Electric Car Aluminum Battery Box

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I am new to welding. I am converting a 1992 Mazda Miata into an electric car. I am getting ready to weld boxes to hold the lithium-ion battery cells. For the battery boxes, I will be using 3/16", 5052 series Aluminum. I have a Millermatic 211 (MIG) welder with aluminum spool gun and 5000 series aluminum filler.My main question is whether it is better to weld both the outside and inside welds/joints, or to weld only the outside welds.Some important information regarding the project: The individual battery cells are quite heavy and there will probably be about 200-250 pounds of batteries per box.My original thought was that I should weld both the outside and inside welds, to maximize strength. However, I am concerned about burn-through/weakening of the zones immediately adjacent to the welds and am now concerned that if I weld both sides (outside and inside), I will be over-weakening the adjacent areas, thus negating any potential strength benefit of welding both sides. (Of note, I will be clamping two large hunks of brass adjacent to the area I am welding to act as a heat sink to try to prevent wall weakening).Any advice/words of wisdom on whether it is better to weld both the outside and inside of the aluminum box vs. just the outside would be greatly appreciated.  Thank you!
Reply:Some drawings or sketches would help.Are you up to snuff on making decent AL welds with your setup--whichyou've bend tested in a vice, cut thru the cross section to see how much fusionthere actually is?The strength reduction from the HAZ is normally allowed for in the design.NOT butting outside corners, but fitting to make a corner weld is strong.Simply laying down a bead over the top of two edges butted is asking for failure.Inside welding as well probably wouldn't hurt.Stitching rather than full runs is asking for stress cracking.Heat distortion will challenge you. (I like force cooling, some don't, they get all kinds of 'wowing', I don't. ) Pre bending, lots of fitup tacks, short runs, back steppedwelds and allowing for cool down either forced or natural; is needed.The mounting of the boxes--brackets, etc. can easily see cracking, rippingand tearing, since too often, very little thought is given to that area.The total design with the mounts need to be able to withstand additional, asymmetricalloading-G loading, in an impact. This is subjected to much more loading than a fuel tank,in normal operation, let alone in impact.Blackbird
Reply:Will the batteries fit and sit level if you weld the insides?Torchmate 2x2 CNC with Flashcut CNC controlsHypertherm Powermax45 Esab ET220i Razorweld 195 MigRazorweld 200ac/dc TigTormach 770, Tormach xstechRazorweld, Vipercut/Vipermig, SSC Foot Pedal Dealer
Reply:I wouldn't use the aluminum box skin to support any weight, therefore the weld type shouldn't really be a critical factor anyway. The weight should be supported by a structure, probably steel, and skinned with aluminum to isolate and contain the batteries.Last edited by MikeGyver; 10-28-2014 at 02:42 AM.Welding/Fab Pics: www.UtahWeld.com
Reply:I would do it in 16g Stainless.Last edited by Brazin; 10-29-2014 at 06:58 PM.SqWave 200Millermatic 190Airco 200 ACHypertherm PM45Boice-Crane Band SawVictor O/A
Reply:Having the thin sheet hold hundreds of pounds sounds completely dumb to me regardless of steel or aluminum... skin and structure, 2 different things with different goals.Welding/Fab Pics: www.UtahWeld.com
Reply:i have a miller 210 with a spool gun,  i have been trying to weld a thin alumn  for a long time. the only way to do it is to tig weld with a gas peddle..125 is the thinestes alumn i have ever been able to welded with my mig.to weld 3 /16 you have to make little welds pulling trigger for about 1 1/2 seconds spot together i cut and fab my pieces together with mig and take to a friend to tig and make my work look good unless you want to cut 200 2 x 2 x 3/16 alumn and pratice all welds and pure fustration sets in 3/16 alumn is a lot better  to pop rivet try building a frame out of 1/8 inch alumn and pop rivet thin alumn skinfor strainth weld two pieces of 1/8 together on the sides and try to bend,  works to make a curve hold its shape as well
Reply:I would use an outside corner joint, and weld from the outside. Like figure C in this first picture.Second, and third pictures is a 16-GA corner joint I did with my spool gun. Attached ImagesDon’t pay any attention to meI’m just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400