Finishing of artificial knee femurs – 4 x faster and fully automated

In addition to knee implants made from cobalt chrome alloys, a leading implant manufacturer expanded its product range with artificial knees made from titanium. For the final surface finishing operation prior to implantation the company is utilizing the Rösler multi-surf finisher RMSF 4/800 including cost-efficient and sustainable process technologies, also supplied by Rösler. Compared to the drag finishing technology, usually employed for such finishing tasks, the required cycle times are 4 times shorter. Depending on the initial surface roughness readings of the raw components, the grinding operation with plastic processing media – specially developed for medical engineering applications – produces surface roughness readings of less than Ra  = 0.1 µm in cycle times of about 20 minutes. Moreover,  the critical “box” surface area, frequently requiring a manual  grinding operation, can be fully automatically ground and polished.
This was made possible with the innovative surf-finishing system, the most intensive mass finishing technology. Surf-finishing was developed for treating high-value work pieces with complex shapes requiring the targeted finishing of precisely defined surface areas. Similar to drag finishing the knee femurs are mounted to a rotary spindle equipped with a servo motor. The actual treatment of the work pieces takes place in a rotating processing bowl filled with grinding, respectively, polishing media. Individually adjustable tilting and rotary motions guarantee the highly precise and absolutely repeatable surface treatment of the various implant components on precisely defined surface areas. The process parameters, such as cycle time, rotary speed and direction, are stored in the equipment PLC as part of work piece specific processing programs. Pneumatic clamping of the work piece fixtures and a loading window, as part of the standard machine version, allow easy automation of the loading operation with an industrial robot.

A solution that saves space, resources and energy 
Besides short cycle times the intensive treatment in multi-surf finishers offers additional benefits. These include that the process stage pre-grinding with ceramic grinding media – a must for drag finishers – is no longer needed. This reduces the number of required machines for surface grinding and polishing to two multi-surf finishers, as opposed to three drag finishers. This results not only in savings for capital expenditures but also reduces the consumption of energy and resources and demands less space for the surface finishing operation. An additional benefit is that the processing times for costly grinding on CNC machines can be shortened by transferring some of this work to the multi-surf finisher.

Maximum process stability through visualization and digital process water management
To ensure a maximum of process safety and stability Rösler augmented the standard equipment controls with a process visualization module. This allows the machine operators to visually monitor the individual process stages, which the work pieces undergo at any moment in time.
The cleaning and recycling of the process water from the wet surface smoothing operation is handled by a fully automatic Z 1000 centrifuge. The control panel of the centrifuge is equipped with the digital process water management module “Advanced” from Rösler Smart Solutions. This innovative, interactive software continuously monitors, records and evaluates up to 14 process parameters, for example, the compound concentration, the pH value, the microbiological load, etc. As soon as one or several of these parameters drift out of the pre-defined range, such discrepancies are displayed. In addition, the operators obtain easy-to-understand recommendations for immediate corrective action. This allows employees with no special knowledge and training to quickly adjust the process water parameters to the pre-defined values and thus ensure a consistently high product quality. Moreover, the continuous recording of the parameters over a longer period of time provides a clear indication as to when the process water quality has deteriorated to a point where it must be replaced with new water. This results in substantial water and compound savings and guarantees that the product quality does not suffer. Finally, the continuous recording of the process water parameters can also be used as proof of the process quality and stability for quality audits and documentation purposes.