SURFACE HARDNESS AND RESIDUAL STRESS IN WIRE-EDM-CUT CK45 STEEL ENHANCED BY ULTRASONIC PEENING TREATMENT (UPT)

This work examines the application of ultrasonic peening treatment (UPT) to CK45 alloy steel specimens produced by wire electrical discharge machining (WEDM) under three surface-generation conditions: finishing, semi-finishing, and rough machining. The ultrasonic peening system was integrated with a conventional lathe to perform the treatment. The influence of key processing variables, including the number of peening passes, feed rate, and machining condition, was evaluated while maintaining a constant vibration amplitude. Experimental trials were planned according to the Taguchi design approach. The findings revealed that ultrasonic peening effectively altered the residual stress state of all wire-cut specimens, transforming the initially tensile stresses into pronounced compressive stresses. The maximum compressive residual stress obtained was 1635[Formula: see text]MPa. An increase in the number of treatment passes promoted the development of higher compressive residual stresses, whereas higher feed rates resulted in their reduction. Surface microhardness measurements demonstrated noticeable hardening after the first peening pass in specimens produced under semi-finishing, finishing, and rough machining conditions. Further increases in the number of passes led to additional improvements in hardness, confirming the effectiveness of UPT in enhancing the surface integrity of CK45 steel components.