I might make some people mad with this. A lot of guys who fuse do so because they don't know how to weld. Not everyone of course but from my experience I have seen guys who think they can weld and all they know how to do is fuse weld. I am a big believer in adding filler wire!! Especially with stainless. Don't get me wrong, fusing has it's place.
The first thing you learn when you start off TIG welding is how to fuse. This basically is when you melt two pieces of metal together without any filler wire. This is good when you are assembling something and you need to stick it together and you don't want to run over any big tack welds. One of the difficulties of fusing is that if you don't have a tight fit up, you're not going to be able to fuse.
When you have thin gauge sheet metal, it's the preferred method. You might also want to take into consideration if you have to clean up the weld. If you just fuse, you can't grind off too much.
One of the main reasons I don't like to just fuse is because you don't get the strength as you would with filler wire. If you add a little wire in there it will be a lot stronger and you also have something that you can grind.
You must think about what you are welding. For example, if you are making something that is going to be exposed to any vibrations, fusing alone will not be enough. It will hold for a little while but you will be right back welding it again. When I made stainless steel tables for restaurants they wanted us to fuse everything! Yeah, it's faster and there is no clean up but a few years down the road after that table is in a restaurant and it's being abused every which way, welds will break! In this day and age, company's want things done fast. People just don't want to pay for quality work these days. They have the mentality that once it's out the door it's not their problem anymore. I can't stand that!!
I know some company's would fire you if you get caught fusing!! Anything in the aviation field must be welded to be strong. Fusing is a big no no! Then again, when dealing with food or liquid pipes fusing is preferred because germs and bacteria can be trapped in the ripples left by adding filler wire, so each one has it's place. Your job is to figure out what is needed.
