各種アルミニウム板の深絞り加工における速度効果

Abstract

Eight kinds of industral aluminium sheet, i.e., 1050, 1100, 3004 and 5052 of both annealed material (O) and half-hard material (H/2), are used.According to the tensile test by an instron type machine, r value, which is an important property for the press formability, scarecely varies with the strain rate.Speed dependence of the flow stress is evaluated by m value. The figure of m value for various aluminium sheets is less than 10−2, and the range of these values is narrow. However, m value of these materials apparently decreases with the amount of alloying elements and with the hardness which results from the tempering. This means the decrease of the fraction of thermally activated component in the dislocation motion, for example, cross slip. Flow stress is higher for the material in which the cross slip is more difficult to occur. As a result, m value is inversely correlated to the flow stress through the thermally activated processes.These m values influence the drawing load and the fracture load in the Swift’s cupping test. But LDR defined as the forming limit hardly depends on m value, because strain rates of stretching portion and drawing portion are of the same order; the variation of deformation resistance with drawing speed is the same in both the portions. The relative speed of material to the tool surface in each portion changes by a few orders, contrary to the strain rate. Characteristics of the liquid lubricant vary widely with speed. Material in the drawing portion is better lubricated than that in the stretching portion, because the relative speed of the former is higher than that of the later.Speed effect of LDR is concluded as speed effect of the lubricant.