WELD PORN —
TIG WELDING STAINLESS
PREPARATION
When you want to start welding stainless steel, there are a few points of the TIG process that are very important in order to maintain stainless steel’s corrosion resistance and strength. As with MIG welding, stainless distortion is a problem, so minimizing heat input is a priority. Choosing the correct TIG filler rod is also similar to the process with MIG. Some people actually use MIG wire as a TIG filler. When welding 300-series stainless, keep to the simple fillers — I would suggest 316LSi. Joint preparation is more important when welding stainless steel than when welding mild steel, mostly because of distortion. Bracing, strong backs, or heat sinks are all good options, so try to make room for one of these options when choosing a joint prep. A clean, dry, and oil-free set-up is also vital.
I won’t get into the different types of TIG machines, but what you need is a DC power source. High-frequency start is a bit of a luxury; I don’t mind using scratch start or lift start. TIG welding stainless uses argon gas. A negative electrode, positive earth should be the terminal set-up, with argon gas set at around 6–10 litres per minute.
Use a thoriated tungsten electrode ground to a point. The size of tungsten is dependent on the amps being used and the thickness of the material. I use a 2.4mm for everything from 1mm to 10mm. TIG torch cup sizes range from 6mm diameter to 15mm. Larger sizes give the operator a wider envelope of shielding gas but can make seeing the end of the tungsten more difficult. The answer to that would be to use a gas lens set-up. A gas lens streams the argon gas through the nozzle more like a beam or channel. This means that the tungsten can be protruding up to 20mm or more if you turn the argon flow up. This is awesome for teaching welding, as it makes seeing and controlling the weld pool so much easier. The thing about the TIG welding process on any material is that you are welding the lowest manual welding deposition rate and normally at very slow welding speeds. This can make welding stainless steel much harder than normal mild steel. Learning and improving your TIG-welding technique will enable you to weld faster, while still retaining the same weld quality. This has an effect on heat input and therefore results in less distortion. By the way, when good results are achieved, for goodness’ sake record the settings. Thoroughly clean the area to be welded. Cleanliness cannot be stressed enough. It’s not like MIG or stick, where you might get away with welding over a bit of oil or unclean metal. If you try to TIG weld over oil, grease, paint, or heavy oxide, you will contaminate the tungsten electrode and the weld pool and upset the weld chemistry.
Make sure that the weld joint area and the filler rods are as clean as possible. This is an important preparation. Remove all oil, grease, paint, rust, and dirt. Contaminants such as these may result in arc instability, contaminated welds, and/or contaminated tungsten.
GOOD WELDS
What constitutes a good weld? Look for good penetration into the base material, not too much penetration or oxide on the underside, a nice flat bead profile, or a nice flat mitre fillet if doing a fillet weld. Good bead width and good fusion at the edges of the weld are also important. Beware of ‘undercut’. This is where the ‘toes’, or edges, of the weld have burnt grooves into the base material. If this is the case, you have probably welded too slowly, at too hot a temperature, starved the weld pool of filler rod, or a mixture of all of these variables. The amount of filler rod is something the operator will decide on, depending on the profile needed. Practise on an offcut first. Keep the tungsten as close as possible to the weld pool — this will give you good penetration and aid in reducing heat input. Remember to let the argon flow until the tungsten has stopped glowing. If you have post-flow, set it at 10 seconds or more. An oxidized tungsten makes for a dirty start or tack.
Oxidization and discolouration of the weld area can really spoil a nice weld. If sanding or polishing to clean up welding beads, make sure you use iron-free abrasives or you will quickly see the rust spots forming. You will get oxidation on the back side of thin sheet. This chromium oxide should be cleaned off, as it will rust or oxidize. Back purging will stop this happening. There are also tapes and fluxes available, such as solar flux. Passivating or pickling paste is a good alternative for cleaning up welds, especially if you want to show them off. But be prepared for criticism, as everybody becomes a welding expert when they find out you’ve done it yourself.
GRIND IT
Every good welding professional, if they are honest, will tell you they were proficient with the angle grinder or the scrap bin long before they were proficient with good welding techniques. Nothing is different in my shed; my trusty angle grinder sometimes gets a good workout, mostly by my choice. The reality is that no matter how magnificent the weld looks, or which process is used to do the welding, if you have good penetration and the weld is going to be ground flush anyway, who cares how pretty or ugly the original weld looked? I am a realist. I might not quite be a Rembrandt with a welder but I am certainly a Michelangelo with a 4½-inch (115mm) grinder and a flap disc.