Lower surface roughness and sharper cutting edge are beneficial for improving the machining quality of the cut?ting tool, while coatings often deteriorate them. Focusing on the diamond coated WC?Co milling cutter, the...Lower surface roughness and sharper cutting edge are beneficial for improving the machining quality of the cut?ting tool, while coatings often deteriorate them. Focusing on the diamond coated WC?Co milling cutter, the abrasive flow machining(AFM) is selected for reducing the surface roughness and sharpening the cutting edge. Comparative cutting tests are conducted on di erent types of coated cutters before and after AFM, as well as uncoated WC?Co one, demonstrating that the boron?doped microcrystalline and undoped fine?grained composite diamond coated cutter after the AFM(AFM?BDM?UFGCD) is a good choice for the finish milling of the 6063 Al alloy in the present case, because it shows favorable machining quality close to the uncoated one, but much prolonged tool lifetime. Besides, compared with the micro?sized diamond films, it is much more convenient and e cient to finish the BDM?UFGCD coated cutter covered by nano?sized diamond grains, and resharpen its cutting edge by the AFM, owing to the lower initial surface roughness and hardness. Moreover, the boron incorporation and micro?sized grains in the underly?ing layer can enhance the film?substrate adhesion, avoid the rapid film removal in the machining process, and thus maximize the tool life(1040 m, four times more than the uncoated one). In general, the AFM is firstly proposed and discussed for post?processing the diamond coated complicated cutting tools, which is proved to be feasible for improving the cutting performance展开更多
An approach is presented to characterize the stress response of workpiece in hard machining, accounted for the effect of the initial workpiece hardness, temperature, strain and strain rate on flow stress. AISI H13 wor...An approach is presented to characterize the stress response of workpiece in hard machining, accounted for the effect of the initial workpiece hardness, temperature, strain and strain rate on flow stress. AISI H13 work tool steel was chosen to verify this methodology. The proposed flow stress model demonstrates a good agreement with data collected from published experiments. Therefore, the proposed model can be used to predict the corresponding flow stress-strain response of AISI H13 work tool steel with variation of the initial workpiece hardness in hard machining.展开更多
Bobbin tool friction stir welding(BT-FSW)is a variant of conventional friction stir welding(FSW).It can be used to weld complex curvature structures and closed sections by adding an extra shoulder instead of a rigid b...Bobbin tool friction stir welding(BT-FSW)is a variant of conventional friction stir welding(FSW).It can be used to weld complex curvature structures and closed sections by adding an extra shoulder instead of a rigid backing anvil,which expands the potential application of FSW in aerospace,railway,automotive and marine industries.BT-FSW has some signifi cant advantages over conventional FSW such as no root fl aws,full weld penetration,low stiff ness requirements for machines and fi xtures,balanced heat input,lower distortion and thus has broad prospects for development.At present,there have been numerous research reports on BT-FSW,but its widespread use is still restricted due to various factors such as tool life,process stability,control complexity and implementation cost.In this paper,the domestic and foreign research progress of BT-FSW is reviewed from four aspects of bobbin tool design and classifi cation,temperature fi eld and fl ow fi eld during welding,microstructure and mechanical properties of welded joints as well as industrial application,and then the possible research hotspots of BT-FSW in the future are pointed out.This paper mainly aims to help researchers have a comprehensive and in-depth understanding of BT-FSW.展开更多
A novel dual-rotation bobbin tool friction stir welding （DBT-FSW） was developed, in which the upper shoulder （US） and lower shoulder （LS） have different rotational speeds. This process was tried to weld 3.2 mm t...A novel dual-rotation bobbin tool friction stir welding （DBT-FSW） was developed, in which the upper shoulder （US） and lower shoulder （LS） have different rotational speeds. This process was tried to weld 3.2 mm thick alunlinum-lithium alloy sheets. The metallographic analysis and torque measurement were carried out to characterize the weld formabiliW. Experimental results show that compared to conven- tional bobbin tool friction stir welding, the DBT-FSW has an excellent process stability, and can produce the defect-free joints in a wider range of welding parameters. These can be attributed to the significant improvement of material flow caused by the formation of a staggered layer structure and the unbalanced force between the US and LS during the DBT-FSW process.展开更多
For friction stir welding （FSW）, a new idea is put forward in this paper to weld the thin plate of Al alloy by using the rotational tool without pin. The experiments of FSW are carried out by using the tools with in...For friction stir welding （FSW）, a new idea is put forward in this paper to weld the thin plate of Al alloy by using the rotational tool without pin. The experiments of FSW are carried out by using the tools with inner-concave-flute shoulder, concentric-circles-flute shoulder and three-spiral-flute shoulder, respectively. The experimental results show that the grain size in weld nugget zone attained by the tool with three-spiral-flute shoulder is nearly the same while the grain sizes decrease with the decrease of welding velocity. The displacement of material flow in the heat-mechanical affected zone by the tool with three-spiral-flute shoulder is much larger than that by the tool with inner-concave-flute shoulder or concentric-circles–flute shoulder. The above-mentioned results are verified by numerical simulation. For the tool with three-spiral-flute shoulder, the tensile strength of FSW joint increases with the decrease of welding velocity while the value of tensile strength attained by the welding velocity of 20 mm/min and the rotation speed of 1800 r/min is about 398 MPa, which is 80% more than that of parent mental tensile strength. Those verify that the tool with three-spiral-flute shoulder can be used to join the thin plate of Al alloy.展开更多
An analysis of the hydromagnetic free convective flow past a vertical infinite porous plate in a rotating fluid is carried out. The temperatures involved are assumed to be very large so that the radiative heat transfe...An analysis of the hydromagnetic free convective flow past a vertical infinite porous plate in a rotating fluid is carried out. The temperatures involved are assumed to be very large so that the radiative heat transfer is significant, which renders the problem very non-linear even on the assumption of a differential approximation for the radiative flux. The temperature and velocity fields are computed using a generic software tool based on the Nakamura finite difference scheme. The genericity of the software tool is in the sense that it is a common solution to the category of time dependent laminar fluid flows expressed in one spatial coordinate. The input equations, together with other relevant parameters, are transformed into postfix code which will be farther interpreted in the computation process. The influence of the various parameters entering into the problem is shown graphically followed by a discussion of results.展开更多
A simulation was carried out on an unsteady flow of a viscous, incompressible and electrically conducting fluid past an infinite vertical porous plate. A generic computer program using the Galerkin finite element meth...A simulation was carried out on an unsteady flow of a viscous, incompressible and electrically conducting fluid past an infinite vertical porous plate. A generic computer program using the Galerkin finite element method is employed to solve the coupled non-linear differential equations for velocity and temperature fields. The diffusion equation, the energy equation, the momentum equations and other relevant parameters are transformed into interpretable postfix codes. Numerical calculations are carried out on the flow fields both in the presence of cooling and heating of the plate by free convection currents. The effects of the dimensionless parameters, namely, the Prandtl number, the Eckert number, the modified Grashof number, the Schmidt number and the time on the temperature and velocity distributions are discussed.展开更多
为保证机床混流装配车间生产的机床准时交付,提出一种基于改进的深度多智能体强化学习的机床混流装配线调度优化方法,以解决最小延迟生产调度优化模型求解质量低、训练速度缓慢问题,构建以最小延迟时间目标的混流装配线调度优化模型,应...为保证机床混流装配车间生产的机床准时交付,提出一种基于改进的深度多智能体强化学习的机床混流装配线调度优化方法,以解决最小延迟生产调度优化模型求解质量低、训练速度缓慢问题,构建以最小延迟时间目标的混流装配线调度优化模型,应用去中心化分散执行的双重深度Q网络(double deep Q network,DDQN)的智能体来学习生产信息与调度目标的关系。该框架采用集中训练与分散执行的策略,并使用参数共享技术,能处理多智能体强化学习中的非稳态问题。在此基础上,采用递归神经网络来管理可变长度的状态和行动表示,使智能体具有处理任意规模问题的能力。同时引入全局/局部奖励函数,以解决训练过程中的奖励稀疏问题。通过消融实验,确定了最优的参数组合。数值实验结果表明,与标准测试方案相比,本算法在目标达成度方面,平均总延迟工件数较改善前提升了24.1%~32.3%,训练速度提高了8.3%。展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51275302)China Postdoctoral Science Foundation Special Funded Project(Grant No.2016T90370)China Postdoctoral Science Foundation(Grant No.2015M580327)
文摘Lower surface roughness and sharper cutting edge are beneficial for improving the machining quality of the cut?ting tool, while coatings often deteriorate them. Focusing on the diamond coated WC?Co milling cutter, the abrasive flow machining(AFM) is selected for reducing the surface roughness and sharpening the cutting edge. Comparative cutting tests are conducted on di erent types of coated cutters before and after AFM, as well as uncoated WC?Co one, demonstrating that the boron?doped microcrystalline and undoped fine?grained composite diamond coated cutter after the AFM(AFM?BDM?UFGCD) is a good choice for the finish milling of the 6063 Al alloy in the present case, because it shows favorable machining quality close to the uncoated one, but much prolonged tool lifetime. Besides, compared with the micro?sized diamond films, it is much more convenient and e cient to finish the BDM?UFGCD coated cutter covered by nano?sized diamond grains, and resharpen its cutting edge by the AFM, owing to the lower initial surface roughness and hardness. Moreover, the boron incorporation and micro?sized grains in the underly?ing layer can enhance the film?substrate adhesion, avoid the rapid film removal in the machining process, and thus maximize the tool life(1040 m, four times more than the uncoated one). In general, the AFM is firstly proposed and discussed for post?processing the diamond coated complicated cutting tools, which is proved to be feasible for improving the cutting performance
基金supported by the Jiangxi Provincial Natural Science Foundation of China(No.550067)Jiangxi Provincial Education Commission Foundation(No.2005-26).
文摘An approach is presented to characterize the stress response of workpiece in hard machining, accounted for the effect of the initial workpiece hardness, temperature, strain and strain rate on flow stress. AISI H13 work tool steel was chosen to verify this methodology. The proposed flow stress model demonstrates a good agreement with data collected from published experiments. Therefore, the proposed model can be used to predict the corresponding flow stress-strain response of AISI H13 work tool steel with variation of the initial workpiece hardness in hard machining.
文摘Bobbin tool friction stir welding(BT-FSW)is a variant of conventional friction stir welding(FSW).It can be used to weld complex curvature structures and closed sections by adding an extra shoulder instead of a rigid backing anvil,which expands the potential application of FSW in aerospace,railway,automotive and marine industries.BT-FSW has some signifi cant advantages over conventional FSW such as no root fl aws,full weld penetration,low stiff ness requirements for machines and fi xtures,balanced heat input,lower distortion and thus has broad prospects for development.At present,there have been numerous research reports on BT-FSW,but its widespread use is still restricted due to various factors such as tool life,process stability,control complexity and implementation cost.In this paper,the domestic and foreign research progress of BT-FSW is reviewed from four aspects of bobbin tool design and classifi cation,temperature fi eld and fl ow fi eld during welding,microstructure and mechanical properties of welded joints as well as industrial application,and then the possible research hotspots of BT-FSW in the future are pointed out.This paper mainly aims to help researchers have a comprehensive and in-depth understanding of BT-FSW.
基金support of the National Natural Science Foundation of China(No.51705027)the fund of the State Key Laboratory of Solidification Processing in NWPU(No.SKLSP201722)
文摘A novel dual-rotation bobbin tool friction stir welding （DBT-FSW） was developed, in which the upper shoulder （US） and lower shoulder （LS） have different rotational speeds. This process was tried to weld 3.2 mm thick alunlinum-lithium alloy sheets. The metallographic analysis and torque measurement were carried out to characterize the weld formabiliW. Experimental results show that compared to conven- tional bobbin tool friction stir welding, the DBT-FSW has an excellent process stability, and can produce the defect-free joints in a wider range of welding parameters. These can be attributed to the significant improvement of material flow caused by the formation of a staggered layer structure and the unbalanced force between the US and LS during the DBT-FSW process.
文摘For friction stir welding （FSW）, a new idea is put forward in this paper to weld the thin plate of Al alloy by using the rotational tool without pin. The experiments of FSW are carried out by using the tools with inner-concave-flute shoulder, concentric-circles-flute shoulder and three-spiral-flute shoulder, respectively. The experimental results show that the grain size in weld nugget zone attained by the tool with three-spiral-flute shoulder is nearly the same while the grain sizes decrease with the decrease of welding velocity. The displacement of material flow in the heat-mechanical affected zone by the tool with three-spiral-flute shoulder is much larger than that by the tool with inner-concave-flute shoulder or concentric-circles–flute shoulder. The above-mentioned results are verified by numerical simulation. For the tool with three-spiral-flute shoulder, the tensile strength of FSW joint increases with the decrease of welding velocity while the value of tensile strength attained by the welding velocity of 20 mm/min and the rotation speed of 1800 r/min is about 398 MPa, which is 80% more than that of parent mental tensile strength. Those verify that the tool with three-spiral-flute shoulder can be used to join the thin plate of Al alloy.
文摘An analysis of the hydromagnetic free convective flow past a vertical infinite porous plate in a rotating fluid is carried out. The temperatures involved are assumed to be very large so that the radiative heat transfer is significant, which renders the problem very non-linear even on the assumption of a differential approximation for the radiative flux. The temperature and velocity fields are computed using a generic software tool based on the Nakamura finite difference scheme. The genericity of the software tool is in the sense that it is a common solution to the category of time dependent laminar fluid flows expressed in one spatial coordinate. The input equations, together with other relevant parameters, are transformed into postfix code which will be farther interpreted in the computation process. The influence of the various parameters entering into the problem is shown graphically followed by a discussion of results.
文摘A simulation was carried out on an unsteady flow of a viscous, incompressible and electrically conducting fluid past an infinite vertical porous plate. A generic computer program using the Galerkin finite element method is employed to solve the coupled non-linear differential equations for velocity and temperature fields. The diffusion equation, the energy equation, the momentum equations and other relevant parameters are transformed into interpretable postfix codes. Numerical calculations are carried out on the flow fields both in the presence of cooling and heating of the plate by free convection currents. The effects of the dimensionless parameters, namely, the Prandtl number, the Eckert number, the modified Grashof number, the Schmidt number and the time on the temperature and velocity distributions are discussed.
文摘为保证机床混流装配车间生产的机床准时交付,提出一种基于改进的深度多智能体强化学习的机床混流装配线调度优化方法,以解决最小延迟生产调度优化模型求解质量低、训练速度缓慢问题,构建以最小延迟时间目标的混流装配线调度优化模型,应用去中心化分散执行的双重深度Q网络(double deep Q network,DDQN)的智能体来学习生产信息与调度目标的关系。该框架采用集中训练与分散执行的策略,并使用参数共享技术,能处理多智能体强化学习中的非稳态问题。在此基础上,采用递归神经网络来管理可变长度的状态和行动表示,使智能体具有处理任意规模问题的能力。同时引入全局/局部奖励函数,以解决训练过程中的奖励稀疏问题。通过消融实验,确定了最优的参数组合。数值实验结果表明,与标准测试方案相比,本算法在目标达成度方面,平均总延迟工件数较改善前提升了24.1%~32.3%,训练速度提高了8.3%。
