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Sheet metal fabrication design: punching, bending, extrusion

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Sheet metal manufacturing process design
Craftsmanship: The degree of difficulty of the product in various processing processes such as punching, bending, etc.
Process requirements: This manufacturability should be met when designing sheet metal fabrication.
The basic processing methods are: punching, bending, stretching, forming, etc.
Sheet metal manufacturing process design
Sheet metal manufacturing process design

7 design considerations for punching workpieces

Ordinary punching: currently the most used

Precision punching: requires precise punching dies and high-precision punching equipment, and the cost is higher than ordinary punching and is generally used in relatively precise products.

The appearance is as simple as possible

The depth and width of the protruding or concave part of the punching part, in general, should not be less than 1.5/t (t is the material thickness), and at the same time, narrow and long cuts and too narrow grooves should be avoided in order to increase the mold. The edge strength of the corresponding part.


Try to minimize the waste when the punching parts are laid out, thereby reducing the waste of raw materials, and increasing the number of products with the same raw materials, thereby reducing waste and reducing costs.

Shape and the inner hole should avoid sharp corners

Sharp corners will affect the life of the mold. When designing products, pay attention to the transition of the corners at the corners, and the radius of the corners is R≥ 0.5t (t is the thickness of the material).

Holes and square holes

The hole of the punching part is preferably a round hole. When punching, it is limited by the strength of the punch, and the diameter of the punch should not be too small, otherwise, the punch will be easily damaged. The minimum punching size is related to the shape of the hole, the mechanical properties of the material, and the thickness of the material.

The minimum size of punching holes is generally not less than 0.40mm, and holes smaller than 0.40mm are generally processed by other methods, such as corrosion, laser drilling, etc.

Hole Spacing and Hole Margin

When designing the structure of sheet metal parts, there should be enough materials between holes and between holes and margins to avoid cracking during stamping.

Distance between hole wall and straight wall

When punching a hole in a stretched product, in order to ensure the shape and position accuracy of the hole, and to ensure the strength of the mold, a certain distance should be maintained between the hole wall and the straight wall.

Designs that avoid notches and sharp corners

The sharp corners of the notch will cause the die punch to be sharp, which is easy to damage the punch, and cracks are also likely to occur at the sharp corners of the product.

7 Design Requirements for Bending in Sheet Metal Manufacturing

The principle of bending: refers to making straight edge, bevel edge, bending, and other shapes on sheet metal parts, such as bending sheet metal parts into L shape, U shape, V shape, etc.
Die bending: generally used for sheet metal products with complex shapes, small sizes, and high output.
Bending by CNC plate bending machine: generally used for sheet metal products with large product dimensions and small batch production.

Design Requirements 1#: Minimum bending radius

When the material is bent, the outer layer is stretched and the inner layer is compressed over the fillet area. When the thickness of the material is constant, the smaller the fillet of the inner layer, the more serious the tension and compression of the material; when the tensile stress of the fillet of the outer layer exceeds the ultimate strength of the material, cracks and breaks will occur; if the fillet is bent If it is too large, it will be affected by the rebound of the material, and the precision and shape of the product cannot be guaranteed.

Design Requirements 2#: Straight edge height

The height of the straight edge of the bending part should not be too small, otherwise, it will be difficult to meet the precision requirements of the product.

If the straight edge height of the bending part is smaller than the minimum straight edge height design due to the product structure, a shallow groove can be processed in the bending deformation area before bending. The disadvantage of this method is that it reduces the strength of the product, and it is not suitable if the sheet metal material is too thin.

Design Requirements 3#: Minimum hole margin

There are two ways to process holes on bending parts, one is to bend first and then punch; the other is to punch first and then bend. The design of the edge distance of punching after first bending refers to the requirements of punching parts; after punching and then bending, the hole should be outside the bending deformation zone, otherwise, it will cause deformation of the hole and easy cracking at the opening.

Design Requirements 4#: Distance

When bending an adjacent edge close to a bend fillet edge, the bent edge should be at a certain distance from the fillet.

Design Requirements 5#: Process gap

If only a part of one side is bent, in order to prevent cracking and deformity, a process incision should be designed. The width of the process incision is not less than 1.5t, and the depth of the process gap is not less than 2.0t+R, where t is the thickness of the sheet metal.

Design Requirements 6#: Kill edge design

The dead edge of the bending part means that the bent surface is parallel to the bottom surface, commonly known as the dead edge. The previous process of killing the edge is to bend the bending edge to a certain angle, and then kill it to fit. The dead side length of the dead side is related to the thickness of the material. Generally, the minimum length of the dead side is L≥3.5t+R, where t is the thickness of the sheet metal material, and R is the minimum inner bending radius of the previous process of the dead side.

Design Requirements 7#: Process hole design

When designing a U-shaped bending part, the two curved sides should preferably be the same length, so as to prevent the product from being offset during bending and causing waste. If the structural design does not allow the two sides to be the same length, in order to ensure the accurate positioning of the product in the mold, it should be pre-designed in the design. To add process positioning holes, especially for parts that are formed by multiple bending, the process holes must be designed as positioning benchmarks to reduce accumulated errors and ensure product quality.

Sheet Metal Extrusion

Definition: The process of drawing sheet metal parts into round or square, special-shaped, and other shapes with side walls around them, such as aluminum washbasins, stainless steel cups, etc.

5 design points for sheet metal extrusion

Minimum corner radius

The minimum fillet radius between the bottom and the wall of the drawing piece should be greater than the plate thickness, that is, r1>t; in order to make the drawing go more smoothly, generally take r1=(3~5)t, and the maximum fillet radius should be less than 8 times the thickness of the plate, that is, r1<8t.

Deep drawing part fillet radius size

The minimum fillet radius between the flange and the wall of the stretched part should be greater than 2 times the thickness of the plate, that is, r2>2t; in order to make the stretching go more smoothly, generally take r2=5t, and the maximum fillet radius should be less than the thickness of the plate 8 times, that is, r1<8t.

Rectangular Extrusion

The minimum fillet radius between the two adjacent walls of the rectangular stretcher should be r3 ≥ 3t. In order to reduce the number of stretches, r3 ≥ 1/5H should be taken as much as possible, so that one stretch can be completed.


Due to the different stresses in the tensile parts, the thickness of the material changes after stretching. Generally, the center of the bottom maintains the original thickness, the material at the rounded corners of the bottom becomes thinner, and the material at the top near the flange becomes thicker; the material at the rounded corners of the rectangular stretcher becomes thicker. When designing a stretched product, it is clearly indicated on the drawing that the external dimensions or the internal and external dimensions must be guaranteed, and the internal and external dimensions cannot be marked at the same time.

Material thickness

The material thickness of the stretched parts generally takes into account the law that the upper and lower wall thicknesses are not equal in the process of deformation (that is, the upper thickness is thicker, and the lower is thin). When a circular flangeless drawing part is formed at one time, the ratio of height H to diameter D should be less than or equal to 0.4.

In general, when designing the drawing parts, it should be noted that the shape of the drawing parts should be as simple as possible, the shape should be as symmetrical as possible, and the drawing depth should not be too large.