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Bibbt 01-31-2021 11:51 AM

Resistance welding 430 stainless ?
Besides my introduction post, this is my first real post on this forum. Lot's of experts here so hopefully someone can give me some advice. I have searched the web and can only find scientific papers with data only a metallurgist would understand. I need real world advice from someone that welds. Thanks in advance to anyone that can help.

I have a non automotive project where I need to spot/resistance weld 2 pieces of .020 type 430 Stainless together. This is a very small part about the size of a 9 volt battery so I will probably only put 1 or 2 welds on the part. I need to weld roughly 1300 of these parts.

I have a 220v Miller spot welding machine on a stand with timer and foot pedal. I used the thing 1 time on another project years ago and its been sitting. I damn near sold it and glad I didn't.

I haven't done any testing yet but can someone chime in here that's done something similar with Type 430 and give me some tips for success ? I keep reading that some types of Stainless don't don't spot weld very good.

Bibb in San Antonio

Metlmodr 02-01-2021 09:41 PM

welding 430

It is difficult to make a sound structural weld in grade 430 by fusion techniques. The limited phase change at higher temperatures gives coarse ferrite grains with grain boundary martensite films in the HAZ. Precipitation of carbides during cooling also leads to sensitisation. Welds are both brittle and have lowered corrosion resistance. Post weld heat treatment is able to achieve tough, corrosion resistant welds, but the cost may outweigh the cost of using an austenitic grade. The grade is not used for structures.
Grade 430 can be joined by spot, seam, and induction welding. Grade 430Ti gives better toughness and corrosion resistance in the welded zone. However, the surface appearance of 430Ti is inferior to 430 due to the presence of particles containing titanium, which intersect the surface.
Grade 309 filler metal is normally used for fusion welding. It is pre-qualified in AS1554.6:1994 for welding grade 430 to itself, carbon steels and most stainless steels except the duplex grades.
Similar curves apply for many different corrosion situations. Grade 430 has slightly lower chromium content than austenitic grade 304, giving inferior corrosion resistance.

Bibbt 02-02-2021 06:05 PM

Thanks for the very detailed reply. Most of it was way over my head but correct me if Iím wrong but you are basically saying type 430 doesnít lend itself very well to spot welding? How bout type 304 stainless?

Since I posted my question, I acquired some.020 inch type 304 stainless that is 1/2 inch or 13mm wide on a 100 foot roll. It is economical and readily available. This material is used in various industries. In the USA, many traffic signal lights are strapped to poles using this 304 banding strap. The HVAC industry also uses it for securing insulation to large chiller pipes.

I prototyped one of my parts with it and it seems to form nicely and work harden so it retains itís shape. Iím leaning towards using type 304. So far, it checks all the boxes. So what is your opinion on spot welding 304?

Bibb in San Antonio

skintkarter 02-02-2021 11:53 PM

Bibb, certainly not an expert here, but spotwelded 304 is everywhere. Think of anything - BBQ bits, potbelly stove flues and hats, v-bands for exhaust systems etc...

If it were me, I'd be grabbing some of the band-it strapping you have, whacking it through your old welder and giving it the standard panelbeating destruction test (tearing the weld apart).

Is there some nasty environment that your bits are going to end up in which requires a higher grade?

bobadame 02-03-2021 12:08 AM

304 Stainless steel is probably the easiest metal there is to spot weld. Here's a link to a basic spot welding manual in pdf form. There's useful information about the proper welding tip shape and size to use for various material thicknesses. Also time and pressure. You will need to water cool your welding tips due to the quantity of pieces you are welding.

Bibbt 02-03-2021 12:11 PM

Bob and Richard,

Thanks for the helpful input. My device is a battery holder/clip that is used with a 9 volt battery to power a vintage camera. It's really small, think 9 volt battery sized.

The metal isn't subjected to any king of nasty environment unless god forbid the battery leaks. I just chose the 304 stainless banding strap because it has the correct dimensions right off the roll and it is readily available and cheap. It also seems to form nicely and retain it's shape from work hardening. The fabrication shops that made these parts for me in the past used a really obscure aluminum type 5056-H34 that is only available special order in massive quantities so I had to find a more "normal" material to use. I'm sick of dealing with fab shops 2000 miles away so I am bringing all of this back into my garage like when I prototyped this thing 20+ years ago. Sometimes you gotta do things yourself to get it done right and economically. I'm definitely on a shoestring with this pandemic.

I'm gonna drag out my spot welder later today and do some testing. Hopefully the welds are successful and my part retains the "springiness" that is required after heating up. Only way to find out is through real world testing and keeping notes of what I do.

Not exactly sure of the model of Miller welder I have but it is 220v with a timer and is mounted to a stand with a foot pedal to close the tongs and activate the timer. One of you guys mentioned using water-cooled tips/tongs. I don't believe this is an option on my entry grade welder unless someone out there makes a kit to convert it. Please chime in if you know of such a conversion kit. Otherwise, I will just have to go slow and let the machine cool. I'm betting the weld time will be pretty short on .040 total thickness. Thanks for the info guys and I will report how my test goes.

Bibb in San Antonio

Bibbt 02-03-2021 06:54 PM

Ok, so I pulled out the spot welder to do some testing today and had ZERO sucess. I thought this was gonna be easy. I'm thinking the last time I did this it must have been beginners luck. Of course the material was much thicker mild steel though.

Just for the record, my machine is a Miller LMSW-52T 220volt with roughly 6" standard tongs and tips that came with the machine. I'm thinking this might be too powerful a machine for what I am trying to weld. This machine only has time adjustment and NO current adjustment. Even at 1/4 to 1/2 second, the tips burn right through the material. The material is 2 - 1/2" wide x.020" 304 stainless strips. Nice and clean and flat. I tried adjusting the tong pressure and it either burnt a nice clean hole threw the metal or welded the tips together.

Is there any device I can put on my machine to reduce the current? I'm looking for suggestions. Should I be looking at one of the spot welding machines that are used to spot weld battery packs? Any advice is appreciated.

Bibb in San Antonio

bobadame 02-04-2021 02:07 AM

Heat, time and pressure are the main factors you have to work with. Since you have only one heat setting you will have to work with time and pressure. Your machine will have to be set up so that forge pressure and the weld switch are independent of each other so that they can be controlled individually. In other words, bring the tips together against the metal with some amount of squeeze pressure then initiate the timed weld cycle with a switch. Also, be sure that the tips are aligned exactly over each other when they are in the squeezed position. They might flex a little and become misaligned under pressure. If the tips are burning through try to increase their surface area by sanding them. The process is detailed in the Acme pdf. The copper arms can be water cooled easily. You'll need a 5 gallon bucket, an aquarium pump, a few feet of vinyl tube and a couple feet of 1/4" soft copper tube. Wrap a length of copper tube around each of the welder arms. Connect them in parallel with the vinyl tube to the pump then drain them both back to the 5 gallon bucket.

Bibbt 02-04-2021 03:22 AM

I will take everything you said into consideration and give it another try tomorrow. Pretty sure tips are aligned and dressed nicely but I might experiment with making the contact points larger. I see that Miller has a tip with a large flat surface that is recommended if you need one side of the weld to be smooth. Might consider trying one of those tips. Something I hadn't thought of was clamping and activating the timer separately. It's easy to do on my machine. I keep seeing references to reducing current by using longer tongs. The ones I am using are pretty short like 6". Is installing 18" tongs something I should consider? I'm already down around 1/4 to 1/2 second weld time so I can't really go any shorter. Again, your advise is appreciated.

Bibb in San Antonio

Steve Hamilton 02-04-2021 08:53 AM

hi Bibb

Not sure if it will solve your problem but i have had to remove the tips from the arms and clean them. they are threaded and oxidize over time causing more resistance.


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