Hydraulic Die Forming Discussion Group
Deep Drawing Thin Sheet / Control of Wrinkle Pattern

Jack Berry
berry2000@prodigy.net

I have been looking into the effect of the shape of the starting sheet metal (34 ga copper) on the wrinkle pattern formed with deep drawing (3" set). The metal will wrinkle in a pattern which gives the least resistance (a "path of least resistance"). In Figure 1 below a circular shape will wrinkle equally around the perimeter because there is a constant distance from the center of the metal to any edge of the circumference. In the square sheet notice that most of the wrinkles occur in the area of the center of each side (smallest distance from center to edge) while very little wrinkling occurs at the corners of the square because of the greatest distance from center to edge (more metal to wrinkle with the greater distance and gives a greater resistance). This leads to a pattern where the sides of the square wrinkle greatly while the corners remain vertical in the draw. See Figure 2. Two of these vessels have inserts of sterling silver in the macro folds, one crossing the center while the other was skewed to one side and remains entirely on the side of the vessel. Figure 3 shows vessels made with microfolded sheet. Note that the "corners" move slightly in the direction of the shortest distance from center to edge. This is very reproducible and a "mirror image" can even be produced by turning the sheet over to the other side before drawing (see Figure 3).

Square vs round sheet

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