Characterizing Galling Conditions in Sheet Metal Stamping

Multiple experimental studies were performed on galling intiation for variety of tooling materials, coatings and surface treatments, sheet materials with various surface textures and lubrication. Majority of studies were performed for small number of samples in laboratory conditions. In this paper, the methodology of screening experiment using different combinations of tooling configurations and sheet material in the lab followed by the high volume small scale U-bend performed in the progressive die on the mechanical press is discussed. The experimental study was performed to understand the effect of the interface between the sheet metal and the die surface on sheet metal flow during stamping operations. Aluminum sheet AA5754 2.5mm thick was used in this experimentation. The sheet was tested in laboratory conditions by pulling between two flat insert with controllable clamping force and through the drawbead system with variable radii of the female bead. Comparing pulling forces during sheet metal flow through the testing setup provides information on flow resistance along the interface between the sheet and the tool surfaces. Onset of galling can be detected by the growth of the pulling force. In addition, it is defined by measurement of the surface of the tool and the scratches on the surface of the samples. Typical galling is seen as lines of sheet material deposit on the surface of the die parallel to the sheet material sliding. Most of galling is observed in the areas where lubricant can be forced out of the contact zone, such as edges of the strip, die entry radii or female bead radius.