Factory Information System

Statistical process control

What does the Statistical Process Control module do?

The Statistical Process Control module supports the use of statistical methods to control your manufacturing processes. It allows you to set up an inspection plan for each operation on every part you make. Inspectors or machine operators use it to record sample measurements. It displays control charts so that setters can adjust a machine before it makes scrap parts. The samples for a works order are stored for future reference, particularly if the customer has a problem with the parts. The module controls calibration of the gauges used for inspection.

Key features

  • Controls gauge calibration.
  • Interfaces with electronic gauges and instruments.
  • Displays a wide range of charts.
  • Easy for shop-floor staff to use.

Is it suitable for my business?

The Statistical Process Control module was designed to be easy to use by shop-floor personnel taking frequent small samples from high speed machines. Consequently it will probably not be ideal for measurements using a co-ordinate measuring machine on a complex casting, but will be ideal for attributes and variables measured with hand-held instruments.

Gauge library

The module allows you to maintain a library of gauges. You can set up classes of gauge, such as micrometers, height gauges, and plug gauges. Within each class you specify individual types of gauge such as 0-25 mm micrometer, 25-50 mm micrometer and so on. Finally you record the individual gauges of each type with their serial numbers, calibration procedure, and calibration interval. You can specify those gauges which have a computer interface.

Calibration control

The module produces a calibration schedule for your gauges, prompting you when each gauge requires calibration. You can record who carried out the calibration and when.

Inspection plans

You can create an inspection plan for each operation on every part you make. An inspection plan specifies variables and attributes which must be measured on a sample of the part. You can specify which type of gauge from the gauge library to use for each measurement. You also specify the number of parts in a sample, and the number of measurements of each dimension which must be made.

You can use the Document Management module to store inspection drawings and instructions which will be displayed to the operator when he takes sample measurements.

If you have families of similar parts, you may be able to set up one inspection plan to cover an entire family.

Once you have created an inspection plan, you can attach it to all the operations to which it applies.

Record actual gauges used

When you start an operation on a machine, you must tell the Statistical Process Control module. If you are using the Machine Monitoring or Works Order Processing modules this will be done by one of these modules. When you take the first sample, the module will ask you for the serial numbers of all the gauges you are using to inspect the sample. It stores the gauge used with each measurement taken, so that you can trace a measurement back to the gauge which was used to make it.

Record sample measurements

Sample measurements are recorded using a PC on the shop-floor. The software can accept readings directly from electronic gauges, scales, and so on. The module provides tools to specify which gauges are attached to each port on each PC.

Attribute measurements default to 'pass'; so that the user only needs to enter data when a part fails an attribute inspection.

Variable measurements are read directly from an electronic gauge, or entered by hand.

The module displays mean and range control charts for each dimension as soon as the sample measurements have been entered. Thus the operator can see trends on the control chart immediately.

If you are using the Machine Monitoring module, the machine monitoring terminal can prompt the operator when a sample should be taken.

Add notes to a sample

You can add notes to a sample on the control chart to record the nature of a problem, or what corrective action you have taken.

Alarms

You can set up alarm conditions which alert the operator when a sample goes outside control limits, or when a trend in the mean is detected.

Continuous monitoring of process variables

Instead of statistical sampling at regular intervals, you can use the module to record process variables for each cycle of the machine. For example you might want to record the material temperature and injection pressure of a moulding machine for each part made. These would be obtained automatically from sensors on the machine and moving average control charts displayed to the operator.

Reports

Sample measurements are stored against the operation and works order from which they were taken. Quality control staff can display and print control charts on any PC on your network, allowing them to monitor processes remotely.

You can print control charts to send to your customers if they require them.
Chart types
The module can produce the following types of control chart.

Mean
Range
Standard deviation
Cumulative sum
Exponentially weighted moving average
Fraction nonconforming
Nonconformities

Capability studies

You can use the Statistical Process Control module to perform process capability studies. The software will record measurements from a large sample, and then calculate capability coefficients for the process.

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