T-joint 3mm box to 8mm plate

[BOOF]

Evening all!

I'm about to start fabricating a car transporter trailer, I am having some parts laser cut from 8mm plate steel as joining flanges, hinges, brackets etc.

I'm just a bit concerned about the welding, as its my first attempt at welding this sort of joint. (the reason for this type of joint, before anyone asks, is its a modular trailer)
I'll be welding 8mm plate flanges to the end of 80x40x3mm square section mild steel. Basically im worried about blowing through the 3mm, not getting enough penetration into the 8mm, and/or warping the 8mm flange plates by trying too hard to get penetration!

I'm running an ESAB c151 MIG welder on .8mm wire and argon/co2 mig gas.

tips / tricks /do's / donts?!! !

Thanks in advance :-)

 

[Wendelspanswick]

Your on the limit with a 150amp mig and 8mm plate so you need to direct the weld onto the thicker steel and wash over the thinner box. You want a good root gap and I would run a root and a couple of overlapping caps if it's a critical joint.
The plate will warp, you just have to smack it back with a hammer while it's hot.

 

[RonA]

Evening all!

I'm about to start fabricating a car transporter trailer, I am having some parts laser cut from 8mm plate steel as joining flanges, hinges, brackets etc.

I'm just a bit concerned about the welding, as its my first attempt at welding this sort of joint. (the reason for this type of joint, before anyone asks, is its a modular trailer)
I'll be welding 8mm plate flanges to the end of 80x40x3mm square section mild steel. Basically im worried about blowing through the 3mm, not getting enough penetration into the 8mm, and/or warping the 8mm flange plates by trying too hard to get penetration!

I'm running an ESAB c151 MIG welder on .8mm wire and argon/co2 mig gas.

tips / tricks /do's / donts?!! !

Thanks in advance :-)

Whilst I'm sure your trailer will end up a fine piece of work & don't want to rain on your parade, aren't there new Legal certification issues you have to comply with when fabricating new trailers.
RonA

 

[BOOF]

Yes, it has to pass an IVA test, and all running gear needs certificates of conformity - which they have.

 

[pedrobedro]

Your on the limit with a 150amp mig and 8mm plate

More like 50 amps under the limit. You need more power to get into the thicker metal especially if you are using them for carrying heavy loads.

 

[Kent]

you haven't enough power in that little MIG set to get adequate heat into a bit of 8mm flat. Pre-heating is an option but why 8mm plate and only 3mm wall in the box, seems sort of odd?

 

[Bill Edwards]

I must say that I think 150a on a MIG is a bit low for comfort. The trouble with MIG is that without enough power it's easy to get a cold weld, I think there is a risk of that when going onto 8mm plate. Safer with MMA, but I'm guessing you don't have one and aren't experienced with one?

 

[BOOF]

Thanks for the input guys, Hmm, I was thinking 150 was going to be enough (based on previous work on 6mm plate not needing full power)
I've fabricated mostly tubular before 3, 4mm, so going up a step here.

Well I do have a (decent, not chinese) 200A inverter TIG, which i could use, but would take forever to build a frame.
It will do Stick too, but i have no experience stick-ing at all other than a "poke and hope" go 10 years ago on a friend's stock car chassis, and the results were, erm, poor to say the least.

How about I just pre-heat the s**t out of the 8mm plate? get it glowing... would probably help minimise warping too.

 

[Kent]

If you can heat I should 200amp capable MMA should get it done cold though! The issue is welding down flat onto the 8mm plate it will act as a big heat sink- very different than say doing an open Butt on 8mm with prep. I figure it might be a bad thing if the plate and the box parted company on the road right?

 

[bigbadbugga]

Set up the stick and some samples of the material and practice practice practice until you get the weld you want.

 

[Bill Edwards]

140 amps with a 3.2mm rod should suffice with MMA, 8mm to 3mm box doesn't need anything too powerful. But a 150a MIG isn't likely to be OK.

The trouble is though, a bad MMA weld still isn't going to be streets ahead of a cold MIG weld if the operator doesn't know what to do.
Some practice with the MMA might be the way forward here.

 

[Kent]

It seems of late that MMA (stick) welding is getting more and more referred to like its a mysterious dark art. It honestly isn't so don't be put off, the good thing is if a run looks good it most generally is good (unlike MIG were good looking beads can often be weak). Just spend a while practicing on similar get your settings, angle of dangle sorted and a few destructive tests and go for it

Just a quick tip 3.2mm is the max you can run off 13amp and 120 is about the safe limit for the fuse to work all day (depending on your set), this should get the job in question done but there are differences set to set, rod to rod. A trick I often use if dealing with a poor supply is burn a smaller than usual rod a lot hotter than I normally might but still within the limits stated for that rod (presently using a 2.5mm at 100 amp on a job welding 20mm solid round bar to 10mm flat and trust me its going right in there), just watch you can still keep a tight short arc.

Undercut on the top of the bead onto the box is the factor I should watch out for in practice