Vibration-assisted milling of hard to machine materials

In order to meet the constantly increasing requirements with regard to lightweight construction and energy efficiency, materials that are difficult to machine such as hard metals, ceramics and fibre-reinforced plastics are increasingly being used. These materials can only be machined with great effort using conventional machining processes due to the high tool wear. Ultrasonic machining has proven to be a suitable means of counteracting this disadvantage. In ultrasonic machining, an additional high-frequency oscillation is superimposed on the kinematics of the conventional machining process. This generates vibration amplitudes in the range of a few micrometers at the tool cutting edge and thereby causes a high-frequency change in the cutting speed or feed rate. The resulting effects include a reduction in cutting forces, an increase in tool life and an improvement in workpiece quality. In milling and grinding, it has already been shown that some of these positive effects already occur during vibration excitation axial to the workpiece, i.e. perpendicular to the cutting direction. In contrast, a further improvement of the process results can be achieved by superimposing an oscillation in the cutting direction on the processes and thus modulating the cutting speed at high frequency. The aim of the research project is therefore to create the basis for vibration-supported milling and grinding with ultrasonically modulated cutting speed. To this end, an ultrasonic actuator system will first be constructed with which a longitudinal torsional ultrasonic oscillation can be superimposed on both the milling and grinding tools. Subsequently, fundamental investigations on vibration-supported milling and grinding are carried out. During milling, a titanium alloy Ti-6Al-4V that is difficult to machine is machined. The influence of conventional process parameters (cutting speed, feed rate, cutting depth and tool geometry) and vibration parameters (frequency and amplitude) are investigated. The effects and interactions that occur are analyzed with the aim of minimizing tool wear and increasing workpiece quality. At the same time, basic investigations for the grinding of hard brittle materials with ultrasonically modulated cutting speed are carried out, in which the interactions between the conventional process parameters and vibration parameters are also investigated.