Tom,
I have been welding auto body sheet metal for about 25 years and have welded
both passenger cars and roll cages in every possible position. It can be
frustrated trying to learn to weld, even with a mig, as it seems pretty
simple ... pull a trigger wire spits out and if you are close to the car...
it welds! Then once you are on your back under the car and you experience
the glee of a molten ball landing on your chest or one finds its way under
your shoelaces you get to join the "Manly Man Club".
Here are some tips that I practice just for sheet metal. The timing is good
as I just spent the last weekend fixing my cutouts and repairing fender
aprons and clearancing a firewall for twisted wedge heads and Aluminum
covers. The work I did took about 3 hours on the Firewall, 3 hours on the
inner apron behind the wheelhouse, and 5 hours to rebuild and reinforce both
exhaust cutouts (On my Back .... Lots of souvenirs on my cheeks and chest).
Wire size:
.023 is great for thin sheet metal like new Hondas and will do a great job
on Tigers
.030 would not work well on New Hondas as the wire is thicker than the sheet
metal you are welding and will require too much power to melt the wire
compared to what it will take to blow through the < of that Honda. It is
perfect for the Tiger sheet metal and in fact is the thickness I would
recommend for everywhere on the Tiger as a moderately skilled person should
have little trouble with this.
.035 is what I use in my welder and takes a little more skill as the power
again is higher to melt the wire than what is required to melt the panels
being welded.
Welder setup:
Typically if things are welding great it could be any number of setup
issues. Rollers loose as was previously mentioned. Are the rollers for the
wire you are using...what wire diameter are you using? I checked my welder
and with Argon /CO2 mig mix from Praxair my ball float gauge is at 40-45 on
the gauge and I think it is in CFM. I think it is overkill but I was working
with the garage door open and the purpose of the shielding gas is to create
an Oxygen free environment for the weld to be created in. All you need is
enough gas to deprive the weld of outside air. If it is windy or breezy it
may be impossible and you will obtain crappy results. If it is in a still
garage you would be able to turn the gas way down unless a furnace is
blowing on you creating a breeze.
Butt Welding:
Welding butt welds is possible but not advisable as it creates too much heat
induced warpage and in fact produces a marginal repair but does have
applicable uses where you want to restore both sides of a panel. The problem
is that when butt welding the weld is now more brittle than the surrounding
area and if it is a < panel or some other structural panel on our cars the
normal flexing is likely to introduce a crack as the flexible steel flexes
against the brittle and stiff weld. I use butt welding only where I may want
to weld two pieces together and I do not want an edge as I may want to metal
finish the area and use no filler likely in low flex areas. Always leave a
gap between the two pieces the same thickness of the metal you are joining.
As you weld if you choose to run a constant bead (Very bad idea from a heat
warpage perspective) always moving in a small figure 8 motion back and forth
to permit the puddle you are carrying to cool somewhat. If you tip the
welder so that it is pointing in the direction of the weld you just did you
will achieve less penetration and lower chance for a blow through. The
better method is to perform a stitch weld.
Stitch Weld to avoid Warpage and Blow Through:
In welding sheet metal due to the relative inability for metal to transfer
heat, the heat is not able to dissipate throughout the panel as quickly or
easily as say, Aluminum. The heat expands the metal near the heat source but
the metal immediately next to the area you are working but the other metal
try's to remain the same size and the two fight each other and you have
WARPAGE> The best method is to do small stitches or spots to limit the
amount of heat you introduce at one time to the panel and also the amount of
HEAT. By limiting the heat in the panel you also limit the amount of blow
through. One principle that should be remembered is that it takes more power
to start a weld than to keep it going but most people set the machine based
on a spot. There is a trade off higher power is good for short < inch
stitches as it will produce a good penetrating spot but will blow through
very quickly if you try to weld a continuous seam. Tom, this sounds like
your situation as you said you get going and then after you go a ways you
blow through. My Technique here is to tack weld the panel every 4 inches or
so. Drill holes and use small screws to secure the panel if it is large to
ensure correct fitment and that it does not move. Then tack the panel
ensuring it remains flat against the part you are repairing. Start at the
Middle and work to the edges initially being quite a distance apart until
the panel is secure then split the difference until you are at about 4
inches apart. Now tack weld small "stitches" of around =-3/4 of an inch long
at the maximum against each spot and move around the panel permitting the
panel to cool each time depending on the distance apart. If the panel is too
hot to touch with a thin work glove it is too hot and you should let it
cool.
Lap Weld:
This is the most common method used for joining sheet metal and usually
involves placing steel over the top of other steel. Like in a rust patch.
This is fine but typically the metal is now thicker or protrudes out from
the surrounding areas requiring filler to blend it in and while it is now
smooth and flush it has that "fat" rust repaired look. The preferred method
is to use a Metal Flanging Tool (A tool that presses a small step into flat
sheet metal I have a hand operated one) to press a small step into the
original steel so that the new metal is even with the surrounding metal when
the patch panel is fitted into place. At edges or seams you will use the
Butt weld technique to ensure that you do not increase the overall thickness
of the part you are repairing at an edge or seam. Make your patch slightly
smaller than the high side of the flanged opening and then weld so that the
entire weld is below the high side of the flange. Grind the weld with care
as it is easy to grind the original panel too thin on the corner of the
flange.
Spot welds versus solid edge welds:
Most people assume that a continuous edge weld is stronger than a spot weld.
Well this is not true as in crash tests quarter inch spots placed a quarter
inch apart significantly outperform an edge weld. One reason is there is
more welded surface area to pull through the other is that the solid weld
once it starts to tear can continue very easily. The only reason to
continuously weld an edge is to prevent moisture from creeping. Don't think
you will improve the rigidity of your car by welding up seams as you may
just create areas for cracks to form.
Blow Through:
The mark of a tradesman is how well he fixes his screw ups and I pride
myself as being one of the better screw up fixers since I usually make a
bunch. I usually get my share of blow through and I will try to explain the
process I use to fix them.
OK, we got a little carried away with the heat or the metal is lightly
corroded but still serviceable and the Mig wire pushed through the puddle
for some reason and blew a hole. It is unlikely that the gas pressure is too
high as it would be difficult for it to create enough surface pressure to
cause a blow through unless the welder was way too close to the weld. The
electrode tip should be about a quarter of an inch away from the weld when
actually welding and the outside shield could actually be resting on the
panel with the welder gun angled pointing at the weld just completed. The
way to repair it is to use a series of quick spots with lots of time to cool
between each attempt to try and build up a heat sink (Think of the thick
weld as pulling heat away from the thin metal) so you can close the hole.
Always point the electrode towards the largest side of the weld and build
the hole in from the welded side. In extreme case you may want to pull the
weld back from the work area to a distance of half an inch and give a quick
zap so that you get about a 3/8 inch length of wire with a little ball of
weld on the end. This will help build the metal up faster but will lead to
poor penetration as you increase the distance. Once the hole is filled in I
always use a straight at shot with the welder to strike an arc and reflow
the ugly mess in a smooth little blob.
Tom I hope that helps out even though it is a little late. I too am in
California, in Mission Viejo, I would be happy to come over on a Saturday
(if you are close) and drink your beer and give you a welding tutorial.
Best Regards,
Tim Ronak
Business Development Manager
Akzo Nobel Coatings
OFF: (949) 305-5393
VM: (800) 234-6747 ext. 2257#
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