On-line annealing in cold forging

Abstract

The required parameters for recrystallization annealing by induction heating after a cold extrusion process of the tested steels QSt 34-3 (AISI 1008), Ck 15 (1015) and Ck 45 (1040) were determined to carry out a consecutive cold extrusion process producing crack-free components. Without an intermediate annealing operation, cracks were generated during a forward tube extrusion process of Ck 15 and Ck 45. Due to the previous backward cup extrusion process (BCE, cupping), the limit strain of the deformed materials was decreased and the generation of cracks took place in the extruded tube part of the workpieces during the second stage of the production sequence. By means of induction annealing of the components over a time of about 1.5 s the ductility of these steels was increased and crack free extrusion in the second forming stage of the production sequence (forward tube extrusion, FTE) was made possible. A simulation of a real on-line mode of operation for induction annealing was carried out by using two presses with different tool set-ups (forward bar extrusion, FBE, and open die extrusion, ODE), an intermediate lubrication process, and an induction annealing system between the presses. By means of this arrangement, a production rate of about 12 strokes per minute was simulated. In comparison with the non-annealed condition the extrusion force of the second stage of production (open die extrusion) was decreased by 15%. By using a press with a multistage die with an automatic handling device in combination with a lubrication and an annealing stage inside the die set-up, the production rate can be increased drastically.