Spot Weld Testing

[drawoh]

I am preparing a drawing of a stainless steel sheet test piece to test the set up of a spot welder. Our customer has called up a McMaster Carr part number that points to Stainless Steel 304 hardened to Rc40. Is (work) hardness a factor in spot welding? I assume we will try to rip this thing apart to test the spot weld. Will it be hard in the heat affected zone (HAZ)?

Basically, does the hardness matter, or can I just write STAINLESS STEEL 304 on the drawing?

--
JHG

 

[r6155]

Code ??
Regards

 

[mfgenggear]

Very good question.
It depends on the weld prep, how clean and oxide removed is more important.
Here's what I say. Write down a standard procedure. Then destructive test using samples. Record the best settings.
Weld, test, record.
Use different settings.

 

[DVWE]

Is (work) hardness a factor in spot welding

It is not. Settings may vary slightly between different work hardened levels, but not greatly.

Will it be hard in the heat affected zone (HAZ)?

Not by much. Because of its austenitic structure, it is not hardenable by heat.

Basically, does the hardness matter, or can I just write STAINLESS STEEL 304 on the drawing?

Really more of a question for your customer. It will depend on its end usage. Perhaps they will need similar hardness numbers in the welds.

I agree with mfgenggear’s post above, except that I wouldn’t worry too much about removing the oxide layer prior to welding. I would simply wipe down the parts with acetone or similar solvent for cleanliness.


The devil is in the details; she also wears prada.

 

[mfgenggear]

Good comment by DVWE, except I would try ot with and with out oxide . It may not be as critical
With spot welding. But I seen better results.
And every machine is different and a starting schedule may or may not need adjustment.
I worked with stainless on the atlas program.
Spot welding was very critical. Scotch bright
Works wonders and only takes a few seconds.

 

[DVWE]

I agree on critical applications, but in those cases you will want to remove the oxide layer with a flapper disc or wheel. Scotch brite by hand after a few second scrub will only break down the oxide layer slightly. Spot welding is such a quick, intense heat from resistance that the oxide layer is vaporized. For normal applications and especially high volume stuff, not necessary.

The devil is in the details; she also wears prada.

 

[mfgenggear]

They do make it for rotary power tools
Let the results show the final results.
No harm in it . , if it does not need it fine.
But let the op have options. Famous last words not necessary. It is in critical welds[code

 

[DVWE]

You know what they say about assuming…but……

A part ordered from McMaster Carr is probably not going to be used for a critical application, but I digress. It definitely wouldn’t hurt to try.

For what it’s worth, my facility does about 1,000 spots welds a day on 4 machines and all different materials including carbon, stainless, and nickel based sheet, and combinations of all those materials. However, these are mainly for covers and skins. Definitely not critical. We don’t do anything more than a simple clean.

The devil is in the details; she also wears prada.

 

[mfgenggear]

Fair enough DVWE

 

[drawoh]

DVWE,

I suspect that they wanted stainless steel and they searched McMaster Carr for it.

Thanks everybody.

--
JHG

 

[mfgenggear]

I worked with every type of welding , sheet metal, machine shop and sub assemblies and major installations. Both commercial and aerospace. That said i am forgetting stuff.
Most fun was welding aluminum , the prep work was most important. But the stuff I worked on had to pass visual, zyglow, or mag, UT, and xray.
Some times pressure test. So I could be over reacting for non critical , no safety issues.
But never know when that may come up in one's career.

 

[EdStainless]

If that strength is what they will be using in production, then that is what you need to test with.
They may be buying this from McC because they just want a small amount for testing.
ASK
The harder material may require higher clamping forces, but the rest should be the same.
It will be a factor in the pull-apart strength.
The welds and HAZ will be softer.
Just wiping clean is typical for SS.
If you use acetone, it cannot be open to the air.
It will absorb moisture, and you will be leaving water on the surface.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[mfgenggear]

Then again it could pass, then fail as production start due to lack of fusion, clean with acetone must be prior to welding it does evaporate very fast.
Some cities or state don't alow it.
From what remember. Get acetone for work environment, you know epa stuff.

 

[mfgenggear]

Not sure I belive test were run were with test samples, were spot welded for first article. Then it was machined into a tbone to tensile test in shear.
It passed 99% of the time.
Very important no matter if commercial or aerospace to have a very loose
SOP, with lots of leeway. Give operators plenty of elbow room to adjust but yet have the minimum requirements.