# Roll bending – inducing a curve into metal sheets

Roll bending at Rime is carried out using a modern CNC 4-roll bending machine, for bending metal sheets and plates to your wishes. The diversity of shapes is very large. We can roll bend half-shells, conical curves, transitions and rings for you. The smallest possible diameter is 260 mm. The maximum thickness of a sheet is 6 mm.

Roll bending is similar to bending, as the material is formed by applying a force. The metal sheet is not cut and no material is removed. For this reason, roll bending of metal sheets is one of the chipless sheet metal forming methods. Roll bending is used if a metal sheet panel is to be given a larger, smooth radius, which we can only produce in our press brakes with step bending.

## Basic principles of roll bending

Before a metal sheet panel can be bent, the minimum bending radius must be determined. This value represents the limit, at which the material can still be bent without defects. If the radius used is less than the minimum bending radius the metal can tear at the edges or can spall.

Torn workpieces can then no longer be used. This radius differs from material to material.

There is a rule of thumb for calculating the smallest possible bending radius:

- In the case of steel sheet or plate, the sheet thickness is multiplied by a factor of 1 to 3
- In the case of aluminium this factor is 0.8 to 1 and is significantly smaller compared to steel sheet.

This means that a steel sheet or plate that is 10 mm thick can be bent with a minimum radius between 10 and 30 mm. The closer the lower limit of this range is approached during roll bending, the greater the risk of fracture. With our CNC-controlled roll bending machine, before each bending operation the radius is set optimally to the material type and sheet or plate thickness, so that no material damage occurs.

## The possibilities of roll bending

This machine can be used to bend half-shells and conical curves, transitions and rings. The CNC controls also enable creative shapes to be produced to the customer’s wishes.

### How does roll bending work?

As the name says, our four-roll bending machine has four rolls. The arrangement of the individual rolls relative to each other is important so that the metal sheet can be bent uniformly round.

In principle, there are two rolls at the side, whose height is fixed. Between these two rolls, two further rolls are attached vertically above each other. The height of these two rolls can be changed in comparison to the two fixed side rolls. In the home position the three bottom rolls are all on one level.

There is a narrow gap between the two middle rolls, through which the metal sheet is fed. In this setting a metal sheet panel would pass through the machine without being bent. After entering the type of material, sheet thickness and bending radius the CNC machine sets itself to roll bending, by adjusting the middle rolls downwards in relation to the two side rolls. The deeper these rolls are set the smaller the bending radius. The smallest bending radius is equal to the upper roll diameter.