Effects of partial tool engagement in micro-EDM milling and adaptive tool wear compensation strategy for efficient milling of inclined surfaces

Compensation of tool wear in micro-EDM milling of inclined surfaces is a difficult task due to variations of the radial engagement conditions of the tool with the workpiece. Traditional compensation methods based on off-line wear prediction are likely to be inaccurate, while methods involving tool measurements are time-consuming. In this research, the process dynamics when the tool is not fully engaged with the workpiece are investigated by performing repeated milling tests and analysing the effects on the discharging process and tool wear behaviour. An adaptive tool wear compensation strategy is accordingly developed, combining traditional linear compensation method (LCM) and tool wear sensing. In this strategy, simultaneous monitoring of the normal discharge pulses and tool displacement is used for determining the tool engagement conditions. This allows to adapt the milling process to the expected tool wear behaviour when the tool is in partial engagement. The proposed control strategy has been tested for an industrially-relevant case, i.e. the shaping of a diffuser for a turbine blade. A machining accuracy in the range of the applied milling layer thickness was obtained without the need of tool measurements.