OBRABOTKAMETALLOV technology Vol. 27 No. 1 2025 Introduction The evolution of modern mechanical engineering is intertwined with the development of new, technically advanced products and designs. Manufacturing high-quality products is a primary objective. The operational demands placed on these products are becoming increasingly rigorous, leading to ever-stricter requirements for their performance characteristics. To ensure that products meet the required operational standards, it is essential to utilize materials with enhanced physical and mechanical properties. Key factors in ensuring a product’s competitiveness include its mass and dimensional characteristics. Consequently, increasingly intricate and spatially complex designs are employed, enabling the minimization of product mass and dimensions while still satisfying strength and rigidity requirements. Traditional machining methods are the most prevalent technologies for manufacturing products with complex geometries. However, conventional blade processing techniques suffer from significant cutting tool wear when processing high-hardness materials. They also require the use of additional equipment for multi-axis machining of complex profiles, and they cannot be used to process thin-walled components due to the force action of the cutting tool [1–3]. When manufacturing complex-shaped products from materials with enhanced physical and mechanical properties, it is advantageous to employ alternative electrophysical processing methods that can process materials of any hardness with virtually no cutting forces. Electrical discharge machining (EDM) is one such method [4–10]. A significant disadvantage that limits the application of this electrophysical method is the thermometallurgical transformations that occur in the surface layer of the material being processed. During the removal of material particles from the surface, pyrolysis of the working fluid takes place, leading to changes in the structure and properties of the product’s surface layer [11, 12]. The EDM process is characterized by localized overheating of the material in the processing zone, which can cause a phenomenon known as brittle fracture. In brittle fracture, thermal stresses arise due to overheating of the surface layer of the processed material. When these thermal stresses exceed the material’s tensile strength, material is removed from the processing zone. In this case, the material particles are not subjected to melting and evaporation processes but are removed in the solid phase, resulting in chips and cracks [13, 14]. As a result of significant overheating in the processing zone, the material being processed undergoes re-hardening and tempering. Internal stresses arise, which, in conjunction with the altered physical and mechanical properties of the material, can lead to premature product failure during operation or defects during the manufacturing stage [15]. The phenomenon of brittle fracture of the material during EDM results in a surface with a high density of microcracks [16]. The presence of microcracks on the working surfaces of the product can lead to its premature failure due to their propagation into the base material, ultimately leading to the failure of a component or the entire product. The zone of the surface layer containing the greatest number of defects is the so-called white layer. The white layer has a fine-grained structure with high chemical resistance. The thickness of the layer varies from tenths of a millimeter to 1.5 mm. The white layer formed on the surface being processed during the EDM process exhibits increased brittleness. Its presence significantly reduces the material’s strength characteristics, particularly its resistance to cyclic loads. A review of the literature in the field of EDM indicates that an increase in the thickness of the white layer leads to a decrease in the material’s fatigue life [17]. The thickness of the white layer and its multiple occurrences on the workpiece surface are determined by numerous factors [18]. One key factor is the processing mode. The electrical process parameters can significantly influence the thickness of the white layer [19]. Increasing current and pulse duration causes a larger volume of material to melt and evaporate due to the increased energy supplied to the workpiece [11]. Reducing the pulse-on time on an electrical discharge machine allows for a decrease in the thickness and continuity of the white layer due to the lower energy input in the processing zone. Decreasing the voltage also leads to a reduction in the white layer thickness [20].
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