| Advanced ceramics are attractive to many engineering applications, but their use is restricted by the high machining cost of ceramic components. Two machining techniques, viz. creep feed grinding and high speed grinding, promise a significant cost reduction. Successful implementation of these techniques relies heavily on proper application of the grinding fluid. The present study investigates flow of Newtonian fluids in grinding with non-porous wheels, with the emphasis on: (1) average flow field and hydrodynamic pressure generated in the grinding zone, (2) fluid rejection off the rotating wheel, and (3) influence of fluid delivery parameters on the effective flow rate through the grinding zone. Fluid flow between a rotating wheel and a flat workpiece has been modeled using the classical Reynolds equation of lubrication and its two modified versions, which account for surface roughness and for turbulence, respectively. The range of applicability of the theoretical models has been discussed, and verified experimentally in terms of the hydrodynamic pressure developed. Fluid rejection off a smooth rotating wheel has been studied experimentally and analytically. It has been found that under conditions corresponding to typical grinding situations fluid rejection from a smooth wheel is never complete. This phenomenon can significantly affect cooling and wheel cleaning. The critical wheel speed, below which no fluid is rejected from the wheel, has been predicted and found to be inversely proportional to the initial fluid film thickness. The development of instabilities on the fluid surface has also been observed. A physical model which links fluid delivery parameters and grinding parameters with the appropriate inlet boundary conditions for the Reynolds equation has been developed and verified experimentally. The model has been used as an optimization tool with the main goal of maximizing the effective flow rate through the grinding zone. An experimental method for the determination of nozzle efficiency (fraction of the nozzle flow rate that reaches the wheel-workpiece contact) has also been developed. The proposed qualitative relations between the effective flow rate and fluid delivery parameters can be used along with the nozzle evaluation method, in order to find the optimal nozzle type and position for any particular grinding situation. |
