Laser scanning makes it easy to keep older military equipment running by enabling companies to create spare parts that perfectly duplicate the originals at a reasonable cost. Manufacturers of weapons systems are taking advantage of new technologies, particularly the ModelMaker laser scanning system, which makes 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 expected life, being in many cases older than the soldiers, airmen and seamen who operate it. The aging of the nation’s military hardware is creating a tremendous need for spare parts. The drawings and documentation of these parts no longer exist because many of the companies that used to build the equipment have left the business. Now, a new breed of entrepreneurial company 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. One such company is MILPARTS, which has produced spare parts for the H53 helicopters, SH-60 Seahawk helicopters, the M-242 25 mm cannon, the M-60 gun for the H-3 helicopter, T-700 engines and S-3 Viking military systems. MILPARTS belongs to Radian Technology Group, which is an operating unit of Engineered Support Systems (ESSI), a diversified defense holding company.

Stocks of military equipment are getting much older than they once did. Even if the Department of Defense increases purchases for current projects, the military hardware base will continue to grow older. This is because after the end of the Cold War the Department of Defense 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, and in some cases procurement dropped to zero. Ideally, the Department of Defense would like to have the average age of its equipment at half the planned-service life, which would be the case if systems were distributed equally between newly delivered systems and those nearing retirement. While half the planned-service life of the fleet of light attack and scout helicopters ranges from 10 to 18 years, their 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.

Limitations of previous reverse engineering methods
Radian was founded in 1977 and currently holds prime contracts and subcontracts supporting all Department of Defense services, civilian agencies and commercial clients worldwide. The seeds of the division that now provides spare parts were originally sown about a decade ago when a small group of people working for a technology-transfer company began discussing the military’s parts-supply problems. They studied the issue and determined that there was a significant need for parts that had been orphaned because their original manufacturer was no longer in the business. At about the same time, the people working on the military reverse-engineering problem joined Radian and formed an operating unit within the company. They began working with the reverse-engineering tools available at the time to produce drawings and specifications needed to build parts that would perform as well as the originals in situations where failure wasn’t an option. Primarily, they used a coordinate measuring machine (CMM) to capture points one-by-one 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 to be measured, while the device captures points one at a time. But to accurately model the shape of a complex 3D contour, such as is found on many military parts, the operator needs millions of points, sometimes many millions, to get the geometry exactly right. Generating this number of points with a CMM would take months, since the most that can be captured in a week is probably somewhere in the tens of thousands. Although, it’s possible to intelligently select those points to capture the most critical areas, the operators are often left approximating contours and can never be totally sure that they aren’t missing important points. Another problem with trying to reverse-engineer a 3D 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, since they can extrude from the lines and curves, it isn’t effective for complex shapes, because the area in between the sections isn’t a straight line. As a result, constructing CAD surfaces from CMM data is a very labor-intensive process.

Laser scanning provides a better approach
Laser scanners are able to quickly measure large parts, while generating far more data points than CMMs without the need for templates or fixtures. Laser-stripe sensors are significantly faster than simple laser-point sensors. The laser scanner’s sensors are available in 35 mm, 70 mm and 140 mm laser-stripe width. Some systems comprise a 3D laser sensor; a portable CMM on which the sensor is attached; a PC; and 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 should hold the laser sensor so that a line of laser light appears on the part. The laser system will freely move about the object, allowing the technician to capture data with much the same motions as spray painting. As the technician moves the sensor over the surface of the object, real-time rendering of the data on screen gives immediate feedback. This is important because it lets the technician see areas that were missed and fill them in with another pass. Some systems combine the coordinate data with the Cartesian and angular coordinates generated at each position of the mechanical arm. The result is a dense cloud of 3D data describing the surface of the object.

The key advantage of laser scanners is that they generate many data points in a small amount of time. Depending on the size of the part and level of accuracy required, companies are able to capture tens of millions of points for each part. Measurements aren’t affected by the operators to any significant degree because they’re simply passing a beam of light over the object.

Meeting the military’s need for spare parts
The process may begin when one of the service branches approaches a manufacturer with a request for a new part. Typically, all they have is a new or used physical part and possibly some incomplete technical documentation. The manufacturer of weapon systems scans the physical part with the laser scanner and then uses software provided with the device to convert the point cloud into a surface model that can be imported into its CAD software. The resulting CAD model is used as the basis of a technical data package for the part. The manufacturers often use stereolithography to create a first article that can be used for checking by the customer and to assist in the quoting process. It then sends the technical data package 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’s used to cast the part.

Even in cases where the company that originally built the parts is still in existence, modern manufacturers of weapon systems can often provide spares faster and less expensively than the original vendor. In one case, the original equipment manufacturer was willing to remanufacture engine cowlings for the H-53 helicopter but quoted a 600-day lead time, which was much longer than the customer wanted. Some manufacturers are able to reverse-engineer the part and deliver spares in only 300 days.
A company for example, is able to move quickly if the Coast Guard asks it to reverse-engineer the anchorage system on a cutter. With the only existing part being on an operating boat that’s going to stay at the port for a short period, the manufacturer can bring its laser scanner, remove the dripping-wet part, scan it in a warehouse near the dock and return the part to the boat the next day so it can sail on time. With every branch of the military operating at a very quick tempo, the ability to quickly and inexpensively produce spare parts is going to become even more important in the future.