Fundamental Investigation on the Influence of a Cryogenic Process Cooling on the Process Behavior of Drilling Tools
The coherences between a new cooling concept of carbon dioxide snow blast cooling and the process behavior of different drilling tools are analyzed within this project supported by the German Research Foundation the objective. In comparison to conventional dry machining processes, the burr formation shall be reduced by cooling the exit side of the workpiece. The decrease in the flow stress caused by the process is minimized by using the cooling and the corresponding increase in the ductility of the material is avoided. So, the resulting more brittle material behavior leads to a reduced burr formation. Furthermore, the process cooling will be used to reduce the thermal tool loads for an increase of feed velocities under the purpose of tools loads comparable to dry machining processes. In the third part of this project, the applicability of the process cooling for an impact on the chip form will be analyzed. In this part of the project, a variation of the cooling channel exits is projected. This is done to optimize the supply position of the cooling medium into the gap between rake face and created chip. Besides the extensive experimental investigations, a simulation using the finite element analysis is projected. With this simulation the resulting workpiece temperatures will be calculated. With this knowledge, suitable process parameters shall be deduced.
In the first focus of the project, the influence of the process cooling on the bore hole quality will be analyzed. Here, the approach is followed that the material properties can be influenced to a more brittle material behavior by the process cooling. This influence on the material properties will be used for an increase in the bore hole quality, especially for an reduced burr formation. For a detailed analysis, the thermomechanical loads will be detected and the burr formation process will be analyzed by using a high speed camera. In the second part of the project, the process cooling will be used for an increase in feed velocities under the purpose of tool loads comparable to dry machining processes. In this context the feasibility of the process cooling for an optimization of the process concerning process time reduction will be analyzed. Therefore, tools will be prepared for an inner supply of the carbon dioxide snow blast. In this context, cooling nozzles will be brazed into the cooling channel exits of the tools. Based on the application of the cooling medium in the near of the cutting zone, the process is cooled effectively and a potential for an increase in cutting parameters is created. In the third part of the project, the chip formation is in focus of the experiments. Here, the process cooling and the connected impact on material properties will be used for the manipulation of chip formation to shorter chip length. These shorter chips are easier to remove out of the bore hole and can increase the reliability of the process. Here, the position of the cooling nozzles and their cooling power are of importance. The position and cooling power of the nozzles will be optimized for an optimization of chip formation. Therefore, a preparation of the tools is necessary. These tools have the cooling channel exits in the rake faces of the drills to apply the cooling medium into the gap between rake face and chip. Furthermore, a simulation using the finite element method will be done to calculate the resulting workpiece temperature based on the interference of the process cooling and the process heat created by the cutting process.
- Figure 1: Targets for the application of CO2-snow blast cooling in drilling operations