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Repair-welding cast aluminum

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  • Repair-welding cast aluminum

    Lately I have had the opportunity to repair cast aluminum transmission cases for a local transmission shop that have cracks in them from minor to severe. When I get them, the cases have been degreased in a commercial quality 180 degree parts washer-cleaner.

    As clean as they seem to be they still have oil impregnated residue which as you know causes nothing but trouble while welding. I have successfully welded a number of cases however the best method I found involves weld grind, weld grind, etc., until a clean weld base is established for 100% pure build up.

    Has anyone found a more successful cleaning procedure where the impregnated oil can be drawn out of the case pores, prior to welding? Any ideas would be appreciated.

  • #2

    Cast aluminum is always tough to get clean because of the pores holding contamination. I've always pre-heated aluminum castings before welding and this seems to cook the oil out of the pores although not 100% it's much better than welding on it cold. I've tried all kinds of solvents including Acetone and Xylene(sp?) and they help but don't solve the problem. The heat has always worked the best for me. If the aluminum was cast in a sand mold the casting sand has oil in it to allow the sand to be compacted and hold it's shape once the pattern has been removed. Even new castings will have oil contamination in them. Cast aluminum is always tough to weld but it sounds like you're having success in welding it, so consider yourself a good welder. It takes work and I don't think there is an "easy" way to do it.

    Now Hawk would probably use this example to emphasize the pulse feature on the Dynasty series as you can adjust the pulse to shake the puddle and bring the trash to the top.

    Also I like to grind a groove in the crack so I can get better penetration with the weld, along with drilling a small hole at each end of the crack so I don't end up chasing the crack the entire length of the casting. I discovered that trick one time while welding (actually brazing) a cracked engine block. Cast iron has the same problem of retaining oily residue and pre-heating was the best way I've found to reduce the contamination on that as well.

    Well good luck in your venture with the transmission shop and hopefully they'll keep you as busy as you'd like to be repairing transmission housings.

    Blondie (Owner C & S Automotive)

    Colt the original point & click interface!

    Millermatic 35 with spot panel
    Miller 340A/BP
    Victor O/A torches
    Lincoln SP125
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    03 Ram 1500
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    • #3

      The method you use is what is called "tinning" and I do it the same way. About the only additional help I can offer is increase your heat by adding 25%-50% helium to your argon. I have found it to be very effective. Also as Blondie mentioned a high pulse rate of 300+ will help agitate the weld puddle and bring the trash to the top of the weld bead. Many times you still have to weld and grind to tin the base, but the process is quicker and cleaner with the pulse.


      • #4
        What does everyone use for a grinding wheel for the aluminum? Ive aleays come across contamination in the base when using conventional wheels. I currently use carbide burrs in a right angle die cutter with lots of wax as a releasing agent.
        Trailblazer 302g
        super s-32p
        you can never know enough


        • #5
          I use the carbide burs made for aluminum. Grinding discs are a no-no. One way to get alot of the oil out is to bake the part i an oven with some kitty litter. This draws alot of grease and oil out.


          • #6

            The carbide bit on an straight or angle pneumatic grinder works the best. For non-critical work I use a 4 1/2" "SAIT" brand grinding disc made for aluminum. They are the black wheels similar looking to a standard grinding disc, but are marked for aluminum only. They really do a good job.

            A few other companies make some similar discs that are beige to tan in color. They are of a much denser compaction than standard grinding wheels. I bought 2 of them and never again. They are expensive and load up in just a few minutes!!!


            • #7
              I also have found the carbide burr made for aluminum and used with a die grinder to offer the most effective method of aluminum joint prep and also second the “SAIT” brand grinding disc for aluminum. It is amazing they do not clog solid with the spent material.

              Also, do you or others have some examples where you have experienced the AC output Hertz control that is available (with the inverter machines) to be well worth the investment over a regular transformer Syncrowave?



              • #8

                The higher the arc frequency the narrower the arc cone all other factors being equal. I use a helium/argon blend to increase the heat to boil off oxide inclusions in some applications like cast aluminum. While the heat of the arc is increased the arc cone is widened due to the helium. The adjustable arc frequency can be increased to narrow the arc cone.

                Different joint configurations weld better with different arc frequencies. A fairly wide arc at 110 HZ makes a great fillet while I like a narrower arc (175HZ) works better for corner joints. The more you experiment the more uses you will find. I do not view ajdustable arc frequency as a have to for most applications. However, it sure can make things go together easier.


                • #9
                  The thing i like about the Frequency adjustment is

                  Speed. I started out with a non-squarewave 330a/bp and would have to preheat, and even with that i would be waiting forever to get the puddle to start. Now that i own a dynasty, i can take a aluminum cylinder head out of 30 deg weather and get the puddle to start almost instantly and that is without preheating. {the bigger the HZ frequency, the quicker the heat, other benefits like HAWK says is arc shaping for control }

                  No matter how clean you get a trans case you will always fight the poor quality aluminum that the case is casted with. They have a ton of zinc in them which makes them a little on the tough side to weld. The top of your weld bead will have what looks like pepper floating on top {really nothing you can do about it}.

                  Since you have a transformer here is something to try. groove out the crack with an aluminum burr, then use a cleaner such as brake kleen, acetone, etc, wait till the cleaner air dries, then take a torch and with just the accetelene {spelling?} lit, carbon up {soot} the groove, then get the torch up and running with the oxygen and pass it up and down the crack untill the carbon in the groove is gone, then weld away. This should weld pretty good with out having to weld,grind,weld,grind.

                  I use a mix of 75% ar/25% helium for all my aluminum work. It seems to burn off the oxides a lot better than straight argon
                  Mike. R

                  Dynasty 300dx tig runner w/ 3 torch Versa-Tig torch changer {wt-20f, wt-24f, mt-125}
                  MM 251/30a/4015 roughneck
                  Miller portable spot welder
                  Inferno >>> Big Window Elite


                  • #10
                    HAWK, I always enjoy reading your posts. You should write a book. I would certainly buy a copy.


                    • #11

                      I did not have the luxury of such a great tool as this forum or even the internet when learning and working the art of welding. Looking back it was just as hard as I remember it. I am an active member here hoping to help some folks along in their welding by relating experiences and knowledge gained along the way. Most of all I am here because I enjoy it! Thank you for such kind words.

                      The HAWK.


                      • #12
                        I appreciate all the input concerning this thread. I now have to ‘demo’ two machines this spring because of this forum, 300DX, MM350P. Going to have to treat the wife a little extra nice!



                        • #13

                          One of each would be a sweet combo. It won't matter which machine is your number 1 or number 2 favorite, but better keep the wife number one!


                          • #14
                            My wife placed the order for my mm210, and she was a driving force in me getting the D200DX. Some wifes are not as understanding as mine, so could I recomend flowers first .

                            I have used the D300DX and you'll love it and the mm350p is the slickest mig I've ever seen. Fact is they are the only machines I would substitue for mine!



                            • #15
                              HAWK, I will abide by your advice and keep the wife #1.

                              pjs, you are a lucky man, don’t let that one get away!