2. z
INDRODUCTION TO STATISTICAL
CONTROL
Statistical control, also known as statistical process control (SPC), is a
method used in quality control to monitor processes and ensure they
remain stable and predictable over time.
It involves collecting and analyzing data to detect any variations or
deviations from the expected performance.
The goal is to identify and address any factors that may cause the
process to produce defective products or services.
Statistical control typically relies on techniques like control charts, which
visually display process data over time, helping to distinguish between
common cause variation (inherent to the process) and special cause
variation (due to external factors).
3. z
CONTROL CHARTS FOR PROCESS
CONTROL
Control charts are a fundamental tool in statistical process
control (SPC) for monitoring and managing processes. They
help distinguish between natural process variation and
significant deviations that may indicate an out-of-control
situation.
4. z
Important uses of the control chart.
Most processes do not operate in a state of statistical control.
Consequently, the routine and attentive use of control charts will
identify assignable causes.
If these causes can be eliminated from the process, variability
will be reduced and the process will be improved.
The control chart only detects assignable causes.Management,
operator, and engineering action will benecessary to eliminate
the assignable causes.
5. z
X Bar Chart
The X-Bar chart, also known as the Xchart, is a widely used
control chart for monitoring the central tendency or average of a
process over time. It’s particularly suitable for situations where
the quality characteristic being measured is continuous and
normally distributed.
Control Limits: X-bar Chart:
Upper Control Limit (UCL) = CL + (A2 x R- bar)
Lower Control Limit (LCL) = CL (A2 x R-bar)
6. z
Sigma Chart
Sigma chart, also known as a Sigma control chart or Sigma
capability chart, is a statistical tool used in quality control to
monitor the stability and performance of a process over time. It
displays the process capability in terms of sigma levels, which
indicate how well the process is meeting its specifications. The
higher the sigma level, the fewer defects per million
opportunities (DPMO) the process produces. Sigma charts help
organizations identify areas for improvement and maintain
consistent quality standards.
7. z
R Chart
An R chart, also known as a range chart, is a statistical tool used
in quality control to monitor the process variability by plotting the
range (the difference between the maximum and minimum
values) of a subgroup of samples taken from a process over
time. It helps in identifying any shifts or changes in process
variability, which can indicate potential issues or improvements
needed in the manufacturing process.
R=Maximum(data)−Minimum(data)
