08/18/2010

Rösler Oberflächentechnik GmbH Werk Memmelsdorf

Drag Finishing – More than just „Another“ Mass Finishing Process Excellent Surface Finishes on Medical Implants

Extremely smooth and a high gloss finish – these are the surface finish requirements for medical implants. To achieve these finishing goals reliably and economically, more and more medical implant manufacturers are utilizing the drag finishing technology.

Increasing life expectation and the practice of extreme sports are leading to increased wear of bones and joints. The last resort to overcome these problems is the implantation of an artificial joint. The use of such implants, such as artificial knees, hips, elbows, ankles, etc., has been growing rapidly all over the world. To meet their growing demand, medical implant manufacturers are expanding their capacity for products made from titanium and other high-alloy metals, and they are looking for solutions for economic and high-quality production of these precision castings. A major focus lies on the surface treatment of these components. To prevent contamination, their surface must be extremely smooth. Compared to robotic grinding and buffing, Rösler drag finishing systems offer many advantages. They allow the grinding/polishing of 24 parts, distributed over four workstations at a time. With drag finishing, the parts never touch each other. Another big advantage of the drag finishing technology is that the parts are completely ground/polished, irrespective of their shape. Several implant manufacturers are already using the Rösler drag finishing technology for their products.

Drag Finishing Reduces the Rz from 18 μm to Rz 0,2 μm
The surface reading on implants prior to drag finishing is usually Rz = 18 μm. The implants are mounted to parts-specific parts fixtures, which are in turn mounted to the four rotary workstations of the drag finisher. The parts are then “dragged” through a bowl filled with grinding or polishing media. RPM and rotational direction of the independent workstation drives can be adjusted. To achieve the required surface finishes, the operating angle of the workstations can also be adjusted. Usually the finishing of implants requires multiple steps. Each process is documented and stored in the system PLC. The first two steps are generally




pre-grinding with ceramic media, followed by a fine grinding step with plastic media. The subsequent high gloss polishing is done in specially prepared dry polish media. The four workstations are equipped with quick connect couplings for easy mounting and dismounting of the work piece fixtures. The specially developed fine grinding plastic media provides surfaces finishes of down to 0.2 μm!