Sixteen types of stamping and stretching forming process

Stretch forming is a stamping method to form a flat blank into an open hollow part by using a die. As one of the main stamping processes, drawing is widely used. Thin-walled parts with cylindrical, rectangular, stepped, spherical, conical, parabolic and other irregular shapes can be made by drawing process, and parts with more complicated shapes can be made if they are matched with other stamping processes.

The stamping equipment is used to carry out stretch forming processing of products, including stretching processing, re-stretching processing, reverse stretching and thinning stretching processing.

When using stamping equipment for stamping and stretching, it includes the following 16 types:

1. Round drawing: the drawing of cylindrical products with flanges. Both the flange and the bottom are planar, the cylinder side wall is axisymmetric, and the deformation is evenly distributed on the same circumference, and the blank on the flange produces drawing deformation.

2. Ellipse drawing: the deformation of the blank on the flange is tensile deformation, but the deformation amount and deformation ratio change correspondingly along the contour shape. The greater the curvature, the greater the plastic deformation of the blank; Conversely, the smaller the curvature, the smaller the plastic deformation of the blank.

3. Rectangular drawing: a low rectangular part formed by one-time drawing. During stretching, the tensile resistance at the fillet of flange deformation zone is greater than that at the straight edge, and the deformation degree at the fillet is greater than that at the straight edge.

4. Hill drawing: When the side wall of the stamping part is inclined, the side wall is suspended during the stamping process, and the die is not attached until the end of forming. The deformation characteristics of different parts of the side wall are not exactly the same during forming.

5. Hill drawing: The blank deformation of the hill cover plate in the forming process is not a simple tensile deformation, but a composite forming in which both tensile deformation and bulging deformation exist. The deformation of the blank on the blank pressing surface is tensile deformation (tensile stress in radial direction and compressive stress in tangential direction), while the deformation of the blank inside the profile (especially in the central area) is bulging deformation (tensile stress in radial direction and tangential direction).

6. Hemisphere Drawing with Flange: When the spherical part is drawn, the blank partially contacts with the spherical top of the punch, and most of the rest is in an unconstrained free state. Therefore, the main technological problem of drawing this kind of spherical parts lies in the serious thinning of local contact parts or the instability and wrinkling of curved surfaces.

7. Flange drawing: shallow drawing the flange part of the drawn product. Its stress and strain are similar to compression flanging. Due to tangential compressive stress, it is easy to wrinkle, so the forming limit is mainly limited by compression wrinkling.

8. Edge stretching: angular re-drawing is performed on the flange of the product drawn in the previous process, which requires the material to have good plasticity.

9. Deep drawing: A product that exceeds the limit of drawing processing needs to be stretched for more than two times before it can be completed. The products that have been drawn in the depth direction of the previous station are re-drawn in the depth direction. The wide flange drawing part is drawn to the required flange diameter at the first drawing, and the flange diameter remains unchanged at the subsequent drawing.

10. Taper drawing: For deep conical parts with h/d > 0.8 and α = 10 ~ 30, the deformation degree of the blank is large due to the deep depth, and the forming force is transferred only by the local area where the blank contacts with the punch, which easily leads to excessive thinning or even fracture of the blank, and it needs to be gradually formed through multiple transitions. Step stretching method is to stretch the blank into a stepped transition piece, the stepped shape of which is tangent to the inner shape of the conical part, and finally expand to form a cone. The drawing times and process of the stepped transition piece are the same as those of the stepped cylinder piece.

11. Rectangular redrawing: The deformation of high rectangular parts formed by repeated stretching is not only different from that of deep cylindrical parts, but also very different from that of low box parts. Figure 1-46 shows the changes of the shape and size of the product with the drawing height during the process of multiple drawing when the multi-station automatic conveying press processes the high rectangular box.

12. Surface forming: a stamping method for forming a hollow product with a curved surface with non-straight wall and non-flat bottom, in which the outer flange part of a metal flat blank is reduced and the inner flange part is extended.

13. Step drawing: Re-draw the initially drawn product on the left side to form the stepped bottom on the right side. The deep part is deformed at the initial stage of drawing, and the shallow part is deformed at the later stage of drawing. The sidewall of the step change part is easy to induce shear stress to deform.

14. Reverse drawing: reverse drawing the workpiece drawn in the previous process is a kind of re-drawing. The reverse stretching method can increase the radial tensile stress and achieve good results in preventing wrinkling. It is also possible to improve the tensile coefficient of re-stretching.

15. Ironing: Different from ordinary stretching, ironing mainly changes the thickness of the tube wall of the drawing part during stretching. The gap between the male and female dies is smaller than the thickness of the blank, and the straight wall of the blank is under a large uniform compressive stress when passing through the gap. While the wall thickness becomes thinner in the drawing process, the deviation of the container wall thickness is eliminated, the smoothness of the container surface is increased, and the precision and strength are improved.


16. Panel drawing: The panel product is a sheet metal stamping part with complex surface shape. In the drawing process, the deformation of the blank is complex, and its forming nature is not simple drawing, but composite forming in which drawing and bulging coexist.

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