The medical engineering market embraces many products and manufacturing processes. Control units must be versatile, covering turning, milling, whirling etc in series and piece part production, tackling high precision and surface quality requirements.

Medical engineering is an increasingly important industry sector, partly as a consequence of global demographic change. As technical requirements grow more demanding, suppliers are responding with 10% of generated turnover being reinvested into research and development.

The study ’MedTech2020’, carried out in September 2009 by VDE (German association for electrical engineering and electronic information technology), questioned over 600 specialists about trends in medical engineering. This survey revealed a strong innovation culture in prosthetics and implants; metal processing plays an important role (alongside plastics).

The production spectrum includes many processes such as turning, milling, grinding and whirling. Standard products, such as bone nails and screws are manufactured in volume, whereas special products may be produced as one-offs. Materials present a challenge for both machine and control unit; titanium, cobalt-chrome or ceramics require considerable know-how to achieve the desired level of precision and surface quality.

Companies with expertise in other high-technology sectors have succeeded in this market as much knowledge can be transferred from mould and die, automotive, aerospace and micro-engineering applications. The machine tools and controls used are readily adapted to the new challenges of medical engineering, delivering quality, precision and process safety.

Machines most in demand include long turning automatic screw machines, making bone screws and bone marrow nails, implants and instruments. The trend is towards complete machining. Alongside turning, mostly milling and peck drilling operations are necessary for complex products.

Innovative machinery manufacturers offer automatic lathes equipped with multiple turrets and additional axes; driven tools carry out milling, drilling and thread processes. For example, to machine bone nails in a complete process, turning, peck and cross hole drilling plus milling processes must be carried out. With five axes operation possibilities, the bone nails with grooves and reinforcement humps can be efficiently milled. To enable this, high performance controls are needed, such as the Fanuc CNC 30i series. In this example five or six axes must be interpolated, and seven spindles controlled. Additional programming support is needed, and operators can use the Fanuc Function Path Table Operation (PTO) alongside a conventional CNC interpolator. This enables synchronisation of all axes allowing particularly delicate movements to be programmed.

Implants may incorporate complex, in part freely formed, profiles and require high surface quality, for which many manufacturers are using 5-axes machining centres. High performance control units such as the Fanuc CNC 30i and 31i-A5 series offer numerous special five axes functions, including compensation possibilities for tool length, direction and radius (TCP, TPC and TRC). Control of surface quality is enhanced by functions such as nano-interpolation; and ’Smooth TCP’ and ’Smooth TCP2’ which build on the Tool Centre Point function. Smooth TCP compensates for deviations in the initial settings and ignores redundant commands regarding the machine tool centre point position. Smooth TCP2 optimises the machine tool direction compensation - also in existing programs - in order to achieve a more even movement for side machining. In addition, both functions help to shorten cycle times.

A further auxiliary function ensures a high level of process safety. The 3D-Interference Check, available for any machining process, is an integrated function in the CNC core of the 30i and 31i series units. Unlike many offline interference protection systems that offer only limited safety, it facilitates an interference protection of almost 100%. Although integrated in the CNC, the machining speed is not reduced.

Complete machining is also popular for manufacturing medical instruments, where the trend is towards large numbers of variants and smaller numbers. For driven, handheld dental instruments with high rotational speeds, tolerances on diameter, length, shape and position are becoming ever more exact; and the same is true for laboratory centrifuges used in the medical and pharmaceutical sectors.

Should complete machining not be possible due to complexity, a further auxiliary function - Workpiece Setting Error Compensation - is useful when a workpiece is removed after a machining process, for instance for measurement, and returned to the machine to be processed further. Small deviations in measurement compared to the initial fixturing are unavoidable, but this function can include measurement results as correction factors for subsequent machining processes.

http://www.theengineer.co.uk/mwp/news/fanuc-supplies-

cnc-solutions-for-healthcare-applications/1004109.article