Abstract
This paper describes simulation studies regarding the application of the centrifugal minimum quantity lubrication (MQL) method simultaneously with the delivery of a compressed cooled air (CCA) stream in the internal cylindrical grinding process. The idea of a new hybrid cooling and lubrication method connecting centrifugal (through a grinding wheel) lubrication by MQL with a CCA stream is described. The methodology of computational fluid dynamics (CFD) simulation studies, as well as the results of numerical simulations, are presented in detail. The aim of the simulations was to determine the most favourable geometrical and kinematic parameters of the system in the context of air-oil aerosol and CCA flow, as well as heat exchange. In the simulation, the variables were the grinding arbor geometrical parameters, the angle of CCA supply line outlets, and the grinding wheel and workpiece peripheral speed. As a result of the simulation studies, the most favourable geometrical parameters were designated, determining the orientation of the ends of the two CCA supply line outlets before and after the grinding zone, the number of openings in the drilled-out grinding arbor, and the influence of the grinding speed on the parameters of the coolant flow and temperature of objects in the grinding zone. In addition, the results of simulation tests made it possible to visualise the velocity vectors of the two-phase coolant flow in a complex system of air-oil aerosol delivery centrifugally through an open structure of a very fast rotating porous layer (grinding wheel), with an additional supply of CCA using an external cold air gun (CAG).
Highlights
Internal cylindrical grinding processes are among the most demanding types of grinding processes, mainly due to their kinematics [1,2]
The results obtained for 27 variants of the simulations carried out in accordance with the experimental plan made it possible to determine the mathematical models of the research object (MMRO) together with the values of the multidimensional correlation coefficient R, which is a measure of model adequacy assessment
The models developed describe the effect of change in the number of channels in the grinding arbor nchannels and change in the angle α of inclination of the CCA delivery line outlets on the flow velocity of compressed cooled air vCCA, air-oil aerosol flow velocity vMQL, maximum ΘGWAS max and minimum grinding wheel temperature ΘGWAS min and maximum Θw max and minimum workpiece temperature Θw min in the system under analysis
Summary
Internal cylindrical grinding processes are among the most demanding types of grinding processes, mainly due to their kinematics [1,2]. The mechanical energy entered into the grinding as a result of relative movement of the tool and the workpiece is largely converted into heat [1,2]. This leads to a significant increase in temperature in the grinding wheel/workpiece contact zone, caused by friction and deformation leading to chip. An increasing temperature in the grinding zone causes excessive wear of abrasive grains and bond This leads to plasticisation of the vertices of active abrasive grains. A rapidly changing temperature gradient in the abrasive tool may cause excessive thermal stress, resulting in a drastic decrease in the strength of the entire tool and its tearing
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