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  • Punch Die question

    A buddy is looking for an inexpensive way to make round slugs out of 3/8" thick Ultra high molecular weight polyethylene (UHMW). He needs two different sizes, 1.465" and 1.100" diameter (no holes, just a blank slug) - and the quantities would be in the range of 2,500 to 5,000 a year.

    He's thinking that a punch die in a hydraulic press would be the way to go. Seems to me he'd still need custom made hardened steel tooling for these non-standard size blanks. He says a couple of toolmakers he's approached have blown him off, so I offered to post the question here. He's trying to get a home-based business going so cost is a major concern.

    I've wondered if he could get round stock turned to the right diameter, then slice off 3/8" pieces with a chop saw. But the kerf waste would be a factor.

    I've suggested laser cutting in the past, but don't know how good this material is for lasering, would appreciate any suggestion on tooling sources or other ideas welcome!

    Thanks, Bob

  • #2
    I think it may tend to "extrude", rather than "shear". It would be an ideal candidate for water jet cutting. They have little waste, just buy the UHMW by the sheet and have it done. Water jet will leave very little burr to deal with. As most conventional cutting processes will leave a rather furry burr, that will need to be dealt with.

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    • #3
      Pierce die

      W9RAN I am a tool & die maker and may be able to help. I am on my way to work at this time so look for my post tonight when I get home from work
      Donnie
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      • #4
        I second ADGO's view. At slow press speeds PE will extrude more than shear and a hydraulic press is slow. The other thing with punching is going to be the edge - soft materials in particular distort during the process and so the edge is not going to be square or straight (or probably clean either) - that is, the diameter in the middle of the punched part is likely to be smaller than at the top and bottom surfaces. It depends on what the discs are being used for but tolerances may come into play.
        Michael

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        • #5
          can uhmw be cast or injection molded? it's a thermoplastic, so i'd assume so?

          that way, you'd be able to minimize your waste
          -paul

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          • #6
            Originally posted by W9RAN

            I've wondered if he could get round stock turned to the right diameter, then slice off 3/8" pieces with a chop saw. But the kerf waste would be a factor.
            If you lay out a bunch of circles on a flat sheet the waste is going to be
            almost the same as the kerf between two peices cut from a rod.
            ( It seems to me ) :-)
            ...lew...

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            • #7
              I have made a similar item using acetal. I used a power miter box and a 80 carbide tooth blade and a stop. Use slow feed rate Use a thin kerf blade to avoid as much waste as possible.
              The edge quality is the big determinate in die cutting. if a rolled edge is un acceptable your going to have to saw it. A 4140 die plate at about 40 rockwell C and an A2 punch 62 rockwell peen and shear the die to punch size and position so it will be a zero clearance die stroke press as fast as possible

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              • #8
                For that annual quantity, I'd do it on a pin router. The amount of scrap is negligible compared to the tooling cost...meaning, you aren't going to recover the cost of scrap by using a more efficient (and expensive) method like injection moulding or punching. You can make a pin router out of about $15 of wood from home depot, any basic router and some fasteners.
                Last edited by snowman; 04-07-2010, 08:36 PM.

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                • #9
                  Maybe,....

                  Pin router would be a decent idea for a regular not-too fancy piece...... particularly since the tooling is expensive, and to get a decent edge and sized part you'd probably need to rough blank and then trim the part.... two operations, two costs for tooling (might share a punch and use different dies, I suppose) and twice the labor time.

                  With the pin router you could likely do two or even 3 at a time by stacking the sheets.

                  Problem with pin router is with sizing.... not really accurate, except by woodworking standards.

                  You showed 3 place decimals, implying low thous accuracy.... maybe to 5 thou... Ain't gonna happen with the pin router, you need that much clearance for the pin in the template, easy.

                  Does the 3 place sizing you showed mean what it says?

                  He could turn the rods, and then gang saw them off in a horizontal mill, for instance.... cutting as many as a dozen at a time even
                  1601

                  Keep eye on ball.
                  Hashim Khan

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                  • #10
                    Good point. In that case, I'd do it with a circular saw and a homemade rotary arbor. The part is clamped between two "pads" that rotate. The circular saw can be moved perpendicular to a radii the distance required for the diameter required. Saw is slowly plunged down as part is turning at slow rate.

                    Or hell, just pin route the blanks and clamp between live center pad and faceplate pad and pop the blanks out by the 100.

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                    • #11
                      Pierce Die

                      Sorry I took so long to respond.
                      I am not here to tell you how to do this job but I would like to help you understand what you may encounter by piercing so you can make your desecion as how you would like to do it.
                      First thing as mentioned in an above post you will not be able to get a squire edge on your slug (blank) if you pierce. Your edge will be concave.
                      Next you will need to develop your punch and button size. When piercing metal the size of your slug will be the same as the button. Not so with rubber. Rubber will compress before it shears. After it shears it will expand back making it larger then the button. If you decide to pierce I would sugest you use a cheaper CRS or HRS to experiment with different button and punch sizes until you get it right then make them from tool steel.
                      You will also need to experiment with the clearance between your punch and button. This clearance will efect curvature of the concave edge. the finish and size of the burr.
                      Last but defiantly not least you will need some type of die set to mount the punch and button because the ram on a hyd. press it not precision enough to guide the punch into the button.
                      I am extrapolating here but I think you would need less then .010 clearance on your punch which is a lot less then you would need on metal .375 thick
                      Sorry for getting long winded here just wanted to let ya know that not all toolmakers will blow you off. Most of us are very willing to help when we can.
                      Last edited by Machinist-Guide; 04-08-2010, 12:46 AM.
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                      • #12
                        Machinist Guide, if He was to make the punch with a slightly concave end and then some serrations to give it shear would it produce a better slug in Your opinion?
                        Does uhmv punch like rubber?

                        Steve

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                        • #13
                          Concave punch

                          Originally posted by doctor demo
                          Machinist Guide, if He was to make the punch with a slightly concave end and then some serrations to give it shear would it produce a better slug in Your opinion?
                          Does uhmv punch like rubber?

                          Steve
                          I have never tried a concave punch but I can see where you may be coming from
                          If the punch point is concave it may help prevent the material from compressing so much

                          Does uhmv punch like rubber?
                          I think its much harder to achieve the desired dimension with uhmv then it is rubber. Because of the elasticity I have had to in the past use a .600 punch to get a .500 hole. As the punch applies pressure to the material the material flows away from the punch when the punch is stripped from the material the material flows back toward the hole causing a under size hole
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                          • #14
                            How about turning a custom sized hole saw on the lathe and then using this hole saw to cut the pieces out of sheet goods? This would avoid punching and the associated distortion but admittedly might leave a burred edge.

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                            • #15
                              the scrap rate for taking the part from flat stock will be huge punching makes it even worse the closer it get to the last part the more stripper pressure you'll need. the hole saw is the best idea for coming from the flat for the volume

                              concave punch hasn't helped me on the ultra high density but zero clearance high press speed and making it a compound die might help keep things flat

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