Do you trust your co-ordinate measuring machines? Take Messier-Dowty’s lead and actively monitor CMM performance

Trusting your CMM

Messier-Dowty, a SAFRAN Group company, designs and manufactures landing-gear systems for the world's best-known commercial airliners, jet fighters and military transport aircraft. In an industry sector well known for its commitment to quality, Messier Dowty has a control procedure for almost everything; even monitoring the accuracy of its co-ordinate measuring machines (CMMs).

Organisations such as Messier Dowty don't take chances with quality; they invest in the very best co-ordinate measuring machines (CMMs) and have strict quality control procedures for checking the accuracy of those machines.

But why is it necessary to periodically check a high-precision measuring device such as a modern CMM? For exactly that reason: because it is a high precision device and because occasionally its accuracy can be compromised by environmental factors and excessive or heavy use.

If you own a high performance car or motorcycle, it almost certainly has an on-board computer that continually monitors the vehicle's performance. If it detects an engine anomaly, a light or message will alert you to the problem, often recommending that you contact the service centre at the earliest opportunity.

In a way, that's exactly what the Renishaw Machine Checking Gauge (MCG) is designed to do. It gives owners of CMMs the ability to regularly ascertain the performance of their investments, alerting them to accuracy problems before they impact manufacturing or quality control processes.

CMM accuracy

Messier Dowty takes the matter of CMM accuracy very seriously, which is the reason why Pete Willis, a Principal Engineer within the manufacturing engineering department at the Gloucester facility, has established a regular and thorough program of checks for the company's seven measuring machines.

"Before we invested in a Renishaw MCG we had no way to monitor the accuracy of our CMM machines, we were unable to understand the impact on performance related to our specific working conditions. The consequence of not having this appreciation meant that we could not determine the appropriate interval for service and calibration; we were totally dependent on the recommendations of the CMM supplier".

Part of the challenge at Messier Dowty is that its CMMs are located on the factory floor, rather than in clean-room environments. What's more, they're worked for three shifts a day, often 7 days a week.

"We don't have any complaints with the machines themselves," states Mr. Willis. "On the contrary, problems are normally caused because we work them very hard and because they're susceptible to environmental conditions. Operational and environmental factors gradually degrade the performance of components like the air bearings, and ultimately the accuracy of the CMM."

The Renishaw MCG is a straightforward test that allows users to check the volumetric accuracy of a CMM, whatever its size.

Based on a simple alternative to the widely used 'Ball-bar principle' - typically used to check the accuracy of machine tools - the Renishaw MCG provides fast, automatic machine evaluation in accordance with ISO 10360-2, the international standard for the acceptance and re-verification of co-ordinate measuring machines.

Thorough

Whether you're running the household accounts or a multi-million pound business budget, you're probably familiar with the adage look after the pennies and the pounds will look after themselves. Of course, anyone who works in the aerospace sector knows that quality does indeed start and finish with the details. In fact, few industries are as detailed obsessed.

As its batch sizes are small – often less than 4, and frequently just one-off -Messier Dowty checks all of its machined parts for dimensional accuracy. Pete Willis is unequivocal about the importance of detail and control and the need to regularly check the company's CMMs.

"In aerospace, parts and systems are becoming much less fault tolerant, so we can't afford to leave anything to chance. A CMM that gives spurious results could, ultimately, have catastrophic consequences."