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Machining weldments

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  • Machining weldments

    I'm (obviously) a newbie. What sort of problems should I expect trying to machine welded parts, or shapes cut from plate via oxyacetylene cutting? Won't the heat from the cutting/welding harden the metal (mild steel)? Will I need carbide tooling?

    All input appreciated.

    Jeff Greenblatt

  • #2
    Good question... I'm looking forward to some good answers myself.. Thanks for asking..



    • #3
      Jeff, yes you will get some heat affected zones in flame cut parts , but it is relativly shallow. But the slag is as hard as rock,so knock it off with a grinder before machining.High speed tools will tolerate it if you adjust your feed&speed of cut . As far as weldments go, as long as you are not machining the weld itself most 1018-1020 steel will machine normally.The weld will depend on the filler material used, and the welding process. Most 60 series fillers (ER6011, 6013,stick,er60s mig)will machine o.k. with high speed steel . The 70 series is a little tough, but still doable with HSS, but carbide would be nice. If you are Gas welding , the weldments will be normalised, or annealed after the weld is completed,(returened to their soft state) as long as you do not quench them in water or cold air (winter, compressed air). Weldments are machined every day with predictable results, so take a deep breath , and take the plunge, theres no better way to learn than by doing...just proceed with care, it'll be alright. Good luck Shawn


      • #4
        Cutting profiled plate is hard on a machine.
        You need to go deep enought to get under the skin but if it's an interupted cut it bangs and can chip or shatter tipped tools.

        I save old turning tips and when I have a job to do like this I lick a new edge on them with a diamond wheel and use these to rough out with.
        I tend to increase the tip radius so it's not so prone to chip.
        When they do go you don't feel so bad as if it was a new tip.

        On biggish jobs you may loose 4 or 5 edges getting down to where you need to be, it depends on how good the profile cutter was.

        I'm doing some big 24" starter ring gears at the moment they are 24" OD and 22" ID in 1" plate.
        The OD is quite good 0.2" will get it to clean up but the ID is anyhow. The one I did tonight took nearly 0.35" to clean up and three regrinds,
        So far no new tips, all regrinds.
        I'd be lost without this little diamond grinder. I must be the only guy to get 12 edges off a triangular insert

        John S.

        Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


        • #5
          Sorry Hickups

          [This message has been edited by John Stevenson (edited 01-07-2005).]

          Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


          • #6
            Dang!!! A double post: Stevenson's disease. Must be catching.

            [This message has been edited by Forrest Addy (edited 01-07-2005).]


            • #7
              Yup. Remove the slag between passes, make clean welds free of slag inclusions, grind the scale off flame/plasma cut edges, and in general work clean durign fabrication.

              Welded fabrications frequently have lots of locked-in stresses thanks to the large heat gradients. Weld strikes can be particularly hard. I keep a weed burner, a pile of old firebrick, a piece of ceramic fiber cloth, and a bed of pea gravel where I can stack up bricks to make a crude stresss relief furnace covered with the cloth. I raise the work temp to about 1200, let it soak on a slow fire and close the oven. Next day the work will be cold and I can machine it without fear for my tooling.


              • #8

                Have you tried ceramic inserts? Recently I had a couple of small burnouts to machine(1045 steel 15" o.d.,4" i.d.,5" thick) and they kept eating the carbide. I put in a piece of ceramic,set the rpm's slow and took about a .125 d.o.c. per side and went right through it. It got under the scale and lasted longer than the carbide. Not to mention that 1045 is heat treatable also, which played a part in the overall hardness of the scale to a certain depth.

                [This message has been edited by threeboys (edited 01-07-2005).]


                • #9
                  Posting Deleted - Moved to new post

                  [This message has been edited by CCWKen (edited 01-07-2005).]


                  • #10
                    For me at least E6011 is most difficult to turn. E7018 and 7014 can be turned ok. MG-80 welds good and turns best. Slag after cutting is nigh impossible to mess with. I try to grind it off after cutting then machine or better yet just profile saw all you can to avoid flame cutting the things you plan on machining. Interupted cuts are doable with high speed tools but expect many regrinds.


                    • #11
                      If you have to maachine a weld rough it using a cemented carbide tool (brazed on a steel holder) or the stronger negative inserts - these3 ar3e good for cleaning up rusting crap too. If you can use minimal heat with a torch or TIG and the weld is easier to machine (aircraft style welding). Arc welding is going to be tough to really bad depending on the material. Remember that Stellite and other super hard materials are routinely machined with Ceramic and/or Silicon Nitride Wisker reinforced inserts after hard-surfacing operations but these inserts require high horsepower and a very rigid machine. There is not many materials on the plaset that cannot be chewed away by a milll or lathe these days and many inserts are actually replacing grinding operations (Hard turning).

                      This is where talking to your Kennametal, Sandvik Coromant, Iscar rep can help you get the right tools for your shop at minimal cost and maximum versatility.


                      • #12
                        I weld for a living and in my home shop I probably weld things I shouldn't...cuz it's easier...sometimes! What I've found..With HSS bits, I fought this for quite some time till I learned to grind and hone a radius on the tool bits. Also...when using tig I now hold the heat on it a while longer. Seems to anneal the area and make for easier turning. Same with stick. I preheat the area and burn it in hot. Same thing,,,makes for easier turning. When in Forrest said..I put the works in the wood stove for the night. Turns nice the next day! Learned that HERE!!!!!!
                        I have tools I don't even know I own...


                        • #13
                          just dont climb mill it, that way you are cutting the hard edge from inside out.