Process Variability
natural or inherent (i.e., random) variability
in a process, in terms of process standard deviation
Process Capability Analysis
Study of how inherent variability in process
compares with product requirements
Uses of Process Capability Analysis
Predicting how well a process holds tolerances
Assist developers in selecting or modifying
process
Selecting between competing vendors
Reducing variability in a manufacturing process
Capability Analysis:
Determines whether the inherent
variability of the process output falls within the acceptable range of the variability allowed by the design specifications for the process output.
Cp can be misleading if _________________
the process mean is not centered between the upper and lower specifications
Assumptions of Cp
1. The quality characteristic has a normal distribution.
2. The process is in statistical control
3. In the case of two-sided specifications, the process mean is centered between the lower and upper specification limits.
If any of these assumptions are vi
T/F
If process is not centered then Cp should not be used.
True
The appropriate process capability index for an off-centered is____________________
Cpk
Cp represents the _________________ process capability index
potential
Cpk determines the __________________ process capability index.
current
A vendor's process with Cpk value of 1.25 is considered _________________
capable
A vendor's process with Cpk value of 1.33 is considered
highly capable
A vendor's process with Cpk value of 2 is considered
world-class capable (six sigma)
The ___________________ gives the fraction of the designed tolerance used by the distribution of measurements. In other words, it determines the % of tolerance used by the process distribution.
capability ratio
Product variability
variability that is inherent to the product itself
Gage Variability
measurement variability which is the variability due to measurement error
T/F
For a centered process, Cp= Cpl=Cpu=Cpk
True
Process capability ratio is defined as ____________________
.
the percentage of design tolerance used by a process.
It is ratio of Design Tolerance to Process Width. It is also reciprocal to Cp