Shop Solutions: Machining Gears 'Not-As-Gears' Pays Off
Look beyond the obvious and you may well find a better way to machine a part, and serve your customer better. That’s the lesson illustrated in a gear-machining application at Allied Specialty Precision Inc. (ASPI; Mishawaka, IN). To make a long story short, the company dramatically improved the material removal rate and yield while reducing fixture cost and delivery lead time on a family of gears by “not treating them as gears.”
First, the tooth-forming operation was moved from a traditional gear shaper to a CNC multitasking center. Next, the tooth throat was treated as a short slot rather than the usual tooth throat, using a form-matched Chip-Surfer replaceable-tip carbide slotting tool from Ingersoll Cutting Tools (Rockford, IL).
Step one enabled “done-in-one” machining, which led to simpler in-process parts handling and shorter delivery lead times as well as reducing total machining cycle time by more than 2 to 1. Step two streamlined the tooth-cutting operation itself, the longest operation on the part, by about 3 to 1.
Running 24/6 with 60 employees in the shop, Allied Specialty Precision has earned a reputation as the “go-to guys” for challenging manufacturing projects, said CEO Pam Rubenstein. Because of its location and that reputation, ASPI has become a preferred supplier for aerospace manufacturers.
“When you see a gear, you naturally think of a stroker-type gear shaper, equipped with the familiar single-point high speed steel form tool,” said Todd Stoddard, ASPI manufacturing engineer. “But completing this particular part is more about machining the web, hub and stepped shaft bore—seven operations in all—than just cutting the teeth. Now we grab the part once and complete all seven operations.”
A typical workpiece is a sector gear, machined from solid 17-4PH bar stock, that looks like half a gear with a lever arm attached. Measuring about 3½" (89-mm) diameter with 46 teeth over a 180° arc, the gear goes into helicopter flight controls. Annual volume for the earliest orders was just 100 pieces, all similar.
In 2008, ASPI initiated the “done-in-one” approach on a plant-wide basis. To that end, the company moved the job to a new Integrex CNC multitasking center from Mazak Corp. (Florence, KY) with all available auxiliary axes. “In effect it’s a 9-axis machine,” said Stoddard.
Originally on the new Integrex, teeth were formed with a 2" (51-mm) high speed steel (HSS) gear gasher, essentially a slitter with form-matched teeth. It completed the teeth in two roughing and one finishing pass. Total cycle time for tooth machining was 28 minutes, the same as before on the shaper. The big savings were in the other operations and in reduced part handling.
Orders for the sector gears started to increase in 2011, and expanded into a family of about a dozen different part numbers. Total annual volume grew to around 500 pieces. The parts varied in diameter, arc, number of teeth and extra features like linkage arms, but used just two different tooth forms. In other words, the job became a big enough piece of business to warrant some additional process optimization. Tooth formation, the most time-consuming of the seven operations, naturally became a prime target.
Stoddard reached out immediately to Ingersoll’s Andy Thornburg who, in Stoddard’s words, “knew more about gear machining than I did—especially nontraditional gear machining. It’s a pretty specialized area.” Thornburg suggested treating the teeth as short slots and machining them with a 1" (25.4 mm) form-matched Chip-Surfer T-slotting mill oriented like a slitting tool. The cutter features a small replaceable tungsten-carbide tip mounted on a threaded carbide shank.
By itself, moving from HSS to carbide would enable much higher machining rates and extend edge life. “The replaceable tip design, moreover, would minimize the amount of carbide used and enable in-spindle tip replacement. The carbide shank, which was reusable, would stiffen the cutting system for a better finish on the wear surfaces of the teeth,” said Thornburg.
During trials, Stoddard and Thornburg worked together to optimize parameters for the new process. They decided to quadruple the surface speed and double the feed rate, and to take just one roughing and one finishing pass. Final settings for the 1" (25.4-mm) tool are 1500 rpm, 0.060" (1.5-mm) depth of cut for roughing and 0.010" (0.25 mm) for finishing. This process change reduced cycle time for the teeth from 28 to 11 minutes.
Once the new process went operational for a couple of months, tool life could be compared. The Chip-Surfer tips typically last through 50 pieces in this application, while the gear gasher needed a regrind every 10–20 pieces, reducing stoppages for tool replacement and cutting tool inventory costs as well.
Even though it is form matched, the Chip-Surfer tip costs about $125 apiece, the same as one regrind on the gasher. Keeping spares is much more economical, too, because a single gasher can cost more than $400 and $100 a pop to regrind and can take weeks for delivery. Bottom line: tooling cost per part dropped from $20 to $2.56, an 8 to 1 reduction.
The improvement in throughput stems from the proven capability of carbide over HSS, plus the Chip-Surfer’s free-cutting presentation geometry that enables higher feeds and speeds without chatter, said Thornburg. The Ingersoll Chip-Surfer mill features a replaceable carbide chip that screws onto a threaded shaft with 0.0002" (0.005-mm) repeatability to datum. Tips can be swapped out right in the spindle. The shaft can be either alloy steel or carbide depending on stiffness requirements and impact loads. “Even with the carbide shaft, the only throwaway carbide is the tip,” said Thornburg. Ingersoll custom-grinds a standard Chip-Surfer T-Slot tip to match ASPI’s required form.
Modified standard Chip-Surfers are very common for slotting and T-slotting and die and mold applications. “As in the ASPI case, it’s a simple matter of a custom grind on a standard Chip-Surfer T-slot tip, which is always available off the shelf,” said Konrad Forman, Ingersoll’s national milling product manager. ME
For more information from Ingersoll Cutting Tools, go to www.ingersoll-imc.com, or phone 815-387-6600.
EDM, HSM Support Precision Medical Stamping
There are certain high-volume medical parts for which stamping processes can represent a fast and cost-effective alternative to machining. That concept is proven daily at Brunk Industries Inc. (Lake Geneva, WI). The company has spent more than half a century refining its stamping processes to serve medical component makers around the world with a comprehensive range of precision metal stampings. Founded in 1960 by journeyman tool and die maker Bertil Brunk and his wife Ulla, the company has grown from a tool and die shop in a family garage to an 80,000 ft2 (7432-m2) facility with 215 employees, 40 of whom are skilled tool and die makers.
The Swedish immigrants grew their tool and die business to serve a wide variety of industries and added stamping capability in 1970. Over the last 20 years, the shop has focused much of its effort on serving the medical industry with stamped components for surgical instruments and implantable devices. Today, the company is run by their son Lars Brunk, company president. “Stamping medical parts entails enormous responsibility,” Brunk said. “You are making parts for surgical instruments and life-sustaining devices. The marketplace is highly regulated, and there is a lot to learn and understand. It is the number one market that we service.”
Brunk doesn’t manufacture complete medical instruments or implants. “We make the stampings and subassemblies that go within them,” said Rick Eisel, tool design and toolroom manager. Large medical manufacturers build their final products on their own assembly lines using components from suppliers like Brunk. Many parts stamped for medical applications don’t fit the conventional image of stamped metal components. “The stamped medical parts often are thin and long. Many surgical instruments are engineered to reach deep into the patient while minimizing the size of an entry incision,” said Eisel.
Key requirements for medical part manufacturing at Brunk, of course, are precision and repeatability. To maximize control of the stamping process, the shop builds its own stamping tooling. It produces many of the stamping punches, dies, and other parts on electrical discharge machines (EDMs) and high-speed milling machines from GF AgieCharmilles (Lincolnshire, IL). The shop’s equipment includes a Vertex F fine-wire unit, Progress series machines for larger parts, and a Hyperspark die-sinking EDM for 3D machining. According to Eisel, 50– 60% of the company’s tooling is machined with wire and/or sinker EDM, and achieving fine finishes is paramount.
“With the larger machines, we achieve 3.0 µin. Ra as a standard and 2.0 µin Ra or better with the Vertex. We want fine finishes because punches with smooth finishes run higher quantities of parts with less required maintenance,” Eisel said. The smaller Vertex machine with 11.81 × 7.87 × 3.14" (300 × 200 × 80-mm) workpiece capacity uses 0.003" (0.076-mm) and 0.004" (0.100-mm)-diameter wire to produce precise features on smaller parts. While the shop’s larger machines generally cut with wires in the range of 0.008" (0.2-mm) diameter, wire as thick as 0.013" (0.33-mm) diameter may be used depending on part thickness.
Frequent application of exotic materials is another characteristic of Brunk’s medical part manufacturing operations. The shop’s primary workpiece material for medical component stampings is stainless steel, including special implantable stainless alloys. Titanium is the second most widely used material, but medical applications regularly involve less-common alloys such as “niobium, platinum iridium, gold, tantalum—materials you have to reference an element chart to see,” Eisel said, adding that those alloys are mostly utilized in implantable components.
Adopting stamping as the process of choice depends on what volumes of parts are to be produced. Cost-efficient, high-volume production is a major advantage of the stamping process, as the size of some of Brunk’s production runs demonstrates. A few jobs run as high as 42-million parts a month for a single customer, Eisel said, while others might only require a few thousand parts monthly.
When Brunk does develop a stamping process to replace machining, savings can be substantial. “There have been situations where we saved a company millions of dollars per year based on stamping a part rather than machining it,” Eisel said, “Companies have had full rooms of machining centers or turning centers making certain parts, then we were able to stamp the same parts with only two dies. When they switch high-volume parts to stampings it can really save a lot of equipment and costs.” Savings also result from more efficient use of workpiece material, and the actual performance of some parts may in fact improve by taking advantage of part strength that results from metal grain alignment generated in the stamping process.
Eisel pointed out that stamping, alone, is not the optimal manufacturing process for many parts. Sometimes specific part geometries, such as multiple thicknesses that vary greatly in range, are unable to be produced in a stamping operation. “We can’t move that much material around in coining,” Eisel said, “There are limitations to how much we can flow the material.” However, a combination of stamping and machining may do the trick. “If need be, we can start with stamping, get a lot of the features close, then come in and machine it to get to the proper tolerances and thicknesses in certain areas,” Eisel said.
In these situations, Brunk relies on its GF AgieCharmilles Mikron HSM 500 high-speed machining center with a 42,000-rpm spindle and integrated pallet changer. The machine is used mostly in tooling production, but Eisel said the shop recently is taking on more jobs that require machining, either in finishing operations on stampings or as full machining situations as necessary.
To address large volumes efficiently, Brunk often runs its GF AgieCharmilles wire EDM machines 24/7. Eisel said the machines provide that continuous uptime without the use of robots. One way the nonstop production is achieved, he explained, is by making multiple setups on the machine table. “We completely fill the machine up with components. We just use the machines to their fullest ability, using what they have on them as far as being able to self-thread and so forth.”
Machine reliability is crucial for 24/7 operation, and Brunk addresses that issue by maintaining a yearly maintenance program—Uptime+-- with GF AgieCharmilles. “They come in and do a thorough check of the entire machine, so unexpected downtime is eliminated,” he said, “We found that the added expense of the program is far outweighed by the piece of mind we gain in the fact that nothing weird is going to happen throughout the year. The program has really made operations stable for us.” ME
For more information from GF AgieCharmilles, go to www.us.gfac.com, or phone 847-913-5300; for more information from Brunk Industries, go to www.brunkindustries.com, or phone 262-248-8873.
Automation Drives Auto Tier 1 Delivery
When annual production volumes exceed 1.5 million parts and required takt times are 30 seconds or less, it’s important to find and exploit every process advantage.
As a Tier 1 supplier in the automotive industry, Eagle Manufacturing (Florence, KY) can attest to the unforgiving demands for on-time delivery and consistent quality. Yet Eagle thrives under the pressure by strategically integrating high-volume automated machining technologies that produce the best quality output at the lowest cost possible.
A subsidiary of Linamar Corporation, Eagle supports the network’s manufacturing division by producing engine blocks and cylinder heads for the world’s leading automotive manufacturers, including two of the “Big Three” original equipment manufacturers (OEMs) in North America. A web of automated production lines that run 24 hours a day, seven days a week cover Eagle’s 300,000 ft2 (27,871-m2) facility in Northern Kentucky.
Since 2006, Eagle has integrated Makino (Mason, OH) horizontal machining centers into eight different production lines with a total of 20 individual cells. The most recent installation was an expansion line designed to bypass several other machines undergoing maintenance. The scope of the project included two cells: a cell with two a51nx horizontal machining centers and a cell with three a61 horizontal machining centers. The cells were equipped with pedestal robots, conveyor systems and 2D data matrix tracking. Delivery and integration of the systems were completed within a short lead-time of only six months.
Makino’s responsiveness in delivery has enabled Eagle to meet shorter lead-times and seize market opportunities. “This level of transparency and reactive communication has been a tremendous benefit to our turnaround on proposals and has enabled us to get new lines and expansions installed and running before our competitors,” said Lord.
In addition to equipment availability, Lord highlighted the advantages of Makino’s integration services strategy, which rewards engineers for completing an installation not only correctly but also ahead of schedule. “On multiple occasions, we’ve ordered equipment from Makino several weeks after alternative suppliers, and yet Makino still installed the system first. This strategy, combined with an unrelenting pursuit of perfection, has been a huge asset for us on short lead-time jobs, allowing us to start making parts sooner,” said Lord.
A critical component of Makino’s integration services is its single source of dedicated project management and site coordination services. From the moment Eagle submits an RFQ, a dedicated representative is assigned to the project. This project leader coordinates with Eagle and Makino’s engineering group to establish a comprehensive, cost-effective solution. This detailed understanding of the project is transitioned with the project leader throughout the installation and post-installation phases to ensure all objectives are met according to the original proposal.
“From the moment we deliver a request for quote, Makino assigns us with a single point of contact for the entirety of the project. Their team of engineers handle all aspects of the integration process including machining technologies, third-party equipment, material handling, application engineering, fixtures, on-time delivery, on-site installation, test runs, training and post-production support. The result is a very tightly integrated system where the cutting process, machine control, fixtures, interfaces and automation systems work together seamlessly. We trust Makino to develop and deliver the best solution for our manufacturing system, including layout, cycle time and total production rates. They have always quoted us accurately and lived up to their guarantees,” said Lord.
The most critical component of any automated cell is the machining center. If a machine goes down for maintenance, the whole cell goes down, meaning substantial losses in productivity. According to Lord, every RFQ distributed by Eagle includes a requirement for 99% machine uptime over a five-year production timeline. “When dealing with takt times of 30 seconds or less, extended machine downtime is unacceptable. Every second lost is money falling through the cracks,” said Lord. “Our machines have to be tough in order to hold up against the stresses of a 24/7 production schedule. Not every supplier is able to deliver on this level of commitment.”
“It’s a tough production environment, but the expectations remain high,” said Lord. “Our Makino investments have proven that machines can be built tough enough to endure rigorous production routines. Makino’s robust control software also interfaces seamlessly with other automation systems, ensuring the highest level of operational efficiency. And with error reports directly tied to our database, technicians are able to resolve issues quickly and easily, minimizing downtime.”
As Eagle continues to seek new opportunities and growth, the company pursues additional plans for optimizing its production processes. One innovation under consideration is the implementation of part-tracking technologies.
“Historically, tracking considerations were low on our list of priorities, but as production timelines continue to grow tighter, we are evaluating every possible way to get the most out of our investments,” said Lord. “Additionally, our customers appreciate transparency. To have the ability to track, record and share the manufacturing process of each part will give our customers an added layer of confidence.” According to Lord, the addition of these capabilities is not without additional challenges. To address those concerns, Eagle continues to rely on its partnership with Makino to ensure perfect integration for long-term reliability. ME
For more information from Makino Inc., go to www.makino.com, or phone 513-573-7200.
This article was first published in the June 2013 edition of Manufacturing Engineering magazine. Click here for PDF.