Effect of process variables on microhardness, grain size and strain during machining of various die steels with powder-mixed electric-discharge machining using dummy treated experimental design

Abstract

This experimental study investigates the effect of process parameters in a powder-mixed electric-discharge machining process on the microhardness of the deposited and the non-deposited region of the machined surface. The microscopic observations using a scanning electron microscopy revealed a transfer of material on to the workpiece during machining, leading to a formation of compounds resulting in improvement of its properties. The X-ray diffraction plots were used to assess the grain size and the micro-strain for each die steel material. The addition of tungsten or graphite powder affected the microhardness significantly, while aluminium or copper had no effect. The grain size was affected by the cooling rate and the powder used during machining besides process parameters, such as current and pulse-off time. The average grain size varied between 18 to 40 nm. Trials conducted with low melting point metallic powders slowed the cooling rate, resulting in finer grains. HCHCr, H13 or H11 die steel workpieces showed a higher average strain as compared with EN31.