文档介绍：Process Capability Analysis
(Measure Phase)
Scope of Module
Process Variation
Process Capability
Specification, Process and Control Limits
Process Potential vs Process Performance
Short-Term vs Long-Term Process Capability
Process Capability for Non-Normal Data
Cycle-Time (Exponential Distribution)
Reject Rate (Binomial Distribution)
Defect Rate (Poisson Distribution)
Process Variation
Process Variation is the inevitable differences among individual
measurements or units produced by a process.
Sources of Variation
within unit (positional variation)
between units (unit-unit variation)
between lots (lot-lot variation)
between lines (line-line variation)
across time (time-time variation)
measurement error (repeatability & reproducibility)
Types of Variation
Inherent or Natural Variation
Due to the cumulative effect of many small unavoidable causes
A process operating with only chance causes of variation present is said to be “in statistical control”
Types of Variation
Special or Assignable Variation
May be due to a) improperly adjusted machine
b) operator error
c) defective raw material
A process operating in the presence of assignable causes of variation is said to be “out-of-control”
Process Capability
Process Capability is the inherent reproducibility of a process’s
output. It measures how well the process is currently behaving
with respect to the output specifications. It refers to the uniformity
of the process.
Capability is often thought of in terms of the proportion of output
that will be within product specification tolerances. The frequency
of defectives produced may be measured in
a) percentage (%)
b) parts per million (ppm)
c) parts per billion (ppb)
Process Capability
Process Capability studies can
indicate the consistency of the process output
indicate the degree to which the output meets specifications
be used parison with another process petitor
Process Capability vs Specification Limits
a)
b)
c)
a) Process is highly cap