Stripper Plate/Spring Force Design

[Finglas]

I've been taken on in a job recently as a Production Engineer but because of my background in machine design (only about 2 years) and my experince with SolidWorks I've been asked to do some design work. The program used at work is Unigraphics (NX6) and it's a completely different beast to SolidWorks in my opinion. There are no tutorials available unfortunately and I don't think the company are keen on sending me on a training course as my contract is only for 9 months. To make a long story short, I've spent most of the past week familiarising myself with the program and the design is coming on rather slowly as a result. It's quite simple though.

I'm using a press jig to remove material from a component. The material (acetal copolymer - not sure of the specifics here and now) is about 2mm thick. Haven't done anything in the way of presses before but one of my colleagues recommended I include a stripper plate in my design. this is the prevent the component from getting stuck in the punches (or to remove it from the punches might be a better description) as you all probably know.

I need help in selecting springs for the stripper plate. What factors do I need to take into consideration when doing this? I suppose obvious ones would be:

1. Spring will be strong enough to remove workpece when press arm is released
2. Size it correctly so it doesn't deform
3. Select suitable spring material

Any good website for spring calculations?

 

[ajack1]

The blanking / piercing force is the total perimeter of cut x material thickness x shear strength of material the stripping force is 5-10% of the blanking force.

With regard to springs most press shops will have approved suppliers and would use off the shelf items. I would suggest you start by looking at Misumi, Berger, Danly or A.W. Precision or whoever is a preferred supplier for where you are, or do a search for die springs.

All of these will give the forces for all springs as well as maximum recommended deflection etc for tool life / number of strokes.