More than a dozen stamping and drawing processes, how much do you know?

Stretch forming is a stamping processing method that uses a mold to form a flat blank into an open hollow part. As one of the main stamping processes, drawing is widely used. Thin-walled parts with cylindrical, rectangular, stepped shapes, spherical, tapered, parabolic and other irregular shapes can be made by the drawing process, and more complex parts can also be manufactured if combined with other stamping and forming processes.

The use of stamping equipment for the stretching and forming of products, including: drawing, redrawing, reverse drawing, thinning and drawing.

Stretching process: Using the pressing plate device, using the punching force of the punch, part or all of the flat plate is pulled into the cavity of the concave mold and shaped into a container with a bottom. Stretching of the side wall of the container parallel to the direction of stretching is a simple stretching process, while stretching of conical (or corner pyramid) containers, hemispherical containers, parabolic containers, etc., also includes expansion processing.

Re-drawing process: that is, for the deep-drawn products that cannot be completed by one stretching process, the formed products that are stretched again need to be stretched to increase the depth of the shaped container. 

Reverse drawing machining: This is a process in which the stretched workpiece of the previous process is reversed stretched, and the inside of the workpiece becomes the outside, and the outer diameter is reduced.

Thinning and stretching processing: the formed container is squeezed into the concave mold cavity slightly smaller than the outer diameter of the container with punch, so that the outer diameter of the container with a bottom becomes smaller, and the wall thickness becomes thinner, which not only eliminates the deviation of wall thickness, but also makes the surface of the container smooth.

When using stamping equipment for metal stamping and drawing processing, the following 16 types are included:

01 Round drawing

Stretching of products with flanged (flanged) cylinders. The flange and the bottom are both plane shaped, the side wall of the cylinder is axisymmetric, and the deformation is evenly distributed in the same circumference, and the blank on the flange produces drawing deformation.

02 Ellipse drawing

The deformation of the blank on the flange is tensile deformation, but the amount of deformation and the deformation ratio change accordingly along the shape of the profile. The greater the curvature, the greater the plastic deformation of the blank, and conversely, the smaller the curvature, the smaller the plastic deformation of the blank.

03 Rectangular drawing

A low-rectangular part that is formed by a single stretch. When stretched, the tensile resistance at the fillet of the flange deformation zone is greater than that at the straight edge, and the degree of deformation at the fillet is greater than that at the straight edge.

04 Hill drawing

05 Hill drawing

The blank deformation in the forming process of the mound cover plate is not a simple tensile deformation, but a composite forming with both tensile and bulging deformation. The deformation of the blank on the pressing surface is tensile (tensile stress in the radial direction and compressive stress in the tangential direction), while the deformation of the blank inside the contour (especially in the central area) is a swelling deformation (both radial and tangential tensile stresses).

06 With flange hemisphere drawing

When the spherical part is stretched, the blank is in partial contact with the spherical top of the punch, and most of the rest is in an unconstrained free state suspended in the air. Therefore, the main process problem of the stretching of such spherical parts lies in the severe thinning of the local contact part, or the instability and wrinkling of the curved part.

07 Flange drawing

The flange part of the stretched product is processed by shallow drawing. The stress-strain profile is similar to that of a compression flange. Due to the tangential compressive stress, it is easy to wrinkle, so the forming limit is mainly limited by compression wrinkling.

08 Flange drawing

The flange part of the pre-process stretched product is angled and restretched, which requires the material to have good plasticity.

09 Deep drawing

Stretching products that exceed the drawing limit need to be stretched more than twice before they can be completed. Products that have been stretched in the depth direction of the former station are redrawn in the depth direction. Wide-flange stretches are stretched to the required flange diameter for the first stretch and remain the same when they are then stretched.

10 Taper drawing

H/d>0.8, α=10 ° ~ 30 ° deep conical parts, due to the large depth, the degree of deformation of the blank is larger, only rely on the local area of the blank and punch contact to transmit the forming force, it is easy to cause the blank to be over-thinned and even cracked, and it needs to be gradually formed after many transitions. The stepped stretching method is to first stretch the blank into a stepped transition, the stepped shape is tangent to the inner shape of the tapered part, and finally form a tapered shape. The number of stretching times and process of the stepped transition piece are the same as the stretching of the stepped cylindrical piece.

11 Rectangular redrawing

The deformation of a highly rectangular part formed by multiple stretches is not only different from that of a deep cylindrical part, but also from that of a low box-shaped part. The picture shows that when the multi-station automatic conveyor press is processed for high rectangular boxes, the shape and size of the parts change with the stretching height during the multiple stretching process.

12 Surface forming

The surface is stretched and formed, so that the outer flange part of the metal flat blank is reduced, and the inner flange part is elongated, and it becomes a stamping and forming method for hollow products with a curved surface shape of non-straight wall and non-flat bottom.

13 Step drawing

The left primary drawn product is redrawn and formed into a stepped bottom on the right. The deeper parts are deformed at the beginning of the stretch form, and the shallower parts are deformed at the later stage of the stretch. The sidewall of the changing part of the step is prone to induce shear stress and deformation.

14 Reverse drawing

The workpiece that is stretched in the previous process is reversed and re-stretched. The reverse tensile method can increase the radial tensile stress, which can be better for preventing wrinkling. It is also possible to increase the stretch coefficient of restretching.

15 Ironing

Different from ordinary stretching, thinning stretching mainly changes the thickness of the cylinder wall of the stretched part during the stretching process. The gap between the convex and concave dies is less than the thickness of the blank, and the straight-walled part of the blank is under the greater uniform compressive stress when passing through the gap, and the wall thickness becomes thinner during the stretching process, while eliminating the deviation of the wall thickness of the container, increasing the smoothness of the surface of the container, and improving the accuracy and strength.

16 Panel drawing

Panel products are sheet stamping parts with complex surface shapes. In the drawing process, the deformation of the blank is complex, and its forming properties are no longer simple stretch forming, but compound forming with deep drawing and expansion at the same time.