2. Methodology
2.1. Experimental apparatus
An open-fronted, mechanical press was used for the trimming experiments. The press has a maximum tonnage of 125 tonnes and punch velocity of ∼0.1 m/s at the point of contact with the sheet. The experimental die, shown schematically in Fig. 1, consisted of two identical mild steel blocks, the first acting as the punch, or upper tool, and the other as the die, or lower tool. Both steel blocks had removable inserts that acted as cutting blades. The top half of the die had a synthetic rubber stripper attached that led the punch and clamped the sheet in place before trimming. The stripper pressure was a constant value of approximately 1 MPa for all tests. The stripper was necessary to simulate a panel in a production die, which is generally tightly constrained on the die side. Blanks of size 900 mm × 400 mm were used, with the trim-line along the longer dimension of the blank. Clearances were varied from approximately 3 to 35% of the sheet thickness from each material.