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  • Advice on how to make this punch needed

    I would like to make a punch that will trim the ends of some 22 ga. CR mild steel (0.030") strips. I have 10ft long by 1 1/2" wide strips that I will be cutting down into roughly 1 ft sections. I want to trim two ends at once so I can push the strip up to a stop, punch, drop out the cut piece, and then push the stock in to the stop again. The punch is cutting the back end of the first piece and the front end of the second at the same time.

    Here is the shape that I want to cut:



    The punch can go past the edges of the strip so I am really making 2 shear cuts simultaneously.

    I was thinking of making the die out of a 1 1/4" x 2" x 1/4" tool steel and the punch out of 3/4" x 1 3/4" x 1/4" tool steel. I can attach these to heavier pieces of mild steel for rigidity.

    I have an oxy/acetylene torch but no heat treating oven.
    I have a Grizzly (Sieg SX3) mill.
    I have a 20 ton shop press, a 3 in 1 shear/bend roll, and a couple of small manual arbor presses.
    Assume a quantity of 100 pieces to start.

    Any suggestions on the tool steel to get?
    Is 1/4" too thin?
    Is there a better way to do this? (I am trying to avoid trimming each end of a 1ft strip because that make 3 operations per piece)

    Neil

  • #2
    Hi,

    I know you said 100pcs to start, but what total number are you looking at? First thing you need to do is figure out how you are going to keep the punch and die aligned during use. Are you going to purchase a die set of some kind? I normally use S5 or S7 for punches and dies when I make them. But those are for commercial use, with life expectancy running into 1000's of punches before replacement. For lesser life, I have had very good luck with 4140 when cost is paramount.

    I would make the die from 3/4" thick flat, large enough to attach a stripper to also. The punch I would make from a round, but the punch holders I normally use work best with round punch bodies.

    The R.036" radius is kind of a stinker to deal with, but it is doable. Depending on the tolerances needed, a 1/16" endmill could suffice. I would make the .140" a bit wider for strength, maybe .25" if you can stand the waste. A CNC mill would be easiest to make this, but that's out. A rotab would be handy to have. But a bit of hand work could blend the angle between the two radii.

    I know this is kind of general, but hopefully it helps kickstart some ideas for you.

    dalee
    If you think you understand what is going on, you haven't been paying attention.

    Comment


    • #3
      This is a common type of punch press operation. I would use 1/2" thick A2 or D2 material for the punch and die. You will need to mount all this on a die shoe to keep the punch and die in alignment with each other.

      For the punch, mill the cutting edge 1/4" deep, leaving the other 1/4" to stabilize the thin bits. Use a 1/4" sheet of Neoprene that is 1/2" wider than the punch all the way around for a stripper. Once the die is made you can punch the Neoprene in the hydraulic press. Then it will ride up and down with the punch and keep the material flat and push it off the punch.

      I would make the die 2 x 2 x 1/2 to avoid thin parts around the outer edges. You may want to make a radius on the outer corners of the punch to keep from having sharp inside corners on the die. Make sure all your bolt and dowel holes are done and check to make sure everything fits right before hardening. I would send it out for heat treat. It doesn't cost that much and hard to do properly with a torch.

      Comment


      • #4
        I would just ask a local wire EDM shop to cut that from already hardened material, usually they have small pieces and cutouts from other work pieces for things like this. All they need to do is pop a starting hole and cut out the punch and the die for you.
        Amount of experience is in direct proportion to the value of broken equipment.

        Comment


        • #5
          You need a DIE SET, PUNCH, PUNCH HOLDER, DIE, STRIPPER of some kind. Also a Stop.
          Have the die, punch and punch holder cut by Wire EDM. Cut the die with 1/2deg. taper and 1/8 land.
          Mount the punch in the punch holder (also wire cut) using screws in the thickest part of the punch and a plate on top.
          Align everything in a die set and mount some stripper - a bridge on both sides of the punch to hold your parts in place.
          Die to punch 0.001 to 0.002 clearance. Punch to punch holder - light press fit.

          Comment


          • #6
            I think you need to do it in two operations. With all the contact area around the projections, they're going to bend upward on the return stroke. I doubt that oiling the punch is going to reduce the drag enough to keep the projection from bending at the narrowest section.

            Leave a short straight section joining the projections when you're punching the rest on the first op, then trim the joiners on the second.

            You might get away with one op if you angle the end of the punch so the outer edges cut first, and the center part only goes just deep enough to shear the material.
            Last edited by winchman; 10-29-2013, 02:46 AM.
            Any products mentioned in my posts have been endorsed by their manufacturer.

            Comment


            • #7
              Neil,

              For 100 (or 1000) pieces, I would get a quote from a laser cutter.

              From an 8'x4' sheet you can get over 200 pieces.

              And if you want to modify the design - just change the drawing and give it a revision number...

              Comment


              • #8
                +1 to jaakkos answer, it would be a pig to make on just a mill, the die maybe using inserts, i.e. making it in bits, the stripper can be cruder but the punch with the pockets would be difficult.
                Cerromatrix the die into a ring bolster pops into mind, but im thinking fly press job.
                Edm is the way to go without a full die shop handy, i did one years ago of similar design for those spring screw things, it was a test to get a job, seriously not funny, i got the punch done with a template on a pantograph, think it was a deckl but it could have been somthing else, i didnt have to put clearance on but there were clearance bits there, bout 2 degree i think, you could even make the die on a drill, mill and die filer, old school as it were, possibly the punch too if youve a mind to.
                Mark

                Comment


                • #9
                  I thought about it a little more, and you could make a hold-down with four L-shaped projections. The punch would go through it, and it would keep them from bending as the punch came back up. That would let you do it in one op.
                  Any products mentioned in my posts have been endorsed by their manufacturer.

                  Comment


                  • #10
                    Harden the die. Rough out the punch as close to the final shape as you can. Press the soft punch through the hardened die,

                    Comment


                    • #11
                      My suggestion is also wire EDM. If you get the right shop they'll have a good deal of experience in die making and able to offer design suggestions. It won't be dirt cheap though.

                      It may be that the budget isn't there for EDM. Then it's doable as a home shop project. A good learning experience and could be frustrating too. In my area professional heat treat runs a minimum of $125 last time I looked, well worth it to get a nice clean scale-free part of known hardness back.

                      Comment


                      • #12
                        Originally posted by winchman View Post
                        I thought about it a little more, and you could make a hold-down with four L-shaped projections. The punch would go through it, and it would keep them from bending as the punch came back up. That would let you do it in one op.
                        If the parts would be wire EDM'd, one could use the off-cut from cutting the punch as a stripper directly, just wire EDM some pin and screw holes at the same time while it is in the tank.
                        Amount of experience is in direct proportion to the value of broken equipment.

                        Comment


                        • #13
                          Originally posted by winchman View Post
                          With all the contact area around the projections, they're going to bend upward on the return stroke. I doubt that oiling the punch is going to reduce the drag enough to keep the projection from bending at the narrowest section.
                          The tabs will be bent 90 degrees in a subsequent operation so if they are a bit distorted out of the punch, that is ok.

                          What tool steel would be best?

                          I do have access to a small cnc mill through a local Hackerspace.

                          Comment


                          • #14
                            Originally posted by Spookydad View Post
                            The tabs will be bent 90 degrees in a subsequent operation so if they are a bit distorted out of the punch, that is ok.

                            What tool steel would be best?

                            I do have access to a small cnc mill through a local Hackerspace.
                            Basically any steel goes as klong as it can be hardened. But I would look to the cold working steels like W.Nr. 1.2510 (also known as "Arne" by Sten&Co.).
                            Amount of experience is in direct proportion to the value of broken equipment.

                            Comment


                            • #15
                              Originally posted by Spookydad View Post
                              The tabs will be bent 90 degrees in a subsequent operation so if they are a bit distorted out of the punch, that is ok.

                              What tool steel would be best?

                              I do have access to a small cnc mill through a local Hackerspace.
                              A-2 Tool steel 59-61RC would be my choice. O-1 would be OK.

                              Comment

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