General Motors' initial process study requirements

[xiong_xj]

In General Motors' customer specifics handbook, there is a requirement about inital process study for PPAP: When utilizing X-Bar and R charts, at least twenty-five subgroups (minimum of four pieces per sub-group) are required to obtain sufficient data for decision-making. When this amount of data is not available, control charts should be started with whatever data is available, or contact the authorized customer representative to develop a suitable plan.

I don't know the meaning of "When this amount of data is not available, control charts should be started with whatever data is available". Who can help to explain how to understand this sentence in detail?

Thanks a lot.

Singa

 

[Jim Wynne]

In General Motors' customer specifics handbook, there is a requirement about inital process study for PPAP: When utilizing X-Bar and R charts, at least twenty-five subgroups (minimum of four pieces per sub-group) are required to obtain sufficient data for decision-making. When this amount of data is not available, control charts should be started with whatever data is available, or contact the authorized customer representative to develop a suitable plan.

I don't know the meaning of "When this amount of data is not available, control charts should be started with whatever data is available". Who can help to explain how to understand this sentence in detail?

Thanks a lot.

Singa

If X-bar/R charts are appropriate, what they're telling you to do is start charting. There is also a requirement for a "significant production run" and if you've done that (or if you're going to do it) you should be able to generate enough data to complete the intitial study. If you aren't doing enough production to satisfy the default quantity of 300 pieces, or if, for example, it takes only 10 minutes to produce 300 pieces, you should talk to your customer and settle on a method for satisfying the initial process study requirement. Don't wait until the PPAP is due.