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Design information for bending

Bending is a forming process used to create three-dimensional products from flat sheet metal. Various bending processes allow classically welded or bolted assemblies to be combined into a more cost-effective single part. In industry, bending has become established for both small and large parts.

Minimum leg length

The smallest possible leg length is a tool-related minimum dimension that must be observed in the part design. If a leg length is too short, the workpiece cannot be bent according to the design.

For a 90° bend, the width W can be used to determine the smallest leg length Smin:

Smin = √2/2 * W

The following table lists the respective guide values for a 90° bend. As the material thickness increases, the minimum leg length Smin changes as a result of the tools used.

Steel sheets

Material thickness, 90°-bend

Minimum leg length Smin

1mm

6.5mm

1.25mm

1.25mm

1.5mm

8mm

2mm

9.5mm

2.5mm

12.5mm

3mm

12,5mm

4mm

19mm

5mm

31mm

6mm

31mm

8mm

39mm

10mm

61mm

12mm

76mm

Stainless steel sheets

Material thickness, 90°-bend

Minimum leg length Smin

1mm

6.5mm

1.25mm

8mm

1.5mm

8mm

2mm

9.5mm

2.5mm

12.5mm

3mm

19mm

4mm

19mm

5mm

31mm

6mm

31mm

8mm

54mm

10mm

61mm

12mm

76mm

Aluminium sheets

Material thickness, 90°-bend

Minimum leg length Smin

1mm

8mm

1.25mm

8mm

1.5mm

8mm

2mm

9.5mm

2.5mm

12.5mm

3mm

19mm

4mm

19mm

5mm

31mm

6mm

31mm

8mm

54mm

10mm

61mm

12mm

76mm

Minimum distances to the bending edge

Workpieces that have a hole or a cut-out near the bending line in the uncoiled state must maintain a minimum distance Lmin. If the distance falls below Lmin, the cut-outs will be deformed during the bending process.

The minimum distance Lmin is calculated with the die width W as follows:

Lmin = 0.75 * W

A quick, workshop-friendly method for determining the minimum distance is to use the smallest leg length. Cut-outs and holes that have a distance to the bending line that is greater than the smallest leg length can be produced without deformations.

Z-bends

In the case of two successive bends, so-called Z-bends, a minimum step dimension Xmin must be maintained due to the bending tool used.

Steel sheets

Material thickness, Z-bend

Minimum step size Xmin

1mm

12.5mm

1.25mm

13mm

1.5mm

13.5mm

2mm

16mm

2.5mm

20mm

3mm

20.5mm

4mm

27.5mm

5mm

37.5mm

6mm

39mm

8mm

48mm

10mm

70mm

12mm

85mm

Stainless steel sheets

Material thickness, Z-bend

Minimum step size Xmin

1mm

13mm

1.25mm

13mm

1.5mm

13.5mm

2mm

17mm

2.5mm

21mm

3mm

28.5mm

4mm

30mm

5mm

40.5mm

6mm

41.5mm

8mm

62.5mm

10mm

74mm

12mm

90mm

Aluminium sheets

Material thickness, Z-bend

Minimum step size Xmin

1mm

13mm

1.25mm

13mm

1.5mm

12.5mm

2mm

17.5mm

2.5mm

19.5mm

3mm

26mm

4mm

27mm

5mm

38mm

6mm

40mm

8mm

61mm

10mm

72.3mm

12mm

86.6mm

Bend reliefs

The run-out of the bending lines should not pass directly into the material, otherwise the compression and expansion at the bending zone will be impeded and cause cracks. Attached relief slots minimize the notch effect and thus ensure the desired bending result.

Sloping edges

Sloping edges towards the bending line must be avoided, otherwise homogeneous bending along the intended edge is not possible due to the tooling.

This can be remedied by a perpendicular distance to the bending line with the dimension of the minimum leg length or by cutting the slanted edge free.

Free bore for bending bead

For process reliability and to avoid unsightly corners when bending edges meet, a corner notch D should be provided at the intersection of the crossing bending lines. Corresponding minimum dimensions are listed in the following table depending on the material thickness.

Material thickness

D ± 0.5

≤ 2mm

3mm

> 2mm ≤ 4mm

5mm

> 4mm - 6mm

7mm

Closed corners

The bending manufacturing process can only be used if the entire sheet metal part can be unwound.

Consequently, if three bending lines intersect, one must be split open. If this edge also has to be closed afterwards, a weld seam or another manufacturing process must be used.