Surface generation and strengthening mechanisms in ultrasonic strengthening cutting of 18CrNiMo7-6 alloy steel for enhancing wear resistance

Ultrasonic vibration cutting (UVC), as an effective machining process for improving workpiece machinability and surface integrity, has not yet been systematically investigated regarding its underlying mechanisms. To thoroughly explore the mechanisms of ultrasonic vibration, this study proposes an ultrasonic strengthening cutting (USC) process. Through theoretical analysis and experimental validation, the strengthening and surface generation mechanisms of USC were systematically investigated, and the surface integrity and wear resistance were evaluated. The outcomes demonstrate that compared with conventional cutting (CC), USC-machined surfaces exhibit surface micro-texture morphological characteristics and significant surface strengthening effects, leading to higher microhardness (339.14–368.81 HV_0.5), superior compressive residual stress (up to −783.76 MPa), greater residual stress affected zone (approximately 150 μm), greater plastic deformation layer depth (17.11–44.82 μm), and reduced wear area (the highest decrease percentage of 39.96%). Theoretical analysis and experimental investigations demonstrate that the ironing effect acts predominantly on the workpiece surface, governing the machined surface morphology, surface roughness, and residual stress, whereas the impacting effect operates on the subsurface layer, inducing more pronounced plastic deformation that enhances the surface microhardness and compressive residual stress. Through the synergistic action of both effects, USC effectively promotes the surface integrity and wear resistance of the workpiece. As an integrated process combining cutting and strengthening, in-depth research on USC provides a reference for the machining and strengthening of difficult-to-machine materials.