Shop Solutions: Five-Axis, Pallet System Suit Job Shop
Automation often is thought of as technology to be applied in high-volume, low-variable operations making thousands of the same parts around the clock. Small shops, however, can reap significant benefits in flexibility, quality, and production throughput by combining advances in metalworking technology with material-handling automation systems.
Case in point: K-M-S Industries (Middleburg Heights, OH), a self-described contract machining house specializing in precision parts for performance racing, energy, transportation, and aerospace applications. Launched in 1980, the shop employs 28 and works two shifts, seven days a week.
Low-volume but lucrative, the manufacture of high-performance components such as clutch floater plates and blowers for top-fuel and funny car drag racers (as well as boats) represents about half the shop's business. Another major workload category is contract machining of custom wheels, mostly for the automotive aftermarket. The typical mix of workpiece materials is 80 - 90% aluminum, with the rest being alloy steels. Limited-volume parts coming off one at a time are the norm.
|Five-axis VMC coupled with pallet system boosts productivity and quality at K-M-S Industries.
In 2001, K-M-S purchased a Variaxis 630 high-speed vertical machining center with an integral tilting rotary table from Mazak Corp. (Florence, KY). The machine was acquired to allow simultaneous five-axis machining of parts such as supercharger end caps and housings, as well as contoured spokes and features on custom wheels.
To take full advantage of the VMC's throughput capability, K-M-S also selected a Mazak Palletech manufacturing cell with 16 pallets that can be preloaded and queued while the machine is making chips. In so doing, the company became the first US shop to couple the pallet system with the Variaxis machine.
With 16 pallets of pre-fixtured parts on tombstones feeding the five-axis VMC, K-M-S can run untended for eight hours. Once the production schedule is inputted to the cell controller, pallets are automatically transferred from the pallet stocker to the machining center, and the machining starts automatically. When machining is finished, the completed pallet is automatically changed with the next one according to the production schedule.
Pallets can be resequenced after fixturing to respond to customer-driven schedule changes. "With a single setup and the ability to run untended, we have much more flexibility to move to a build-to-order system and run what we need when we need it," says company founder Dick Malone.
Machinists are freed up to prep upcoming projects or run other machines. Most important, part fixturing time does not subtract from machining time. The result is increased throughput compared with the previous system, which required multiple setups on two separate horizontal machining centers, according to Malone.
The VMC's five-axis capability plays a big part in improving productivity. The combination of a rotary trunnion table with an A-axis tilting range of 150º gives K-M-S tremendous flexibility in terms of angles for approaching the work with a tool. Both the A axis and the rotary table can index in 0.001º increments.
Each part is handled less because it can be completed without refixturing. Programming is simplified for contoured parts, such as wheel features, and the machine can efficiently blend radii on a wheel to reduce stresses. On prismatic parts, the Variaxis can machine the top and four sides of the workpiece as well as inclined faces and angled holes. "Going the way we did eliminated all this extra setup time," Malone says. "Total cycle time reduction is substantial."
Overall part quality also is improved because the part is kept in one fixture and not moved between machines. And, surface finishes are improved to the point where secondary operations on some forged custom wheels are no longer necessary. "With the Variaxis, we can use standard tools normal to the surface and eliminate secondary buff and polish operations," Malone explains.
Summarizing the significance of his shop's new approach, Malone is adamant: "I'll never buy another three-axis machine again," he says. Instead, K-M-S will run traditional three-axis parts as well as prismatic five-axis parts on its Variaxis pallet cell.
"Workholding is simplified, since I only need to grab the part one time," Malone continues. "Second, I get better geometries and closer tolerances. Third, with Palletech, I can set up parts while the machine keeps running.
"You really get the best of both worlds: improved machining accuracy and a pallet changer for untended operation. In my opinion, it's the future for most low-volume machining operations," he concludes.
Small CMM Redefines Portability
Manufacturing aerospace parts presents 3-D complexities that are sometimes beyond the scope of conventional mechanical measuring devices. For example, weldments between windswept surfaces and internal braces are rarely straight, but usually conform to an airfoil or duct shape. The same is true for the fixtures used to make the parts.
But complexity is only one of two basic obstacles of aerospace manufacturing. The other is precision--and precision measuring is the key to making complex aerospace structures perform as designed.
Skill-Metric (Delray Beach, FL) is a job shop that has prospered by becoming familiar with the specialty market of support for military and government aircraft. The company builds flight hardware--parts for everything but engines. Skill-Metric also manufactures and overhauls production tooling and evaluates fixtures used to prepare aircraft for missions, such as those used to position ordnance on the underside of wings.
Because Skill-Metric often makes or reconditions only a single part or tool for a given order, there are no prototypes or production parts on which tooling can be dialed in and processes honed. But, the item must be right the first time, and tolerances are typically ±0.005" (0.13 mm).
Holding tolerances this close with mechanical measuring instruments was difficult, if not nearly impossible, on complex 3-D parts, according to quality manager Ken Bentz. "We used almost all the conventional measuring techniques you can think of, from a surface plane to gage blocks to dial indicators," he says.
Measuring throughput and reproducibility were issues, Bentz reports. "With conventional implements, it's possible for two technicians to measure the same dimension and get two different numbers," he says. "And, errors can be additive from one measurement to the next. We needed something more certain, more absolute, and faster."
What they found was the Faro Gage, from Faro Technologies (Lake Mary, FL). A smaller version of the company's FaroArm portable articulating coordinate measuring machine, the device's small size is an advantage in machine shops or production environments.
The Gage extends with a spherical reach of 24" (610 mm) to allow measurement of frame points, hole locations, flatness, parallelism, and other characteristics. With measuring accuracy of 0.0002" (5 µm), it's more precise than mechanical measuring implements. Accuracy is not operator-dependent, and measurements are communicated directly to a companion laptop computer where they are stored for reports or for comparison to existing designs.
Designed to be portable, the device can be mounted to a flat plate or rectangular bar and be ready to measure in seconds. It can be used just about anywhere one would carry a caliper or micrometer. Skill-Metric technicians, for example, attach it to the ways of a lathe to measure shafts that are being turned, then bring it to a milling machine and check a part being cut there. In the course of a day, the Gage may be moved many times.
The device is an integral part of every assembly project at Skill-Metric. Structures such as engine nacelles or forming tools are measured as they are assembled. Technicians create a digital template of the part in the system's computer and check the location of critical points on the on-going assembly to ensure that they are positioned correctly.
"This is when the ability of the Gage to accurately measure in three dimensions becomes important to us," Bentz said. "The CMM and its software allow us to evaluate 3-D relationships between parts with much greater certainty than we could before."
To measure the geometry of a surface that changes shape over three axes, for example, the unit's stylus is dragged over the surface to obtain data points are taken at the required density--more for tight curves, fewer for flat areas. In this way, an engine duct or stabilizer fairing can be precisely measured in a minute or two.
One of the more creative applications of the device at Skill-Metric is to evaluate how well support hardware works. Technicians often take the Gage out of the shop to check the alignment of fixtures that load ordnance beneath aircraft wings. "The loading fixture must lift and place bombs or other ordnance precisely on the attachment hardware. If the lift is skewed, then the ordnance may not hang right on the plane and may not release properly in the air," Bentz explains.
Technicians mount the gage on the frame of the lifting system, then measure the 3-D gap between the attachment hardware, recreating the space between the mating surfaces. Using a digital template in the computer that shows the ideal alignment of parts, the technicians can quickly determine if the alignment is correct.
"Few things have so positively affected our business as the Faro Gage," Bentz concludes. "It has greatly reduced the time that we spend qualifying parts, and given us absolute certainty that they are qualified correctly."
Grinders Keep Going and Going and...
At Dana Corp.'s Torque-Traction Mfg. Technologies Inc. plant in Pottstown, PA, they've discovered that some things do indeed get better with age.
And that adage can even include production equipment. An example is provided by the plant's Ultraline UL2 high-production ID grinders, some of which have been in service since 1994.
|Dana Corp.'s Torque-Traction Mfg. Technologies Inc. plant in Pottstown, PA uses 30 Bryant machines to grind bearing race IDs of carburized 1013 steel universal joint cups.
Supplied by Bryant Grinder Corp. (Springfield, VT), the machines were purchased, tooled, and arranged for one job: to grind the ID of bearing races for carburized 1013 steel universal joint cups used in light-duty trucks. Since purchasing the original eight grinders in 1994, Torque-Traction Mfg. has added seven in 1998, five in 2000, five more in 2001, and yet another five in 2003. The grand total: 30 Bryant UL2 ID grinders just for this one part family.
Optimized for fast production work using cubic boron nitride (CBN) superabrasives, the machines apply high-speed motion-control technologies such as frictionless, hydrostatic slides and rigid, low-profile platforms. Programmable logic controllers direct the operation of the grinders.
"These machines are still the fastest and most accurate ID grinders available," opines Pottstown engineering manager Bill Schutt. "The eight machines installed in 1994 are still in production. They have ground well over 30 million parts each, and still process typical parts in a 7 to 9-sec cycle time, depending on part size. Further, they do it with Ppk numbers in the 5 - 6 range, or 0.000020" (0.5-µm) sigma value."
Many factors contribute to the machines' ability to maintain this performance level. Each grinder features post-process gaging, a state-of-the-art coolant filtration system, and CBN superabrasives. Bryant's high-power, precision motorized wheel spindles, ball bearing workhead spindles, and high-frequency motorized dresser spindles complete the package. And, the technology is coupled with Dana's preventive maintenance program.
|Indianapolis Motor Speedway's SAFER barrier repair truck features two Ranger 250 engine-driven welder/generators as well as a Pro-Cut 55 plasma cutting system from The Lincoln Electric Co.
According to Schutt, machine uptime is well over 90% and scrap is nearly non-existent. "We report zero percent scrap," he says. "In the rare instance we do get a reject, it is normally attributed to a previous operation."
Asked if he would purchase more of the machines if the demand was there, Schutt responded by saying, "Absolutely! And, make them identical to the 30 Bryant machines we already have."
Welders Support SAFER Racing
At the Indianapolis Motor Speedway, welding is an important part of fabrication and maintenance/repair both on-track and off. Grandstands, signs, fences, and the track's new steel and foam energy reduction (SAFER) barrier system represent just a few of the speedway systems that require welding.
Track personnel use equipment from The Lincoln Electric Co. (Cleveland) for the various welding tasks. For repairing and fabricating fences, gates, and other track equipment, the choice is a Lincoln Invertec V205-T AC/DC portable unit. Weighing just 38 lb (17 kg), the inverter supports stick and TIG welding for quick repairs in the field.
For in-shop fabrication, welder John Cleveland, who says he "grew up on a stick welder," uses a Lincoln SP-135 Plus compact unit for MIG and flux-cored welding. The wire feeder/welder makes short work of most fabrication projects, according to Cleveland. "It does a great job on the galvanized steel we use for the gates," he says. "Using a stick welder for all those years, I would have never imagined the increased speed the wire feeder provides, and it's very easy to use, with easy-to-understand voltage and wire feed speed controls."
Doug Castillo, head of maintenance at the speedway, gained experience with Lincoln equipment while fabricating two Indy Racing League safety trucks for the track. The modified Chevrolet 3500 pickups had to be equipped with fire suppression equipment, brooms, blowers, and spreaders to accommodate oil dryers. Various types and sizes of steel and aluminum were welded during this process.
The trucks each hold two Lincoln engine-driven welder/generators, which are positioned in an enclosed bed to protect them from the elements and to make the trucks more aesthetically pleasing. Shielding gas tanks are stored under the welders, which slide out of their enclosure on a fabricated moveable base for use.
Castillo also prepared a truck specifically to repair the speedway's new SAFER barriers, which are designed to dissipate the energy of crashes and make racing safer for drivers. This truck holds two Lincoln Ranger 250 engine-driven welder/generators side-by-side as well as a Pro-Cut 55 plasma cutting system.
The Jack Elrod Co. installed the SAFER system at Indy, and is the only company in the world currently doing this type of work. The company also is contracted to handle wall repairs during qualifying and races. Repairs mainly consist of welding 3/16" (4.75-mm) mild steel plate and tubing. If damage occurs, repairs must be made thoroughly but quickly to let the on-track action resume.
According to Elrod's Joe McMullen, the company began using Lincoln equipment because the speedway furnished it. But he quickly became sold on its benefits. "We have since purchased the same Lincoln setup the speedway uses for our own trucks," he says. "The Lincoln welders are dependable and user-friendly, and they run nice and smooth, even when we're welding out of position."
This article was first published in the July 2004 edition of Manufacturing Engineering magazine.