Welding question - how to weld mild steel to stainless?

[rv_safetyman]

Quote from boogiethecat:  Fortunately it's not difficult to learn what is a good weld and what isn't, and even easier with todays Mig technology to learn to do good welds even if you're not a seasoned welding guy.

I never thought I would question Gary, but I kind of do on this statement.  He qualified his statement by suggesting you work with someone who can look over your shoulder.

I live in fear of MIG welding.  It is the one welding process that can look pretty good and be a terrible weld.  It is so easy to lay down a good looking bead and not have good penetration on one or both sides of the weld.  I have worked with several folks who wanted to learn MIG welding.  It is amazing that each one got to the point of producing a pretty good bead and still did not have much penetration.

IF YOU DO TRY TO TEACH YOURSELF TO WELD:  be sure to do it on small pieces that represent the type and shape of metal you will be working with AND TEST THE WELD!!!!  You should cut the part to see the penetration, and do some bend/fatigue tests on the part.  I would also strongly suggest you slow the torch movement down and bump up the heat until you burn through the material.  That way you know what it takes to get 100% plus penetration.  You then know how to back off the weld. 

By far, the major mistake of MIG welding, in my opinion, is trying to move the torch too fast.  Slow it down and wait for a good puddle to form.  As Gary said, you should also listen for the "sizzling" sound that is an indication you have the heat and wire feed balanced for the work being done.

One other point that has been made in this and other threads, is that you should spend the money for a good welder.  You can produce a good weld with a cheap welder (if you are a good welder), but it will be very difficult to get the job done, and the duty cycle will suck.

Lastly, I cringe when I hear of folks welding thicker parts (say over 1/8 inch) with a 110V MIG welder.  It can be done, but you really have to know what you are doing.  Increase the thickness and I would be 90% plus sure that the weld will not match the strength of the rest of the structure (even with multiple passes.

If I was running a welding school today (am certainly not qualified to do that), I would have the students start with gas welding.  That really teaches you penetration and metal flow (as well a gas balance which is not applicable to other kind of welding, but does emphasize the impact of oxygen on the weld and the need for a clean weld area).

For those of you who learned on stick welding, you probably fall into the same trap as me -- you can weld dirty material with some rods.  We get lazy and don't do the proper prep work.  I have taken a couple of classes lately that really opened my eyes.  Oil on a weld will increase the carbon content just as too much acetylene did with gas welding.  Makes a hard brittle weld.  Oxides will screw up a weld much like too much oxygen.

Sorry for the soap box, but this is a very touchy subject with me.  I have been welding for 40 years and still produce some pretty crappy welds, if I don't really concentrate on the process.  Now I am working with TIG and I am back to square one.  Will take lots of time to make pretty welds, but at least you can see the penetration as you go.

Jim

[rcbishop]

Very well stated...and informative....and helpful.

Thanx, Jim

RCB