RPM-Synchronous Grinding: An Innovative and Efficient Manufacturing Method for the Production of Non-Circular Workpieces

RPM-Synchronous Grinding (RSG) opens up a wide range of applications, as this manufacturing process enables the efficient production of components with a functional macro geometry as well as a functional micro geometry of the surface.

Unlike conventional non-circular grinding approaches, the RSG process strategy requires no oscillation of the infeed axis of the grinding spindle generated by coupling with the rotating workpiece spindle. By using a fixed ratio of grinding wheel and workpiece spindle speed in conjunction with a non-circular grinding wheel geometry, almost all workpiece macro geometries including circular, two-dimensional non-circular and even three-dimensional non-circular can be produced in a simple plunge grinding process. In the RSG process, grinding wheel and workpiece always meet at the same surface points. This feature is fundamentally different from conventional grinding processes, where a constant change of contact points with each revolution is responsible for the random surface texture on the workpiece. The RSG process behaviour thus enables the production of workpieces with almost any macro geometry and the functional micro geometry of the surface in only one production step.

The topology of the grinding wheel, the kinematic parameters of the dressing and grinding process and the material parameters of the workpiece must be sensibly matched to each other for an advantageous application of the process in series production (drive train parts for combustion engines, E-axis, optical industry, precision engineering).

The contour of the grinding wheel is usually not known and must therefore be derived from the desired workpiece geometry using a specially developed software. For the oscillating dressing process a cam contour grinding compiler is used to realise the required non-circular geometry on the grinding wheel. In order to be as flexible as possible with regard to the required macro and micro geometry of the grinding wheel, the dressing process is performed with a cylindrical form roll. The plunge grinding process itself is specified by a high-precision coupling of grinding and workpiece spindle axis, combined with a suitable speed and feed definition.

The Institute of Production Engineering (IFT) at Graz University of Technology is equipped with a unique grinding machine that meets the technical requirements for the RSG process specifications. First RSG test series have basically confirmed the expected process potential.

Experiments can help to identify relationships, but simulation tools are needed to derive general predictions. Therefore, Molecular Dynamics Simulation (MD) is used to analyse the process. By breaking down the simulation of synchronous grinding to the atomistic level, the material laws, which are normally subject to large uncertainties, can be completely eliminated and elementary relationships of the RSG process can be studied.

In the test series presented, defined cam geometries are produced for a range of established steel materials using conventional vitrified grinding wheels in the RSG process. The surface quality and geometric accuracy of the manufactured workpieces are evaluated and confronted with results from RSG results performed for circular workpieces as well as with results from conventional grinding operations. The applied molecular dynamic simulation model for the grinding process (workpiece, abrasive and their interactions) is presented, the simulation results are described and last but not least compared with experimental results from grinding tests.