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To maintain premium manufacturing quality and repeatability for powerful on-and-off-road diesel engines, Cummins Rocky Mount Engine Plant (RMEP) runs 24/7 inspection using 11 Metris LK CMMs. Enforcing tighter tolerances on key engine parts enables further enhancements to engine performance, fuel consumption and exhaust emission. In the manufacturing process of cylinder blocks, connecting rods and cylinder heads, Metris CMMs automatically verify dimensions and features through touch probing and scanning. To respond to even more demanding precision and productivity requirements, Cummins RMEP recently invested in a Metris XC laser scanning probe for non-contact 3D feature and free-form inspection. Cummins RMEP sees innovative Metris metrology equipment as a critical enabler to further increase engine quality and produce more engines.
Establishing higher dimensional accuracy means better engine
Established in 1980, Cummins RMEP manufactures diesel engines and components. Engines from the Rocky Mount Engine Plant are shipped worldwide to power agricultural and industrial applications, as well as buses, trucks and boats. At its 110,000m2 facilities in Whitakers, North Carolina USA, the company counts approx 1,750 employees who turn out 600 engines per day, ranging between 70 and 00 horsepower. RMEP’s non-stop metrology operations dedicate 4 Metris CMMs to four-valve cylinder head production, 4 to cylinder blocks, 1 to connecting rods and 2 for two-valve cylinder heads. For key engine parts, RMEP production personnel apply all their manufacturing excellence to obtain tighter geometric tolerances, which in turn further increase horsepower and reduce engine emission.
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RMEP non-stop metrology operations dedicate 4 Metris CMMs to cylinder block scanning.
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Connecting rods measurement includes bore diameter measurement at 6 micron accuracy.
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When production began, RMEP used as its primary measurement tools manual gauges and fixtures. These so-called dog house gauges were built to locate manufactured engine parts and evaluate their geometric consistency. Although these gauges provided immediate pass or fail status, it required a lengthy and costly process to modify these structures according to latest design changes. “It did not take too long for CMM technology to supersede the doghouse gauges,” states RMEP’s Quality Engineering Manager. “A much higher degree of flexibility, and live electronic SPC, are needed to efficiently set up and run routine metrology tests in order to monitor the quality of our daily manufacturing operations. At the time when Cummins introduced four valve engines, and steadily increased the number of engine configurations, we incorporated Metris CMMs as an integral part of our manufacturing process.”
Acquiring, sharing and leveraging engine metrology data
Following a typical sampling rate of 1 in every 100, machined engine components as well as manufactured engine subassemblies are subjected to precision inspection. Located adjacent to production lines, Metris CMMs are set up for fast execution in separate temperature controlled rooms, away from dust and dirt. After clamping the samples on the CMM, a trained technician selects the appropriate metrology routine and starts the measurement run. It is a full-automatic routine that picks the right probe and points and scans numerous positions to evaluate milled surfaces and the position and profile of other features. The Metris CMMs consistently guarantee accurate measurement, as they monitor tight dimensional tolerances: 6 microns on connecting rods bores, 10 microns on valve guide diameters, and 25 microns of flatness on finished faces.
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Metris Camio software offers full off-line simulation of 4-valve cylinder head measurement.
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Probes point and scan numerous positions to evaluate milled surfaces and features such as chamfers.
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Every day, hundreds of parts pass CMM inspection. The Metris Camio software platform manages the operation of the CMMs and streamlines the data flow of the acquired geometric data. A Technical Specialist of the Rocky Mount Engine Plant explains that in order to keep track of all measurement data, RMEP made sure that the data are automatically processed and maintained in a dedicated Visual SPC database. “Over 300 operations managers, manufacturing and product engineers and quality professionals regularly use this structured RMEP knowledge base to consult measurement reports or look up specific data items. As CMMs acquire massive amounts of measurement data, we opted for concise reports for the production operators that only show the measurements that are outside of tolerance limits. It is important that we maintain the link between the inspection of engine parts and the production workers who manufactured the parts. Discussing key test results motivates our production people, because it maintains their involvement and allows them to improve their production practices. Over the years, Metris CMMs helped us develop manufacturing skills to machine characteristics at a capability we were unable to measure, let alone maintain, in the past.
Metris CMMs increase manufacturing quality and productivity
“To support the 1000+ engine configurations that we currently offer, Cummins RMEP strategically opted for high-performance quality control. “When we decided to standardize on Metris CMMs, we understood that the most efficient use of the systems required professional programming overhead,” clarified the Technical Specialist. “To keep our 11 CMMs going around the clock in 3 shifts with minimum operator intervention, we allocated a full-time programmer to create and simulate hundreds of inspection programs off-line. We are satisfied with the Metris Camio software, which provides full simulation capability of all machine moves, probe touches and probe head indexing. The software also manipulates the position and orientation of the CAD model and runs full off-line collision detection. Recently, RMEP successfully completed the rather lengthy migration process to DMIS, which on average cut 30-40% off from inspection lead-times.”
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Located adjacent to production lines, Metris CMMs are set up in separate temperature controlled rooms.
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Cummins runs many touch sensor inspection tasks, including the scanning of surface valve cover sealing.
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To cash in on the trend to capture geometry faster and with greater data density, RMEP recently purchased a Metris CMM laser scanner device. It is a multi-stripe Metris XC cross scanner that offers superior 3D scanning efficiency by enabling non-contact scanning over clamped parts, digitizing freeform surfaces as well as areas inside holes and deep pockets. Compared to the programming effort that is required for tactile probing sequences, the definition of scan paths for the CMM mounted laser scanner is fairly straightforward. This is because the CMM only needs to move the scanner from one point to another to perform a partial scan of the inspected object, following a linear or polygonal motion path. At the fabulous scan rate of nearly 20,000 measurement points per second, a complete scan adds up to millions of measured points that altogether represent a digital 3D copy of the scanned surface. Acquiring more in-depth information about parts being manufactured will enable the Rocky Mount Engine Plant to make better informed decisions that will further drive manufacturing excellence.
Up to tighter part specification and higher daily output
Although RMEP was convinced about the quality and accuracy of Metris CMMs, the company ultimately selected Metris for its service and support package that fitted its specific needs. Metris provided in-depth CMM training at RMEP to compress the learning phase for programmer and users, and remained available for extra assistance. On the hardware level, Metris organized a local support engineer who periodically calibrates the systems and is available in case a machine needs repair. “Yearlong experience at RMEP demonstrates that this way of working guarantees nearly 24/7 operation on 11 CMMs, and reduces standstill time to an absolute minimum,” concludes the Quality Engineering Manager of Cummins RMEP. “As part of our ambitious plans for the future, we identified Metris CMMs as a critical enabler to produce components to even tighter specification and increase our daily output to over 750 engines.”
Download: Metris 24/7 quality control at Cummins Rocky Mount Engine Plant (PDF file)
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