Experimental Study of the Effects of the Ultrasonic Peening Treatment on Surface Hardness and Hardness Depth of Wire EDMed Workpieces

Wire EDM is a modern machining process that uses electrical discharge to cut workpieces. High temperatures generated by wire EDM can cause surface cracking due to metallurgical changes. A new approach is to use the ultrasonic peening treatment to cause surface severe plastic deformation to improve the mechanical properties, especially the hardness. In this study, the focus was on exploring the impact of cutting types in wire EDM, feeding rate, and the number of peening passes as input parameters on Mo40 (1.7225) alloy steel. The experiments were designed using the multilevel factorial design method. The average hardness values were then analyzed based on the input parameters. The maximum hardness value was determined through optimization using the multilevel factorial design method. Analysis of variance was used to evaluate the impact of parameters on hardness. The highest hardness value of 952.7 (HV) was obtained with a feeding rate of 0.12 (mm/rev) and 3 peening passes in roughing mode, leading to a 48% increase in hardness. A mathematical model with 99.87% desirability was developed to study the correlation between input parameters and response variables. The hardness distribution in the peened workpieces continued up to 200 micro;m below the surface layers. The highest hardness was found at a feeding rate of 0.12 (mm/rev), which influences the time needed to alter dislocation density and form a new sublayer structure. Overall, increasing the feeding rate decreases hardness, while increasing peening passes increases it. According to a single-objective optimization, the cutting types, feeding rate, and number of peening passes respectively affect hardness value.