Abstract

In recent years, incremental sheet forming (ISF) has shown significant potential for economically fabricating sheet metal products required in low volume. Despite its advantages of reduced forming forces and higher material formability, manufacturing complex shapes with acceptable geometric accuracy is still a challenging task. Two-point ISF (TPIF) is one variant that uses a support die to a fabricate part with intricate features. In this study, effects of material squeeze factor in the TPIF process is investigated on part accuracy and formability. Material squeeze factor is defined as the amount of sheet thickness squeezed between the forming tool and support die. It is integrated as one of the processing parameters for generating a pre-defined toolpath of the forming process. However, the effective material squeeze (SFe) obtained in experiments is either zero or significantly lower than the squeeze factor programmed (SFp) in the toolpath due to machine and tool compliance. SFp values are heuristically chosen in literature studies to maintain steady contact between the sheet and die surfaces and avoid forming through degenerated SPIF rather than the “true” TPIF process. For a 67° cone, the part kept losing contact with the die surface below SFp = 30% whereas uniform contact between sheet and die surface is achieved for SFp = 40%. Also, the geometric deviation is significantly reduced from 0.61 mm to 0.39 mm along the wall region with the higher squeeze factor. Similar results are obtained for a benchmark heart shape part.

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