Experimental research of the stress-strain state when drawing aluminum-copper bimetal parts rectangular in plan

Abstract

The stress-strain state of the aluminum-copper bimetal blank flange was studied when extracting boxes rectangular in plan. The studies were carried out using the grid method with assumptions about the material isotropy and incompressibility; uniform deformation within each cell; monotonous deformation, plane stress and three-dimensional strain state, while elastic strains were neglected. A CAD modeling program was used to minimize coordinate grid measurement errors and reduce the time for processing the information obtained. The blanks were rectangles of certain sizes with an explosion-welded AD aluminum and M4 copper layers subjected to preliminary heat treatment before the drawing operation. Rectangular blanks were successively drawn to a height of 10 mm with grid and test sample thickness measurements after drawing. Blank samples were photographed with the same focal length and loaded into the application program. In the program, coordinate points were applied to grid nodes with the distances and coordinates of these points measured before and after strain. According to measurement results, the highest strain was observed in the blank corner areas where compressive stresses increased from the angle bisector to the walls. These stresses led to bimetallic blank stratification and corrugations formed along the copper layer. 20 blanks were drawn, and corrugation was observed on the flange in each case. Varying the hold-down pressure from 0.25 to 0.5 MPa gave no positive results. The highest strain intensity is observed at the end part of the box flange, and this value decreases by 20 % at the approach to the die hole. The effect of angular shear stresses leads to a discontinuity in the transition zone featuring by the presence of an intermetallic layer with reduced plastic properties.