June 2011 / Volume 63 / Issue 6|
By Jim Destefani, Senior Editor
Courtesy of Bill High Bringing inspection technology to the shop floor for quality control can pay big dividends.
One of the main tenets of lean manufacturing is eliminating any steps in a process that don’t add value for customers. While no one would consider QC a non-value-added processing step, many shops would like to reduce or eliminate the time shop personnel spend carrying parts back and forth to a lab for inspection. One way is to bring inspection technology to the shop floor, and many manufacturers are doing just that.
A combination of factors is enabling shops to use sophisticated measuring technology, such as coordinate measuring machines, vision inspection machines and form or surface finish measurement instruments, on the shop floor, according to Drew Prine, manager of technical services for Stark Industrial LLC, a North Canton, Ohio, contract manufacturer and a representative for inspection equipment supplier Mitutoyo America Corp., Aurora, Ill.
For example, Prine cites machining centers with high-pressure coolant, which aids in chip evacuation and dissipates the heat transferred into the part during the machining cycle. This is helpful in controlling any size change due to increases in part temperature. A climate-controlled shop environment is also essential for control of part temperature and airborne contaminants, he added.Potentially Perilous
Still, “the shop floor can be a perilous environment for sophisticated quality equipment,” said Sam Wilkof, vice president of Stark Industrial. “I don’t know of too many suppliers of metrology equipment who would say, ‘Absolutely yes, our equipment can be used on the shop floor.’ Certainly, we have customers who use such equipment on the shop floor, but it depends a lot on the shop environment.”
QC equipment used in such environments is seldom housed in an enclosure, Wilkof noted. “For the most part, the environments are clean enough that the equipment can be used on the shop floor without too much possibility of contamination,” he said. “And technology such as an air isolation table can isolate the equipment from harmonics or vibrations from, for example, a tow motor moving across the floor.”
Courtesy of Bill High
Another consideration is the regular maintenance and calibration required to keep sophisticated measuring machines in top form, according to Jonathan Wilkof, Sam’s son and a Stark Industrial manufacturing engineer. “A manufacturing environment is never going to be as clean and as controlled as an enclosed lab, regardless of how pristine your shop floor might be,” he said. “Preventive maintenance more like what you might do on a machine tool than what you might perform on measuring equipment in an inspection lab can be very helpful in this regard.”
At regular intervals, inspection machines should be disassembled to the point where critical components can be cleaned, checked for wear and otherwise inspected, Jonathan Wilkof continued. “The machine can also be calibrated at that time. We’ve found that this proactive maintenance can significantly extend the life of QC equipment used on the shop floor.”
According to Sam Wilkof, the frequency of such maintenance and calibration procedures depends, again, on the specific environment. “Some shops might be on a 1-year or 2-year rotation,” he said. “Customers who insist on using instrumentation on the shop floor but maybe don’t have the best climate need that service more frequently, and the cost and time involved in that should be factored into a purchasing decision.” The cost for such service could be $1,500 to $2,500, assuming there are no significant mechanical issues or replacement parts needed, he added.
The following is a look at two other shops that are reaping the benefits of using relatively sophisticated measuring hardware and software on their shop floors.Nuclear Quality
As detailed in “Power Surge,” March CTE, page 36, manufacturers of components for nuclear power applications are required—with good reason—to maintain the strictest quality standards. One such manufacturer is Areva NP Inc., a Richland, Wash., supplier of reactor components.
The company makes replacement parts to support reactors all over the world—Taiwan, Germany, France, England, the U.S. and Japan—and the designs vary. So Areva produces multiple variants of similar parts, and some variants have multiple parts that require machining and inspection, according to Bill High, component fabrication process engineer.
“The nuclear industry doesn’t change very rapidly, but there’s a constant push to improve quality and productivity,” High said. One way Areva is improving is by using a CMM on its shop floor. Supplied by Carl Zeiss Industrial Measurement Technology, Maple Grove, Minn., the Accura CMM is used to inspect components ranging from screw-machined parts less than 1" long to components with dimensions up to 12".
One example is stainless steel end fittings for nuclear fuel assemblies. The components start as CF3 (equivalent to wrought-type 304L) investment castings ranging in weight from 4 lbs. to about 25 lbs., according to High. Areva machines the castings in a cell with two horizontal machining centers and a linear pallet system.
Courtesy of Bill High
“We typically machine the components in four to five operations, with CMM checks in process—sometimes after every machining step and sometimes after two or three steps,” High said. “The cell basically runs unmanned, so we need to make sure the process is robust and doing what it’s supposed to.”
The CMM is about 20 ' from the cell. “It’s a bit of a harsh environment, but we have a temperature-controlled shop and we regularly clean some of the CMM surfaces to keep it operating well,” High explained.
Parts are machined to tight specifications—flatness of 0.002", diameter tolerance of 0.0005" and positional requirements within 0.002" to 0.003", according to High. “A typical order quantity of end fittings for a pressurized- water reactor might be 60 each of upper and lower fittings and, for a boiling-water reactor, 200 of each, so quantities are not huge,” he said. “It used to take us a couple of months to fill an order like that. Now we have the HMC cell and a 36-pallet linear system, and we can flow parts though the system at rates up to 12 to 15 parts per day, depending on the design. We run a big product mix, and we’re trying to get to an economic lot size of one part.”
Before purchasing the CMM more than 2 years ago, the shop used complex dedicated fixtures—High calls them “super gages”—to inspect parts. “We could drop a part into a fixture and read the dimensions off a whole bunch of dial indicators,” he said. “Those gages told us whether parts were good or bad, but we never knew how good or how bad.”
The CMM enables documentation of all checked part features, and uses software that provides Cpk and statistical process control data. Operators perform almost all inspection themselves, High said.
“Our machinists put the parts on the machine and run the inspection program,” he said. “The same guys who write the machining programs also write inspection programs for the CMM, which has dual screens so operators can see how the part is fixtured and get instructions from one screen and then get data output from the other.” Final inspection routines for the end fittings might check hundreds of part features and run for up to 40 minutes, he added (see photo on page 61).
The system enables Areva quality personnel to focus more on process improvement and less on verifying the quality of individual parts. “Our quality people don’t come out and inspect parts,” High said. “They’ll receive the completed parts in the inspection room, do a visual inspection and check a few critical features, then go online and look at the data that’s already been collected. If everything looks good, they’ll accept the part.”
The Accura CMM is a semihardened machine with a scanning contact probe that enables mapping of high and low spots on critical part surfaces. “The CMM has performed well in the shop environment. Before we purchased it, we ran temperature profiles in the shop and got a little variation, plus there’s some misting because we run high-pressure coolant,” High said.
“But we do regular preventive maintenance on the machine and wipe off air bearing surfaces and the granite slab daily. We try to keep it clean, and we have Zeiss come in on a regular basis to keep it tuned up.”
According to High, Areva considered CMMs from several manufacturers before choosing the Zeiss machine. “We’re an international company, and our companies in France and Germany have Zeiss machines,” he said. “Some of our casting suppliers also have Zeiss CMMs, so we could use their routines for incoming inspection if we wanted to.
“Our parts are high-value—we pay a lot of money just for the castings, then add substantial value to each component—so pushing the inspection process back to the operators and trying to give them real-time feedback on how the process is running saves us from producing a bunch of bad parts,” High concluded.Visualizing Custom Tools
Lowell Inc. is a contract manufacturer that has been producing implantable titanium, stainless steel and plastic medical components for orthopedic and cardiovascular applications for nearly 20 years. Located in Minneapolis, Lowell employs 70 people and has 100 CNC machines, ranging from Swiss-style lathes to vertical machining centers, HMCs and multi-task machines.
According to Jim Stertz, quality assurance manager, the shop also makes custom cutting tools that play a big role in the company’s production process. “Custom tools probably make up only 10 to 20 percent of the tools we use, but they’re the most important tools,” Stertz said. “We have hundreds of designs, and there are more every day.”
Courtesy of Lowell
Tools can be odd-shaped and their diameters range from 0.005" to 0.020", according to Stertz. An example is a hook-shaped tool used to produce locking features on the ID of a spinal implant component. The intricate tools have radius tolerances as tight as 0.0002".
Stertz said custom tool development at Lowell is an iterative process that may start with a machine operator or other shop personnel. “Ideas for tool designs can come from just about anywhere.”
Until 2 years ago, Lowell would send its custom tool designs to an outside supplier for production. That’s when issues with quality and delivery got Stertz and other Lowell managers thinking about bringing tool production in-house. The first step in that process was purchasing an EWAG WS11-SP tool grinder. The machine allows grinding and measuring of cylindrical and tapered tools in a single clamping and is operated by an associate with more than 30 years of machining experience.
“Now the idea for a tool flows through our tooling department, to the individual who runs the grinder, to the inspection department,” Stertz said. “The process is now all under our roof, and any tweaks or checks needed for a tool design can be done quickly.”
Courtesy of Lowell
Inspection of hundreds of different specials might be challenging, but Lowell solved the problem by purchasing a SmartScope 400 vision inspection system from Optical Gaging Products Inc., Rochester, N.Y. Centrally located near the tool grinder, the vision system enables rapid inspection of both custom tools and component parts, according to Stertz.
“We trace the form of tools produced on the EWAG machine on the vision system, then import that data into OGP’s SmartProfile software and compare it to the CAD model of the tool,” he said. “That gives us a visual depiction of deviation from nominal geometry.”
For 3-D data, Lowell uses a robotically tended Leitz PMM CMM and a Brown and Sharpe CMM to generate hundreds of data points from a tool or part. The point cloud data is then fed into the SmartProfile software for evaluation.
The system has become a critical part of Lowell’s custom tooling process, and Stertz expects that custom tools will play an even more important role in Lowell’s manufacturing processes as medical components keep evolving. “The parts are getting smaller and the features are getting more detailed as components are designed for minimally invasive surgical procedures,” he said. “We’re talking about extremely complex radii and surfaces that are light-years away from what they used to be. So we can’t use the old tools to make those parts.”
An identical approach is used to inspect the hundreds of part numbers Lowell produces. Lot sizes range from five to 5,000 parts, with runs of 100 to 500 being most common, according to Stertz. “We do in-process inspection using the SmartScope to check parts the same way we check custom cutting tools—by tracing the profile of the part and transferring the profile data to the SmartProfile software for comparison to the CAD drawing.” A graphic display with whisker plots lets operators confirm tool quality at a glance, he added. CTEAbout the Author: Jim Destefani, senior editor of CTE, has written extensively about various manufacturing technologies. Contact him at (734) 528-9717 or by e-mail at firstname.lastname@example.org.
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