Information & Training | SPC and Statistical Methods for Process Improvement.
The SPC Control Chart.
A Control Chart is a visual chart utilized in statistical process control for the monitoring, control and improvement of processes. If there is only one quality characteristic to be monitored in a process, then the chart is known as a “univariate control chart”, if there are more than one quality characteristics to be monitored in a process then a “multivariate control chart” is utilized.An SPC Control Chart consists of a centre line which equates to the mean value of the process being measured. There are two horizontal lines drawn parallel to the mean. These two lines are called the upper and lower control limits.
Statistical Methods for Process Improvement – Information to improve your understanding and build your capability to drive improvement.
Within the lines lies a region where approximately 98% of all data points taken from a process would expect to be recorded. The effect of placing the two lines at this point, is that any data readings which lie outside the control limits, will be immediately obvious and therefore will invite investigation.
Statistical Methods for Process Improvement – Information to improve your understanding and build your capability to drive improvement.
With the SPC Control Chart now drafted, further data points can be recorded from the process and then entered onto the control chart. The data points may be recorded for example on a time basis, i.e. every hour, every shift, every day, etc. The effect will be that a visual representation of the performance of the quality characteristic will be recorded onto the chart.
Statistical Methods for Process Improvement – Information to improve your understanding and build your capability to drive improvement.
With the SPC Control Chart in place and the data being recorded onto the chart, it will immediately become obvious if trends exist, or if any readings outside of “normal” are being seen. In this example we seen there is a clear “cycle” in the data, also one data point is outside the lower control limit, indicating that there is only an approximate 2% chance of such a reading being obtained, so should be investigated to see why a reading so far from the mean is being seen in the process.
Statistical Methods for Process Improvement – Information to improve your understanding and build your capability to drive improvement.
SPC Control Charts can be utilized to measure “variable data” (measurements of length, weight, height, light intensity, chemical formulation, length of time, moisture content, strength, depth, etc., ….) or can be applied to monitor “attribute data” (specific count data such as the total number defective, the number of non-conformances within a batch, number of days, number of people, etc., …).
Information & Training.
SPC & Statistical Methods for Process Improvement.
- Process Capability. Variability Reduction. Statistical Process Control.
- Pre-Control. R&R Studies.
- Process capability indices Cp, Cpk, Cpm, Capability ratio.
- Performance indices Pp and Ppk.
- Variable Control Charts.
- Attribute Charts.
- Pareto Charts.
- Individual – X Charts.
- Histograms / Process Capability Analysis.
- Scatter Diagrams.
- Etc. … Etc. …
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