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  • Pick your brain

    Hi I have a question. We have a millermatic 300 at work it is attached to a rotating welding fixture it welds a 8" diamater girth weld all you do is load the part and turn it on. the problem is on about every other part it will leave a whole in the weld not poreosity or (gas) just one single whole that is about the diamater of the wire .035 it dosent always leave the whole in the same spot it varies. We also wipe all parts down so there is no oil on them.The gas by the way is 75/25 and welding mild steel.I have tried everything I can think of so any help would be appreciated. Thanks

  • #2
    Is it the hole where the weld stopped? Sometimes when the weld is done it leaves a hole....Bob
    Bob Wright


    • #3
      Is the part sealed?
      Professional Auto Mechanic since 1974
      My own shop since 1981
      Cya Frank


      • #4
        The hole is never where the weld stops it will do it randomly during the weld but never at beginning or end.It is not sealed we make a cone shaped piece out of 16 gauge sheet metal then it is welded to a ring that is 8"od. x 2" wide x3/4" thick. So the welder has to run at high heat to get good burn in on the
        thick ring.The cone is pressed over the ring about 3/4"


        • #5
          Have you checked to make sure nothing has contaminated the wire spool or liner. I had a spool one time that had gotten drop or something. Several layers of the wire had a slight crease in them and it would hang up at random points and leave a brief pause in wire delivery. SSS
          Bobcat 250, MM 210, Syncrowave 180, Spectrum 375
          Cat 242B Skid Steer, Challenger (Cat/Agco) MT275
          1 Thessalonians 4:11-12


          • #6

            You may be over volt cap. for the size wire. You might try some pre heat


            • #7
              Pick your brain

              Hi Iron Man. You didn't mention if the hole goes through the 3/4" thick ring.
              I think you gave us a clue when you said it has a hole the size of the welding wire (.035 inch).

              Seems like the work piece is loosing electrical continuity for a split second, the welding wire continues to feed into the puddle, the puddle cools around the wire, the work piece continues to rotate, the arc reinitiates and continues welding until it's done.

              Assuming you're using the right size contact tip. Check that the contact tip is not loose, dirty, or worn out.

              Assuming the work piece isn't out of round. If it were, the wire could possibly be pushed through the puddle without melting completly at the high point.

              Loose or dirty connection. Check where the weld power is connected to the ground cable and the mig gun. Check where the ground cable is connected to (table or rotating fixture), how the work piece is attached to the rotating fixture (clean and tight). Also, check how the ground is transfered through the rotating fixture.

              Best guess.
              I'm guessing that the rotating fixture is never in the EXACT SAME SPOT when the work piece is mounted; hence the hole is not in the same spot. Also, the rotating fixture may not be making good electrical/mechanical contact (work piece expands as it's heated) and as the work piece rotates, it could shift slightly and just briefly losing contact.


              I hope this may help your situation.

              Hot Rod.


              • #8
                Sounds like welding on tourqe converter. If they are not fresh washed and then welded while still hot coming out of the washer, the shop I work with sometimes has issues with them having holes. (porosity) when doing the pressure check.


                • #9
                  Thanks for the info guys, the part is always located in the same position as all the rings are cnc milled and when placed on the welding fixture they are located by a dowle pin, the parts aren't out of round as we have to hold A
                  .010 tolerence. the parts are freshely machined and cleaned so oil or dirt is not A problem. the hole does not go all the way through the ring just a hole in the weld.It is not from lack of sheilding gas there are no fans or grafts in the area.Also it is the correct contact tip. does the same with new or old tip.
                  as for shooting a video I am not allowed to do so. we do gouvernment contracts for military defense. not that it is top secret or anything like that LOL, just not allowed to freely give out info.The idea on the ground is the best so far it grounds through a brass spring loaded pin that presses against the back of the fixture it could be getting worn or spring may be weak.
                  again thanks alot


                  • #10
                    are you using mig or flux core? i've been welding duplex stainless with pulse arc for the last year and theese bug holes do just come out of nowhere. my first thought is trash burning out but you shot that one down. we run this pulse arc pretty hot (wire speed of 275 to 350, .045 ni,cr,mo) to burn out the silicone. it may have to do with the heat and speed combo, puting so much down so fast air could get traped.


                    • #11
                      is this the first and only role of wire you are having the problem with ?? i had a role that was baddly roled and would stick on my once, i rolled off about 20 ft and it was obveous the way it was hanging up, put in a new role and all was good. it happens some times. if the spring on the ground or work clamp is good i would take a look at the wire roll, some times they just wind wrong.

                      he is using c-25 gas so i dont think its flux core wire.
                      thanks for the help
                      hope i helped
                      feel free to shoot me an e-mail direct i have time to chat. [email protected]
                      summer is here, plant a tree. if you don't have space or time to plant one sponsor some one else to plant one for you. a tree is an investment in our planet, help it out.


                      • #12
                        I am using solid wire .035 this thing has been doing this for months we have just been spoting up the hole and grinding them, but the I think the guy that does touch up and grinding is getting tired of doing it LOL. We use a 44# spool of wire every two days also I have tried different brands of wire like lincoln, prostar and others I cant even remember I am currently using esab wire. The welder is A millermatic 300 usually set at 640 on wire speed and I think 25.somthing on heat.So it is doing A serious amount of welding. I think it goes back to somthing with the ground as I tried another welder on this same fixture with the same results.


                        • #13
                          Happy Holidays Iron Man.

                          I understand the government/DOD part of your company's work. Let me refraise what I said.

                          Watching a video of the process together with your welding engineer should give both of you some insight into what is happening during the welding process, especially if it could be viewed in SUPER SLOW MOTION (like NHRA drag racing on ESPN2).

                          Is there any way you could attach a jumper cable directly from the work piece to the ground clamp and still use the rotating fixture? This would rule out the rotating fixture as the source of the problem if you still get the same results. If this doesn't work, the problem may be with your machine or the spool of wire you're using.

                          Wire size inconcistency and/or rust spots on the surface of the wire could interrupt electrical conductivity at the contact tip. I'm guessing your wire is in TOP SHAPE.

                          Good luck,
                          Hot Rod.


                          • #14
                            pick your brain

                            Hello Iron Man,

                            Just wanted to know if you were able to isolate the problem of the pin holes in the welds by running the ground wire directly to the work piece, instead of going through the weld rotating fixture?


                            • #15
                              Hey I have that very same problem but I'm using flux core .045 hobart XL71