Superimposing Ultrasonic Waves on the Dies in Tube and Wire Drawing

The forces during wire and tube drawing can be reduced by ultrasonically oscillating dies. It is a major problem of conventional wire and tube drawing to introduce high forces into the forming area. Compared to conventional wire and tube drawing, the forming process limits can be extended by superimposing ultrasonic waves due to decreasing drawing forces. Different techniques can be used to excite the die. One possibility is the variation of the vibration mode. In tube and wire drawing, the dies are usually excited longitudinally. If the vibration direction is parallel to the drawing direction, the main influence will be on the friction between workpiece and die. The Institute for Metal Forming Technology of the University of Stuttgart, Germany started a project to investigate the effect of ultrasonic waves on the tribology and on the formability of the workpiece. The objective of this investigation is to separate the ultrasonic effect on the surface from the volume effects. This paper shows that the reduction of the sliding friction between a longitudinal oscillating die and the workpiece can be explained by the so-called Sliding Friction Vector Effect (SFVE). A statistical evaluation of roughness-measurements makes it possible to show the effect of the ultrasonic vibration on the friction and gives an insight into the operation of the SFVE. The results are compared with wire and tube drawing experiments of copper and Ti-alloys. New tube- and wire-drawing experiments with longitudinally vibrating dies support the theoretical approach. The surface quality of the manufactured workpieces can be improved and the productivity increased.