Weld Spatter and Weld Nut Threads

What is the maximum amount of welding that you can do before you get to the bolt stage ? Welding a frame together then tapping and creating bolts later is not an option ?

Thanks. Inclusion of the weld nuts is an integral part of the chassis assembly process. Some of the sub assemblies already have the weld nuts installed and then when these are welded into the chassis the weld spatter contamination occurs. So unfortunately tapping and creating bolts later is not an option.

Thread compound in the nuts will keep spatter from sticking.

Yes, and we are also considering anti spatter compounds. Problem is that in a production environment any additional operation and the adding of material costs money and will be resisted by the production and finance guys.

You're spot on!

To take the problem a couple of steps further..........next you get fixing bolts losing torque due to damaged threads or worst still parts falling off. The the warranty costs rise, the bean counters sweat and production is forced to do right what should have been done right in the first place!

It may get too hot for this, but, could you use something like a plastic plug that pushes into the threads. (Cap-plug) I know, it's still another operation. Maybe order the nuts with the plug in place? On, no, another P/N and stock location.

I don't suppose a piece of tape/film over the open end of the nut???? left in place till the engaging threads displaces it? Quicky dots? Nope, anything you do will add labor to the part.

Molded PVA plugs which mask the threads then dissolve during a subsequent cleaning operation? Nope, too expensive!

Sounds like you're the problem here. You see a problem where no one else does.

The devil really is in the details.

Good luck!

I'm thinking along the lines of a easy to push in plug but plastic will melt during the welding operation. The plug has to be easy to take in and out and be re-usable. The other consideration is that the frame is swung around and rotated as it progresses along the assembly line so the plugs musn't easily fall out.

Or forget the plugs and retap all the holes with a hand held machine that will correctly retap the threads without damage. Problem here being how does one ensure that the tap enters squarely?

You have listed arguments that production and finance guys will give you. Then it needs to be shown what cost is involved in wages to correct the problem each time it happens.

Can you throw an aluminum (or alternative) bushing over the threads, screw on a nut to tighten and weld away ? Then you could pull them off for final assembly ?

or...... How about utilizing something like car battery terminal cleaners with the wire brush inside to just save time and slide them on to the necessary parts (they may grab the threads tightly if the bolt is large enough) so it doesn't involve you adding time to screw something on, etc. Then you could just pull and pop them off, pop them on ???

How do you hold the nuts in place during welding?

If your fixturing used a pin that matched the ID of the nuts to assist in their location, then the thread is physically protected by that material until the fixture is removed.

Win/Win situation. Nuts always in the right place, no spatter on the threads. (Don't use plastic, and be prepared to replace these fixture points every few thousand repetitions.)

Otherwise, find another fixturing method for the nuts that doesn't involve welding. Such a design change may provide an even greater saving and make the bean counters even happier.

Expulsion (spatter) during nut welding can often be minimized or eliminated by using better weld schedules and equipment. The spatter can be minimized by using a low inertia weld head and increasing the welding force. Spatter is caused by a dynamic drop in weld force that happens as the weld projections collapse. By maintaining weld force on the nut throughout the welding cycle, spatter can usually be minimized or eliminated.

I've used tube ends or caps. The first shinny one from the left. They are reusable and cheaper than thread chasing.

I've used short pieces of rubber hose and I've used bolts too. You could the nuts with thread compound in them.

You could try taking a lead from the Germans. Some of them use a cardboard plug pushed into the thread and leave this on the vehicle, where it's pushed out by the bolt and drops into a body cavity.

Inexpensive, easy to fit, and no removal problems.

Can you fabricate a quick clamp with welding cloth pads to clamp over the nut during the welding process? Something like a clothes pin with heat-proof pads where the jaws meet.

Well one means to solve your problem would be to protect the thread/nut with a preformed cap made out of copper, the weld splatter will not stick to the copper and most likely will not penetrate through the copper skin when welding.

Brian

I find a little dob of vaseline inside the nut keeps me from having that problem.

That was a serious comment guys!

Use to be an engineer for a short time in body metal and I thought there were teflon coated nuts to solve this very issue. It doesn't help your bean counter issue as "they" never track the peripheral costs (OT, rework, etc) that the plant incurs due to "their" unwillingness to pay a few cents extra now. Someone will definitely come up with a brilliant cost saving idea to remove it later, but for now it could get you through. Most suppliers that offer the weld nuts usually have a version with teflon or other coating. good luck.

Order your weld nuts with teflon on the threads. We have the same issue with a Ford grill bracket. The manufacturer of the weld nuts has a process where the teflon is sprayed into the nut after the threads are cut. We use a nut with a M5 thread, but they can do up to whatever... www.premierrivit.com This is who we deal with, I'm sure there's one in your area. We also tried using silicon plugs, but they didn't last, and the cost was a bit much.

Switch to TIG/GTAW and there is rarely any splatter. Done right the weld is very strong and looks very good.

Brad

teflon coated magnets?

Apply fresh grease to threads of bolt. When the weld spatter hits it it will not stick to the metal threads.

It's the nut, not the bolt.

It will work on the nut too

I have past experience with sort of problem in Automotive robotic welding processes. I've tried three solutions with varying levels of complexity and success.

There is a thread coating available called, "Nycote." Nycote reduced the frequency of issues, but in some cases spatter would melt through the coating and stick to the threads anyway. This solution worked well for 6mm and smaller nuts, but we had multiple failures with 12mm nuts and were forced to abandon the practice on larger bolt sizes due to customer complaints.

A second solution is to insert soft plastic plugs into the nuts prior to welding, then remove the nuts when welding is complete. This solution is highly effective at preventing spatter inside the nuts, but you will also need sensors to verify that the plugs are in place in order to ensure that you do not have failures due to operator error.

Another solution is to install Syron(R) Nut detectors embedded inside retractable or fixed (depending on application) locating pins to match the ID of the nuts. This will reduce the amount of spatter that can get inside the nuts and verify that the nuts are in place at the same time. The sensors have adjustable sensitivity which can be used to detect the presence of threads in the nuts.

ok a lil primitive but ... its a copper cap with a pull tab and a v-spring. Push it in the hole the spring holds it there and the copper cap blocks the hole.

Do you know if these exist?

It's a great idea.

I have seen similar in use as a decorative cap ... wouldn't take much to make though if it was something that would decrease your repair time it would be a good investment.

Scrap soap or wax into the nut

Have you considered coating the threads with a high temp silicone material that can be cleaned off after the welding operation is completed?

Your problem is an easy fix as long as the proof is in the pudding before you show it to your supervisors. There are a few ways to fix the problem, you have to decide which is quicker, cheaper and works. To change the jig or structural way in which the process is performed can be costly, To reduce the spatter is your first challenge as it is your root problem. If that is not an option, then shielding by means of anti-spatter spray or a piece of metal or non flammable material not touching but covering the nut over the threads may be an option. It is definitely cheaper to attach a shield once to all weld jigs that spot weld the nuts to the frame then to re-tap or change the nuts all over again.

I am not familiar with your particular operation but making sure that the nut is flush with the chassis may also prevent spatter from going between the nut and chassis to the threads during welding.