melting aluminum

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I have a chinese tig while I save for the Lincoln 225. I can do steel, stainless and copper no problem. But I am having a heck of a time with aluminum. I can run a nice looking stack of dimes on a flat piece of aluminum 1/8" and can butt weld them together too. But trying to repair a crack in a transmission case always fights me. I can get it done and it is a sound weld, but i can get that stack look, it always seems like I am on the verge of turning what I am welding into a blob of moulten aluminum. My machine is a 200 amp acdc Parker unit. It has served me very well for 3 years so far. I have never tig'ed with anything else. Is it my equipment or my technique? I get the puddle going and start moving and adding filler and sometime it just melts. Am I not moving fast enough?
Reply:I'm not exactly sure what your problem is but it could be the material or your preparation methods.
Reply:Most likely the cast your trying to weld.......Skin it off with a sander and die grind a weld prep....if it doesn't weld after that then it probably won't because it sounds like you have it figured out welding wise.....I like 4043 for most cast  applications.......  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:Castings are difficult to weld due to their dirty nature and inclusions from the casting process. Oil contamination will also cause a lot of problems. I have heard of using a different rod (4047 I think) that has a real high silicon content makes the welds go a lot smoother. Also depending on the thickness you might not be able to put enough heat in fast enough. I would try to pre-heat with a propane torch and then try welding it.
Reply:Thanks for the input, I will try more prep and the new rod.
Reply:What method are you using to clean the housing before attempting to weld. It certainly sounds like contamination. Are you veeing out the crack bevore welding? If so, what are you using to do it. If you use a regular grinding disc on an angle grinder, you will just smear the surface. Use a HSS or carbide cutter, and flush the crack and surface with a cleaner. Most brake cleaners or starter fluid work well. Dry it thoroughly, and preheat the casting. If you can get a nice shiny puddle adjacent to the crack, but not when you attempt to make the repair, then the joint is still not clean enough.
Reply:Are you using an air cooled WP-17?  If so, you are probably overcooking it (to be specific, its power cable) with that machine doing the thick aluminum castings.  That machine is probably rated 60% duty cycle @ 200 amps, and 100% duty cycle at about 155 amps.  A WP-17 is rated nowhere close to this.When welding thick aluminum and encountering your problem, feel your TIG torch cable for warmth.  If the cable is getting very warm or hot to the touch, the hot conductor inside the hose is probably melting the PVC material inside of the hose.  See attached picture for a view of what this looks like inside.  When this happens PVC vapors are offgassed into your shielding gas stream, and the shielding gas can no longer do its job.  The result is oxidation/contamination of your weld and tungsten.  Oxidation when welding aluminum will cover your molten puddle with a "skin", which seems to be what you are describing.One workaround is to preheat your thick aluminum pieces before you strike an arc, so when you do start welding, you can get the weld done with less energy through the TIG torch.  Another stop-gap measure might be, if you have one of those covers around your cables, remove it to let the cable "breathe" and dissipate heat a bit better.  Increasing your argon gas flow rate may also help by increasing cooling of the cable from within.  But those options are all kind of beating around the bush.  The real fix is to upgrade your TIG torch and power cable to a different setup, capable of handling anything your machine can dish out.  Hope this helps. Attached Images
Reply:One reason I usually drape the power cable/hose over my neck - which is more sensitive than my gloved hand and sleeved arm - with the 180 SD is to keep an "eye" on the operating temp of the air cooled WP-17.MM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!