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  • Plastic Punching question

    Discussion in 'The main mechanical design forum' started by pottsvillain, Jan 6, 2012.

    1. pottsvillain

      pottsvillain New Member

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      Hello all, this is my first post, so I hope its in the correct place and that my questions makes sense.

      We are currently milling slots in an extruded plastic part on a 3 axis router. I'm investigating the possibility of punching these slots.
      Does anyone have experience with punching plastic or can recommend some one who does?
      Here are the basic specs on what needs to be accomplished:
      Slot dimensions- .3125" x 2.25" rounded ends
      Material- .25" thick PVC (possibly other material in future)
      Rate- see below

      Based on the rate I want to accomplish, I probably need a tool that punches multiple slots per hit. I'd like to be able to punch 100 of these slots per minute.
      I have a machine builder who can definitely accomplish this rate with a servo driven feed, but they (and I) lack knowledge of plastics to be confident of the process.
      Some concerns are:
      punch style required for job (flat, rooftop, other?)
      Part finish/potential burrs
      Fracturing in the part relative to how fast it can be punched
      tool performance when cold vs. heated after running for hours

      Any help is greatly appreciated.
      Thanks,
      Dave B
       
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    3. Dana

      Dana Well-Known Member

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      You might be able to punch it, but I don't know how clean the cut will be... .25" is pretty thick to punch. The edge distance may be a factor, too.

      Your best bet is to experiment, build a simple male/female die that you can hit with a hammer or squeeze in a vise, try it on some scrap material. If it works you can then move to the next step of automating it.

      How long is the part? If it's just a short cut off section of the extrusion you might find that molding it might be a more effective solution.
       
    4. Two-Shoes

      Two-Shoes Member

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      I think you are going to find it is hard to keep the punch sharp, plastic seems to dull edges fairly quickly.
      I am of the opinion you would be further ahead to use a multi-head router to cut PVC of this thickness.
       
    5. pottsvillain

      pottsvillain New Member

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      I tried punching a piece, which seemed to work fine. I used a 1" x 1" punch, with clearances set for 14 gauge steel, in a mechanical press. So it punched pretty fast, but there was no fracturing. My main concern was how the punch should be designed. Our machine builder has built an in line 14 head router that we use in line, so I know that can and will work. I was hoping to come in a bit less expensive with punching. With milling we would need at least 3 servos and many high speed thrust bearings which drive up the cost significantly.
       
    6. kevin.koehler

      kevin.koehler Member

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      Hi Dave,

      I'm here to learn, and it's a good day, because I did. You referred to a "rooftop punch style." I had to look that one up, so here's a bit of info to save other people some searching.

      http://www.thefabricator.com/article/toolanddie/solving-punch-breakage-problems---part-ii

      And I'm sure you've thought of this, but you don't necessarily need to engage the entire length of the slot at once. Rather, the punch can make contact at one end, and shear it's way across the part.

      Also, have you thought about using the hardness/softness of the PVC to your advantage? It can be softened chemically (acetone seems to work). Temperature can harden and soften plastics. Just a couple important "knobs" you can tweak while you are refining your process.

      Best wishes,
      Kevin
       
    7. JeffYates

      JeffYates Member

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      Hi.
      Some years ago a company used press to punch up to 5 mtr lengths of allum and plastic extrusion through a single side.
      These were approx 25mm X 5mm obround slots punched 5 at a time. The full length took around 2-3 mins to complete.
      The rig and punch tool was around 500mm longer than the longest work piece required and was accurate to +/- .25mm.
      Basically used indexing on one of the rails of the rig which operated the press by air.
      Could knock up a sketch in Solidworks from memory good enough for your guy to work from and send in pdf if you have no cad software.
      If this can help mail me at jny.engineering@btinternet.com
      Regards.
      Jeff Yates.
       
    8. pottsvillain

      pottsvillain New Member

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      Jeff,

      Thanks for the offer. I am now pretty confident that punching is the way to go. As far as the equipment goes, I have a pretty good feel for what we need to build. I'm really looking for some expertise on punch and die geometry. Any thoughts?

      Thanks

      Dave
       
    9. tonycro

      tonycro Well-Known Member

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      Hi there,

      The company we use for punching our insulation is www.rayburn.co.uk - well worth a call

      tony
       

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