Tim, Great article on welding from a practical point of view. I passed the
American Welding Society test years ago, but learned quickly, that theory and
the art of welding are 2 different things.
This is a keeper, and I hope Steve puts it in the United site.
Thanks.
Larry
"Ronak, TP (Timothy)" wrote:
> 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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