Process Design and Process Capability

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Transcript Process Design and Process Capability

Process Capability and Capacity
COB 300 C
Dr. Busing
Process Capability
• Processes are inherently variable.
• Engineering sets tolerances or
specifications that tell range of values in
which individual units must fall in order to
be deemed “acceptable.”
• Statistical limits that reflect the extent to
which sample statistics can vary due to
randomness alone are called control limits.
Process Capability (cont’d)
• Process variability is natural or inherent
(i.e., random) variation.
• Capability analysis is used to determine
whether or not the inherent variability of the
process output falls within the acceptable
range of variability allowed by the design
specifications for the process output. It
refers to the ability of a process to meet the
specifications set by the customer or
designer.
Process Capability (cont’d)
Process Capability Ratio, Cp 
upper specificat ion - lower specificat ion
6
Process Capability (cont’d)
• Meaning – Process capability of 1.00 or greater means that
the process will produce virtually 100 percent
conforming output (the range of the process
output permitted by specifications is larger than
the actual range of the process).
– Process capability of less than 1.00 means that
the process generates output over a larger range
than the specification limits permit.
Process Capability (Example)
•
Food served at a restaurant should be between 38o C and 49o C when it is
delivered to the customer. The process used to keep the food at the correct
temperature has a process standard deviation of 2 o C. What is the process
capability of the process?
•
If the mean temperature of the food prior to delivery is 43.5 o C, what
proportion of all meals will be delivered at an acceptable temperature?
•
If management wants to ensure that only 0.1% of meals are delivered either
too warm or too cold, what specifications should they set for delivery
temperature?
•
What other course of action could management take to make sure that only
0.1% of meals are delivered either too warm or too cold?
Process Capability (Example)
Food served at a restaurant should be between 38o C and 49o C when it is delivered to the customer.
The process used to keep the food at the correct temperature has a process standard deviation of 2 o C.
What is the process capability of the process?
Process Capability (Example)
If the mean temperature of the food prior to delivery is 43.5 o C, what proportion
of all meals will be delivered at an acceptable temperature?
Process Capability (Example)
If management wants to ensure that only 0.1% of meals are delivered either too warm or too cold,
what specifications should they set for delivery temperature?
Process Capability (Example)
What else could management do?