Advice: cleaning/prep pre-tacked workpiece

[Ali]

Hi Folks,

A friend has asked me to weld up some parts that he's tacked together using a MIG with flux cored wire. They're parts for engine mounts for a kit car he's building. He did a fairly good job of cleaning things up first, and has removed all the mill scale, but then drenched the parts in WD-40 to prevent rust. I've become quite fastidious about cleaning / prep, as it really makes all the difference, so I need to figure out a) how to get rid of the WD-40 and b) the best way to work with the tacks and whatever is underneath them.

I can't take it apart and clean it properly, as it was set up in position and then tacked.

I was thinking I could dunk the parts in brake cleaner for a bit, then remove the tack from one side, clean up as best as I can with a belt grinder / disc, getting right into the corners of the fillets, re-tack, then move on to the next side, working my way round like that until I've got it held in place for final welding. I won't be able to get to the underside of the joints, but I reckon they'll be free of any rust and the brake cleaner should remove any gunk.

What do you think?

Grateful for your input, as always.

 

[gordon stephenson]

Clean as you suggest, then put a couple of small tacks of your own before removing the flux core ones.

 

[MoreWellie]

put a couple of small tacks of your own

+1

be gentle with the cleaning before you add your tacks, his fabrication/preparation skills look good but I am surprised that the parts survived the journey to you without coming apart

 

[Richard.]

Removal of the tacks in place almost certainly requires a flick with a grinder/flap disc which could mark the surface finish. Does that matter?? If not go ahead it's great advise. If so then add your own tacks as suggested then blend the original ones out and flat with the Tig torch. Then put your run with filler straight over the lot. If you blend em nice and flat you'll never see them.

 

[Ali]

Thanks chaps.

Finish isn't a big issue, but was thinking of taking out the old tacks with a little cutting wheel on a dremel to keep it tidy.

 

[eSCHEn]

I'd personally not be bothered about the removing the tacks as like Richard says, you can easily blend them in the bead as you go. They look like they've got a good hold and it seems a shame to waste that effort if they're not problematic

Definitely clean them though. IPA is cheaper than brake cleaner for when you next need to buy.

 

[slim_boy_fat]

@Ali Don't forget the pics of the finished job.

 

[Kent]

At least he didn't put them all on the corners!

 

[norlander]

IPA is cheaper than brake cleaner for when you next need to buy.

you use beer? you got it wrong, you don't drink brake cleaner and clean up with beer, its the other way round.

 

[Richard.]

I think it would of been better if they were on the corners. That way you wouldn't need to touch them with a grinder. You could light up on them get them fluent and start filling when you run off them and at the end of the run stop filling before you approach it and blend in around the corner. Tacking in the centre is less convenient IMO.

 

[Kent]

I think it would of been better if they were on the corners. That way you wouldn't need to touch them with a grinder. You could light up on them get them fluent and start filling when you run off them and at the end of the run stop filling before you approach it
and blend in around the corner. Tacking in
the centre is less convenient IMO.

Well there you go that's an opinion different to mine

I just like nice corners without stop, starts or freaky bulges. If a weld breaks it will near always start at a corner

I don't have any experience with flux core to speak of used it once on a totally rubbish plant and inspected a boat that had cracks and splits all over it ( built in Poland only a year prior to failing with some sort of flux core)
Not sure I should want to run a bead over it on the corners? but there you go.
It's certainly easier to grind them off if they were there placing new tacks centre prior I grant you that 100%

 

[eSCHEn]

you use beer? you got it wrong, you don't drink brake cleaner and clean up with beer, its the other way round.

Well yeah man. Beer's just not strong enough any more. Besides, it always tastes lush when you mix it with bru

 

[Richard.]

Well there you go that's an opinion different to mine

I just like nice corners without stop, starts or freaky bulges. If a weld breaks it will near always start at a corner

I don't have any experience with flux core to speak of used it once on a totally rubbish plant and inspected a boat that had cracks and splits all over it ( built in Poland only a year prior to failing with some sort of flux core)
Not sure I should want to run a bead over it on the corners? but there you go.
It's certainly easier to grind them off if they were there placing new tacks centre prior I grant you that 100%

Id just remelt them on the corners and push them round till I ran out of fill then start filling around. If it looked a particularly bad or ropey tack or was a critical part Id cut them right out and do the whole thing with Tig. I'm the opposite. I hate central tacking on box section. Id much prefer to start on a tack and stop on it blending it in if it doesn't need grinding off but then my tacks would be done with the process I was using to weld it with

 

[Paul.]

I would put them on the corners too, then grind out the old tacks, tig does not like being run over flux core or mma welds, as for lumpy corners a good tig welder wont get them,

 

[Ali]

Think I'll be grinding them out - want to give myself every chance of a good finish. Some more experienced welders seem to be able to get away with things like this. Not me. There will also be lumpy corners!

 

[Ali]

Update. Need advice! RTech 161, WP26 Air cooled torch, on the pedal. DC, mild steel. 2.4 tungsten.

It was all going so well. Loads of practise, invested in a gas lens setup, and was happy with how things were coming along. This job being the first bit of tigging which will actually be put to use rather than just sticking stuff together for fun, I wanted to get it right. However, for all my work so far I've had the luxury of having as many chances to practise as I need - for this job (like most proper weldors encounter every day), I only get one go at this and don't have any matching stock to mess about with.

Here's a practise piece welding a piece of 4mm wall box to some 3mm thick plate:

All in all, I was pretty happy with these. I've hit various stages with this process where it has suddenly just 'clicked', and I thought I had it with this - not perfect, but I had lots of control. This was at 100a.

So I hit the job I've been asked to do. NOTE: THIS IS 3MM BOX WELDED TO 5MM PLATE.

As per plan, cleaned as well as possible in the corners, and added my own tacks here, then went at it with a die grinder and cleaned as well as possible, removing all old tacks:

Bit worried about when I get to this bit, but I'll do this last when I've got a feel for the material. That's what the pedal's for right? Might even cut the sharp point back 5mm or so, it's going to melt whatever I do like this.

All seemed to be very clean.

Washed off again with IPA. Had a crack at welding it. DISASTER!

Not sure what went wrong here - possibly too much juice? As I was successful with 100A for the 3mm / 4mm, I've upped things to between 115/130A for this job. I'm not using all of it, apart from when lighting up.

It's probably not as bad as I'm making out, but I'm disappointed with it compared to the other stuff. There did seem to be a lot of crap in there despite all the cleaning, and I struggled to get a nicely shaped pool.

Let everything cool down and tried again the following evening. Still couldn't get it flowing nicely:

Yuk. Travel speed / consistency was rubbish as I was focusing all my attention on getting a decent pool to form. I took a second pass at this without filler, thinking I could tidy it up. BAD IDEA! Soooo much heat in there.

NOTE: I tend to weld fillets by positioning the work in such a way that I'm welding flat into the root. Works for me usually, I know I'm a dirty cheat.

Usually I can reason these things out by leaving it alone for a while, and the solution comes to me. Not sure about this. Maybe I need more amps...faster travel speed....less heat?

Advice welcomed, I'm not touching it again without a second opinion.

 

[Richard.]

I do see inconsistency between test and final runs but I can only put it down to driving.
Your current range is exactly where I would be and your set up sounds like one that I would adopt too.
Now the only thing (other that your steady hand) that I can see to be a potential change is that you state your using a foot pedal. Why? It's simply not needed for dc welding and unless your flooring it at the set current you don't know what your putting out. Again if this is the Micky mouse pedal supplied by RTECH it may be way off your desired output anyway giving you inconsistency. First thing Id do is swap to a switch and set it where you want it then try again. If that doesn't help then it's driving all the way!

 

[Ali]

Thanks Richard. I'd come to the conclusion that my best work is with the button so will give it another go this way, as you say I'll then know what I'm getting. I think driving was part of it, but as I've been practising with a perfect fit up and material I've cleaned myself I was getting distracted by the problems and having the pedal there makes it tempting to adjust the amps to try to sort it out...and before you know it everythings gone pear shaped.

What about the knife edge bit...light up on it and move away or go the other way and release the trigger when approaching and use the downslope. Or pulse it?

Thanks.

 

[Richard.]

The knife edge is i assume why your using a pedal. This like you say will cut away as you approach it with the heat. Both methods are gonna work. If your welding toward it you could let a 2-3 second downslope sort out the last few mm or you can start on it and work toward the crease. Because you've got both sides to do you'll have to do both. Im lucky enough that ive come across enough situations where I have learned to Tig weld right and left handed. Not essential here so do it using both methods with your strongest hand. I don't think a pulse is useful here. It's very rare I ever bother with it and material that thick with joints that short it's a waste of time IMO.

 

[eSCHEn]

I'd be doing a wee little manual pulse on the button to finish the point end. Never thought of actually doing it all on a long downslope before - nice one mate