Bump bending a radius using a press brake
- Peter Dawber
Are you using bending rolls to form a radius in sheet or plate material? This is by far the easiest option if you are rolling a full cylinder or a partial segment, but what about if you need a curve between two flat parts with accurate dimensions? This can be tricky, but there is another option……
When rolling a partial radius between two flat parts, even a small amount of over rolling can spoil the component, therefore the start and stop points of the curve need to be carefully controlled. This can be quite difficult to achieve manually using bending rolls and the part typically needs comparing to a template and tweaking until the desired result is achieved. Producing this job on a press brake using radius bending - otherwise known as bump bending - is quick and easy to program and can be controlled precisely. So what do I need to know to get started?
An overview of radius bending
How does radius or ‘bump’ bending work?
Radius bending on a press brake involves making a large number of bends close together at a small angle which in total produce the desired angle and radius. The more steps used to produce the bend, the smoother the radius will appear; there is a trade off here between the appearance of the part and the time taken to produce it.
Can it be programmed on a CNC press brake?
Press brake controls such as the ESA S660 W have built in functions to calculate radius bends. The operator will enter the desired radius, the overall angle and the number of steps required; the control will calculate the distance between bends and the required bending angle for each bend. If the final angle isn’t exactly as required, a correction can be entered to enable very accurate parts.
Does radius bending need special tooling?
A top tool with a specific radius can be used to produce small radius bends, however mostly the same top tool and vee die which is used for standard angle bending is utilised. This means the radii from small to large can be formed using the same tool; a range of different tools would be costly and potentially require high tonnage. Different vee die widths can be utilised to produce the best effect.
What other options are available?
A radius bend can also be produced on a power folder using a similar principle to the press brake method. On some models the folding beam is brought to a small angle and the clamping beam is used to bump the radius; the lower beam and the folding beam of the folder work like the two sides of a vee tool in a press brake and quickly form the radius. The FX30 CNC Folding Machine from Cidan Machinery is a model which is easily used for this application.
Conclusion; so why use bending rolls in the first place?
Is there a better way to roll a precise segment? While utilising the standard features of a press brake or folder is ideal for one-off or complex parts, rolling a radius is a lot faster and in production environments will make significant time savings. If the start and stop points of the segment and the radius of the bend can be easily controlled, then rolling will still be the best option. This can be achieved by using NC or CNC bending rolls which can control the material feeding axis, normally known as the X axis, as well as the position of the pre-bending and pinch rolls. Controls which do this well are the Nexus NC or the Touch Command EVO CNC controls from MG srl in Italy. For any advice, videos and demonstrations of these different processes, please get in touch here.