Effect of tangential misalignment in ultrasonic burnishing

Abstract

Ultrasonic burnishing is a surface finishing process that produces fine surface roughness, improved geometrical accuracy, high compressive residual stresses and increased hardness. The method is suitable for finishing dies or other double curvature surfaces and it does not require changing of the fixturing setup after a machining process. The method has not however become commonly used in industry, because the technology has not been extensively tested. Technological parameters in ultrasonic burnishing includes the surface speed, distance between consecutive passes (or in machining terms, feed) and contact force. Ultrasonic burnishing is based on forging at an ultrasonic frequency of over 20,000 impacts per second and there is no material removal associated with the process. The technological parameters have been tested and recommended values have been recorded for some common work materials. One important parameter is the tangential alignment of the burnishing tool in regard to the workpiece surface normal. This parameter is easy to control in turning operations or with planar surfaces, but with a double curved surface the control of the angle is more difficult. All the previous research has been done on cylindrical or planar workpiece and therefore the tangential misalignment or the sensitivity of the surface integrity regarding the tangential misalignment has not been studied. This paper investigates the effect of the tangential misalignment of the burnishing tool and the effect on surface integrity. The results show that ultrasonic burnishing is suitable method for finishing workpiece surfaces even with inclined tool angle. The ultrasonic burnishing produced a beneficial surface integrity state on the workpiece surface with hardened material and improved surface quality. The surface micro-hardness increased by 1.4-6.7 %. At the same time, the average surface roughness (Ra) values decreased by 50-85 % depending on the misalignment angle.