Some of you reading this are about to take your first TIG welding certification test in the aerospace industry. Maybe you are transitioning from another industry like pipe welding where you welded stainless and carbon steel pipe, or food service where you welded stainless steel sheet metal. Either way, let me tell you a few tips that might help you get ready:
Everything is thinner and smaller. The tig torch, electrode, filler wire, and possibly even the tig welding machine will be smaller than you are accustomed to. In pipe welding for example, a 1/8 inch rod is considered the big tig welding rod. In Aerospace tig welding, a 1/16 inch rod is big.
Everything needs to be cleaned better. All joints are normally x-rayed in an aerospace tig welding certification test. Metals like titanium, aluminum, and magnesium are prone to porosity. Remember the 3 C's ...clean, clean, clean. Especially important is filing the sheared edge of metal that will be welded. That sheared edge looks pretty clean but it is a trap for oil and corrosion products. File it and when you think you have filed it enough, file some more.
Everything makes a difference. Little things like the size of your tack welds, how you position the test plates in the fixture, how much flow rate is used on the purge gas, angle of torch, angle of filler metal rod, what kind of abrasive you use to clean the metal, how pure the argon or other shielding gas is...you get the picture. Like my old coach used to tell me...nothing is fair, but everything matters.
Everything needs to be shielded better. The hot tip of the filler rod will put oxides in your puddle. You can get away with a little of that in pipe welding stainless and mild steel, but it will kill you when welding something like .020" 15-7 precipitation hardening stainless or .032" inconel 718. To keep the end of the rod perfectly shielded , use a tig cup that is at least 3/4 inch id. With a diffuser that provides a nice soft blanket of argon shielding to the puddle. ..and you need to test it on a scrap piece of titanium to make sure it is working before lighting up on your tig welding certification plates.
About 1 amp per 1 thousands of thickness welded will get you in the ball park. Set the tig welding machine amperage accordingly plus about 10 more amps just in case and use the foot pedal to adjust. This will keep you out of trouble by limiting your amperage. usually a bead width of 4 times the thickness welded will get the penetration needed for butt welds. Use the smallest electrode that will get the job done. And sharpen it really good with scratches running lengthwise. long tapered works better for really thin (.020") and less of a taper is better for thicker welds Use the smallest filler wire that will work with having to feed too much. Too big a tig welding rod will draw too much heat out of the puddle and will cause you to use more amperage than is required . Too small a filler wire will cause you to feed too much and you cant keep up.