Trend monitoring is a powerful tool in the control of the process and allows the operator to make timely adjustments to the machine so that tolerances are not exceeded.

To determine trend in its simplest form may involve measuring the size of every tenth item off the production line and measuring and recording the dimension on a graph that has the upper and lower tolerances marked on it.

By taking note of the trends displayed on the graph it is then possible to predict when the process is going to produce components with dimensions that exceed the permitted tolerances, and take corrective actions such as adjusting the tool setting.

Data obtained from the measuring equipment and SPC can be fed back into the production process to allow for the relevant adjustments to be made to the machines, thus giving the opportunity to implement a prevention strategy.

A basic SPC control chart that plots the process variation with time

The basic aim of SPC is to minimise variation. By taking notice of the trends displayed it is then possible to predict where the process is going to produce components with dimensions that exceed the permitted tolerances, and take corrective actions such as adjust the tool setting.

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Good practice online modules

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• Dimensional
• Overview of basic design & interpretation of an engineering drawing
• An introduction to datum
• An introduction to geometric tolerancing
• An introduction to the designer's role in the design & interpretation of an engineering drawing
• An introduction to the manufacturer's role in the design & interpretation of an engineering drawing
• An introduction to the inspector's role in the design & interpretation of an engineering drawing