Reverse engineering faces a bit of a chicken-and-egg dilemma in the aerospace industry. Companies know the value of digitizing legacy parts to reduce physical inventories, maintain digital data on parts that are no longer manufactured in the country of origin, and modify products for which they don’t have blueprints.
But instituting change in a massive aerospace organization with hundreds of suppliers is not a simple matter.
“A company is lucky if it has digital models of 1% of inventory”, said Jeff Brehm, president of Computer-Aided Measurement Surfaces (CAMS), a com- pany that provides data capture services for the aerospace industry. “Companies need a real good excuse to create a digital model of a part–it might be a unique part or a part that will never be made again in this country.”
The automotive industry has had some decided advantages over aerospace in implementing reverse engineering: Automotive products are not nearly as large and their assemblies not as complex as those in the aerospace industry. But although these are obstacles, they also serve as compelling reasons why reverse engineering could be more beneficial to aerospace companies.
The other big reason is legacy parts. GM can leave obtaining a transmission for a 1968 Pontiac GTO to hobbyists and collectors, but the 1968 models of air- craft, with designs barely changed, are likely to be more prevalent in the air than models from the twenty-first century. This creates a huge inventory of legacy parts to be stored and maintained.
Most airplanes designed 30 years ago are still flying today, and they were de- signed without any 3-D CAD models. Keeping aging airplanes flying is one of the most cost-efficient and technically challenging areas for aerospace companies, and one that deserves more investment.
Figure 8.1. A Navy C20G (Gulfstream IV) that suffered nose, wing, and tail damage from a tornado
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Most aerospace companies have been doing reverse engineering for about 5 or 6 years. The processes have become faster and better with improvements in scanners, surfacing software, and computers, but they are still performed by specialists, those with what Brehm calls “tribal knowledge”.
On the surface, reverse engineering appears to be a simple process: measure, reverse engineer with software, and verify. But, those doing the work need to know what tools to use for what jobs–collecting too much data bogs down the compu- ting process; not enough data requires going back to rescan the physical part.
Different data capture hardware is typically needed according to the job. The more complex the shape geometry, the more points are needed. That’s where the tribal knowledge comes in. Those with experience in reverse engineering can look at a part or assembly and know the level of detail that has to be captured.
It’s a fine balance between capturing enough for accuracy, but not so much to bring processing to a standstill.
“It would be a waste to capture a wing with a structured-light scanner that might generate a model with 40 million points”, said Brehm. “On the other hand, you might need 40–100 million points to capture the radii and complex shapes of an actuator.”
For master parts that require capturing a large shape, the cuts for the wings and fuselage of a 747, for example, a laser tracker is often used. Laser trackers can capture large surfaces fairly quickly, as long as high detail is not required.
Complex parts with tight contours that require lots of data to generate an accu- rate model are captured by a structured-light or laser scanner. For small, intri- cate parts, a scanning arm with an integrated scanner head is likely to be used.
The size and type of data also determine what kind of software is used to process it. Traditional surfacing and CAD software cannot handle large point clouds. The new generation of reverse engineering software can handle very large data sets, although for interactive editing and viewing, it is difficult to get real-time graphic response if the model has more than 5 million points or
Figure 8.2. Digital surface of landing gear door generated from data captured by a laser tracker
10 million triangles. For computation only, new reverse engineering software packages such as Geomagic Studio, Polyworks, or Rapidform can handle 50–100 million points.
As might be expected, accuracy requirements vary widely. Hole patterns re- quire accuracy within ± 0.005 of an inch, whereas a mold line requires much less accuracy. For a large 1968 part, all that might be required is to verify that the cuts are good.
During the coming years, aerospace should see more automation from re- verse engineering software. Moreover, the combination of reverse engineering and surfacing capability will be able to create a surface that is not evident in the point cloud data but was part of the original design intent.
The obvious justification for the aerospace industry to invest in reverse engi- neering is the cost of storage space and keeping parts maintained. In the next case study, we will take a look at cost reductions of hard tooling.
Figure 8.3. Boeing 747 landing gear door
Figure 8.4. Digital surface of a landing gear door generated from data captured by a laser tracker
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