Quality optimization for aluminum precision forging processes in completely enclosed dies of long forging parts by prediction and avoidance of thin flash generation

摘要

The technology of flashless precision forging enables the manufacturing of complex shaped high strength parts by a cost and material efficient process. Due to geometrical tolerances and complex thermal expansions of the tool elements, small gaps must exist between punches and dies even in precision forging processes. In hot precision forging processes material flows into these gaps unintendedly and the so called thin flash generates. The generation of thin flash in a forging process complicates workpiece positioning in subsequent forming processes and leads to positioning and tolerance defects in subsequent cutting operations. In this paper, the investigation of thin flash generation in a precision forging process of an aluminum long part using finite elements analysis (FEA) and corresponding forging trials is described. For this purpose, the forging processes were varied by use of different preforms with equal volumes but different mass distributions, while the geometrical parameters of the final part were not varied. The forging processes were analyzed by FEA with focus on the value of the form-filling simultaneity depending on the preform geometry. Afterwards, corresponding forging trials were carried out for validation. The experimentally forged parts were analyzed concerning the amount and location (part area) of the generated thin flash to validate the FEA results. The results of the experiments and the FEA showed good agreement concerning the part areas were thin flash generation was predicted by FEA and actually occurred in experiments. It was shown, that the preform geometry strongly influences the generation of thin flash. Preforms with higher values of form-filling simultaneity showed less thin flash generation while preforms with lower values of form-filling simultaneity showed significantly increased thin flash generation. Based on the results, it is very likely that by using a preform geometry, which would lead to a complete simultaneous form-filling, thin flash generation could be completely avoided under ideal technical conditions.