Process optimization for design of duplex universal joint fork using unequal thickness flash

Abstract

To avoid defect formation, a two-step forging process for duplex fork was developed and optimized using an unequal thickness flash. The large cross-sectional difference between the different parts of the complex shape of the duplex fork made it difficult to forge. Crack defects formed during initial forging were observed and analyzed by finite element simulation, and the metal flow lines and velocity distributions on the main cross section were studied. A non-uniform velocity distribution with a large difference in the dangerous area and large amount of oxide scale most likely caused the crack defects. An optimized two-step forging process was developed, preupsetting was used to remove the oxide scale, and final forging using a die with an unequal flash gutter depth was used to obtain a reasonable velocity distribution. The effect of different process parameters on the optimized forging process was determined. The parameters included the pre-upsetting stroke, the friction factor, the workpiece mass, and the offset of the preform, and the results were used to improve the process stability. A duplex fork of acceptable quality and without any cracks was forged in successful trial production using the optimized process in the forging plant.