CMMs automate part measurement

Traditional inspection methods and devices, like surface plates, height gauges, air gauges and dedicated hard gauges, can be expensive to purchase and maintain. They also can be rendered obsolete as jobs come and go. In addition, a gradual increase in the use of geometric dimensioning and tolerancing has made the application of hand tools challenging when measuring things like the true position of holes. Coordinate measuring machines have proliferated in this evolving manufacturing environment.

Introduced in the late 1950s, CMMs have become increasingly common over the past two decades. CMMs have not always been affordable for some part manufacturers. However, as advances in software, machine construction and manufacturing techniques have significantly reduced the cost of CMMs, industry has seen a steady increase in their use.

A CMM can be more desirable than measuring with manual instruments, such as micrometers, calipers and height gauges, because a CMM automates the process. Automating part measurement with a CMM can decrease the need for skilled personnel in the same way a CNC machine tool can. It is common for experienced personnel to program and set up CMMs and then have other employees operate them.

Removing Rigidity

Flexibility is another common reason for buying a CMM. Hard gauges, as their name implies, are rigid. They are built for one part or family of parts—often for measuring just one feature. If the part or process changes, hard gauges must be reworked. CMMs, on the other hand, require only a revision in their program.

Paired with machine tools in a manufacturing cell, a CMM can collect, process and transmit data to be acted on by the other manufacturing equipment. This arrangement substantially lessens the need for humans to interact with the manufacturing process, thereby eliminating opportunities for error.

Although acquisition costs have decreased, the overall ownership costs can be daunting, with calibration and repair being most significant. Calibration of a CMM necessitates a visit from the manufacturer, often lasting several days, with costs that can run easily into the tens of thousands of dollars. Most mechanical repairs of a CMM require recalibration after completion, so ensuring that machines receive proper maintenance and care to prevent mechanical failure is critical to controlling costs. Fragility of CMM technology—sometimes real, sometimes perceived—often drives users to segregate CMMs from the shop floor by installing them in climate-controlled quality labs or special enclosures.

Keeping a CMM sequestered from the shop floor calls for the parts needing inspection to travel to the CMM, wait for inspection and then travel back. If deviations are found and the machine tools must be adjusted, the process will begin again. The result is a lot of nonvalue-added activity.

CMM power and flexibility have encouraged manufacturers to aggressively adopt CMM technology, but the fragility of the machines historically has made their use inefficient. Lean manufacturing and basic economics of production have driven demand for machines that can be near the work.