holes at end of weld - help!

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I am robotically welding a triple pass fillet and randomly get a blowhole or wormhole that forms at the very end of the last pass.  Research tells me the official term is "crater pipe".  It sounds like it may have something to do with rapid solidification of the weld puddle.  We've tried numberous thing to work it out.  Currently we reduce travel speed, wire speed, and voltage near the end to cool down the weld puddle.  We get the crater pipe randomly and it's about 20-30% of parts welded.  I'm just looking for a brainstorm of ideas of things to try in hopes that I've missed something simple.  Thanks.
Reply:Pictures please..We are not mind readers and pics will clear up any misconception.....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:If your getting. Crater crack at the end of the bead slope the amperage down slowly until the metal solidifies then ramp out the rest of the way.  But pictures would be a better indicator of what is going on. Also material, thickness, shielding gas, and wire type.ThanksMiller bobcat 225g  - spoolmatic 1Mm250 - 30a spoolMiller spectrum 375Thermal arc 95 Everlast Ex 250As the boiler turns, these are the days of our lives
Reply:Maybe reverse direction for half an inch before shutting off current??
Reply:What kind of robot are you using? There should be options in your weld schedule to allow for proper crater fill.
Reply:I am running,  .035 steel wire, 75/25 Ar/CO2 mix, welding on 1018 CRS 7/16" thick, we are welding a single bevel groove weld partial penetration in 3 passes (currently working on getting down to 2 passes), crater filling on the last pass.  I'll try to get some pictures on here soon.  Thanks for the suggestions so far.
Reply:I finally have a picture.  Unwelded part on the left and welded on the right.  This particular welded one does not have the hole at the end of the last pass but just imagine a worm crawling out of the crater at the end there.  These parts have been sitting a while so they are dirty and rusty.  We don't run dirty/rusty parts in production.  Again any brainstorm of ideas would be much appreciated.  Thanks. Attached Images
Reply:Sounds like a blowhole to me. Are you venting at all?Air pressure can build up in the pipe during the weld. At the end the air is trapped and has no where to go but up and out of your crater.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Shovelon,We are not venting at all.  It has been mentioned to me before though.  Just to clarify, the round bar is solid bar not pipe.  I'm not sure if venting is an acceptable possibility yet.  Thanks.
Reply:Originally Posted by toonautiShovelon,We are not venting at all.  It has been mentioned to me before though.  Just to clarify, the round bar is solid bar not pipe.  I'm not sure if venting is an acceptable possibility yet.  Thanks.
Reply:I've done a bit of orbital welding. Normally I slope down the amps during the last 180 degrees of welding. No problem with holes. When I hand TIG I always walk the cup / puddle off to the edge slightly and lower the amps.Lincoln SA200's... at least 15 - 20. They come and go. Growing partial to the "Short Hoods" in my old age. Last count on Short Hoods was 13 in possession.
Reply:Does that bar go through the plate? If yes how tight is the fit up? One thing I've noticed over the years, mostly tig welding, is if you have an extremely tight fit up (where you actually have to bang it) or if it doesn't go all the way through. If you don't have 100% penetration, you'll have a small air gap in the corner of the weld. That air gap once you get to the end, is bridged and blows out your weld. If I were tig welding this, on my root pass, I would use as little filler as possible to ensure the weld is fully washed out into both parts. And actually I usually "backlash" the weld so that it doesn't have a little gap on the back side of the weld. Its easy to find out if thats what happening. Cut one of your parts in a cross sections and see if you can spot that opening. Mind you there will still be a small gap under the part but its not that much volume. To make your life easier, have a stronger part, if those bars don't go all the way through, you should make them as such. You can get 2 welds on there (where you're welding and on the backside of the plate. You can have it so that the weld is sitting halfway the bar. But making that bar go all the way through, it creates a gap for the air to escape.