spc - statistical process control software

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In traditional manufacturing Production to make the product and the Quality Department inspect it. After-the-event inspection is expensive and wasteful because:

• The product has already been made

• Costly re-work is not always possible

It is much more cost effective to avoid waste by monitoring and analysing the process during manufacture. This is the basis of statistical process control (SPC).

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Dataputer Datastat SPC Software

Dataputer’s Datastat computer spc software program provides the means to display the production process and highlights when the process violates control limits. Datastat can predict future violations and therefore improve the production process. Datastat has a comprehensive range of data entry options, charting capabilities, reporting functions and other useful features to help the production engineer minimise waste and ensure product quality.
 

Dataputer Datastat SPC CSV Software

Using advanced programming techniques, Dataputer’s Datastat CSV (Client Server Version) is a powerful SPC software program, which gives professional results in an easy-to-use package. Using Client/Server technology with open database connectivity (ODBC), Datastat CSV can be linked to existing data and also allows multiple Users to share a common database. Datastat CSV is available in two versions, Administrator and Shopfloor.

 

 

 

Statistical Process Control (SPC) Software

Controlling The Process

For a product to be made without scrap, it must be manufactured within specified limits. But factors can prevent this from happening:

Natural Variation: inherent in the machining process and cannot be changed without using a different process or machine

Assignable Variation: outside influences that are controllable: temperature, sharpness of the blade, speed of manufacturing, skill of machinist etc.Costly re-work is not always possible

An Example of Variation - A machine cutting straws to length will give an error from straw-to-straw. This is because of the inherent tolerances of the machine - Natural Variation. This is less significant than someone who cuts the same straws to length, using a ruler - Assignable Variation.

This raises the question - Is the manufacturing process able to manufacture within specification?

Testing The Process Capability

Continuing our example, cut a number of straws to the required length (usually 50). Accurately measure the straw lengths. Plot the lengths on a graph to identify the variation.

Histogram and Capability charts can be used for this purpose. Once it has been determined that the process is capable, the process can be monitored over time.

Monitoring The Process Over Time

In an ideal world, every product that is being made would be measured. In the real world, there is not enough time or resource to do this so a sample group of product is measured on a regular basis. These groups are known as subgroups.

The subgroups of data are plotted on to a graph - in chronological order:

The average value of each subgroup is then used to generate the Process Control Chart - building up the actual manufacturing process over time, known as an Xbar Chart.

Setting Control Limits

In order to prevent scrap, a set of “early warning limits” known as Control Limits are established. These limits are set inside the upper and lower specification limits and warn the operator before scrap is produced.

 

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