Any metal fabrication shop had to go a long way to complete a sheet metal-made part for their client. Laser cutting, plasma cutting, metal bending, welding, metal rolling, stamping, etc. require several stages of actions to finish the parts.

But as always, the operators of the machines used for all the aluminium fabrication, steel fabrication, and stainless steel fabrication processes constantly run around in search of some simpler way to get things done instead of such lengthy processes that they have to do over and over again.

Even I was asked a few of them several times. Most common was if there is any way to make double bend easier and be done with in a single wipe bending operation.

The Answer

If I have to pick yes or no to answer this question then I’ll say “yes” for the sake of answering in yes or no.

Actually, there are a lot more than “yes” to answer the question. Keep in mind that when you do the double bending in a single wipe bending operation, you might get a slightly different result than getting the double bend done in multi-stage bending operations.

While bending in one single operation, the operator must pay full attention to get the best die design as well as build techniques.

Producing undistorted bends

When done in a single operation, the parts show strong evidence of flatness loss in a specific area. This distortion or curling is most probably caused the metal deformation as it skids or passes over the main forming radius in the punch. In order to produce undistorted bends, it is important that the amount of deformation is reduced.

Understanding the deformation: Pin & Dough

To understanding the deformation, we can think of a pin and dough.

When a pin is rolled over a flat dough, the dough shows the tendency to wrap around the pin. This is what happens.

Analyzing the deformation

For the dough, the curling or wrapping is a product of continuous strain patterns on both sides. Same for the bending. Also, as the diameter of the pin gradually increases, the curling or deformation decreases.

For the sheet metal, the curl or distortion is caused by the metal skids on the punch point. In this situation, we can compare the punch pin with the rolling pin. Also, metals that don’t go over the punch point are bent into a curved shape and once they are bent, it’s difficult to flatten them.

Reducing the distortion while double bending

To decrease the curling distortion while double bending, there must be some modification made to the lower forming section.

As a part of the lower forming section is removed or relived, the sheet metal is allowed to come closer to the finished position. Consequently, the amount of unbending and bending of the part’s wall is greatly reduced.

This very small yet important change to the machine can have a positive impact on reducing distortion on the metal. Additionally, by increasing the diameter of the forming punch, distortion or curling can also be reduced to an extent.