Sensing Size on the Shop Floor
Match metrology to production requirements
By Jim Lorincz
Sophisticated technology for the highest-accuracy dimensional metrology applications is well-known in laboratory-like environments. It isn't uncommon to find devices that rely on capacitance, inductance, optics, and ultrasonics to probe everything from largescale prismatic parts to the tiniest electronic components. Lasers, white light, and some probes with what can only be described as a feather-light touch have all found their specialized uses.
Unlike the laboratory, however, out on the shop floor measuring machines must be protected from the vagaries of shop operation, including chips, fluids, and other potentially accuracy-robbing contaminants. Though CMMs are no longer limited to clean rooms or gage rooms, the legacy of those days is deep-rooted.
"Inserting the CMM into the production line requires a paradigm shift, not only because they are purchased from capital rather than expendable budgets, but also because they must be embraced by manufacturing engineering and made integral to the production plan," says Art Whistler of Helmel Engineering Products Inc. (Niagara Falls, NY).
Whistler points to the availability of CMMs that have been "shop hardened" for the harsh environment of the production floor. "They generally have mechanical bearings in common for reliability and durability, with ways, bearings, motors, and scales guarded, shielded, or otherwise protected. These machines do not need a separate room or enclosures, but dirt and temperature must be managed for good results, by cleaning or cooling or compensating for heat. These systems can be integrated with automation, and even with process control, while providing all the data output anyone would require."
Taking CMMs to the shop floor affords the user access to their traditional advantages. "CMMs are programmable, hence flexible for any number of products and even for mixed production," says Whistler. "They are true 3-D devices capable of analyzing full 3-D relationships and conditions according to GD&T standards. As automatic systems, CMM data are accurate, repeatable, and without operator influence, and for the information provided they are fast." Moreover, as new products or programs are introduced, the CMM can be reprogrammed to handle the new measuring parameters.
Out on the shop floor where real estate is at a premium, the large size of CMMs has been something of a drawback. Helmel has addressed this problem by offering a broad size range of mechanical-bearing CMMs.
Helmel's latest addition to its lineup is the Microgage, a small fixed-bridge design with travels of 6 x 9 x 5" (152 x 228 x 127 mm) and an overall machine size less table of 16 x 24" (406 x 609 mm) that has found acceptance in the EDM, medical device, and fuel systems markets.
An important consideration when thinking about measurement as part of lean manufacturing and process flow is using the right measurement device for the job. Think of the difference between the measuring range of a football compared with that for a watch component, says Fred Mason of Optical Gaging Products Inc. (OGP; Rochester, NY). He explains: "When considering measurement in the manufacturing environment, it is always important to think about the capabilities of each measuring device relative to part design tolerances. Many times the decision of how to measure parts is based on what is already available. How many times is the CMM the place to go for measurements? Not only might the measurement capabilities be inappropriate, the queuing of too many measurements at one machine might create a bottleneck."
Mason suggests using measuring machines that take a particular range of part sizes into account and multisensor measuring systems that provide useful data and the appropriate resolution and accuracy. The combination of sensors on OGP's multisensor SmartScope Flash 302 machine makes it possible to get all necessary measurements of a part in a single setup. Automated measurement routines that include use of several sensors, some of which may be deployed and replaced without user involvement, can improve over process efficiency. The SmartScope Flash's video measuring capabilities enable finding edges, even edges with no physical boundary such as where an area of one color ends and another begins. The through-the-lens (TTL) laser enables deriving accurate surface contours that can be related to NURBS and splines in a CAD file, and a touch probe, can access areas on surfaces not easily measured by video or laser.
The mechanical design of the device will determine how well the different sensors perform, and the repeatability of their measurements. The elevated bridge design of the Flash 302 moves the X-Z-axis assembly, which rides on a pair of ground shafts as a unit above the independent Y axis. The design of the Flash 302 makes it capable of supporting the use of specialized microsensors for the metrology of intricate parts.
The array of Hexagon Metrology brands continues to grow with the acquisition of CogniTens Ltd., a provider of shop-floor noncontact dimensional measurement technology. CogniTens joins Brown & Sharpe, DEA, Leitz, Leica Geosystems, Sheffield, Romer, PC-DMIS, and Tesa brands under the Hexagon AB (Nacka Strand, Sweden) corporate umbrella.
"The acquisition of CogniTens gives Hexagon a new technology in the high-speed, noncontact, shop-floor measurement and scanning segment of the metrology market," says Ola Rollen, CEO and president of Hexagon AB. The addition of the technology is expected to enable "Hexagon to position itself in all segments of the rapidly growing noncontact sheetmetal market, combining CogniTens 3-D measurement products with the laser-tracker technologies from Leica Geosystems and the articulated arms technologies from Romer," Rollen explains.
"CogniTens technology is a structured white light that enables pictures to be taken of a part to provide a rapid 3-D representation of the part's contour. It can be incorporated into an automated cell and used, for example, to obtain information about auto bodies in white, as they crawl past a line. Alternatively, it can be incorporated into the manufacturing environment," explains William Fetter of Hexagon Metrology.
"We have just launched a portable 1.2-m measuring arm, the Romer Infinite 5012, that can access the work envelope of a VMC to do quick checks while in the middle of a machining cycle. Other possible applications include benchtop measuring anywhere needed, CAD-Compare, and desktop engineering, in addition to quick dimensional checks inside a machine tool," says Fetter.
The Infinite 5012 features WIFI connectivity and onboard battery power for cable-less portability. It features automatic probe detection that allows quick probe changes without recalibration, and software packages including PCDMIS Portable, DOCS, and Delcam PowerInspect.
Hexagon's PC-DMIS NC makes it possible to build inspection paths in standard G and M formats to develop, test, and debug NC inspection routines on 2-D and 3-D CAD models off-line without interrupting machine utilization. Measurement data can be collected and evaluated as they are generated without operator intervention, and the resulting information can be sent in a format best suited to its intended user audience. Process-control feedback enables users to monitor operations while parts are on the machine, comparing measured features to the CAD model, and using the built-in SPC module to track and evaluate any processes.
The shop floor doesn't seem to be the most conducive environment for form, dimensional, and positional tolerances of shaft-type parts in submicron detail. The Opticline noncontact CNC shaft gaging system from Hommel-Etamic (Rochester Hills, MI) is a flexible shaft gaging system that accommodates shaft-type part sizes from 0.2 to 480-mm diam, in lengths from 1 to 2500 mm, with measuring accuracies to ±1 µm. The optical measuring machines are available in a range of capacities for medical, aerospace, automotive, and other applications producing complex parts such as hip joints, bearings, and turbine blades. The Opticline can be used in a manned SPC measuring station on the shop floor, or in fully automatic systems for 100% inspection in production applications.
Applications for Opticline include gear shafts, cam shafts, crank shafts, joint shafts, and engine valves. Contour, diam, length, roundness, concentricity, cones, angles, flatness, parallelism, eccentricity, stroke, and threads can be recorded during a single pass of the optical measuring head. Manufacturing checks, automatic tool correction, dimensional measurement, initial sample measurements, and machine setup are typical applications for the family of gages.
Using Opticline, the workpiece is scanned optoelectronically according to the shadow principle. The complete contour of the workpiece can be evaluated precisely due to the high resolution per measured value. Data of the outer contour are also recorded during rotational movement for dynamic measurements. If no measuring program is available, the workpiece is loaded, then scanned completely and saved in the program memory. Characteristics are then defined according to the production specifications, such as nominal value and tolerances. A normal new test plan with about 20 characteristics can be created within five minutes.
The desire of manufacturers for economical shop-floor CMMs with a high level of accuracy and the ability to measure to repeatable precise tolerances led to the introduction of the X-Checker series of CMMs by Wenzel GmbH (Germany) and Xspect Solutions Inc. (Wixom, MI). The X-Checker is designed with an X-shaped machine base cast from polymer mineral resin. The design objective is performance in shop-floor production applications where environmental conditions are inconsistent. It combines stable granite components with frictionless bearings, pneumatic counterbalance, and gage R&R consistent performance.
The X-Checker can be used as a touch probe or scanning CMM, and features Renishaw TP20 and TP200 probing systems or the SP25 scanning probe. The machine is supplied with the OpenDMIS CAD software, allowing for both CMM programming and reporting using the CAD model. The X-Checker has a maximum 3-D measuring speed of 700 mm/sec with maximum acceleration of 2 m/sec2. Measuring range is 750 x 1000 x 500 mm (X,Y,Z).
European automakers have benefited from the capability and flexibility of the GageMax 3-D measuring machine from Carl Zeiss IMT Corp. (Maple Grove, MN). The Visteon factory in Duren, Germany, manufactures several thousand pinions and drive wheels per day. It has used the GageMax for over a year directly in production of bevel gears, without an enclosure for climate control. The quality inspection of finished bevel gears occurs at intervals under the responsibility of the respective machine operator.
The Visteon measurement strategy with GageMax has achieved the required flexibility as other products, particularly prototypes, can be accommodated. The plan calls for corrected values to be immediately transferred to the production machine. Data are stored and evaluated with qsSTAT and Zeiss Calypso software. The GageMax has proven insensitive to the temperature, vibration, and dirt typical of the production environment.
At the Volkswagen Saxony GmbH engine plant in Chemnitz, Germany, Zeiss measuring machines, two GageMax and three CenterMax machines with manual and automatic loading systems, have been instrumental in transferring a portion of the traditional measuring tasks to production personnel.
The entire parts spectrum requires two measuring systems: balancer shaft housing and cylinder head covers are suitable for measuring with GageMax, which has a measuring range of 500 x 700 x 500 mm. With its large measuring range of 900 x 1200 x 700 mm, CenterMax was suitable for cylinder crankcases and cylinder heads. The measuring systems can take over for each other in an emergency.
Switching to Calypso software made system integration possible. This is especially important as the measuring machines deliver a denser information base for process monitoring than earlier strategies. In addition, their flexibility permits fast, problem-free process conversions and process optimization.
Electronic calipers and micrometers from L.S. Starrett Co. (Athol, MA) continue to be improved for the harshest manufacturing environments. The 797 Electronic Caliper series features IP65 protection and resist coolant, water, dust, dirt, and metal chips. According to IEC529, IP65 stands for a "6" protection against ingress of dust and particles and a "5" protection against water jets projected by a nozzle from any direction for a duration of three minutes. The 797 meets DIN962 Linear Accuracy and has a 0.0005" (0.01-mm) resolution.
The 795 and 796 Series of Electronic Micrometers achieved the IP67 level protection in harsh shop environments. In addition to being coolant and water-resistant, 795 and 796 micrometers offer protection against chips, dirt, dust, and other contaminants. The IP67 indicates a "6" protection against ingress of dust and particles and "7" protection against the effects of immersion in water under certain stated conditions of pressure and time. The 795 and 796 micrometers feature 0.00005" (0.001-mm) resolution and accuracies of ±0.0001" (0.002 mm).
The Way It's Done On The Shop Floor
Art Whistler, Helmel Engineering Products Inc., describes the traditional devices for shop floor measurement: "In production today, it is common practice to rely on functional gages like rings, plugs, and snap gages to check for "go and no-go" conditions; hand tools such as calipers and micrometers to obtain actual feature measurements; and fixture gages that will check feature form and even relationships such as flatness, runout, or concentricity.
"These venerable means of dimensional verification have both pluses and minuses. Go, no-go checks filter out bad parts, but provide no data for statistical analysis or process management. They are generally low in cost, and fast, but are limited to discrete feature checks, are subject to wear, and require certification. Hand tools today are digital, and can feed back to recording devices for SPC and archiving purposes, although many users still log hand entries that are subject to errors. They can be influenced by user technique, so repeatability is diminished, and they are generally limited to evaluating one dimension at a time. Cost is low, but wear is an issue, and frequent calibration is important. Fixture gages require custom design and build, and usually need high-precision setting masters that themselves must be certified. Costs are higher, and lead times can be long. Engineering changes may require redesign, costly changes, and delays. These gages may have dial indicators with no output, but most incorporate LVDTs or have air gages with conversion to digital output. Fixtures wear over time with hard use, but are usually rugged, durable, and repeatable."
This article was first published in the November 2007 edition of Manufacturing Engineering magazine.