Tool design and experimental verification for multi-stage cold forging process of the outer race

The outer race of constant velocity joints with six inner ball grooves has conventionally been produced using a multi-stage warm forging process, which consists of 9 operations such as billet cutting, forward extrusion, upsetting, backward extrusions, necking, ironing, sizing, and machining. In this study, a multi-stage cold forging process derived from process assessment to replace the traditional warm forging is presented. Detaily, both backward extrusions of the conventional one are redesigned as one operation, and the necking, ironing and sizing are combined into a single necking-ironing-sizing process, thus the proposed cold forging consists of 6 operations. To solve the tool interference in the combined necking-ironing-sizing process, and to facilitate extraction of the forged workpiece from the die cavity, a solid groove punch for shaping the inner ball grooves is redesigned with six-segmentalized grooving knives. Numerical simulation of each sequence is performed to ensure the appropriateness of the suggested process, and the structural integrity is also evaluated. Experimental investigations are carried out using SCr420H billet material. It is shown that this multi-stage cold forging process could be applied to the mass production of the outer race, with the dimensional variation of under 2.0% between the required and the forged geometries.

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