Outlook Medical
Machining with Advanced CNC
Critical machining demands are noth- ing new in medical part production. Te industry has progressed at light speed, however, in its need for faster turnover, especially in the orthopedic arena, where the one-off is the standard, requiring very expensive machining centers to be used for hip joint or knee replacements that are unique to each patient. In addition, the emergence of cobalt chromes, ceramics and assorted high-performance refractories have made the job of the machine shops and production departments all the more difficult. In the worlds of tooth and bone implants, bone screws, prosthetics and other end products, success relies on the quick translation of the cutting require- ments to the machine with seamless execution in the spindle speed and feed rates, as well as the part and tool han- dling strategies. To compete in this arena, smart
shops are turning to more advanced machining centers, oſten true five-axis and 3+2 machines with ancillary de- vices to accomplish this work. Te loop integrating the CAD program, CAM program and execution of the cycle on a CNC machining center has never been more precise. Tese functions include the exact measurement and calibration of multiaxis kinematics and the coupled motion of the tool orientation. Every time a new part is required,
the machine tool must be adjusted. In bygone days, this setup oſten required substantially more time than the actual machining. Te old maxim that says there is no straight line in the human body is unchanged. However, with the new CNC technologies currently in
the market, the setup and machining scenario has changed substantially. Te onboard features of look-ahead, data compression and milling path veloc- ity, all of which are made possible by the algorithms of the CNC technology, keep the cutting velocity much more consistent across the entire cutting curve and thus the workpiece surface. ISO data and double spline interpola- tion at both the tool pivot point and tool tip have combined in the CNC to cut more effectively and consistently on five-axis machines. Highly sophisticated CATIA soſtware sees curves as curves, not as linear paths, to put it simply. Tis improvement in motion control has cut the machining and setup times by a substantial amount.
The industry has progressed at light speed in its need for faster turnover—especially in the orthopedic arena.
Te combination of these CNC ad-
vanced surface finishing features and the compact flash card for data transmission and rapid program modification have made it possible for even a 3+2 machine to be used effectively for the production of medical parts. A combined spline in- terpolation and transformational surface execution now accomplishes a surface integrity previously delivered by only a true five-axis machine, in many cases. With certain higher-level CNC units,
this spline interpolation and transfor- mational surface technology combine with auto-measuring and 3D simulation onscreen to create a graphical represen- tation of residual material detection.
Randy Pearson
International Business Development Mgr., Drive Technologies Siemens Industry Inc. Elk Grove Village, IL
Tis enables a second or third tool for rapid removal of residual stock on a workpiece cut most efficiently with a first-pass tool. All the above cutting strategies and
monitoring capabilities can now combine in the most sophisticated CNC units with a true five-axis transformational kinematic, 3D radius compensation and, when appropriate, the same volumetric compensation used in aerospace, where the calculations are based on actual tool tip and workpiece orientation, to achieve the optimum surface finish and part accuracy in relation to the actual math model in the CAD program. CNC technology has also been
enhanced to provide collision avoid- ance between the stationary and moving parts on the machine tool. In doing a program simulation, the CNC can perform an accurate modeling to show potentially dangerous points of contact between headstock, spindle, trunnion and gantry. Over a million knee and hip re-
placements were done in 2010 and the estimates range beyond four million annually for such procedures by 2030. Tis fact, combined with the additional surgical instruments and related com- ponents needed for such procedures, bodes well for the medical parts pro- duction industry. As the material com- position changes and more ceramic or derivative materials become prevalent, machine shops and contract manufac- turers will need to be more flexible and reactive than ever. Finally, it should be noted the medical manufacturing market is ripe for the introduction of additive manufacturing.
Medical Manufacturing 2014 21
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