Viewpoints: Medical Market Offers Challenges And Opportunities
By Rajas Sukthankar
Director of Sales - Motion Control
and Machine Tool Segment Manager
Siemens Industry Inc.
The production of medical implants involves an entire process chain, starting with the doctor and ending with the finished device. Doctors use the imaging data of a complex fracture, acquired with a CT scan, to select an appropriate implant and then position it in the fracture area of the patient on the computer. Of course, this is only possible if the implant geometries are stored in a database, and the doctor has implants in stock or can access them immediately from a manufacturer.
In plastic surgery, where implants are made specifically for each patient, implants are custom made with the help of 3D imaging and additive manufacturing instead of being premade. Here, the machine tools are controlled using the implant geometries. Calculated contours and shapes are acquired by the CT scan to make implants that are literally a perfect fit. However, the feasibility of the planned production process can first be determined on a monitor using, for example, a graphic simulation process.
High-speed cutting (HSC) is a machining process with high processing speeds. HSC machine tools achieve high spindle speeds, combined with feed rates that are much higher than those of conventional machine tools. Consequently, they require control systems and part programs that perform equally fast. Today’s advanced CNC is specifically designed for the requirements of medical technology and this precision-part HSC work. Integrated functions onboard the CNC assist users with setup and programming, thus allowing faster and more precise production sequences.
The CNC system and appropriate software form a package that allows machine operators rapid access to the functions they need. Thanks to graphic function display and plain language input dialogs, cycles can be used quickly and effectively after brief training. Even the smallest errors can be corrected during operation, using multiaxis kinematic analysis.
As a real-world example, the production of artificial knee joints on a linear milling center can be fully controlled and monitored by a CNC system. With its broad range of functions, this milling center is particularly well suited for use in the medical sector. It is equipped with linear drives on all axes and can accelerate at more than 2g. The machine can also generate a surface finish down to 0.2 μm Ra. The liquid-cooled machining spindle operates at speeds up to 42,000 rpm, covering an extensive range of potential applications in the medical sector, where such materials as titanium, chromium-molybdenum, tantalum and niobium are typically milled.
To achieve maximum precision during implant production while also maintaining a consistently high level of quality, parametric measurements must be taken continuously from both the machine and workpiece. Probes, for example, on HSC production machines measure tool dimensions in-process, detect broken tools and set up and measure workpieces. In medical machine shops the targeted use of such measuring probes can reduce setup times by up to 90%, while substantially improving process control.
Metal parts used in medical technology are often extremely complex. Choosing the right tooling can have a great impact on quality. Proper cutting tools ensure that the machined parts are absolutely precise and require no further finishing work. Although the materials used for many medical parts are often difficult to machine, the tools must meet high-performance requirements with respect to the precision and surface quality of the implants. Many suppliers offer a program for monitoring the use of precision tools on turning, drilling, milling and finishing jobs. They also help users assess the performance of nonvibrating carbide milling cutters, which are well suited for machining implant materials. Plus, they can offer information on more cost-effective, efficient machining processes.
Smart shops are turning to more advanced machining centers, often true five-axis and 3+2 machines with ancillary devices. They are finding that the loop integrating the CAD program, CAM program and execution of the cycle on a CNC machining center has never been more precise. These functions include the exact measurement and calibration of multi-axes kinematics and the coupled motion of the tool orientation. Innovative machine technologies must enable medical engineering products to be matched precisely to a patient’s individual requirements.
As material composition changes and more ceramic or derivative materials become prevalent, those producing these products will need to be more flexible and reactive than ever. ME
This article was first published in the May 2014 edition of Manufacturing Engineering magazine. Click here for PDF.
Published Date : 5/1/2014