How to compensate for deflection of a press brake

When bending sheet metal on a press brake, the released forces can cause the upper and lower beam to deform. This leads to a more open angle in the centre of the bend and is also known as the ‘canoe’ effect. The amount of angle deviation depends on both the bend operation and the press brake model. But how can you compensate for this? Over time, several solutions have been developed.

Shimming

One way of compensating for deflection is to add paper or metal strips underneath parts of the bottom tools. This is a trial-and-error method which is time consuming, inaccurate and inflexible. Shimming, as it’s called, has to be carried out by a skilled operator, who can be hard to find these days.

Another method is to create an opposite curve along the length of the press brake. This is called crowning.

Pre-crowned lower beams

Several manufacturers design press brakes with a pre-crowned lower beam. This can result in consistent bends for certain standard situations, but mostly pre-crowning is not very accurate. The reason for this is that the deflection depends on the amount of force and the type of bend, while the crowning curve in the lower beam is a fixed curve. This can be solved by adjustable crowning.

Adjustable crowning

Adjustable crowning systems are a very effective way to compensate for deflection during bending. It is important that a crowning system covers the whole length of the machine because top tooling must penetrate bottom tooling at the same depth across the whole machine. Crowning systems are available in mechanical and hydraulic versions. 

Hydraulic crowning

Hydraulic crowning systems are built into the machine itself and use one or more cylinders in the lower beam of the press brake. The more cylinders, the higher the accuracy. Hydraulic crowning systems cannot be integrated into an existing press brake.

Mechanical crowning

Mechanical crowning systems use wedges to create a curve across the whole length of the press brake. Various mechanical systems are currently available on the market.

Each press brake model has different deformation characteristics. There is no one-type-fits-all solution for crowning. It is really important that a crowning system is tailored to the characteristics of a specific press brake model. At WILA we do just that with our crowning systems with WILA Wave Wedges.

WILA’s advice

WILA offers Tool Holders with integrated crowning and alignment, that can be fitted to existing press brakes as well. For detailed information, check out our web site, catalog, or just give us a call!