Nozomu Kawai

The Frictional Mechanism on Surface of Metals Plastically Deformed : 3rd Report, Effects of the Bulk Plastic Deformation on the Frictional Shear Stress

Using the two-dimensional drawing-type friction testing machine reported in the 2nd report, the experiments on aluminium sheets have been first carried out. The following have been concluded. (1) The frictional shear stress τf on the blank-holder surface is proportional to a real contact pressure Pr in every lubricant. This is similar to that obtained on the sheet metal drawing and the U-bending reported previously. After all it has been concluded that τf is not influenced by the plastic deformation but by Pr only, on the frictional surface where the apparent surface area does not increase. (2) The values of τf on the die surface are always larger than those on the blank-holder surface. It has been found newly that τf is influenced by an increase of the apparent surface area besides Pr, on the die surface. (3) Variations of τf on both the blank-holder and the die surface correspond consistently to variations of the appearance of the frictional surfaces. (4) Consequently, it has been concluded that the bulk plastic deformation influences mainly the frictional mechanism through an increase of apparent surface area.

The Effects of Processing Variables on Formability of Aluminium Sheets : 2nd Report, The Effect of Annealing Temperature

The optimum processing conditions of commercially pure aluminium sheet for the pressformability are clarified in correlation with the tensile properties, crystallographic orientation and microscopic structure, by testing sheets differently cold-reduced and annealed at various temperatures. It is concluded that the drawability is governed by the minimum value of r in the sheet plane, similarly to the case of the as-rolled sheets in the previous report. Therefore, the processing conditions which increase the minimum value of r are effective in improving the drawability. The r-value of the tensile specimen taken at 0° to the rolling direction is minimum in the asrolled sheets, but the r-value at 45° becomes minimum in the fully annealed sheets. The numerical order of the r-values in the three directions is in most cases reversed by annealing. The minimum value of r becomes largest at the transition point of this reversal, where recrystallized grains are partially observed. In addition, at this point, the earless condition is satisfied. The heavier the cold reduction prior to annealing the higher becomes the minimum value of r.