Process Capability & Inspection Frequency: Is there any relationship?

D

Don Watt

#1
Hi,
I'm relatively new to Quality in Manufacturing and I'm trying to establish how often we need to do a confirmation check on parts from a grinding process.
Is there any recognised correlation between process capability indices and inspection.
e.g. for a Cpk <1.33 recommended minimum inspection frequency = 1 in 50 ??

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Marc

Hunkered Down for the Duration
Staff member
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#2
Not that I know of - maybe one of the experts can comment on this.
 
#3
No expert here,but,I will make the assumption that you are using SPC charting. If so, and the process is in statistical control, then there is no defined interval. Watch the chart for trends and act accordingly.
On the other hand ,if you are asking how many times do you check and record on the chart; minimum of once per shift. IMO I would use sampling based on number of parts produced to determine how many times to take a subgroup.
Don has some excellent articles on his web site for sampling.
 
D

Don Winton

#4
<font COLOR=BLUE><BLOCKQUOTE>Is there any recognised correlation between process capability indices and inspection. e.g. for a Cpk <1.33 recommended minimum inspection frequency = 1 in 50 ??</BLOCKQUOTE></font>

As far as I know, there is not a recognized relationship between process capability and sample frequency. This is probably best defined by your process.

Regards,
<A HREF="http://saturn.spaceports.com/~dwizard/home.html" TARGET="_blank">dWizard</A>
 
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