Bending: A Visual Analysis of the Process

Have you ever looked at a metal object and wondered how it was shaped so precisely? The answer, more often than not, is bending. But not all bends are created equal! In this article, we’ll explore the three main sheet metal bending processes: air bending, bottom air bending, and coining.

What is bending and why is it important?

Bending is a plastic deformation process that allows metal sheets to be shaped. It is a fundamental operation in many industrial sectors, from automobile manufacturing to furniture.

tipi di piegatura, coniatura, piegatura in aria, piegare lamiera

The three main bending processes

1. Bending in the air:
Imagine bending a sheet of paper. Here, bending in the air works more or less like this. The sheet is only partially supported by the die, while the punch folds it. This method is the most common and requires relatively little force.
2. Bending in the air at the bottom of the die:
In this case, the sheet metal is bent until it touches the bottom of the die. This process provides greater accuracy and repeatability than bending in air, but requires greater force.
3. Coining:
Coining is the most complex method and requires even more force. The sheet metal is pressed against the die with sufficient force to ‘coin’ the desired shape. This process is used to obtain very precise and defined folds, but is only suitable for small sheet thicknesses.

Let ‘s analyse them in detail:

Springback:

  • Bending in air: The material tends to ‘reopen’ somewhat after bending, due to the high springback. This results in a lower accuracy of the final angle.
  • Bending in air at the bottom of the die (bottoming): The springback is lower than for bending in air, but higher than for coining.
  • Coining: The springback is minimal, ensuring the highest accuracy of the bend angle.

Let's read the graph: what does it tell us?

The graph in the image shows us the relationship between the bending angle and the force required to perform the operation. We can see that:

Minting requires the greatest force: the blue line, representing minting, is always above the other two.

Air bending at the bottom of the die requires an intermediate force: the green line is positioned between the blue line and the red line.

The air bend requires the least amount of force: the red line, representing the air bend, is always below the other two.

This means that, given the same bending angle, coining will always be the most energy-intensive process, while air bending will be the least energy-intensive.

What is the best process?

The choice of folding process depends on several factors, including:

Sheet metal thickness: for reduced thicknesses, coining is preferable, while for greater thicknesses air bending or die bottom bending are generally used.

Precision Required: If extreme precision is required, minting is the ideal solution.

Cost: Minting is the most expensive process, both in terms of equipment and energy.

Contact us

Powered by Formful