Gage R&R Opinions: Are they effective ?

It’s a small thread but hopefully get some good feedback;

What is everyone’s professional and personal feeling on carrying out R&R’s?
Are they effective?

 

Least to say, Gage R&R is effective in addressing the customer requirements.
PS: Always wonder how they made the acceptance criteria. Such as <10% is good, 10%~30% is acceptable with connsideration of cost, >30% is unacceptable.

 

Depending on your manufacturing process it can be useful or completely useless. In our case, stamping, it is generally useless.

 

@Golfman25
Out of curiosity, could you please explain further why it is useless in the stamping process? Love to know more about other manufacturing process.
@Bev D
Sir, sometimes I really wonder the customers (auditers) really understand the essence of the Gage R&R. They just want to know whether you are doing it or not, and whether you do it in the AIAG`s way.
What makes it worse is that the one who is responsible for MSA in my industry also just do the same without a real study of the interaction between the process and the MSA tool. He/She just follows the book, not questioning the book.
When you got some kind of knowledge of how Gage R&R works, you can definitely use the excel to fabricate the data using some functions without trace.
It is a shame.

 

Stamping just isn't a precise enough process to make measurements beyond .000 useful. We find we have to use over precise gages to find enough variation to make the calculations work. And then you're always .00000 "off" which you can't fix anyway. In our case, we do draw forming and there is just way too much within part variation to do anything. Unfortunately many expect the process to act like precision machining or something. It just doesn't work that way.

 

To me, "way too much within part variation" means each measurement on the same sample using the same gauge would be quite different from each other. Am I right? If so, how to ensure the validity of the inspection measurement even with over precise gauges? Just can`t think it through. Or there is another way available to ensure the dimension requirements have been met?

 

So think of a part shaped like a cup. Maybe 1 or 2 inch deep. And lets say you have an OD dim of 2.500 +/- .002. You literally have an infinite number of measurement points around the entire OD and up and down the wall. And part isn't perfectly round and the wall isn't perfectly straight. And then you have the radius blends into the bottom of the cup. You basically need to measure the same places at the same depth to have any chance. Very hard to do with a hand gage.

How do you ensure the validity of the inspection measurement? Sometimes close enough, is good enough. You might be paying $0.10-$0.50 per part vs. machining them for over $1.00.

 

Now that assumes you can do something about the within part variation or do 100% inspection. With stamped parts, neither is feasible in most circumstances.

 

Can`t agree more on this sentence.

 

Sir, I am quite curious about how the failed MSA caused the catastrophic shutdown, and how the improved the MSA prevented it from recurrence.

 

The averaging is less about the gage R&R and more about how you want to measure the part. Vary rarely have we gotten a "good" gage R&R with averaging. Our best bet is to pick a single location on the part to measure.

We have dealt with this problem for 75 years. We frequently discuss with customers "how are you going to measure this?" Because how you do, will determine whether we even have a shot at making a "good" part. To use the example, our walls are never uniform thickness because we stretch metal. We have know that since fire was invented -- it's simple physics. So we can use an average, or pick a specific point, and send you parts. Or we can find the "bad" spot and never send you a part. Pick your poison. That is what a $0.10 ea. process gives you. If you need more, then you have to find a different process usually at significantly more expense. In most cases, you don't really need more. It's just the math and statistics that are telling you that you do.

In the above case, if you can dial in your process to make the part consistent over it length, then great. In our case it would require a re-writing of the laws of physics -- simply not possible.

 

@Golfman25

With all these years experience in the LED industry, although lack of the real opportunities to contact the customers directly (I am not a CS and we have the oversea HQ to handle the important customer, in these cases, we are just the information provider and the instruction follower), regarding the product SPECs customer gave to us, sometimes some of them are quite important. If you failed to answer them, you would definitely get into a BIG REAL trouble. Sometimes some of them are just not THAT importance. When you failed to answer them, nothing would happen.

 

I think part of the problem, as everyone is saying, is that it has become a check box. The actual calculations are only part of the R&R and everyone seems to forget it is a DESIGNED experiment. They just grab 10 parts, measure them 3x3 and plug, chug and hope. Consider the car itself - MOST cars only see normal city/highway driving, with some weather effects. But when they TEST cars, they salt spray, desert, climb mountains. (Aside: Sometimes referred to Multiple Environment Over Stress Testing, or MEOST). Why do this when the intended use is normal, every day driving? The answer is you learn more from exercising the car throughout it's POSSIBLE operation range, which is usually larger than it's INTENDED operation range.

An R&R is like this. For capability, we want a normal, in control process where we randomly take short subgroups. Hopefully, these cross shifts, etc, so we can see how stable the process is. But we are testing the process, so we set it up that way.

An MSA (the Gage R&R is a piece of this) is testing the measurement system. So we want to verify it on more than random, but well centered parts from the process. In the simplest case, imaging a scale on an assembly line that's rejecting things by weight to make sure some container is full. Almost anyone, when asked, to confirm it works will come to the conclusion they need to see the scale reject some as well as pass some. Some for under weight, some for over. We ask "Where's your rabbit parts?" or you no-go master.

An MSA is no different than this.

To intrinsically ask "are they bad?" is like asking "do hot peppers taste bad?" The don't in scrambled eggs, but ice cream? It depends on how skillfully they are applied. This is why it's not sufficient to know how to put the number in Minitab (or whatever) and click the right things to spit out an R&R. You have to understand what it is actually trying to do, and feed it appropriate test subjects. Which may in fact change based on what you are trying to confirm.

 

Great discussion! Really pays to read from people who are passionate with their fields.