Variables Gage R&R study for 8 Cavities tool - Die casting industry

P

pejcinovski

#1
Hello everyone,

i work in die casting indystry. I have tool with 8 cavities. For R & R study, should i take only one same part for every trial, every operator, or all of them???

Thank you:)
 
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P

prototyper

#2
Re: R & R study

Is this an attribute or variables study?
What type of gauge are you using?
 
P

prototyper

#4
Re: Variable R & R study for 8 Cavities tool - die casting industry

The R&R study is to assess how suitable the gauge is for the application so it doesn't matter which mould the parts come from. The important thing is that you select parts which cover the full range of the process.

Part selection is one of the most important aspects of conducting an R&R study and it is where most people new to R&R go wrong.
 
P

pejcinovski

#5
Re: Variable R & R study for 8 Cavities tool - die casting industry

So i should take and measure the same part and same dimension in every trial, and for every operator???

Thanks
 
R

RickHiller

#6
Re: Variable R & R study for 8 Cavities tool - die casting industry

Part selection is one of the most important aspects of conducting an R&R study and it is where most people new to R&R go wrong.

Could you expand this statement? I am dealing with small rubber parts molded in tools having hundreds of unmarked cavities.
 

bobdoering

Stop X-bar/R Madness!!
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#7
Re: Variable R & R study for 8 Cavities tool - die casting industry

Could you expand this statement? I am dealing with small rubber parts molded in tools having hundreds of unmarked cavities.
The point of gage R&R is to determine if the gage is the correct gage for the job. That is not related to the number of cavities, except for the fact that the sample of parts you are verifying with the gage should be representative the the amount of variation that specific dimension will have. Which cavities the samples come from are not important.

Also, mark the parts and have the operators measure the dimension at the exact same location every time.

I prefer 3 operators, one very well trained, one of the least trained that would likely use the gage, and someone in the middle. This generates a result that should be applicable with any potential future operator. I would suspect that is particularly important when measuring rubber!

Make sure you watch the gage R&R process - observe the technique variation (another common error). If the gage R&R fails, you may need to control the technique to get it to pass, rather than buy a more expensive gage. If you have the AIAG book, be sure to pull out the list of between and within errors, and watch for them during the Gage R&R process.
 
P

prototyper

#8
Re: Variable R & R study for 8 Cavities tool - die casting industry

The parts selected should be representative of the whole population of your product, i.e. take one part from the lower end of the population, one part from the upper end of the population and the rest somewhere in between.

One of the reasons for conducting GRR is to determine if the gauge can distinguish between distinct categories of parts within the population. If you take consecutive parts from a process they are unlikely to include all of the variation you would expect over a long period of time and you will more than likely get a poor result on the GRR.
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#9
Re: Variable R & R study for 8 Cavities tool - die casting industry

Could you expand this statement? I am dealing with small rubber parts molded in tools having hundreds of unmarked cavities.
Also, for rubber parts, watch out for gage pressure. Low pressure or non-contact gages should be the preference, especially as the lower the durometer gets.
 

Miner

Forum Moderator
Staff member
Admin
#10
Re: Variable R & R study for 8 Cavities tool - die casting industry

The parts selected should be representative of the whole population of your product, i.e. take one part from the lower end of the population, one part from the upper end of the population and the rest somewhere in between.
Be very careful with this statement. If the gage will be used for inspection and the metric used is the P/T Ratio (%Tol), this statement is fine as is.

However, if the gage will be used for process control and the metric used is %GRR (%SV), this statement is misleading. The standard deviation of the samples used must match the standard deviation of the process. You may or may not achieve this by sampling as you suggested.
 
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