An ultra-smooth planarization method for controlling fluid behavior in cluster magnetorheological finishing based on computational fluid dynamics

The machining method for controlling the behavior of Bingham fluids in cluster magnetorheological finishing (MRF) is a novel ultra-smooth planarization method. It is necessary to simulate cluster MRF fluid state during machining to optimize the surface microstructures on the polishing disk. The behavior of MRF fluids in a magnetic field is determined by using a rheometer. On this basis, a simulation model is established for fluids during the machining for controlling the behavior of Bingham fluids in cluster MRF pads using the computational fluid dynamics (CFD). The influences of different surface microstructures on polishing disks on the magnetic flux density modulus, size of polishing pads, fluid velocity, and fluid pressure are studied. Surface microstructures on the polishing disk can increase the magnetic flux density modulus, decrease fluid velocity, and increase fluid pressure, and can enhance the polishing effect of soft abrasives. In addition, these surface microstructures reduce slip between the polishing pads and the polishing disk, thus slowing the wear of the polishing disk. Simulation results show that the polishing disk with micro-holes demonstrates the largest magnetic flux density modulus and forms the most extensive polishing pressure. Polishing tests are conducted using sapphire wafers with a diameter of two inches (50 mm) as workpieces. Compared with using a smooth polishing disk, the material removal rate (MRR) is 68.4% higher, while the roughness Ra and peak-to-valley (PV) values are decreased by 34.1% and 75% when using the polishing disk with micro-holes. The test results match the simulation results arising from the use of the model.