Tool Wear Characterisation and Parameter Optimisation in Micro-manufacturing Processes

Increases in demand for miniaturised static parts, actuators and devices has presented challenges in machining; requiring fast advancement in the field. This work examines two processes: Wire Electrical Discharge Machining (WEDM), and micro-milling. While very different processes, both of these have in common the fact that their behaviour and the phenomena seen differ from those seen in conventional subtractive machining. Capability of machine tools has increased to allow highly intricate parts to be produced, but there are significant challenges in achieving excellent surface finish, geometrical accuracy and tool life.
WEDM is appropriate for cutting complex shapes without long set-up times, but cutting very thin workpieces represents difficulties in achieving stable machining, while the process results in a recast layer which can affect wear and transmission. This work focuses on investigating optimal parameters for machining micro-gears. This has traditionally been challenging because the limited area for spark generation between wire and workpiece leads to unstable machining, resulting in poor machining rate and surface finish. Investigations into significant machining parameters have taken place, followed by a feasibility study cutting brass gears of 0.3 mm thickness. The results indicate that the depth of the recast layer can be minimised while maintaining an acceptable Material Removal Rate (MRR), by considering gear geometry. This work suggests that WEDM is a valuable tool in prototyping miniature gears.
Micro-milling allows small, accurate parts to be produced, but micro-tools wear quickly and unpredictably, therefore tool wear is difficult to measure. This results in a high rate of tool changes and reduced productivity. A protocol for measuring tool wear has been produced to allow a common method to be used across research institutes. This presents a method for analysing and reporting micro-mill tool wear which will allow transfer between research institutions and industry, to extend tool life and improving process efficiency. This protocol has then been used to investigate tool coatings on the micro scale, and compare the tribological processes seen on micro-tools to their macro counterparts. This work has resulted in extended tool life for industrial micro-mills and has been applied to industrial situations.