Ironworker/punch/calculations/springs

Problem Statement:

Specify springs for a Piranha style punch Knowns:

• Max punching force: 90T
• Max stripping force: 25% of punching force, or .25*90T=22.5T
  • The study mentioned *UP TO 25%*, with an average of under 10%, which would come to 9T, which is well within spec. This depends on a few factors:
    • How many times the punch has been used (after 7, the force decreases, as punch smoothens out)
    • Whether or not the punch is lubricated
    • The clearance between punch and die

Unknowns:

• Necessary compressive force for spring
• Spring Length, solid and stretched
• Spring constant
• Spring Diameter

Calculations

Max Compressive force

=Force/# of springs

- 22.5T/2 = 11.5T, at 1", or any other application which requires 90T of force.

Spring Specs

Thoughts

• Since the machine can theoretically do a cut which uses 90T of force in infinitely thin material (the diameter of the hole would need to be really big!) we should use springs which will have close to the 11.5T of force with very little distance moved. Also, this would not need to change too much as the machine progresses towards making 90T punches at the 1" thickness.
  • What this tells me is that we should use a spring with spring constant (k) relatively low with relation to it's diameter, and compress it to install. This way, we won't be needing to overcome more force than necessary.
    • IE if we need 11.5T for 1/4" steel, we have two options use the low constant or the high one.
      • If we use the low one, precompressed, the force will be relatively close to that, maybe a max of 15T or 20T, if we are punching thru 1" thick.
      • If we use a high constant, the force would quadruple over that distance, making it 46tons. If you don't understand this, take a physics class.
• Research on how Piranha does it:
  • http://www.youtube.com/watch?v=W6BeFhm3xTk

• Perhaps the easiest solution is to buy a set of piranha urethane strippers, as they are relatively cheap ($76 here).
  • Problem with this is that it requires same length of bit and attachment as piranha, which we don't have access to... we could guess from videos and get close, but this is not preferable.
• Another option is to buy the polyurethane die strippers from McMaster, and do a design like piranha. It appears they don't have anything which offers enough resistance... but perhaps it is something which can be tested, as the most expensive pair would be $23, instead of $76.
• Final option is strippers which are punch specific, like here

Analysis of Slant From Vertical on Punch Element

• At 51" arm length going down 1"
• Result: 0.01" deviation. Die clearance is ~0.03", so it's acceptable.
• See dxf:

File:Punchanalysis.dxf