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Making Medical Miracles

Geoff Giordano
By Geoff Giordano Contributing Editor, SME Media

Changes in health care are driving more innovative tooling, including new machining strategies and complex cutting tools that help deliver more patient-centered solutions.

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Rollomatic internal workholding in operation using a hybrid-bond diamond wheel. (Provided by Rollomatic)

As health care becomes more personal and portable, traditional machining of precision components is being married to 3D printing and “black” marking of medical devices to ensure they are tracked throughout their life cycle.

Extraordinary demand for health care is driving more innovative tooling. For instance, robotic surgeries re-quire more complex cutting tools that doctors manipulate remotely. Doctors are also requesting more complex tools. The core driver is a more patient-centered approach to care in a more competitive environment.

For medical cutting tools like orthopedic drills, saw blades and shavers, Swiss-style CNC lathes continue to be the go-to equipment. And now, whereas tool grinding used to be an art, said Eric Schwarzenbach, president of Rollomatic Inc., Mundelein, Illinois, it is more of a standardized process and integrated into lean manufacturing.

“Lot sizes are becoming smaller,” he explained, “and there is also price pressure” to reduce the cost of making orthopedic tools. “OEMs do a lot more R&D and work more closely with doctors, and there’s a lot more feedback than there used to be. There is more innovation and competition,” which means tool designs change frequently.

Rollomatic emphasizes its automatic loading and unloading solutions to meet these demands, including an automatic stent loader for long, thin parts like drills and Kirschner wires, which are used in medical and dental procedures as guides for cutting tools and sometimes to conduct electricity. “We have a special holding system” for grinding these almost fragile parts, he noted. “We use a half-round steady rest to capture the part that’s been ground,” for instance for the flutes, relief, and points of drills. This eliminates pushoff and deflection, he added.

But at the core of Rollomatic’s medical portfolio are its GrindSmart six-axis tool grinding machines—featuring three linear and three rotary axes—that provide more flexibility than five-axis machining, according to the company. The unique angles of surgical drill points are a prime example; the sixth axis inclines the grinding spindle up to 230° to accommodate such tools.

The sixth axis also holds two wheel packs that can be flipped into position as needed in about two seconds. This facilitates production of a growing range of brand-specific, quick-disconnect features on cutting tools that fit into handpieces. These quick-connect features “are all over the place,” Schwarzenbach said. “Some have notches, some have reduced sinks, some are hexagon types. We can grind them all with this flipper.”

The company’s peel grinder is a less-complicated, more cost-effective machine for companies manufacturing a lot of disconnect devices. But a six-axis tool grinding machine allows machining of notches at the back of these tools as well as shaping of cutting geometries.

Optimizing that flexibility and reducing setup times is Rollomatic’s proprietary 2D and 3D simulation software, which locks in the angles, radii and diameters of various grinding wheel packs. And, in keeping with Industry 4.0 connectivity, its grinding machines can all be interconnected as well as joined with enterprise resource planning (ERP) software through its RConnect, providing the essential front-to-back project traceability required by medical contractors, who might have 30 to 40 machines.

The accuracy of Rollomatic’s software for six-axis machining means that “when you 3D simulate a part and then take it to the machine, the first or second part you grind is correct.”

In terms of market outlook, Schwarzenbach noted that “when we started to ship machines into the medical area, it was only to contract manufacturers” before OEMs began building their own grinding departments. OEMs are still outsourcing a considerable amount of work, he added, keeping the simpler components in-house or specializing in certain instruments, like orthopedic burrs that shape bone. Outsourcing can be cheaper, too, since contractor fabricators can make blanks and perform heat treating.

One-Two Punch

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Star’s highest-end 38 mm machine, the ST-38, features three turrets with 10 stations on each to hold enough tools to make complex parts and many tool families. (Provided by Star CNC Machine Tool)

At Star CNC Machine Tool Corp., Roslyn Heights, N.Y., its 38-mm machines with a full B axis “have been around for a number of years, but the combination of the two has made a big difference” in the medical industry, noted National Sales Manager Ed Garber.

“Part of the reason everyone wants a B axis is that doctors are getting more creative in their designs,” he explained, “because they know these features can be machined now” and they want them produced in one operation. Of course, performing all functions with one fixturing ensures more accuracy.

Also, the larger capacity of a 38-mm machine means features requiring fabrication from a 1.5″ (38.1-mm) bar are possible.

The highest-end machine in the line, the ST-38, features three turrets with 10 stations on each to hold enough tools to make complex parts and many tool families. For instance, one customer used it to produce 20 families of screws with 30 variants per family with changeover of five minutes or less between parts. “The end user viewed that as paying up front for the labor costs to change over from one job to another,” said Garber.

On the other end of the spectrum is the SV-38R, which accommodates fewer tools but is Star’s most popular 38-mm machine.

A major growth area for Star is tools to guide implants into the body, particularly in young people. “Top orthopedic companies are constantly coming up with their own concepts, and a big part of that is how products with new designs are implanted into the body, measured and adjusted,” Garber said.

Surfacing of tools is one of the benefits of the B axis, he added. Generally, instruments that are not cylindrical or flat are surfaced with the custom feel and appearance doc-tors desire. Trauma plates are often also surfaced.

The B axis also allows tools like center drills or ¼” (6.35-mm) end mills to be used at any angle as opposed to taking up a cross-working station and a face-working station. “It cuts down on the number of tool positions you need in your machine,” he said.

In terms of materials, staples like 316L or 17-4 stainless and various titanium-based alloys continue to hold sway instead of more difficult-to-machine metals like cobalt chrome or 455 stainless. Star offers high-frequency turning (HFT) to help break up chips in the rare instances those tougher materials are used.

In terms of saving material, Garber noted that bar feeder companies can now track where the pusher collet is and communicate to Star’s machines how much material is left on the bar in the feeder. Star software can then decide what part to run next. In the medical world, that means a few more implant screws of shorter lengths can be made instead of scrapping a costly bar remnant.

Hybrid Power

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Medical ball burrs for orthopedic surgeries ground on a Rollomatic GrindSmart 630XS in stainless steel. (Provided by Rollomatic)

The marriage of traditional machining with the complementary precision and power of laser processing has paid off particularly well in medical applications, according to Randy Nickerson, laser product manager for Marubeni Citizen-Cincom Inc., Allendale, N.J.

Previously, the company’s nine- and 10-axis machines functioned as a one-stop solution for multiple processes. Now, having a laser under the hood in its Cincom L series and its Miyano BNA 42 GTY machines eliminates steps that were often outsourced, like cutting holes in tubes. And having one less machine to validate in the highly controlled world of medical manufacturing can make a world of difference in throughput.

With a laser at his disposal, Nickerson noted, he continues to discover ways to refine an array of medical parts, often from bar stock to finished part. At the EASTEC trade show in May, the company demonstrated production of a 316 stainless flexible bone screw.

“When a doctor drills a hole, very often the hole doesn’t go straight,” Nickerson explained. “They tend to drill them by hand,” although robotics are coming into play in some instances. Drilling through the marrow can make the path deviate a bit, so “when you put a stiff screw in there it will bore the hole as it crosses over and go awry. That means the threads are not holding correctly on the far side because the screw is boring the hole bigger. Using the laser, I cut a slice in the screw to give it a bit of wiggle, and it can follow the hole so you get better strength and stability.”

Meanwhile, tubing—like many other medical components—is getting smaller. “I have a test cut I have to do out of 0.0165″ [0.42-mm] diameter tubing,” roughly the diameter of about four human hairs. The tube features a three-pointed drill tip to bore through bone or arteries.

Compared with end mills, which must be fed slowly to avoid breaking while executing fine features, lasers are non-contact and want to run faster. “With the laser, if I go too slow it overburns,” Nickerson said. The company incorporates lasers of various powers and beam diameters.

Marubeni’s hybrid machine has been on the market about six years, and now “people understand that it really does work,” he said.

Spindle Speed Success

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Achieving ultra-tight tolerances for medical components often requires spindle speeds in the 60,000-80,000 rpm range. NSK is seeing increasing demand for its iSpeed3 high-speed spindles for medical applications. (Provided by NSK America)

Achieving the ultra-tight tolerances of contemporary medical components requires spindle speeds often in the 60,000- to 80,000-rpm range. NSK America Corp., Hoffman Estates, Illinois, is seeing increasing demand for its iSpeed3 high-speed spindles for medical applications.

Whereas spindle accelerators use gears that can generate heat, vibration and premature wear on Swiss-style machines, NSK’s high-speed spindles feature integral motors. This is why gear speeders generally run comfortably for about 30 consecutive minutes, while NSK’s high-speed spindles enable potential 24/7 operation.

NSK recently calculated the long-range cost benefits of these spindles for high-value production, said Mike Shea, industrial product sales manager. Among the time savings possible, these spindles eliminate hand deburring of parts, added Industrial Sales Manager Mike Gabris. For instance, a customer drilling very small holes in about two million parts a year encountered burrs when using standard spindles at 8,000 rpm; NSK eliminated those burrs by running its spindle at 45,000 rpm.

NSK’s high-speed spindles are an increasingly attractive option when micro-tool makers’ specifications for the surface footage at which those cutting tools are run is beyond the capacity of a given machine. “We see an increase in tool life because the tools are running where the manufacturer specifies they should be running,” Shea noted. Generally speaking, he added, a 1-mm end mill machining tool steel of 30 to 40 HRC should run at 38,000 to 60,000 rpm.

Furthermore, control of NSK spindles can be integrated with CNC controls so they can monitor and maintain proper tool loads, although most customers use NSK’s load meter, which features green, yellow and red condition lights.

“Our spindle needs to be treated like an instrument,” advised Greg Nottoli, senior product manager. Being guaranteed to 1 µm, “it’s not a hammer, it’s a needle,” he added.

Ultimately, of course, “it’s all about cycle time,” Gabris concluded—and the difference between running microtools at 8,000 or 40,000 rpm is substantial.

Consider the need to mass produce medical parts like orthopedic bone screws. A surgeon going into the OR might bring a bag of about 50 to 100 screws of varying lengths, use only 10 and throw the rest away because they are no longer sterile. If an operation is running anywhere from 50,000 to 500,000 medical parts, saving “just a few seconds a part can save a customer tens of thousands of dollars a year,” Shea concluded.

Track-and-Trace Marking

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Dental tools, reamers and burrs ground on the Rollomatic GrindSmart Nano5. (Provided by Rollomatic)

The U.S. Food and Drug Administration’s Unique Device Identifier (UDI) program mandates that medical devices be marked to identify them throughout their distribution and use. These human- and machine-readable codes must remain readable through repeated sterilizations, as they will be instrumental in helping manage device recalls. Information relating to these devices will be maintained in the global UDI database (GUDID).

To ensure those marks endure as required, laser marking companies are providing medical manufacturers with a new solution using ultrashort pulse laser systems. Picosecond lasers in particular are being used in a process known as black marking, in which the laser creates structures that trap and absorb light to produce high-contrast details. Previously, marks were prone to fading.

“The energy transfer and interaction time that is happening from laser pulse to material is so fast that the material does not hold a memory of it getting hot,” explained Salay Quaranta, industry manager for Trumpf Inc., Farmington, Conn. “The process is already finished before a heat-affect-ed zone (HAZ) can be created.”

Trumpf’s cold-processing approach produces a matte-black finish using the same TruMicro lasers used in precision stent cutting. “Couple this with 3D marking software, vision systems and extreme accuracy, and we’re marking implantables and devices that were previously believed to be impossible to label,” she said.

These marking systems are offered in standalone work-stations with Ethernet connectivity or as integration-ready, capable of being plugged into multiple workflows.

“We all want to automate, digitize and adopt more effective methods to stay competitive and bring greater transparency to production,” Quaranta noted. “Networking machines with one another is undergoing a revolution. While the networking is easy enough, it’s what you do with it that makes the competitive difference.”

Trumpf’s predictive condition-based monitoring solutions optimize machine capacity and product lifecycle. “Our dashboards give you direct insight into the operating statuses, message histories and program and maintenance information to accurately measure and increase availability and thus productivity. Imagine if you could identify weak points before they manifest and get a solution started before it turns into a problem. This is modern manufacturing.”

That said, she added, it remains “a bit of a ‘black art’ to make a black mark.” There are so many variables that determining whether nano-, pico- or even femtosecond lasers are the ideal tool continues to be a material science challenge. But “the laser parameter process development window is much more forgiving when you use an ultrashort pulse laser,” said Quaranta.

3D in the Workflow

Complementing machining processes is the growing use of additive manufacturing (AM), or 3D printing, to manufacture patient-specific devices impossible to make with traditional methods. Orthopedic implants and surgical guides are two well-established and growing uses of AM.

EOS North America, Novi, Mich., offers a prime example of a 3D printing company expanding its repertoire of materials and machines to make new medical products.

For instance, EOS and Aetrex are developing customized orthotics that match unique pressure points on an individual’s foot, said Laura Gilmour, global medical business development manager. Meanwhile, EOS and Shapeways have launched an environmentally friendly PA11 nylon derived from castor oil to make cost-effective braces and prosthetics.

Medical industry designers “often take preference in using materials that are historically used in device manufacturing,” she explained. “From a metal perspective, there has been limited creation of new materials as it is easier to use a material that has long clinical history. The path to biocompatibility testing, animal testing, and clinical trials can take time, and materials like titanium, cobalt-chrome, and stainless steels that have clinical history are still the preferred materials for medical devices.”

Similarly, additive processes are subject to the same level of accuracy, quality and material contamination risks of any manufacturing approach, which means companies must invest time and money into R&D before AM parts are ready for market.

But beyond the familiarities of medical manufacturing, 3D printing offers a world of new design opportunities.

“It is critical to design with additive in mind from beginning to end,” Gilmour said. “Post-processing shouldn’t be considered an afterthought, but included in the design and test phase, and throughout the process chain. For example, material selection in the design phase should be considered in the end aesthetics of a device.”

3D printing simplifies processes like adding a porous surface layer to implants precisely where needed to improve bone growth. With traditional processes, a porous layer would have to be sprayed on, risking delamination. Porous structures can be printed inside the graft windows of spinal cages to encourage bone growth and fusion. This also allows “a more open structure on the outside to maintain visibility of the desired fusion in imaging post-surgically. Post-processing methods such as bead blasting and cleaning must also be kept in mind in the design of the structure, so the desired porosity and pore size is met,” she said.

As the medical industry’s comfort with additive grows, regulatory affirmation is gearing up. With the FDA clearing more than 100 additive manufactured devices currently on the market, Gilmour said, “the FDA has put significant focus on providing a regulatory pathway in an attempt to keep up with the rapid pace of adoption.”

Another element to increasing AM adoption is workflow integration. For example, EOS offers EOSCONNECT software to connect to on-premise MES/ERP solutions “but also to serve upcoming digital marketplaces and IoT platforms,” Gilmour said. “All the machine and production data collected can be made usable on a live basis. EOS offers an open interface capable of providing integration into either intelligent EOS applications providing productivity increases or third-party applications. This way, we lay the foundation for companies to truly integrate additive manufacturing in industrial production environments.”

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