Complexity index of axisymmetric parts in the forging process based on variation in geometric changes

A novel complexity index for axisymmetric forged components in forging processes is introduced based on their overall geometric shape and degree of deformation. This approach involves extracting the circumferential section area of axisymmetric forgings, characterizing the variation in this geometric feature using fractal dimension analysis, and calculating the area ratio between the cross-section and circumscribing rectangle of the forging. To verify this approach, H-shaped forgings were selected, and the proposed complexity index and three existing shape complexity factors were calculated. A hot forging process was performed virtually and practically to check the processing difficulty of H-shaped parts, and the analysis results from the simulation and experimental tests demonstrated that the complexity index was more reasonable for evaluating the difficulty of forging parts. To further validate the applicability of the complexity index, several published cases involving one-stage, two-stage, and multistage forging processes were investigated in detail. Finally, the potential application was discussed with published cases and an actual case from the industry. Regarding the actual five-stage forging process of the bushing part, the deviation of the complexity index calculated at each stage from the ideal value is within a small range between 1.3 and 6.9%, and the statistically shortest average die life of different stages reaches 190,000 pieces. The promising results could further demonstrate that the novel complexity index could work as a useful tool to support the process design of the multistage forging process.