Gages adopt high technology features to measure parts rapidly and reliably in production
Sophisticated metrology equipment, like coordinate measuring machines (CMMs) and laser scanners, are increasingly seen outside quality labs. “Many companies have cut costs by moving inspection from the lab to the shop floor,” said Matteo Zoin, head of marketing and new market development for Marposs Corp., Auburn Hills, Mich. It is far better to control production by measuring close to where parts are made compared to a far-off quality lab. Sophisticated metrology systems supply more data and flexibility in today’s production lines, not to mention job shops.
Does this trend spell the end of simple comparative gaging? No. “Despite these advanced precision measurement systems,” said Zoin, referring to CMMs or scanners, “there is always a need for simple and customized gages.” However, gaging solutions have adapted both to emerging needs and new technology that makes them better than ever.
Variety Meets the Need
In the history of manufacturing, producing parts with reliable dimensions enabled mass production, eliminating the need for skilled craftsmen to create guns, steam engines, or looms one-by-one. “This led to the innovation of quality control tools,” said Zoin. “Such devices include height, depth, ring, bore, plug and snap gages. The most visible trend in the market over the past few years is increasing demand for 100 percent inspection,” he said.
Why choose one over another, a simple indicator gage over a CMM? “Budget, personnel, training, warranties, manufacturing methods, materials, general company policies, and measurement cycle time all influence the effectiveness and cost,” he said. Often, tallying up the score, a simple gage first designed 50 years ago might be the right choice over a CMM or a shop-floor laser scanner.
To stay competitive, gaging is evolving and improving as well. “Gaging is becoming simpler to use than in the past, reducing the number of steps and adjustments so as to measure different parts on the same gage,” explained Zoin. Sending the data to a process control system wirelessly or through Bluetooth is also important, something the simple gage of the past cannot do.
“Marposs offers several electronic embedded solutions, our Merlin and E9066 families of devices, that can be integrated easily into any manufacturing information system,” said Zoin. “The recent pandemic is pushing the adoption of new IoT technology, promoting a digital transformation of gaging as well. To mitigate any future risk due to human [error], there will be more automated gaging in manufacturing.”
Speedy Production, Automated Metrology
Speed is where special-purpose gaging often proves its worth. Taking measurements on the production line often can take no more than a few seconds, according to Johni Riesen, product manager and key account manager, automotive for Blum Novotest Inc., Erlanger, Ky. His company’s measuring machines division offers tailored systems, often built around a core design, such as for brake discs, wheel hubs, camshafts and flywheels. “These [machines] are post-process and will be installed inside the production line, connected to the machining centers. We focus on dynamically measuring asymmetrical parts for waviness, roundness, concentricity, parallelism and more,” he said.
Not only is measuring speed important, but the data needs to be sent to a monitoring system. “Everything has to be traced back, and it all needs to be confirmed to a data protocol,” said Riesen. “We build quality systems that not only seek out bad parts, [but also] trace back to which tool on which machine was responsible for which feature. And we automatically update the correction values next to the machining centers so that we have a closed-loop process.”
To Touch or Not to Touch
Riesen also stressed that while a special-purpose gage is just that, it can employ all the sensors a CMM can, such as touch probes, scanning probes, vision or air gaging. “That choice is always part dependent,” he said.
Scott Lukomski, director of sales, metrology for Jenoptik Automotive North America LLC, Rochester Hills, Mich., agreed that gages today can employ optical, tactile, or air methods. “We work in high-volume production work, and our offerings reflect that,” he said.
For example, the company’s Opticline line of shaft measuring systems uses projected light to measure a resulting shadow, tuned to the light’s frequency, to give precise measurements within seconds. “It provides more than just go/no-go information, even though it uses a calibration specimen so that it is really a comparative gage,” explained Lukomski. “It’s a gage that gives you a deviation from an ideal size, so that you can perform statistical process control, for example.” The system provides flexibility in that it can measure everything from a large diesel crankshaft to a small medical device, like a bone screw.
While optical is often ideal because of its speed and precision, there are still times when other technologies are best, such as tactile gages that use linear variable displacement transformers (LVDT). The presence of dust, dirt, or oil can be a problem, as is trying to measure clear parts that are not ideal for optical. There are practical reasons as well. “Tactile gaging, driven by LVDTs, are easier for people to understand and easier to maintain,” he said.
For the best in resolution and accuracy, Lukomski recommends air gaging. While contact probes driven by LVDTs can measure in microns, air gaging can measure to fractions of a micron. The pressurized air flow is itself an advantage. “In a dirty environment, you use the air to blow the surface clean, like removing coolant on parts,” he said. However, their range is limited, so air gaging doesn’t always fit the need.
While Jenoptik is committed to supplying high-volume production work, the nature of that work is changing. Flexibility is becoming more important in the design of special purpose gages. “The advantage of an Opticline-type gage is that you can look at not only lengths and diameters and runout, but also undercuts and fillets, features normally that couldn’t be measured in a hard gage,” said Lukomski. He stressed building fixed gages to maintain a degree of flexibility. If something should change, say a diameter gets bigger or smaller, a minor adjustment of a probe keeps the gage working.
Special-Purpose Hybrids as Gages
If fixed gages are becoming more flexible, more like all-purpose CMMs, providers of CMM technology are providing equipment that is edging into the high-end realm of variable gaging. A prime example is the Renishaw Equator. According to Ben Spokes, business development manager, gauging products for Renishaw Inc., West Dundee, Illinois, the company provides shop-floor solutions ranging from the Equator to the REVO five-axis, multi-sensor system.
“Gages have a number of benefits over CMMs when used on the shop floor,” explained Spokes. “They are likely to achieve shorter takt times than most CMMs—dependent on demands.”
In part, speed is gained by measuring at the point of manufacture and measuring only what is required. Being close also means providing better closed-loop process control by directly updating tool offsets on the machine tool control, keeping part dimensions close to nominal and well within process control limits. Any process drift is quickly corrected, improving part quality and manufacturing capability, along with reducing scrap.
But doesn’t the Equator appear to be a CMM? “One of the main misconceptions about Equator is that it is an absolute device, like a CMM. It is not. It is a comparator. And there are many advantages for a comparative gage on the shop floor. One is when there are large temperature changes, especially when the rate of change is significant,” said Spokes. The Equator measures in the range of 5-50o C (41-122o F).
Another point Spokes made is that it is not a delicate “quality-room” device. “It is shop floor hardened and will take a certain level of contamination; in cases of extreme contamination it can be supplied with an enclosure. This is particularly useful since it is often employed in fully automated cells. With compact size and easy software configuration, Equator systems are ideally suited to integration into cells, for shuttle and robot loading in smart factories,” he said. “It is typically four times faster than most shop floor CMMs, with similar accuracy.” Repeatability is quoted on Equator systems as a comparison uncertainty of ±0.002 mm. Accuracy is a function of both the Equator system repeatability and the certified accuracy of the calibrating device (e.g., CMM, bench gage, or calibrated hand gage) for the master part.
The Equator’s ability to use a scanning analog probe as well as take touch points with a touch-trigger probe enables short cycle times, according to Spokes. “Usually Equator customers want to match the manufacturing process cycle time, especially if they are performing 100 percent inspection,” he said. Spokes also believes Equator is suited to a manufacturer making many small-batch parts, where the Equator can switch between programs in a matter of seconds to measure a different part number.
Zeiss Industrial Quality Solutions, Brighton, Mich. is a maker of traditional CMMs that developed its own line of shop-floor CMMs—the DuraMax, GageMax and CenterMax. “A misconception is that it’s hard to use and set up a CMM to program and use it. This is not true,” said David Wick, manager of product management.
Especially with the growing practice of attaching product manufacturing information (PMI) to CAD models, including GD&T callouts, it is easier today to get software that can create a measurement program almost automatically. This means Zeiss shop-hardened CMMs are appropriate for flexible gaging, and are easy to reprogram with the ability to collect data over complex surfaces and devices, according to the company.
“The DuraMax is not a comparative gage in the sense that we measure against a golden part; we compare to the dimensions of a specification, drawing, or a CAD model,” explained Wick. Using its scanning analog probe, the DuraMax collects data on complex, freeform contoured surfaces, like turbine blades. The GageMax can also be fitted specifically as a gear measuring device. The DuraMax is dust and moisture protection per IP54, with an optional rotary table, and the high-temperature gradient version collects data accurately up to 40º C (104º F).
Precision accuracy is a key feature. For example, the GageMax, equipped with a Zeiss VAST XTR gold probe, has a maximum permissible error of 2.2 + L/300 µm (as measured against ISO 10360). The CenterMax version also has a Zeiss ROTOS surface roughness measurement probe. The ROTOS has a skidless version for access to common surfaces and skidded version for high accessibility in deep recess regions. The skidless measures Ra 60 nm (±5 percent) while the skidded measures Ra 15 nm (±5 percent).
Mixed Systems, Good Results
Is there really a need to decide between a high-end, multipurpose metrology device and a simpler fixed gage or even hand-held micrometer? Perhaps not. It might be more a case of how best to meld all available tools into the best system possible. An example comes from Tim Cucchi, precision hand tools product manager, The L.S. Starrett Co., Athol, Mass. Starrett is one of the largest suppliers of hand-held metrology devices, including 350 different types of micrometers as well as calipers, indicators, gage blocks, and surface plates. The company also delivers vision, optical, and laser measurement systems as well as special purpose fixed gages made for specific applications. “Sketch out on a napkin the tool you need or the application you need to solve, and we will design, engineer and make it,” said Cucchi.
Since Starrett makes its own tools, it is only natural for them to use Starrett metrology devices to make them. “Six months ago, we instituted a Starrett vision system in our indicator manufacturing cell,” said Cucchi. The five different vision systems used for first article inspection (FAI) include some with 3D measurements and they capture a complete picture of each new part, say a spiral gear used in a indicator. “We capture all the details and store that information in our quality system,” he said. When production starts, operators will periodically measure parts using hand tools or specialty gages, collecting less information than needed for FAI, but enough to know the process is under control and quality products are being manufactured. “One technology does not displace the other,” Cucchi said.
Like all those interviewed for this article, he stressed the need for metrology devices to send their data for use in process and quality control. “A lot of people in the baby-boomer generation trust mechanical gages over electronic, but that is beginning to change with more use of digital readouts (DROs),” Cucchi said. “The generation that grew up with a cell phone or smartphone in their hand, that is what they want.”
Perhaps this fact will lead manufacturers into Industry 4.0 more than anything else. Starrett offers its DataSure wireless collection program that, coupled with IP67-rated electronics on its handheld equipment, can transmit data hundreds of yards. DataSure eliminates manual, error-prone data entry, collects data up to five times faster than other methods, and works with Starrett electronic hand tools and other manufacturers’ tools, according to Cucchi.
Wick from Zeiss agreed there is room for all technologies. “There is no set of macro trends that will eliminate traditional gaging versus super sophisticated flexible gaging. There are applications for both everywhere,” said Wick.
He does point to a new idea for how best to employ this growing mix of devices and the data it collects—artificial intelligence. AI Is best employed when data is noisy or when judgment between options is needed—not in programming a device to take 50 measurements, but in deciding if those 50 measurements are needed.
“Let’s say I noticed that I have taken 1,000 measurements of 50 characteristics and 27 of them never change, or are within an extremely tight distribution,” Wick explained. An AI program can recognize that and advise against taking those unneeded 27 measurements, thereby shortening the metrology part of a production process. “Increasing use of AI can make a gaging system more productive,” he said.
That depends on the ability to collect the data, transmit it, and use it in an AI calculation, which involves much more than choosing between fixed and variable gaging.