Stamping and drawing is a common forming process, also frequently seen in the industrial sector. Drawing forming is a stamping method that uses a die to form a flat blank into an open hollow part. As one of the main processes for stamping parts, drawing is widely applied. Through the drawing process, thin-walled parts with irregular shapes such as cylindrical, rectangular, stepped, spherical, conical, and parabolic forms can be produced. If combined with other stamping processes, parts with more complex shapes can be manufactured. So what are the types of metal stamping drawn parts?
Stamping equipment is used for product drawing and forming, including drawing processing, redrawing processing, reverse drawing, and ironing.
Drawing processing: Using a blank holder device and the punch force, part or all of a flat sheet is drawn into the die cavity to form a container with a bottom. The container side walls are processed parallel to the drawing direction, while the drawing of conical (or pyramidal) containers, hemispherical containers, and parabolic containers also involves expansion forming.
Redrawing processing: For deep-drawn products that cannot be completed in a single drawing operation, the formed product needs to be drawn again to increase the depth of the formed container.
Reverse drawing processing: The workpiece from the previous drawing process is drawn in the reverse direction, turning the inner side of the workpiece into the outer side, thereby reducing its outer diameter.
Ironing processing: The formed container is squeezed through a punch into a die cavity slightly smaller than the container's outer diameter, making the bottomed container smaller in outer diameter and thinner in wall thickness, which both eliminates wall thickness deviations and smooths the container surface.
When using stamping equipment for hardware stamping and drawing, the following 16 types are included:
1. Cylindrical drawing processing
Drawing of cylindrical products with a flange. Both the flange and bottom are flat shapes, the cylindrical side wall is axisymmetric, deformation is uniformly distributed on the same circumference, and the blank on the flange undergoes drawing deformation.
2. Elliptical drawing processing
The deformation of the blank on the flange is tensile deformation, but the amount and ratio of deformation vary 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 deep drawing
Low rectangular parts formed in a single drawing operation. During drawing, the drawing resistance at the corner of the flange deformation zone is greater than that at the straight edge, and the degree of deformation at the corner is greater than that at the straight edge.
4. Conical (V-shaped) deep drawing
When the side wall of the stamped part is an inclined surface, the side wall is suspended and does not contact the die during the stamping process, only contacting the die at the end of forming. The deformation characteristics of different parts of the side wall during forming are not entirely the same.
5. Dome-shaped deep drawing
The deformation of the blank during the forming of a dome-shaped cover is not simple tensile deformation, but a composite forming process involving both stretching and bulging deformation. The deformation on the blank holder surface is tensile deformation (radial tensile stress, tangential compressive stress), while the deformation of the blank inside the contour (especially the central area) is bulging deformation (radial and tangential tensile stresses).
6. Hemispherical deep drawing with flange
During the drawing of spherical parts, the blank is in partial contact with the spherical top of the punch, while the rest is mostly in a free, unsupported state. Therefore, the main process issues for such spherical parts are severe thinning at the locally contacted area or instability and wrinkling in the curved surface area.
7. Flange deep drawing
The flange portion of the drawn product is formed using shallow drawing. Its stress-strain behavior is similar to that of compression flanging. Due to the presence of tangential compressive stress, wrinkling is prone to occur, so the forming limit is mainly restricted by compression-induced wrinkling.
8. Edge Drawing
The flange portion of the product drawn in the previous operation is subjected to angular re-drawing, which requires the material to have good plasticity.
9. Deep Drawing
Products that exceed the drawing limit require two or more drawing operations to complete. The product drawn in the depth direction in the previous station is re-drawn in the depth direction. A wide-flange drawn part is drawn to the required flange diameter during the first drawing, and the flange diameter remains unchanged during subsequent drawing operations.
10. Conical Drawing
For deep conical parts with H/D>0.8 and α=10°–30°, due to the large depth and significant deformation of the blank, the forming force is difficult to transmit solely through the contact area between the blank and the punch, which can easily lead to excessive localized thinning or even cracking of the blank. Therefore, multiple transitional steps are required to gradually form the shape. The stepped drawing method first draws the blank into a stepped transitional part, whose stepped shape is tangent to the inner contour of the conical part, and finally forms the cone. The number of drawing operations and the process for the stepped transitional part are the same as those for stepped cylindrical parts.
11. Rectangular Re-drawing
The deformation of tall rectangular parts formed by multiple drawing operations differs not only from that of deep cylindrical parts but also significantly from that of low box-shaped parts. When processing tall rectangular boxes on a multi-station automatic transfer press, the shape and dimensions of the part change with the drawing height during the multiple drawing process.
12. Curved Surface Forming
Curved surface stretch forming is a stamping method that shrinks the outer flange portion and elongates the inner flange portion of a flat metal blank to produce a hollow product with a non-straight wall and non-flat bottom curved shape.
13. Stepped Drawing
The initial drawn product on the left undergoes redrawing to form a stepped bottom on the right. The deep portion deforms early in the drawing process, while the shallower deep-drawn portion deforms later. The side walls at the stepped transition are prone to induced shear stress and deformation.
14. Reverse Drawing Process
Reverse drawing of a workpiece previously drawn in an earlier operation is a type of redrawing. Reverse drawing can increase radial tensile stress, which is highly effective in preventing wrinkling. It is also possible to increase the drawing coefficient of the redrawing process.
15. Ironing (Wall Thinning) Drawing
Unlike conventional drawing, ironing primarily changes the wall thickness of the drawn part during the drawing process. The clearance between the punch and die is smaller than the blank thickness, so the straight wall of the blank is subjected to significant uniform compressive stress as it passes through the clearance. When the wall thickness is reduced during drawing, variations in container wall thickness are eliminated, surface smoothness is improved, and precision and strength are enhanced.
16. Sheet Metal Drawing
Sheet metal products are stamped parts with complex surface shapes. During the drawing operation, the blank undergoes complex deformation, and its forming nature is not simple stretch forming but rather a combined forming process that simultaneously involves both drawing and stretching (bulging).