Winning at Manufacturing Takes Better Feedback
Modern measurement machines expose hidden problems that can hold you back
By James R. Koelsch
Excellence is the key to winning, whether it's in the marketplace or on the racetrack. Just ask Richard Childress, president and CEO of Richard Childress Racing (Welcome, NC). Not only did all three of his teams qualify for the Chase for NASCAR's Nextel Cup last year, but Clint Bowyer also finished third. Kevin Harvick, moreover, won that year's Daytona 500, and Jeff Burton won the Samsung 500 in Texas.
As important as drivers are, they are only part of the story in motorsports. RCR builds about 650 high-performance engines and nearly 50 chassis and suspension systems every year. Racecars are products, and like any other product, they must be designed and built. Another set of design and manufacturing teams, therefore, works together in close collaboration behind the scenes to improve designs and build ever-better cars.
Because automotive performance demands perfection, every part and every fit must be exactly right. For this reason, RCR is taking a cue from the big automakers and other manufacturers of highly engineered products. The company is using CMMs and other scanning devices to extract intelligence from their products and processes for a continuous-improvement program. The objective is to use metrology to boost engine performance and improve the aerodynamics and torsional stability of RCR's racecars.
Two years ago, RCR invested millions of dollars in metrology equipment and consulting services from Metris USA Inc. (Brighton, MI). "The technology involved in NASCAR today continues to grow," explains Childress. So, the technology in his engine and fabrication shops must keep pace. The combination of tactile and optical measurement is part of the pace of the technological evolution at RCR.
In engine production, for example, a Libero CMM fitted with touch probes and an XC50 LS laser scanner work around the clock to automate the inspection of machined components. Because inspectors no longer check them with micrometers, calipers, and other manual gages, it's now practical to check each component against the original CAD model as the part arrives from the supplier. These data also provide a basis for the dynamic performance tests that the shop conducts after every race to track and study the differences in each engine over time.
The CMM uses a touch probe most of the time, because portions of the studies require the probe's micronlevel accuracy. Yet, it also uses the laser scanner to capture the thousands of points necessary for measuring complex surfaces. The scanner collects 19,200 datum points/sec along any 3-D surface in its line of sight. Its spatial resolution is within 20 µm, and accuracy is within 10 µm.
Because of the size of its products, the chassis-and-suspension shop relies on a different optical technology to ensure that the structures it measures comply with evolving NASCAR rules and RCR's own design specifications. This Krypton K600 six-dimensional coordinate-measuring system consists of a hand-held probe and a row of CCD (charge coupled device) cameras on a tripod. Using triangulation, the cameras automatically follow the probe throughout the working envelope as the inspector touches the probe to the required points on the chassis-and-suspension system.
Because the probe is not attached to the camera module, the operator is free to move about the chassis unencumbered. The range is not limited to the length of an arm, as it was when the staff made these measurements with an articulated measurement arm. Because "leapfrogging," or moving the base of the arm, to measure the entire length of the chassis is no longer necessary, the job takes 40% less time.
Not only do these savings generate more time to fine-tune new suspension designs, they also streamline the engineering studies performed on the chassis after each race. During the racing season, engineers have access to the cars for only a few days between races. The accuracy and repeatability of the measuring system also helps the shop to reproduce exactly each chassis and suspension to design specifications, and to repair any wear or damage sustained during a race.
A kind of global-positioning technology from Metris has launched coordinate measurement into the space age. Called iGPS, or indoor global positioning system, this coordinate-measurement technology relies on laser transmitters mounted on the walls and ceiling, much like an actual GPS uses satellites. As an inspector touches parts with a probe that resembles a walking staff, the system calculates the X, Y, and Z coordinate points within 90 µm.
Richard Childress Racing has transformed its entire fabrication shop into a giant surface plate by installing 10 of these laser transmitters. Engineers and technicians there use the system for body engineering and manufacturing, an art that balances aerodynamics against handling. The shop shapes and welds the sheetmetal together, aligning the body and chassis to conform to both NASCAR regulations and its own optimal design. In the process, technicians use the iGPS for intermediate measurements as the body is being built, fine tuning at the end of the process, and final verification.
Because the iGPS covers the entire shop, the staff can measure several car bodies simultaneously anywhere in the shop. An inspection of a body usually involves 130 points. The conventional methods—which included levels, plumb bobs, and tape measures—used to take five to 10 mandays. Now, one person can do the same work in a few hours.
Advanced laser-based metrology is not just for exotic applications like racing. Commercial automakers are also using it to bring their products to market. Take Skoda Auto (Mlada Boleslav, Czech Republic), the Czech automaker that has been a member of the Volkswagen Group for 17 years. Since becoming part of VW, it has undergone a modernization program and evolved into a kind of new-model laboratory. For example, the just-released Skoda Fabia is the first vehicle with VW's new subcompact platform, which is shared by the Seat Ibiza launched in June, and will be used by the forthcoming VW Polo.
Metrology has played a key role in the company's evolution through the work of the prototyping department, which provides development and limited inspection services to the rest of the company. During the modernization program, photogrammetry for digitizing parts supplanted conventional probing in many applications. The old techniques had been providing too few reference points, especially on contours. As scanning technology advanced, the department eventually bought a kind of laser-based portable CMM from Leica Geosystems (Miamisburg, OH), a Hexagon Metrology company.
The heart of this system is its manufacturer's Laser Tracker, which is essentially an automated theodolite that locks onto sensors and tracks them through space. To measure parts, it follows sensors on a gun-like device that an operator manipulates in space. Its internal software then calculates 3-D coordinates based on signals from the sensors. The tracker at Skoda follows two kinds of handheld devices, a T-Probe and a T-Scan, which give operators the option of either touching features with a probe or scanning them with a laser.
As an internal service provider, the prototyping department uses the tracker to inspect welding and drawing tools, digitize physical models of cars, and check the fit in final assemblies. In the case of welding tools, technicians take both a probe and the tracker to the job. "Thanks to the system's portability, we can easily move it around the plant, eliminating the time required to transport the tools," says Monika Grubnerova, prototyping quality assurance engineer. The system takes about 10 min to set up and measures within 0.3 mm.
For inspecting drawing dies the scanner is the better tool, because it's faster at digitizing the surfaces that will be compared to the original CAD files. Even better applications for the scanner are inspecting interiors and digitizing scale models of vehicles. Inspecting interiors has been a challenge because the small space limits the size of the equipment that can be brought inside. "Besides, many surfaces [and gaps] that we need to inspect are hard to reach," adds David Vanek, quality assurance engineer, 3-D inspection. "Neither an articulated arm nor a traditional CMM machine are suitable for this work."
Another benefit is that the laser head automatically adjusts the intensity of light for each point being measured, making it possible to digitize parts that differ in color or reflect light differently. This ability is a boon for digitizing models, because conventional laser scanners often require applying a reflective coating to the surfaces being measured to ensure that enough light bounces off them. "When we digitize models, we are not allowed to spray or powder them, because these models are going to be shown in various presentations," explains Vanek. "So, we have to be able to scan them without modifying them in any way."
Virtual assembly will probably be the next application that the prototyping department will develop for the laser scanner. The expectation is to be able to import scans of sheetmetal panels into the vehicle's CAD data. Using gap specifications, the software would then be able to offer feedback about the assembly, such as whether there are some collision or inference problems to resolve.
In the past, the only option to solve such assembly problems was to bring the parts to the metrology lab. "This process could easily rob us of 1–2 workdays," says Jan Novak, department manager. It also interrupted the workflow. "So, we wanted to be able to measure in one part of the building today and be somewhere completely different tomorrow." For him, scanning with the laser tracker is the most time-efficient method for finding errors with the least disruption to the manufacturing process.
As useful as these lasers are, the conventional CMM is still a more down-to-earth technology for production lines, especially given the innovation going into modern machines. "Lasers are great for gathering large amounts of data very rapidly, but they have challenges with reflectivity and inherent inaccuracy," says Craig Borkowski, Carl Zeiss IMT Corp. (Maple Grove, MN). "They are very good for reverse engineering, but not for measuring an engine block."
This is true for a few reasons. First, contact probes on a CMM are between five and ten times more accurate than lasers. "For automotive powertrain, the true position of a bore is typically within 20 µm of a datum reference," says Borkowski. "A 10% gage R&R for a 20-µm tolerance is normally deemed acceptable." A laser would probably score within 200 to 300 µm.
The second reason for probing being far more common in powertrain inspection is that lasers need to be able to see the surface. "What a laser can't see, it can't measure," notes Borkowski. A probe, on the other hand, can reach deep into cylinder bores and touch hidden features."
The shop-hardened CMMs available today, moreover, suit the environment of automotive factories. Modern materials give these machines enough thermal stability that they can sit right on the factory floor, outside an air-conditioned enclosure. To produce thermally stable axis scales, for example, Zeiss' CMM business borrowed a material that a sister division had developed for lenses used in outer space. Called Zerodur, this material's coefficient of expansion is only 0.13. Likewise, the material for its probe extensions, a carbonfiber composite with a double-helix weave, has a coefficient of expansion of 0.1.
The CMM builder also seals its shop-hardened CenterMax machines to keep dust from getting inside, and makes their foundations from a polymer concrete to protect them from water. As stable and solid as granite is in a dry environment, it is unsuitable outside an air-conditioned room. "Granite is like a sponge," explains Borkowski. "It will soak up moisture from the air and swell."
Given the stability of these machines, Ford Motor Co. (Dearborn, MI) installed seven of them next to its diesel-engine line in Dagenham, England. Five monitor the production of crankcases and cylinder heads, and two check crankshafts. In the testing phase, Prismo 10 CMMs in the plant's climate-controlled quality-control labs verified that their hardened counterparts in the factory were consistently generating comparable results.
As part of the service stipulated in the contract, Carl Zeiss' experts worked with Ford's engineers in a three-month concurrent engineering project to optimize the measurement routines and integrate the CMMs into the rest of the process. They used Zeiss' Calypso planner software to program and simulate the motion of the machines. The programs automatically choose the correct probes for each measurement, and specify the shortest measuring routines. The measurements then flow into Ford's SPC system, which monitors production and helps the automaker manufacture efficiently and win in the marketplace.
When Your Business is Measuring Small Parts
When you're a precision dimensional-measurement laboratory, you're something of a job shop. And as one, you need versatile inspection equipment that gives you the capacity to get the work done and out the door as quickly as possible. Yet, you don't want the added burden of any more capital equipment than is absolutely necessary.
This is why the Galileo video-based, multisensor measurement machine from the Kinemetric Engineering Div. of the L.S. Starrett Co. (Laguna Hills, CA) is a strategic piece of equipment for Q-Plus Labs Inc. (Irvine, CA). The machine resembles a machining center in that it can select a tool—touch probe, video camera, or laser scanner—best suited to the feature it's inspecting. So, the ISO 9000-registered and ISO-17025 accredited lab uses the machine to inspect parts that are smaller than 6" (152 mm) and that require various measurement tools for inspection.
"Because we're a general-purpose measurement lab, we have something different coming in every day, so we need versatility," says Mike Knicker, president. "Nobody, moreover, sends us his easy work. Everybody's nightmare winds up being our status quo." So, his lab needs equipment that can measure the tough stuff repeatably to submicron accuracies.
Knicker compares the Galileo multisensor machine to a CMM because the two machines are universal measurement devices. He notes, however, that the chief difference between the two is that the Galileo is basically a video-based machine that also uses a touch probe and a laser scanner. A CMM, on the other hand, is basically a touch-probe machine that can also use a laser scanner.
The video-based construction makes the Galileo suitable for checking holes and extremely fine details on small parts. With a high-power lens, the camera can see details that might be too small or flat for a probe to touch or that just take too long to check with a probe. An example is a recent job inspecting a plastic injection-molded automotive housing. "For the through-holes, the video can accurately rip through the position of those holes," says Knicker. "Yet, there are many other features that are more conducive to probing."
This ability to perform a variety of measurements reduces setups, which saves both time and money. Not only does it save the time involved in having a technician move parts from machine to machine, but it also reduces the number of different kinds of machines that the lab needs to buy. Even more importantly, "the more times that you have to re-establish coordinate systems to perform a measurement, the more it affects the final accuracy," concludes Knicker. "And that accuracy is our final product."
This article was first published in the September 2008 edition of Manufacturing Engineering magazine.