OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 Fig. 7. WLT for Expt. 12 (Table 4) at the vertical cross-section of a square hole (a), the horizontal cross-section of the square hole (b) current is 16 A. Thus, the white layer in this case is thicker than in the fi rst two. However, the thickness of the white layer is typically less than 20 μm, indicating that molten metal is eff ectively removed from the workpiece surface by dielectric fl ushing. The white layer refers to a thin layer of recast material that forms on the surface of the workpiece after the electrical discharge process. This layer has diff erent physical and chemical properties compared to the base material. The thickness of the white layer depends on various factors, including the EDM process parameters and the material being machined. Higher discharge energy increases material removal, resulting in a thicker white layer. Longer pulses provide greater energy transfer and may result in the formation of a thicker white layer. BeCu alloy has specifi c thermal and electrical conductivity properties that can aff ect the white layer formation. The composition and microstructure of the alloy can also play a role. Proper fl ushing of the machining zone helps remove debris and control the heat generated during the process, which can infl uence the white layer formation. The observed white layer thickness at a lowmaterial removal rate for the horizontal surface is a minimum of 6.38 μm and a maximum of 10.47 μm. Similarly, for the vertical surfaces, the maximum and minimum are found to be 13.83 μm and 6.99 μm, respectively. The observed white layer thickness at a high material removal rate on the horizontal surface is at least 12.92 μm and a maximum of 14.24 μm. Similarly, for the vertical surface, the maximum and minimum are found to be 15.58 μm and 11.67 μm, respectively. Crack formed on the machined surface The EDM process involves the generation of high temperatures on the workpiece surface. Rapid heating and subsequent cooling cycles can induce thermal stresses. These thermal stresses can lead to crack formation. Adequate cooling and fl ushing of the machining zone are crucial in EDM to control the temperature and remove debris. Insuffi cient fl ow or cooling of the dielectric fl uid can result in excessive heating and thermal stress, increasing the likelihood of crack formation. Figure 8, a and b and fi gure 9? a–d show the crack and recast layer on the machined surface of the workpiece. The cut section of the workpiece was examined using scanning electron microscopy. Photographs were taken of the bottom surface of the workpiece and the wall surface (fi gure 9 e, f). The specimen has very few surface cracks at low, medium and high material removal rates because the workpiece has superior thermal properties and a thinner white layer is formed on the surface. Cryogenic treatment of the workpiece and external magnetic strength prevented the formation of surface cracks and the formation of white layers. Conclusions In the current study, the material removal rate, white layer thickness, and crack formation on the walls and bottom surface of a square hole produced by electrical discharge machining (EDM) were investigated by considering the eff ects of cryogenically machined combinations of copper-beryllium (BeCu) workpieces
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