SPC for special characteristics - CSR - Control of SC and CC

Hendor

Involved In Discussions
Good morning everyone
A query

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I would like your support in interpreting these specific requirements of my client for the control of SC and CC. In current practice we use XR but do not pay much attention to cpk. And the truth is that XRs are a headache, because we have many characteristics of this type, in addition to our control plans, sampling is usually every 1 or 2 hours for the vast majority, so in order to do a good job we would need a army of inspectors.
My expectation is to simplify it so that it really adds value to our process, complying with the requirement, in your experience what tools you can recommend me to use, or what alternatives could I have?
Could it be CPK and Histogram? What do you think?
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
For those processes with random, independent outputs where traditional Shewart charts apply, SPC and Capability are not even connected. Two divergent calculations that they are asking to be met simultaneously. SPC charts are nearly meaningless if you are using them for any other reason but to make decisions on a process - decisions that lead a person to interreact with the process. (THAT is the value of charting.) If they are effective, operators only interact based on SPC charts indicating the need - avoiding overcontrol. That means, you should have about 5 data points between interactions to have enough resolution to catch the process before it wanders out of control. You need to collect time-ordered sequence data to see how long the process can operate without intervention to determine the frequency of checks. Then, divide that time or number of parts by 5. That is your frequency. That frequency could be once a day, or every other part. The process determines the frequency (voice of the process) - not your convenience or comfort. Also, often controlling one characteristic may be adequate to assure other characteristics are in control - so you may not need to chart the other characteristics.
 
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