|
|
Hey guys I was hoping some people could give me some ideas as to the cause of this problem I have been having. I do production welding and this "worm hole" occurs about every 3 parts in the same weld on each part.Pertinent information:Process: GMAW-PWire: ESAB Coreweld 77HS (metal core wire)Machine Settings: 350 IPM, 24.8 VGas: 90:10 at 40 CFMJoint and Material: 1/4 Wall A500 Steel Tubing fillet welded to 3/4" 1018 Steel PlateThis is an automated weld so travel speed, stickout, and push angle are consistent between parts. I do not grind off the mill scale from the tubing but I don't think this would cause this problem. The thing that really confuses me is that there is an identical weld made on the other side of the part (part is symmetrical) and this defect never occurs there. Here are some pictures of the defect in question.
Reply:Looks like a air pocket some how there's air being pressurized
Reply:I weld couplers into oil and water separators. I get the same thing but not over and over like you. But I also do a lot of prep work. The hole I had yesterday was identical to that one. I will ask around my shop and see what they say about it.Sent from my SCH-I535 using TapatalkJoe
Reply:Hello Duke, looks to be square tube welded down to an end plate. Do you know if the identification paint has been removed from the end of the tube? That stuff stinks when when you weld over it and often times causes the sort of "hole" that I see in your pictures due to off-gassing and the weld solidifying before the gasses have completely escaped. Another thought, if the tubing hasn't been wiped down and the rust inhibitor that they spray on it hasn't been removed completely a similar thing can occur. This can also be influenced and compounded by having the inhibitor being present internally as well. In some cases you might clean the end inside and out and then when you are welding the part in the orientation that the photos show the heat from the welding causes the inhibitor that is further up inside the tube to heat up and run down into the backside of the weld joint, wick out to the outside, and WAH LAH you end up with the pore or worse. Just a couple of additional things for you to consider. Good luck and best regards, Allanaevald
Reply:looks like a gas vent.
Reply:Is that the close out weld? If so, you are getting air pressure build up. You need to let the parts cool before the close out or drill a vent hole in a place that doesn't matter.Two turn tables and a microphone.
Reply:strange stuff, I had similar problems but with bronze wire. check gas lines and try to lower gas flow (that was the solution for my problem). Also why not using normal solid wire.
Reply:I see a tapped hole above the weld. Is it possible some left over tapping fluid is running down into the weld zone?And judging from how dark your lone silicon island at the end of the weld is I'd say maybe you need a change of wire to one with more deoxidizer in it. I'd tend to think that your welding right over the mill scale has probably used up most of that wire's deoxidizing capabilities. If you're absolutely married to using that particular wire it might be necessary to put a little more effort into the prep by getting the mill scale off and making sure there's no other source of contaminants like paints, oils or other hydrocarbons.
Reply:Need to look at your weld start parameters also. Your starting point looks like it could be backed up a 1/4 to 3/8 of an inch. Also may be just a touch of dwell time at the very beginning before starting the travel.
Reply:Originally Posted by aevaldHello Duke, looks to be square tube welded down to an end plate. Do you know if the identification paint has been removed from the end of the tube? That stuff stinks when when you weld over it and often times causes the sort of "hole" that I see in your pictures due to off-gassing and the weld solidifying before the gasses have completely escaped. Another thought, if the tubing hasn't been wiped down and the rust inhibitor that they spray on it hasn't been removed completely a similar thing can occur. This can also be influenced and compounded by having the inhibitor being present internally as well. In some cases you might clean the end inside and out and then when you are welding the part in the orientation that the photos show the heat from the welding causes the inhibitor that is further up inside the tube to heat up and run down into the backside of the weld joint, wick out to the outside, and WAH LAH you end up with the pore or worse. Just a couple of additional things for you to consider. Good luck and best regards, Allan
Reply:Ok Duke, it just dawned on me to ask this question: the side/weld that has the pore, is there a tapped hole on all of the sides where the welds have the pore? If so, there could be residual machining fluid that is in the thread grooves of that hole that might become liquefied and runny when the welding starts and then run down on the inside of the tube and be drawn into the backside of the weld and cause the problem. My mention of identifying paint has to do with the stock ends of tubing as they come from the mill. Likely, if these are saw cut this end has been trimmed off as most factory ends have quite a burr and are also generally not very square, if they have trimmed off enough, this paint will be gone and not be an issue unless somebody got over zealous and really piled it on. Your response to another poster states that you have tried from 35 to 45 CFH of gas flow. What sort of electrical stick-out and visible stick-out are you running? What size of nozzle? If you can, give all of the details of your machine parameters and such. You may already be aware, but "venturi effect" and "turbulence" can often also draw unwanted atmosphere into the weld zone and cause detrimental results. Be interested to hear what you finally attribute those pores to. Good luck and best regards, Allanaevald
Reply:1-Is this porosity on the last weld of the four weld sequence?If so, that indicates that residual heat buildup is, as others have commented, drawing hot melted oil into the puddle.(in flat welding, oil can literally be seen racing into a weld puddle)It only takes a micro-sized amount of oil to cause big time porosity and that hole belies what's under it-even more.If the tapped hole seen in the pics is only on this porosity weld side and doesn't exist on the other 3 tube sides,that's a big clue----residual oil from lackadaisical cleaning.[On a production assemble/weld job I've done for a local, medical/aerospace CNC shop for 20 years, thelast 6 or so, I've finally been able to get parts that are squeaky clean. They understand that if I find one oilypart--all the parts are going back to them for another dis-assemble and clean.] 2-Pulsed spray welding over mill scale is begging for contamination problems.It acts as a sponge, holding crap from the rolling mill and any other post-processing.Mill scale can and will hold/trap contamination that won't clean up without simply sanding/grinding it off;which is a pittance of the time/grief/embarrassment of dealing with porosity after the fact.3-As Allen mentions--the relative position of the contact tip face to the nozzle face--can make ALL THE DIFFERENCEin shielding gas flow turbulence inducing porosity. Big contact tip stickout (1/4" or more) can raise hell anddo so-intermittently.4-And, of course, the electrode wire, feed rolls, gun liner are clean and spiffy. If you've got automatic tip/nozzlecleaning/reaming, that might be changing the relative position of the nozzle face to contact tip face, as well.Blackbird
Reply:Originally Posted by 4956Need to look at your weld start parameters also. Your starting point looks like it could be backed up a 1/4 to 3/8 of an inch. Also may be just a touch of dwell time at the very beginning before starting the travel.
Reply:10-4. This is only the second time this part has been run (I didn't have any problems with porosity on the first run). I'm still dialling in the program.The tube is machined on a CNC, so no tapping fluid, just coolant, but I think you, aevald, and dave may be onto something with this. The confusing part is that there is an identical weld on the other side of the part (the weldment is shaped like an H and this weld is on the lower outside of one of the legs) and this is not a problem there.......a trace of coolant can produce lots of porosity--anything that can vaporizeI am running 5/8" visible stick-out, so about 1/2" electrical stick-out. The nozzle is 5/8" bore with 1/8" contact tip projection (this is to get into some of the tight joint on other weldments we run). The gun is at a 45* angle to the joint with a 15* push angle travelling at 18 in/min. I am aware of the affect that to much gas flow can have on a weld, but the fact that this is just a single hole and not the typical multiple bubbles you see from lack of gas coverage leads me to believe that this is not the case. 1. Yes, this is the last weld of the sequence (in fact, it's the last weld on the whole weldment). Looking though the parts, this defect seems to occur pretty much the same point along the weld. I'm thinking that this point may be when the part reaches a certain temperature and the little amount of residual oil from machining finally gets hot enough to drip down and contaminate the weld. I think you (and the other people who mentioned it) may have hit the nail on the head with this one.......the oil or coolant can literally race into the molten puddle after enough heat soak and spread into the weldment. ????Is this the only tapped hole close to a weld on that tube???2. We run pulsed spray over mill scale on pretty much every part we make and we very rarely see issues with contamination. My understanding is that pulsed spray is hot enough to cut through the mill scale. I could be mistaken though. Other than simply mechanically cleaning the mill scale off, what else would you recommend? Would running in true spray be better perhaps? I like the pulsed spray because it seems to handle variations in fit-up pretty well.......yes spray will fuse thru contaminated mill scale, but that's still dicey to do as a standard practice. Even running spray/pulsed spray, one may not be getting the desired amount of root/corner fusion thatthey wish--until the weld is sectioned for inspection, and often adjusting parameters to suit. There's nothing wrongabout using pulsed spray.If this is a high strength application, doing so to verify fusion vs. setup parameters is suggested.3. As previously stated, the contact tip projects 1/8" from the nozzle.4. Every thin is clean and tidy. The gun cleaning station does have a nozzle reamer, but I haven't had any problems with moving the nozzle around.Thanks again for the suggestions everybody. I greatly appreciate it. My thoughts right now are that I am going to change the weld sequence so that this is not the last weld made on the part. I'm hoping that will help prevent any residual oil from running down from the threaded hold and contaminating things. We run this part about once a month so I will report back with my findings then.Blackbird |
|
发表于 2021-8-31 22:24:09