| dc.description.abstract | Abstract
The Electrical discharge machining (EDM) surfaces have the defects of microcracks, pores and residual stresses formed by the strong temperature gradient during machining. These defects result not only in poor surface precision, but also in a shortened service life of machinery parts. Thus, the machined surface modification and machining efficiency need to be considered simultaneously for EDM applications, and they are also the interesting topics in this investigation.
From the experimental results show that Cu-Cr composite electrodes with a Cu-20wt.%Cr mixing ratio and a 20 MPa sintering pressure obtained an excellent MRR. Moreover, this work also reveals that the composite electrodes obtained a higher MRR than Cu metal electrodes; the recast layer was thinner, and fewer cracks were present on the machined surface. Furthermore, the Cr contained in the composite electrode migrated to the work piece, resulting in good corrosion resistance of the machined surface after EDM. Moreover, workpiece surface modification by adding urea into the dielectric used in machining pure titanium metal. Experimental results indicate that the nitrogen element decomposed from the dielectric that contained urea, migrated to the work piece, forming a TiN hard layer, resulting in good wear resistance and exhibited improved friction of the machined surface after EDM. In addition, added conductive particle into urea solution could widen the discharge gap to facilitate the expelling of debris and divide the discharge energy to reduce the surface roughness. Moreover, the added powder could be transferred and penetrated to the machined surface by ionization of the discharge channels. Therefore, the machined surface achieves the modification and reinforcement. | en_US |