What the well-run shop needs: precision machining technology heads the list.
Processes performed, in addition to conventional metal removal, include micromachining, threading, deburring, lasing, etching, heat-treating, finishing, passivation (rendering metals inert by chemical treatment), and parts cleaning. We are well into the "micro" stages of processing as in micromachining, microdeburring, and anything that smacks of producing the smallest, finest, smoothest, or most accurate parts.
You don't have to look at the human skeleton too hard to find out where medical devices are used to repair and/ or replace broken, worn, or missing bones. Typically these small, complex devices include dental implants, maxillary facial screws, micro screws, bone screws, hip screws, transfixing pins, spinal fixation, femoral nails, suture anchors, and the like. They are used in orthopedic procedures such as general bone surgery, setting bone fractures, joint replacement, and dental implants. Larger orthopedic devices include the implants that become replacement hips and knees to replace damaged and arthritic joints. And, of course, there are all the instruments and devices, in different sizes, shapes, and forms that are used by surgeons to perform the required procedures.
No miss with Swiss
Swiss-type turning machines continue to be one of the most important classes of machines in demand for medical device, as well as other small precision parts manufacturing. Encouraging this growth in demand are new capabilities that are being added. Leading suppliers include Marubeni Citizen, Star, Tsugami/REM Sales, Tornos Technologies, Gildemeister, Emco-Maier, and Index/Traub.
Swiss-style CNC machines are able to machine small, complex precision parts in one setup, performing such processes as turning, milling, drilling, tapping, and threading from close tolerance bar stock in diameters typically up to 1.50". Unlike conventional lathes where the part is stationary and the tool moves, a Swiss-type turning center allows the part to move in the Z-axis. The bar stock is held in the machine and advanced through a guide bushing. Only the portion being machined is exposed from the guide bushing, allowing the material to be held tightly, virtually eliminating deflection and increasing accuracy. In addition to the live tools, many Swiss-style lathes have drills and boring tools on backworking tool stations. When the part is held in the subspindle (also called the pick off spindle), machining the part can be finished by these tools.
Medical threads are among the most difficult to machine and long threads are especially difficult to make on Swiss-type machines, according to Mark Saalmuller, sales and marketing manager, Tornos Technologies. Thread forms for screws of all types are as individual as the doctors who often design them. They are characterized by sharp angles machined in tough materials such as stainless steel (316, 3161, and 304) and titanium, says Saalmuller.
One solution that has become quite popular with Swiss machines is thread whirling. Internal and external threads can be whirled and completely machined to the final dimension in one pass without having to be reworked. Compared with conventional processes such as thread chasing and tapping, short chips are produced with thread whirling and screws with a diameter from only 1 mm or less can be threaded. ID whirling is 60 percent faster than tapping, and OD whirling requires no pre-turning, says Saalmuller, and burr-free threads are easily made. It's estimated that about 60 percent of all threads for dental and medical devices are currently whirled. With these multiple processes, Swiss-type machines offer an excellent model of the capability of multitasking machines that are in demand for machining of parts of all sizes: one clamping, many processes performed. Tornos Technologies, www.rsleads.com/506tp-167
Beyond the ordinary
For some time, Electrical Discharge Machining (EDM) has been a standard within the medical parts industry in various forms such as wire EDM, plunge EDM, and microhole EDM. There are many reasons. Benefits of EDM result from the fact that there is no contact or force to deform even thin wall parts. Electrodes can generate shapes not easily done with cutting tools. Burr-free surfaces are created as vaporized material is flushed away. Parts are easy to fixture since no stress or vibration is involved in processing, and any conductive material however hard can be EDM'd.
For these and many other reasons, EDM still commands an important role in medical device manufacturing. For one thing, explains Gisbert Ledvon, marketing manager for Charmilles, the technology doesn't depend on the specialized skills of the operator, and the process can be easily documented--an important consideration in medical parts manufacturing. "EDM delivers consistent results in surface finish, particularly for implants and spinal fixation," Ledvon explains. Charmilles" CC machines are especially well-suited where cleanness of the surface is require& says Ledvon, because they avoid redeposit of material on the surface of the workpiece. The type of implant being machined makes a difference. For trauma-type implants, cleanness of surface is more critical than accuracy. For dental implants, however, where tight tolerances within a tenth or two must be held, EDM is almost a must.
The Brother HS70A wire EDM machine has proven very popular for EDMing medical parts and titanium alloys, says Ledvon. The HS70A offers a B-axis, the AE (anti-electrolysis) generator, and linear glass scales. The automatic wire threading systems threads the wire in 15 seconds. "It's fast and economical." says Ledvon. The newest addition to its product lineup is a wire EDM with a unique "turn and burn" capability that combines a moving B-axis with a wire cutting in the X and Y axes to realize contouring cutting with the wire. Charmilles, www.rsleads.com/ 506tp-168
Multitasking and more
Mazak is putting the multitasking capability of its Integrex 100-IIIST to work making three separate components for an oxygen control valve in a single setup. A recent demonstration at the Medical Device & Manufacturing (East) expo was designed to show the power and accuracy of a CNC machining center with the capability of 5-axis simultaneous multitasking lathes. The separate components can be nested and produced one after the other from the same bar stock and be shipped as a kit. Adding an automatic bar feeder and parts catcher transforms the Integrex into an automated solution for both high- or low-volume parts manufacture. Mazak, www.rsleads.com/506tp-169
The requirements of serving the orthopedic device manufacturing market require the ability to move quickly and produce smaller lots of parts like bone screws, and hip joints with the shortest possible leadtime, explains David Austin, manager, engineering information, Mori Seiki U.S.A. Inc. Medical manufacturers have been the largest single segment of users for Mori Seiki's MT series of multitasking machines. In addition to cutting down on leadtime, direct benefits can be found across the board. "Direct benefits include reduced setup time, no need for re-fixturing, and, most important, accuracy and surface finish, so critical to the medical device manufacturing industry, are superior," says Austin. Multitasking machines like Mori Seiki's MT series typically replace several machines reducing fixturing requirement and cost and are available in several configurations, including chucker style, equipped with subspindle, and lower turret. "It all depends on the application, whether the user is machining long slender cylindrical parts or short stocky parts," he says. Mori Seiki USA, www.rsleads.com/506tp-170
One-hand tool with RP
The ability to visualize the design of medical devices and instruments through CAD/CAM programs that can be translated into actual prototypes is well established through rapid prototyping. For an instrument used to fasten set-screws to a corrective implant on a patient's vertebrae and break off the screw heads at a preset torque level, Sofamor Danek engineers recently designed a ratcheting counter-torque surgical instrument using two types of rapid prototyping processes, FDM (fused deposition modeling) and PolyJet (UV-plastic jetting) machines available from Stratasys.
The design of the surgical instrument replaced the existing surgical procedure, which required surgeons to use two separate tools, working them in opposite directions using both hands. The result was often a violent impulse that occurred at the moment each set-screw head broke off. Using ProEngineer for the CAD image, a working model of the ratchet prototype was made from tough polycarbonate using FDM. Outer and inner shafts were built using an Eden333 machine with PolyJet technology that can produce fine horizontal resolution layers of 16 microns, enabling models to be built with fine detail in a variety of UV plastics. Stratasys, www.rsleads.com/ 506tp-171
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|Title Annotation:||medical manufacturing|
|Comment:||What the well-run shop needs: precision machining technology heads the list.(medical manufacturing)|
|Publication:||Tooling & Production|
|Date:||Jun 1, 2005|
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