Porosity in weld

admin

I'm a new hobby welder and I've been playing with my new mig -  butt welding various scraps of 1/4" and 1/2" together and cutting them apart to see how they look and I've noticed some porosity in the welds.  The C25 flowmeter is set at 20cf/h and I'm getting the "sizzle sound" when welding so I think that I'm close to the proper settings on the machine, but I'm wondering if my shielding gas is set too low or my gun angle is too flat relative to the work piece.  I'm using .035 solid wire.  I realize there may be other things that I'm doing wrong but would either of these be an obvious reason for the porosity?Also, should I push or pull the weld if I have the option to go either direction?Thanks for any advice.
Reply:You have plenty of gas, maybe too much.  I think 14 cfh is best.  The gun "Leads" the weld.  Backhand, not forhand. The gas should be heading toward the finished weld.  15 degrees (give or take a little) tilt for flat work. work in the front of the puddle.  Try  a weave.  Welding each piece in a zig zag motion pausing a little on each side. What welder?  Wire speed?  Volts or Amps? Have funDavid
Reply:The welder is an HTP 2400.  It uses tapped power settings (1-4 coarse settings and 1-6 fine settings with a digital readout).  I tried to peek at the digital display without setting myself on fire and it was around 175 amps.  I never checked the voltage output.  Too busy just trying to remember to turn on the helmet and keeping the gun running on the seam among other things.  The wire speed control is on a scale of 1 to 10 so based on the machines maximum feed speed of 625in/min, I'm assuming I was at around 400+ in/min (6.5 on the dial).Just so I am understanding this correctly, should I be moving the gun forward toward the unwelded area with the weld bead laying down behind the gun?  The forehand/backhand description is a little confusing to me.I realize that there may be a dozen things that I'm doing wrong, but I figure that actually using the welder and asking a few questions can't hurt the  learning curve.
Reply:Lower your gas, try between 10 and 15 for optimum.John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:Just so I am understanding this correctly, should I be moving the gun forward toward the unwelded area with the weld bead laying down behind the gun?
Reply:some pic's would real help,anyway how far from work to tip is your gun wen you weld?ChuckASME Pressure Vessel welder
Reply:Originally Posted by SandyIf you tilt the top of the gun away from the bead slightly and in the direction of travel (drag) you will be pointing the wire and arc into the puddle as you travel it will allow the bead to stay molten longer. This will allow more time for gasses and impurities to finish floating out. We're talking decimals of seconds here.  BackhandIf you do the opposite, angle the top of the gun away from the direction of travel and the tip into the unwelded area (push), it will focus the wire and arc into the base metal with the motlen puddle behind the main force of the arc. This allows the puddle to freeze slightly faster. Forehand
Reply:I have been resting the edge of the nozzle on the work surface, starting with about 1/2" of wire protruding, and using the drag method.  I'm sure that my gun angle is way too flat, probably 45 degrees.  I'll get more vertical with the gun and see how that works and turn the gas down a little.At the heat settings I've been using, I can see (after cutting through the seam) that the weld is penetrating almost half way into the 1/2" angle iron stock.  Good, bad?  I haven't cranked the machine all the way up to its 240 amp max yet.  Maybe try that and work down?One other question.  If I am welding 1/4" plate to 1/2" plate should the welder "heat" be set for the thinner piece?  My novice logic tells me that if I cranked the machine up to the level recommended for the 1/2" I'd be toasting the thinner 1/4" stock.   Or do you use a setting somewhere in between? Thank you all for the helpful information.  I will try to take some pictures today and post.  Feel free to chime in with any other advice.Dave
Reply:I have been resting the edge of the nozzle on the work surface, starting with about 1/2" of wire protruding, and using the drag method.
Reply:For a great amount of information and easy-to-view and understandable pictures, read this: http://www.millerwelds.com/education...tips/MIG_tips/Very thorough and complete, it may answer all your questions. John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:Use your second hand to adjust the distance from the work, don't rely on the nozzle... lift it off the work and keep it at a right angle from the work.***************************************Lincoln AC225 stick welderLincoln HD100 WeldPak flux core wire feed welderThree of the cheapest grinders money can buy
Reply:Did you clean the pieces before welding?To answer your question about the thickness.  Set the machine for the smaller plate.  If you are getting 1/2 penatration, then the other side will make it full.  No need in welding a 1/2" weld on both sides of a 1/4" plate.My Lincoln wirematic 250 only goes up to 5/16 by the chart and that is Really Hot.  I think its 20 volts, 360 ips for .035 wire and C25.  My memory could be off.It would be easier if you bevel the edge , ran a little less heat and made a second pass.DavidLast edited by David R; 02-16-2007 at 06:35 PM.
Reply:David,Thanks for the tip on differing metal thicknesses.  I used a flap wheel to take the metal down to "bright and shiny" however I did not use acetone as I've heard others talk about.  Is that a must?  Also, if you are making a second pass, should you stop and clean the first weld bead or can you merely go over/around it?My practice butt-weld pieces were two 1/2" angles so, with the rounded edges, a bevel was sort of built in.  I see that the learning curve is pretty steep at first but I'm feeling a little more comfortable with each attempt.  ThanksA second question popped into my head after I posted this.  When it's said that you can weld a certain thickness in one pass, does that mean, for instance, that on 1/2" stock your weld will penetrate all the way through the 1/2", or that the total of the depth of penetration into the base metal + the thickness of the weld bead adds up to 1/2"?  It would seem that depth of penetration into the base metal is critical to the weld's strength in cases where you can't get at the opposite side for a second weld.  Is this a situation where you cut your bevels on the two pieces almost to the backside of the metal you are welding?   Kind of like this:       |___V___| (hard to draw with a keyboard)Last edited by ddonnell; 02-17-2007 at 09:02 AM.