Tahhan Antar, Mohammad (2011)
Ph.D. thesis, University of Birmingham.
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The research focused primarily on the effects of WEDM on the surface / subsurface integrity of Ti-6Al-2Sn-4Zr-6Mo titanium alloy and Udimet 720 nickel base superalloy, and encompassed measurement of surface roughness and contamination, workpiece microhardness, recast layer thickness, residual stresses and fatigue performance. Associated productivity and manufacturing costs were also evaluated in respect of blade root slot machining in aerospace turbine / compressor discs. Preliminary tests results showed that machined surfaces with Ra of ~0.5μm, less than 2μm of recast layer and almost neutral residual stresses were obtained following a roughing and four finishing passes. In a subsequent phase it was possible to reduce the number of finishing passes into only 2 while maintaining similar surface integrity figures, where also it was possible to wire machine firtree slots geometrical accuracy of ±7μm. This phase also entailed extensive assessment of the impact of pulse shape on surface integrity when using similar pulse energies. Fatigue performance tests proved no statistically significant differences between WEDM and flank milling at 5% level. The research also investigated the use of coated wires and oil based dielectric compared to standard brass wire and de-ionised water, where significant differences in productivity were recorded.
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