I have a fair bit of sheet aluminium fabrication to look forward to soon, so with this in mind I have been taking a bit of time to practise some extra skills. Usually my preferred choice for welding aluminium is by oxy – acetylene which has the side effect of annealing the workpiece as the weld progresses. Since some of the aluminium found in ancient vehicle bodies was somewhat less than sophisticated in comparison to modern alloys, any annealing which takes place is very desirable indeed. For working with more recent classics or for manufacturing items from new sheet aluminium there is a huge advantage to using the Tungsten Inert Gas process – more commonly known these days as ‘tig’ and to the previous generation as ‘heliarc’.
Tig welding has changed somewhat over the years: Helium gas has given way to Argon for shielding the weld, moving core transformers have given way to electronic circuit boards for controlling the ‘droop’ of the circuit and symmetrical sine wave converters have given way to square wave asymmetrical inverters. Not only this but tig has now become susceptible to the demands of fashion: There is a certain ‘look’ which is found on everything from racing car components to mountain bikes; it originates in America and is usually known as the ‘Stack of Dimes’:
If you have ever purchased (in the words of the catalogue) a “beautifully hand crafted oil catch tank” or a quality mountain bike, this weld will probably look familiar and in some quarters it is becoming the expected look. It isn’t a look which quite fits a vintage or classic car, but somehow that sounds like a rather hollow excuse for not producing it. Instead I think that I’d prefer to respond to such expectations with an explaination of how tig welds used to look before mountain bikes existed…. and then to offer to produce the ‘stack of dimes – if that’s what you want’.
It’s taking a bit of practise to get it just right and the technique is proving well worth learning for other reasons to do with controlling the heat from the torch and the control of the filler rod. Which is just as well because most of my work requires the weld to be filed or ground flush at the end of the job anyway….