Wire drawing with ultrasonically oscillating dies

Abstract

The drawing forces during wire drawing can be reduced by applying ultrasonically oscillating dies. A major problem of conventional wire drawing is to introduce high forces into the forming area. Compared to conventional wire drawing, the forming process limits can be extended due to the decreasing drawing forces. Different techniques can be used to excite the die. A possibility is the variation of the mode of oscillation. In tube and wire drawing, the dies are usually excited longitudinally. However, in certain cases it would be advantageous to excite the dies in a radial mode. Furthermore, there is the possibility of varying the vibration direction. If the vibration direction is parallel to the drawing direction, the influence on the friction force will be the greatest. If the vibration direction is perpendicular to the drawing direction, the influence on the forming properties of the workpiece will be the greatest. Since longitudinally oscillating dies at their natural frequency generate a standing wave, there is additionally the possibility to locate the die into the nodal- or into the antinodal points. With ultrasonically oscillating dies, the static forming forces can be reduced. The superimposed dynamic stress reduces the measured static forces because of the oscillating movement of the die. One reason for the force decrease is the reduction of friction between die and workpiece. Another reason is the absorption of sonic energy by the lattice dislocations and the change of the forming properties of the workpiece. Mounting pins were developed to induce the dynamic oscillation and to realize high static loads upto 10 kN. In these investigations, the die oscillates longitudinally at the resonant frequency of approximately 22 kHz. There is an oscillating movement of the die with a velocity of maximal 0,5 m/s and an amplitude of maximal 10μm. The experimental equipment was installed in a hydraulic drawing machine. The experiments were performed with highly alloyed austenitic stainless steel wires. Diameter reductions from 3,7 mm to 3,5 mm, from 3,7 mm to 3,0 mm, and from 3,7 mm to 2,5mm were investigated. The drawing velocity was varied in the range between 1 m/min and 10 m/min. Two longitudinally perpendicular excited dies were used. Type A was in the antinodal point of the standing wave and type B was in the nodal point of the standing wave. The experimental results show that applying die-type A, a drawing force reduction of nearly 12 % can be achieved. However, the side-effect of this die-type was the activation of another vibrational mode in the workpiece. Because of resonant effects, the drawing force decreases periodically up to 40 %. Therefore, the wire-diameter has changed at the corresponding locations. Using die-type B, it is possible to achieve drawing force reductions upto 20 %. Compared with the die-type A, the drawing force curve was smoother. Corresponding to the drawing force curve, the wire surface was smooth.