June 2008 Edition

SWISS TURNING

A Swiss Turning Center Turns Problems into Profits

Minimizing turning operations between centers was the goal
and a new Swiss turning center met it

Medieval philosophers once argued about how many angels could dance on the head of a pin. The people at Metal Craft Machine & Engineering don’t worry about angels, they’re more concerned with the tiny medical devices that are small enough to fit on a pin’s head.

The company, based in Elk River, MN, has earned a reputation for precision and reliability among the leading suppliers to the medical, food and drug, aerospace, and computer industries. Metal Craft is known for turning out multiple-use and single-use medical and surgical tools, instruments, and implants used in orthopedic, cardiac, spinal, and other surgical procedures. In addition to precision instruments, Metal Craft makes larger surgical tools for applications such as hip replacement.

"Our medical customers form a Who’s Who of the industry," Sean Mowry, vice-president, and son of the founder, Jack Mowry, said. "We make parts for 90 percent of the major orthopedic medical companies."

Machining small parts is the foundation of a business housed in two plants totaling 60,000 ft² of production space. The facilities operate around the clock during the week and one shift on the weekends. The company runs the gamut of machining operations, including gun drilling, turning, milling, wire EDM, multi-axis CNC grinding, laser etching, and passivation. Passivation is used to delay the onset of oxidation of stainless steel.

Meeting Customer Expectations

"Our customers expect us to meet very close tolerances and require the parts we make to be 100 percent quality," Mowry said. "Ninety-five percent of our deliveries are on-time, a track record we are improving. We have no time for re-work."

Some of the surgical tools manufactured by Metal Craft – drill bits, end mills, reamers, taps, pins, and blades for example, can fit on a postage stamp. Some parts can fit on the head of a pin. Tolerances are extreme, and, in a competitive global market, so are profit margins. The costs of quality control issues related to conventional CNC milling and drilling were rising. Production time and hours are an issue, but quality trumps both when traditional methods don’t work.

The surgical products, which feature long parts and small diameters, once required multiple operations when they were turned between centers. There was always the risk of deflection. The limitations of conventional CNC milling and CNC turning required machining individual pieces and welding them together. This not only required additional production time but it also exposed parts to dimensional variations associated with multiple re-fixturings. Also, the welds required more machining to bring parts to spec.

"Our goal was to get away from multi-piece construction and minimize the number of turning operations between centers," Sean Mowry said. "In our search for a solution we discovered the Maier Swiss ML26-DY Turning Center from Maier USA, Webster, MA. It had a tooling flexibility that let us complete most parts in one operation. It had the power and rigidity to make deep cuts while maintaining tight tolerances. With stroke length, machining flexibilities, the number of tool stations, and high horsepower, the Maier had the right stuff."

The Swiss turning center the company chose could address productivity and quality issues. It could be fitted with up to 22 tools, 14 of which could be driven and three of which could machine parts simultaneously. The ML26-DY’s main and opposed spindles work together and reach speeds up to 8,000 rpm while an accessory slide works the interior diameter.

Surgical Precision

"Surgical tools lend themselves well to the Maier Swiss-type automated lathes because we can use full power for deep cuts on long parts and significantly improve cycle time reduction," Mowry said.

"Using a typical CNC turning center, a long part tends to flex," Ryan Fulin, CNC Metal Craft machinist and programmer, said. "With the Swiss machine, that doesn’t happen because the machining happens close to the headstock where it’s held by a heavy bushing that exposes only the amount to be machined."

Mowry found one of the features is its ability to apply a stream of coolant at 2,000 psi. This makes it possible to gun drill on the Maier, and broadens the types of parts it can handle. The 2,000 psi coolant stream, which can be fed through tools lets Metal Craft use high power and take a deep cut. Without it, gun drilling would not be possible.

A second feature is under the machine. The Swiss turning center uses a solid polymer concrete machine base that eliminates almost all vibration in the machining process. Studies show that the polymer concrete base is a critical factor in holding accuracies of up to 0.0001". By eliminating the effect of vibration, cutting tool life is extended by more than 30 percent when compared to the machines with iron bases.

Eliminating vibrations is critical, Mowry said. The center makes faster, deeper cuts while maintaining its accuracy and extending cutting tool life for his company.

The turning center proved more versatile and easier to use than other types of Swiss lathes in the shop.

"The layout and axis design of the Maier is much more efficient than on our other Swiss machines," Fulin said. "With the power and tooling available, the sub-spindle is almost as capable as the main. It’s more flexible and the tool and axis layout has few limitations."

Company operators report liking the versatility of the turning center. All options are available and turned on. Also, the 10" stroke is critical when machining long parts.

Cutting Multiple Operations

According to Fulin, three-tool simultaneous machining using the turning center with simultaneous milling and drilling capabilities has been the key to eliminating multiple operations and the frustrations of welded parts.

"With 10" of headstock travel, we machine most of our long parts in a single pass without re-gripping, with more efficient operations programming," he said. "The Y-axis option creates more tooling capacity for the sub-spindle which shifts more machining time to the sub-spindle. It lets us work on the internal diameter of a piece while machining the outside diameter, and the sub-spindle finishes the back work."

"The ML26-DY let us eliminate multi-piece construction," Mowry said. "With the Maier, we’ve seen productivity improve by more than 40 percent."

The Swiss turning center simplified machining many products and allowed fast turnover, an important factor when the typical run is 100 to 200 pieces at Metal Craft. On some pieces, Metal Craft reduced the number of operations from nine individual moves to a single, start-to-finish, machining operation.

"We’re reducing our production time because we can complete parts in fewer operations," Fulin said. "And, by completing a part in a single operation, our compliance checks and associated paperwork are much more manageable."

"When every part comes out of the machine as an almost completed piece, quality control is also simpler," he said. "If we discover a problem, resolving the issue is quicker when dealing with a complete part, made on one machine, instead of trying to trace errors via multiple machines and operations."

According to Mowry, the addition of the ML26-DY improved productivity and quality, as well as expanding the company’s capabilities.

"Having the turning center opened our market to a more diversified product base and new opportunities," he said. "There is a lot of competition in the medical and surgical market. It’s not just regional, but a national market. We need to be fast, flexible, and accurate to survive, and the Maier is helping us do that." Maier USA

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