In this study, liquid nitrogen was applied to grind SiCp/Al composites with high volume fraction and large SiC particle at different levels of cutting conditions, and the effects of grinding depth and speed on grindin...In this study, liquid nitrogen was applied to grind SiCp/Al composites with high volume fraction and large SiC particle at different levels of cutting conditions, and the effects of grinding depth and speed on grinding force, surface morphology, and surface roughness were investigated. At the same time, the effect of cryogenic cooling was also compared with that of conventional wet grinding. The experimental results indicated that cryogenic cooling is effective in enhancing supporting function of Al matrix to the SiC particles and improving surface quality. Additionally, the brittle fracture of SiC particles was suppressed and some ductile streaks on SiC particle could be observed.展开更多
A honeycomb structure is widely used in sandwich structure components in aeronautics and astronautics;however,machining is required to reveal some of its features.In honeycomb structures,deficiencies,such as burrs,edg...A honeycomb structure is widely used in sandwich structure components in aeronautics and astronautics;however,machining is required to reveal some of its features.In honeycomb structures,deficiencies,such as burrs,edge subsiding,and cracking,can easily appear,owing to poor specific sti ness in the radial direction.Some e ective fixation methods based on a filling principle have been applied by researchers,including approaches based on wax,polyethylene glycol,iron powder,and(especially)ice.However,few studies have addressed the optimization of the cutting parameters.This study focused on optimizing the cutting parameters to obtain a better surface roughness(calculated as a roughness average or Ra)and surface morphology in the machining of an aluminum alloy honeycomb by an ice fixation method.A Taguchi method and an analysis of variance were used to analyze the e ects and contributions of spindle speed,cutting depth,and feed rate.The optimal cutting parameters were determined using the signal-to-noise ratio combined with the surface morphology.An F-value and P-value were calculated for the value of the Ra,according to a"smaller is better"model.Additionally,the optimum cutting parameters for machining the aluminum honeycomb by ice fixation were found at different levels.The results of this study showed that the optimal parameters were a feed rate of 50 mm/min,cutting depth of 1.2 mm,and spindle speed of 4000 r/min.Feed rate was the most significant factor for minimizing Ra and improving the surface morphology,followed by spindle speed.The cutting depth had little e ect on Ra and surface morphology.After optimization,the value of Ra could reach 0.218μm,and no surface morphology deterioration was observed in the verified experiment.Thus,this research proposes optimal parameters based on ice fixation for improving the surface quality.展开更多
One of the crucial factors affecting the carrying capacity of the cryogenic liquid launch vehicle is the effective volume of the tank.Theoretical and experimental investigations on vortex breaker mechanisms have propo...One of the crucial factors affecting the carrying capacity of the cryogenic liquid launch vehicle is the effective volume of the tank.Theoretical and experimental investigations on vortex breaker mechanisms have proposed promising schemes applied in the oxygen tank of the liquid-propellant launch vehicle to ensure the normal operation of the engine.In this paper,the liquid surface profile functions of the laminar core when the vortex generates were derived based on the Rankine vortex model.The dimensionless residual volume V/d3 and the Froude number were applied to compare the theoretical prediction of critical height with the actual simulation data of liquid oxygen.This comparison method can improve the model’s accuracy.The efficiency of different basic shapes of vortex breakers was tested by conducting CFD modelling on a non-vertical outflow tank under a specific operating condition.Simulation results suggest negligible effects of heat transfer and surface tension.A circular plate is considered the optimal vortex breaker shape in traditional vertical outflow tanks,while a higher optimize efficiency was discovered in the half baffle basic shape in a non-vertical outflow tank by comparing the dimensionless residual volume and flow coefficient.A 34.26%reduction in flow resistance of half baffle breaker can be reached when applying a twenty-degree outlet pipe chamfering setting compared to a zero-degree chamfer.Considering practical operating limitations,it is concluded that a vortex breaker mechanism in a half baffle basic shape with a radius of 2.5d and a height of 4/d is the optimal scheme,which is suitable for all types of tanks.Its optimization efficiency of the residual volume reduction is about 56.68%compared to a nobreaker installation case.Lastly,a general equation based on CFD simulation for predicting the residual volume under a certain outflow velocity was proposed:V=d3yaFr0:3,which trend is consistent with that of mathematical prediction V=d3yaFr1=3.This consistency proves the accuracy and applicabil展开更多
基金financially supported by the National Natural Science Foundation of China (No.50975184)
文摘In this study, liquid nitrogen was applied to grind SiCp/Al composites with high volume fraction and large SiC particle at different levels of cutting conditions, and the effects of grinding depth and speed on grinding force, surface morphology, and surface roughness were investigated. At the same time, the effect of cryogenic cooling was also compared with that of conventional wet grinding. The experimental results indicated that cryogenic cooling is effective in enhancing supporting function of Al matrix to the SiC particles and improving surface quality. Additionally, the brittle fracture of SiC particles was suppressed and some ductile streaks on SiC particle could be observed.
基金Supported by National Key Research and Development Program of China(Grant No.2019YFB2005400)National Natural Science Foundation of China(Grant No.U1608251)+1 种基金Open project of State Key Laboratory of high performance complex manufacturing(Grant No.Kfkt2016-05)Changjiang Scholar Program of Chinese Ministry of Education(Grant No.T2017030).
文摘A honeycomb structure is widely used in sandwich structure components in aeronautics and astronautics;however,machining is required to reveal some of its features.In honeycomb structures,deficiencies,such as burrs,edge subsiding,and cracking,can easily appear,owing to poor specific sti ness in the radial direction.Some e ective fixation methods based on a filling principle have been applied by researchers,including approaches based on wax,polyethylene glycol,iron powder,and(especially)ice.However,few studies have addressed the optimization of the cutting parameters.This study focused on optimizing the cutting parameters to obtain a better surface roughness(calculated as a roughness average or Ra)and surface morphology in the machining of an aluminum alloy honeycomb by an ice fixation method.A Taguchi method and an analysis of variance were used to analyze the e ects and contributions of spindle speed,cutting depth,and feed rate.The optimal cutting parameters were determined using the signal-to-noise ratio combined with the surface morphology.An F-value and P-value were calculated for the value of the Ra,according to a"smaller is better"model.Additionally,the optimum cutting parameters for machining the aluminum honeycomb by ice fixation were found at different levels.The results of this study showed that the optimal parameters were a feed rate of 50 mm/min,cutting depth of 1.2 mm,and spindle speed of 4000 r/min.Feed rate was the most significant factor for minimizing Ra and improving the surface morphology,followed by spindle speed.The cutting depth had little e ect on Ra and surface morphology.After optimization,the value of Ra could reach 0.218μm,and no surface morphology deterioration was observed in the verified experiment.Thus,this research proposes optimal parameters based on ice fixation for improving the surface quality.
文摘One of the crucial factors affecting the carrying capacity of the cryogenic liquid launch vehicle is the effective volume of the tank.Theoretical and experimental investigations on vortex breaker mechanisms have proposed promising schemes applied in the oxygen tank of the liquid-propellant launch vehicle to ensure the normal operation of the engine.In this paper,the liquid surface profile functions of the laminar core when the vortex generates were derived based on the Rankine vortex model.The dimensionless residual volume V/d3 and the Froude number were applied to compare the theoretical prediction of critical height with the actual simulation data of liquid oxygen.This comparison method can improve the model’s accuracy.The efficiency of different basic shapes of vortex breakers was tested by conducting CFD modelling on a non-vertical outflow tank under a specific operating condition.Simulation results suggest negligible effects of heat transfer and surface tension.A circular plate is considered the optimal vortex breaker shape in traditional vertical outflow tanks,while a higher optimize efficiency was discovered in the half baffle basic shape in a non-vertical outflow tank by comparing the dimensionless residual volume and flow coefficient.A 34.26%reduction in flow resistance of half baffle breaker can be reached when applying a twenty-degree outlet pipe chamfering setting compared to a zero-degree chamfer.Considering practical operating limitations,it is concluded that a vortex breaker mechanism in a half baffle basic shape with a radius of 2.5d and a height of 4/d is the optimal scheme,which is suitable for all types of tanks.Its optimization efficiency of the residual volume reduction is about 56.68%compared to a nobreaker installation case.Lastly,a general equation based on CFD simulation for predicting the residual volume under a certain outflow velocity was proposed:V=d3yaFr0:3,which trend is consistent with that of mathematical prediction V=d3yaFr1=3.This consistency proves the accuracy and applicabil
