A novel inner surface enhancement method for holes utilizing ultrasonic cavitation

Holes in housings, shafts and flanges lead to stress concentrations when the components are working under high dynamic loads. Peening methods are commonly used to improve the stress concentration and extend the working life. These methods, however, are difficult to treat the inner surface of the holes in the components because these surfaces are fully shadowed and limit the access of the shot streams, water jets or laser beams. A new developed method using ultrasonic cavitation can be expected to solve these problems by using a sonotrode with a special shape. The working principle is that the fluid enters through a narrow gap between the sonotrode and the inner surface to create a cavitation. In this paper, a new sonotrode was designed and manufactured, then tested at a resonance frequency of 23.8 kHz. The sono-chemiluminescence experiments were carried out to detect the cavitation intensity on the inner surfaces. The stainless-steel tubes were treated, and their surface properties were evaluated as well. The results show that the cavitation intensity is strongest at the working distance of 1 mm. The hardness increased by about 12% without the significant change of surface roughness.