Measuring the benefits of CMMs

CMMs are more robust and refined than ever, providing users with accurate, fast measurements directly from the factory floor, but how do the results add up for manufacturers? Katherine Crichton reports.

CMMs are more robust and refined than ever, providing users with accurate, fast measurements directly from the factory floor, but how do the results add up for manufacturers? Katherine Crichton reports.

NO longer restricted to the sterile confines of a laboratory or research office, co-ordinate measurement machines (CMMs) can now be found on the frontline of most manufacturing operations.

Improvements in temperature compensation, high-speed data gathering, sensor technology and advances in software design are making CMMs as robust and flexible as any machine on the factory floor.

David Eldridge, GM of Hi-Tech Metrology says shop floor measurement, control and reporting are now becoming the norm rather than the exception.

“With machines becoming more accurate, with the ability to analyse measurement results against the same 3D model as those used to initially create the part, all feedback coming from a CMM can be instantly utilised to not only monitor, but to dramatically improve manufacturing processes,” Eldridge told Manufacturers’ Monthly.

“Machines are now rugged enough to be situated adjacent to the production machinery, further enhancing productivity gains,” he said.

With real time measurement data providing machine operators with immediate feedback, manufacturers can improve overall productivity and fine-tune operations to account for production variables.

While fixed CMMs still tend to offer higher precision with more consistent measurements, portable CMMs are becoming more accurate, with some machines getting down to around +/-5micron in a 1.2m measuring volume.

However Eldridge says fixed machines still tend to be more accurate mainly due to the portable CMM taking its readings from a minimum of six precision rotary encoders to calculate a position, as opposed to the three precision linear encoders on a fixed CMM.

Immediately there is double the number of possible error sources, but in saying that, there are many applications throughout manufacturing applications where fixed CMM accuracies are not required but instead fast, portable and reliable measurement are still needed.

“You need to know how much accuracy you need. If you understand this, it means you are not wasting money and resources on precision measurements that you may not need,” Eldridge said.

Adding up the benefits

Developments in CMM software has also contributed significantly to overall measurement accuracy, with software refined to the point that no computer programming knowledge is required to run even the most sophisticated programs.

Walter Giardini, project leader for the length project at the National Measurement Institute, says while CMM software can be very responsive and user-friendly, accurate measurements can be compromised if operators don’t entirely comprehend the measuring process.

“CMMs can offer manufacturers many benefits but these can be lost if they are not optimised to their full potential by people who don’t completely understand the geometries of what they are measuring and how the software interprets these measurements,” Giardini explained.

“It is when you get to the minute measurements such as one or two microns, where even measuring something simple like a setting ring involves a more sophisticated understanding of the measure process or you run the risk of producing calculations that are not really useful for the purpose.”

Like most industries in Australia, the current skills shortage is affecting the availability of skilled CMM operators, and according to Giardini, this is impacting on Australia’s global competitiveness.

“There is no doubt in my mind that when we are talking about how we can significantly improve the Australian leverage or effectiveness that we get from using these machines, the number one issue is operator training and support,” he told Manufacturers’ Monthly.

Already in countries like Germany, operator competency levels are being introduced to ensure there are certifiable levels of proficiency for using CMMs.

Other factors that can impact on machine accuracy include environmental factors, and despite the increasing robustness of measurement machines, both Eldridge and Giardini stress that CMMs are sophisticated pieces of equipment and users should keep this in mind.

“A number of clients don’t appreciate the need to keep the machines clean and well-maintained. CMMs are high precision measuring instruments and need to be treated with due care and proper basic maintenance regimes,” Giardini explained.

“When the environmental conditions, i.e. heat and humidity exceed the manufacturer’s operating range, the use of CMMs is not recommended.

“In these cases a temperature controlled environment for the CMM is the best approach, though with Automatic Temperature Compensation (ATC) now standard on most machines, these requirements are no where near as onerous now as they were just five years ago,” he said.

Future calculations

As technology improves, Eldridge and Giardini say CMMs will continue to evolve, with advances in computer technology, electronics and materials continuing to make the machines more flexible, faster, more accurate and completely integrated into the manufacturing process.

Both men say that there is a future trend towards integrating non-contact measurement devices with existing touch trigger probing systems for use in both portable and fixed CMMs.

“There will be a convergence of available technologies – hard probing CMM, laser scanning systems and photogrammetric systems; as well as multiple technology platforms, i.e. the incorporation of a laser tracker with a portable CMM to provide highly accurate measurements over large distances and volumes,” Eldridge said.

Giardini says with the increasing use of nanotechnology, machines can now measure below a sub micron, giving manufacturers the ability to measure smaller volumes with higher accuracy.

I think there will also be more focus on machines that can operate in less favourable conditions -with increased emphasis on temperature control etc,” he said.

CMMs have revolutionised manufacturing measurement in the last 10-20 years and they will continue to do so. What we need to be able to do is bring out the full capability of the machine and optimise it.

“Software and operator training are key parts of achieving this, and in order to do this successfully, you need to have industry support.”

Eldridge believes CMM software will become more advanced with enhanced functionality and ease of measurement use.

There maybe a trend towards a ‘universal’ CMM software platform that will be adopted by all major CMM manufacturers,” he said

Hi-Tech Metrology 03 9702 3911.

National Measurement Institute 02 8467 3678.

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