Spot Weld Nugget - MSA Gage R&R

#1
After lurking in the shadows for some time now and using the search bar to gain knowledge rather than pester you all with the same questions, I've decided my first post will have to be just that, pestering you all for help with regards to MSA, so here it goes...

I work in the automotive industry supply chain and have been tasked with conducting an MSA study (Gage R&R) on the process of measuring spot weld nugget sizes using the external faces of a vernier caliper.

My first question is,

Considering I have previously conducted studies relating to the use of external faces of a caliper (eg: plug gages) would a study on weld nugget sizes need to be carried out? Should there be an MSA study for every in-house measurement process we use a caliper for, or should the focus be on the caliper and every function of it that we use rather than each individual process?

We use alternative methods like Ultrasonic non destructive testing to confirm spot weld integrity and size. The focus on MSA and nugget sizes has came from above due to certain spot welds being classed as "Important A" characteristics.

My second issue is,

I can create samples using the same spot weld, off process, and have the actual nugget sizes confirmed to create a nominal value for each sample. I am aware there is a standard calculation for average spot weld sizes relating to material thickness and also a minimum standard for nugget sizes expected after a teardown but as far as I am aware, there isn't a tolerance that we work to that we can apply to the measurement results. (eg, nugget size = 6mm dia / ±1.0)

If anyone has been successful with a similar study, knows how to set this up or has any input / information at all, it would be greatly appreciated.

Thanks for your time.

Paul.
 
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#2
I work in the automotive industry supply chain and have been tasked with conducting an MSA study (Gage R&R) on the process of measuring spot weld nugget sizes using the external faces of a vernier caliper.

My first question is,

Considering I have previously conducted studies relating to the use of external faces of a caliper (eg: plug gages) would a study on weld nugget sizes need to be carried out? Should there be an MSA study for every in-house measurement process we use a caliper for, or should the focus be on the caliper and every function of it that we use rather than each individual process?

We use alternative methods like Ultrasonic non destructive testing to confirm spot weld integrity and size. The focus on MSA and nugget sizes has came from above due to certain spot welds being classed as "Important A" characteristics.
I recommend that you begin by reading my blog on Creating Gauge Families.
  • In regard to the question "...would a study on weld nugget sizes need to be carried out?", yes, you should perform a study on nugget size because the measurement of a highly irregular feature is much more difficult than measuring a highly uniform object such as a gauge pin.
  • For the second question "Should there be an MSA study for every in-house measurement process we use a caliper for...", no. It is not quite as simple as just studying the caliper and every function that you use (i.e., outer dimensions, inner dimensions and depth), but you can create gauge families as described in my blog.

My second issue is,

I can create samples using the same spot weld, off process, and have the actual nugget sizes confirmed to create a nominal value for each sample. I am aware there is a standard calculation for average spot weld sizes relating to material thickness and also a minimum standard for nugget sizes expected after a teardown but as far as I am aware, there isn't a tolerance that we work to that we can apply to the measurement results. (eg, nugget size = 6mm dia / ±1.0)
Based on this, may I assume that this measurement will be used for the purpose of process control (e.g., SPC) rather than for inspection, or do you mean that you do not have a bilateral tolerance, but a unilateral tolerance? If the latter, see my blog on MSA for unilateral tolerances.

What do you mean by "...using the same spot weld, off process..."? Do you mean using the same welding equipment, the same materials being welded, etc.? Will these welds faithfully represent the actual manufacturing process?
 
#3
Thank you for the reply Miner.

I've been asked to conduct the MSA study due to the measurement process being documented on the control plan. What I mean by using the same spot weld is that each spot weld on a part is identified with a number. I can then create samples using an amount of parts needed, taken from the actual manufacturing process, and focus on the same spot weld per part / sample, maybe weld number 1 for example. So maybe,

x10 samples (torn down to reveal weld nugget and nugget size confirmed / agreed upon)
x3 Appraisers
each measuring spot weld number 1, 3 times.

As for the tolerance, the customer standard suggests there is only a minimum nugget size based on material thickness.


Thanks for the links to the info, I will indeed be reading up on those.
 
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