Never Seen This Before

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I've got a program, welding aluminum cylinders with a lil less than 1/8" wall.  Had the material rolled, so I just have to do a seam weld.  Using a Jetline seamer.105 amps15 volts DCSP (I know, seems like a long arc, but that's what this machine requires)22 inches per minute travelWire feed 75 inches per minute 4043 filler Gas - 75 He/25 ArTungsten, 3/32, 30 degree included angleMonster 1 1/2 gas lensParts are chemically de-oxed to remove all oxidation prior to weld.Worked out the parameters just on the straight plate (no seam) so I wouldn't waste material.  Did a weld, rolled it over a little, made another weld.  The parameters I used above made a beautiful weld, great re-enforcement on the top with a nice drop-through on the bottom.Set up a part, lined up the seam, and ran the part.  Again, beautiful looking weld on the outside of the part.  Removed the part from the seamer, and no, absolutely none, re-enforcement on the ID.  I've never seen an application where parameters that would weld through plate wouldn't weld the same thickness seam.Tried several different setups, what finally worked is running the above parameters on one pass (still no drop through), make a second pass same as above with no filler metal addition (gives an underbead), and then a third pass at lower power and less rod to take care of the underfill from the second pass.Any ideas?  I hate like hell having to make 3 passes to get a compliant part.  For those of you wondering why the idiot is using DCSP instead of AC, the parts must pass penetrant inspection in the as welded condition (no brushing or finishing allowed) and the AC arc cleaning adjacent to the weld always holds penetrant.  DC welds pass every time.I r 2 a perfessional
Reply:With aluminium getting root reinforcement on a piece of plate doesn't compare to getting complete fusion on a butt IMO. I agree it's odd to have absolutely no signs of drop throughThrowing some thoughts out there, i would guess that oxide may be part of the issue...If the joint is a closed root then i would question the quality of the oxide removal on the joint faces. If the blanks were cut with laser or plasma the cut edges would also be more heavily oxidised. I'd go back to the un-formed plate but set up a joint this time and up the heat input a bit, see if that fixs the fusion issueHave you tried a high frequency pulse?
Reply:I appreciate the input.  Banging my head at this pointThe plates were sheared, and then prior to weld, they were chemically cleaned by:1.  Hot alkaline soap rinse for 20 minutes (removes grease)2.  Rinsing with a solution of 5% hydroflouric acid, 10% Nitric, balance Deionized water, for 3 minutes (removes the oxide and about 1/2 a mil of the base metal)3.  Rinsing in a solution of 50% Nitric acid, balance DI water, for 5 minutes (removes any smut from step 2)4.  Rinsing in a room temperature DI water rinse for 5 minutes.5.  Rinsing in an elevated temperature DI water rinse for 5 minutes.6.  Blown dry with nitrogen and placed in sealed bags until they were ready for weld.The parts, from removal of bag to start of weld, are only exposed to atmosphere for less than 5 minutes.I haven't tried a high freq. pulse, I think that's probably a good idea, we'll give it a shot.I r 2 a perfessional
Reply:Originally Posted by kbnitWorked out the parameters just on the straight plate (no seam) so I wouldn't waste material.  Did a weld, rolled it over a little, made another weld.  The parameters I used above made a beautiful weld, great re-enforcement on the top with a nice drop-through on the bottom.Set up a part, lined up the seam, and ran the part.  Again, beautiful looking weld on the outside of the part.  Removed the part from the seamer, and no, absolutely none, re-enforcement on the ID.  I've never seen an application where parameters that would weld through plate wouldn't weld the same thickness seam.
Reply:Pulser,"They" are right, the oxide does begin forming immediately upon exposure to air, but studies have shown that it doesn't get tenacious for a few hours.  Most aerospace specs allow 4 hours after chemical cleaning before the parts have to be cleaned again.  We try never to get that far, if we're past an hour or so, we'll wire brush to within 1/2" of the faying edge, solvent wipe, then weld.Arc length is a little longer, running about 1/16th inch.  Could dial it down closer, but then as the puddle builds, I'd have to rely on the voltage feedback to compensate the lift on the torch, and sometimes that can get a little squirelly.The bead on plate was an actual part, just not across the seam, so I could get multiple passes and only ruin one part, so the clamp pressure, geometry, and heat sinking was identical.  Even made sure the parts cooled down to room temperature between passes so that I wouldn't have heat buildup start to affect DOP.So now maybe I'll run hotter with a High Freq pulse.I r 2 a perfessional
Reply:I know it's been a while on this thread, but finally came up with the solution.  As stated above, the weld worked perfectly when I ran it bead-on-plate (no joint), but didn't work when I positioned the torch directly above the joint.Oxide contamination on the faying edges was not the issue, took a file to several pieces immediately before welding, no change.Changing the high freq helped a little bit, but still had a sizeable length of the joint with lack of fusion.Solution - Offset the torch .040" off the joint, so the tungsten was tracking down the base metal.  Since the weld on this part is about 1/4" wide, the joint is consumed, and I get full penetration with dropthrough.Still scratching my head, but, hey, it's working now.I r 2 a perfessional
Reply:That is a bizarre solution. In my experience there's always some oxides issues (however slight) with DCEN- if there weren't the weld pool would be better defined.Can't think of any other explanation but then i can't get my head around offsetting the torch 1mm  fixing the issue eitherStill, like you say, it's sorted now
Reply:would sheering the seem change the density of the alloy at the seem ( would act like extruded alloy) so heating and cooling to change the molicules back then reclean the part. I have only welded a few different aluminum pieces before and found this with extruded parts. To fix the problem I baked the part prior to welding thus weakening the entire part but was easier to weld.Last edited by kneedeep; 08-25-2008 at 10:16 PM.
Reply:Kneedeep,Changing the heat treat condition of the part isn't an option on this part, as it's part of the structure that holds a jet engine inside the aircraft.Best regards, KbnitI r 2 a perfessional