reverse engineering
or unable to supply a replacement at a reasonable price and lead time. In many cases, the documentation needed to make another part doesn’t exist. Faced with this challenge, the aircraft operator must re- verse engineer the part and assemble enough data in the right format to enable remanufacturing. And if his multi- million dollar plane is grounded, he has to do this quickly. Luckily today’s laser scanners and associated software of- fer exactly this capability, albeit with limitations.
How Laser Scanners Work Laser scanners use one of two different approaches to define a part’s shape. One approach uses triangulation. The scanner sends a laser line or single point across an object and a sensor picks up the reflected laser light. Be- cause the system knows the distance and angle between the laser source and the sensor very precisely, it can use trigonometric triangulation to calculate the distance from the scanner to the part. By building up millions of these measurements it creates a point cloud that defines the shape of the part. This approach is suitable for small-to- medium sized parts in situations in which the scanner can be positioned within about 1 m of the part. For mid- to long-range scanning (over 2 m from the part), “time-of-flight” systems are the better solution. This technique measures the time it takes pulses of laser light to reflect back to the sensor. Since the speed of light is a known constant and since these systems can mea-
sure the time interval to within picoseconds, they can ac- curately calculate distances based on the length of the intervals. These systems often rotate the laser and sen- sor to capture up to a full 360° view of the area, further enhancing their ability to scan entire airframes or other large components.
Beyond the two basic approaches, there are variations in mounting and moving the laser scanner, systems that combine laser scanning with other techniques, different workflow and output options, and of course differing de- grees of accuracy depending on the quality of the equip- ment. Either system can be highly accurate and both have inherent limitations.
Scan, Probe, or Both?
As Stephen Strand, applications engineer at API Services (Newport News, VA) said, “Choosing the right laser scan- ning solution depends on the work scope, both in terms of the size of the application and the accuracy requirements, plus factors like the surface type. For example, certain la- sers won’t get any return on a chrome or mirror-like finish.” In fact, most light-based systems have problems with
highly reflective parts, like turbine blades. Strand said the usual work-around is to “spray a developer on the part to create a matte surface. But with aerospace components you’re often working with very tight tolerances, so the thickness of any coating may be a significant consideration in any measurement.”
Á A USAF B-52 lands at Al Udeid Air Base, Qatar, April 9, 2016. The last B-52 was built in 1962, but 76 are still in service. Maintaining and upgrading them often requires reverse engineering various components. NVision once scanned the bomb bay on such a project.
LF20
AdvancedManufacturing.org
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