Laser Scanning in Military Applications

Laser scanning keeps older military equipment running by enabling the creation of spare parts that perfectly duplicate the originals at a reasonable cost. MILPARTS and other companies are taking advantage of new technologies, particularly the ModelMaker laser scanning system, which make it possible to rapidly reverse-engineer existing components and produce duplicates in less time and at a lower cost than was possible in the past. It’s no secret that much of the United States’ military hardware is or soon will be in use long past its predicted lifespan. The aging of the nation’s military hardware is creating a tremendous need for spare parts, even though many of the companies that built the equipment have long since left the business, and the original drawings and documentation no longer exist. A new breed of entrepreneurial companies has moved into this space, offering the capability to quickly reverse-engineer needed parts and economically produce them, usually on the latest computerized numerical control (CNC) machinery. A typically example is MILPARTS, of Willoughby, Ohio, which has produced spare parts for the H53 helicopter, SH-60 Seahawk helicopter, M-242 25 mm cannon, M-60 gun for the H-3 helicopter, T-700 engine and S-3 Viking military systems. MILPARTS is part of the Radian Technology Group, which is an operating unit of Engineered Support Systems, a diversified defense holding company. Stocks of military equipment are getting much older than they have been in the past. Even if the Department of Defense increases purchases as current plans project, the military hardware base will continue to grow older. At the end of the Cold War, the DoD cut its procurement funding more deeply than it cut its forces. Average purchases over the past decade sank well below the quantities needed to sustain the forces; in some cases, procurement dropped to zero. Ideally, the DoD would like to have the average age of its equipment at half its planned service life, which would be the case if systems were equally distributed between newly delivered systems and those nearing retirement. But while the half planned service life of the fleet of light attack and scout helicopters ranges from 10 to 18 years, the average life was actually 21 years in 1999 and is expected to rise to 28 years in 2007. The Air Forces tanker fleet has a half planned service life between 25 and 33 years but the actual average age was 44 years as of 2004.

Radian was founded in 1977 and currently holds contracts supporting all DoD services, civilian agencies and commercial clients worldwide. The seeds of the division that now provides spare parts services were originally sown about a decade ago, when a small group working for a technology transfer company began discussing the military’s part- supply problems. A study of the issue determined that a significant need existed for parts that had been orphaned because their original manufacturer was no longer in the business. At about the same time, a group working on the military reverse-engineering problem joined Radian and formed an operating unit within the company. They began working with the somewhat limited reverse-engineering tools available at the time to produce the drawings and specifications needed to build parts that would perform as well as the original in situations where failure is not an option. Primarily, they used coordinate measuring machines (CMM) to capture points by touching the probe to the surface of the part. They experienced some positive results but also major difficulties with this approach.

The primary limitation of a CMM is that the operator must manually move the steering system to track each point, and the device captures points one at a time. But to accurately model the geometry of a complex 3-D contour, such as that which is found on many military parts, you need millions of points, sometimes many millions, to get the geometry exactly right. Generating this number of points with a CMM would take months, while the most that can be captured in a week is probably somewhere in the tens of thousands. Of course, it’s possible to intelligently select points to capture only the most critical areas, but you’re often left approximating contours and can never be completely sure that you aren’t missing important points. Another problem with trying to reverse-engineer a 3-D component with a CMM is that the end result of a scan with a contact device is a series of sections. Designers must generate surfaces from the sections. Although this works well enough with simple surfaces that extrude from the lines and curves, it isn’t effective for complex shapes since the area in between the sections is not a straight line. As a result, constructing CAD surfaces from CMM data is a very labor-intensive process.

Radian began looking at a number of different products; the best results were obtained from NVision’s ModelMaker. The ModelMaker integrates with a portable CMM and can switch from scanning contour surfaces to capturing individual points with the push of a button. Laser scanners are able to quickly measure large parts while generating far greater numbers of data points than CMMs, without the need for templates or fixtures.

Laser stripe sensors are significantly faster than simple laser point sensors. The ModelMaker sensor is available in 35 mm, 70 mm and 140 mm laser stripe widths. The ModelMaker system is comprised of a 3-D laser sensor, a portable CMM on which the sensor is attached, a PC, and ModelMaker software that extracts, displays, manipulates, and exports the data as points, polylines, and polygons, in all industry-standard CAD/CAM formats.

To record the shape of a component, the technician simply holds the laser sensor so that a line of laser light appears on the part. The ModelMaker system moves freely about the object, allowing the technician to capture data much in the same way as spray painting. As the technician moves the sensor over the surface of the object, real-time rendering of the data on-screen provides immediate feedback. This is important because it allows the technician to see areas that were missed and fill them in with another pass. The system combines the coordinate data with the Cartesian and angular coordinates generated at each position of the mechanical arm. The result is a dense cloud of 3-D data describing the surface of the object.

The key advantage of the laser scanner is that it generates more data points in a smaller amount of time. Depending on the size of the part and level of accuracy required, the company typically captures tens of millions of points for each part. Measurements aren’t affected by the operator to any significant degree because he or she is simply passing a beam of light over the object.

MILPARTS typically begins a military project when one of service branches presents a request for a new part. Typically, all they have is a new or used physical part and possibly some incomplete technical documentation. The physical part is scanned with the ModelMaker and then the software provided with the device converts the point cloud into a surface model that can be imported into CAD software. The resulting CAD model is used as the basis of a technical data package for the part. Stereolithography is often used to create a first article that can be used for checking by the customer and to assist in the quoting process. The technical data package is then sent out for bid to small and medium-sized contract manufacturers. The winning bidder uses the 3-D model produced during the laser scanning process to generate a CNC program that either produces the finished part or builds a mold that is used to cast the part.

Even in cases where the company that originally built the parts is still in existence, MILPARTS can often provide spares faster and less expensively. In one case, the original equipment manufacturer was willing to remanufacture engine cowlings for the H-53 helicopter but quoted a 600-day leadtime, much longer than the customer wanted. MILPARTS was able to reverse-engineer the part and deliver spares in only 300 days. The company had to move even more quickly when the Coast Guard requested a reverse-engineering of the anchorage system on a cutter. The only physical part was on an operating boat, which was about to come into port for a short maintenance stop. A laser scanner was brought to the dock, where the dripping-wet part was removed, scanned, and returned to the boat the next day so it could sail on time. With every branch of the military operating at a very high tempo, the ability to quickly and inexpensively produce spares is going to become even more important in the future.

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