Welding help required

[Lewis]

This weekend whilst doing a bit of fabrication i struggled slightly with some welds

Firstly

As you can see the weld has undercut the material on the left (5mm wall hollow section) which was being welded to 4mm plate. This undercutting didn't occur on the full bead just where the weld approached the closest edge of the 4mm plate.

What causes this? I'm guessing the usual combination of current/wire speed was too high, but why only undercut around 1/3 of the tube welded?

Second

No picture this time, but whilst welding some 4mm plate to more 4mm plate I lost the usual "sizzling bacon" sound of a decent weld - I just got a steady hum. The weld is visually perfect with uniform penetration of the workpiece and almost no splatter. What caused this change in sound? Presently I'm putting this down to my fanatical cleanliness in removing the mill scale and degreasing, does this sound right?

Thanks in advance

[steve b]

Hi Lewis

good to see you around and still building

maybe slightly too high current , but I'd have a look at your torch angle to the weld joint

and torch traverse speed

cheers

Steveb

[pete3000]

I'd go with what Steve says, torch angle tipped over to left bit too far and either too much power, or loitering with not enough wire speed.

[Maverik]

You sometimes get that under cutting when you are getting slightly too much penetration, but its difficult sometimes when you're welding 2 different thickness materials together.

As regards the lack of sizzling bacon, from what I notice with my welding, the cleaner andsmoother the material, the quieter the wleding gets, but generally always get some noise as I do primarily flux core welding.

[Hybrid_From_Hell]

^^ Yup

Torch Angle and smoothness of movment forward.

One trick I leant was when you are welding this sort of joint it tricky to "See" the workpiece

so use the edges of the shroud as guides, when yiou weave from left to right and push forwards with the torch have the shroud edges "Touch" the workpieces each side

this way you can "Feel" where the torch / weave / weld is and you get a remarkably even weld.

The other thing is that when you "Weave" left to "Right" ALSO move forwards, otherwise you do spend more time

at the edges. also try you "Curve" the torch as well, otherwise just Left / right means big weld pool leaving high weld on the join.

Try curving almost making the weld left to right a single motion of Down from the left to the centre and then curve up to the right

and then forward and down to the centre and up to the left type motion

ie NOT left / right /centre / forward .......

or even as above but Curve and Zig Zag and forwards, or even curve and circles and forward

Try them all see which works best for you

HTH

Nige

[Astro_Al]

On your second point Lewis, sounds like you started welding in spray transfer mode instead of short arc mode, which is what most consider 'normal welding'.

In spray transfer the sound will change to almost a whine - really smooth and very different to the bacon-sizzling mode. You'll get much less spatter, typically. Its a much nicer way to weld.

Mode is dictated by, primarily, the voltage across the arc. If you had cranked up the settings before that weld, then that might explain the change. Smaller wire dia also encourages the shift up to spray transfer mode. Note that between short arc and spray you get globular / long arc mode which is horrible, spattery and generally to be avoided!

Al.

[dirtyninety]

I think your slightly lacking wire speed. Only very slightly, in both situations.

[Lewis]

Thanks for the input all, on reflection I think that a combination of torch angle, slow wire speed and slow speed of torch movement are to blame, I'll just put it down to more practice then :-)

Is anyone concerned about the quality of weld or will it be adequate despite it's deficiencies?

Astro_al when you refer to the differing stages of weld I assume that these are a function of material thickness/torch angle/current & wire speed rather than settings on the welding plant? I guess that I had just stumbled upon the sweet spot

[Astro_Al]

No, they are a function of the voltage & current of the arc. Directly related to a host of things - wire dia, all machine settings etc etc.

It's not so much a 'sweet spot' as crossing over a threshold, arc voltage-wise. Above which, given all other parameters fixed, you will always be in spray transfer mode. Instead of a series of short-circuits depositing droplets of wire into the weld pool (during 'normal' short-arc mig welding), you get effectively a spray of filler out of the nozzle - the wire doesn't need to get so close to the weld pool and doesn't short out in discrete 'events' - more like a spray can of liquid metal. You'll know if you stumble across it.

Al.

[Maverik]

I bet you didn't know you had crossed a threshold... I'm actually fascinated with welding, an interesting thread.

http://www.mig-welding.co.uk/forum/showthread.php?t=2590

A thread on the mig welding forum adds some intresting back-up info too...

[steve b]

That's a good description Al of the difference between spray and short-arc

as for is it good enough? , Lewis, you know the stuff you will be doing/risking so if you are not happy grind it back

and run another one over it . Not a bad weld imo

cheers

Steveb

[bishbosh]

Can't say if it is good enough until we know what is and what it will be used for!

[Lewis]

Its a chassis crossmember, it replaces the LR g/box crossmember and incorporates a mount for the front wishbone (one link)

In fact, while youre here Bish, would you be so kind as to inspect the design?

This is the bush mounted to the crossmember, 5mm wall 76mm od tube, tubed with 9mm wall 36mm od to take the M18's which mount the bush cross pin

Webbed in

With side plates, 4mm x 230mm x 340mm, 12mm clearance holes (chassis is tubed for M12), 4mm used for the front (long) and rear (short) gusset, 6mm for the vertical gussets (its what i had, I would have chosen to use more 4mm)

Complete overview, Above

Below

In truth I wasnt sure whether the vertical gussets (6mm) were really neccessary, the standard LR 4cyl crossmember has them, whilst the 300tdi does not. They cannot be made any larger with having to fillet them due to packaging issues

So, how does it look to an engineer? Am i somewhere near?

Apologies all for the variable photo quality, these were taken on a number of devices, all of which are outdated

[qwakers]

welding looks muck better than mine.... but then i always have voltage issue where i weld so its amazing i manage to weld at all

[dirtydiesel]

I think your welding will be fine. it doesn't look as though there is enough clearance behind the bush for deflection.

I also think you will bend the tube, can you brace the center of the crossmember back to anything else?

[Lewis]

It doesn't look as though there is enough clearance behind the bush for deflection.

There's 11mm clearance, I had originally intended to give enough room for the rubber to completely disintegrate before the bush housing touched the crossmember, but it just wasn't practical. Time will tell, but given that the bush I'm using has done almost 1,000,000km already I think I've seen all the deflection I'm gonna get

I also think you will bend the tube, can you brace the center of the crossmember back to anything else?

This also has been a concern for me, perhaps I can make a brace which picks up on the M18's at the rear of the crush tubes

Thanks for your input

[bishbosh]

Looking good. Taking Dan's concerns on board, can you weld a piece of channel section full width across the back of the tube?

[Lewis]

Like some 4" x 2" channel? Sure I could but wouldn't that look a bit naff and be a bit weighty?

With regards to a brace I was thinking two tubes picking up on the M18 boltheads at the rear of the crossmember and tying into the chassis rails diagonally at 45degree. Would that do the trick or am I way off?

[bishbosh]

That would do it.

[Lewis]

Great thanks for the help