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View Full Version : MIG welds look too smooth and convex?



Jefff
09-02-2013, 09:18 PM
I used a MIG (GMAW) welder (Miller Milermatic 130xp w/ C25 gas) for the first time this weekend. I really like how its welds look compared to the welds of my Hobart 125 flux core (FCAW) welder that I've been using.

However, on my 16g square steel tubing the GMAW welds are perfectly smooth, they have no ripples or "stack of dimes" look to them. They do have complete penetration. They also appear to be to "tall" or convex, but I'm not sure as I don't have any formal welding training.

Should I be concerned about the strength of welds given that they don't look right to me?

Here's some pics of what I'm talking about. I also took some comparing GMAW and FCAW welds side-by-side. The FCAW seems to have more ripples in person, but the camera didn't pick them up.

I used various different travel speeds, voltages, weave patterns, and wire feeds in the pics in an effort to get them to look how I think they should ("stack of dimes"), to no avail.

Comments welcome.

GMAW welds too smooth?
https://picasaweb.google.com/lh/photo/hPURWmZWUIQP7W1n1dkT4GslVuoRtWwDuzqoklvyMnE?feat=d irectlink

GMAW welds too convex?
https://picasaweb.google.com/lh/photo/6iTxBd_TG_zOri63edmMfWslVuoRtWwDuzqoklvyMnE?feat=d irectlink

GMAW vs FCAW top
https://picasaweb.google.com/lh/photo/rM2p5E2jgAHX5mwmvm_gr2slVuoRtWwDuzqoklvyMnE?feat=d irectlink

GMAW vs FCAW underside
https://picasaweb.google.com/lh/photo/iUmihwl7DNPxBJCTzqadkmslVuoRtWwDuzqoklvyMnE?feat=d irectlink

IrvJamison
09-02-2013, 10:36 PM
Your MIG welds look great but not the Flux core. I have a flux core welder but no longer use it as the welds look bad and there is too much clean-up. I could purchase a stick welder but I found a shop that uses TIG and the welds look very professional. They do such a great job and charge me so little that its not worth it for me to go and buy a stick welder.

stormbird
09-03-2013, 02:10 AM
Hi there

Some good stuff here :- http://www.mig-welding.co.uk/mig.htm

regards Paul

HHJJ
09-03-2013, 05:49 AM
They look pretty good to me.
I'm just a a beginner though.
I think on one vid I saw the guy said making the stack of times was more of an aesthetic on mig than essential.

This guy demonstrates assorted wrong setting on welding
http://www.youtube.com/watch?v=PJDv7Y6dUi0

Have you tried joining two bits together at right angles yet?
I found that another learning curve again after doing the lines on a surface.

farst1
09-08-2013, 07:41 PM
The welds look ok.
The reason you can't see any ripples is because the mig is set up to do spray transfer as oppossed to globular transfer.
Those stacked dimes you see are actual globs of molten metal being transfered from filler wire to work piece.
Try decreasing amps while raising wire speed unless the welder has automatic wire speed like mine does. If that's the case the there should be other parameters that could be adjusted.
The beady look of the weld at the start of the weld is because the parent metal is cold compared to how hot it is at the finish of the weld. Weld is flatter at end.
Not Gospel. Just my opinion.
Farst1.

Jefff
09-08-2013, 10:00 PM
The welds look ok.
The reason you can't see any ripples is because the mig is set up to do spray transfer as oppossed to globular transfer..

Thanks, I'm going to read up on that.

Jefff
09-08-2013, 10:29 PM
The last few minutes of this video demonstrate spray vs globular transfer with some pros and cons:

http://youtu.be/xb1gvHf0H6w

grburnett
09-09-2013, 12:01 AM
First, if you have an alternative, forget the flux core.
If you don’t have an alternative, get one.

If the welder you have is what I think it is, I would be surprised if it can actually go clear to axial spray.
There are basically 3 weld modes in basic MIG (not including pulse) and the difference is the voltage input-
Short arc, Globular Transfer, and axial spray.
Below 20ish or so is short arc and that is where you hear the sizzle people want to hear in MIG. Between 20ish and 26-27ish you are in globular transfer and it sounds like crap. There is lots of popping and spitting because that is what it is doing, spitting globs across the arc gap. Above 27 you are into axial spray and you will be able to tell for a couple of reasons. First, it is HOT! and second, there is almost no sound and VERY little spatter. If too close or too far it will sound different and you will get more spatter; at the right distance the sound and spatter will almost completely disappear. I like welding in axial spray as I seem to get more consistent results.

The stack of dimes thing is purely cosmetic and I theorize actually a waste, albeit a very small waste; the weld is only as strong as the amount of metal at the bottom of the grooves, the blobs are excess weld filler. If you like it, work towards it… if you don't care, don't bother.

Your welds might be humped up like that for a couple of reasons...
1. Not quite hot enough to melt/flow down properly
2. Too high wire speed/too slow travel piling up filler too quickly/before you move on
3. Combination of the above

To me the hardest one to adjust is travel speed; I just seem to have a speed that I travel at and if I try to speed up, I eventually slow back down.

Before you try adjusting things too much, try a fillet weld in a corner; I think they are much easier to get good results and learn from than beads on a plate. OR, lay one bead and then lay subsequent beads right up next to the previous one, about 50% overlap and just keep working across the piece. Another thing that might help will be to make longer welds; an inch at a time doesn’t get you the feel.

Jefff
09-11-2013, 07:05 PM
The Miller machine I have doesn't tell me how many volts? it is outputting. To configure the welder I just follow the chart on the inside of the machine that is keyed off of the wire diameter and thickness of material.

I like the welds of my Hobart 125 flux core welder on steel that is 1/4" or thicker. I was never really satisfied w/ how it welded the 16 gauge metal required by many Atomic Zombie plans.

Just today I got the parts (electronic valve, hoses, etc) required to convert my Hobart 125 from flux core to MIG welder. I'm very curious to see how that machine welds w/ solid wire and MIG gas having used it for a couple years as only a flux core welder. It will also be interesting to compare its MIG welds to those of the Miller MIG machine in my original post. Compared to flux core, MIG is so much easier b/c there is less/no smoke so you can see the molten puddle quite clearly.

I will do some more practice and see if I can change the appearance of my welds.

ChadClancy
10-01-2013, 12:14 PM
All other things equal, from a structural standpoint, the stack of dimes appearance may have more aesthetic appeal to some but a smooth weld will perform better. Stress concentrations appear at discontinuities valleys of ripples) so this is why a smoother weld is actually better (assuming welds are properly sized, have a good profile and adequate penetration).