Darcy’s law is widely used to describe the flow in porous media in which there is a linear relationship between fluid velocity and pressure gradient. However, it has been found that for high numbers of Reynolds this ...Darcy’s law is widely used to describe the flow in porous media in which there is a linear relationship between fluid velocity and pressure gradient. However, it has been found that for high numbers of Reynolds this law ceases to be valid. In this work, the Ergun equation is employed to consider the non-linearity of air velocity with the pressure gradient in casting sands. The contribution of non-linearity to the total flow in terms of a variable defined as a non-Darcy flow fraction is numerically quantified. In addition, the influence of the shape factor of the sand grains on the non-linear flow fraction is analyzed. It is found that for values of the Reynolds number less or equal than 1, the contribution of non-linearity for spherical particles is around 1.15%.展开更多
The flexible extrusion forming process (FEFP) is a sand mold patternless manufacturing technology that enables digital near-net shaping of complex sand molds. But, it is difficult to achieve the gradient sand molds wi...The flexible extrusion forming process (FEFP) is a sand mold patternless manufacturing technology that enables digital near-net shaping of complex sand molds. But, it is difficult to achieve the gradient sand molds with high surface strength and strong interior permeability by FEFP. To solve this problem, an extra-squeeze forming method based on FEFP for gradient sand mold was developed. To further reveal the extra-squeeze forming mechanism, based on the Johnson-Kendall-Roberts (JKR) theory and “gluing” notions, the single and double-sided squeeze models of gradient sand molds were established using the EDEM software. The squeezing processes of sand molds with different cavity depths of 60, 100, 140, 180, and 220 mm were systemically studied under single and double-sided squeeze conditions. The variation in the void fraction of sand mold as also investigated at a variety of extra-squeeze distances of 2, 3, 4, 5, and 6 mm, respectively. Simulation and test results show that a deeper cavity depth weakens the extrusion force transmission, which leads to a decrease in strength. The sand mold permeability and void fraction are identified to be positively correlated, while the tensile strength and void fraction appear to be negatively correlated. The void fraction of sand molds decreases with a longer extra-squeeze distance. A 6 mm extra-squeeze distance for the sand mold with 220 mm cavity depth results in a 26.8% increase in tensile strength with only a 5.7% reduction in the permeability. Hence, the extra- squeeze forming method can improve the quality of the sand mold by producing a gradient sand mold with high surface strength and strong interior permeability.展开更多
A new intelligent tester system for measuring multiple mechanical properties of foundry molding sand is introduced and has been patented for the invention in China. The testing process can be simultaneously controlled...A new intelligent tester system for measuring multiple mechanical properties of foundry molding sand is introduced and has been patented for the invention in China. The testing process can be simultaneously controlled with a build-in chip microcomputer communicating with a PC through a serial port. The testing system applies dynamic testing technology. During the measurement for compression, relaxation, shearing and tensile processes of sand specimens, the corresponding characteristic curves and eight mechanical property parameters can be obtained in a short time, simply by consecutively testing on four sand specimens. The properties and parameters to be measurable by the tester include compressive strength, elastic modulus, plastic deformation threshold, springback potential, shear strength, shear deformation limit, toughness and tensile strength. These properties and parameters for sand specimens can be defined as the corresponding characteristic curves with precise physical meanings, carried out by the tester, Two of them, namely plastic deformation threshold and springback potential, as well as their testing methods, have been invented for the first time. The testing system applying advanced data measurement technology as well as performing excellent functions is an important breakthrough and creativity in foundry molding sand property testing field. The parameters acquired by the testing system are stable, accurate and reliable. The test data can be instantly displayed or printed out or stored in the PC. As evidence, many experimental data obtained by the tester practically from both laboratory and foundry floor tests indicate that the tester system can be widely applied in foundry industry.展开更多
Applying the air impact molding method to mold the complicated pattern with wider opening surface and deeper concave, there always exist vaulted phenomenon and lower compactibility of sand mold over the entrance and t...Applying the air impact molding method to mold the complicated pattern with wider opening surface and deeper concave, there always exist vaulted phenomenon and lower compactibility of sand mold over the entrance and the concave regions. Using the air-stream and synchro-formed clamp plate impact molding, however, this problem will be preferably solved. In this paper, the compact mechanism of the new molding method and the effect of some configuration factors, such as the area flowed by compressed air and the highness of the protruding block displacement around the diffluent clamp plate, on the compactibility of sand mold were discussed.展开更多
The insulation effect of the air cavity surrounding the riser in a 3D printed sand mold was studied. The influence of the air cavity on heat flux was theoretically analyzed. The results demonstrated that the heat flux...The insulation effect of the air cavity surrounding the riser in a 3D printed sand mold was studied. The influence of the air cavity on heat flux was theoretically analyzed. The results demonstrated that the heat flux of the air cavity in the 3D printed sand mold was significantly less than that of resin-bonded sand. The insulation effect of the air cavity in sand molds for a cylinder casting and a stress-frame casting were simulated using software COMSOL. The results illustrated that the air cavity could be used to insulate the riser and it was more suitable for a lower melting point metal casting. An air cavity with 10-15 mm width and 5-10 mm away from the riser can significantly prolong the solidification of the riser by over 10%. Meanwhile, the sand mold for the stressframe was made by 3D printing technology and poured with aluminum alloy A356 melt. The experiment results showed that the presence of the air cavity led to a 12.5% increase of the solidification time of its riser.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
The cooling control of the melt during the casting process is of great significance. A comprehensive closed-loop cooling control of castings by adopting a skeletal sand mold design was proposed. The skeletal sand mold...The cooling control of the melt during the casting process is of great significance. A comprehensive closed-loop cooling control of castings by adopting a skeletal sand mold design was proposed. The skeletal sand mold consisting of an adaptive shell, functional cavities and a support was designed and created based on the finite difference meshes of a casting. It was applied to a round wall test casting. Two kinds of skeletal sand molds, one with lattice support and the other with enforcing ribs for this casting were designed and printed out by the 3 D printing(3 DP) method. Aluminum alloy A356 was cast by using these two sand molds. The first mold was cooled by natural convection, the other one by water spray cooling. Two sound castings were obtained. The sand mold temperature, cooling curves, microstructures, mechanical properties, residual stress and deformation were measured, compared and discussed. Water spray cooling hastened the cooling rate by 62%, increased the content of Mg and Cu in the α-Al matrix, improved the mechanical properties, and altered the surface residual stress state.展开更多
The solidification behavior of AISI DC 53 cold work tool steel was investigated by means of a cooling curve and its first derivative. Copper and sand wedge-shaped molds were used to obtain various solidification rates...The solidification behavior of AISI DC 53 cold work tool steel was investigated by means of a cooling curve and its first derivative. Copper and sand wedge-shaped molds were used to obtain various solidification rates. To reveal the cooling rate degree during solidification,the secondary dendrite arm spacing of the steel alloy was examined by scanning electron microscopy(SEM). The solidification rates of each section for both wedge steel samples were calculated by means of the secondary dendrite arm spacing using a research-based empirical relation from the literature. Experiment results revealed that at the tip region of the cast specimen in the copper wedgeshaped mold,the carbide size was 7–8 μm,where the solidification rate was approximately 4,830 °C·s-1. The greatest carbide size obtained in the upper region of the sand cast wedge-shaped specimen was 250–270 μm.展开更多
Solidif ication and f luid f low analysis using computer simulation is a current common practice. There is also a high demand for thermal stress analysis in the casting process because casting engineers want to contro...Solidif ication and f luid f low analysis using computer simulation is a current common practice. There is also a high demand for thermal stress analysis in the casting process because casting engineers want to control the defects related to thermal stresses, such as large deformation and crack generation during casting. The riser system is an essential part of preventing the shrinkage defects in the casting process, and it has a great inf luence on thermal phenomena. The analysis domain is dramatically expanded by attaching the riser system to a casting product due to its large volume, and it makes FEM mesh generation diff icult. However, it is diff icult to study and solve the above proposed problem caused by riser system using traditional analysis methods which use single numerical method such as FEM or FDM. In this paper, some research information is presented on the effects of the riser system on thermal stress analysis using a FDM/FEM hybrid method in the casting process simulation. The results show the optimal conditions for stress analysis of the riser model in order to save computation time and memory resources.展开更多
Casting defects that are closely related to entrapped air bubbles and metallic oxides occur very frequently in the sand mold casting process. Many researchers have shown that these defects can be reduced by adopting a...Casting defects that are closely related to entrapped air bubbles and metallic oxides occur very frequently in the sand mold casting process. Many researchers have shown that these defects can be reduced by adopting an appropriate gating system design. However, it is difficult for field engineers to identify a specific gating system that is more appropriate for their products. In this study, we tried to draw a comparison between two gating system designs with and without a ceramic foam filter. The ceramic foam filter was added to the horizontal runner just after the down sprue to prevent air bubble generation and reduce turbulence without a change of gating system design. The water modeling experiment was conducted with four different amounts of the initial volumes of water in the reservoir to verify the effects of initial pouring velocity. The results of the experiment applying the filter showed remarkably changed flow characteristics. The use of the filter was found to convert the flow pattern of water in the desired direction. The ceramic foam filter performed well to reduce flow velocity and stabilize the water stream.The flow pattern without a filter can be improved significantly even with the the use of just a 10 PPI irregular filter. Although the study confirmed that use of the filter may change the flow characteristics, it needs to be noted that the use of the ceramic filter alone cannot solve all the problems caused by a poorly designed gating system.展开更多
Owing to its exceptional casting performance,substantial utilization of recycled sand,and environmen-tally sustainable characteristics,frozen sand mold casting technology has found extensive application across diverse...Owing to its exceptional casting performance,substantial utilization of recycled sand,and environmen-tally sustainable characteristics,frozen sand mold casting technology has found extensive application across diverse sectors,including aerospace,power machinery,and the automotive industry.The focus of the present study was on the development of frozen sand mold formulations tailored for efficient machin-ing,guided by the performance and cutting fracture mechanism of frozen sand molds.A regional tem-perature control device was developed for the purpose of conducting cryogenic cutting experiments on frozen sand molds with varying geometrical characteristics and molding materials.The impact of milling process parameters on the dimension accuracy of both sand molds and castings,as well as castings’surface roughness,were systematically investigated by a whole-process error flow control method.The findings indicate that precise and efficient processing of complicated sand molds was achievable by using sand particles with sizes ranging from 106 to 212μm,and water content between 4 and 5 wt.%,freezing temperature below-25℃,and cutting temperature within the range of-5 to 0℃.Through the frozen-casting of representative components,it was validated that the machining error of the frozen sand mold was within±0.25 mm.Additionally,the dimensional accuracy of the flywheel shell casting conformed to the CT8 specifications.This study provides theoretical guidance for the selection of frozen-casting sand formulations and close-loop control of process size chains for complex metal parts,as well as an overall solution for the realization of sustainable development of green casting.展开更多
The effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroidal graphite cast iron have been studied, considering the parameters of carbon equivalent, inocula...The effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroidal graphite cast iron have been studied, considering the parameters of carbon equivalent, inoculation, casting modulus, mold type (green or dry) and pouring temperature within specific ranges of these variables. Based on the orthogonal experiments, the metallurgical and processing parameters of the minimum casting shrinkage and the maximum casting shrinkage were obtained, and the effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroids graphite cast iron castings were discussed. Finally, two regression equations relating these variables to the formation of shrinkage porosity were derived based upon the orthogonal experiments conducted.展开更多
Compared to the resin sand mold casting process, frozen casting is more environmentally friendly, providing a better working environment and enhanced supercooling degree. The interfacial heat transfer coefficient (IHT...Compared to the resin sand mold casting process, frozen casting is more environmentally friendly, providing a better working environment and enhanced supercooling degree. The interfacial heat transfer coefficient (IHTC) between frozen sand mold and metal is an important parameter that significantly influences the final mechanical properties and microstructure of the castings. This paper solved the inverse heat conduction problem using the finite difference method (FDM). In addition, the conjugate gradient method (CGM) was adopted to calculate the temperature distribution and heat flux in the molten metal. At the same time, the particle swarm optimization algorithm (PSO) was used in temperature distribution determination in frozen sand mold. The interfacial heat transfer coefficient (IHTC) was estimated during the solidification of ZL101. The results showed a good agreement between calculated and experimental data, obtaining accurate casting interface temperature Tm, frozen sand mold interface temperature Ts, heat flux q, and IHTC. The analysis of the IHTC variation revealed a water content value within the range of 4 wt.% to 5 wt.% resulted in IHTC in two types of interpretation, called ‘fluctuation type’ and ‘turning type’.展开更多
In response to the demand for environmentally friendly and sustainable manufacturing processes for intricate castings used in advanced equipment, binder jetting technology has emerged as a leading method for achieving...In response to the demand for environmentally friendly and sustainable manufacturing processes for intricate castings used in advanced equipment, binder jetting technology has emerged as a leading method for achieving rapid casting design and manufacturing. This technology has attracted much interest from research institutions, universities, and enterprises worldwide. Binder jetting-based sand-mold additive manufacturing can be used to manufacture complex sand molds (cores) directly and does not require traditional molds, expediting the produc- tion of complex castings and the accompanying process refinement. The exceptional design and manufacturing versatility afforded by this technology has enabled a profound transformation in the foundry industry, advancing the digitization, sustainability, and intelligent evolution of sand casting. This paper explores the recent research progress and achievements in the field of binder jetting sand-mold additive manufacturing in four dimensions: materials, design methods, process technologies, and system equipment. Finally, the characteristics and applica- tion advantages of binder jetting technology are analyzed, and the future development trends and challenges of binder jetting-based sand-mold additive manufacturing technology are investigated.展开更多
In order to further improve the precision forming efficiency of a sand mold digital patternless casting and reduce the amount of sand mold cutting, a method for near-net forming of the sand mold with digital flexible ...In order to further improve the precision forming efficiency of a sand mold digital patternless casting and reduce the amount of sand mold cutting, a method for near-net forming of the sand mold with digital flexible extrusion technology was put forward. The theory, optimization algorithm and technology for sand mold nearnet forming were studied. Experimental results show that the sand mold forming efficiency can be increased by 34%, and the molding sand can be reduced by 44%. The method for near-net forming of a sand mold with digital flexible extrusion technology can effectively promote the application of digital patternless casting technology in the mass production of castings and thus greatly improves the efficiency and automation of sand mold manufacturing.展开更多
The important supporting component in a gas turbine is the casing,which has the characteristics of large size,complex structure,and thin wall.In the context of existing 3DP sand casting processes,casting crack defects...The important supporting component in a gas turbine is the casing,which has the characteristics of large size,complex structure,and thin wall.In the context of existing 3DP sand casting processes,casting crack defects are prone to occur.This leads to an increase in the scrap rate of casings,causing significant resource wastage.Additionally,the presence of cracks poses a significant safety hazard after the casings are put into service.The generation of different types of crack defects in stainless steel casings is closely related to casting stress and the high-temperature concession of the sand mold.Therefore,the types and causes of cracks in stainless steel casing products,based on their structural characteristics,were systematically analyzed.Various sand molds with different internal topology designs were printed using the 3DP technology to investigate the impact of sand mold structures on high-temperature concession.The optimal sand mold structure was used to cast casings,and the crack suppression effect was verified by analyzing its eddy current testing results.The experimental results indicate that the skeleton structure has an excellent effect on suppressing cracks in the casing.This research holds important theoretical and engineering significance in improving the quality of casing castings and reducing production costs.展开更多
Based on a great number of laboratory experiments, a new technique has been developed for producing wear resistant ring-hammers. In this technology, lost foam casting with iron sand was combined to make mold; a specia...Based on a great number of laboratory experiments, a new technique has been developed for producing wear resistant ring-hammers. In this technology, lost foam casting with iron sand was combined to make mold; a special alloy was used to inoculate the molten steel, and proper heat treatment was used to further improve mechanical properties of wear resistant ring-hammers. The influence of this new production technology on the microstructure and mechanical properties of wear resistant ring-hammers was studied. Results show that iron sand molding, having the inherent characteristic of sand molding, changes the type of metallic compounds, refines crystal grains and increases the fineness of microstructure. Practical experience verified that the properties of the ring-hammers produced with this new technique are as follows: tensile strength (Rm) 720 MPa, impact toughness (ak) > 210 J·cm-2 and hardness > 200 HB. After water quenching from 1,080℃ (holding for 4 h) and tempering at 320℃ for 3 h, the best wear resistance is obtained, and the wear resistance is 1.6 times higher than that of common high manganese ring-hammers.展开更多
In order to investigate the sand mold strength after the aeration sand filling-high pressure squeeze moldingprocess,a tree-dimentional(3D)numerical simulation was introduced.The commercial finite element method(FEM)so...In order to investigate the sand mold strength after the aeration sand filling-high pressure squeeze moldingprocess,a tree-dimentional(3D)numerical simulation was introduced.The commercial finite element method(FEM)software ABAQUScombined with a revised Drucker-Prager/Cap model was used to simulate the squeeze compaction process.Additionally,the sand bulk density after the aeration sand filling process was tested by a specially designed experiment,which divided the whole sand bulk in the molding chamber into5x9regions and it was used as the input to simulate the squeeze process.During the simulation process,the uniform modeling simulation and the patition modeling simulation methods were used a d the3D numercal simulation results were compared with correlative benchmark testings.From the3D numerica simulation results,it can be concluded that the uniform sand bulk density distribution can obtain a high quality sandmold and the revised Drncker-Pager/Cap model is suitable for handling the situation with the complex paaern.The3D numerical simulation results can predict well the sand mold strength distribution and can be used as guidelines for the production practice.展开更多
Sand mold 3D printing technology has been recognized as a digital,high-quality,and promising sand mold forming method.However,sand mold 3D printing technology has drawbacks,such as single molding material and long cur...Sand mold 3D printing technology has been recognized as a digital,high-quality,and promising sand mold forming method.However,sand mold 3D printing technology has drawbacks,such as single molding material and long curing time,which limit its further industrial application.Therefore,this study proposes a method for forming composite sand molds based on a layer-stacking structure and a strengthening method based on interlayer heating.The influence of the process parameters on the properties of traditional and composite sand molds was systematically studied.Experimental results demonstrated that when the heating temperature was 150℃,the enhancement of the sand mold was obvious,with an increase of approximately 20%compared to untreated sand mold.When the composite sand mold with a laminated thickness of 1.5 mm was heated at this temperature,its tensile strength reached 1.53 MPa,and compressive strength reached 5.80 MPa,which met the casting requirements.The composite sand mold printed by interlayer heating has excellent casting performance and economic advantages,which provide theoretical guidance for the high-performance printing of sand molds.展开更多
Frozen sand mold additive manufacturing is a new process that utilizes water-based binder phase transition freezing in a low-temperature environment to create sand molds. The aim is to reduce resin binder pollution. H...Frozen sand mold additive manufacturing is a new process that utilizes water-based binder phase transition freezing in a low-temperature environment to create sand molds. The aim is to reduce resin binder pollution. However, binder migration and phase transition behavior require further investigation. This study uses CFD method to numerically simulate the droplet size, injection frequency, and environmental temperature in the migration behavior of water-based binder. The results show that changes in process parameters lead to alterations in the binder migration path, which in turn affects the structure of the binder bridge network. The pore throat guides binder migration, leading to a higher concentration of binder near the sand layer surface. At 268 K, the freezing rate of the binder is much faster than the migration rate of the binder during the slow development stage, significantly affecting the migration behavior of the binder and the binder bridge network structure.展开更多
文摘Darcy’s law is widely used to describe the flow in porous media in which there is a linear relationship between fluid velocity and pressure gradient. However, it has been found that for high numbers of Reynolds this law ceases to be valid. In this work, the Ergun equation is employed to consider the non-linearity of air velocity with the pressure gradient in casting sands. The contribution of non-linearity to the total flow in terms of a variable defined as a non-Darcy flow fraction is numerically quantified. In addition, the influence of the shape factor of the sand grains on the non-linear flow fraction is analyzed. It is found that for values of the Reynolds number less or equal than 1, the contribution of non-linearity for spherical particles is around 1.15%.
基金This work was financially supported by the National Innovation Center Fund of Lightweight Material Forming Technology and Equipment(No.111902Q-D)the State Key Laboratory Fund of Advanced Forming Technology and Equipment(No.SKL2020008)the National Key Research and Development Program(No.2020YFF0217703).
文摘The flexible extrusion forming process (FEFP) is a sand mold patternless manufacturing technology that enables digital near-net shaping of complex sand molds. But, it is difficult to achieve the gradient sand molds with high surface strength and strong interior permeability by FEFP. To solve this problem, an extra-squeeze forming method based on FEFP for gradient sand mold was developed. To further reveal the extra-squeeze forming mechanism, based on the Johnson-Kendall-Roberts (JKR) theory and “gluing” notions, the single and double-sided squeeze models of gradient sand molds were established using the EDEM software. The squeezing processes of sand molds with different cavity depths of 60, 100, 140, 180, and 220 mm were systemically studied under single and double-sided squeeze conditions. The variation in the void fraction of sand mold as also investigated at a variety of extra-squeeze distances of 2, 3, 4, 5, and 6 mm, respectively. Simulation and test results show that a deeper cavity depth weakens the extrusion force transmission, which leads to a decrease in strength. The sand mold permeability and void fraction are identified to be positively correlated, while the tensile strength and void fraction appear to be negatively correlated. The void fraction of sand molds decreases with a longer extra-squeeze distance. A 6 mm extra-squeeze distance for the sand mold with 220 mm cavity depth results in a 26.8% increase in tensile strength with only a 5.7% reduction in the permeability. Hence, the extra- squeeze forming method can improve the quality of the sand mold by producing a gradient sand mold with high surface strength and strong interior permeability.
文摘A new intelligent tester system for measuring multiple mechanical properties of foundry molding sand is introduced and has been patented for the invention in China. The testing process can be simultaneously controlled with a build-in chip microcomputer communicating with a PC through a serial port. The testing system applies dynamic testing technology. During the measurement for compression, relaxation, shearing and tensile processes of sand specimens, the corresponding characteristic curves and eight mechanical property parameters can be obtained in a short time, simply by consecutively testing on four sand specimens. The properties and parameters to be measurable by the tester include compressive strength, elastic modulus, plastic deformation threshold, springback potential, shear strength, shear deformation limit, toughness and tensile strength. These properties and parameters for sand specimens can be defined as the corresponding characteristic curves with precise physical meanings, carried out by the tester, Two of them, namely plastic deformation threshold and springback potential, as well as their testing methods, have been invented for the first time. The testing system applying advanced data measurement technology as well as performing excellent functions is an important breakthrough and creativity in foundry molding sand property testing field. The parameters acquired by the testing system are stable, accurate and reliable. The test data can be instantly displayed or printed out or stored in the PC. As evidence, many experimental data obtained by the tester practically from both laboratory and foundry floor tests indicate that the tester system can be widely applied in foundry industry.
文摘Applying the air impact molding method to mold the complicated pattern with wider opening surface and deeper concave, there always exist vaulted phenomenon and lower compactibility of sand mold over the entrance and the concave regions. Using the air-stream and synchro-formed clamp plate impact molding, however, this problem will be preferably solved. In this paper, the compact mechanism of the new molding method and the effect of some configuration factors, such as the area flowed by compressed air and the highness of the protruding block displacement around the diffluent clamp plate, on the compactibility of sand mold were discussed.
基金funded by the National Science and Technology Major Project of the Ministry of Science and Technology of China under Project No.2016YFB1100703
文摘The insulation effect of the air cavity surrounding the riser in a 3D printed sand mold was studied. The influence of the air cavity on heat flux was theoretically analyzed. The results demonstrated that the heat flux of the air cavity in the 3D printed sand mold was significantly less than that of resin-bonded sand. The insulation effect of the air cavity in sand molds for a cylinder casting and a stress-frame casting were simulated using software COMSOL. The results illustrated that the air cavity could be used to insulate the riser and it was more suitable for a lower melting point metal casting. An air cavity with 10-15 mm width and 5-10 mm away from the riser can significantly prolong the solidification of the riser by over 10%. Meanwhile, the sand mold for the stressframe was made by 3D printing technology and poured with aluminum alloy A356 melt. The experiment results showed that the presence of the air cavity led to a 12.5% increase of the solidification time of its riser.
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.
基金funded by the National Natural Science Foundation of China (No. 51875308)。
文摘The cooling control of the melt during the casting process is of great significance. A comprehensive closed-loop cooling control of castings by adopting a skeletal sand mold design was proposed. The skeletal sand mold consisting of an adaptive shell, functional cavities and a support was designed and created based on the finite difference meshes of a casting. It was applied to a round wall test casting. Two kinds of skeletal sand molds, one with lattice support and the other with enforcing ribs for this casting were designed and printed out by the 3 D printing(3 DP) method. Aluminum alloy A356 was cast by using these two sand molds. The first mold was cooled by natural convection, the other one by water spray cooling. Two sound castings were obtained. The sand mold temperature, cooling curves, microstructures, mechanical properties, residual stress and deformation were measured, compared and discussed. Water spray cooling hastened the cooling rate by 62%, increased the content of Mg and Cu in the α-Al matrix, improved the mechanical properties, and altered the surface residual stress state.
文摘The solidification behavior of AISI DC 53 cold work tool steel was investigated by means of a cooling curve and its first derivative. Copper and sand wedge-shaped molds were used to obtain various solidification rates. To reveal the cooling rate degree during solidification,the secondary dendrite arm spacing of the steel alloy was examined by scanning electron microscopy(SEM). The solidification rates of each section for both wedge steel samples were calculated by means of the secondary dendrite arm spacing using a research-based empirical relation from the literature. Experiment results revealed that at the tip region of the cast specimen in the copper wedgeshaped mold,the carbide size was 7–8 μm,where the solidification rate was approximately 4,830 °C·s-1. The greatest carbide size obtained in the upper region of the sand cast wedge-shaped specimen was 250–270 μm.
文摘Solidif ication and f luid f low analysis using computer simulation is a current common practice. There is also a high demand for thermal stress analysis in the casting process because casting engineers want to control the defects related to thermal stresses, such as large deformation and crack generation during casting. The riser system is an essential part of preventing the shrinkage defects in the casting process, and it has a great inf luence on thermal phenomena. The analysis domain is dramatically expanded by attaching the riser system to a casting product due to its large volume, and it makes FEM mesh generation diff icult. However, it is diff icult to study and solve the above proposed problem caused by riser system using traditional analysis methods which use single numerical method such as FEM or FDM. In this paper, some research information is presented on the effects of the riser system on thermal stress analysis using a FDM/FEM hybrid method in the casting process simulation. The results show the optimal conditions for stress analysis of the riser model in order to save computation time and memory resources.
文摘Casting defects that are closely related to entrapped air bubbles and metallic oxides occur very frequently in the sand mold casting process. Many researchers have shown that these defects can be reduced by adopting an appropriate gating system design. However, it is difficult for field engineers to identify a specific gating system that is more appropriate for their products. In this study, we tried to draw a comparison between two gating system designs with and without a ceramic foam filter. The ceramic foam filter was added to the horizontal runner just after the down sprue to prevent air bubble generation and reduce turbulence without a change of gating system design. The water modeling experiment was conducted with four different amounts of the initial volumes of water in the reservoir to verify the effects of initial pouring velocity. The results of the experiment applying the filter showed remarkably changed flow characteristics. The use of the filter was found to convert the flow pattern of water in the desired direction. The ceramic foam filter performed well to reduce flow velocity and stabilize the water stream.The flow pattern without a filter can be improved significantly even with the the use of just a 10 PPI irregular filter. Although the study confirmed that use of the filter may change the flow characteristics, it needs to be noted that the use of the ceramic filter alone cannot solve all the problems caused by a poorly designed gating system.
基金supported by the National Key R&D Program of China(grant No.2021YFB3401200)the Jiangsu Provincial Basic Research Program(Natural Science Foundation)Youth Fund(grant No.BK20230885)the Special Technical Project for Equipment Pre-research(grantNo.30104040302).
文摘Owing to its exceptional casting performance,substantial utilization of recycled sand,and environmen-tally sustainable characteristics,frozen sand mold casting technology has found extensive application across diverse sectors,including aerospace,power machinery,and the automotive industry.The focus of the present study was on the development of frozen sand mold formulations tailored for efficient machin-ing,guided by the performance and cutting fracture mechanism of frozen sand molds.A regional tem-perature control device was developed for the purpose of conducting cryogenic cutting experiments on frozen sand molds with varying geometrical characteristics and molding materials.The impact of milling process parameters on the dimension accuracy of both sand molds and castings,as well as castings’surface roughness,were systematically investigated by a whole-process error flow control method.The findings indicate that precise and efficient processing of complicated sand molds was achievable by using sand particles with sizes ranging from 106 to 212μm,and water content between 4 and 5 wt.%,freezing temperature below-25℃,and cutting temperature within the range of-5 to 0℃.Through the frozen-casting of representative components,it was validated that the machining error of the frozen sand mold was within±0.25 mm.Additionally,the dimensional accuracy of the flywheel shell casting conformed to the CT8 specifications.This study provides theoretical guidance for the selection of frozen-casting sand formulations and close-loop control of process size chains for complex metal parts,as well as an overall solution for the realization of sustainable development of green casting.
基金The paper was financially supported by the National Natural Science Foundation of China(Grant No.59235102).
文摘The effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroidal graphite cast iron have been studied, considering the parameters of carbon equivalent, inoculation, casting modulus, mold type (green or dry) and pouring temperature within specific ranges of these variables. Based on the orthogonal experiments, the metallurgical and processing parameters of the minimum casting shrinkage and the maximum casting shrinkage were obtained, and the effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroids graphite cast iron castings were discussed. Finally, two regression equations relating these variables to the formation of shrinkage porosity were derived based upon the orthogonal experiments conducted.
基金supported by the National Key R&D Program of China(No.2021YFB3401200)the Jiangsu Provincial Basic Research Program(Natural Science Foundation)Youth Fund(No.BK20230885).
文摘Compared to the resin sand mold casting process, frozen casting is more environmentally friendly, providing a better working environment and enhanced supercooling degree. The interfacial heat transfer coefficient (IHTC) between frozen sand mold and metal is an important parameter that significantly influences the final mechanical properties and microstructure of the castings. This paper solved the inverse heat conduction problem using the finite difference method (FDM). In addition, the conjugate gradient method (CGM) was adopted to calculate the temperature distribution and heat flux in the molten metal. At the same time, the particle swarm optimization algorithm (PSO) was used in temperature distribution determination in frozen sand mold. The interfacial heat transfer coefficient (IHTC) was estimated during the solidification of ZL101. The results showed a good agreement between calculated and experimental data, obtaining accurate casting interface temperature Tm, frozen sand mold interface temperature Ts, heat flux q, and IHTC. The analysis of the IHTC variation revealed a water content value within the range of 4 wt.% to 5 wt.% resulted in IHTC in two types of interpretation, called ‘fluctuation type’ and ‘turning type’.
基金supported by National Key R&D Program of China(Grant No.2021YFB3401200)Jiangsu Provincial Basic Research Pro-gram(Natural Science Foundation)Youth Fund of China(Grant No.BK20230885)the Special Technical Project for Equipment Pre-research(Grant No.30104040302).
文摘In response to the demand for environmentally friendly and sustainable manufacturing processes for intricate castings used in advanced equipment, binder jetting technology has emerged as a leading method for achieving rapid casting design and manufacturing. This technology has attracted much interest from research institutions, universities, and enterprises worldwide. Binder jetting-based sand-mold additive manufacturing can be used to manufacture complex sand molds (cores) directly and does not require traditional molds, expediting the produc- tion of complex castings and the accompanying process refinement. The exceptional design and manufacturing versatility afforded by this technology has enabled a profound transformation in the foundry industry, advancing the digitization, sustainability, and intelligent evolution of sand casting. This paper explores the recent research progress and achievements in the field of binder jetting sand-mold additive manufacturing in four dimensions: materials, design methods, process technologies, and system equipment. Finally, the characteristics and applica- tion advantages of binder jetting technology are analyzed, and the future development trends and challenges of binder jetting-based sand-mold additive manufacturing technology are investigated.
基金financially supported by the National Science Foundation for Distinguished Young Scholars of China(Grant No.51525503)
文摘In order to further improve the precision forming efficiency of a sand mold digital patternless casting and reduce the amount of sand mold cutting, a method for near-net forming of the sand mold with digital flexible extrusion technology was put forward. The theory, optimization algorithm and technology for sand mold nearnet forming were studied. Experimental results show that the sand mold forming efficiency can be increased by 34%, and the molding sand can be reduced by 44%. The method for near-net forming of a sand mold with digital flexible extrusion technology can effectively promote the application of digital patternless casting technology in the mass production of castings and thus greatly improves the efficiency and automation of sand mold manufacturing.
基金financially supported by the National Natural Science Foundation of China(No.52175352)the Xing Liao Ying Cai Project of Liaoning Province(No.XLYC2008036)the Shenyang Youth Innovation Talent Support Program(No.RC220429)。
文摘The important supporting component in a gas turbine is the casing,which has the characteristics of large size,complex structure,and thin wall.In the context of existing 3DP sand casting processes,casting crack defects are prone to occur.This leads to an increase in the scrap rate of casings,causing significant resource wastage.Additionally,the presence of cracks poses a significant safety hazard after the casings are put into service.The generation of different types of crack defects in stainless steel casings is closely related to casting stress and the high-temperature concession of the sand mold.Therefore,the types and causes of cracks in stainless steel casing products,based on their structural characteristics,were systematically analyzed.Various sand molds with different internal topology designs were printed using the 3DP technology to investigate the impact of sand mold structures on high-temperature concession.The optimal sand mold structure was used to cast casings,and the crack suppression effect was verified by analyzing its eddy current testing results.The experimental results indicate that the skeleton structure has an excellent effect on suppressing cracks in the casing.This research holds important theoretical and engineering significance in improving the quality of casing castings and reducing production costs.
文摘Based on a great number of laboratory experiments, a new technique has been developed for producing wear resistant ring-hammers. In this technology, lost foam casting with iron sand was combined to make mold; a special alloy was used to inoculate the molten steel, and proper heat treatment was used to further improve mechanical properties of wear resistant ring-hammers. The influence of this new production technology on the microstructure and mechanical properties of wear resistant ring-hammers was studied. Results show that iron sand molding, having the inherent characteristic of sand molding, changes the type of metallic compounds, refines crystal grains and increases the fineness of microstructure. Practical experience verified that the properties of the ring-hammers produced with this new technique are as follows: tensile strength (Rm) 720 MPa, impact toughness (ak) > 210 J·cm-2 and hardness > 200 HB. After water quenching from 1,080℃ (holding for 4 h) and tempering at 320℃ for 3 h, the best wear resistance is obtained, and the wear resistance is 1.6 times higher than that of common high manganese ring-hammers.
基金The National Natural Science Foundation of China(No.51575304)the National Science and Technology Major Project of the Ministry of Science and Technology of China(No.2012ZX04012011)
文摘In order to investigate the sand mold strength after the aeration sand filling-high pressure squeeze moldingprocess,a tree-dimentional(3D)numerical simulation was introduced.The commercial finite element method(FEM)software ABAQUScombined with a revised Drucker-Prager/Cap model was used to simulate the squeeze compaction process.Additionally,the sand bulk density after the aeration sand filling process was tested by a specially designed experiment,which divided the whole sand bulk in the molding chamber into5x9regions and it was used as the input to simulate the squeeze process.During the simulation process,the uniform modeling simulation and the patition modeling simulation methods were used a d the3D numercal simulation results were compared with correlative benchmark testings.From the3D numerica simulation results,it can be concluded that the uniform sand bulk density distribution can obtain a high quality sandmold and the revised Drncker-Pager/Cap model is suitable for handling the situation with the complex paaern.The3D numerical simulation results can predict well the sand mold strength distribution and can be used as guidelines for the production practice.
基金supported by National Key R&D Program of China(Grant No.2021YFB3401200)Jiangsu Basic Research Program(Natural Science Fund)Youth Fund(Grant No.BK20230885)Special Technical Project for Equipment Pre-research(Grant No.30104040302).
文摘Sand mold 3D printing technology has been recognized as a digital,high-quality,and promising sand mold forming method.However,sand mold 3D printing technology has drawbacks,such as single molding material and long curing time,which limit its further industrial application.Therefore,this study proposes a method for forming composite sand molds based on a layer-stacking structure and a strengthening method based on interlayer heating.The influence of the process parameters on the properties of traditional and composite sand molds was systematically studied.Experimental results demonstrated that when the heating temperature was 150℃,the enhancement of the sand mold was obvious,with an increase of approximately 20%compared to untreated sand mold.When the composite sand mold with a laminated thickness of 1.5 mm was heated at this temperature,its tensile strength reached 1.53 MPa,and compressive strength reached 5.80 MPa,which met the casting requirements.The composite sand mold printed by interlayer heating has excellent casting performance and economic advantages,which provide theoretical guidance for the high-performance printing of sand molds.
基金supported by the National Key R&D Program of China(grant No.2021YFB3401200)Jiangsu Basic Research Program(Natural Science Fund)Youth Fund(grant No.BK20230885)+2 种基金the International Joint Laboratory of Sustainable Manufacturing,Ministry of Education and the Fundamental Research Funds for the Central Universities(grant No.NG2024012)State Key Laboratory of Materials Processing and Die&Mould Technology,Huazhong University of Science and Technology,China(grant No.P2024-007)other projects.
文摘Frozen sand mold additive manufacturing is a new process that utilizes water-based binder phase transition freezing in a low-temperature environment to create sand molds. The aim is to reduce resin binder pollution. However, binder migration and phase transition behavior require further investigation. This study uses CFD method to numerically simulate the droplet size, injection frequency, and environmental temperature in the migration behavior of water-based binder. The results show that changes in process parameters lead to alterations in the binder migration path, which in turn affects the structure of the binder bridge network. The pore throat guides binder migration, leading to a higher concentration of binder near the sand layer surface. At 268 K, the freezing rate of the binder is much faster than the migration rate of the binder during the slow development stage, significantly affecting the migration behavior of the binder and the binder bridge network structure.
