that is suitable for use in a wide range of metal-absorbing operations for aluminum and iron alloys. The QUAKER 3755 BIO coolant is diluted with water in concentrations ranging from 2-10% to produce a milky cooling emulsion. The exact concentration required will depend on the intensity of the application. The product is suitable for use with water with a hardness of up to 300 ppm CaCO\({}_{3}\).  
The advantages of cooling emulsion prepared in this way are as follows:  
* Stable lubrication for high-quality surface treatment;
* Excellent corrosion protection for machined parts;
* No sticky residues on the workpiece;
* Phosphate-, sulfur-, or chlorine-free;
* It is biostatic and free of triazine.  
The cooling of the tool in the machining device is ensured by a system of devices consisting of a low-pressure pump, a high-pressure pump, a filter, and a magnetic filter for small metal particles. The low-pressure pump provides the necessary pressure for standard cooling of the turning tools and the pilot drill bit, their lubrication, and de-chipping. In this case, a Wall Plus pump is used, which supplies the coolant at a pressure of 18 bar and a flow rate of 10.5 L/min. The pump used for standard cooling, the high-pressure pump, and the filter unit can be seen in Figure 5.  
To cool the gun drill, a Grundfos MTS high-pressure pump is used, the technical parameters of which are listed in Table 1. The Grundfos MTS high-pressure pump is a screw pump designed for pumping lubricants and cooling oils in machine tools, where the required pressure is about 40 bar. These pumps are designed to be mounted on top of the tank. They consist of two main elements, namely the engine and the hydraulic part.  
During the drilling process, it is necessary to keep the coolant at the desired temperature. This is ensured by a cooling unit from JDK-WDE-S1K (up to 43 kW) with a plate evaporator of the box design, a built-in storage tank, and a pump.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Pump Type** & **MTS 20–40** \\ \hline Flow & 22.3 L/min \\ Pressure & 40 bar \\ Power & 2.4 kW \\ RPM & 2900 min\({}^{-1}\) \\ Frequency & 50 Hz \\ Viscosity & 1 mm\({}^{2}\)/s \\ \hline \hline \end{tabular}
\end{table}
Table 1: Parameters of the high-pressure pump used.  
Figure 5: Standard cooling pump, high pressure pump, and Mahle filter unit.