Modeling and Simulation of Hydrodynamic Pressure in Cutting Zone

The conventional method of delivering grinding fluid that floods delivery with high supply fluid pressure and nozzle fluid rare to achieve high performance grinding. However, the hydrodynamic fluid pressure can be generated ahead of the contact zone due to the wedge effect between the wheel’s peripheral surface and the workpiece surface. Indeed, this reduces the depth of cutting and increases grinding wheel spindle deformation and overall grinding resistance, thereby affecting machining accuracy. In this paper, a theoretical hydrodynamic pressure model is presented for the flow of coolant through the grinding zone during high-speed precision grinding. The simulated results show that the hydrodynamic pressure was proportional to the velocity of the grinding wheel and inverse proportional to the minimum gap between the wheel and the workpiece. Furthermore, the hydrodynamic pressure peak value was only generated in the minimum clearance region where a higher fluid pressure gradient was observed. It can also be deduced that the hydrodynamic pressure distribution was uniform in the direction of the width of the wheel. Introduction Grinding processes are techniques employed widely as a finishing in all industrial fields. However, during the grinding process, high temperatures may lead to thermal damage to the work surface, inducing micro-cracks and tensile residual stresses at the ground surfaces. Such cracks and stresses deteriorate the surface quality and integrity of the ground surface. This damage can be reduced by the application of flood delivering coolant fluid that removes the heat created and lubricates the two surfaces in order to decrease the amount of friction. A number of investigations have focused on ensuring a large volumetric flow rate into the grinding zone in order to overcome the boundary layer of air. However, due to the wedge effect between the wheel and the work surface, a considerable amount of hydrodynamic pressure is generated during the grinding process. Moreover, conventional methods of flood delivering coolant fluid via a shoe nozzle tangential to the wheel are not believed to fully penetrate this boundary layer of air. Consequently, the majority of grinding fluid is deflected away from the grinding zone [1,2]. Therefore, the flood delivery of a grinding fluid not only that increase hydrodynamic lift force, result in reduce the depth of cutting, and increase grinding wheel spindle deformation, but also that increase high disposal costs in production. The goal of this project is to model the hydrodynamic fluid pressure during high-speed precision grinding both theoretically and experimentally so as to find the quantitative relationship between the hydrodynamic pressure and grinding conditions. Theoretical model The problem to be investigated is presented schematically in Fig. 1, which represents a typical surface precision grinding in which the wheel depth of cut is very small and can be neglected. It is assumed that the entrance is well flooded with fluid. It should be noted that the method by which the fluid is delivered is not considered. The workpiece speed is neglected, as it is typically much smaller than the wheel speed. It is assumed that both the wheel and the workpiece are smooth and that surface roughness is almost negligible because the average film thickness is larger than 1.5 times the root-mean square roughness [3]. The coolant fluid is Newtonian, uncompressible steady flow, constant viscosity, no slip on the surface of wheel and workpiece. Constant pressure along the film Advanced Materials Research Online: 2010-10-27 ISSN: 1662-8985, Vols. 148-149, pp 186-190 doi:10.4028/www.scientific. net/AMR.148-149.186 © 2011 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific. net. (Semanticscholar.org-17/03/20,15:31:35) thickness direction, negligibly small inertia force compared with viscous force because of the small gap near the grinding contact region. The flow field and the developed hydrodynamic pressure, or p (x, y), need to be determined as a function of the wheel speed, the minimum film thickness, and the physical properties of the fluid. The problem is investigated using a continuous equation and Navier-Stokes equations. The Navier-Stokes equations are simplified to the following equations using the above assumptions [4]: