The metal bending process
The metal bending process
Let’s get technical and explore the intricacies of metal bending and the information we require to bring your project to life.
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BOXES – CLEARANCES
When producing a box or an item where two adjacent flanges intersect at a corner, the tolerances, desired clearances between them and their bending sequence must be considered.
When producing a box or an item where two adjacent flanges intersect at a corner, the tolerances, desired clearances between them and their bending sequence must be considered.
We recommend a minimum clearance of 0.2mm to account for any variation in material thickness, linear and angular tolerances.
When bending items with offset flanges, the bending sequence becomes important. During forming the workpiece is bent beyond the desired angle so it forms correctly after spring back once pressure from the tooling is released.
Ensuring the flanges are bent in the correct sequence avoids collisions with tooling or other flanges.
Step Bending
STEP BENDING ALSO KNOWN AS BUMP FORMING
When the internal radius required is larger than what can be achieved with a single bend, step bending is necessary. With the help of our machines, parts that are typically rolled can be bent repeatedly to produce the desired result.
The parts that are intended to be on rollers and those that have been redesigned to be step-bent on press brakes are displayed below. We can generate an almost precise match. Maintaining consistency in flange lengths is essential when crafting step bends, as it contributes to a more polished appearance.
The length of each flange will depend on the thickness and material of the part. For instance, a part made of 3mm mild steel will require the flanges to have a minimum length of 13mm. This length requirement applies to the very last flange as well, as it needs to rest on the die in the press brake.
The distance between each bend will depend on the thickness and material type. Thicker materials and more rigid/less flexible (higher tensile strength) materials require more pressure to bend. To exert enough pressure, whilst remaining within the Press brake’ tonnage limits, necessitates the use of tooling with wider grooves. Thus the thicker, more rigid/less flexible materials are prevented from having smaller distances between bends.
Unbent flanges beyond the end of the bend are unavoidable. To form bends without distortion, as the Punch descends onto the workpiece, the workpiece must remain in contact with the top edge of the Die (bottom tooling) without slipping into the tool. Therefore an area either side of the bend remains unformed.
Flange Lengths
We have specified minimum flange lengths based on the thickness and material of the parts. These requirements ensure that all bent components are fabricated to the highest quality standards and have no risk of deformation.
The minimum flange length is determined by the die length. As material thickness increases, the die size also grows. Consequently, the thicker the part, the larger the required flange length
View all of our material flange lenghts in relation to material thicknesses below.
| THICKNESS – MILD STEEL | MINIMUM FLANGE LENGTH |
|---|---|
| 0.7, 0.9, 1.2 | 8 |
| 1.5, 2 | 9 |
| 2.5 | 11 |
| 3 | 14 |
| 4 | 20 |
| 5 | 25 |
| 6 | 30 |
| 8 | 40 |
| 10 | 60 |
| 12 | 75 |
| THICKNESS – STAINLESS STEEL | MINIMUM FLANGE LENGTH |
|---|---|
| 0.5, 0.7, 0.9 | 8 |
| 1.2, 1.5 | 9 |
| 2 | 11 |
| 2.5 | 14 |
| 3 | 20 |
| 4 | 25 |
| 6 | 30 |
| 8 | 40 |
| THICKNESS – ALUMINUM | MINIMUM FLANGE LENGTH |
|---|---|
| 0.5, 0.7, 0.9, 1.2, 1.5 | 8 |
| 2 | 9 |
| 2.5 | 11 |
| 3 | 14 |
| 4 | 17 |
| 5, 6 | 25 |
| THICKNESS –COPPER | MINIMUM FLANGE LENGTH |
|---|---|
| 0.9, 1.2 | 8 |
| 1.5, 2 | 9 |
| 2.5 | 11 |
| 3 | 14 |
| 4 | 20 |
| 5 | 25 |
| THICKNESS –BRASS | MINIMUM FLANGE LENGTH |
|---|---|
| 0.9, 1.2 | 8 |
| 1.5, 2 | 9 |
| 2.5 | 11 |
| 3 | 14 |
| 4 | 20 |
| 5 | 25 |
Bend Reliefs
Using bend reliefs is crucial in metal bending. Without them, metal is at risk of tearing and deforming. Bend reliefs enable controlled bending, resulting in a clean finish.
The images below show how including or omitting bend reliefs impacts the forming process. Without them, deformation risks increase, and flanges may pull on adjacent, non-bent areas, leading to tearing.
In contrast, adding bend reliefs ensures easy, clean bends by preventing distortion. These small cutouts, typically matching the bend radius, are placed around the bend zone to facilitate smoother bending and avoid unintended distortions.
Internal radiuses
The chart indicates what internal rads we can achieve per thickness for each material. Different grades / types of material such as Galv, Zintec, S355, 316 will mean the rads will vary slightly but are likely to vary no more than +/-1mm.
| MILD STEEL CR4 | MILD STEEL S275 | STAINLESS STEEL – 3042B | ALUMINIUM – 5251 | BRASS | COPPER | |
|---|---|---|---|---|---|---|
| 0.5 | 1.5 | 1 | ||||
| 0.7 | 1 | 1.5 | 1 | |||
| 0.9 | 1 , 1.5 , 2 | 1.5 , 2 , 2.5 | 1 | 1 , 1.25 , 1.5 | 1 | |
| 1.2 | 1 , 1.5 , 2 , 2.5 | 2 , 2.5 , 3.5 | 1 | 1 , 1.25 , 1.5 | 1 | |
| 1.5 | 1.5 , 2 , 2.5 , 3 | 2 , 2.5 , 3.5 , 4 | 1 , 1.25 | 1.25 , 1.5 , 2.25 | 1 , 1.5 | |
| 2 | 1.5 , 2 , 2.5 , 3 , 4 | 2.5 , 3.5 , 4 , 4.5 | 1 , 1.25 , 1.5 , 1.75 | 1.25 , 1.5 , 2.25 , 2.75 , 3 | 1 , 1.5 , 1.75 , 2 | |
| 2.5 | 2 , 2.5 , 3 , 4 , 5 | 3.5 , 4 , 4.5 , 5.5 | 1 , 1.25 , 1.5 , 1.75 , 2 | 1.5 , 2.25 , 2.75 , 3 , 3.5 | 1 , 1.5 , 1.75 , 2 , 2.5 | |
| 3 | 2.5 , 3 , 4 , 5 , 5.5 | 2.5 , 3 , 4 , 5 , 5.5 | 3.5 , 4 , 4.5 , 5.5 , 7.5 | 1.25 , 1.5 , 1.75 , 2 , 2.5 | 2.25 , 2.75 , 3 , 3.5 , 4.5 | 1.5 , 1.75 , 2 , 2.5 , 3 |
| 4 | 4 , 5 , 5.5 , 6 | 5.5 , 7.5 , 9.5 | 1.5 , 1.75 , 2 , 2.5 , 3.5 | 3 , 3.5 , 4.5 , 6 | 1.75 , 2 , 2.5 , 3 , 3.5 | |
| 5 | 5 , 5.5 , 6 , 12 | 5.5 , 7.5 , 9.5 , 15 | 2 , 2.5 , 3.5 , 5.5 | 3.5 , 4.5 , 6 , 10 | 2 , 2.5 , 3 , 3.5 , 5.5 | |
| 6 | 5.5 , 6 , 12 | 7.5 , 9.5 , 15 | 2 , 2.5 , 3.5 , 5.5 | |||
| 8 | 6 , 12 , 15 | 15 , 17 | ||||
| 10 | 12 , 15 | |||||
| 12 | 15 |
Holes In The Bend Zone
Holes near the bend zone often risk deformation as they may fall into the fold, altering their shape and size. The hole could also catch on the die, causing tearing and damaging the part. To avoid this, holes near the bend zone can be added as a secondary operation after bending, unless distortion is intended.
Limited options exist to fix warped holes. Some parts may work on supportive dies for a smaller internal radius, but this may not suit specific radius or angle requirements. During quoting, we’ll assess compatibility with alternative dies to ensure the best outcome.
