WIRE DRAWING WITH ULTRASONICALLY OSCILLATING DIES

The drawing forces during wire drawing can be reduced by applying ultr asonically oscillating dies. A major problem of conventional wire draw ing is to introduce high forces into the forming area. Compared to con ventional 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 oscilla tion. In tube and wire drawing, the dies are usually excited longitudi nally. However, in certain cases it would be advantageous to excite th e dies in a radial mode. Furthermore, there is the possibility of vary ing the vibration direction. If the vibration direction is parallel to the drawing direction, the influence on the friction force will be th e greatest. If the vibration direction is perpendicular to the drawing direction, the influence on the forming properties of the workpiece w ill be the greatest. Since longitudinally oscillating dies at their na tural frequency generate a standing wave, there is additionally the po ssibility to locate the die into the nodal- or into the antinodal poin ts. With ultrasonically oscillating dies, the static forming forces ca n be reduced. The superimposed dynamic stress reduces the measured sta tic forces because of the oscillating movement of the die. One reason for the force decrease is the reduction of friction between die and wo rkpiece. Another reason is the absorption of sonic energy by the latti ce dislocations and the change of the forming properties of the workpi ece. Mounting pins were developed to induce the dynamic oscillation an d to realize high static loads upto 10 kN. In these investigations, th e die oscillates longitudinally at the resonant frequency of approxima tely 22 kHz. There is an oscillating movement of the die with a veloci ty of maximal 0,5 m/s and an amplitude of maximal 10 mu m. The experim ental equipment was installed in a hydraulic drawing machine. The expe riments 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 m m, and from 3,7 mm to 2,5mm were investigated. The drawing velocity wa s 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 poi nt of the standing wave and type B was in the nodal point of the stand ing wave. The experimental results show that applying die-type A, a dr awing force reduction of nearly 12 % can be achieved. However, the sid e-effect of this die-type was the activation of another vibrational mo de in the workpiece. Because of resonant effects, the drawing force de creases periodically up to 40 %. Therefore, the wire-diameter has chan ged at the corresponding locations. Using die-type B, it is possible t o achieve drawing force reductions upto 20 %. Compared with the die-ty pe A, the drawing force curve was smoother. Corresponding to the drawi ng force curve, the wire surface was smooth.