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Improving the Design of Sheet Metal Parts – Sheet Metal Design Guidelines

Improving the Design of Sheet Metal Parts – Sheet Metal Design Guidelines

Estimated reading time: 9 minutes, 48 seconds.

When designing product parts, it is important to consider ease of manufacture. Try to think of ways to make it easy to process, but also to save material, and to increase strength without scrap. As a result, designers should pay attention to the following manufacturing aspects

Sheet metal parts’ machinability refers to the degree of difficulty in cutting, bending and stretching of the parts. A good process should ensure less material usage, less number of processes, simple design of the mold, high lifespan and stable product quality. In general, the most significant influence on the processability of sheet metal parts is the material performance, part geometric, size and accuracy requirements.

How to fully consider the requirements and characteristics of the processing process when designing the structure of thin sheet metal components, several design guidelines are recommended here.

 

1 simple geometry guidelines

The simpler the geometric shape of the cutting surface, the more convenient and simpler the cutting down, the shorter the path of cutting, and the smaller the cutting volume. For example, a straight line is simpler than a curve, a circle is simpler than an ellipse and other higher-order curves, and a regular shape is simpler than an irregular shape (see Figure 1).

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines1

(a) Irrational structure (b) Improved structure

(Figure 1)

The structure of Fig. 2a makes more sense only when the volume is large; otherwise, when punching, cutting is troublesome; therefore, the structure shown in Fig.2b is appropriate for small volume production.

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines2

(a) Irrational structure (b) Improved structure

(Figure 2)

2 Material saving guideline (conformation guideline of punching and cutting parts)

Saving raw materials means reducing manufacturing cost. Scraps of off-cuts are often disposed of as waste material, so in the design of thin sheet components, the off-cuts should be minimized. Punching rejects are minimized to reduce material waste. Especially in the volume of large components under the material effect is significant, reduce the off-cuts in the following ways:

1)Reduce the distance between two adjacent members (see Figure 3).

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines3

(a) Irrational structure (b) Improved structure

(Figure 3)

2)Skillful arrangement (see Fig. 4).

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines4

(a) Irrational structure (b) Improved structure

(Figure 4)

3) Removal of material at large planes for smaller elements

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines5

(a) Irrational structure (b) Improved structure

(Figure 5)

3 Sufficient strength stiffness guidelines

1) the bending edge with beveled edge should avoid the deformation area

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines6

(Figure6)

2) if the distance between the two holes is too small, there is a possibility of cracking during cutting.

The design of punching holes on the part should be considered to leave a suitable hole edge distance and hole spacing to avoid punching cracks. The minimum distance between the edge of the punching hole and the shape of the part is limited by the different shapes of the part and the hole. When the edge of the punching hole is not parallel to the edge of the part shape, the minimum distance should be not less than the material thickness t; when parallel, it should be not less than 1.5 t. The minimum hole edge distance and hole spacing are shown in the table.

 Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines7

(Figure7)

The round hole is the most solid and easy to manufacture and maintain, and the opening rate is low. The square hole has the highest opening rate, but because it is 90 degree angle, the corner edge is easy to be worn out and collapse, causing the mold to be repaired and stop production line. And the hexagonal hole opening its 120 degree angle greater than 90 degrees than the square hole opening more solid, but the opening rate in the edge than the square hole is a little poorer.

3) thin and long slats with low stiffness are also easy to produce cracks when cutting, especially serious wear on the tool.

The depth and width of the protruding or recessed part of the punching part, in general, should be not less than 1.5t (t is the material thickness), and should also avoid narrow and long cutouts with and overly narrow grooves in order to increase the edge strength of the corresponding part of the die. See Figure (8).

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines8

For general steel A ≥ 1.5t; for alloy steel A ≥ 2t; for brass, aluminum A ≥ 1.2t; t – the thickness of the material.

 Figure(8)

 

4 Reliable punching guidelines

Figure 9a shown in the semi-circular tangent structure punching processing is difficult. Because it requires accurate determination of the relative position between the tool and the workpiece. Accurate measurement of the positioning is not only time-consuming, but more importantly, the tool by can wear and installation errors, the accuracy usually does not reach such high requirements. Once such a structure is slightly deviated from the machining, the quality is difficult to guarantee and the cutting appearance is poor. Therefore, the structure shown in Figure 9b should be used, which can ensure reliable punching processing quality.

 Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines9

(a) Irrational structure (b) Improved structure

(Figure 9)

5 Avoid sticky knife guidelines (the configuration guidelines of the penetration parts)

In the middle of the component punching and cutting will appear the problem of tool and component bonding cross-tight. The solution: (1) leave a certain slope; (2) cutting surface connected (see Figure 10 and Figure 11).

 Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines10Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines11

          (a) Irrational structure (b) Improved structure   (a) Irrational structure (b) Improved structure

(Figure10 ) (Figure11)

When the lap is made in a process with punching and cutting method into 90 ° bending edge, the selection of materials should pay attention to the material should not be too hard, otherwise it is easy to break at the right angle bend. Should be designed in the position of the curved edge process cut to prevent rupture at the corner of the fold.

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines12

(Figure12)

6 bending edge vertical cutting surface guidelines

Sheet in the cutting process after the general further forming process, such as bending. Bending edge should be perpendicular to the cutting surface, otherwise the risk of cracking at the intersection is elevated. If the vertical requirements can not be met due to other restrictions, the cutting surface and the intersection of the bending edge should be designed a rounded corner, the radius of which is greater than twice the thickness of the plate.

 

7 Gentle bending guidelines

Steep bending requires special tools, and high cost. In addition, too small a bending radius is prone to cracking and wrinkling on the inside face (see Figure 13 and Figure 14).

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines13

(a) Irrational structure (b) Improved structure

(Figgure13)

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines14

(a) Irrational structure (b) Improved structure

(Figure14)

Guidelines for avoiding small circular rolled edges

The edges of thin plate components are often rolled edges structure, which has a number of benefits. (1) strengthen the stiffness; (2) avoid the sharp edges; (3) beautiful. However, the rolled edge should pay attention to two points, one is the radius should be greater than 1.5 times the thickness of the plate; second is not completely round, so that the processing is difficult, Figure 15b shows the rolled edge than the respective a rolled edge easy to process.

 Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines15

(a) Irrational structure (b) Improved structure

(Figure15)

9 Slot edge not bending guidelines

Bending edge and slot hole edge to be separated by a certain distance, the recommended value is the bending radius plus two times the wall thickness. The bending area is complicated by the state of the force, and the strength is low. Notch effect of the slot hole should also be excluded from this area. Both the entire slot hole away from the bending edge, but also the slot hole across the entire bending edge (see Figure 16).

 Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines16

(a) Irrational structure (b) Improved structure

(Figure16)

 

10 Complex structure combination manufacturing guidelines

Space structure is too complex components, completely by bending forming is difficult. Therefore, try to design the structure as simple as possible, in the case of non-complicated, available combination of components, that is, a number of simple thin plate components with welding, bolting and other ways to combine together. The structure of Fig. 20b is easier to process than the structure of Fig. 17a.

 Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines17

(a) Irrational structure (b) Improved structure

(Figure17)

11 Avoid the straight lines to penetrate component guidelines

The thin plate structure has the disadvantage of poor transverse bending stiffness. Large flat structure is easy to bend instability. Further will also bend fracture. Usually use pressure groove to improve its stiffness. The arrangement of the groove has a great influence on the effect of improving the stiffness. The basic principle of groove arrangement is to avoid straight through in the area without grooves. The narrow band of low stiffness through is easy to become the axis of inertia of the whole plate buckling instability. The instability always revolves around an axis of inertia, therefore, the arrangement of the pressure groove should cut off this axis of inertia and make it as short as possible. In the structure shown in Figure 18a, multiple narrow strips are formed in the area without pressure slots. Around these axes, the bending stiffness of the entire plate is not improved. The structure shown in Fig. 18b has no potential connected destabilizing inertia axes, and Fig. 19 shows the common groove shapes and arrangements, with the stiffness enhancement effect increasing from left to right, and the irregular arrangement is an effective way to avoid straight through.

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines18

(a) Irrational structure (b) Improved structure

(Figure18)

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines19

(Figure19)

12 Guidelines for pressure groove continuity arrangement

The fatigue strength of the end of the pressure groove is weak, and if the pressure groove is connected, part of its end will be eliminated. Figure 20 is a battery box on a truck, it is subject to dynamic load, Figure 20a structure in the pressure groove end fatigue damage. The structure in Figure 20b does not have this problem. Steep pressure groove ends should be avoided and, where possible, the pressure groove is extended to the boundary (see Figure 21). The penetration of the pressure groove eliminates the weak end. However, the intersection of the pressure slots should be large enough so that the interaction between the slots is reduced (see Figure 22).

 

 Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines20

(a) Irrational structure (b) Improved structure

(Figure20)

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines21

(a) Irrational structure (b) Improved structure

(Figure21)

22

(a) Irrational structure (b) Improved structure

(Figure22)

13 Spatial pressure groove criterion

The instability of spatial structure is not limited to a certain aspect, therefore, setting pressure groove only on one plane cannot achieve the effect of improving the anti-destabilization ability of the whole structure. For example, in the U- and Z-shaped structures shown in Figure 23, their instability will occur near the edges. The solution to this problem is to design the pressure groove as a space (see Fig. 23b structure.)

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines22

(a) Irrational structure (b) Improved structure

(Figure23)

 

14 Partial slackening guideline

Wrinkles occur when partial deformation is severely hindered on the thin plate. The solution is to set up several small pressure grooves near the crease, so as to reduce the local stiffness and reduce the deformation obstruction (see Figure 24).

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines23

(a) Irrational structure (b) Improved structure

(Figure24)

15 Configuration guidelines for punching parts

1) Minimum punching diameter or minimum side length of square hole

Punching should be limited by the strength of the punch, and the size of the punch should not be too small, otherwise the punch will be easily damaged. Minimum punching diameter and minimum side length are shown in the table.

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines24

* t is the thickness of the material, the minimum size of the punch is generally not less than 0.3mm.

2) Punching notch principle

Punching notch should try to avoid sharp corners, as shown in a figure. Pointed form is easy to shorten the service life of the die, and the sharp corner is easy to produce cracks. Should be changed to as shown in the b figure.

Improving the Design of Sheet Metal Parts - Sheet Metal Design Guidelines25

R ≥ 0.5t (t – material thickness)

a Fig. b Fig.

Sharp corners should be avoided in the shape and bore of the punched part. At the connection of a straight line or curve to have a circular arc connection, the radius of the arc R ≥ 0.5t. (t is the material wall thickness)

 

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Post time: Mar-30-2022

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