(A) study on the new extrusion-forging processes

Abstract

The present practice in the pedalshaft manufacture employs five processes without the annealing heat-treatment. Many defacts, such as creacks, folding and bending, were found in the final products of the current five-process system. In the conventional method, extrusion stage and forging stage have been separately performed. The present study aims to reduce the number of processes by developing a new extrusion-forging process and also to achieve elimination of the product defects found in the current factory processes. Besides, prolongation of the tool life is pursued in the new processes. Theoretical analysis on open-die extrusion and forging was made by upper-bound approach for the optimum design and to find the workability limits at every process. Extensive materials tests were done to back up the process design. The thecretical results agreed quite well with the experimental ones in extrusion. Dominant factors in open-die extrusion were brought to light and optimum conditions were sought. A correction-land die was introduced to eliminate bending defects. Both as-drawn and as-annealed billets were used in the experiment for comparison. A new concept of plastic buckling stability(PBS) was defined to elucidate the buckling behavior in upsetting of short bars with bulk deformation and to help find means to raise the stability during upsetting. From this analysis, annealing heat-treatment and coning-punch preforming were mandatory for the stabler forming. A new three-process system was designed and experimented on the basis of the experiments made on the extrusion and forging together with theoretical backup. Beside reducing the number of processes, many defects were found to be eliminated in the new system through the experiment. Some improvements to be made from the experiment of the system were reflected on the modified three-process design. A corrected extrusion-die schedule was brought forward and included in the modifed design. Finally, an integral factory...