Quality Control and Measurement - the fundamentals

In nearly all industry sectors quality control is part of the developing, engineering or manufacturing process in order to ensure that the designed and fabricated products meet the customers’ expectations or stay within previously defined tolerances. QC is a part of Total Quality Management (TQM).

Quality starts at the design stage. A TQM (Total Quality Management) system will quantify, by means of precise measurement, the production capability (including measurement capability) of the organisation. This will facilitate improved tolerancing for functionality of the product, the identification of areas of capability associated with specific tolerance (customer) demands. Simply put - measurement is the tool that is used to quantify the capabilities of the people, the processes, the tools, the machines and therefore the organization. The correct application of the above will greatly facilitate right-first-time manufacturing.

To support the production department and the customer as a fully integrated function of the process. Quality and measurement are not add-ons. All processes should include the quality checks for process verification and validation. A major function of Quality control is to control process variation within the defined process capabilities. Most of the data worked with will be captured via measurement systems and processed statistically.

The enemy is variation:
y is a function of the variables (x....) within the process. When the variables x1 through xN are not under control and acting in an unknown way then y will always be at risk of failure. The systematic control of process variables through good measurement, analysis and actions will result in y (the product) being within specification. Control of the variables is achieved with good measurement to reduce variation.

Good management acts on accurate and timely information, but how does one get one's hands on good information? In measurement it is really quite simple.

We select validated products and systems for process, product and business improvement based on our knowledge and beliefs. We are quite happy to measure a product to evaluate it as OK or not OK, so shouldn't we be validating our measurement methods and procedures to see if they too are OK or not OK?





Having validated your measurement system you can now confidently capture your product and process performance data. This data is then the key to process improvement; the control of the variables.

Once you have identified your measurement and process capability you can plan and schedule work according to performance capabilities and, humans aside, you are on the road to right-first-time production.

Good production processes exhibit only small amounts of variation, good measurement processes exhibit much less variation.

A Coordinate Measuring Machine (CMM) captures 3D data from objects to give the position in XYZ, vectors etc. of the object under investigation. CMMs are used by manufacturing companies to ensure that parts or components are within defined tolerance levels for quality, and to capture statistical process capability data.

There are many types of CMMs. Traditional CMMs include the bridge type, cantilever type, gantry type, etc. These are floor-mounted machines that require you to bring the parts to the CMM, they are generally kept in a controlled environment and are used only by very skilled personnel. The portable CMM (generally known as measurement arm, laser tracker or laser scanner) is designed to be fully portable and therefore can be used anywhere the measurement is needed - the machine goes to the part.