Defect Analysis and Improvement Method of Eccentric Camshaft Forging by Vertical Upsetting Extrusion Forming

Eccentric camshaft components serve as critical elements in emergency pump systems for commercial vehicle steering mechanisms. To optimize material utilization efficiency, reduce production costs, and enhance manufacturing throughput, this investigation implemented a vertical upsetting extrusion forming methodology for camshaft forging production. Initial trials revealed defect formation in forged components. By analyzing the causes of the defects, an improved process method was developed to eliminate them. The chemical composition, macroscopic and microscopic morphologies of defects, forging process, and metal streamlines were analyzed and studied by means of a direct reading spectrometer, high-resolution camera, metallographic microscope, DEFORM finite element analysis software, and chemical etching. Findings indicate that the observed defects constitute forging-induced cracks, with subsequent normalizing heat treatment exacerbating decarburization phenomena in defect-adjacent microstructures. During the forging process of the forgings, the metal continuously extruded into the die cavity, and the inflowing metal pulled the dead zone metal downward, causing the flow lines aligned with the contour to bend into S-shaped metal streamlines. Cracks formed when the tensile stress in the dead zone metal exceeded the material's critical tensile stress. An improved process was proposed: adopting a vertical upsetting extrusion forming method with a 40° diversion angle at the junction between the first step and the thin rod in the die cavity. Numerical simulations confirmed complete elimination of deformation dead zones in the optimized process. Experimental verification demonstrated crack-free forgings. Therefore, the eccentric camshafts formed by the initial process exhibited forging cracks, and the proposed improved method of vertical upsetting extrusion forming with a diversion angle effectively eliminated the forging cracks.