The problem of chatter vibration is associated with adverse consequences that often lead to tool impairment and poor surface finished in a workpiece, and thus, controlling or suppressing chatter vibrations is of great...The problem of chatter vibration is associated with adverse consequences that often lead to tool impairment and poor surface finished in a workpiece, and thus, controlling or suppressing chatter vibrations is of great significance to improve machining quality. In this paper, a workpiece and an actuator dynamics are considered in modeling and controller design. A proportional-integral controller(PI) is presented to control and actively damp the chatter vibration of a workpiece in the milling process. The controller is chosen on the basis of its highly stable output and a smaller amount of steady-state error. The controller is realized using analog operational amplifier circuit. The work has contributed to planning a novel approach that addresses the problem of chatter vibration in spite of technical hitches in modeling and controller design. The method can also lead to considerable reduction in vibrations and can be beneficial in industries in term of cost reduction and energy saving. The application of this method is verified using active damping device actuator(ADD) in the milling of steel.展开更多
Milling the free-end of cylindrical parts, which are vertically fixed on the machine table,often suffers from large chatter vibrations. This kind of phenomenon is harmful to the cutting process. Therefore, it is of gr...Milling the free-end of cylindrical parts, which are vertically fixed on the machine table,often suffers from large chatter vibrations. This kind of phenomenon is harmful to the cutting process. Therefore, it is of great importance to develop means to suppress these undesirable chatters.This paper proposes a new idea for designing a tunable mass damper(TMD) to reduce vibrations in milling of cylindrical parts. Frequency response function(FRF) of the milling system is derived to comprehensively reveal the influence of both the dynamic response of the machine tools and the TMD. Critical axial depth of cut, which is usually used to characterize the process stability, is formulated by considering the FRFs of both the milling system itself and the TMD. Maximization of critical axial depth of cut is taken as objective function, while kernel dynamic parameters of TMD,which are involved in the derived expression of critical axial depth of cut, are extracted as designable variables. Optimization procedure is carried out to adjust the parameters of TMD by using sequential quadratic programming algorithm. A series of experiments with a designed passive TMD validate that the design has a good performance in reducing vibrations and improving stability of milling process.展开更多
Separation of C_(2) gases(C_(2)H_(2)/C_(2)H_(4),C_(2)H_(6)/C_(2)H_(4) and C_(2)H_(2)/CO_(2))mixtures is one of the most important and energy-demanding processes in chemical industry.Traditional separation methods(fine...Separation of C_(2) gases(C_(2)H_(2)/C_(2)H_(4),C_(2)H_(6)/C_(2)H_(4) and C_(2)H_(2)/CO_(2))mixtures is one of the most important and energy-demanding processes in chemical industry.Traditional separation methods(fine distillation separation and selective catalytic hydrogenation separation)have the shortages of high energy consumption and inefficient use of resources,affecting the achievement of peak carbon dioxide emissions and carbon neutrality targets.Separation based on adsorption is considered as one of the best ways to achieve low-energy separations.Therefore,it is of great importance to synthesize materials that enable the effective separation and purification of C_(2) gases under mild conditions.As an emerging class of porous materials,metal-organic frameworks(MOFs)show great promise in the field of gas separation and purification due to their ultra-high specific surface area,easily modifiable pore surfaces,structural designability and functionalization.Herein,we summarize recent research advances by use of MOFs sorbents for the separation and purification of C_(2) gases,including C_(2)H_(2)/C_(2)H_(4),C_(2)H_(6)/C_(2)H_(4) and C_(2)H_(2)/CO_(2).Relationship between structures and separation mechanism is also explored.Furthermore,challenges and possible research directions related to the further exploration are also discussed.展开更多
This paper focuses on optimization of the geo-metrical parameters of peripheral milling tools by takinginto account the dynamic effect. A substructure synthesistechnique is used to calculate the frequency responsefunc...This paper focuses on optimization of the geo-metrical parameters of peripheral milling tools by takinginto account the dynamic effect. A substructure synthesistechnique is used to calculate the frequency responsefunction of the tool point, which is adopted to determinethe stability lobe diagram. Based on the Taguchi designmethod, simulations are first conducted for varying com-binations of tool overhang length, helix angle, and teethnumber. The optimal geometrical parameters of the tool aredetermined through an orthogonal analysis of the maxi-mum axial depth of cut, which is obtained from the pre-dicted stability lobe diagram. It was found that thesequence of every factor used to determine the optimal toolgeometrical parameters was the tool overhang length, teethnumber, and helix angle. Finally, a series of experimentswere carried out as a parameter study to determine theinfluence of the tool overhang length, helix angle, and teethnumber on the cutting stability of a mill. The same con-clusion as that obtained through the simulation wasobserved.展开更多
This paper presents a high-efficiency technique based on dielectrophoresis (DEP) for assembling metal, semiconductor, and polymer nanorods, which are synthesized by electrochemical deposition (ECD). The assembly patte...This paper presents a high-efficiency technique based on dielectrophoresis (DEP) for assembling metal, semiconductor, and polymer nanorods, which are synthesized by electrochemical deposition (ECD). The assembly patterns of these nanorods (width: 20 nm; length: 7 μm) were designed using a finite element method (FEM) simulation tool. Further, these nanorods were used in our experiment after their assembly patterns were fabricated. The assembly yield was found to be approximately 70% at an AC voltage of 30 Vp-p and at frequencies of 20 and 30 kHz, and the DC voltage prevented the random alignment of the nanorods at the edge of the assembly pattern. Moreover, the above-mentioned nanorods, which had different permittivities, were found to have similar assembly yields. The proposed method can be improved and applied to nanostructure device fabrication.展开更多
基金supported by National Natural Science Foundation of China(Grant No.51675440)Fundamental Research Funds for the Central Universities of China(Grant no.3102018gxc025)
文摘The problem of chatter vibration is associated with adverse consequences that often lead to tool impairment and poor surface finished in a workpiece, and thus, controlling or suppressing chatter vibrations is of great significance to improve machining quality. In this paper, a workpiece and an actuator dynamics are considered in modeling and controller design. A proportional-integral controller(PI) is presented to control and actively damp the chatter vibration of a workpiece in the milling process. The controller is chosen on the basis of its highly stable output and a smaller amount of steady-state error. The controller is realized using analog operational amplifier circuit. The work has contributed to planning a novel approach that addresses the problem of chatter vibration in spite of technical hitches in modeling and controller design. The method can also lead to considerable reduction in vibrations and can be beneficial in industries in term of cost reduction and energy saving. The application of this method is verified using active damping device actuator(ADD) in the milling of steel.
基金supported by the National Natural Science Foundation of China(No.51675440 and 51705427)National Key Research and Development Program of China(No.2017YFB1102800)the Fundamental Research Funds for the Central Universities of China(No.3102018gxc025)
文摘Milling the free-end of cylindrical parts, which are vertically fixed on the machine table,often suffers from large chatter vibrations. This kind of phenomenon is harmful to the cutting process. Therefore, it is of great importance to develop means to suppress these undesirable chatters.This paper proposes a new idea for designing a tunable mass damper(TMD) to reduce vibrations in milling of cylindrical parts. Frequency response function(FRF) of the milling system is derived to comprehensively reveal the influence of both the dynamic response of the machine tools and the TMD. Critical axial depth of cut, which is usually used to characterize the process stability, is formulated by considering the FRFs of both the milling system itself and the TMD. Maximization of critical axial depth of cut is taken as objective function, while kernel dynamic parameters of TMD,which are involved in the derived expression of critical axial depth of cut, are extracted as designable variables. Optimization procedure is carried out to adjust the parameters of TMD by using sequential quadratic programming algorithm. A series of experiments with a designed passive TMD validate that the design has a good performance in reducing vibrations and improving stability of milling process.
基金The Postgraduate Innovative Research Projects of Tianjin。
文摘Separation of C_(2) gases(C_(2)H_(2)/C_(2)H_(4),C_(2)H_(6)/C_(2)H_(4) and C_(2)H_(2)/CO_(2))mixtures is one of the most important and energy-demanding processes in chemical industry.Traditional separation methods(fine distillation separation and selective catalytic hydrogenation separation)have the shortages of high energy consumption and inefficient use of resources,affecting the achievement of peak carbon dioxide emissions and carbon neutrality targets.Separation based on adsorption is considered as one of the best ways to achieve low-energy separations.Therefore,it is of great importance to synthesize materials that enable the effective separation and purification of C_(2) gases under mild conditions.As an emerging class of porous materials,metal-organic frameworks(MOFs)show great promise in the field of gas separation and purification due to their ultra-high specific surface area,easily modifiable pore surfaces,structural designability and functionalization.Herein,we summarize recent research advances by use of MOFs sorbents for the separation and purification of C_(2) gases,including C_(2)H_(2)/C_(2)H_(4),C_(2)H_(6)/C_(2)H_(4) and C_(2)H_(2)/CO_(2).Relationship between structures and separation mechanism is also explored.Furthermore,challenges and possible research directions related to the further exploration are also discussed.
文摘This paper focuses on optimization of the geo-metrical parameters of peripheral milling tools by takinginto account the dynamic effect. A substructure synthesistechnique is used to calculate the frequency responsefunction of the tool point, which is adopted to determinethe stability lobe diagram. Based on the Taguchi designmethod, simulations are first conducted for varying com-binations of tool overhang length, helix angle, and teethnumber. The optimal geometrical parameters of the tool aredetermined through an orthogonal analysis of the maxi-mum axial depth of cut, which is obtained from the pre-dicted stability lobe diagram. It was found that thesequence of every factor used to determine the optimal toolgeometrical parameters was the tool overhang length, teethnumber, and helix angle. Finally, a series of experimentswere carried out as a parameter study to determine theinfluence of the tool overhang length, helix angle, and teethnumber on the cutting stability of a mill. The same con-clusion as that obtained through the simulation wasobserved.
基金Project supported by the Basic Research Program of the Korea Science & Engineering Foundation (No. R0120060001027202006)the Basic Science Research Program through the National Research Foundation of Korea (No. 2010-0001882)
文摘This paper presents a high-efficiency technique based on dielectrophoresis (DEP) for assembling metal, semiconductor, and polymer nanorods, which are synthesized by electrochemical deposition (ECD). The assembly patterns of these nanorods (width: 20 nm; length: 7 μm) were designed using a finite element method (FEM) simulation tool. Further, these nanorods were used in our experiment after their assembly patterns were fabricated. The assembly yield was found to be approximately 70% at an AC voltage of 30 Vp-p and at frequencies of 20 and 30 kHz, and the DC voltage prevented the random alignment of the nanorods at the edge of the assembly pattern. Moreover, the above-mentioned nanorods, which had different permittivities, were found to have similar assembly yields. The proposed method can be improved and applied to nanostructure device fabrication.