When a contract manufacturer sees an opportunity in the competitive aerospace market, it sets priorities aimed at providing the right combination of processes required to meet the industry’s exacting demands. Precision machining and finishing, parts inspection, and, of course, certifications from OEMs and industry alliances are at the top of the list. Increasingly, aerospace suppliers like Volvo Aero Connecticut (Newington, CT) are benefiting from five-axis machining, advanced CNC controls, motors and drives, robotic deburring, and on-machine inspection for a competitive advantage.
Investments made in the latest machining technology have enabled Volvo Aero Connecticut to make significant inroads in supplying aerospace OEMs with precision-machined components. Parts include fan cases for aircraft engines and gas turbines, fan and compressor structures, compressor rotors, low-pressure turbine cases (LPT), and military parts. According to Martin Thordén, engineering manager, the company machines workpieces as large as the 3.5-m diam fan casing for the GE90 engine for the Boeing 777, as well as fan casings for the GEnx and Rolls Royce Trent 1000 engines for the Boeing 787 Dreamliner, among others.
In the six years since Volvo Aero (Trollhättan, Sweden) acquired Aero-Craft (as the basis for its growth in the fan-casing segment), Volvo Aero Connecticut’s employment has grown from 35 to more than 110 in step with the growth of its aerospace business. The acquisition immediately opened up the availability to expand Volvo Aero’s fan-casing business with aerospace OEMs like Pratt & Whitney, GE, and Rolls Royce, through larger machining capabilities. To strengthen this fan case growth plan, the company also entered into an alliance to machine forgings from Carlton Forge Works, a California-based supplier of nonferrous rolled rings for fan cases used in aircraft engines and gas turbines.
"Our business is built on three legs," Thordén explains, "machining fan cases; semifinish machining of forgings, removing scale and leaving 0.040" [1 mm] for finish machining; and machining smaller to medium-sized fan cases. In order to build the best manufacturing shop for large fan cases, we added a Zimmerman FZ42 five-axis, five-side portal milling center to our machining lineup that includes four and five-axis milling machines, VTLs, and a robotic deburring machine."
The five-axis Zimmermann FZ42 milling center is equipped with a Siemens Sinumerik 840D CNC control and Siemens motors and drives to support precision machining spindles that can be readily changed: a high-speed spindle for machining aluminum, and a high-torque spindle for machining titanium and other difficult-to-machine materials like Inconel and Waspaloy.
"The Sinumerik 840D CNC controls all machine motions, as well as a series of subsequent measurement and test operations, plus the temperature-control system, which is an integral part of the machine’s design," Thordén explains. "In this way, it’s able to accurately perform all the complex machining tasks required, and also perform the probing required to transform the machine into a CMM for inspection of finished parts." The FZ42 features a 4.5 × 5 × 1.5-m working area and a feed rate of 60 m/min. The milling head is equipped with the Zimmermann multiple spindle technology (MuST) changing system. "After machining, the machine tool can be used as a CMM because of the accuracy of the 840D CNC and the 90° angle heads supplied as a part of the MuST spindle technology. Heads are stored in side stations that are used for inspection, measurement, and comparison of actual to predetermined CAD/CAM values on parts," Thordén says. Programming is done with Mastercam, NX, and simulation by Vericut.
The temperature control system of the FZ42 is built into the machine’s structure through the use of a special fiber-reinforced compound in the side columns. Accuracy of the machine is facilitated by built-in cooling ducts in the portal and Z-axis slide, independent cooling circuits for the A axis, C axis, and spindle, and ground surfaces on the guide ways for the Z axis. The machine has a 120-position tool carriage that holds HSK63 and HSK100 tools for machining the largest parts.
"All roughing and subsequent finish passes on any material can be achieved in one setup, saving as much as 10% in preparation time and overall production costs, and there is no need for additional machines and material-handling time between machines," Thordén says.
Volvo Aero Connecticut’s approach to fixturing and the more recent addition of robotic deburring to its processing capabilities relies heavily on the parent company’s research and application engineering. "Because our agreements involve long-term commitments, we put a lot of effort into designing fixtures, which can be quite heavy. Parts can be as thin as 0.060" [1.5-mm] thick. In the case of the FZ42, we chose a stationary fixture rather than a rotary table for a number of reasons. Tool movements are small, and it’s better to have the tool move around the workpiece rather than move the mass of the fixture and workpiece on a rotary table to accurately machine these features. Working with the X-Y axes and the C axis in the head instead of the table made so much more sense for these moves, and the Sinumerik 840D gives us the precision control of tool movement that we required," says Thordén.
In developing robotic deburring with the ABB IRB6600 robot equipped with an ABB control, Volvo Aero considered the quality of the workpiece, as well as the benefit of eliminating a manual process that had negative health-related issues for its operators. "We are deburring about 90% of all features on the fan cases we have introduced to the cell. What we especially like is that with the robot we get a consistent edge break, and the operators can run it overnight or while deburring other parts that we have. It requires limited operator intervention," says Thordén.
"As demand for more fuel-efficient engines for the latest aircraft grows, parts are being machined thinner and thinner from lighter materials, requiring stable machining processes without vibration in tools and cutters, which is another reason for the careful attention to fixtures. Workpieces must be accurate, because they are parts of assemblies," says Thordén. Volvo Aero Connecticut also semifinish-machines forging parts for low-pressure turbines and sends them out for finish machining.
In addition to certifications with its principal OEMs, Volvo Aero Connecticut has AS9100 and ISO 14000 certifications. ME
For more information on Siemens, go to www.usa.siemens.com/cnc, or phone 847-640-1595; on Volvo Aero Connecticut, go to www.volvoaero.com, or phone 860-667-8502; on Zimmermann, go to www.zimmermann-inc.com, or phone 248-305-9707.
Continuous Three-Axis Dressing Cures Shop Heartbeat
Heart arrhythmia, more commonly known as "irregular heartbeat," is caused by random electrical signals from aberrant heart tissue which interferes with normal electrical activity of the heart. Left untreated, an irregular heartbeat can reduce a person’s energy level, cause fatigue, and can result in stroke, cardiomyopathy, or even heart failure.
The same can be said of grinding shops. Like heart arrhythmia, irregularities in job shop production can cause operation disruption or worse, outright business failure. So rooting out machining and process problems on the shop floor is essential to healthy business operation for a company like B&H Technical Ceramics (San Carlos, CA).
B&H is a supplier of two machined ceramic components used in atrial fibrillation ablation devices. The two critically dimensioned, wafer-thin mating parts that B&H has been producing for seven years are the components that emit the high-frequency signals that target aberrant heart tissue. Annual production has been as high as 30,000 pieces per year, apparently because this method of atrial fibrillation ablation is effective.
When the machining process was being developed, Gunther Horn, company president, who founded B&H in 1976, wasn’t sure the parts could be profitably machined in a production operation, given customer budgets. Dimensional tolerances of the ceramic parts are within ±0002" (0.005 mm) and surface finishes are 16 µin. (0.00041 mm) RMS or better. Moreover, two different types of ceramic material, Macor Ceramic and C5800 PZT, caused excessive loading of the grinding wheel and grinding wheel wear was uneven and unpredictable in the prototype stage.
These parts presented some unique challenges that needed to be solved if the job was to be run successfully. During prototyping, the machine operator painstakingly hand-ground each part on a high-precision reciprocating surface grinder, sometimes requiring up to 60 min/part. Many parts were scrapped, often because surface finish and tight tolerance requirements weren’t achieved. Helmut Koehler, B&H vice president says, "We thought that even if we got the production order, we couldn’t run the job as we had during prototyping, because it was too erratic and unpredictable, and demanded too much time and attention."
In a way, for B&H, this job was like an irregular heartbeat. Part-to-part quality was inconsistent, and making the parts was time-consuming and caused excessive shop fatigue. Without stabilizing the process, this job might sap the shop’s capacity and keep the company from taking on other jobs. But because B&H had many years of experience machining ceramics of all shapes, sizes, and tolerances, they were confident that they could solve the problems and proceeded to deliver prototypes to their customer.
The good and the bad news came at the same time soon after submitting samples—B&H was awarded the production job. Amidst all the challenges of making the prototypes, the experienced team at B&H Technical Ceramics learned a lot. They learned how to hold many parts at a time using a ground-on-the-table vacuum chuck that guaranteed distortion-free parts while multiplying the number of pieces they could run per cycle. Years of experience machining other types of ceramics helped them zero-in on the ideal grit for the silicon-carbide wheel.
The biggest challenge they faced, however, was the need to frequently dress the wheel without sacrificing cycle time. They learned that wheel loading could only be managed with almost constant dressing, without which surface finish quickly degraded. Frequent dressing was also needed to ensure size control. Not only did the wheel require frequent dressing, the wheel shape was complex and incompatible with form dressing, because different speeds and feeds were needed when dressing the constantly changing wheel diameter. Additionally, optimized dressing would require axial adjustability of the point of contact between the dressing tool and the grinding wheel. To make things even more challenging, during prototyping it was determined that the best dressing tool for the job was a rotating universal dressing disk, not a conventional static diamond point.
For B&H, when it comes to machining ceramics, defining the problem is a major part of the solution. To get all the way there, B&H first called in a local machine tool distributor, John Franchuk, president of Die-Mold Machinery (Alamo, CA), to discuss their application. Die-Mold Machinery is an exclusive representative of United Grinding, (Miamisburg, OH), the North American arm of Körber Schleifring. After reviewing the job, Franchuk detailed the key challenges to United Grinding’s Phil Wiss. They agreed that the unusually demanding conditions pointed to a unique grinding technology solution that just might solve the dressing problems identified by B&H.
According to Reinhard Koppen, United Grinding’s applications manager, the Jung PA37K profile dresser system, jointly developed by Blohm and Jung, both German grinding machine builders, offered a truly unique solution. In the case of the B&H parts, Koppen was convinced that the PA37K dressing system would solve the "arrhythmic" production problems they would otherwise be facing. Because the Jung PA37K dressing system is programmable in three axes, changing the tangency point of the dresser for different radii of the wheel form would be easily accomplished using the Jung GRIPS 32 programming system.
Since the dressing station is powered and can be equipped with a programmable-speed spindle, varying rotational speed of the diamond disk as it dressed different grinding wheel diameters ensures optimized surface footage conditions for longer wheel and dresser life. The biggest breakthrough of all was the PA37K’s ability to continually dress during the grinding operation without cycle interruption. This is achieved by mounting the dresser directly to the grinding spindle head assembly, thus enabling the dresser to move independently of the grinding wheel.
Continuous dressing would eliminate wheel load, thereby ensuring surface-finish repeatability while dramatically reducing cycle time. This feature would also enable easy maintenance of size control as wear patterns were established. After hearing the promise of the technology, B&H agreed to purchase a six-axis CNC Jung grinding machine equipped with the PA37K dressing system, with the understanding that United Grinding would turnkey the process.
Koppen, who headed the project asserts, "The programmable dressing system solved all the key problems on this job by introducing control of so many variables within the process. Complete programmability of the dressing tool removed the guesswork, so that a predictable and reliable process could be realized." During runoff, a validated process was developed by combining United Grinding’s knowledge of the machine, Jung’s unique dressing technology, and B&H’s ceramic grinding experience. ME
For more information on United Grinding, go to www.grinding.com or phone 937-859-1975; on B&H Technical Ceramics, go to www.bhceramicsinc.com, or phone 650-637-1171.
Laser Inspection for Specialty Fastener Maker
As the son of a steel industry sales executive, Ted Murray learned early on the importance of customer satisfaction. His insight into anticipating customer needs propelled him to a successful career in fastener sales. Since starting his own business manufacturing specialty fasteners for an international client base, he has continually sought improvements in all areas affecting customer satisfaction. One way was by adopting a laser-based inspection system to speed and improve quality control for his specialty fastener manufacturing company, Industrial Forge Inc.
"Most business people have only a superficial understanding of what it takes to keep customers satisfied," Murray says. "For the most part, they’re very manufacturing-centered. Looking at the entire picture, you realize that there are many elements involved. For instance, when I started the business, we were located in South Florida. As taxes and expenses increased, we realized that the pass-along cost would have a negative effect on our pricing structure. Also, South Florida was not centrally located, which added to distribution costs. After an intensive search, we discovered the community of Alma, GA. Located along US 1 and equally convenient to both Jacksonville and Savannah, we’ve quickly improved our delivery times and reduced distribution costs. The favorable tax structure enabled us to become more competitive as well. Since we’ve relocated, our business has expanded, and 2010 was our best year yet."
"As a specialty manufacturer, it’s essential that we maintain a zero-defects program—and that includes everything. For instance, we use a $35,000 hand-held sensing device to verify materials prior to manufacture. We utilize a wide range of materials and alloys, including stainless, Monel, silicon, bronze, and exotics, and we can’t take the risk that something is mislabeled."
Exhaustive quality control has been an essential factor in the success of Industrial Forge. For certain customers, literally every piece has to be hand-inspected and, utilizing manual gaging, the inspection process had become a bottleneck. "I knew that if we were going to move ahead and expand, we had to find a better, faster means of inspection," Murray says. "Also, maintaining so many manual gages was expensive from the standpoint of recalibration."
Murray found the answer to his problems in LaserLab, a versatile laser-based inspection system manufactured by General Inspection LLC (Davisburg, MI). Designed for parts from 2 to 38 mm in diam, LaserLab accommodates part lengths to 300 mm. Fixtured parts are held stationary in an upright position. A comprehensive recess bit kit is standard with the unit. Bits not only hold the part in place but measure recess depth. Once the part is securely fixtured, a series of LEDs specifically designed for inspection purposes scan the part.
According to Greg Nygaard, General Inspection vice president, "The two key advantages of LaserLab are speed—most parts are inspected in 20 sec or less—and documentation. On the first inspection, a part template is created using our specially engineered Windows-based software. The template can be developed from a prototype or sample part, or from a CAD file or print. Templates feature both graphic representations and numerical data. Once created, they are stored in LaserLab’s memory and can be recalled at any time."
Profile inspection covers 100% of all part characteristics including lengths, diameters, radii, tapers, min/max material, hex, across flats/corners, threads, trilobe/taptite, straightness, concentricity, runout, perpendicularity, parallelism, wrench height, recess depth, first/last scratch thread, and first/last full thread. During the scanning process, a real-time comparison is made to the template, and any deviations are recorded. After each scan, LaserLab automatically recalibrates itself via a NIST-traceable calibration device. As a result, quality does not deteriorate over time or with changing environmental conditions.
"LaserLab has thoroughly streamlined our inspection process. We use a whole variety of manufacturing techniques, extending from machining to thread rolling. LaserLab has helped us detect machine and tooling related deviation, and we’ve been able to correct the situation right away. It has also radically reduced inspection time. In one case, a part that required 18–25 min of painstaking hand gaging is now inspected in 18 sec," Murray says.
"The real advantage, though, comes in the ability to document our inspections. Recently, we produced a series of parts for an international company in the energy industry. It was a complex design involving a collar, multiple diameters, and high-tolerance threading. The materials are Monel and silicon bronze. When the parts were delivered, the customer contacted us with word that they were out-of-spec. We immediately accessed the inspection reports and forwarded them to the customer. They quickly got back to us, and confirmed that there was no problem. I wouldn’t be surprised if they were looking at a LaserLab installation before long."
In addition to inspecting parts, Industrial Forge utilizes the LaserLab to recalibrate other gages. "The faster, more-accurate inspection capability has enabled us to expand our business, and we know that what we are shipping is correct. When you’re producing complex, high-tolerance parts in exotic materials for demanding applications, accuracy is critical to customer satisfaction. I haven’t seen a system as good as LaserLab," Murray concludes. ME
For more information on General Inspection, go to www.geninsp.com, or phone 888-817-6314.
This article was first published in the March 2011 edition of Manufacturing Engineering magazine. Click here for PDF.