ATTN Welders: MIG weld smoothing

I have a question for you guys. This seems like a no brainer, but I've heard some conflicting info on this subject.

Let's use an example so I have something to base my question off of.

Let's say you are **** welding two pieces of thick-walled tubing together. Let's say 2x4x3/16 structural welded steel.

If the two pieces are prepped properly, V'd correctly, etc., to get the proper penatration, is there any reason that the tops of the weld couldn't be taken off to smooth and blend the weld with the rest of the material around out? Let's say 1/3 of the weld or less was sticking out that was to be removed.

Seems to me that if you had a good clean weld, no porosity, with good penatration that things would be just fine, but I really want some feedback. I'm trying to improve my welding skills everytime I weld and this is something that has been weighing on my mind for awhile. I had planned on smoothing some or most of my welds where they were going to be visible on my frame and I see people doing it all the time, but I never know the cir***stances by which it is done.

Thanks guys!

 

ive been welding for about 2 1/2 yrs for a company and was told u should never grind a weld smooth it takes away all strength to the area but if u bevel the box tubing right u could have the weld lay close to flush so u wouldnt have to grind at all ... but if u want the clean look u can prolly blend the one side and keep the other sides that are hidden welded up and will not affect it

 

I always look at it as much load is the area going to have to support, the only way to really see if you have good weld penertration on pipe is using NDI. Or hack it apart, but kinda defeats the purpose of welding it. De-stressing the weld will relieve any tension around the area.

 

this is true as well

 

If all is good. Grind it flat.... but a ****y weld will get ****ier<--new word..it will not hurt a good weld

 

See... this is the conflicting info I'm getting. I've been told both ways (***uming a perfect weld) and I see TONS of guys smoothing out their welds on their frames, bones, etc...

Rule of thumb for V-ing two pieces is like 45 degree bevel and like 1/2 the thickness, right??? Yet the weld puddle itself will flow into that v-groove that's formed at that joint and fuse with the base metal beyond that.

 

always prep it right and you should have only a little bit above the material, but you dont want to grind away to much as this will break with any stress

if your worried bout grinding to much on a **** weld and its not in sight then fish plate it

 

Increase your bevel degree, might have to run more than one bead, but over all your lapping the material enough to give it structural rigidity ** If your laying good weld** If you do this thou, you will have to de-stress it. Then smooth it out.

 

i'd say it depends on what the piece is used for? anything structural i would leave the weld alone (but if you v'd it and gaped it correctly there souldn't be much weld above the surface) but if you really want to grind something smooth, just plug weld a backing plate to the area for safety. if its a frame rail you should be doing that anyway.

 

What are you doing to de-stress? Rose-bud O/A, let cool naturally to room temp?

 

I have used a smaller tube inside the main tube, V bevel and pickup metal from all three pieces in the puddle. To get a snug fit you usually have to use thin wall into thick wall or vice versa. You can also just use short pieces inside to provide a backing.

 

welder/fabricator here been welding for most of my life i see people do it
but i wouldn't mine are to pretty to grind but 3/16 tensile strength is 60.000psi so a good **** weld should almost match that of the parent metal with 100&#37; penetration if it's a frame as noted above use a backing inside always if so you should feel reasonably safe to grind a little

 

Anyone ever see a welding test done ?
The test sample is ground down smooth and flush,then bent.

Grinding down a GOOD weld shouldn't be a problem.
But it is also a good way to hide a ****py weld.

 

in the steam field they state a weld ground flush is supposed to be 100&#37; like the parent metals , like when but welding the seam on a steam drum

 

The direction of the grinding marks should NOT run parallel with the weld seam.
They should run across the seam,and be as smooth as practical.

 

I agree with Unkl Ian. With good penetration it should be fine. But in some cases it's better safe than sorry. On my frame where I've ground down all the welds I'm going to fish plate the inside rail and cut a vertical slot in the rail and weld 3/16" plate into it. I'll grind the top down but leave the bottom. Kinda creates a re-enforced rail. Wishbones I'm not worried about...



Does that make sense? Maybe I'm just crazy...

 

The stresses are highest on the outside edges.


Sometimes,incorrect reinforcement causes failure,by creating stress risers.

 

Should I not use the fish plates? I'm unsure now. The slot-plate thing I read about in an aircraft engineering article, but god knows where, it has just stuck with me.

 

The practice of grinding welds flat, to the height of the parent material will affect the strength of the joint. Welded joint calculations are done using ***umed weld-thicknesses; these thicknesses are based on the standards and conventions used in the welding profession. Now, while grinding a weld will reduce joint strength, it will not (provided the weld is done properly) reduce it below the level of the parent material. In some cases, grinding welds smooth is required to reduce stress concentrations in critical areas, so it can be an accepted practice.

It sounds to me like your instincts on this one are correct.

 

Key word..Aircraft. Most welding applications performed on A/C is with TIG, also all welding down on A/C is NDI inspected along with strict post-weld processes to give the airframe optimal load tranfer and dispersion.

 

When **** welding tubing, I like to cut the joint at a angle to give more weld area.

 

slot plates are a good idea, I used them on the kick up on an A frame as i wanted to grind the welds flush on the outside of the rail, as i had suspension points going over the join. I left the plate proud about 1/4" and ran a bead down each side of it, and left it unground, its an interesting detail if done nicely.

 

Yes! We know this!

 

This is the frame of mind I was in right here!

Also, on my frame I had plants for appropriately located gussets and fishplates, but mostly I was more concerned about the general theory related to a simple **** weld since those tend to be the worst case.

 

Hey bud, just sent you a little reading material, enjoy. Got a bunch of american welding society gouges also if you want them.

 

Awesome! Thanks man! Sending you a PM...

 

im 100 percent with you on that .. all bend test cupons are smothed and polished

 

I have been welding for a living for 12 years and cant think of anything that these guys have overlooked, you are getting good advice.

 

Yeah, all this sounds like good advice man. I've never had a weld break yet *crosses fingers* and I've pretty much been doin it the way most of these guys have been steering you with great results.
-GothY-

 

I would have no reservations on grinding the welds flat/flush, "if" you beveled correctly and you use a "hot" enough welder.
If it's welded right, it will hold and then some.