Choose the load rating (clamp size) needed to exceed the requirements of the most demanding die.
Clamp size is driven by the maximum die weight that will be run in the press. Typically, you should choose a clamp force for the upper clamps equal to four times the die weight, and then divide that by the number of clamps. Balance the press using an equal number of bottom upper clamps.
Required force per clamp = (Maximum die weight × 4) ÷ No. of clamps
For example, if the ram will be equipped with four clamps and the die weighs 8,000 pounds, you would calculate the per-clamp force as 8,000 × 4 = 32,000 lbs. ÷ 4 = 8,000 lbs. per clamp. Choose the clamp size that exceeds the calculated rating.
Alternatively, for large presses that require many small clamps to distribute the load, determine the quantity of clamps by reversing the formula:
(Maximum die weight × 4) ÷ Clamp force (each) = No. of clamps needed
For proper balance, round up this quantity to the nearest even number of clamps.
For example, if the maximum die weight is 9,000 lbs., and the force per clamp is 8,000 lbs., you would calculate the number of clamps needed by multiplying 9,000 × 4 = 36,000 lbs. ÷ 8,000 lbs. force = 4.5 clamps. Then you would round up to the nearest even number, or 6 ram clamps. Using an equal number of clamps for the bolster totals 12 clamps.
To develop a plant standard, consider all the data from several presses, rather than a single press, when possible.
Warning: Large clamp forces are needed because the press movement causes dynamic loading. These calculations are general recommendations for moderate press speeds and should not be used to determine a particular press requirements without consulting manufacturer recommendations and internal company policy. You must review press speeds and forces and choose the clamp force and quantity to match your application and internal standard operating procedures.