Large Radius Bending – Tackling Springback and Multi-Breakage
What is large (or profound) radius bending?
Inside radius (IR) equal to or greater than eight times the material thickness (MT).
Two challenges common to forming large radius bends are:
- Excessive springback
When the bending force is removed from a large radius bend the part relaxes, the angle opens up, and the inside radius gets larger due to springback. The larger the ratio between IR and MT the more the part will springback.
The challenge with excessive springback is that it is nearly impossible to accurately (within normal tolerance) predict what the final angle and radius will be.
There are springback calculators available but experience has shown us that these calculators are best used to get a ballpark estimate of the final angle and radius. They are not exact but they are a great tool to help select the correct press brake tools to be used.
The calculator that we use here at Mate Precision Tooling was developed by “Bending Guru” Steve Benson and it can be downloaded free of charge at: TheArtofPressBrake.com
The charts below show how the amount of springback increases as the IR/MT ratio increases. A .500 IR in .135 MT is an IR/MT ratio of 3.7 and the chart shows 1.8 degrees of springback with a final radius of .510 (0.2% larger than the punch radius).
With a 3.00 IR in .036 MT the IR/MT ratio is 83.3 and the chart shows 34.8 degrees springback with a final radius of 4.90 (61% larger than the punch radius).
The tooling solution for the .036 MT with a 3.00 radius is to use a die that is 60 degrees or less so the part can be over-bent by at least 34.8 degrees and use a 2.12 radius punch to achieve the 3.00 final radius.
Mate offers a wide selection of standard large radius punch inserts in 25 radii sizes to make it easy to achieve the radius you need.
Multi-breakage (Also called advance bending)
The phenomenon known as multi-breakage is when the material lifts away from the punch during the bend. When this happens the final bend radius is smaller than the punch radius in the center of the bend. There are two effective solutions for multi-breakage.
Option #1: Urethane
The most common solution is to provide counter pressure such as a urethane pad to keep the material in contact with the punch during the bend. Mate offers a variety of urethane pads and holders.
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