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  • Welding Chromoly Tubing

    A friend has asked me to work with him on a car to be used for SCCA racing. He would like to fab a cage from chormoly. As a result I have been doing some research here to learn more about what I will be needing to do.

    My understanding is that chromoly tubing can be welded with either the MIG or TIG process. My friend for whatever reason is stuck on using the MIG process. My guess is that he has seen it done and believes it to be the fastest. However, I am not sure he saw it done correctly.

    If using the MIG process my understanding is that the weld area should be preheated. The filler should be ER80-D2, ER70S-2 or ER70S-6.

    If using the TIG process no preheat is required and the same filler metal as listed above is used. However the fit-up would be more critical than that for the MIG.

    Am I on the right track?

    I have been reading the "Driver Protection Structures" portion of the SCCA rules to better familiarize myself with what is required. It is also worth noting that the welding is to be done in accordance with AWS D1.1:2002 Structural Welding Code, Steel Chapter 10, Tubular Structures. If anyone has a copy of this code that they could share it would be greatly appreciated.

    Thank you in advance for all the help.
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  • #2
    You're on the right track. Preheating is not a complete necessity with MIG, but is if you're getting welds that cool too quickly and that's obvious if they crack. If you lay proper convex mig welds with adequate heat, no cold lap, and smooth fusion, preheating may not (or shouldn't) be necessary if you're working in a room temperature or higher temp environment. As always I'd suggest a few test joints for judging settings, technique, and overall quality. However, a few hundred degrees of preheat will not hurt a thing.

    BTW, does SCCA allow mig welded 4130? I know lots of racing rules prohibit that.

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    • #3
      My understanding of AWS D1.1
      To use GMAW (mig) you must first prove a wedding procedure, (PQR) This is a way of testing the weld procedure that you intend to use, that it will brake at the desired tensile. This very involved process. And requires special equipment as well as training.

      I would be very careful with the fit up. Remove any burs left from the saw to the point of using a file an each cut. I would use acetone on all mating surfaces to ensure no oil contamination. I would use some small amount of pre-heat, if for no other reason than to reduce cold lap at starts and re starts. I would feather grind all re starts. I would use 75/25 mix gas and .030 or .035 wire. I would run it very hot the goal would be to make the mig weld look almost like a tig weld. Take your time do not rush this work remember your friends life may depend on your work. Also if it looks like a good weld ( looks like the pictures in the welding books) then is probably is. Do not hesitate to grind out a weld or just grind down excessive build up till you get down to a smooth transition between the parent metals and the filler.


      I speak from knowledge. I am a Certified Welding Inspector (AWS -CWI). I am the chief safety inspector for the Alaska Sports Car Club, www.aksportscarclub.org . I have built many dozens of safety cages for automobiles and aircraft.
      Good Luck and send progerss photos


      [email protected]
      TJ______________________________________

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      • #4
        http://www.lincolnelectric.com/knowl...hrome-moly.asp
        http://www.rcautoworks.com

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        • #5
          Thank you all for the replys.

          Billet Benny,
          The SCCA does not call out any specific process in their rules, instead they refer to the AWS code that I mentioned.

          Fat-Fab.com,
          It I have my way about it the fit-up will be as precise as humanly possible. I like to run as hot and fast as I can. I am not the most experienced but I plan on getting some tubing and practicing until I am comfortable with the results. Also because the work environment is likely to be cold I will most likely use preheat. One question though, you mention feather grinding the restarts, what exactly do you mean?

          90blackcrx,
          My initial research led me to that article already. Thanks for posting though.
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          • #6
            Their is a post either on motorsports or welding project that shows a guy welding a fuel tank and he posted a few pics of his restart grinding.

            Well let's see If I can describe it Spelling don't count here... right?


            Say you can't get all the way round the tube in one trigger pull at the termination of the weld you take your grinder (I use a thin disc on a 4 " or a cutting wheel on a stick grinder) and releave a bit of the weld do you have a place to restart with out having a lot of build up and cold lap you make a ramp of sorts.


            Lookup fusionking he has a post on this forum called feathering stops.
            Not fusionking its Pilebuck sorry
            TJ
            TJ______________________________________

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            • #7
              Use the ER80-D2 rod. I have spoken with several chassis builders about this & this is the rod to use. What ever you do don't go for the tiny pretty welds. Feed some rod to it.
              Bob Kraemer/Licensed Electrical Contractor

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              • #8
                Originally posted by katiebo View Post
                Thank you all for the replys.

                Billet Benny,
                The SCCA does not call out any specific process in their rules, instead they refer to the AWS code that I mentioned.
                Sounds good then... If you can get a solid procedure down you should be good to go. Post pictures!

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                • #9
                  Originally posted by Bob Kraemer View Post
                  Use the ER80-D2 rod. I have spoken with several chassis builders about this & this is the rod to use. What ever you do don't go for the tiny pretty welds. Feed some rod to it.
                  He's asking about GMAW and I think you're talking GTAW.

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                  • #10
                    Originally posted by Billet Benny View Post
                    He's asking about GMAW and I think you're talking GTAW.
                    The E in the filler desination is Electrode denoting that it is the conductor.
                    Electrode Rod 80,000 Tensil don't know what D2 is.

                    TJ
                    TJ______________________________________

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                    • #11
                      If you are welding cages, I believe you should be welding to a standard where you do not have to grind your welds (feathering for stop starts excepted with the GMAW process). If you cannot weld to this standard, do you really want to sell your welds to someone who may trust their life to them? Just my 2 cents worth.

                      [/QUOTE]
                      Do not hesitate to grind out a weld or just grind down excessive build up till you get down to a smooth transition between the parent metals and the filler.


                      I speak from knowledge. I am a Certified Welding Inspector (AWS -CWI). I am the chief safety inspector for the Alaska Sports Car Club, www.aksportscarclub.org . I have built many dozens of safety cages for automobiles and aircraft.
                      Good Luck and send progerss photos


                      [email protected][/QUOTE]

                      Comment


                      • #12
                        From what I understand & was told the ER80D2 spec. is for a triple deoxified rod.
                        I may be wrong because I am not even in the same ball park as 99.9% of the guys & gals here. I don't have any schooling in welding was shown the basics years ago & taught my self from there.
                        Bob Kraemer/Licensed Electrical Contractor

                        Miller 330 ABP
                        Tree Mill W/DRO
                        South Bend Lathe
                        Tennsmith Brake
                        Tennsmith Shear
                        Beverly Throatless Shear
                        JD/2 Bead roller
                        O/A Torch
                        Drill Press
                        Grinders, Belt Sander Etc!
                        And more hand tools than I know what to do with

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                        • #13
                          Originally posted by Fat-Fab.com
                          The E in the filler desination is Electrode denoting that it is the conductor.
                          Electrode Rod 80,000 Tensil don't know what D2 is.

                          TJ
                          I know what E stands for.. I was speaking of his talk of avoiding pretty welds and feeding rod which leads me to believe he's not talking about mig. Has nothing to do with the filler he mentioned.

                          er80s-d2 is a low alloyed filler with additions of molybdenum that makes it different than typical -6 or -2. Many recommend it for 4130 to 4130 welds that will be used as welded. It will respond mildly to heat treating. I have used it a ton, myself, but still think -2 is often a better choice, but I don't feel like getting into it now, I've beaten this issue to death. Its tensile strength is in the 90,000 psi range.

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                          • #14
                            Originally posted by Billet Benny View Post
                            edit... but still think -2 is often a better choice, but I don't feel like getting into it now, I've beaten this issue to death. Its tensile strength is in the 90,000 psi range.
                            I have read many of your posts Benny, and will be using ER70S-2 for the tig work.

                            Just as a note, I was talking with my friend last night and it looks like we will probably go the TIG route is we end up using 4130. The SCCA rules permit the use of either DOM of alloy tubing. I will practice with both before embarking on any actual cages.
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                            • #15
                              Sorry Billet Benny I did not intend to step on your toes. I hope my 13E's didnt leave any marks.


                              Kelzweld: Nothing in the code about not grinding. On the other hand I do take what you are saying if one is spending an inordinate amount of time grinding (on the cap) then maybe one should get some more practice.

                              When I first started inspecting the safety cages for the ASCC I was stunned at the bubble gum and bird droppings I found. A well designed cage for a street car will depend as much on the design as the welding for its strength. The weld just holds the main two hoops in place. Now I am not saying that I let them continue racing with out addressing the deficient welds. Triangulation is the one true key to a safe cage. The more triangles one can make the better. One of the biggest safety concerns is having the driver’s seat attached to the car chassis and the harness belts attached to the cage. In this scenario the driver and the car can move one direction and the cage and the belts move another. That’s sounds painful.

                              TJ
                              TJ______________________________________

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