Tricks of the Trade
Q: Your catalog provides formulas for selecting V-openings for specific material thickness. However, I have been told that these formulas do not apply in large radius bending. If this is true, what formula should I use?
 A: Yes, it is true that the formula for selecting a V-opening for large radius bending is different than those listed in our air bending force chart. When air bending with large radius punches (punches with a tip radius of .375" or 9.5mm or larger), the punch tip radius must be taken into consideration when selecting a die. In this type of bending, the punch tip radius is often greater than the material thickness.
For example, the recommended V-opening for 16 gauge (.060"/1.52mm) mild steel is .394" (10mm) [see illustration "A"]. This V-opening is unable to accommodate the combination of 16 gauge material and a punch with a tip radius of .375" (9.5mm) or larger.
To calculate the correct V-opening for large radius bending, simply add the punch radius and the material thickness and multiply that value by 2.2 i.e. (PR + T) x 2.2 = V. Using the above example, the formula would be (.375 + .060) x 2.2 = 1.088 [see illustration B"].
Often the formula will suggest a V-opening that is not available. When this happens; simply use the next larger V-opening that is available. It is also a good idea to use acute angle dies whenever possible to provide greater control over spring-back.
Large radius bending will yield a finished part radius larger than the punch tip. For example, if a .750" radius is required, a radius smaller than .750" would be required to achieve a .750" radius on the finished form.
Contact our sales desk at 800.445.4518 for assistance in determining the exact size needed to achieve your finished form.
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