Process capability (Cp & Cpk) , Standards and quality , General studies , UPSC ESE

 Process capability

• It is used to measure the goodness of processs specification.
• A common measure of process capability is given by 6sigma which is also called as process width.
• It is used to measure the goodness of process performance and it is used to measure whether your process is capable of producing 99.73% of the product within the specification limit.
• Cp if the ration of specific width to process width.

Specific limit

• It is determined by the need of customer , what customer want in the product or services is analysed through market research , the limit are placed on the product are decided by designer and engineer.

Case 1

• Process is capable and centred
• 
  Process is capable but not centred.
• 
  Process is neither capable nor centred.

Case 2

• Process is just capable and centred
  
• The process is neither capable nor centred
  

Case 3

• Process is not capable nor centred.

Result

Question: when process mean is outside the specific limit in the value of Cpk is ----------

Question: when the process mean is coincide with specific limit , what is value of Cpk-------

Answer : Cpk = 0

Capability ratio (CR)

Question: the relative humidity in a green house is excepted to be 65 % and 85% , randon sample taken over a span of 1 week yield the following value 60%,80%,78%,70%,84%,81%,85%,60%,75%,88%. find the capability ratio and capacity ratio.