Development of cylindrical wire electrical discharge machining process and investigation of surface integrity and mechanical property of EDM surface layers

The cylindrical wire Electrical Discharge Machining (EDM) process was developed to generate precise cylindrical forms on difficult-to-machine materials. A precise, flexible, and corrosion-resistant underwater rotary spindle was designed and the spindle error was analyzed. The mathematical models for material removal rate and surface finish were derived. Experimental results indicated that higher maximum material removal rate might be achieved in the cylindrical wire EDM than the 2D wire EDM. Effects of some key process parameters, wire feed rate, pulse on-time and part rotational speed, on the surface finish and roundness are explored. For WC-Co parts, the arithmetic average surface roughness and roundness as low as 0.68 and 1.7 μm, respectively, can be achieved. Surfaces and subsurfaces of the cylindrical EDM parts were examined using Scanning Electron Microscopy (SEM) to identify and quantify the recast layer and heat-affected zone. This study used nanoindentation to investigate the influence of cylindrical wire EDM process on the mechanical properties of WC-Co composite. The heat-affected zone had more compact microstructure less indentation cracking. The recast layer had lower hardness and modulus of elasticity than the original material and heat-affected zone. EDS X-ray and X-ray diffraction were used to analyze the material compositions of the recast layer. The micro-blasting process was applied to remove the unwanted recast layer and improve the surface integrity of the part machined by wire EDM. Experiments with different process parameters were conduced and the surface roughness could be reduced significantly using micro-size SiC abrasives.