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Welding Chromoly Tubing

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  • #16
    sorry to jump in late but in reading a previous post from fat fab, "remove any burrs left from the saw". I think coping each and every joint to precise fitment, is a must for chromoly. A saw will not give you the fit you need for 4130, unless you have many hours of experience with said saw(this only counts if we are talking about a hole saw in a joint coping jig). In my opinion you should not fit 4130dom tubing with out a bridgeport or similar milling machine(lathes work well with the right clamp on the tool rest, as do those saning belts with interchangable rollers, for specific tube diameter). Precise fitment of 4130 is as, if not more, important than weding procedure, as the stresses in your joint need to be distributed through the tubing, not the weld. Dont get me wrong the weld is extremely important, but the fitment of the joint is more so. A tight joint will also reduce the amount of dwell time as welding there fore reducing heat input, and creating a strong non brittle joint. 4130 will become very brittle when overheated and crack easily with stress. Using a precise joint you could use er80 or er70 just to secure the joint. With mig I would use .023 er70 s-6, .023 because its so much easier to control the puddle, and reduces heat input greatly from .035, and a darn good amount from .030. er70 s-6 because its readily available has a good tensile streangth, the s-6 has a great deoxidizing additive that does not reduce the strength of the puddle. And as always with criticle work, clean clean clean, I use a stainless wire brush on a grinder motor then clean with acetone, before welding. And as far as starts and stops, wire brush and acetonebefore each start.

    As this may seem like a lot of work, it is. Find a reputable chassis builder with a few notable vehicles under his belt and ask him for a price to build a chassis, youll find its a lot more than you think. Ive heard of guys charging upwards of $80,000 for just a chassis, no motor no trans no body no nothing just a chassis with no wheels. Its time consuming meticulus work, and very few of us(including myself) are able to achieve the level of craftsman ship these professionals have the patience to .do.
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    • #17
      Originally posted by dyn88 View Post
      As this may seem like a lot of work, it is. Find a reputable chassis builder with a few notable vehicles under his belt and ask him for a price to build a chassis, youll find its a lot more than you think. Ive heard of guys charging upwards of $80,000 for just a chassis, no motor no trans no body no nothing just a chassis with no wheels. Its time consuming meticulus work, and very few of us(including myself) are able to achieve the level of craftsman ship these professionals have the patience to .do.
      Well said...you get what you pay for. bOb
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      bOb
      Bobs Welding Service

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      • #18
        Hello Katiebo,
        I am very much a novice in this field, but I have a few pieces of information that may help you. There is an excellent publication "Performance Welding" by Richard Finch. He is a very experienced weldor who has done everything from aircraft to race cars. He has even welded on the Apollo rockets for NASA. This book covers every conceivable aspect of performance welding. In fact he strongly cautions preheating 4130 with a torch as it is detrimental to the weld. He goes on to say "This is incorrect, and doing so is one more way to "hurt" your 4130 steel structure. First of all, the experts say that preheating is not necessary for 4130 under 1/4 of an inch thickness. Then, the next reason to not torch-heat 4130 steel is that you really don't know what temperature it is heated to if you are just passing a flame over it...". If you read the Lincoln web site that was posted I do believe that they recommended it. Anyway if you are doing research this book is quite comprehensive. A great deal of the book is dedicated to 4130.

        Capter 3 Fitting and Cleaning

        Chapter 4 Jigging

        Chapter 5 TIG Welding 4130 Steel Tubing

        I hope this helps you.

        Thanks,

        Nick

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        • #19
          [QUOTE=dyn88;78828] joint will also reduce the amount of dwell time as I use a stainless wire brush on a grinder motor

          Hey Dyn88,
          In the book I referred to in my previous post the author Richard Finch says "do not attempt to remove mill scale or oxidation with a power wire brush because the brush will embed metal from its bristles into the metal to be welded, and this wire will contaminate your welds. Also, if the power wire brush is quite stiff, it will actually erode the parts to be welded and cause them to be weakened in the weld zone where you cleaned them." So is the use of a power wire brush an accepted practice on 4130 tubing?
          Thanks,
          Nick

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          • #20
            [QUOTE=KIWI;78839]
            Originally posted by dyn88 View Post
            joint will also reduce the amount of dwell time as I use a stainless wire brush on a grinder motor

            Hey Dyn88,
            In the book I referred to in my previous post the author Richard Finch says "do not attempt to remove mill scale or oxidation with a power wire brush because the brush will embed metal from its bristles into the metal to be welded, and this wire will contaminate your welds. Also, if the power wire brush is quite stiff, it will actually erode the parts to be welded and cause them to be weakened in the weld zone where you cleaned them." So is the use of a power wire brush an accepted practice on 4130 tubing?
            Thanks,
            Nick
            I use sandpaper and sometimes powered scotchbrite.. Always acetone.. Never a powered wire brush.. This is for 4130 tube work. I do also say powered wire brush is a bad weld prep tool.

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            • #21
              Originally posted by dyn88 View Post
              sorry to jump in late but in reading a previous post from fat fab, "remove any burrs left from the saw"........

              A hole saw is not such a bad tool.... It is absolutely no different fitment wise from what you will do on a mill with a large bit.. I'm looking to convert a horizontal mill into a dedicated notcher, but I still notch all my tube with a holesaw notcher. However, that is not the end of the process.. I guess I more or less rough to size and then flap disk to the proper shape and fit to remove all thin spots and cut marks.. If it fits then it's ready for weld prep and then good to go..

              You speak a lot of reducing haz, but this is not the main thing to be conscious of when welding 4130 tubular structures. Tig is such a great process cause it's heat input per weld size is greater than that of gmaw.. If I were to MIG the stuff I would stay far away from .023 unless I'm doing really thin tube, but then it's really time to pull out the tig. With mig the heat input is borderline low and allows the weld to cool too fast thus leading to the hard, stress sensitive condition.. Rarely trouble occurs from "over-heating". I do say to minimize the haz, but this is not to say smaller is better.. It is to say excessive haz can be both detrimental and unnecessary but a certain sized haz is expected and proper.

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              • #22
                Thanks again for all the advice. I plan on getting some material and practicing alot. I think I will end up using TIG though. The ability to control heat input is just too compelling. I will post photos when I have some. Be patient though, it going to be a while before I have material and all the other things I need.
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                • #23
                  the wirebrush seems to leave no residual cantamination, as far as eroding, its entirely possible if one were to have at it like a caveman,you may remove a substantial enough amount of material to affect the joint. A little finess and itll be fine. I agree that scotch brite is a better media, but you ever weld through a joint loaded with that fuzzy leftover(it often times get stuck between two materials on me), its tough to do, at least for me.
                  Thhe hole saw, I said was fine, is a great tool and I wasnt trying to take anything away from it. They work great, Ive never gotten the results I wanted out of one though. Perhaps I should spend a few more hours practicing with one. I preferr a milling machine, mainly because of the abbility to make small adjustments and remove just a little out of an existing joint. to get the perfect fit up with zero gaps all the way around the joint.
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                  • #24
                    My process of tube building goes something like this. And feel free to debate the process for the better. Note this is a aircraft frame.
                    Once designed and drafted, I set up a flat table with several references
                    relative to the plans to align the tubes in correct alignment relative to a
                    center point.



                    The whole frame is built prior to welding and will usually stay together in
                    proper alignment with only wooden jigging and masking tape



                    Once all notched and joined in proper alignment, (note I will spend nearly 1
                    hr per tube in more complex situations if not more) as no notcher or end
                    mill will do what good old experience will do in more complex joints as
                    there are too many variables going on to get optimum fit.
                    Once all fit up and I am happy with the dimensions and gaps then I note
                    where all the tubes go with a sharpie or masking tape.
                    Then disassemble all tubes and de scale, de burr and de grease inside and
                    out



                    To descale I prefer rough scotch bright and a lathe if the piece will chuck
                    up safely. And second choice is 220 grit emery cloths

                    To de burr and radius I use carbide burrs and my second choice is a sander
                    then a grinder.
                    You need to deburr and radius the inside as well so a burr is necessary
                    here.

                    To clean I use break cleaner and paper towels as I get it for free and I like how it works.
                    Clean the inside of the tube as well using a wetted paper towels with break
                    clean usinglike a wad and force it through like cleaning a gun barrel.

                    Now to re assemble all the tubes back into the jig table and what some
                    people may not know is that most tubes will not get welded all the way
                    around they will get welded only on the outside once loaded in to there
                    respective positions.

                    Once all in position I tack the tightest apex of all the clusters It’s the
                    hardest point to get to but in my experience it reduces total frame
                    distortion by reducing shrinkage by locking in the area of greatest
                    shrinkage.

                    Now I re check dimensions and tack to the outsides of the clusters to lock in the tubes in all axis usually 3 tacks per tube.
                    Once happy with the dimensions its time for the EASY part WELDING. I start from the tight apex and work from there one side then the other.
                    With work like this .035 tubing I make small welds as it reduces overall shrinkage and gives me a very accurate part.

                    And after a few months I am near finished with this custom aircraft frame.
                    Proper fit is necessary to get the accuracy I strive for as any gapage will cause extra shrinkage
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                    • #25
                      now look at that fit. (whistle here) Very nice wok
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                      • #26
                        Buzz Job, Very impressive, I could really enjoy seeing that in person. Extremely accurate , I like your style

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                        • #27
                          Looks solid enough for acro......what is it?
                          Dave P.

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                          • #28
                            Originally posted by FM117
                            Looks solid enough for acro......what is it?
                            Dave P.
                            Yes this is a acro capable design and should easily take 10Gs at 1200 # with 1.5 safety factor. It is my personal design and I haven’t figured on a name yet.

                            It is a designed from my last aircraft I built ((One design)pictured below)) but incorporates things I thought would help comfort and control.


                            Here is a web site I half started that has more info if you’re interested.
                            http://onedesign1.smugmug.com/
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                            • #29
                              Thank you all for your input, it is greatly appreciated. When things start moving along I will post photos.
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                              • #30
                                no pre heat

                                Originally posted by katiebo View Post
                                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.
                                you do not want to use pre heat or mig you also do not want to run it hot trust me i have welded and built many car i also seen top fuel cars being built and they do not run it hot chrome moly is very brittle when over heated you dont need to grind the starts either ive worked on car running 6 sec and never had a failure just my two cents that what i do.

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