Orthopaedic hip surgery numbers are forecast to increase at a rate of 5% year on year to 2026. This is no surprise given the growing aged population around the world. With this comes increased demand for tools and components to support these procedures. ANCA’s process for femoral ball grinding, developed together with grinding wheel manufacturer Tyrolit, delivers quality and consistency in the finished femoral ball, using specialised machine control and application technology on the market-leading MX7 Linear CNC grinding machine.
Figure 2: surface finish measurement of the finished ball is <0.01micron Ra
The first step in the process is grinding the initial part accurately to size. Using plated CBN grinding wheels, excess stock material is removed from the rough turned part. This operation makes upstream processes easier by relaxing the tolerance demands for the blank part that the ANCA MX7 will grind.
Next are a series of fine honing processes that produce incremental improvement in the surface finish. Application Engineers from ANCA and grinding wheel manufacturer Tyrolit, teamed up to develop a process that delivered stable production results on the femoral ball.
Tyrolit wheels have been specifically developed for femoral ball applications but are known to naturally wear during the production process. ANCA was uniquely positioned to deal with this challenge, being the designer and manufacturer of its own LinX linear motors as well as the CNC and servo drive system that controls the machine and grinding wheel movement. ANCA’s System Engineers developed an entirely new control algorithm for this application. This allowed the operator to program the desired forces applied by the honing wheel on the femoral ball. With this programmed force, the wheel feeds into the ball at a constant rate as it wears away. The three different Tyrolit wheels used could be programmed with their own unique grinding force parameter to achieve a mirror surface finish and consistent part size tolerance.
Additionally, automatic wheel measurement was developed that ensures each honing operation starts from the correct infeed position. This ensured consistency in the process regardless of the wheel wear that is experienced after each honing operation.
A final buffing operation is the last step, delivering a mirror finish on the working surface of the ball. This is critical in ensuring mechanical friction and wear is minimised in the final hip implant.
This content was originally published on the ANCA website.