Turning Implants

As the orthopedic implant market grows, manufacturers and shops search for new turning center technology to ensure a competitive edge.

America’s aging baby boomers, intent on maintaining an active lifestyle, are driving a buoyant orthopedic implant market that’s expected to rise 9.8 percent per year, to $23 billion by 2012, according to the Freedonia Group, a Cleveland-based market research firm.

The market’s four leading segments—knee, spine, shoulder and hip implants—all are machined on turning centers. And as demand for the orthopedic devices grows, so does competition among turning center builders and job shops.

Courtesy of Haas Automation

The Haas Automation SL-10 turning center features a 15-hp (peak) vector drive spindle that provides speeds up to 6,000 rpm for high surface feed rates.

Industry representatives contacted for this story stressed the importance of maintaining an edge. Many are trying to do so with new technology to improve and speed production. Some shops also highlight the fact that their machining methodology—and thereby the ensuing products—adhere to high standards.

At Jade Precision Medical Components LLC, Southampton, Pa., maintaining ISO certification has been a prime factor in staying competitive, said Robert Bradby, the company’s production manager.

“It’s a huge sales tool for us. [Implant manufacturing] is all about traceability, processes and procedures. That’s what most customers want to see,” he said.

Bradby estimated that Jade Precision, which focuses primarily on spinal implants, produces about 4,000 to 6,000 components per week. “Ninety percent of our product is Ti6Al4V, which is an implantable-grade titanium,” he said. “The other 10 percent is 316-L stainless steel.” Bradby explained that companies order implants made of stainless for people who, in rare cases, are allergic to titanium, or if the surgeon plans on removing the implant in the near future. Stainless steel is the preferred option in the latter case because “tissue adheres to and grows around titanium much better than it does steel,” said Bradby.

From Bradby’s vantage point, the thrust of advances in turning technology has been to boost production speed. “Most of it is through noncutting movement, getting from one tool to another quicker so you can decrease cycle time and increase throughput,” said Bradby. “It doesn’t necessarily make my job easier, but it does get things out the door quicker, which is a good thing.”

While Jade Precision previously had only Star turning machines to produce spinal implant components, it recently acquired five 5-axis milling machines to handle some of the work that couldn’t be accommodated on the Swiss-style automatics. “We will be able to go after more of the market than when we only had Swiss machines,” he said. “In some cases, you can machine with up to three axes, but in the end the [Swiss] machines are lathes and not mills, which is why we now have a 5-axis milling department.”

Multitasking Matters

In addition to providing turning centers with three or more axes, machine builders offer a range of technologies for turning implants. For example, one development at Mori Seiki USA, Rolling Meadows, Ill., is the combination of milling, turning and grinding its NT and MT series of machines.

“They’re mill/turn/grind centers,” said Greg Hyatt, vice president of engineering and chief technical officer of the company’s Machine Technology Laboratory. “They can improve quality and productivity. For example, sometimes the sequence of operations doesn’t allow you to do all the turning in one operation and all the milling in another.”

To prevent workpiece deformation, he continued, machinists may need to do all of the roughing on turning and milling machines before completing the finishing on either. “That would involve more setups and poorer response time, which is critical for the specialized components that may be patient-specific,” he said. “So the more specialized the component and the more responsive the manufacturing needs to be, the more valuable these integrated machines are, which in some cases can finish [an implant] in a single operation.”

Another development at Mori Seiki is the recently introduced Spinning Tool for lathes. “While the definition of a lathe tool is a static tool with a rotating workpiece, in this case the workpiece rotates like on a normal turning center but the tool also rotates,” he said. “So when cutting difficult alloys, we don’t have one spot on the tool constantly engaged with the work, creating one hot spot on the tool and forcing us to reduce productivity to keep the tool from overheating and failing prematurely.”

Hyatt explained that by rotating the tool at high speed, no point on the tool is engaged with the workpiece for more than a millisecond. Consequently, abrasion and the heat around the tool circumference are equally distributed.

Adaptive Balancer

While multitask centers offer advantages, they can come at a cost. When one machine mills and turns, the balance often changes during milling operations, causing spindle vibration. To adjust for balance deviations and ensure stability during both milling and turning operations, Mori Seiki recently introduced its Adaptive Balancer.

The device senses any imbalance and compensates for it by applying an equal force and opposite vector in the workpiece. The Adaptive Balancer is attached to the chuck and rotates with the part. It uses two independent, counter-weighted rings in its interior to compensate as balance changes in the workpiece.

The device is especially useful for some orthopedic implants. As Hyatt explained, shops typically produce a family of parts with variations—in the case of hip implants, for example, there may be different stem lengths to accommodate patients of various height and weight.

“Therefore,” he continued, “when you move from one part in the family to another part—a hip joint with a longer stem or whatever the variable is—the imbalance forces change and unless you rebalance the workholding for every part in the family, you can end up compromising the quality of the workpiece or the tool life. Because these are critical parts, customers typically reduce the speed of the chuck so the quality of the workpiece is not compromised. But then they end up compromising productivity and cost.”

Job Shop Input

Feedback from shops accounted for one of the latest developments at Mazak Corp., Florence, Ky. Chuck Birkle, vice president of marketing for the company’s Cybertec Div., said space-conscious customers often seek machines with smaller footprints. To that end, the company introduced its new generation Integrex i-l50 multitask machine.

The model takes up 58 sq. ft. of floor space, 6 ‘ fewer than Mazak’s smallest Integrex machine. “We were able to design a large work envelope with a small footprint by building it without a second spindle,” said Birkle. “Usually these machines have a second spindle to grab the part and perform backside operations. However, the second spindle itself takes up room. This machine has a workhandling unit that grabs the part once it’s machined, lifts it and points it up at the milling spindle.”