Spot weld spatter

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Hi everyone! First time poster with a quick question. Does anyone know of a method to prevent weld spatter from a resistance spot welder? I work with the automotive industry and right now I'm having trouble coming up with a solution to this. We use anti-spatter sprays with our mig welding but it is not practical to use with spot welding. It's too messy and dries before the welding is complete. Any suggestions would be appreciated.
Reply:There was actually a pretty good article on just that a few months back in Body Shop Business, one of the factors being the proper amount of pressure has to be applied to the material being joined. too much pressure is as bad as not enough, the common mistake being to squeeze the crap out of your work and let fly with the sparks. Contrary to popular belief this actually causes the area you are joining to melt and squeeze out from under the tips, making your joint paper thin. I don't have any experience using the equiptment, but the article states you should expect NO sparking if you have the machine set up right. I would suggest you do a web search for the proper settings for your machine if you don't have the paperwork or manufacturer support available. You can also try searching through past issues at http://www.bodyshopbusiness.com/ and see if you have any luck, 2006 article. Good luck!Last edited by Clanweld; 01-25-2007 at 04:27 PM.If you don't have the time to do it right, then you definitely don't have the time to do it over.
Reply:PawBill, I'll tell you of my experience with resistance welding, it's somewhat different, but the basics should hold for your application.  The process I used was called resistance upset welding.  Four threaded studs, something like a 1/4-20 bolt with a round head rather than the hex, were resistance welded onto the surface of cylinder a couple inches in diameter and maybe four inches long.  The studs were in a square pattern and had to be very straight and perpendicular to the top of the cylinder.  The part and the studs were precisely held in a fixture with drill bushings guiding hollow Elkonite electrodes, to apply force and current through the head of the stud, and the part. The welding machine was essentially a huge press, and the studs were welded one at a time with about 2000 lbs of force and 10,000 amps for about 5/60th of a second.  The studs were welded into counter-bores in the cylinder, with the head of the stud being bigger than the counter-bore, so when first loaded up, the stud sat up on the top edge of the counter-bore, and as current was applied, the interface around the stud heat and counter-bore heated, and the stud was squished down in to fill the counter-bore.So, to continue making a short story long, the original process used a much longer, 1 second weld time, and a lower amperage, around 8000 amps.  This process had three major problems, 1. the tensile strength of the weld was too low, 2. the electrodes overheated, mushroomed, and stuck to the surface,  and 3. the studs all leaned toward the center of cylinder.This was all solved by reducing the weld time to 5/60th of a second, and raising the current to around 10,000 amps.  This short/hot weld increased the concentrated heating at the weld interface and increased tensile strength.  The short time prevented excess heat transfer away from the joint into the electrode and surround base metal, thus eliminating the electrode problems and the stud tilting.  The tilting occurred because of nonuniform current flow around the stud.  With little cylinder mass between the stud and the O.D. of the cylinder, less current and heating occurred here.  Toward the cylinder I.D., more heating caused thermal contraction to pull the studs inward.  The short duration weld, with concentrated heating, minimized heating difference between the I.D. and O.D.Regarding spatter, also called expulsion.  Resistance welding is primarily a solid state bonding process, where the metal is not melted, it is heated and pressed together allowing atomic diffusion across the joint to make two pieces into one.  In most cases, some melting does occur, and sometimes it is squirted out from under the electrodes, hence expulsion.If the force on the electrodes is too little, the resistance between the electrodes and the base metal, and the resistance in the joint, may be too high, resulting in localized melting and expulsion, as well as electrode sticking.So the force has to be high enough, but no so high as to squish the joint entirely when welding.  The weld time and current and have to be balanced.  Shorter times allow higher current and more concentrated heating, while longer times must be paired with lower current and more bulk heating.  The short/hot weld is probably more prone to expulsion, since heating is concentrated, and the operating range of current is narrow.Maybe you can find more info through AWS and the RWMA.http://www.aws.org/rwma/articles.html