Fabrication of zirconium diboride-copper for electrical discharge machining via selective laser sintering and simulation for copper cathode erosion of plasma torch.

摘要

It is of interest to produce ZrB2-Cu using SLS and to use the electrode in place of normally used electrodes, copper and graphite, in EDM industries because frequent replacement of the electrodes, due to their high wear rates, causes high cost of operation. Performance evaluation of ZrB2-Cu employed EDM where steel was used as a cathodic workpiece and the cermet was used as an anodic tool. Compared to the performance of copper, graphite, and W-Cu tools, ZrB2-Cu yields the highest workpiece removal rate. At high heat flux conditions, the wear rate of ZrB2-Cu is comparable to that of W-Cu but lower than those of Cu and graphite. This electrode could have a significant impact on the EDM industries owing to its lowest wear ratio. SEM, EDS, and elemental mapping analyses reveal that ZrB 2-Cu electrode wears by a combination of dominant evaporation and melting of the Cu, negligible melting and thermal spalling of the ZrB2 phase, quick refreezing of metal back to the surface, and the deposition of the steel on the tool surface.;The objective of the computer simulation of copper cathode erosion in a rotating arc plasmatron is to create a two-dimensional, cylindrical heat conduction model for predicting the erosion rate. We use a concentrated Gaussian distribution of local current density, Jxy , as a boundary condition, and find that the cathode erosion rate is well correlated with the experimental data. Such highly focused current densities of Jxy at an arc root's center result in the formation of an inner hot spot, a cause of cathode erosion. This explains why other erosion models fail to forecast any erosion although erosion tracks and cathode weight loss are clearly observed. For Ar + 0.3% CO gas plasma, a residence time of the arc root in the region of high arc velocity and the grouping of individual arc spots within the arc root in the region of low arc velocity are the main reasons for the result of a bell-shaped relationship between arc velocity and erosion rate, while the temperature upon arc return is unimportant to the cooling rate of cathode and thus its erosion.