Understanding Multi Pass Weld Settings!

[Nick DV]

Apologies if this is a dumb question, but how do you work out what mig settings to use when doing a multi pass mig weld? Although I’m unlikely to need this soon – although one never knows - I’d like to understand how you determine welder settings for multi pass welds. I’ve watched a ton of Y/Tube showing multi pass welds being made, however not seen many that give welder settings and not seen any giving a full explanation of how you determine them!

I have a 240 amp mig and for example, I want to butt or fillet weld two pieces of 12mm or thicker steel together. Obviously, this would be beyond the welder’s capabilities to do in a single pass, therefore how would I work out the welder settings in order to make a decent multiple pass weld?

Confused? I am

 

[Tom O]

Aren’t you just compensating for the thickness of the previous weld?
I’m not a welder just to let you know.

 

[Nick DV]

Aren’t you just compensating for the thickness of the previous weld?
I’m not a welder just to let you know.

Possibly, but not sure hence my post

 

[Popcorn]

I always thought that you V the joint out and then use as many passes until you've filled the full thickness of the metal.
So you run one bead at the bottom of the V, then two welds above that and so on. Slowly filling the V until one bead above the surface of the metal.

 

[Nick DV]

I always thought that you V the joint out and then use as many passes until you've filled the full thickness of the metal.
So you run one bead at the bottom of the V, then two welds above that and so on. Slowly filling the V until one bead above the surface of the metal.

Sorry for not making myself clear, but I’m fine with what multi pass is, what it’s for etc, it’s just I’m unclear on how you work out the mig settings for running the multiple beads

 

[Popcorn]

Don't take anything I say to factual Nick, thats just how I've always done it.
It's a really good question and I'd like to here from someone who knows what there doing as well

 

[Nick DV]

Don't take anything I say to factual Nick, thats just how I've always done it.
It's a really good question and I'd like to here from someone who knows what there doing as well

No probs, I’m always open to learning something new The settings question is one that I’ve been meaning to ask for ages, just haven’t got round to it!

 

[Munkul]

I'm not a welder either. But I do look after WPQRs for our lads at work.

Multi runs are specified on the WPS, it's worked out empirically. ie. choose what you want to do, if it works, then write it in the WPQR.

Now we don't have any WPQRs of our own for multi run mig but I have a booklet of someone elses. Our MIG stuff is for ourselves so no extra quals or testing needed, we do our own cut, etch and bend tests for our own satisfaction.

For fillets - We would run 3 beads for 20mm mild steel plate fillets at around 280-300 amps each. We're looking for a a weld leg length of 3/4 x thickness.

We have a few procedures for TIG butt welds on pipe, multi run. They specify 5 runs on the WPQR as that was how it was qualified, but others being tested to this spec qualified in 4, and the inspector didn't mind.

There's always a BIT of leeway/wiggle room for the guys doing the welding, as everyone is slightly different. Some will put slightly hotter and faster runs in than others. Usually you get a range to work to.

 

[Brad93]

Multipass welds are about reinforcement by increasing the throat thickness, if you're not getting the penetration in the first pass then sticking more over the top isn't going to help.

 

[Nick DV]

I'm not a welder either. But I do look after WPQRs for our lads at work.

Multi runs are specified on the WPS, it's worked out empirically. ie. choose what you want to do, if it works, then write it in the WPQR.

Now we don't have any WPQRs of our own for multi run mig but I have a booklet of someone elses. Our MIG stuff is for ourselves so no extra quals or testing needed, we do our own cut, etch and bend tests for our own satisfaction.

For fillets - We would run 3 beads for 20mm mild steel plate fillets at around 280-300 amps each. We're looking for a a weld leg length of 3/4 x thickness.

We have a few procedures for TIG butt welds on pipe, multi run. They specify 5 runs on the WPQR as that was how it was qualified, but others being tested to this spec qualified in 4, and the inspector didn't mind.

There's always a BIT of leeway/wiggle room for the guys doing the welding, as everyone is slightly different. Some will put slightly hotter and faster runs in than others. Usually you get a range to work to.

Multipass welds are about reinforcement by increasing the throat thickness, if you're not getting the penetration in the first pass then sticking more over the top isn't going to help.

Thank you both for your answers.

Apologies again, but I maybe missing something in the answers, but in answer to my example question, how do you work out the settings for the root pass then the subsequent passes, or are you saying that if I wanted to weld a butt or fillet weld on 12mm or thicker steel with my 240 amp mig, it wouldn’t be possibly even with a multi pass weld?

If it is possible, how do I work out the settings?

 

[Munkul]

Easiest way to do it is to make sure you're in spray transfer, you'll (generally) get plenty penetration that way If you use 1mm wire over 200 amps with argoshield you'll get it. You'd also get it in 1.2mm wire above 250 amps.

You should do some testing Nick, get some scrap 20mm plate, turn your machine up to max, spray it in, cut and etch.

There isn't one set "this is the only amps that will work" once you get into spray transfer. It's more a case of deposition rate and bead size.

I have the following qualified weld procedure specs in front of me:
20mm plate to plate fillet - 3 runs at 283-314 amps spray arc, flat
10mm plate to plate fillet - 1 run at 258-289 amps spray arc, flat
10mm plate to plate fillet - 1 runs at 125-145 amps short arc, vertical up

Qualified means someone did a weld at these settings and it passed NDT and mechanical tests. Therefore, someone else with these settings (and a bit of skill) should be able to achieve the same.

The 10mm at 125 amps short-arc will have taken a bit of skill, mind! The only reason it worked is because it was vertical up. Weld filler stays down under gravity, and the arc can burn right into the root and parent metal.
Try the same settings on the flat, and the filler metal will roll down and stop the arc burning in properly, you will not get penetration.

 

[MoreWellie]

I don't think there is a definitive answer and @Munkul gave you the best answer of you being the person who has to be happy with the result

I am not a qualified welder and I haven't attempted either of these joints on 12mm. If I am unsure if something can be done then test pieces are the way to go

If you want someone elses thought processes on how they might go about attempting this then here you are

Let's start by saying 12mm is a bit over what you can really expect a 240amp set to handle. Oxford spec their 240amp set to 8mm so you may be heading for disappointment

I would use a minimum of 1mm or 1.2mm wire and start with the wire speed around 7 and adjust that and torch speed until the weld felt right

For a butt joint I would V out until I had a root face of about 6 mm and maybe a 2 to 3mm gap then run a pass down that. If a short run then I would start at about 3/4 voltage so maybe 9 or 10 out of 12, for a longer run I might knock that down to 8 or 9 out of 12.

A fillet joint would have me starting at 12 out of 12 on voltage and see what it looked like and how it tested.

subsequent passes for both butt and fillet I would run at 12 of 12 as you are unlikely to blow holes with a 240amp set

Examine the results after each pass and adjust settings accordingly

lots of things will affect the result. your welder and its duty cycle, what the plates are resting on, how long you let it cool between passes, ambient temperature so aim for consistency in your test pieces

You are the one who needs to be comfortable that the resulting joint quality is good enough for its intended purpose and your only way to prove it is testing testing testing

 

[Robert Mullins]

When I was an apprentice boy,(1978-1983) I ask a very similar question of one of the old welders, his reply, if you're not burning through, it's not too hot!
A lecturer at Swindon Skillcentre advised me (1987) "mig is horrendously prone to lack of side wall fusion, any doubts whatsoever, spray transfer weld it"
Where I'm working in heavy engineering, all the weld procedures call for spray transfer, even the 6mm fillets,
With the larger multi-run fillets, the settings aren't changed, rather the weld is allowed to cool, prior to the next pass being completed:
If you get lack of root fusion within a fillet weld, the whole of the weld has to be removed to repair it, avoid it via this age old technique:
USE AS MANY VOLTS as you can, with 15mm+ plate I'd have no hesitation with using 32/33/34+ volts and as much wire as possible; watch the root, it should burn away as soon as you pull the trigger:
ALWAYS remove the silicone from along the weld toe prior to depositing the next pass:
Basically, keep it clean, run it hot

 

[Munkul]

This age old technique:
USE AS MANY VOLTS as you can

... Which is incorrect. Its the extra wirespeed that gives you the penetration. The extra volts just wastes heat in arc length.
Sorry Robert, I know it works for you, but it's simply incorrect advice. It always has been, and always will be.

 

[Nick DV]

Easiest way to do it is to make sure you're in spray transfer, you'll (generally) get plenty penetration that way If you use 1mm wire over 200 amps with argoshield you'll get it. You'd also get it in 1.2mm wire above 250 amps.

You should do some testing Nick, get some scrap 20mm plate, turn your machine up to max, spray it in, cut and etch.

There isn't one set "this is the only amps that will work" once you get into spray transfer. It's more a case of deposition rate and bead size.

I have the following qualified weld procedure specs in front of me:
20mm plate to plate fillet - 3 runs at 283-314 amps spray arc, flat
10mm plate to plate fillet - 1 run at 258-289 amps spray arc, flat
10mm plate to plate fillet - 1 runs at 125-145 amps short arc, vertical up

Qualified means someone did a weld at these settings and it passed NDT and mechanical tests. Therefore, someone else with these settings (and a bit of skill) should be able to achieve the same.

The 10mm at 125 amps short-arc will have taken a bit of skill, mind! The only reason it worked is because it was vertical up. Weld filler stays down under gravity, and the arc can burn right into the root and parent metal.
Try the same settings on the flat, and the filler metal will roll down and stop the arc burning in properly, you will not get penetration.

Thanks for the response. I will get hold of some thick plate as you suggest and have a go.

My mig is 240 amp, so if I take your second welder spec "10mm plate to plate fillet - 1 run at 258-289 amps spray arc flat", this is not going to be possible as it's above the mig's capability. Therefore, would my machine be capable of a multi pass run to produce a strong weld, and if so would the root pass be made with the mig at full whack?

Of course I may be barking up the wrong tree, and it's as simple as if the mig can't weld a certain thickness in a single pass, then it won't be able to do so using multiple passes?

Perhaps I need to stop watching 'experts' on Youtube!

 

[Munkul]

My mig is 240 amp, so if I take your second welder spec "10mm plate to plate fillet - 1 run at 258-289 amps spray arc flat", this is not going to be possible as it's above the mig's capability. Therefore, would my machine be capable of a multi pass run to produce a strong weld, and if so would the root pass be made with the mig at full whack?

That 2nd welder spec says "i can do this weld at amps between 258 and 289 in spray transfer"
It doesn't say "this weld is impossible to do at amps below 258" If you see what I mean.
What wire are you using? Assuming 1mm? That's realistically what you need to be on. Gas? Wants to be 15% CO2 but you SHOULD be able to do it on 5%, you'll just get less penetration.

1. Find the highest setting you can on your machine. On the 240, it won't have too many volts. Do it like Robert says - max the voltage out, and find the highest wirespeed that still gives a nice weld. That's your realistic top end amps, whatever that is. Do remember that too low a wirespeed gives as much spatter as too high. You want a loud nasty crackle without much spatter.

Then weld a 10mm fillet, single pass, on the flat. The weld leg length might be a little on the small side, but that's ok. Travelling too slow to fill the joint up is bad, as the weld pool rolls forward and limits root penetration.
Do a few at different travel speeds, try a few techniques.
Cut the best looking ones up.
Polish the edge, warm it up with a blowtorch, and etch it with phosphoric acid. (relatively safe and easy to get hold of, compared to the proper stuff which is Nitric!)

This is what you're looking for - penetration.
This was one of my early tests of the Miller pulse settings on 6mm plate, I wasn't impressed with it. You can see it's in there, but it's not amazing on the flat piece, it doesn't have the arc energy to burn into it. 410ipm 1mm wire


This was CV spray around 28 volts, 480 ipm wire. Right in there, no problems with penetration.


Right, so my point, after all this?
1. achieve spray transfer
2. check good root penetration.
3. If you have good root penetration into a cold joint, then you will PROBABLY have plenty amps to get good fusion on a multi-run weld, especially if hot from the root run.

So then, your next test will be to get some more 10mm plates, and run some multi-pass. 1st run is into the root. 2nd run is pointing into the lower toe of the root and washing into the root and the lower piece. 3rd run is pointing into the upper toe of the root and washing into the upper piece and into the 2nd run.

Cut, etch, check for fusion. You MUST be able to see that fusion into the previous run.

TL;DR - you have to do a weld and test it!

 

[Nick DV]

That 2nd welder spec says "i can do this weld at amps between 258 and 289 in spray transfer"
It doesn't say "this weld is impossible to do at amps below 258" If you see what I mean.

Absolutely see what you're saying.

Find the highest setting you can on your machine. On the 240, it won't have too many volts.

Oxford say that max volts is 32V.

Right, so my point, after all this?
1. achieve spray transfer
2. check good root penetration.
3. If you have good root penetration into a cold joint, then you will PROBABLY have plenty amps to get good fusion on a multi-run weld, especially if hot from the root run.

So then, your next test will be to get some more 10mm plates, and run some multi-pass. 1st run is into the root. 2nd run is pointing into the lower toe of the root and washing into the root and the lower piece. 3rd run is pointing into the upper toe of the root and washing into the upper piece and into the 2nd run.

Cut, etch, check for fusion. You MUST be able to see that fusion into the previous run.

TL;DR - you have to do a weld and test it!

I'll most certainly do this. Beginning to get my head round this now, so appreciate your help

 

[Brad93]

28V, 12.0m/min would be a good starting point

 

[Nick DV]

I don't think there is a definitive answer and @Munkul gave you the best answer of you being the person who has to be happy with the result

I am not a qualified welder and I haven't attempted either of these joints on 12mm. If I am unsure if something can be done then test pieces are the way to go

If you want someone elses thought processes on how they might go about attempting this then here you are

Let's start by saying 12mm is a bit over what you can really expect a 240amp set to handle. Oxford spec their 240amp set to 8mm so you may be heading for disappointment

I would use a minimum of 1mm or 1.2mm wire and start with the wire speed around 7 and adjust that and torch speed until the weld felt right

For a butt joint I would V out until I had a root face of about 6 mm and maybe a 2 to 3mm gap then run a pass down that. If a short run then I would start at about 3/4 voltage so maybe 9 or 10 out of 12, for a longer run I might knock that down to 8 or 9 out of 12.

A fillet joint would have me starting at 12 out of 12 on voltage and see what it looked like and how it tested.

subsequent passes for both butt and fillet I would run at 12 of 12 as you are unlikely to blow holes with a 240amp set

Examine the results after each pass and adjust settings accordingly

lots of things will affect the result. your welder and its duty cycle, what the plates are resting on, how long you let it cool between passes, ambient temperature so aim for consistency in your test pieces

You are the one who needs to be comfortable that the resulting joint quality is good enough for its intended purpose and your only way to prove it is testing testing testing

Thanks for this MW. I appreciate what you are saying and certainly starting to make this clearer for me.

 

[Nick DV]

When I was an apprentice boy,(1978-1983) I ask a very similar question of one of the old welders, his reply, if you're not burning through, it's not too hot!
A lecturer at Swindon Skillcentre advised me (1987) "mig is horrendously prone to lack of side wall fusion, any doubts whatsoever, spray transfer weld it"
Where I'm working in heavy engineering, all the weld procedures call for spray transfer, even the 6mm fillets,
With the larger multi-run fillets, the settings aren't changed, rather the weld is allowed to cool, prior to the next pass being completed:
If you get lack of root fusion within a fillet weld, the whole of the weld has to be removed to repair it, avoid it via this age old technique:
USE AS MANY VOLTS as you can, with 15mm+ plate I'd have no hesitation with using 32/33/34+ volts and as much wire as possible; watch the root, it should burn away as soon as you pull the trigger:
ALWAYS remove the silicone from along the weld toe prior to depositing the next pass:
Basically, keep it clean, run it hot

Thanks for your input Robert. I don't think I'm likely to ever be welding 15mm - although would be nice to be able to