The effect of scanning pitch of nozzle for a cavitating jet during overlapping peening treatment

The objective of this paper is to optimize the pitch at which the nozzle of a cavitating jet is scanned during peening. The evaluations of an effect of the pitch on overlapping treatment are done, firstly theoretically, by estimating the aggressive intensity of the jet based on a Gaussian distribution in order to uniformly and effectively treat the surface in applications such as cavitation peening and cleaning. Experimentally, cavitation peening was conducted with the nozzle scanned at various pitches. Striped patterns, due to the non-uniform treatment, were formed in aluminum when pitches of 6, 8, 10 or 12 mm were used, whereas with pitches of 2 and 4 mm the patterns were uniform. The compressive residual stress introduced into type 316L stainless steel by cavitation peening was approximately 380 and 400 MPa for pitches of 2 and 4 mm, respectively. From the viewpoint of not only the uniformity but also effective and efficient treatment, the optimum pitch for scanning was determined to be 4 mm, since this requires half the number of scans compared to 2 mm.