Enhanced debris expelling in high-speed wire electrical discharge machining

Abstract

Surface machined by high-speed wire electrical discharge machining (HS-WEDM) at high energy (average current >8 A) suffers from surface burn and reduced cutting speed increase-rate, a major problem which is investigated in this paper. According to the study, the debris is mainly expelled out of the inter-electrode gap by the liquid medium. When machining at low energy, the gap is full of water-based medium, and the debris is mainly expelled by this medium. However, at high energy the medium in the gap is enormously vaporized and is then reduced due to a thermal load at high energy. Thus, the debris cannot be removed from the gap in time, resulting in its deposition and eventually leading to the surface burn. To overcome this limitation, it is suggested that within a range of discharge energy levels, the erosion products of the HS-WEDM process should be driven by a medium carrier with a higher melting point and vaporization point to ensure that there is sufficient liquid medium in the gap at high energy to carry and expel the debris out of the machining zone. Experiments were conducted by increasing the JR1A (traditionally used dielectric medium) -to-water ratio to increase the content of high-melting-point medium, thus validating the theory. Based on the experimental results, a new type of dielectric medium, JR1H, was formulated to ensure that there is still sufficient liquid medium to expel the debris at large energy machining. A greater threshold of stable cutting speed (more than 330 mm2/min) was achieved with the machining current of 15 A using JR1H, which is a significant breakthrough in higher efficiency HS-WEDM.