Automotive Metrology Speeds Ahead
In automotive manufacturing metrology, speed and accuracy are paramount. To meet tight time-to-market challenges and strict quality-control demands, automotive OEMs and suppliers must get the utmost performance from tools that enhance part production throughput while meeting quality goals.
The latest trends in automotive metrology include the continued migration of measurement and inspection tools onto the shop floor, where users can best utilize highly accurate CMMs and portable CMM equipment that is located either within production workcells or close to production lines. Advances in CMMs, handheld gages, probe tooling, and metrology software all contribute to better, more reliable powertrains as well as the greatly improved sheetmetal fit-and-finish for today’s vehicles.
“The trend is consistent. The Big 3 as well as the supplier base are looking to split microns—they’re looking for tighter and tighter tolerances—and at the same time, they’re looking for more throughput,” notes Ken Gibbs, strategic account manager to Ford and Chrysler, Carl Zeiss Industrial Metrology LLC (Maple Grove, MN). “These machines that I deal with personally are not completely integrated into the manufacturing cells, but they’re located out in the production areas. We’re very big on turnkey solutions.”
“These machines have bar-code
readers, where they can track
every engine that they make.”
One of the reasons CMMs now typically reside on the shop floor, inside or nearby workcells, is that the measurement machines do not always require special climate-controlled rooms or enclosures due to the systems’ improvements in thermal compensation techniques. “There are two approaches,” Gibbs notes. “We do supply machines that can sit out in the production environment with no enclosures and no temperature-controlled rooms. In some locations, we put enclosures up with a different kind of machine. It’s all price-driven, whether they want shop-floor installations or they want laboratory-type enclosures out on the factory floor.”
For automotive operations, Zeiss primarily offers three lines of CMMs—the company’s CenterMax, GageMax, and DuraMax systems—all of which can exist on the factory floor, notes Jeff O’Brien, Zeiss account manager for General Motors Corp. (Detroit). “Those all live on the floor with no help for the environment,” says O’Brien. “One of the advances in our product to make these machines really live out there is the probe tooling. There’s been a lot of advanced technology put into the probe tooling, because once we came up with a machine that was accurate and repeatable on a factory floor with constantly changing temperature, the probe tooling became the next critical item to improve.”
With these changes to its ThermoFit probe tooling, Zeiss CMMs now can more easily thermally compensate for any changes in automotive component sizes due to temperature fluctuations on the factory floor. “It was designed for these types of machines, because once you have the machine stable, if your probe’s moving around or your probe head, there’s no advantage to having a stable machine,” O’Brien adds. “Something we’ve been constantly improving is the tooling for those machines. And then when you see the [Zeiss] Prismos, Accuras and Conturas, those’ll go in environmental rooms on the factory floor.
“More than 90% of the machines we sell to automotive powertrain plants are on the factory floor,” he adds. “One of the things it’s helping is that most, well all, of the automotive factories if they’re new, have a tempered environment. I don’t want to say that it’s totally controlled, but it’s tempered—the swings are less. I would guess they’re between 60° to 80–85°F [15° to 26–29°C], they’re more tolerable.”
Probe tooling advances and machines on the factory floor are pushing productivity, allowing automotive suppliers to measure parts much faster. “On the probing, we have a unique feature where we can actually pick up a temperature probe from our probe rack, go to the part and get real-time part temperature, so we can do the correct material compensation,” Gibbs states. “It’s a development that’s more and more accepted and used in these plants.”
Zeiss CMMs are used in both powertrain and sheetmetal operations, although there is a higher rate of usage in powertrain operations. With more powertrain components being built from aluminum because of the trend to lighter more fuel-efficient vehicles, temperature variations can be even more critical. “Because most of the parts in powertrain now are aluminum, they move,” O’Brien notes, “so after they machine them and wash them, before we measure them, we need a stable part. That’s one of their biggest problems is to give us a stable part that won’t change during the measurement.”
Many auto builders are most comfortable with stable, proven technology, Gibbs adds. “Our powertrain customers, they are stubborn. When we supply them a piece of machinery, they want it to be proven,” he adds. “It does not incorporate risk. They don’t like change.
“Automotive manufacturers stay with what’s comfortable, because their product is dependent on these machines,” Gibbs says. “These machines have bar-code readers, where they can track every engine that they make. We supply them with loaders that shuttle the parts to the machine, they lock it in with no operator intervention, the programs are initiated, and the machine makes sure it’s got the right part on it. Their production is dependent on these machines, so turnkey solutions is what we specialize in.”
“Point density, accuracy, and speed are most critical to powertrain customers.”
Along with the probe tooling advances, Zeiss is introducing a performance package to its machines, O’Brien notes. “That’s a combination of a new probe head, which looks the same but it’s got new technology built into it, with which we’ll be able to do probe changes much faster. It’s like a tooling change on a CNC machine; we’ll be able to drive the machines faster, and we’ll be able to do uninterrupted scanning.”
For example, O’Brien describes a Zeiss CMM scanning an automotive cylinder head or block. “If you look at a deck face on a head or a block, there’s a bunch of holes in it,” he says. “They need to know the flatness of that surface, because that’s where the two pieces go together, and you don’t want it to leak in your car. We can scan those now right over the holes and we never see the holes. In other words, we’re scanning the surface, but we don’t have to go around the holes. We scan right over them. The probe head knows when it’s coming to a void in the geometry.”
The resulting increase in throughput gives automakers a big boost in productivity, some of which comes from Zeiss’ recent updates to its Calypso off-line programming software package. “There’s some software functionality that’s included in there, and we’re dramatically improving the Calypso offline programming capability. What that does for users is they can actually create part programs a lot faster than they used to. There’s a lot of new simulation tools in the software, both for the machine, and the fixtures, and the probe tooling, and the probe changes. There’s been significant advantages in the offline programming.”
Point density, accuracy, and speed are most critical to powertrain customers, Gibbs adds. “In the powertrain facilities, there’s more and more point density needed, and the reason is so that we can collect more data, so that we can analyze more data and bring a better accuracy with the data. The old technology was touch probes with single-point probing; it would come in and measure a point, then it would move and measure a point. These [newer CMM] machines are all full-contact scanning machines, so in other words, when it goes into a piston bore or any kind of geometry, our probe remains in contact with the surface. Instead of measuring 50 points on a bore, in the same amount of time, we can measure 5000 points in a bore.
“That’s still very popular in the assembly plants where they’re doing sheetmetal,” he adds of touch probes. “With powertrain the geometry is, in most cases, clean geometry—a hole is a hole. In sheetmetal, a lot of times, a hole is an oval, or the surface moves, and you can have springback on a fender, or problems with a plastic part. With a powertrain part, the geometry is there. So we can go very fast, and we can collect a lot of data on that geometry.”
Sheetmetal production for automotive depends on fast, accurate measurements obtained from technologies like the white-light sensors offered by the Cognitens brand of Hexagon Metrology Inc. (North Kingstown, RI), which is part of Hexagon’s Portable Group. While not a new technology, white-light scanning has been employed widely in automotive sheetmetal production, notes Cliff Bliss of Hexagon.
“The first target was automotive sheetmetal,” Bliss says, noting GM was Cognitens’ first larger customer. “It’s utilized pretty much throughout the entire process, and it starts way back in die development, so you’re able to quickly ascertain information about your die as soon as it’s cut. That does a couple things; it gives you your baseline, and then as you tune-in that die, either based on your first-off parts back to CAD or eventually, if you’re using a functional build strategy, you’ll go ahead and get a ‘golden’ part and then document that versus CAD.
“If that die happens to wear or break, then you can go back to your ‘fingerprint,’ if you will, versus having to go back to CAD and having to redo the entire process.”
White-light scanning offers automakers a fast, very precise method for scanning sheetmetal, he adds. The technology shortens the time taken to get usable data, to acquire data, analyze it, and get a report. “It’s a quick turnaround, faster than traditional CMMs or stationary products,” Bliss notes. “The Romer arm is a fantastic tool if you have smaller parts. Very quick, portable, and you can get to either a probe or a scan, either one very quickly. If you have a larger part, that means you have to move the arm, or leapfrog, then you can lose a little bit of accuracy. Now, if your tolerance parameters are open, it’s not a big deal, but if they are a little tighter, it takes a little bit longer, and you’ll lose a little bit of accuracy.”
With the white-light scanners from Cognitens, which now use blue-light LEDs, users can measure very large airplane-sized objects, he adds. “For larger parts, we combine it with photogrammetry,” Bliss notes. The company has made inroads into the aerospace market in the past few years, including the Lockheed Martin F-35 fighter aircraft program.
Last year, Hexagon introduced a new white-light sensor for its portable and automated 3-D measurement systems, with the new Cognitens WLS400 product family. The company’s white-light measurement uses digital stereo vision technology to generate highly accurate 3-D data and is aimed at quality-control automotive applications. Customers can now choose between a portable configuration and an automated system that can be operated with industrial robots, and the turnkey systems include the CoreView software suite developed by Hexagon Metrology.
The latest Cognitens software includes CT Measure, which is the main program that brings in CAD data and does all the analysis, Bliss notes. At that point users can view the results in Cp and Cpk charts in the CoreView software. “The automotive industry is looking for versatility, and that’s where Cognitens shines, because we can acquire the data in about a millisecond and the stereo vision negates any vibration. You can operate it right next to a big press.”
The use of a blue wavelength has a few advantages, he adds. “It’s a short wavelength, and it doesn’t reflect as much, so you’re able to take shots of very shiny metal parts,” Bliss says. “Autos are looking for speed—speed and versatility. They want data fast, and they want it right.”
Portable-arm measurement tools continue to be widely used in automotive applications. Racing programs, including those in NASCAR and Formula 1, use the technology for inspection and conformity projects. For measuring larger automotive parts, or a full car, files can get very large and unwieldy, notes Philip Hewitt, international product manager for the PowerInspect inspection software from CAD/CAM developer Delcam plc (Birmingham, UK; Windsor, ON, Canada). Delcam recently updated its platform-independent PowerInspect software, which is now available in a Windows 7-based 64-bit version.
“Autos are looking for speed—speed and versatility. They want data fast, and they want it right.”
“Automotive is interesting because you’ve got a lot of portable measurement. Obviously, if you’re measuring the whole car, you’re dealing with huge files” observes Hewitt, noting 64-bit systems help immensely with a much larger memory addressability compared to Windows XP systems. “That’s very important in a couple of respects. The memory really helps for very large files. Increasingly, people are using 64-bit CAD systems, they’ve grown hugely in the last few years. If you’re inspecting large parts, like body information, you’re now suddenly dealing with CAD files that are much bigger than those of 32-bit CAD systems. Windows 7 is another hit, and there’s quite a lot of pent-up demand, due to the memory size.”
Delcam’s PowerInspect inspection software is being used with two measuring arms from Zett Mess AMPG (St. Augustin, Germany) to inspect chassis prototypes in the Process Technology Prototype Development area of the BMW Group (Munich, Germany). The system gives faster results, and is suitable for both inspection specialists and for production experts who haven’t had training in measurement technology. The PowerInspect software works with a wide range of inspection devices, including CMMs, and optical and laser-based systems, but is most often used with portable arms.
At BMW, every new chassis prototype comes to the prototype team as a CAD file, which is used to weld the design. Welding distortions of 3 mm are the norm and have to be eliminated in a continual process of welding, inspection, correction, inspection. In the past, the inspection process for some of the parts required up to two hours; with PowerInspect, only five minutes are needed. This gives significant time savings, since up to five inspection passes are required per component. “Users are able to measure out the coordinates much faster,” notes Stefan Schneider, Delcam GmbH application engineer. “Every measured point can be compared to the CAD data with PowerInspect. The inspection software immediately and precisely shows the deviations within the specified tolerances.”
Handheld gaging tools like the surface roughness testers from Hommel-Etamic also are very critical to automotive metrology, where users want to have the best measuring tools available on the shop floor. As the industry increasingly moves toward lightweight vehicles, requirements on tolerances and surface finishes are magnified, according to Andreas Blind, vice president and managing director, Hommel-Etamic (Rochester Hills, MI; Villingen-Schwenningen, Germany). “In general, we are seeing that the tolerances are becoming tighter, ” Blind notes. “New smaller engines have different requirements. As tolerances become tighter, surface finish gets finer, and that can be a definite challenge for our customers.
“Surface finish has a significant impact on part tolerance. In the past, when you looked at generic diameters on a part, let’s say it’s a crankshaft,” he says, “surface finish had a nominal impact on a part’s overall diameter tolerance. Back then you would have had a 10-µm diameter tolerance, which today is typically less than half that. An Rz (average peak to valley height of a surface) surface finish tolerance of 4 µm now has significant influence on overall part tolerances.”
Due to this fact, surface finish tolerances have become finer in general, he adds. “If you have a surface finish of Rz 1 or 2, controlling that feature directly on the shop floor becomes much more challenging,” Blind notes. The new W5 surface roughness tester from Hommel-Etamic gives workers a high-accuracy mobile gage usable anywhere in the plant, he adds. “What we can also see is that people want to get away from the traditional way of measuring in a laboratory utilizing sophisticated stationary roughness systems,” Blind states. “They now want to have metrology solutions right on the shop floor. They want to use a surface finish unit and apply it at the point of use, by taking a measurement and walking away with an immediate result.”
Form-measuring equipment from Hommel-Etamic offers all the features needed today on the shop floor, with measuring systems offering automatic roughness, form, and contour measurements all in one unit. “One of the megatrends in the manufacturing industry is optical measurements,” Blind observes, citing the company’s Opticline flexible shaft measuring solution for tolerances and forms. “We have optical measuring systems that replace the old style fixture gages, which were dedicated to one workpiece and needed part mastering. The Hommel-Etamic Opticline is an extremely accurate and flexible noncontact gaging system. It allows the end user to put parts in our gage, press a button, and 30 seconds later you have 40-50 measurement results.”
Another innovative gaging system used in automotive is the new three-axis Equator 300, a versatile, custom gage from Renishaw Inc. (Hoffman Estates, IL). The system is being used along with Renishaw’s other measuring devices including the REVO measurement system and the new PH20 probe head.
“We’ve focused a lot especially in the last year on improving process control,” says Renishaw’s Denis Zayia. The REVO five-axis system has been out for some time, and has had some successes in the aerospace industry, he notes. “What’s been interesting is when doing engine blocks, the average inspection takes about 20 minutes, and we’re doing that in five minutes or less—without the loss of accuracy,” Zayia adds. “The REVO scans thousands of points a second with no degradation of the data. Obviously, the automotive tolerances are much tighter.”
The new Equator, with its 300-mm volume, is aimed more at measuring smaller parts. “We’re mostly doing connecting rods and other components with it,” says Zayia. “We’re not doing engine blocks. The big picture is throughput and process control—controlling the process, making more parts quicker, and not making scrap.” ME
This article was first published in the September 2011 edition of Manufacturing Engineering magazine. Click here for PDF.