Weld Nuts

By ssbn727 (*****)

Date 10-16-2014 08:22

Hi Tim,
I don't know if this is going to help without knowing more details regarding your application so, maybe this will steer you in the right direction:

http://spotweldinc.com/downloads/nut_bolt_spec/Inch-Bolt_cap_screw_torque_values.pdf

http://spotweldinc.com/set_up_guide.html

This is TWI's guidelines:

http://www.twi-global.com/technical-knowledge/faqs/process-faqs/faq-what-are-the-guidelines-for-projection-welding-weld-nuts/

This is an article from The Fabricator which may help:

http://www.thefabricator.com/article/shopmanagement/projection-welding-for-nut-and-bolt-attachment

You might want to call these folks and find out what they know:

http://www.internationalwelding.com/pdf/technical.pdf

I know that this may not be what you're looking for but, I thought it might be useful if you're considering an alternative method of inspection... And this article basically compares torque testing and UT for weld nuts. fasteners, etc.:

http://www.ndt.net/article/wcndt2012/papers/466_Stocco_Rev1.pdf

then there's these folks:

http://www.aws.org/rwma/

http://pubs.aws.org/c/424/resistance-welding?orderby=20&pagesize=50&viewmode=list

Here's the RWMA Directory index with plenty of contacts that may help in pointing you in the right direction:

http://www.aws.org/rwma/docs/2014-15_RWMA_Directory/index.html#/46/

You never know, these guys may be helpful also:

http://www.spotweldingconsultants.com/service.html

Here's some research from a university study regarding weld nuts, and the references use to write this paper show that Volume 2 of the Eighth edition AWS Welding Handbook was used in this study so take a look @ pages 531 to 579 and also in this book: Recommended Practices for Resistance Welding, 4th ed.,chapter 5, Projection welding, American Welding Society, pp.63-67.:

http://imtuoradea.ro/auo.fmte/files-2013-v3/BurcaM-IMT-Oradea-2013.pdf

Well, that's it for now Tim... I hope this helps.

Respectfully,
Henry

By TimGary (****)

Date 10-16-2014 14:31 Edited 10-16-2014 14:43

Thanks Henry and SJ.
I found a lot of the same links you posted Henry during my research. Good info there.
I was hoping that AWS has a definitive minimum values table somewhere, like they do for weld studs in B2.1 and D1.1, but maybe that's too much to hope for.

Does anyone have the RWMA - RESISTANCE WELDING MANUAL, REVISED 4TH ED?
Does it have weld nut torque requirements in there?

Thanks again,
Tim

By S J

Date 10-16-2014 17:27

Tim,

Maybe the RWMA would be the best folks to answer your question if you email them with your specific details. If their manual provides the information you are seeking, then you might want to consider investing in one.

Or, you could check with your local community college or AWS chapter welding publications library.

But, again, it depends on the materials, and then the weld nut sizes, and not all materials might be included in the tables.

Some of the weld nut suppliers MIGHT have tables with torque values; but, you might want to consider if the values are based upon optimum, nominal, or worst case parameter inputs.

If you are contemplating production QA test limits, you might want to also consider measuring the projection set-down - but, this approach requires the proper technology if in process monitoring is desired. As you might be aware, set-down is a measurement of the amount of collapse when the projections melt. In "theory", set-down might be used as another indicator of weld nut torque limits, but this presumes the projections are properly formed and the welding process is well controlled.

At the end of the day, do the weld nuts perform their intended functions? I have seen weld nuts so well anchored that test studs had their threads stripped off during torque testing. And, I have seen others with no weld whatsoever - due to missing projection buttons. Then too, some manufacturers use automated systems to perform in process torque testing on every unit - and you are probably wise, in cases like this, to seek the minimum torque value.

By S J

Date 10-16-2014 14:12

The short answer is that there probably is no existing AWS specification for torque test values for projection weld nuts; and the last time I checked, RWMA did not offer one either. But, this was several years ago, and the situation might have changed by now.

The longer answer is that many manufacturers that use projection weld nuts develop their own minimum torque test value limits based upon simple practical application needs.

As you are probably aware, the results attained may vary greatly depending upon the material chemistry, processing, surface treatment(s), size, and resistance welding parameters.

For this application, the least controlled parameter might be the weld force - but it really depends on the equipment design and condition, and how preventive maintenance is implemented.

Without proper process documentation and control, the development of a limit may not yield the optimum results for all the stakeholders who care about this issue.