madforfishing
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| posted on 23/11/03 at 08:00 AM |
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Welding Technique
Guys, especially accomplished welders:
I always set up my MIG set by using a few offcuts and doing some test welds first. I then stick these test pieces in a vice and beat the cr*p out of
them with a lump hammer before I set about any real work.
What I want to know is, does anyone else use the same welding technique as me, that is 'continuous spot welding' where the spots all
overlap? It seems to make no difference to the strength of the weld, penetration is good if the settings are correct and you get fantastic looking
welds using this technique. It almost looks like it is TIG'd, especially with Argoshield.
...Standing by for huge rollockings from pro welders...
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type 907
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| posted on 23/11/03 at 11:15 AM |
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Hi Rick,
One of the problems with mig welding is cold lap at the start of the weld. This where molten metal flows onto cold base metal. Another problem is fish
eye; this is the little dot (or crevice) in the centre of the solidified weld pool when you finish a weld. These two faults are oftern why you can end
up with leaks (ie. when welding a sump or petrol tank)
Using your techneque would greatly increase the chance of weld faults, unless..... each subsequent spot does not allow the previous spot to cool and
that it overlaps to cover the possible fish eye.
There is a process used by "professionals" called pulsed tig where you can set a main current and a lower current and the welder
automaticly pulses between the two, frequency of the pulses can also be adjusted. ie. twice a second: this would have the same effect as what you are
trying to do.
When testing the integrity of welds you should not fully weld the joint. ie not all four sides of a piece of box section, but weld one side only and
then break it by bending it back against the weld. In the case of say a Tee joint weld the fillet and test, then also weld a butt and test. The metal
should break and not the weld.
Throw away your big hammer! you shouldn't need it. 
Even us so called professionals get shot down as well.
Hope this has been of help. U2U me if you like.
Paul G.
Too much is just enough
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Mark Allanson
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| posted on 23/11/03 at 09:51 PM |
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Madforfishing, do two welds, one 'make and break', and one continuous. Carefully cross section both with a hacksaw, smooth the welds with
a file, then fine emery and look at the results.
You will fine tiny cracks in your welds, each one just waiting for the chance to fail.
PS Buy you wishbones!
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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suparuss
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| posted on 24/11/03 at 01:49 AM |
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when i was making my compressor i was trying to spot weld my bsp connectors into the main tank in that way, leaked like hell, then i started contiuous
welding them and it was perfect. if you are worried about the weld distorting the frame, just do some good deep tack welds on all sides of the tube so
it doesnt move (also a good idea to minimise gaps as that is where most distortion happens ie- the weld will contract and try to pull the gap closed)
then weld it continuous along each side.
Russ.
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craig1410
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| posted on 24/11/03 at 12:50 PM |
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On the subject of gaps, I have heard it said that you should leave a gap approximately the same size as the wire you are using to weld with (ie. 0.6
or 0.8mm typically)
Is this correct or is zero gap optimum? I certainly seem to get better penetration with a small gap and I can avoid distortion with good tacking and
systematic seam welding of opposite faces.
On the subject of continuous spot welding I would agree with what has been said above that it is better to seam weld in longer sections. However, a
welding book I bought a while back does recommend that you don't weld more than 100mm at a time as it is difficult to maintain a good torch
position for longer than this. This rule should minimise distortion too.
Cheers,
Craig.
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Hugh Paterson
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| posted on 24/11/03 at 04:26 PM |
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Welding gaps
Craig, to minimise distortion the "ideal" is a precise fit and a bevel edge on the tube that forms the butt, Prior preperation prevents
piss poor performance. Although I have access to a linisher that makes this a Skoosh case, a good tip I also use is to set up a 4 1/2 grinder with a
flexible backing pad and an 80 grit cutting back disc on the front, in lieu of a solid grinding disc, very good way to prepare the metal surface for
welding (nice and shiny good for making a bevel edge)
Shug.
[Edited on 24/11/03 by Hugh Paterson]
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