Measuring Aerospace Parts

From long and heavy to tiny and complex, aerospace parts are among the most difficult to measure

April 1, 2010

A proper probing strategy is necessary when measuring prismatic parts.

Canada’s aerospace industry has a long history of success in the world marketplace.

Not only does the country have a base in aviation and spacecraft component companies, but also in the production of regional aircraft, avionics, helicopters, landing gear, and engine technology.

This industry is made up of more than 400 companies and employs more than 80,000 Canadian workers. Since 1990 sales have more than doubled, reaching $23.6 billion in 2008, and 80 percent of this is from exported products.

Canadian aerospace manufacturing companies are often at the forefront of technology, and a highly skilled work force is a definite necessity.

During the manufacturing process and immediately following machine work, parts must be measured to ensure that the proper quality is met. This means that an aerospace company’s measurement and metrology department is an important hub of activity.

“Metrology is a critical function to aerospace manufacturers,” said Bill Pyles, western regional sales manager for Carl Zeiss IMT.

This is because so many aerospace products, such as airplanes, missiles, satellites, and navigation systems, contain thousands of mechanical parts, many of which have very tight tolerances that need to be inspected before being assembled into the final products. 

Zeiss, which has been heavily involved in the aerospace sector since the 1980s, has witnessed a recent trend of outsourcing both manufacturing and the necessary measurement tasks to suppliers.

“We do see a lot of large aerospace companies choosing to outsource component manufacture, and the responsibility of producing compliant parts shifts to the smaller companies,” said Pyles.

Large or small, however, aerospace manufacturing shops, like other sectors, are asking for more accurate machines, shorter deliveries, easy-to-use software, and, of course, lower prices.

Measuring Parts

Large structural aerospace parts are usually measured on bridge on gantry CMMs.

Two types of parts in this industry are often quite difficult to measure.

Long, heavy parts such as airframe structures and spars pose measurement challenges simply because of their form.

“Large components with tight manufacturing tolerances are often measured on large bridge or gantry CMMs,” said Pyles. “Other large or long components can be measured with laser trackers or photogrammetry systems.”

Laser trackers have become popular in recent years partly because of their portability. By having the measuring device come to the part, rather than the other way around, complicated logistics of moving these large parts around a shop have been eliminated.

“If very few large parts are to be inspected, then portable systems such as a laser tracker or arm might be used. If the parts have tight tolerances over long distances, such as 0.005 in. over 20 feet, and if numerous parts will need to be inspected, then a CMM is often selected as the device,” said Pyles. “It depends on the tolerances, the size of the part, and the number of parts to be inspected.” 

New challenges present themselves when a part has prismatic properties.

In these instances, a probing strategy needs to be developed that uses the simplest stylus configuration, with a view to maintaining accuracy, minimizing probe changes, and shortening tool paths to optimize inspection time.

“If a CAD model of the component is available, a CMM programmer can use it in an offline license of the CMM software with simulation capability to build stylus configurations and create the inspection strategy and probe path in a simulated environment,” explained Pyles. “In this way, the physical machine is not tied up during the programming phase, and instead can be used exclusively for measuring parts.”

As with any important task in the manufacturing process, the knowledge base of the operator is an important variable. Operators need to receive proper training and can benefit from recurrent training or training on new software features and inspection techniques. 

“Management should support training in order to leverage the investment in people and equipment,” said Pyles. “Metrology departments need to be aligned with the strategic goals of the company.  If a small shop wants to become a favored supplier to the major aerospace companies, metrology will play a critical role in winning the confidence of the customer.”

Even as the larger aerospace companies continue to outsource some of their manufacturing, certain critical components and assemblies will always remain in-house. This means that metrology and measurement knowledge and equipment at the manufacturer and the supplier level are critical.

For more information, visit www.zeiss.com.