Effects of grain size of AISI 304 on the machining performances in micro electrical discharge machining

Abstract

The material removal process of micro electrical discharge machining is based on the instantaneous ultra-high temperature generated by a series of repetitive discharge pulses. Due to the size effects, the polycrystal cannot be considered as continuous and homogeneous material when machining is in micron scale, and the effects of material microstructure should not be neglected. In this article, the thermoelectric characteristics of grain and grain boundary are discussed, and the influence of grain size on the machining performances in micro electrical discharge machining is researched. Two kinds of austenitic stainless steels (AISI 304) which are different in grain size are chosen as the workpieces in experiments. It is verified by both theory models and experimental results that the smaller the grain size, the higher the material removal rate, under the same discharge conditions. Both thermal conductivity and melting point of the grain boundary are lower than those of the grain because of the grain boundary segregation. The effective thermal conductivity and local effective melting point of polycrystalline materials vary with their grain sizes since the grain boundary volume fractions change. As a consequence, the material removal rate of micro electrical discharge machining has direct relationship with grain size of the workpiece.

Advanced Electric Discharge Machining of Stainless Steels: Assessment of the State of the Art, Gaps and Future Prospect

“…The grain sizes of workpiece materials have significant impact on the characteristics of micro EDM [130]. The MRR for micro-EDM has a direct relationship with the grain size of the machined workpiece because the effective thermal conductivity and local effective melting point of polycrystalline materials vary with grain sizes of these materials since the grain boundary volume fractions change [131]. It is worth emphasizing that the material microstructure of the processed workpiece plays a significant role in the performance of the micro EDM process.…”

Wire-EDM performance and surface integrity of Inconel 718 with unique microstructural features fabricated by laser powder bed fusion

“…While the LPBF-3 sample had an average grain size of 12.64 µm, with the increase in laser energy density, the grain size of LPBF-2 and LPBF-1 increased to 20.58 µm and 21.34 µm, respectively (Table 3). Note that the electrical and thermal conductivities of the material, which affect machinability, are altered by the grain size, grain boundary, and grain orientation; thus, the microstructural characteristics of the samples are critical for determining the machining performance [31,[38][39][40][41].…”

Wire-EDM performance and surface integrity of Inconel 718 with unique microstructural features fabricated by laser powder bed fusion

“…It has been reported that the thermal and electrical conductivity of polycrystal materials were in uenced by the grain boundary density (as well referring grain size) composed of defects and impurities [33].…”

“…XRD patterns and SEM microstructure images of wrought and LPBF-IN718 samples are presented in Figure 2 2). Note that the electrical and thermal conductivities of the material, which affect machinability, are altered by the grain size, grain boundary, and grain orientation, thus, microstructural characteristics of the samples are critical for determining the machining performance [29,[33][34][35][36].…”