Aluminium welding

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Hi allI posted some months ago with some questions about aluminium welding thin material. Specifically I was welding box frames that were used to strengthen transport boxes. I made about 2000 frames and in the process learned a lot and also picked up some more questions. If some of my observatios and questions seem silly pllease bear in mind that I am self taught. I used to be a business analyst and through circumstances am forced to make a living as a welder now. To clarify - I love what I do and with that on with my questions and observations:1) I found that with aluminium welding tungsten preparation is crucial. With steel I take the tungsten to the grinder and finished. When doing AC welding I found it very beneficial to smooth the ground area with very smooth - 400 grit sandpaper. I have read about diamond wheels for grinding, but I live in South Africa and draw only blanks when asking about them. My question is whether the diamond wheels give you the type of finish that avoids the arc sometimes emenating from the side of the point. If that is the case could you please let me know the spec for the wheel that I should look for2) I use an Invertec 205. I have really used and sometimes abused it and it is a fantastic welder. One thing I learned is that it is crucial in AC welding to ensure that the arc establishes first time you step on the pedal. If the arc is not established on first try the machine goes to re-start and the point on the tungsten is blunted. I have found that the best way to avoid this re-start is high enough start amperage. The point was brought home to me when I had to weld 0.5 mm aluminium with no sag or mark allowed on the non welded side. At first I kept lowering the start amperage to avoid any burn through, but lowering the start amperage the arc would not establish first try and the re-start caused burn through, even with re-start energy set to minimum. Then the penny dropped and I incresed start amperage and found the balance point. Do I have this correctly?3) I use thoriated or zirconiated because that is all I can get here in South Africa. Having read quite a bit in this forum I get the impression that tungsten choice is a matter of both machine preference and personal preference. Are there any other Invertec 205 users on the forum that have found that a specific type of tungsten out performs all other types on their machine. And if that is the case would it be worthwhile the hassle of importing that type of tungsten4) Last somthing I found out the other day. I use a gas lens when I can. I had some awkward welds to do and was using a number 6 cup. I kept breaking the cups quite often. I found the cups broke at the point where the body of the cup narrows down to form the orifice. I suspect I was a bit brutal with the amps. The last time that it broke I did not bother changing the cup. I wanted to see what would happen. To my surprise I got beautiful colour on my mild steel weld. I then took the cup off completely. I welded with the gas lens only  and got some of the best colour ever on mild steel. This was welding on mild steel with the mill scale on. I left the argon at 5 litres/min ( I think 15 cfh). I am definetly getting bigger gas lens cups, and the question I have: Are there cups that end at the bottom of the lens and if not, why not?Sorry for the long post, but I found this the best forum to ask. I also work alone, so nobody to ask. Other welders here either do not use tig or are reluctant to share knowledge. I have found that the guys on here do share even if sometimes abrasively. If my questions and observations are silly please let me know, but please let me know why they are silly.
Reply:1. I wouldn't go out of your way to bother with a diamond wheel but if you really want to try one then search for 'lapidary wheels'. If nothing local to you then should get results on ebay and a search of this site will probably get you details of an ebay shop. A diamond wheel won't magically transform things but because they're more efficient you can use a finer grit without standing at the bench grinder all day wearing grooves in an aloxide wheel. 2. Sort of... If the initial current is on the low side for the tungsten diameter then yes, poor starting and arc stability. Unless your v205 is a recent one they start the arc with DCEP and then switch (to DCEN or AC). EP will blunt a tungsten quickly so if it's struggling to establish an arc then it'll result in more EP time. Both the HF and starting % (not the initial current selected on the front panel) are adjustable via the 'hidden' menu that can be accessed during start up.3. I use Huntingdon Fusion tungstens which are a mixed flavour containing lanthana, ceria and yttria IIRC. Personally i think they outperform the other usual suspects but it's a not a night and day thing i.e. i wouldn't bother going out of my way and/or paying over the odds for 'em4. The cups extend past the end of the collet body mostly because it's electrically live while welding and partly to direct the gas. If you want a bigger ceramic then there are larger diameter gas lens bodies available that'll accept huge cups. More details here... http://www.weldcraft.com/parts-accessories/. There are also exploded diagram pdfs showing all the different options for each torch on that site
Reply:Hi HotrodderThank you very much for the reply. Answers all my questions and much appreciated. I have admired your previous posts on full penetration on aluminium and after some serious frustration was able to reproduce your results. I found that for me full pen needs welding at the balance point just before the puddle blobs out. It needs high amps, not low amp cumulative heat. Closest I can describe it is that the arc force is what does it, not the time in the puddle  I was only able to do that after reading your post and similar posts in this forum. In a very real sense you and others sharing your experiences have taught me aluminium welding. My invertec is now 7 years old and going strong. I started using it as a stick machine then mild steel tig, then stainless and finally aluminium. I have by now tried all waveforms, played with the pulsing etc. I found the pulsing works really well welding thin stainless laboratory hoods. I have learnt that you have to get your technique right and then start playing with parameters on main menue and hidden menue. If the technique is not right then playing with parameters just confuses you. Thanks again to you and the forum for sharing information so freely.