Measuring with speed and precision

The change has resulted in a reduction in inspection time by as much as a factor of five, ensuring quality control and inspection keep up with its high productivity CNC machine tools.

It's true that in many ways making things is getting easier, at least as far as the technology is concerned. For example, machine tools are simpler to program and operate, rapid prototyping means that product development is faster and cheaper than ever, and user friendly CAD software may even negate the need for physical prototypes entirely. All of this assumes that what you are actually making, or trying to make, is relatively uncomplicated. It's a different matter, however, if you are building complex multi-million dollar aerospace systems, like those engineered by Mecanizados Escribano.

“When we buy a machine tool we specify all the options,” says company project manager Juan Humanes. “But, having the best machines is only part of the equation. Our customers demand very rigorous part inspection, which means there's always the chance that the metrology department can become a bottleneck, especially when the parts are complex and machined to very tight tolerances.

“Depending on what the customer requests, we inspect between 10% and 100% of machined parts. The Renishaw Revo system, recently fitted to a Metris CMM, measures non-prismatic surfaces very quickly, many of which would be difficult or impossible to measure with touch trigger systems. In some cases, such as a complex avionics chassis for the Typhoon, the Revo has increased our inspection throughput by a factor of five; typically, up to an 80% reduction in time per part.”

Improving scanning speed and accuracy

The key attribute of the Revo 5-axis head is its ability to overcome the limitations of three-axis scanning methods, where any attempt to rapidly move the large mass of a CMM results in inertial errors caused by accelerations and decelerations. Therefore, the only possible way to maintain acceptable accuracy in 3-axis scanning has been at the expense of measuring speed. However, Revo uses synchronised head and machine motion when scanning, rapidly following changes in part geometry without introducing its own dynamic errors. The CMM is able to move at a constant velocity whilst measurements are being taken, without impacting accuracy.

Revo also benefits CMM users with infinite head positioning and innovative tip-sensing probe technology, which further improves measurement accuracy by sensing close to the measured surface. This combination of speed, flexibility and accuracy has proven to give exceptional performance in a wide range of scanning measurement applications, including circle, helix, sweep and gasket scanning, plus, if required, rapid single-touch routines.

Expanding to meet increased demand

Any visitor lucky enough to tour the Escribano factory can see the size and significance of the investment required for such production. Humanes reveals it to be between €1million and €1.5million a year, and most of the company's CNC machines are top-end, Japanese or Swiss-built multi-pallet and multi-axis: Makino, Matsuura, Mazak; Sodick wire EDMs and CNC precision grinders from Jung. All of them are the latest models, meticulously maintained and configured to minimise set-up and non-machining time, mostly using Renishaw OMP40 spindle-mounted touch probes and NC4 non-contact laser tool setting systems.

Escribano has outgrown its current building and has designed and built a new facility, where it will relocate in the next few weeks. Until then, the two small rooms adjacent to the main workshop that house the company's inspection equipment will remain crowded. In the larger of the two rooms, three DEA Global Advance CMMs with Renishaw probes check samples of parts for everything from thermal imaging cameras to components destined for the JSF. Alongside the main metrology laboratory is a smaller room housing the company's largest CMM: a Metris LKV CMM equipped with the Renishaw Revo 5-axis measuring head and probe system; part of a recent investment in inspection equipment that totalled around €300,000.

For most precision engineering businesses, the Metris and Renishaw Revo combination would be enough to cater for their metrology needs. But Escribano isn't your typical workshop and its customers are somewhat more demanding, leading to further investments in other advanced metrology systems such as a white light interferometer microscope for measuring roughness, and a contact profile meter capable of assessing the size and texture of a part's surface.

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