The three-dimensional （3D） processing maps considering strain based on the two-dimensional （2D） processing maps proposed by PRASAD can describe the distribution of the efficiency of power dissipation and flow inst...The three-dimensional （3D） processing maps considering strain based on the two-dimensional （2D） processing maps proposed by PRASAD can describe the distribution of the efficiency of power dissipation and flow instability regions at various temperatures, strain rates and strains, which exhibit intrinsic workability related to material itself. Finite element （FE） simulation can obtain the distribution of strain, strain rate, temperature and die filling status, which indicates state-of-stress （SOS） workability decided by die shape and different processing conditions. On the basis of this, a new material driven analysis method for hot deformation was put forward by the combination of FE simulation with 3D processing maps, which can demonstrate material workability of the entire hot deformation process including SOS workability and intrinsic workability. The hot forging process for hard-to-work metal magnesium alloy was studied, and the 3D thermomechanical FE simulation including 3D processing maps of complex hot forging spur bevel gear was first conducted. The hot forging experiments were carried out. The results show that the new method is reasonable and suitable to determine the aoorooriate nrocess narameters.展开更多
The numerical control (NC) precision bending process of thin-walled tube is on e of advanced plastic forming processes with high efficiency, forming precision, strength/weight ratio and low cost, thus it is playing mo...The numerical control (NC) precision bending process of thin-walled tube is on e of advanced plastic forming processes with high efficiency, forming precision, strength/weight ratio and low cost, thus it is playing more and more important role in manufacturing parts in aerospace and automobile industries. However, the determination of parameters crucial to make sure tube parts qualified is heavil y experience-based and involves repeated trial-and-errors in practice, which makes the production efficiency reduce drastically and does not fulfill the deve lopment of high technology. With quick development of computer technology and gr adual perfect of plastic forming theory, computer numerical simulation based on finite element method (FEM) has become one of important tools of researching and developing plastic forming technology. Development trend of NC precision bendin g process of tube is simulating its forming process by FEM. Because NC tube bend ing is of 3D nature, it is of great importance to analyze the forming mechanism and find out the influence law of forming parameters on forming process in the N C precision bending process of thin-walled tube quantitatively by 3D FE simulat ion. Based on the rigid-plastic finite element method (FEM) principle, a 3-dimens ional (3D) rigid-plastic FE simulation system named TBS -3D (tube bending simu lation by 3D FEM) for the NC bending process of thin-walled tube has been devel oped, a reasonable FEM model has been established. By use of this FEM simulation system, a NC bending process of thin-walled has been simulated. And deformed m eshes under different bending stages, stress distribution along bending directio n, relationship between maximal wall thickness changing ratio and bending angle have been obtained. And then some forming laws of NC tube bending obtained are a s follows: (1) NC bending process make tube elongate to some extent; (2) Charact eristic of stress distribution is that the outer area is undergoing tensile stre ss, the inner area is undergoing compression stress, and stress neutral layer mo ves close to the inner area, which is in good accordance with the practice; (3) Maximal wall thinning ratio in the outer tensile area changes only a little with increase of bending angle, and maximal wall thickening ratio in the inner compr ession area increases linearly with bending angle. The above results show that 3 D FE simulation is an important and valid tool of analyzing NC bending process o f tube, this research is beneficial for the practical tube bending process, and it may serve as a significant guide to the practice of the relevant processes.展开更多
粘结剂喷射3D打印(binder jet 3D printing,BJ3DP)是一种无熔化、高效率、低成本的金属增材制造技术,近年来在复杂结构、大尺寸、高精度构件制造中展现出了巨大的应用潜力。相比激光熔化等工艺,BJ3DP具有材料适应性强、工艺温度低、无...粘结剂喷射3D打印(binder jet 3D printing,BJ3DP)是一种无熔化、高效率、低成本的金属增材制造技术,近年来在复杂结构、大尺寸、高精度构件制造中展现出了巨大的应用潜力。相比激光熔化等工艺,BJ3DP具有材料适应性强、工艺温度低、无残余应力等优势,适用于热敏性或易氧化金属材料。总结了金属BJ3DP打印构件的影响因素,包括粉末特性、打印参数、脱脂/烧结工艺等,重点介绍了铁基、镍基、镁基、铝基、高熵合金等合金在BJ3DP成形过程中的物相、微观组织与性能。最后,简要概述了目前存在的问题及未来的发展趋势。展开更多
Sand mold 3 D printing technology is an advanced manufacturing technology which has great flexible manufacturing ability. A multi-material composite sand mold can control the temperature field of metallic parts during...Sand mold 3 D printing technology is an advanced manufacturing technology which has great flexible manufacturing ability. A multi-material composite sand mold can control the temperature field of metallic parts during the pouring process, while the current sand mold 3 D printing technology can only fabricate a single material sand mold. The casting temperature field can not be adjusted by using single sand mold material with isotropous heat exchange ability during the pouring process. In this work, a kind of novel coating device was designed. Multi-material composite sand molds could be manufactured using the coating device according to the casting process demands of the final parts. The influences of curing agent content, coating velocity and scraper shape on compactness and surface roughness of the sand layer(silica sand and zircon sand) were studied. The shapes and sizes of transition intervals of two kinds of sand granules were also tested. The results show that, with the increase of the added volume of curing agent, the compactness of sand layer reduces and the surface roughness value rises. With the increase of the velocity of the coating device, the compactness of sand layer reduces and the surface roughness value rises similarly. In addition, the scraper with a dip angle of 72 degrees could increase the compactness value of the sand layer. The criteria of quality parmeters of the coating procedure are obtained. That is, the surface roughness(δ) of sand layer should be equal to or lesser than half of main size of the sand particles(Dm). The parameter H of the coating device which is the distance between the base of hopper and the surface of sand layer impacts the size of transition zone. The width of the transition zone is in direct proportion to the parameter H, qualitatively. Through the optimization of the coating device, high quality of multi-material sand layers can be obtained. This will provide a solution in manufacturing the multi-material composite sand mold.展开更多
基金Project(2011ZX04014-051)supported by the Key Scientific and Technical Project of ChinaProjects(51375306,50905110)supported by the National Natural Science Foundation of China
文摘The three-dimensional （3D） processing maps considering strain based on the two-dimensional （2D） processing maps proposed by PRASAD can describe the distribution of the efficiency of power dissipation and flow instability regions at various temperatures, strain rates and strains, which exhibit intrinsic workability related to material itself. Finite element （FE） simulation can obtain the distribution of strain, strain rate, temperature and die filling status, which indicates state-of-stress （SOS） workability decided by die shape and different processing conditions. On the basis of this, a new material driven analysis method for hot deformation was put forward by the combination of FE simulation with 3D processing maps, which can demonstrate material workability of the entire hot deformation process including SOS workability and intrinsic workability. The hot forging process for hard-to-work metal magnesium alloy was studied, and the 3D thermomechanical FE simulation including 3D processing maps of complex hot forging spur bevel gear was first conducted. The hot forging experiments were carried out. The results show that the new method is reasonable and suitable to determine the aoorooriate nrocess narameters.
文摘The numerical control (NC) precision bending process of thin-walled tube is on e of advanced plastic forming processes with high efficiency, forming precision, strength/weight ratio and low cost, thus it is playing more and more important role in manufacturing parts in aerospace and automobile industries. However, the determination of parameters crucial to make sure tube parts qualified is heavil y experience-based and involves repeated trial-and-errors in practice, which makes the production efficiency reduce drastically and does not fulfill the deve lopment of high technology. With quick development of computer technology and gr adual perfect of plastic forming theory, computer numerical simulation based on finite element method (FEM) has become one of important tools of researching and developing plastic forming technology. Development trend of NC precision bendin g process of tube is simulating its forming process by FEM. Because NC tube bend ing is of 3D nature, it is of great importance to analyze the forming mechanism and find out the influence law of forming parameters on forming process in the N C precision bending process of thin-walled tube quantitatively by 3D FE simulat ion. Based on the rigid-plastic finite element method (FEM) principle, a 3-dimens ional (3D) rigid-plastic FE simulation system named TBS -3D (tube bending simu lation by 3D FEM) for the NC bending process of thin-walled tube has been devel oped, a reasonable FEM model has been established. By use of this FEM simulation system, a NC bending process of thin-walled has been simulated. And deformed m eshes under different bending stages, stress distribution along bending directio n, relationship between maximal wall thickness changing ratio and bending angle have been obtained. And then some forming laws of NC tube bending obtained are a s follows: (1) NC bending process make tube elongate to some extent; (2) Charact eristic of stress distribution is that the outer area is undergoing tensile stre ss, the inner area is undergoing compression stress, and stress neutral layer mo ves close to the inner area, which is in good accordance with the practice; (3) Maximal wall thinning ratio in the outer tensile area changes only a little with increase of bending angle, and maximal wall thickening ratio in the inner compr ession area increases linearly with bending angle. The above results show that 3 D FE simulation is an important and valid tool of analyzing NC bending process o f tube, this research is beneficial for the practical tube bending process, and it may serve as a significant guide to the practice of the relevant processes.
文摘粘结剂喷射3D打印(binder jet 3D printing,BJ3DP)是一种无熔化、高效率、低成本的金属增材制造技术,近年来在复杂结构、大尺寸、高精度构件制造中展现出了巨大的应用潜力。相比激光熔化等工艺,BJ3DP具有材料适应性强、工艺温度低、无残余应力等优势,适用于热敏性或易氧化金属材料。总结了金属BJ3DP打印构件的影响因素,包括粉末特性、打印参数、脱脂/烧结工艺等,重点介绍了铁基、镍基、镁基、铝基、高熵合金等合金在BJ3DP成形过程中的物相、微观组织与性能。最后,简要概述了目前存在的问题及未来的发展趋势。
基金financially supported by the National Excellent Young Scientists Fund(NO.51525503)
文摘Sand mold 3 D printing technology is an advanced manufacturing technology which has great flexible manufacturing ability. A multi-material composite sand mold can control the temperature field of metallic parts during the pouring process, while the current sand mold 3 D printing technology can only fabricate a single material sand mold. The casting temperature field can not be adjusted by using single sand mold material with isotropous heat exchange ability during the pouring process. In this work, a kind of novel coating device was designed. Multi-material composite sand molds could be manufactured using the coating device according to the casting process demands of the final parts. The influences of curing agent content, coating velocity and scraper shape on compactness and surface roughness of the sand layer(silica sand and zircon sand) were studied. The shapes and sizes of transition intervals of two kinds of sand granules were also tested. The results show that, with the increase of the added volume of curing agent, the compactness of sand layer reduces and the surface roughness value rises. With the increase of the velocity of the coating device, the compactness of sand layer reduces and the surface roughness value rises similarly. In addition, the scraper with a dip angle of 72 degrees could increase the compactness value of the sand layer. The criteria of quality parmeters of the coating procedure are obtained. That is, the surface roughness(δ) of sand layer should be equal to or lesser than half of main size of the sand particles(Dm). The parameter H of the coating device which is the distance between the base of hopper and the surface of sand layer impacts the size of transition zone. The width of the transition zone is in direct proportion to the parameter H, qualitatively. Through the optimization of the coating device, high quality of multi-material sand layers can be obtained. This will provide a solution in manufacturing the multi-material composite sand mold.
