Spot welding thin aluminum?
We are doing the SECOND run of some covers for an electronic assembly. It is formed up of 0.032" 5052 aluminum, and gets 4 spot welds at each end.
We are not spot welding experts, in fact we make the electronics. But for the first run, we used a cheap spotwelder, set up with a pulse timer, and got very acceptable welds. I took some strips, and adjusted tong pressure and time until we got good peel tests( didn't section any nuggets......) All the pieces welded OK, and the after-run peel tests were as good as the before-run. basically it worked fine.
That was months ago. We got another order, and so now I have to get another lot welded. But THIS time, nothing works.... Same time (timer was never re-set) but tong pressure is different, since welder got used for other stuff in between.
I got some "welds", if you can call them that, where I could literally flick the top strip off with my finger.....there was NO nugget. And a few where the tongs burned right through one piece, obviously hot enough.
Went to "millerweld.com" and ran through the setup stuff and troubleshooting, and while that pointed to low tong pressure, it didn't help to increase it.
Just as a tie-breaker, I tried some steel sheet remainders, and that thing welded them like crazy.... couldn't break the weld with any reasonable force. So it isn't totally messed up.
I REDUCED time AND tong pressure, with a slightly better electric outlet, and for some reason got somewhat better welds, with "fair" peel results. But the first electric source is what we used last time, and monitoring primary side voltage and current showed it was not much different from the unsuccessful welds.
All I can think of is to return to as close as I can recall to the original setup, and find the best outlet in the shop..... But I am totally puzzled by the same machine, same time, nearly same tong pressure, same material and job, and such crazy-different results....
Did we have beginner's luck? Shops all over town didn't want to try spot welding the parts, said they didn't do aluminum, so maybe we know now why that was....
Thanks in advance.
Same alloy? Some just will not weld. Are you making certain the surfaces to be welded are clean? Are you brushing these surfaces with a clean Stainless steel brush?
yes, freshly cleaned surfaces were tried.... although we had no trouble that way the first time, and in fact, cannot access some surfaces to clean them anyway, as the flaps are already formed. It is a one-piece part, folded up and then welded.
Oddly, the clean surfaces were the ones that most stubbornly refused to weld...... maybe a bit of resistance gets that area to heat!
Near as I know same alloy, that is what the print calls for. Aluminum alloys can be hard to positively ID..... there are a skillion of them, and many are very close in composition.... 5052 is supposed to be good for welding in the tables I saw. We don't have time to send out for analysis and re-order if wrong anyhow.....
But, the most important issue here is that I have not had them start on the NEW parts..... don't want to blow through them farting around with times and seasons.... I've been checking the setup on cut-up reject parts leftovers from the FIRST run, so it is known that the material which isn't working now is not different from what worked before.
JST - you mention time and pressure, but not power/amperage. Aluminum will require much more amperage than steel for resistance welding. Does your 'cheap' welder have adjustable power/amperage setting ? And yes to your suggestion that "maybe a bit of resistance gets that area to heat!"
I am no expert on spot welding but recently bought 2 huge spot welders and so have been reading much, Here is a quote from a pdf I downloaded from spotweldequip.com (I do not know them):
"typically aluminum’s high electrical and thermal conductivity requires about two to three times the amount of current and about one quarter of the “weld time” compared to spot welding steel".
Again - I have no experience - just quoting what seemed like a good manual on spot welding I found
How much was done on "other stuff" since the original successful job? Has the contact area or shape of the electrode tips changed? Has something changed that would prevent a consistently repeatable tong pressure? Have you verified the integrity of all electrical connections and current paths in the machine?
Originally Posted by JST
Try increasing resistance which increases heat by placing thin pieces of stainless steel between tongs and the aluminum. Aluminum could be conducting heat away to fast to make good spot weld.
Well, for what it is worth, I shifted operations to a location with the nearest suitable outlet to the service entrance area, and got 25% more current, as measured at the primary.
That got the job done, with peel tests before and after the run, and current observed for every weld. There is a limited amount of strength that can be had from 0.030 aluminum, but every peel test pulled metal, at a satisfactory force, so it looks like we solved the problem.
it is just odd that we got such different results with conditions that appeared to be the same as prior run.
Now we will be monitoring the current on welds, with a minimum satisfactory figure. So long as we are pulling that current and peel test is good, we will "pass" the welds in between tests as good. Tong pressure is hard to check, so we will set per the Millerweld suggestion.
Thanks for sparking some ideas......
make sure tong tips are not worn too big. sometimes a coarse file to make tong tips contact area smaller / sharper will concentrate heat so welds maybe smaller diameter but more thoroughly heated/welded. if plugged in to 120volts yes some circuits will have a voltage drop if amps go about 15. for example some welding machines will try to use 30 amps or more at full power but volts during use may drop below 90. also if using an extension cord try using a short heavy gage one like 12 ga rated for 20 amps. i have had machines not run just because extension cord was too long and not the heavier 12 ga but only 14 ga wire
Originally Posted by Tommy
The volts did drop at the original location, but they still drop at the new location. The peak primary current is now 2X the breaker rating, but it works OK on our duty.... need to set up a better power source specifically for this machine. Good reason for the special welder allowances on breakers and wire in the NEC.....
The volt drop isn't a huge deal, the bigger issue is what that does to current. Since we are now getting a primary current which corresponds to almost 80% of the rating, which is given with tongs closed but no workpiece, I called a halt to "more perfection", and stopped worrying about voltage drops.
Using thin scrap steel sheet between the electrodes and the aluminium also works well.
Originally Posted by Gary Hart
Seems like that might put heat where you don't need it, at the OUTside of the joint..... But maybe it insulates the tong tips from the work so they don't suck out so much heat.
Looks like it IS "insulation"...... against the tips pulling out too much heat.
Well it's all about the kVA with aluminum..... we used a machine like the the smallest size Miller, 1.5 kVA, looked a lot like Lazze's, but shorter tongs.
And it worked.... good thing, too, because no way we could put steel in there. no room.
VERY interesting thread here!
I use a Banner 18 kva single phase liquid cooled spot welder with digital control for stainless, but have been taking aluminum to be done on a 75 kva three phase Sciaki with the understanding that a three phase machine was required for aluminum.
Experimentation will begin shortly...