Sheet metal is bent on the press brake between a punch with a certain tip angle and a die with a groove angle. Which angles and combinations are best to choose? And how does your choice affect the maximum load capacity and versatility of the tool?
First, it must be clear which bending method you intend to use: air bending or bottom bending. With bottom bending, the angle in the sheet material is formed by trapping the sheet between the punch and the die. Both tools have the same tool angle. Bottom bending is still in limited use. Read more about the advantages and disadvantages of bottom bending. WILA offers standard tools for bottom bending with 90° angles.
If air bending is used, the penetration depth of the top tool into the bottom tool determines the angle formed in the sheet material. The top and bottom tool are often referred to as ‘punch’ and 'die'. The further the punch is pressed into the die, the sharper the angle in the sheet material.
So you can bend multiple angles with one combination of top and bottom tools. You need fewer tools and less frequent changes. Therefore, this is the most commonly used bending method on the press brake. Read more about the advantages and disadvantages of air bending.
So is a tool combination with the sharpest possible angle always the best choice? This depends on another aspect. A sharp angle also has a disadvantage: the maximum load capacity is less than for tools with a wide angle. For the greatest flexibility, choose the sharpest possible angle, unless maximum load capacity is important to you in the future.
When sheet metal is bent on a press brake, the material will always spring back slightly. The greater the product radius formed relative to the sheet thickness, the greater the springback. To compensate for the springback, the material is bent slightly beyond the desired angle. The amount of springback depends on the bending method, the material and the product radius.
When bending a 90° angle in mild steel or stainless steel, the springback is usually around 2° to 4°. Do you want to air bend a 90° angle in a die that has a high maximum load capacity? Then choose a die that still offers just enough room for springback. For this, WILA offers standard dies with a groove angle of 86° or 80°. Do you bend 90° with diagonal flanges or cut-outs near the bending line? In a die with a groove angle of 86°, the space for bulging is limited.
Do you want to adjust the groove angle yourself? Then use the WILA Tool Advisor.
Are tools with a certain angle already available? For air bending, it is not necessary for the angle of the punch and the angle of the die to be equal to each other. As long as both the groove angle and the tip angle are smaller than the desired angle minus the springback.
For example, a 90° angle can be bent using a punch with a tip angle of 28° and a die of 86°. The same angle can also be bent with a punch of 86° and a die of 30°.
To safely choose a good combination of tools, use bend simulation software or the WILA Tool Advisor. Note that you can never bend beyond the largest angle in the applied top and bottom tools.
First determine whether you want to use bottom bending or air bending. Air bending is the most flexible bending method. With a limited set of tools, you can bend different angles and need to change them less often. Choose a tool combination with a sharp tip and groove angle for the greatest flexibility. If desired, you can use the WILA Tool Advisor to adjust the angle of a standard air bending tool to your needs.