This section was edited by Associate Editor Alan S. Brown.
Technology Focus part 2:
Materials and Assembly
Laser Measure- ment Without the Setup
Looking for a way to measure both the gross dimensions and the nooks and crannies of large objects? Faro Technologies Inc. of Lake Mary, Fla., has developed a system that combines laser trackers and probe arms—without the arduous setup such applications typically require.
Over the past decade, laser trackers and probe arms have earned their places in factories that need to align, inspect, reverse engineer, or simply measure large parts and components. The systems do many of the same tasks as coordinate measuring machines, but are more flexible and portable.
Laser trackers work by tracking a three-sided mirror, called a spherically mounted retro-reflector, as it moves along a surface. Faro's Laser Tracker X, for example, has a 230-foot-diameter range and measures single points within 1 mil accuracy.
Probe arms look like tripod-mounted robotic arms. The arm is designed to swing into those spaces that are hidden from the laser tracker's line of sight. Running the measurement tool, or probe, at the end of an arm over those hidden surfaces provides the measurements. Faro's Platinum FaroArm is accurate down to 0.5 mil.
Both laser trackers and probe arms use the measurements to create coordinate maps. Overlaying those two maps provides a complete picture of the part and how the measurements relate to one another. Creating the overlay, however, is not a simple process.
"In the past, you had to measure a common set of points to align the two coordinate systems," explained Faro's senior technical product manager, Chuck Pfeffer. "You would measure 15 points with the tracker using the retro-reflector, then move the arm to six of those points and take a measurement. That would enable you to transfer the arm's coordinate map into the tracker's coordinate system."
An experienced team could probably run through this setup in 10 or 20 minutes, depending on conditions. But to measure large components (think industrial machinery or aircraft components), they would have to move the tracker/arm system from position to position. That creates lots of downtime.
Faro's new technology lets a team do it in less than one minute, Pfeffer said. The key lies in a retro-reflector that mounts on the probe arm. "The system prompts you to catch the reflector with the tracker laser," said Pfeffer. "Then you move the arm to six random positions. The arm and the tracker take simultaneous measurements of the arm's position and automatically juxtapose the two coordinate systems. It might take all of 20 seconds."
The new system eliminates preparation of the work area, he noted. This makes it much easier to use the tracker/probe arm combination on really large systems, like aircraft fuselages, cars, and big machine parts.
Such precision is not cheap. Trackers typically cost $103,000 to $150,000; probe arms, $40,000 to $60,000; and measurement software runs roughly $18,000. He said that most combination systems run from about $150,000 to $160,000.
Tape That Trailer to Take the Shocks
An acrylic foam structural tape from 3M Co., with high-strength adhesive on both sides, has been around for 25 years. The tape, called VHB, is used to join everything from signs, appliance panels, and electronics housings to architectural panels, glazing, and door and window trim. Yet it is only just now breaking into freight containers.
The reason behind 3M's recent success? Getting close to potential customers, according to Steve Stark, a market development manager in 3M's industrial adhesives and tape division. "Three years ago, we put a team together and started looking at guys in the trailer business," he said. "We decided to forget about our tape and just look at what trailer builders did and did not do well from an engineering and design perspective."
Trailers consist of aluminum side panels screwed into a metal frame. When fabricators tried VHB, they continued to screw the panels into the frame along the top and bottom and tape them to one another where they overlapped lengthwise.
That caused problems. On hot days, thermal expansion causes panels to bulge. Mechanical fasteners constrain that motion. The screws on the top and bottom of the panel transferred all that motion to the lengthwise section where the panels overlapped. Those bulging panels eventually ripped away from the tape and began to pop off.
Most trailer fabricators soured on VHB, but one group stuck with it. They built trailers for people who made their living from race, rodeo, and show horses. Their trailers, which often include living quarters, typically cost $100,000 or more. They liked VHB tape's foam core, which absorbed noise and rattling that spooked horses during travel. Horses in VHB-built trailers recovered faster before competitions.
Fabricators solved the problem of the popping panels by switching to all-tape bonding. They also shortened the panels so they did not butt directly against the top (or bottom) of the frame. This let the panels "float" on the frame. They absorbed thermal cycling easily without showing any signs of bulging.
3M built upon its knowledge. The company took a close look at successful horse trailer manufacturers like Cimarron Trailers Inc. of Chickasha, Okla. "We found that firms who designed VHB into their products from the beginning got better results than those that stuck it on like any other fastener," Stark said.
According to 3M, the tape absorbs thermal cycling and shocks from bumps and potholes. On conventional trailers, those forces eventually loosen mechanical fasteners.
In simulated testing at Bosch Automotive Proving Grounds in South Bend, Ind., 31 percent of the mechanical fasteners on a conventional trailer from a major manufacturer came loose after 36,000 miles. The taped trailer showed no signs of failure after 100,000 miles. The taped trailer also resisted leakage when sprayed with water at 3,200 pounds per square inch. The conventional trailer leaked when hit with a garden hose at 75 psi.
Cimarron said that taping panels is faster and less labor-intensive than screwing them together. The resulting panels are smoother and easier (and less expensive) to paint with a decal. Stark also said 3M is confident VHB tape will last the life of the trailer. He claimed VHB has increased its share of the trailer fastening business to roughly 5 percent from virtually zero five years ago.
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