Surface Integrity Analysis of Ceramics Machined by Wire EDM Using Different Trim Cut Technologies

摘要

Electrically conductive ceramics are increasingly used in tooling and chemical industry, because of their high thermal and chemical resistance. The high hardness of the material is a major challenge for conventional manufacturing processes. Wire electrical discharge machining (WEDM) offers a good alternative, because the machining process is independent of the hardness. Nevertheless, the thermal material removal principle of WEDM leads to a microstructure change in the near-surface layer, which affects the load-bearing capacity of the material. In order to minimize these damages and to increase the load-bearing capacity, trim cuts must be used. Up to now, there are no processing technologies available on WEDM-machines for machining electrically conductive ceramics. Therefore, this study deals with the surface integrity improvement of zirconia/tungsten carbide (TZP-WC) as an electrically conductive ceramic by developing a material-specific technology with main and trim cuts. The surface improvement is verified by means of surface roughness measurements, cross-section analysis and bending strength tests. The dominant material removal mechanisms were identified to be melting, evaporation and spalling. This leads to smooth but glassy surfaces. The variation of the EDM characteristics caused a variation in the structure of the resulting surface. However, the discharge energy has a strong impact on both surface condition and removal mechanism. Bending strengths of over 900 MPa could be achived by creating a smooth and nearly crack-free rim zone. Trim cuts with higher electrical discharge energies cause fatal damage in the surface and lead to a breakdown of the bending strength.