Shortening cycle times, improving production accuracy and processing and handling smaller medical parts are just a few of the areas in which micromachining equipment makers and fabrication shops are honing their work for the medical sector.
For instance, at Marubeni Citizen-Cincom Inc. (Allendale, NJ), a proprietary process called low-frequency vibration cutting that is unique to its Swiss-style machine tools is shortening production time and reducing the risk of part damage from residual chips.
Meanwhile, Omax Corp. (Kent, WA) is increasing the precision of its waterjet manufacturing systems with proprietary cutting software and higher optical resolution.
Custom fabrication shops are also refining their production processes, whether by building their own tooling or creating special systems for handling microparts.
Winning with Waterjet
Having upgraded its MicroMAX machine about a year ago, Omax has better positioned the unit for the medical industry by providing improved positioning and cutting accuracy, said Stephen Bruner, vice president of marketing. “We improved the optical resolution, so there are more steps per unit of measurement along the X and Y axes,” he said. On the machine itself, the company has isolated the catcher tank, which captures the abrasive garnet in the water jet in order to minimize vibration and improve part accuracy.
A new tank cooling package further improves accuracy. “With our rapid water-level control, our waterjets cut under water,” Bruner explained, for sound-reduction reasons. “But even if the substrate is close to the water—not even submerged—most materials expand and contract based on the surrounding temperature. The water coming out of the jet is probably around 70°F, but the amount of kinetic energy happening in the tank can heat that water.” The Omax tank cooling package reduces water temperature “so you have a constant temperature surrounding whatever you are cutting and don’t have those expansion and contraction issues.”
The MicroMAX has an optional Tilt-A-Jet cutting head, which is designed primarily for taper elimination. Also, to reduce the kerf width of the water stream coming from the processing nozzle, the Omax MiniJet can produce a kerf width of about 0.02″ (0.051 mm), resulting in finer features and reduced material waste.
Given the wide range of alloys and polymers used in medical components, waterjet maintains an edge over other technologies by remaining material agnostic and being able to run at full speed without creating a heat affected zone (HAZ), Bruner noted.
“If you’re dealing with true composites, like sandwich materials, you might have to adjust the cutting parameters of the MicroMAX to make sure you are not getting things like delamination in the structure,” he noted. “But in terms of alloys or polymer-based systems with additives incorporated, there are no adjustments necessary for cutting those materials.”
One concern in expanding the use of waterjet technology in the medical device sector is the potential for embedding the abrasive garnet that does the cutting into the substrate, Bruner cautioned. This concern is driving investigation into the biocompatibility of garnet. “There are ways of mitigating embedded particles,” he said. “We are investigating biodegradable abrasives as well as secondary processes” like deburring and electropolishing to remove residual particles.
Omax is also looking into two-step processing, perhaps by first cutting a component followed by flushing the cut area with water alone. “The cutting topography created by the waterjet can be desirable because, according to some industry experts, it may encourage tissue growth if that is the strategy of the device.”
Working in partnership with the Department of Energy’s Pacific Northwest National Laboratory, Omax uses Pacific’s facility to cut materials used in medical devices, after which chemical and mechanical analyses are performed. “We are learning as much as we can so we can help potential customers use this technology.”
Omax also employs proprietary software, including a cutting modeler that assesses the type and thickness of the substrate being cut and the abrasive used to create ideal manufacturing parameters.
Moving Microgrinding Forward
At tool grinder manufacturer Rollomatic Inc. (Mundelein, IL), quality blank preparation, tool runout compensation and precision wheel dressing are the company’s primary concerns in producing medical tools.
During blank prep, “concentricity between the tool neck and shank is vital—otherwise you’ll have wheel deflection during flute grinding,” said Bjorn Schwarzenbach, communications and project coordinator. “Minimizing wheel deflection is possible on the ShapeSmart NP5 as a blank prep application for microtools. On the NP5, the pinch/peel grinding process, along with the shank guide system with V-Block and pressure roller, guarantee perfect tool runout concentricity.”
With its GrindSmart five and six-axis grinder series, Rollomatic manages wheel stability with the PerfectArbor system, which compresses the arbor and centers it on the wheel. This provides a very rigid connection. For the tool, there’s a patented Nanoset steady rest and U-block workholding system, which works together with the wheel arbor to minimize deflection.
Also important for grinding microtools is accurate wheel dressing via CNC control with equipment “such as our ProfileSmart. This is necessary to achieve the extreme precision required for microscale tools, where tight tolerances of 0.000039″ [0.001 mm] are common,” said Schwarzenbach.
To avoid vibration and chatter, Schwarzenbach said, “more toolmakers want to grind microtools with variable helixes. Three years ago, you couldn’t ask for variable helixes in microtools sized down to 0.004″ [0.102 mm]. Now, with enhanced grinding technology and new software, variable helixes are possible.”
Swiss-Style Machining Milestones
With Swiss-style machines remaining “the go-to technology” for micromachining because of the part sizes they hold and tolerances they navigate, low-frequency vibratory (LFV) cutting is a new wrinkle in shortening cycle time. Swiss-style machine builders are also adding laser cutting to the milling stations of their units to enhance their functionality. Exclusive to Marubeni Citizen-Cincom, LFV reduces the amount of chip buildup and chip wrap of metal material common when machining medical devices, explained Glen Crews, Western regional sales manager.
“When you get a buildup of chips, the machine has to be stopped frequently to clear them from the cutting areas,” Crews said, not to mention the potential damage to the part from residual chips. With LFV, oscillation is built into the machine as it is cutting, and the chip is broken up into very fine pieces rather than long, stringy chips thanks to one of the machine’s axes vibrating in time with the spindle rotation. LFV is achieved either by setting the number of oscillations per rotation or the number of rotations per oscillation, producing different chips based on the application.
“It produces a slightly interrupted cut; instead of the cut being continuous, it generates a little flake and then backs away repeatedly,” said Crews.
He noted that LFV works on plastics or steels and allows for deeper drilling by reducing pullouts “because the chips are so small they are flushed out with the high-pressure coolant system. Some companies are making very long spiral drills; by using LFV, everything flushes out in one pass.”
One such toolmaker is Mitsubishi Materials USA (Fountain Valley, CA), whose deep hole drilling product line geared to medical production of 1 to 2.9-mm diam holes “offers a carbide-coated drill with a flute length 30×D in MVS and MWS Series Micro Drills, and up to 80×D in MGS Micro Series uncoated solid-carbide gundrill,” said district manager Aram Fundukian.
“With these Micro Series of length-to-diameter ratio drills that are coolant-through, we would need 1000 psi [6.89 MPa of coolant pressure and a good filtration system—a 3 µm filter bag would cover it—using an appropriate center cutting end-mill to create a pilot hole to act as a guide bushing and some programming,” he explained. "We could then drill continuously to the bottom of the hole without pecking or retracting. We drill coolant-through down to 0.020" [0.5 mm].”
Titanium bone screws are one of the primary parts produced with these drills. “Most often, that deep of a hole has to be done with an electrical discharge machine,” he noted, “which is more costly. If it can be done on the machine shop floor, it can stay in-house to completion at a substantial cost and time savings.”
Swiss in the Shop
Able to produce parts smaller than 0.003″ (0.0762 mm) and tapered up to that measure, Medical Micro Machining (MMM; Colfax, WA), employs three Tornos Deco 10 Swiss-style machines and four Microlution MR4 micro lathe turning platforms among its equipment. The shop, which counts Boston Scientific among its clients, is preparing to purchase another Microlution machine in the near future from machine builder GF Machining Solutions (Lincolnshire, IL).
Working in traditional plastic, titanium, brass and stainless steels as well as Eccosorb, a more exotic plastic material, MMM knows well the sometimes protracted process of seeing a medical component through from a design concept to commercial reality.
The shop’s primary project now is a slightly larger implantable capsule about 0.125″ (3.175 mm) in diameter and almost 0.75″ (19.1 mm) long, noted MMM owner Rob Whitmore. The tubelike part, intended to house electronics, has been in the works since 2005.
On a smaller scale, MMM uses one of its Tornos machines for more intricate parts, for example a component roughly 0.025″ (0.635 mm) diam and 0.016″ (0.41 mm) long with a 0.016″ diam hole drilled in stainless steel. “We have a system that picks them off by vacuum and puts the parts into a container with a really fine mesh screen so we can collect them,” Whitmore said.
Among those microparts are cancer-fighting seeds that bring radioactive material to targeted cells. MMM manufactures the capsules and other system components. For another medical client, MMM produces parts that are swaged onto cables. “We make parts down to where they are being swaged onto a 0.004″ [0.1[0.102 mm]m braided cable,” Whitmore said.
Whitmore holds a patent for a neurological bone screw that he first conceived around 2002. The screws, with an outside diam of 1.5 mm, are “rather unique because they are dual-start thread,” he noted. All others are single-start and single thread, he said. “They react in a unique way, and screw in fast.” Companies including Medtronic have shown interest, and some are testing samples produced on the Microlution MR4.
Further attesting to the ever-changing nature of micromachining medical parts is Phil Miller, CEO of Owens Industries (Oak Creek, WI), and a former managing director for Tornos. At Owens, which produces implants, surgical tools and special devices for the skull, heart and spine, “we get involved with a lot of abrasive materials,” Miller said. “Tool wear and chip control are common concerns. We typically go through a lot of tooling developments for the product and projects we take on. Many times, when we produce microparts, we need to make our own tools because we can’t buy them over the counter.” The prototyping process often reveals that an initial design must be reworked before going to market.
Owens employs five-axis milling and wire EDMing with indexing fixtures and is building a Swiss lathe department to supplement its micromachining capabilities. “A big part of what we do is in parts finishing,” Miller explained. “Everything is inspected 100% and deburred under 30× magnification microscopes. Therefore, finishes are always critical and parts must be free of micro burrs. Our typical lot size is anywhere between one to 50 parts, so we have to get it right the first time. Our real strength is our employees’ skill level and craftsmanship. We typically take on the projects no one else wants to do or can do.”
Tooling and Machining Changes
As medical parts machining evolves, machine builders, tooling manufacturers and medical part makers have responded with a variety of innovations. For example, to help surgical instrument makers impart increasingly fine details, Methods Machine Tools Inc. (Sudbury, MA) offers the Yasda YMC-430, a smaller-taper machine with higher spindle speed “that is still capable of machining pre-hardened materials,” said Steve Previti, Yasda line manager for Methods.
The machine “has a built-in 3R macro chuck and can be fed by up to 90 pallets,” he explained. “Spinal-type parts are being machined on it because of the complex geometries.” For bigger parts like bone plates, Yasda’s 33-pallet PX-30i, a 40-taper machine, is a good choice.
Cutting tool manufacturer Sandvik Coromant (Fair Lawn, NJ) sees growing demand for tight-tolerance Swiss tooling, noted Pat Loughney, product specialist for small-part machining. “With our small-part tooling, customers want an exact fit when they change an insert. They don’t want to worry about changing or indexing an insert and finding the component will be out of tolerance because the tolerances are so small as it is. They rely on us to have more ground-style inserts, where repeatability is always the same throughout the run, saving setup time and reducing scrap.”
Quick tool changeout is also an issue, so Sandvik Coromant offers its QS holding system that goes directly on the gang plate of a Swiss-style machine and functions as a tool and a stop. “If you have to change a tool, you can take it out, change an insert and put it right back in, or have a tool ready to put right back in at the machine. There is such a magnitude of things going on in that machine at one time, and the envelope to work in is very small. The key is to develop tools around the features of the machine,” said Loughney. For example, the wedges that hold the tools in are spring loaded.
With microgrinding of softer materials becoming more prevalent in the medical device sector, “customers are looking at the crystalline structure of metal now,” noted Joshua Jablons, PhD, president of Metal Cutting Corp. (Cedar Grove, NJ). “They’re not just looking at parts at 30× magnification. That’s good for us, because grinding is less damaging than stamping and other cold-forming operations. People are giving us soft materials to grind because if they get stamped they can split and fracture similar to harder metals.”
Components like neurology tubes are getting so intricate, Jablons said, that his company is cutting tubes with ODs of 0.008″ (0.203 mm) and IDs around 0.005″ [0.1[0.1[0.127 mm]>
“We’re impressed that our customers can draw tubes like that” and thinner. For instance, with thin-wall tubing for neurology surgery, “occasionally people will ask us to cut things with a wall less than a thousandth of an inch—perhaps eight-tenths. Our response is, ‘You can draw that and it doesn’t rip or tear?’ A wall below a thousandth of an inch in any metal is paper thin.”