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Shop Solutions: Grinding Big Turbine Blades

 
 
Moeller Aerospace Technologies (Wixom, MI), a division of Moeller Manufacturing Co. Inc., is a supplier to major aircraft and power-generation OEMs such as GE Aircraft, GE Power Systems, Pratt & Whitney, Rolls-Royce, and Siemens Westinghouse.

The company employs 400, and has 115,000 ft2 (10,684 m2) of production space. One hundred and fourteen of its employees work in grinding operations, running two to three shifts per day depending on work load. A Mägerle MFP 160-50 from United Grinding Technologies Inc. (Miamisburg, OH) is used to do root forms for turbine blades used in land-based power generation. 

President Dan Moellering explains: "We generally have two blades fixtured together at a time. To get the full tree form, we have to run both sides of the part at one time. These parts are generally quite heavy, weighing from 35 to 40 lb [15.9-18.1 kg] with some as heavy as 100 lb [45.4 kg] in lengths that vary from 24 to 36" [609-914 mm]. We do the root forms on the Mägerle because of its accuracy, repeatability, and the ability to do heavy stock removal," Moellering says.

There's substantial stock in the root form, and the root is the critical part of the turbine blade; that's where the closest tolerances must be held.

"We typically remove from 0.200 to 0.300" [5-7.6 mm] of stock per blade, usually in three passes. The first passes are pretty deep in terms of depth of cut, perhaps from 0.100 to 0.150" [2.54-3.8 mm]. So we rough in the first pass and then finish the root in the subsequent passes. When the part comes off the Mägerle, the root form is finished. We hold tolerances to +/-0.0005" [0.01 mm] on multiple surfaces."

Moellering notes that since the Enron fiasco the power-generation business has fallen off. Accordingly, he's focusing more and more on aerospace, which is the company's core business. He's interested in the Mägerle seven-axis MFP-50 grinder with automatic toolchanger.

"We'll still run the power-generation jobs, the big stuff, through the Mägerle we have because it's so rigid and accurate, but right now I'm very interested in the new model of Mägerle with the tool-changing capability. The ability to switch between CBN and conventional abrasives looks like it would have a lot of application in many of our aircraft parts—turbine blades, for example. We're looking to increase our flexibility in the future, to be able to run a variety of jobs across the same machine, and the Mägerle with tool changing is very attractive."

Currently, Moeller has a five-axis machine, which performs very well but is limited in some ways. "We have to stack four to five wheels on a spindle," Moellering says, "and when you do this you suddenly have a number of things to worry about, including interference, whether the front wheels are hitting when you get to the back wheel, and whether you might be hitting a fixture. If you're running something that has a higher stock removal rate on a surface that doesn't really lend itself very well to CBN technology, with a toolchanger you can just switch to a conventional abrasive when needed. We see a lot of potential in the flexibility of that machine.

"You might think that the Mägerle with tool changer would be a more appropriate fit for the bigger companies and not for high-end contract manufacturers, but we think of it just the opposite. Our goal is to become more flexible in the future and the capability of automatically changing wheels is a big step in that direction," Moellering concludes.

 

Marking for Quality Checks

To ensure precise identification of its flat-rolled steel coil products, Taylor Coil Processing has installed a Jet-A-Mark R44 8000 ink-jet marking system supplied by Matthews International Corp.'s Marking Products Div. (Pittsburgh) at its Lordstown, OH, facility.

Legibility of the ink-jet marking has been particularly helpful for the company's customers in the aircraft and automotive industries, enabling them to comply with government inspection standards. It's also critical in tracing Taylor Coil's own production cycles.

Taylor Coil, a US division of a Stony Creek, Ontario, Canadian parent company, is a processor of steel coils, which are supplied by steel producers and OEMs for further processing. Capabilities at the Lordstown plant include slitting, leveling, cut-to-length, and inspection services to serve diverse flat-rolled steel markets ranging from automotive, aircraft, and appliances to construction and manufacturing. Its processed steel is used in automotive hoods and doors, residential doors and frames, household appliances, office equipment, and tubular products.

The Matthews R44 8000 series large and small-character ink-jet system is designed for in-line marking of as many as five different locations across a steel strip. It is installed in the cut-to-length equipment line. Typical line speeds range from 50 to 200 fpm (15-61 m/min), although the 8000 is capable of handling speeds to 780 fpm (238 m/min). An encoder wheel tracks the speed of the steel strip as it passes through the line, ensuring consistent print quality at variable line speeds.

Identifying its steel coil output is not a new feature of Taylor-Coil's operations. However, until the Matthews system was acquired, the company had not been able to achieve the desired clarity it now can at current line speeds.

What Matthews is supplying with its five print-head marking system is a staggered set of printed rows of information on the steel strip. The printed data contain seven codes, indicating AMS (Aerospace Material Specification), and grade of the steel, as well as identifying the steel producer and supplier, lot number, time of production, and related information. This information appears on two lines, each 1.5" (38-mm) high in lengths to 24" (609 mm) as specified in customer processing orders.

"We have had a great deal of success with this Matthews 8000 series system," says Pete Adamski of Taylor Coil. "It allows us to help our customers comply with contract directives in supplying OEMs as well as to meet government guidelines to identify parts."

Matthews considers the recently launched 8000 series print-head its most reliable system thus far. Its operation is flexible and simple, and the device has message storage memory to 400 characters per line of text and as many as 200 messages.

 

CMM Pays Untended Dividend

Peer Inc. (Waukegan, IL) has teamed up with Japan's Daido Metal Company Ltd. to offer steel-backed, resin and alloy-coated plain bearings optimized for dry, pre-lubricated, mixed, or fully lubricated applications. Founded in 1990 as a spin-off of Peer Bearing Co., Peer Inc. is located at Peer Bearing's headquarters facility.

While Peer/Daido materials are found in automotive, material handling, and medical applications, the company emphasizes providing bearing solutions for fluid-power applications.

"We offer the fluid-power industry a complete range of solutions wherever wear surfaces are required, from self-lubricated bushings and cradle bearings to wear plates, port plates, and thrust blocks," explains Charles Spungen, Peer Inc. president. "Wherever something is moving or interacting in a fluid-power pump or motor, we're at that interface. We're one of very few companies in the world offering the full range of bearings used in fluid power."

Beyond providing individual bearings, Peer Inc. adds value to bearings by incorporating them into precision housings. One example is found in thrust-block manufacturing. Peer thrust blocks are found in many kinds of hydraulic gear pumps and motors, which are used to provide power transfer and actuation in applications ranging from forklifts and scissor lifts to farm, utility, and construction equipment.

Inside hydraulic gear pumps, a driver gear meshes with a driven gear to create a displacement that generates fluid pressure. In the process, thrust-block bearing surfaces must accommodate two types of loads: radial loads generated by the gear shafts (borne by Peer FR150 steel-backed PTFE self-lubricated insert bushings), and thrust loads where gear-side surfaces ride directly against the aluminum block surface. Blocks are machined from a proprietary alloy known as Peer Alloy 1, which possesses the anti-galling and low-friction characteristics required.

Long-term economics dictated that thrust-block manufacturing needed to be automated in a totally untended operation. To run an untended milling operation and maintain a zero defect rate to meet tight customer tolerances, Peer Inc. decided to design and deploy automation cells that integrate CMM technology. Production is handled by two such cells with two more scheduled to come on line.

Each 30 × 10' (9.1 × 3.1-m) cell consists of two Mori Seiki vertical machining centers, two Fanuc machine-tending robots, a compressed-air blow-out station, two Mitutoyo Crysta-Apex C CMMs supplied by Mitutoyo America Corp (Aurora, IL), and a bushing press with a vision-equipped Fanuc transfer robot.

After manufacture, finished parts are transferred to the Mitutoyo Crysta-Apex CMM for contact inspection, four-at-time, utilizing a Renishaw touch-trigger probe. A number of critical dimensions are measured with the Crysta-Apex in a feedback loop enabling real-time, continuous adjustment to keep the machining center within control limits. Offline inspection of all dimensions is performed per a sampling plan using an identical Crysta-Apex CMM. While the machining center has its own sensors to detect broken tools, compensation for tool wear is directed by the CMM.

"Some of our customers are surprised to see the CMMs running on the shop floor," says Spungen. "Many previously thought of CMMs as a lab technology used for statistical sampling, but here they see these sophisticated Crysta-Apex CMMs running as true production tools. And we're not talking about an isolated clean room environment, either."

Spungen continues, "By incorporating the CMM as a process tool and not as an after-the-fact inspection instrument, you do two things: First, the 100% inspection afforded by in-line CMMs is what really allows you to keep costs down by running 24 hours with some shifts untended. If a robot were to place a piece incorrectly or, say, on a chip, the inspection allows us to reject that part. Second, and perhaps more important, the 100% inspection allows us to make full use of the customer's tolerance zone. Without inspection, a very high Cpk is necessary to ensure zero defects, which might require a much more expensive production process such as grinding or lapping. But in our case, we can center our process and let the CMMs weed out the tails of the normal curve. In addition, the real-time feedback loop allows our control limits to really work hard for us." Beyond that, the CMM's flexibility enables Peer Inc. to adjust, "on the fly" to customer design changes resulting from upgrades or market demand. All that's required is a program change.

 

Top Technology Fuels Growth

With the rise of foreign competition and the ups and downs of the economy, many American manufacturers have instituted lean manufacturing initiatives to remain competititve.

While increased efficiency can play a vital role in increasing profitability, some manufacturers make the mistake of sacrificing too much in other areas in their efforts to become more productive.

Roll-Kraft (Mentor, OH) has expanded to include facilities in both Canada and Illinois, in addition to its 110,000 ft2 (10,219 m2) production facility in Mentor.

Founded in 1963 by George Gehrisch, Roll-Kraft specializes in the design and manufacture of roll-forming products for the metal-forming industry.

While high levels of service and interaction help Roll-Kraft maintain a loyal customer base, the company faces constant pressure to reduce prices and turnaround times.

"Over the last several years, we've seen a real shift in the intensity of demands from our customers," says company President Chuck Gehrisch. "The entire industry has shifted. Our customers need lower pricing and faster turnaround from us, so that they can meet the very same demands from their customers. We stay ahead by constantly examining our processes and implementing new technology to optimize productivity."

"The way we've integrated wire EDMs [from Charmilles Technologies Corp., Lincolnshire, IL] is a perfect example of this strategy," Gehrisch observes.

Many of Roll-Kraft's products require a keyway, a slot within the bore of a part. In the past, the company used broaching machines to complete the slots. Nearly 75% of its products went through the time-consuming broaching process, creating a bottleneck in production. Roll-Kraft turned to wire EDM to eliminate this problem.

"We had never used EDM before that," says Steve Young, plant manager at Roll-Kraft. "After reviewing our options, we decided to bring in a Charmilles' Robofil 440 wire EDM."

Using the Robofil 440 instantly provided faster cycle times, cutting the costs of parts passing through the machine. In addition, the machine easily and accurately held the required tolerances on the keyways, which could reach as low as 0.002" (0.05 mm) Compared to the previously used broaching method, Roll-Kraft has documented savings on parts switched to the EDM ranging from $18.75 to $25.00 per part. Considering that about 800 rolls pass through the Robofil 440 every month, the savings become substantial very quickly.

Another benefit involved operator training. "With the broaching machines, it took six months of training to reach the point where an operator could run the machine alone," says Young. "The user-friendliness of Charmilles' machines really surprised us. We can take someone with no EDM experience, and have them trained and running a Charmilles machine in just under two months. The machines run so reliably that the operator can set a machine up and let it run itself, rather than standing there to monitor it. This increases the efficiency of our workforce," Young says.

Based on its success, Roll-Kraft began looking at other areas where EDM might prove useful. The company had previously outsourced the production of complex inserts that are used in testing products before they are shipped to customers. A second wire EDM, a Charmilles Robofil 240cc, was purchased. Despite the fact that these parts required tolerances as low as 0.0005" (0.01 mm) and high tapers, the Robofil 240cc allowed Roll-Kraft to bring the work back in-house, increasing efficiency and shortening process times with its cutting speed.

"The Robofil 240cc has really helped to shrink our turnaround times," says Young. "We're no longer reliant on outside vendors to complete the complex parts needed to test our products. Once we complete a customer's part, we're able to finish the testing process and get it out the door much faster."

 

This article was first published in the February 2006 edition of Manufacturing Engineering magazine. 


Published Date : 2/1/2006

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