A view of Schütte’s 325linear five-axis grinder and the control displaying its SIGSpro integrated grinding software.
Grinding machine maker Schütte LLC has recently shared a reflection on how five-axis grinding technology, such as that embodied in the company’s 325linear machine, enables high performance in medical applications such as orthopedic implant grinding. For Schütte, two of the biggest advantages of this machine technology are tied up in the relation between the axis drive system and the CNC software platform.
In the following paragraphs, Schütte explains how these machine components interact for medical machining applications.
Direct Drives on All Five Axes Achieve High Grinding Velocity at the Part Surface
A key feature on the 325linear is direct-drive technology in all five axes. The X, Y and Z axes are driven by linear motors as well. According to the company, eliminating ballscrews or gears from the drive system and components facilitates more accurate and dynamic simultaneous movements. The backlash-free drive system onboard also provides fast acceleration without being prone to unwanted wear or other harm to the drives. The combination of this drive setup and the machine’s control scheme enables an effective velocity of over 500 inches per minute at the part surface, according to the company.
This sort of high-speed grinding can help to reduce production costs and enable different cutting techniques on orthopedic implants like femoral knees, tibia trays and hip stems as well as instruments like hip rasps, medical cutters and drills. However, Schütte explains that making the most of these capabilities to program such diverse one-off or low-volume parts using one machine platform requires the right software.
SIGSpro Integrated CNC Software Combines Off-Line Programming and Simulation
When it comes to medical parts like the ones described, which require standard geometry features as well as more demanding freeform surfaces, the potential programming challenges can seem quite extreme.
Schütte’s SIGSpro integrated grinding software combines full off-line programming and simulation for the entire workpiece, from blank to finished product. The software incorporates machine and accessory environments and collision checks, then simulates production before the machining cycle starts. On the one hand, this programming platform promotes stable production with predictable work output; on the other, it saves the production engineering department time in preparing the CNC code.
Program information is stored in a file that gets called up at the machine control panel when it’s time to start the job. Generating such a program, including part handling, part probing, tool measurement, wheel dressing, grinding, milling, abrasive belting and polishing operations, requires only a few mouse clicks, the company says. This makes it easier for those without special coding skills to get going on the machine.
Software Combines with Multifunctional Capabilities for Specialized Applications
This system can also handle specialized applications like grinding orthopedic surgical drill bits or femoral knee implants. Here are some of the ways the company says its 325linear and SIGSpro platform makes some specialty applications easier.
For drill-bit geometries unique to a certain product, the software can import a DXF contour of a special feature and immediately generate a CNC program. Long, thin-geometry orthopedic drills or reamers must be supported exactly at the grinding point. To accomplish this task, the machine can be equipped with a dual auxiliary slide system carrying a tailstock to hold the part on center and a steady rest slide to absorb the grinding forces and hold the part where needed. These slides can be independently programmed, positioned, activated or deactivated during machining.
Dealing with freeform surfaces is mandatory on parts such as femoral knee implants, the company says. Achieving a constant but highly effective velocity at the part surface without losing accuracy by grinding hundreds of parallel lines is a unique challenge. That’s why software offers an interface to CAD/CAM systems that provides the post-processing routine for such high-volume data and complex-geometry toolpath information. According to the company, the software and machine are capable of performing the grinding job within 4-8 minutes, depending on the part size and fineness of the desired surface quality.
The freeform surfaces involved with grinding these femoral knee implants is made easier with the SIGSpro software’s CAD/CAM interface, providing the post-processing routine adequate for such high-volume data and complex-geometry toolpath information.
For operations where milling is an expedient substitution for conventional grinding, Schütte says that the 325linear can switch the drive parameter setting to perform an optimum cutting path. Also, live radius compensation can be applied to milling applications in all five axes of motion to control and offset part dimensions or to compensate for diverse cutter dimensions.
But grinding and milling operations are not the end of the machining sequence option list. In some cases, abrasive belting and polishing can make sense, too. These additional operations are now possible within the machining envelope, as the tool magazine on these grinding centers can be extended from five up to 12 or 24 magazine places to store special belting assemblies and polishing arbors.