Coordinate Measuring Machines – CMMs

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Coordinate Measuring Machines – CMMs

Coordinate measuring machines (CMMs) are used in car design to take three-dimensional data from physical objects and translate it into information that can then be processed by CAD systems. In particular, full scale clay models are scanned in using CMMs in order to produce working CAD models that can then be either modified and remodelled or finished with Class A surfaces ready for tooling and production.

The Basics

CMMs scan three-dimensional objects, and record information about those objects as points in space – coordinates. These large amounts of coordinate data are known as ‘point cloud data’.

Early measurement systems involved large touch probes that were slow and cumbersome and would only record cross-sectional data. From these cross-sections, surfaces were developed and a toolpath created; from this the other half of the clay would then be milled (and balanced). This process would take several weeks.

With the use of optical laser CMMs, it is now possible to scan a full-size vehicle in a day. Millions of coordinates can be recorded in a matter of seconds, meaning a fast process that precisely interprets the design without loss of information. Using this data, a polygonal mesh of the vehicle is created – without the need to rebuild all the surfaces on computer.

Once the data from the model is interpreted by a CAD system, it can then be used for further development as a computer model thus allowing designers to try new ideas and then using the CMM in milling machine guise to create their new vision in clay. Old ideas can even be recorded in CAD and then milled back out should newer variants not prove successful.

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