I know this has probably been discussed before, but I would like to know people's thoughts on TIG vs MIG with regards to strength of a weldment. I ask because I built an axle with spindle bosses that were MIG welded onto l/4" plates I made to get my drop. The spindle bosses sit horizontally and are machined out of 1.5" x 1.5" solid stock. Each one is completely seam welded into place, and has (2) 3/4" rosetta welds on each side. That's about 16" of good MIG weld around a 2.5" square piece. I have to believe with all this weld the spindle bosses will stay put. I will attach a picture.
This is one of those questions where you'll get differing opinions, but in my book MIG is for strength (mainly used for steel), TIG is for lightweight and alloy welding. Heavy duty industrial equipment is virtually all MIG welded and that oughta tell you something.
That is what I thought, too, with regards to seeing heavy tractors and things being MIG welded togeather. However, I was told that TIG was the only way to make sure things are being fused togeather. Don't you just think that as long as you watch for cold lap during welding that MIG is great for making something solid and strong.
Here's my take on it. To me alot depends on the thickness of the base metal you're trying to weld. On something made of lightweight tubing or similar material like a motorcycle or aircraft frame, I think you're exactly right, the TIG fuses the material together better and the weld can be almost as thin as the material itself. MIG welding is much harder on thin material like that because of the tendency to burn through. A MIG requires melting of the base metal and then the base metal and welding wire form into a melt pool which then cools and forms the strength of the weld. On heavy material where the MIG can melt into the base material and join the pieces I think it's safe to say that it is just as good at fusing the material together. I think it also comes down to economics and ease of use. A MIG can lay out huge amounts of material quickly at a low cost and is easy to weld with, TIGS are more expensive to operate, not as handy to fill in with large amounts of welding rod, and more labor intensive requiring more skilled labor.
To clarify the question, let's ***ume that the mig is gas not flux. Mig or Tig both use a filler rod. Mig uses wire off a roll (Metal Inert Gas), and Tig (Tungsten Inert Gas) uses a rod that is added as needed. Both are dependant on good penetration and a uniform weld pattern. To say that Tig is only for light stuff is incorrect in my opinion. Old stick welding is still a viable welding source. What do you think that we welded with before Mig and Tig. All the older industrial stuff and battleships were all stick welded. If I had to choose one, I would probably go for water cooled Tig. The weakest point of a weld is about 1/2 inch away on the parent metal, not the weld itself, if it is a good weld. Cleanliness, preheating heavy stuff, fit, bevel, penetration all are more important than what welder you use. My Opinion
I would also agree with what you said. When I put the riser plates to the spindles there was a natural valley to fill because of the roundness of the spindle stock. Fitment is of utmost importance. I just had a problem because after I did it I started to hear that MIG was unacceptable to for welding structures, when in fact it's still welding, and the strength should be high.
IMHO MIG welding is one of the more dangerous methods of welding out there. I say that because with MIG it is relatively easy to get a good looking bead that has little to no penetration. Does that mean MIG is an INFERIOR weld - absolutely not! MIG is a strong, fast method of welding - but the suggestion that it is superior to TIG for strength goes against what I was taught in school. Sure MIG is used in all sorts of industrial applications - becuase it is ECONOMICAL and gets the job done. TIG is SLOW - slow means expensive. The suggestion that TIG is better suited for thin materials is incorrect -IMHO. -If anything it is BETTER suited for thicker sections as YOU decide when enough heat is in the part to apply filler metal. Granted this may be a sort of Ford versus Chevy discussion as I am sure a skilled welder can achieve sucess with MANY methods. One thing worth considering as much as the process itself - is the design of the weldment - For instance - on my digger the "step down's" are all cut at a 30 or 40 degree angle - this helps to maximize weld area for one thing. FWIW I've seen far more "bird ****" MIG welds than TIG welds.
I think HEMI Rambler said it best, it is welder dependent. As in the person doing the welds. It is easy to get poor penetration on MIG while still having a good looking weld bead. As far as strength, either can be strong, the weakest area is actually the HAZ next to the weld, the weld filler is usually stronger.
I agree with Hotrod1940 that either Tig or Mig will be good for your application if you do the proper prep. Clean weld area, grind slag of of hot rolled plate, bevel joints to be welded have the welder set for the correct heat. A TIG weld will look better. I built a 5X10 foot trailer all with my TIG, but I have a 460 amp job with water cooled torch so I can make a pretty good fillet. Looking at your fabrication it appears that you do not have a plate on the back side of the two triangle plates that your spindle boss is welded to, I would highly suggest that you make a nice filler piece for this area and weld it complete around. If you think about it, it is the front and the back welds that carry most of the load so you appear to need a little additional plating. Rex
I am trying to figure out what you did here - did you lop off the last 4" or 5" of an axle (with the king pin bosses) and weld it directly to the plate? If so, I think you are flirting with disaster. There would be way too much leverage on that weld to keep it attached forever. If thats the route you took, I would TIG (Gas Tungsten Arc Welding or GTAW is the proper name) the axle cut-off to the plate to ensure proper fusion between the two. You could then MIG weld (Gas Metal Arc Welding) on top of it to get some serious meat on there. A lot of structural MIG welding is actually Dual Shield Flux Core MIG (FCAW) welding, where you use a flux cored wire spool (Lincoln Electric 71M) in conjunction with your 75%/25% steel gas mix. It makes for a *****IN' weld and is very strong. It requires a faster spool speed so you can really lay down a lot of metal in very little time. If possible, I would try to leave the axle cut-offs longer - cut a hole through your plate and insert the axle inside it. Weld it to the other plate on the other side (where your drop is), then weld it to the plate where you would have originally welded it. This will support the axle/ king pin bosses in a much safer fashion. That is, of course, unless I am mistaken on your design. Good luck and happy fabbing.
The horizontal portion of the spindle boss is just 1.5" x1.5" solid stock that was cut to 5" in length. I then had a hole drilled in it to accept the king pin. After that I just had some round spacers made for the top and bottom of the square stock to a make up the difference between it and the actual wheel spindle. The spacers are what give the end of the spindle boss its round verticle portion. They are what ride on the bearing if that helps.
I have AWS certifications for MIG up to 1/2", and TIG to 3/8". I stick weld with 7018 pretty regularly, but not enough to need a certification on it. If I was worried about something I was welding, and wanted no doubts about the integrity of the weld, I would TIG it. My reason being; you can see whats going on at all times, and you are in full control of the quality of the weld. In this case though; a good hot MIG weld by someone who knows what they are doing would be fine. Grind all the scale off the joint, preheat it a little before welding, and make sure to remove any stress risers on each end of the joint after the welding is done, and it should be fine. Look at the sloppy **** they use on new vehicles. If the ****py factory MIG welds that are under my wifes car can hold up to 100k miles of driving, then a properly done MIG weld 'oughta last forever. I'm not knocking stick welding either. A good joint done with a 7018 rod is a thing of beauty, and properly done it is about as strong as it gets. On the other hand, if the man operating it doesn't know what he is doing, the joint will have hidden slag inclusions, and other problems that can cause the weld to fail. Also, the slag floating on top of the puddle tends to hide what the filler is actually doing. Non-professional welders tend to watch the slag and adjust their travel speed to it instead of the filler underneath. Another danger, in my opinion, is the proliference of 110v MIG welders in peoples garages. These things are great for sheetmetal and light structural stuff, but way too many hobby welders are trying to use them for suspension and other critical parts. Even if the operator knows what he is doing, it is difficult to get good penetration on heavier material, and the scary thing is, a whole lot of these guys welding frames and suspensions together with these things are amateur welders. You can very easily set a MIG welder where it will make a good looking bead that has absolutely no penetration. Back when I first started welding, about 19 years ago, I ran a bead on a inside corner joint of 1/4" plate without grinding off the scale first. I'm not talking about loose scale, I'm talking about the black scale that looks more like bluing on a rifle that is on new hot roll steel. I had the welder set where it made a beautiful bead; it sounded right as I was welding, and it looked like any other good MIG bead. I had the piece tacked down to the table, and in the process of knocking it loose, my entire 4" bead broke completely off one side of the joint, and both pieces fell flat on the table. After my foremen laughed his *** off at me, he took a hammer and chisel and knocked the bead off the other side of the joint too. It looked like I had sprayed some kind of release agent on the joint before welding it. There were a few little spots where the filler had actually made it through the scale, but otherwise the bead came off in one piece. It sat on my bosses desk for several years after that, and was used as a warning that things aren't always what they seem.
MiG welding is fine for this application. But I have to agree with some of the previous comments that just because it looks good, doesn't mean it's a sound weld. Penetration and fusion are the keys, and that really depends on the operator. As for MiG vs. TiG, the main advantage with TiG welding is you have more control over the process, since you can adjust the heat/penetration and speed at which filler metal is deposited as you weld, which you can't do with MiG. TiG also avoids the problem of cold starts, which is what happens when you pull the trigger on the MiG gun and it starts feeding wire before you have an established weld pool. TiG also has the ability to weld non-ferrous metals using alternating current, which you can't do with MiG. The major down side with TiG, and the primary reason it's not used for big, heavy jobs, is it's slower, and thus, more expensive. I'm going to leave it at that, since this subject has been covered in great length many times before.
I have used mig to weld aluminum on navy ships all day long. So yes you can mig non ferrous metals. I am big on operator qualifications. The factory used mig welds all over the place. It's all up to the operator. I would rather have a pro welder stick weld my suspension than some self taught dude in a barn with a tig. tig/stick/or mig are all more than capable of holding a suspension together in a properly engineered joint. I have seen some SCARY **** on supposed pro built cars that holds together, (self taught welders) which is fine as long as I am not in it. If the weld is critical you always grind out the starts and stops, mig, stick or tig. This is how you p*** an x ray test cert.
Not sure what I was thinking when I wrote that, since I've seen the aluminum wire feeders many times. What polarity do you use for that?
electrode positive in mig according to my memory bank although it's been 10 years. I never thought of the junk lincoln 110 al setups. I was remembering the monster cobra matics I used in the navy. They had the spool in the gun because you can't push aluminum worth a **** thru a long liner.
It doesent matter what you use as long as you know what youre doing. If you dont let somebody who does do the job!!!
Penetration is important to a good weld- CLEAN YOUR METAL FIRST. If you are unsure of your penetration- try and see the other side of the welded area. I f you cant see lots of discoloration along the entire length of the weld zone on the opposite side of the material you just welded- cut it off grind off all weld material- CLEAN YOUR METAL- and try again. Or you might wind up doing an impersonation of a Robert Williams painting.
I oughta do a tech on some of the finer points of these discussions when my neck heals up. Of course any one is welcome to beat me to it.
Weld strength is related to the tensile strength of material. Most high stress situations require a 70,000 lb rating. These are stick rods such as 7010-7018-7024, migs wires also have tensile ratings along with tig rods. As stated before the application is irrelevant as long as its done properly. I can tell you that we used to weld a root p*** with smaller diameter rods to ***ure good burn in. Sometimes it was tig welding in this area. Tig welding is slow and easier to apply the weld correctly when you know how to use it.
Sawracer, is it true the ship's superstructures are made of aluminum? (The hulls are that crazy stainless alloy.. HD-80?).... Lots of stainless and aluminum welding in the Navy yards.
Here is a good site to read up on some of the different welding options. http://www.weldingengineer.com/ I also looked on Millers welding site and downloaded a good manual that is very informative. http://www.millerwelds.com/education/TIGhandbook/ Larry
The older ships I worked on had aluminum superstructures and mild steel hulls. ages cl*** destroyers etc. The later ones I saw coming were steel thru and thru(arleigh burke?cl***). I was a lowly HT or hull technician, shipyard welder for 5 years, not a naval architect so if you need to know more you are barking up the wrong tree.
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