stripping problem when punching fiberglass
stripping problem when punching fiberglass
(OP)
Hi forum users,
We are making a hand held punching machine to punch small (approx 3/16" dia) holes through 2 pieces of aluminum, one of which is .100" thick and the other is .060" thick - between which is a think layer of fiberglass material. It is a less than 2 ton punching requirement. The machine punches well and strips well if the fiberglass is not present, but once the fiberglass is introduced the punch jams up in the die. We have tried heavy duty 1.5" dia stripping springs, coated punches, and played with the cutting clearance from .008-.025," but not had any good results stripping the punch. Any ideas?
Thanks
We are making a hand held punching machine to punch small (approx 3/16" dia) holes through 2 pieces of aluminum, one of which is .100" thick and the other is .060" thick - between which is a think layer of fiberglass material. It is a less than 2 ton punching requirement. The machine punches well and strips well if the fiberglass is not present, but once the fiberglass is introduced the punch jams up in the die. We have tried heavy duty 1.5" dia stripping springs, coated punches, and played with the cutting clearance from .008-.025," but not had any good results stripping the punch. Any ideas?
Thanks





RE: stripping problem when punching fiberglass
I.e., allow a full diameter land behind the punch face to provide material for a few sharpenings, then reduce the punch diameter progressively farther from the punch face to allow clearance between the punch shank and the punched hole.
The idea is that after the punch makes the hole, it will pull some fibers from the material, which will align with the punch and jam the punch in the hole. Providing clearance, so the shank of the punch rattles around in the produced hole, provides room for the fibers projecting inward from the hole to turn around and realign so the punch can be withdrawn from the sheet.
Mike Halloran
Pembroke Pines, FL, USA
RE: stripping problem when punching fiberglass
RE: stripping problem when punching fiberglass
Thanks again.
RE: stripping problem when punching fiberglass
RE: stripping problem when punching fiberglass
MikeH's solution for the tapered punch may well solve your problem. Maybe grind a bit of a cup in the tip of the punch so it is truly shearing the fiberglass fibers not just pushing/pulling and ripping them. They are just jamming up in the space btwn. the punch and the die. But consider these things too:
1. Have the punch hit the thin Al sheet first, so the thicker sheet supports the fiberglass w.r.t. the die. If you hit the thick Al sheet first, with the punch, you aren't punching the fiberglass so much as ripping and crushing it, since it gets no support from the thinner sheet immediately above the die; and the thicker sheet in its deforming doesn't produce a punching/shearing action on the fiberglass.
2. Would any sort of a partial twisting/rotating action of the punch during the punching process help. You Mech. guys will know, better than I do, if this can even be done or how.
3. Maybe your punch should (be in/should have) two cutting actions: the first to punch almost to size; and the second to really shear all three layers to final size. Again, without digging out my books on this stuff, you Mech. guys will know, better than I do, but the lead punch dia.(smaller) would clear a hole so the final punched/sheared materials had someplace to go, but with a cleaner cut.
RE: stripping problem when punching fiberglass
RE: stripping problem when punching fiberglass
They are often willing to help and have a great deal of knowledge and I know for example you can buy dies with a slight nick and spiral in them to help stop slugs coming back up. I have no experience in piercing fibreglass so cannot comment but surely free advice from the people that are trying to sell the product would be a good place to start?
RE: stripping problem when punching fiberglass
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: stripping problem when punching fiberglass
RE: stripping problem when punching fiberglass
or
add plastic spring to strip out the part.