Tim, nice practical response on welding.
Larry
"Ronak, TP (Timothy)" wrote:
> Listers and Brent,
> After about 15 years working as a Body Man and 2 years fabricating race cars
> roll cages and pieces for my buddies I developed a strategy for welding
> upside down. (Just try to weld a cage just once and not get some serious
> buzz burns standing on your head) It involved spotting panels together
> rather than using a continuous weld. In Autobody uni-body construction a
> continuous weld along the edge of a panel is weaker than a series of < inch
> spot welds place on = inch centers < in from the edge of the panel. This is
> the reason most manufacturers use spot welding rather than stitch welding.
> Because you are constantly starting and stopping with welder the power is
> increased compared to the wire speed to ensure a good burn and penetration
> of the first < inch of wire protruding from the tip. If you insist on
> continuous welding upside down and a significant amount of spatter is
> falling it could be; dirty surface, to much power and wire speed for the
> thickness of the metal, inappropriate welding gas, insufficient welding gas
> flow, Insufficient metal overlap, too thick of wire. Other than for plate
> welding 1/16 inch thick or thicker sheet metal, Mig Welders are not best
> suited to butt welding sheet metal. They are exceptionally good at spot and
> lap welding. If you want a high quality sheet metal butt weld use a TIG.
>
> If you are welding sheet metal the best wire diameter to use is .023-.030
> with the thinner wire producing better results with a smaller diameter weld.
> I like a 75%argon / 25% CO2 mix which really cuts back on the spatter
> significantly. I used to use 100% argon but the mix seems to work really
> well. The straight CO2 seems to just create too much spatter and it seems
> that it requires a lot of cleanup of the adjacent surfaces.
>
> There was talk earlier about which welders to use. The welder I have is a
> version of Miller sold by a local distributor (AK 1200 with 200 Amps at 60%
> duty cycle) but has sufficient amperage and wire speed to "spray arc" which
> leaves an unbelievably smooth weld with excellent penetration on plate steel
> 3/8 inch and thicker provided that it is chamfered. This permits me to weld
> up to = inch thick steel with good results. My welder also has the ability
> to accept a spool-matic gun for aluminum Welding. I also have a sheet metal
> gun for the .023 wire and a heavy gun for the .030-.040 wire.
>
> If you do have to do an overhead weld that is a butt weld one method I use
> is the spot stitch method. This requires that you spot on one edge until a
> buildup of steel occurs and then allow it to cool until you can then spot to
> it constantly using the thicker weld as a way "sink" the heat away from the
> panel you are welding. This will get you started and you continue to weld
> using the last spot as your starting point allowing it to cool between
> welds. Always tack both ends and then keep splitting the difference between
> until the entire seam is welded. This may require several quick "on trigger"
> "off trigger" shots - if you will - but it works very well. I have used
> this technique to tub the rear end sheet metal of uni-body cars as well as
> for rust repair. The On/Off trigger method is especially helpful when you
> "blow a hole" due to the power being set too high for the metal thickness
> you are welding. Understand that a spotted butt weld will be weaker than a
> continuous weld because typically the spot weld will not penetrate as well
> to the adjacent weld. This is because the weld is thicker than the
> surrounding metal that the welder is set up to weld and requires a little
> more power to adequately "penetrate" the welded spot. So, when spotting you
> typically step up the power from what you would use if you were continuously
> welding.
>
> Occasionally you will still get the odd "spark in the boot under the laces"
> or even the old "roll down the neck to your chest hair" spatter.......just
> grin and bear it 'cause once you fuse metal with electricity you are now
> initiated into the manly man club.
>
> I hope that helps.
> Best Regards,
> Tim Ronak
> Amateur Welder Extraordinaire
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