Study On Effective Supply Of Grinding Fluid And Convective Heat Transfer In Grinding Zone

Due to high specific grinding energy, the same material removal requires higher energy input in grinding compared to other processing. These energy is converted into grinding heat in the grinding arc area. If it is not cooled in time, a large amount of grinding heat flow enter into the workpiece, which will lead to thermal damage on the surface of the workpiece. In the industrial production, the pouring liquid feeding method which is used to supply a large amount of grinding fluid to the grinding arc zone is used to reduce the heat of entering the workpiece and reduce the heat damage. But the high speed rotation of the grinding wheel drives the surrounding air to form a gas barrier layer, which hinders the grinding fluid into the grinding arc area. Therefore, it is of great theoretical significance and application value to study the characteristics of the grinding gas barrier layer and the flow law of grinding fluid in the gas barrier layer, and to explore the effective supply conditions of the grinding fluid into the grinding arc area. The convective heat transfer of the grinding fluid in the grinding arc zone can reduce the heat of the grinding process and reduce the grinding temperature. Therefore, it is of great theoretical value to establish the model of convective heat transfer coefficient to predict the grinding temperature and to reduce the thermal damage of workpiece.The main work of this paper is as follows:A 3D numerical simulation model of grinding gas barrier layer is built. The velocity and pressure characteristics of the gas flow field in the grinding gas barrier layer are studied. It is found that the pressure of the gas flow field in the gas barrier layer is symmetrical about the plane of the grinding wheel, and the pressure is the largest in the middle plane of the grinding wheel. With the increase of grinding wheel line speed, grinding wheel width and surface roughness of grinding wheel, the pressure peak value increases. The air flow along with the grinding wheel rotation will flow to the two sides of the grinding wheel before reaching the grinding arc area. There is no obvious return flow phenomenon.Using pressure and velocity data from numerical simulation, according to the principle of fluid dynamics, fluid dynamics model of grinding fluid flow trajectory is established. The flow law of grinding fluid in the grinding gas barrier layer is studied. And the supply method is established when nozzle angle and nozzle position is fixed and the grinding fluid can break through the gas barrier layer into the grinding zone.Under sufficient grinding fluid into the grinding arc area, according to the basic theory of thermal transmission, in fixed grinding parameters and grinding fluid supply conditions, determined by the critical Reynolds number and the corresponding critical length, a calculation method of convection heat transfer coefficient is established. When the length of grinding arc length is less than the critical length, the convective heat transfer coefficient is calculated by the laminar boundary layer, and the convective heat transfer coefficient is calculated by the mixed boundary layer when the length of the grinding arc is longer than the critical length.Through the experiment of grinding alloy steel 40Cr with the ceramic bonded corundum grinding wheel, the jet velocity range of the grinding fluid was measured in a fixed nozzle position and angle condition. And the theoretical prediction of the grinding fluid jet velocity range is compared, and it is found that there is a good consistency. Through the experiment of grinding hard alloy YG6 with green silicon carbide grinding wheel, the grinding temperature and the grinding force under different grinding parameters were measured. The convective heat transfer coefficient is compared with the theoretical calculation, and the results are in good agreement with the experimental results.