【作者】 郑钧宜；

【导师】 江征风；

【作者基本信息】 武汉理工大学 ， 机械制造及其自动化， 2008， 博士

【摘要】 磨削液动压力是指磨削液流过旋转砂轮与工件表面之间的楔形空间时,在收敛的楔形域内形成的压力。该动压力的大小,一方面可以反映出磨削液供给是否充足;另一方面,表征作用于砂轮上的法向作用力大小。这两个方面都是磨削过程中重点关注的地方。因此,掌握磨削液动压力在楔形空间的变化规律具有重要意义。本文在对目前国内外有关磨削液动压力的研究现状及发展进行综述的基础上,指出了现存方法在流体力学理论的应用、数学模型的建立及建模假设三个方面所存在的局限性。围绕所存在的问题,本文在理论和实验两个方面进行了系统的研究。理论上,首先,根据磨削过程喷嘴供液的特点,采用气液两相流理论对该流动特性进行理论研究。然后,将VOF方法引入到磨削液动压力的数学模型中,建立了描述磨削液射入旋转砂轮周边空气流场时,所形成的磨削气液两相流的瞬态模型。最后,在不施加特殊的出口压力边界条件下,求解瞬态模型。实验上,自行设计了磨削射流系统,并在MM7125平面磨床上,采用三种不同型号喷嘴供液,进行了磨削射流冷却的实验研究。实验的目的有三个:一是通过实验验证本文所采用的流体力学理论、建立的气液两相流瞬态模型以及对出口压力边界条件的处理三个方面的合理性。二是通过实验获得磨削气液两相流的动压力与喷嘴射流速度之间的关系。三是获取各种实验条件下磨削气液两相流动压力的实验数据,为建立基于人工神经网络的磨削射流冷却预测模型提供训练样本和测试样本。在上述研究工作的基础上,提出以磨削气液两相流的最大动压力与磨削液供给充分时磨削液单相流的最大动压力之比作为评价指标,用于衡量磨削射流冷却的效果。建立了基于人工神经网络的磨削射流冷却预测模型。为了求取评价指标中使用的磨削液单相流的最大动压力,本文对磨削液单相流进行了理论研究。分别建立了磨削液单相层流数学模型和磨削液单相湍流数学模型。通过施加特殊的出口压力边界条件,求解数学模型获得了磨削液单相流的动压力变化规律及动压力的最大值。在确定喷嘴射流速度的临界值时,需要以空气的最大压力作为参考值。为此,本文建立了描述磨削空气流场特性的数学模型。仿真求解获得了磨削空气流场压力的变化规律及空气流场压力的最大值。本文理论模型的仿真结果与实验测试结果吻和得较好。这充分说明:将气液两相流理论用于磨削流场动压力的理论研究,方法是正确的。利用本文所建立的气液两相流瞬态模型模拟磨削流场特性时,获得以下结论:(1)磨削液在离开磨削区进入空闲区时,是贴着砂轮圆周面,而不是贴着工件的表面。(2)磨削区内的磨削液是贴着工件的表面而不是贴着砂轮的圆周面,这有利于对流换热。(3)当喷嘴射流速度达到一定值时,再继续提高射流速度对改善冷却效果无益。(4)MM7125平面磨床的原冷却系统在高速工作时冷却效果不佳,需要进行改进。(5)基于人工神经网络的磨削射流冷却预测模型不仅可用于磨削加工过程中在线监测而且还可用于冷却液供给方式的优化研究。总之,本文所进行的工作对未来智能磨削的应用和发展具有一定的指导意义。更多还原

【Abstract】 Hydrodynamic pressure of coolant is generated in the converged area while coolant flows into the zone between grinding wheel and workpiece. This hydrodynamic pressure, on the one hand, indicates whether the coolant supplied is sufficient. On the other hand, it illustrates how much the normal force exerted on the grinding wheel is. More active researches have been made in these two respects recently. Therefore, it is of great importance to catch on the distribution of hydrodynamic pressure within jet zone and grinding zone.However, through the analysis of the status quo about coolant hydrodynamic pressure, this paper finds out some limitations to the study of coolant hydrodynamic pressure in existence in such three aspects as theory of fluid dynamics adopted, mathematical models constructed and assumptive conditions given. Considering these problems, this paper makes theoretical studies and experimental researches on coolant hydrodynamic pressure of grinding, systematically.In theory, gas-liquid two-phase flow is selected to explore the distribution of coolant hydrodynamic pressure. And then, the method of VOF is inducted into the mathematical model to build up an instantaneous model describing properties of gas-liquid two-phase flow field, which emerges in due course of coolant jetting into gas flow field. Finally, the instantaneous model is solved out in the case of no special pressure conditions exerted on the outlet boundary.In experiment, the system of grinding jet for cooling is designed, and three kinds of nozzles are employed to supply coolant in surface grinder of MM7125. Three purposes of this experiment are: (1) To verify the effectiveness of this instantaneous model of gas-liquid two-phase flow. (2) To explore the relationship between hydrodynamic pressure of gas-liquid two-phase flow and jet velocity of nozzles. (3) To collect experimental results to be used as training samples and test samples for the predictive model of grinding jet for cooling.On the basis of the above studies, one evaluation index of cooling effect is advanced, which is a ratio of the maximum hydrodynamic pressure of gas-liquid two-phase flow to the maximum hydrodynamic pressure of liquid one-phase flow. Moreover, the predictive model of grinding jet for cooling based on ANN is constructed.To calculate the maximum hydrodynamic pressure of liquid one-phase flow, this paper carries out a research for the properties of liquid one-phase flow field. With the result that mathematical model for laminar flow and mathematical model for turbulent flow are built, respectively. Accordingly, the hydrodynamic pressure distribution of liquid one-phase flow and maximum hydrodynamic pressure are obtained.The maximum pressure of gas one-phase flow will be used for reference to fix the critical jet velocity of nozzles. For this reason, mathematical model describing properties of gas one-phase flow is built and solved with gas pressure distribution and maximum pressure gained.It is feasible and effective to employ gas-liquid two-phase flow in the study of hydrodynamic pressure of grinding fluid field in that results of experiments agree by and large with numerical results of calculations.From the foregoing the following conclusions can be drown: (1) Coolant exiting the grinding zone is attached to the surface of grinding wheel, not to the surface of workpiece. (2) Coolant entered into the grinding zone is attached to the workpiece surface, not to the surface of grinding wheel, facilitating to convection heat transfer. (3) It will make no sense to increase jet velocity of nozzles when the velocity comes to a certain value. (4) The original cooling system of MM7125 surface grinder with grinding wheel rotating at the speed of 44m/s is to be modified due to poor cooling effect. (5) The predictive model of grinding jet for cooling based on ANN can be applied both in the test on line during grinding and in navigating coolant delivery for optimization.To sum up, all of the researches in this paper will go a good way with application and development of intelligent grinding in the near future.更多还原