The calibration of metal-forming presses

Current recommendations for the calibration of metal-forming presses that are, for example, contained in DIN 55189, whilst being an advance on previous bases, which relied on the axial stiffness of the press, continues to assume that the forming force is parallel to the main axis of the press. However, it is broadly known that many material-conversion processes impose an oblique load on the press. The proposed approach relies on subjecting the press to forces that have vertical and horizontal components; such conditions are achieved by upsetting cylindrical specimens with parallel or oblique faces, which enables the simulation of most industrial forming operations. The forming forces, in all principal modes, are measured using a specially designed measurement system which incorporates the forming die-surface; sets of displacement transducers enable the measurement of the translational and rotational deflections of the press. The information extracted from the measurement system on forming forces and tooling location enables the computation of the moments that tend to tilt the ram about the horizontal axes (X and Y) and rotate the press ram about the vertical axis (Z). For some cases, the relationship between the forming force and the resulting moment can be expressed in the form of a flexibility matrix comprising translational and rotational press deflection data however, this approach is limited to presses of relatively fundamental design. For presses derived from more sophisticated design approaches, the preferred approach would be to present the behavioural characteristics of the presses as a matrix of graphical information.