Lawd – Laser Assisted Wire Drawing

In conventional wire drawing the diameter of a wire or rod-like workpiece is reduced by drawing it through a conical die. Dieless drawing of a wire or a rod is realized by a localized heating of the work piece. As heat source for example an induction coil can be used. Immediately after having passed the heating zone the work piece is cooled to restrict the heat input on very small region. By applying a drawing force to the workpiece, deformation and thus the required diameter reduction appears in the heated zone. The diameter of the wire can be chosen in a flexible way by adjusting the velocities of the rod or wire in front of and behind the forming zone. Since temperature represents a sensible process parameter, even very small changes can lead to fracture. In the present work, a laser was chosen as a heat source of the dieless wire drawing process, together with closed-loop control of forces and temperatures. Laser heating allows an excellent control of temporal as well as spatial heat input. A wire drawing apparatus has been constructed which used a speed controlled electric motor together with a controllable brake for applying the drawing forces. Heat input was realized by a 1 kW diode laser system. Wires have been cooled by compressed air immediately after the laser heated zone. FEM analysis of the process showed that for relatively low drawing speeds one single laser is sufficient since heat spreads fast enough through the wire. Different wire types and diameters have been used during the experiments. Results of the theoretical and experimental work showed that it is possible to draw wires with this new process. For example, with copperor steel wires it was possible to reduce the cross section of the wires by more than 20 % in one step.