Counter-gravity casting(CGC)is a widely adopted material processing technique in metals due to its notable benefits,including enhanced filling behavior,reduced defect occurrence,and elevated mechani-cal properties.It ...Counter-gravity casting(CGC)is a widely adopted material processing technique in metals due to its notable benefits,including enhanced filling behavior,reduced defect occurrence,and elevated mechani-cal properties.It plays a pivotal role in fabricating intricate,high-quality components.After its inception in the early 1900s,various CGC processes have emerged,such as low-pressure,counter-pressure,vac-uum suction,and adjusted pressure casting,which are explored in this discourse with an eye toward further advancements.Despite CGC’s superiority over traditional gravity casting and other manufacturing methodologies,specific issues and constraints persist within CGC.This paper endeavors to provide a com-prehensive overview of the historical progression of CGC,its recent developments,and the associated re-search aspects,encompassing topics like filling processes,solidification,microstructural transformations,and the resultant mechanical properties of the fabricated products.Additionally,this paper offers insights into the future challenges and opportunities of CGC.展开更多
To investigate the influence of Centrifugal Counter-gravity Casting(C3) process on the solidification microstructure and mechanical properties of the casting, A357 aluminum alloy samples were produced by different pro...To investigate the influence of Centrifugal Counter-gravity Casting(C3) process on the solidification microstructure and mechanical properties of the casting, A357 aluminum alloy samples were produced by different process conditions under C3. The results show that C3 has better feeding capacity compared with the vacuum suction casting; and that the mechanical vibration and the convection of melts formed at the centrifugal rotation stage suppress the growth of dendrites, subsequently resulting in the refinement of grains and the improvement of mechanical properties, density and hardness. A finer grain and higher strength can be obtained in the A357 alloy by increasing centrifugal radius and rotational speed. However, casting defects will appear near the rotational axis and the mechanical properties will decrease once the rotational speed exceeds 150 r·min-1.展开更多
The cast Ti-6Al-4V alloy bars with different section sizes were fabricated by investment casting at counter-gravity condition with the mold temperatures of 300 ℃ and 650 ℃, respectively. The microstructure of the al...The cast Ti-6Al-4V alloy bars with different section sizes were fabricated by investment casting at counter-gravity condition with the mold temperatures of 300 ℃ and 650 ℃, respectively. The microstructure of the alloy was observed by means of OM and SEM, and the effect of mold temperature and casting dimension on tensile properties was studied. Results show that equiaxed grains are obtained regardless of the casting dimension. 13 grain size tends to increase with an increase in mold temperature. Hot isostatic pressing of the alloy was carried out for tensile properties＇ comparison. Room temperature tensile test results show that Ti-6Al-4V alloy produced via counter-gravity casting has good balance of strength and ductility after hot isostatic pressing （HIP）. The alloy shows higher ductility due to the elimination of porosity. In both cast and HIP status, the tensile strength is inclined to decrease with an increase in mold temperature, while the ductility is prone to slightly increase. Both the strength and ductility tend to decrease with an increase in the casting dimension.展开更多
To develop a suitable production process for fiber reinforced investment casting shell mold,three methods were studied:the traditional method(M_(1)),the method of adding fiber into silica sol with mechanical stirring ...To develop a suitable production process for fiber reinforced investment casting shell mold,three methods were studied:the traditional method(M_(1)),the method of adding fiber into silica sol with mechanical stirring and ultrasonic agitation(M_(2)),and the method of adding fiber into slurry with mechanical stirring and ultrasonic agitation for durations of 3,15,30,and 45 min(M_(3)).The bending strength,high-temperature self-load deformation,and thermal conductivity of the shell molds were investigated.The results reveal that the enhancement of fiber dispersion through ultrasonic agitation improves the comprehensive performance of the shell molds.The maximum green bending strength of the shell mold by M_(2) reaches 3.29 MPa,which is 29% higher than that of the shell mold prepared by M_(1).Moreover,the high-temperature self-load deformation of the shell mold is reduced from 0.62% to 0.44%.In addition,simultaneous ultrasonic agitation and mechanical stirring effectively shorten the slurry preparation time while maintaining comparable levels of fiber dispersion.With the process M_(3)-45 min,the fillers are uniformly dispersed in the slurry,and the fired bending strength and the high-temperature self-load deformation reach 6.25 MPa and 0.41%,respectively.Therefore,the proposed ultrasonic agitation route is promising for the fabrication of fiber-reinforced shell molds with excellent fibers dispersion.展开更多
Al-Si-Cu-Mg alloy demonstrates a significant age-hardening effect,with its mechanical properties tunable by optimizing the aging parameters.To enhance this effect,the as-cast Al-8.5Si-2Cu-0.9Mg alloy was subjected to ...Al-Si-Cu-Mg alloy demonstrates a significant age-hardening effect,with its mechanical properties tunable by optimizing the aging parameters.To enhance this effect,the as-cast Al-8.5Si-2Cu-0.9Mg alloy was subjected to either single-stage aging at temperatures of 150℃,175℃,200℃,and 225℃for 0.5 h to 20 h;or double-stage aging:involving a first-stage aging treatment at 120℃for 1 h,3 h,5 h,or 7 h,followed by a second-stage aging treatment at 175℃ for 0.5 h to 20 h.The microstructure and mechanical properties were evaluated for samples aged at 175℃/7 h,175℃/10 h,120℃/5 h+175℃/5 h,and 120℃/5 h+175℃/8 h.XRD analysis reveals that the as-cast Al-8.5Si-2Cu-0.9Mg alloy consists of theα-Al,Si,θ-Al_(2)Cu,and Q-Al_(5)Cu_(2)Mg_8Si_6phases.The aging kinetics exhibit a double-peak behavior in both single-stage and double-stage aging processes.Under single-stage aging at 175℃/x h and double-stage aging(120℃/5 h+175℃/x h),the precipitates'size at the first peak is smaller than that at the second peak.Compared with single-stage aging(175℃/7 h),double-stage aging(120℃/5 h+175℃/5 h)produces a finer precipitate in the alloy.Theoretical calculations indicate that the number density and nucleation rate of both the Al_(5)Cu_(2)Mg_8Si_6 and Al_(2)Cu phases are higher during the double-stage aging(120℃/5 h+175℃/5 h)than those during the single-stage aging(175℃/7 h).Additionally,tensile tests at both room temperature and 250℃demonstrate that double-stage aging(120℃/5 h+175℃/5 h)significantly improves the mechanical properties of the alloy compared to single-stage aging(175℃/7 h),suggesting that double-stage aging is more effective for enhancing mechanical properties for this alloy.展开更多
Airless tires are essential for enhancing the safety,reliability,and convenience of maintenance of electric bicycles.Polyurethane(PU)is considered a promising candidate for such applications owing to its versatile pro...Airless tires are essential for enhancing the safety,reliability,and convenience of maintenance of electric bicycles.Polyurethane(PU)is considered a promising candidate for such applications owing to its versatile properties.However,their use is limited by insufficient heat resistance and excessive dynamic heat generation under cyclic loading.In this study,star-shaped trifunctional polypropylene glycerol(PPG3)was incorporated into conventional poly(tetramethylene glycol)(PTMG)and 4,4'-methylenediphenyl diisocyanate(MDI)-based systems to construct microporous star-shaped casting polyurethanes(SCPU),with water serving as a green foaming agent.Unlike conventional small-molecule trifunctional crosslinkers that create junctions within hard segment domains,PPG3 introduces long flexible arms between the hard segments,anchoring the crosslinking points at its molecular core.The large steric hindrance of PPG3 effectively suppresses soft segment crystallization and lowers the degree of microphase separation,whereas the crosslinked network restricts chain mobility,thereby reducing dynamic heat generation.These structural features also enhance the heat resistance,yielding a softening temperature of 183℃,which is 30.9%higher than that of polyurethane without PPG3.When applied to airless tires by casting SCPU into rubber treads,the fabricated hybrid airless tires achieved a rolling distance of over 3000 km under a load of 65 kg at 25km/h without structural failure,satisfying practical performance requirements.This strategy offers a simple,solvent-free,and environmentally friendly process,underscoring the potential of SCPU for scalable production of high-performance airless tires.展开更多
The Cu-12Fe alloy has attracted significant attention due to its excellent electrical conductivity and electromagnetic shielding capability,high strength,cost-effectiveness,and recyclability.In the present work,the Cu...The Cu-12Fe alloy has attracted significant attention due to its excellent electrical conductivity and electromagnetic shielding capability,high strength,cost-effectiveness,and recyclability.In the present work,the Cu-12Fe alloy strip with the thickness of 2.4 mm was successfully produced by twin-roll strip casting.The microstructure and properties of the Cu-12Fe alloy were tailored by cold rolling and aging treatment.The tensile strength of the as-cast strip is approximately 328 MPa and its elongation is 25%.The Fe phase randomly dispersed in the matrix,and the average size of Fe-rich phase is 2μm.Besides,enrichment of Fe phase is observed in the central layer of the strip,results in the formation of the“sandwich structure”.Moreover,the as-cast strip of Cu-12Fe was directly cold-rolled from 2.4 to 0.12 mm.The directly cold-rolled sample after aging at 450℃for 16 h(ProcessⅠ)shows excellent electrical conductivity of 69.5%IACS,the tensile strength and elongation are 513 MPa and 3.8%,the saturation magnetic flux density is 20.1 emu·g^(-1),and the coercive force is 25.2 Oe.In ProcessⅡ,the as-cast strip firstly cold-rolled to 1.2 mm,then aged at 500℃for 1.5 h,followed by cold rolling to 0.12 mm,finally aged at 450℃for 16 h.The sample after ProcessⅡshows the electrical conductivity of 66.3%IACS,the tensile strength of 533 MPa,an elongation of 3.5%,saturation magnetic flux density of 21.4 emu·g^(-1),and the coercive force of 22.3 Oe.展开更多
The transient phenomena of re-oxidation and slag entrapment occurring in the tundish during the ladle change-over process have been proven detrimental to clean steel production.Therefore,an unsteady three-phase turbul...The transient phenomena of re-oxidation and slag entrapment occurring in the tundish during the ladle change-over process have been proven detrimental to clean steel production.Therefore,an unsteady three-phase turbulence model,coupling velocity,temperature,and phase field was established to study the effect of the ladle shroud immersion depth on the slag eye formation,slag entrainment,slag dragging,air dragging,and flow characteristics during the ladle change-over process of a two-strand tundish.The results showed that reducing the immersion depth decreases the high-velocity region area under the slag layer in the quasi-steady process.During the emptying stage,as the molten bath level gradually decreases,the outlet temperature exhibits a trend of initially decreasing and subsequently increasing across all three shroud immersion depths.However,under a 210 mm shroud immersion depth,molten slag and air are dragged into the shroud,forming slag droplets and causing significant fluctuations,with a maximum scalar velocity of 0.0764 m/s at the monitoring point.In the filling stage,air and molten slag are dragged into the molten bath,forming bubbles and slag droplets at an immersion depth of 210 mm.Bubbles are observed within the molten slag layer,which can readily cause an emulsification phenomenon,making it easier to be dragged as slag droplets.Additionally,the slag eye area measured under 210 mm immersion depth at 45 s is 0.303 m^(2),while the maximum scalar velocity of 2.4259 m/s is detected at 12 s.At an immersion depth of 360 mm,the average area of the slag eye is minimized to 0.06268 m2,with corresponding variances of 0.006753,representing the optimal immersion depth.展开更多
A full-sectional microstructure characterization method was developed to investigate the formation of coarse slag rims during the continuous casting of hypo-peritectic steel.The cross-sectional microstructural analysi...A full-sectional microstructure characterization method was developed to investigate the formation of coarse slag rims during the continuous casting of hypo-peritectic steel.The cross-sectional microstructural analysis of typical slag rims for two highly crystalline powders revealed that their formation was primarily driven by the solidification of the liquid slag.Distinct differences were observed in the microstructures of slag rims from the two powders.Powder A(characterized by a higher breaking temperature and viscosity)displayed alternating lamellar microstructures of coarse and fine phases,with the coarse phases composed of akermanite-gehlenite transition phases.In contrast,powder B(with a lower breaking temperature and viscosity)predominantly comprised regular akermanite-gehlenite crystals interspersed with a certain amount of glassy phases.Numerical simulations of a three-phase fluid flow coupled with heat transfer indicate that slag rim formation correlates with mold oscillation.Solidification of the liquid slag at the slag rim front predominantly occurs during the negative stroke of the mold oscillation.The average heating rate during the ascending stage of the mold reaches approximately 100 K·s^(−1),whereas the average cooling rate during the descending stage attains 400 K·s^(−1).This temperature variation leads to the formation of lamellar microstructures,whereas the ascending stage promotes the formation of coarse structures and thicker slag rims.Based on the powder properties,two distinct formation pathways exist for highly crystalline mold powders.For the powders with a higher breaking temperature,higher viscosity,and narrower solidification range(powder A),coarse microstructures and thicker slag rims were preferentially formed.For powders with lower breaking temperature and viscosity and wider solidification ranges(powder B),the liquid slag resisted rapid solidification,and the extended mushy zone allowed the partial liquid slag to persist at the slag rim front,promoting the formation of a thin slag rim.This study enhances the understanding of slag rim formation in highly crystalline mold powders and provides critical insights into the control of longitudinal surface cracks in hypo-peritectic steel.展开更多
Manual inspection of onba earing casting defects is not realistic and unreliable,particularly in the case of some micro-level anomalies which lead to major defects on a large scale.To address these challenges,we propo...Manual inspection of onba earing casting defects is not realistic and unreliable,particularly in the case of some micro-level anomalies which lead to major defects on a large scale.To address these challenges,we propose BearFusionNet,an attention-based deep learning architecture with multi-stream,which merges both DenseNet201 and MobileNetV2 for feature extraction with a classification head inspired by VGG19.This hybrid design,figuratively beaming from one layer to another,extracts the enormity of representations on different scales,backed by a prepreprocessing pipeline that brings defect saliency to the fore through contrast adjustment,denoising,and edge detection.The use of multi-head self-attention enhances feature fusion,enabling the model to capture both large and small spatial features.BearFusionNet achieves an accuracy of 99.66%and Cohen’s kappa score of 0.9929 in Kaggle’s Real-life Industrial Casting Defects dataset.Both McNemar’s and Wilcoxon signed-rank statistical tests,as well as fivefold cross-validation,are employed to assess the robustness of our proposed model.To interpret the model,we adopt Grad-Cam visualizations,which are the state of the art standard.Furthermore,we deploy BearFusionNet as a webbased system for near real-time inference(5-6 s per prediction),which enables the quickest yet accurate detection with visual explanations.Overall,BearFusionNet is an interpretable,accurate,and deployable solution that can automatically detect casting defects,leading to significant advances in the innovative industrial environment.展开更多
The effects of the high pressure die casting(HPDC)processes on porosity,microstructure,and mechanical properties of heat-treatment-free aluminum silicon(Al-Si)alloys have long been a focal point in automotive die-cast...The effects of the high pressure die casting(HPDC)processes on porosity,microstructure,and mechanical properties of heat-treatment-free aluminum silicon(Al-Si)alloys have long been a focal point in automotive die-casting research.In this work,the combined effect of shot sleeve materials and slow shot speeds on porosity,microstructure and mechanical properties of a newly designed HPDC Al-Si alloy was investigated.Results show that employing a ceramic shot sleeve or increasing the slow shot speed significantly reduces both the average size and area fraction of externally solidified crystals(ESCs),as well as the average pore size and volume fraction.When the slow shot speed is increased from 0.05 m·s^(-1)to 0.1 m·s^(-1),the pore volume fraction decreases by 10.2%in steel-shot-sleeve samples,compared to a substantial 67.1%reduction in ceramic-shot-sleeve samples.At a slow shot speed of 0.1 m·s^(-1),castings produced with a ceramic shot sleeve exhibit superior mechanical properties:8.3%higher yield strength,17.4%greater tensile strength,and an 81.4%improvement in elongation,relative to those from a steel shot sleeve.These findings provide valuable insights for minimizing porosity and coarse ESCs in die castings,offering promising potential for broader industrial applications.展开更多
Automation and intelligence have become the primary trends in the design of investment casting processes.However,the design of gating and riser systems still lacks precise quantitative evaluation criteria.Numerical si...Automation and intelligence have become the primary trends in the design of investment casting processes.However,the design of gating and riser systems still lacks precise quantitative evaluation criteria.Numerical simulation plays a significant role in quantitatively evaluating current processes and making targeted improvements,but its limitations lie in the inability to dynamically reflect the formation outcomes of castings under varying process conditions,making real-time adjustments to gating and riser designs challenging.In this study,an automated design model for gating and riser systems based on integrated parametric 3D modeling-simulation framework is proposed,which enhances the flexibility and usability of evaluating the casting process by simulation.Firstly,geometric feature extraction technology is employed to obtain the geometric information of the target casting.Based on this information,an automated design framework for gating and riser systems is established,incorporating multiple structural parameters for real-time process control.Subsequently,the simulation results for various structural parameters are analyzed,and the influence of these parameters on casting formation is thoroughly investigated.Finally,the optimal design scheme is generated and validated through experimental verification.Simulation analysis and experimental results show that using a larger gate neck(24 mm in side length) and external risers promotes a more uniform temperature distribution and a more stable flow state,effectively eliminating shrinkage cavities and enhancing process yield by 15%.展开更多
The flow behavior of molten steel in the thin slab mold under high casting speed conditions was investigated,with a focus on the multi-mode continuous casting and rolling mold.A steel-slag two-phase flow model was est...The flow behavior of molten steel in the thin slab mold under high casting speed conditions was investigated,with a focus on the multi-mode continuous casting and rolling mold.A steel-slag two-phase flow model was established using large eddy simulation,the volume of fluid,and magnetohydrodynamics methods through numerical simulation.The maximum flow velocity and wave height at the steel-slag interface within the mold are critical evaluation criteria for analyzing asymmetric flow under varying casting speeds and electromagnetic braking.The results indicate that the asymmetric flows within the mold do not occur synchronously.The severity of the asymmetric flow correlates with the velocity difference across the steel-slag interface.A greater biased flow prolongs the time required to revert to a steady state.When the magnetic field intensity is set to 0.24 T and the magnetic pole position is at 390 mm from the steel-slag interface,this configuration can reduce the velocity of the steel-slag interface,thereby mitigating the asymmetric flow.Additionally,it can diminish the velocity,impact depth,and impact intensity on the narrow face of the jet,thus improving the distribution of velocity and turbulent kinetic energy within the mold.This configuration prolongs the time required for the steel-slag interface to transition from a stable state to its maximum velocity and shortens the time for the interface to return to stability from an unstable state.Moreover,it ensures the positional stability of the steel-slag interface,confining its position within−3 mm.展开更多
In order to investigate the effect of die wall thickness on morphologies of defect band,a stepped mold with a wall thickness of 5 mm,4 mm,3 mm,2 mm,and 1 mm was designed to carry out high pressure die casting experime...In order to investigate the effect of die wall thickness on morphologies of defect band,a stepped mold with a wall thickness of 5 mm,4 mm,3 mm,2 mm,and 1 mm was designed to carry out high pressure die casting experiments with AlSi10 MgMn alloy.For castings with wall thickness of 2-4 mm,the ratio of the mean defect band width(w)and mean grain size(d)in the defect band(w/d)ranges 7-18,while it increases to 24.47 for the 5 mm-thick casting.This difference is related with the filling speed and the distribution of externally solidified crystals(ESCs).The mold flow analysis indicates that the filling speed decreases from 25.41 m·s^(-1)to 11.07 m·s^(-1)when wall thickness increases from 2 mm to 5 mm.Due to the decreasing filling speed along the wall thickness,ESCs gradually diffuse from the center to the defect band,which keep the shear strength in the defect band at a high-level during filling.Meanwhile,the shear strength generated during the filling also decreases as the shear rate drops.Finally,the defect bands in the 5 mm-thick region become widen and indistinct,and the porosity is as high as 5.25%.展开更多
A novel counter-gravity infiltration casting device and corresponding fabricating process for producing open-celled aluminum foams were presented. The experimental results show that defects such as insufficient or exc...A novel counter-gravity infiltration casting device and corresponding fabricating process for producing open-celled aluminum foams were presented. The experimental results show that defects such as insufficient or excessive infiltrating can hardly be found in the foam samples prepared by counter-gravity infiltration casting. The foam materials exhibit excellent mechanical properties. The void content strongly affects the mechanical properties of aluminum foams. The yield stress and plateau stress significantly increase with the decrease of void content. Raising pre-heating temperature and increasing packing pressure are effective to lower the void content in aluminum foams.展开更多
The impact of casting defects on the weldability of K4951 superalloy was investigated using tungsten inert gas(TIG)welding.The as-cast K4951 superalloy samples with prefabricated U-shaped grooves of varying depths and...The impact of casting defects on the weldability of K4951 superalloy was investigated using tungsten inert gas(TIG)welding.The as-cast K4951 superalloy samples with prefabricated U-shaped grooves of varying depths and widths were TIG welded,and the microstructures,cracks morphology,and precipitated phases were analyzed using optical microscope,scanning electron microscope,transmission electron microscope,and energy dispersive X-ray spectrometer.The results reveal that the dimensions of casting defects significantly affect the weldability of K4951.Deep defects(greater than 2 mm)lead to rapid crack propagation,while wider defects can moderate the propagation process of cracks.Elemental segregation and the formation of precipitated phases,such as MC carbides,are observed in the fusion zone,contributing to welding cracks.An optimal groove aspect ratio(depth-to-width)between 0.2 and 0.5 minimizes crack formation tendency and enhances tensile strength,resulting in a mixed brittle-ductile fracture mode of joint after high-temperature tensile testing.展开更多
In the foundry industries,process design has traditionally relied on manuals and complex theoretical calculations.With the advent of 3D design in casting,computer-aided design(CAD)has been applied to integrate the fea...In the foundry industries,process design has traditionally relied on manuals and complex theoretical calculations.With the advent of 3D design in casting,computer-aided design(CAD)has been applied to integrate the features of casting process,thereby expanding the scope of design options.These technologies use parametric model design techniques for rapid component creation and use databases to access standard process parameters and design specifications.However,3D models are currently still created through inputting or calling parameters,which requires numerous verifications through calculations to ensure the design rationality.This process may be significantly slowed down due to repetitive modifications and extended design time.As a result,there are increasingly urgent demands for a real-time verification mechanism to address this issue.Therefore,this study proposed a novel closed-loop model and software development method that integrated contextual design with real-time verification,dynamically verifying relevant rules for designing 3D casting components.Additionally,the study analyzed three typical closed-loop scenarios of agile design in an independent developed intelligent casting process system.It is believed that foundry industries can potentially benefit from favorably reduced design cycles to yield an enhanced competitive product market.展开更多
In this work,the influences of surface layer slurry at different temperatures(10℃,14℃,18℃,22℃)on wax patterns deformation,shrinkage,slurry coating characteristics,and the surface quality of the casting were invest...In this work,the influences of surface layer slurry at different temperatures(10℃,14℃,18℃,22℃)on wax patterns deformation,shrinkage,slurry coating characteristics,and the surface quality of the casting were investigated by using a single factor variable method.The surface morphologies of the shell molds produced by different temperatures of the surface(first)layer slurries were observed via electron microscopy.Furthermore,the microscopic composition of these shell molds was obtained by EDS,and the osmotic effect of the slurry on the wax patterns at different temperatures was also assessed by the PZ-200 Contact Angle detector.The forming reasons for the surface cracks and holes of thick and large ZTC4 titanium alloy by investment casting were analyzed.The experimental results show that the surface of the shell molds prepared by the surface layer slurry with a low temperature exhibits noticeable damage,which is mainly due to the poor coating performance and the serious expansion and contraction of wax pattern at low temperatures.The second layer shell material(SiO_(2),Al_(2)O_(3))immerses into the crack area of the surface layer,contacts and reacts with the molten titanium to form surface cracks and holes in the castings.With the increase of the temperature of surface layer slurry,the damage to the shell surface tends to weaken,and the composition of the shell molds'surface becomes more uniform with less impurities.The results show that the surface layer slurry at 22℃is evenly coated on the surface of the wax patterns with appropriate thickness,and there is no surface shell mold rupture caused by sliding slurry after sand leaching.The surface layer slurry temperature is consistent with the wax pattern temperature and the workshop temperature,so there is no damage of the surface layer shell caused by expansion and contraction.Therefore,the shell mold prepared by the surface layer slurry at this temperature has good integrity,isolating the contact between the low inert shell material and the titanium liquid effectively,and the ZTC4 titanium alloy cylinder casting prepared by this shell mold is smooth,without cracks and holes.展开更多
The application of liquid core reduction(LCR)technology in thin slab continuous casting can refine the internal microstruc-tures of slabs and improve their production efficiency.To avoid crack risks caused by large de...The application of liquid core reduction(LCR)technology in thin slab continuous casting can refine the internal microstruc-tures of slabs and improve their production efficiency.To avoid crack risks caused by large deformation during the LCR process and to minimize the thickness of the slab in bending segments,the maximum theoretical reduction amount and the corresponding reduction scheme for the LCR process must be determined.With SPA-H weathering steel as a specific research steel grade,the distributions of tem-perature and deformation fields of a slab with the LCR process were analyzed using a three-dimensional thermal-mechanical finite ele-ment model.High-temperature tensile tests were designed to determine the critical strain of corner crack propagation and intermediate crack initiation with various strain rates and temperatures,and a prediction model of the critical strain for two typical cracks,combining the effects of strain rate and temperature,was proposed by incorporating the Zener-Hollomon parameter.The crack risks with different LCR schemes were calculated using the crack risk prediction model,and the maximum theoretical reduction amount for the SPA-H slab with a transverse section of 145 mm×1600 mm was 41.8 mm,with corresponding reduction amounts for Segment 0 to Segment 4 of 15.8,7.3,6.5,6.4,and 5.8 mm,respectively.展开更多
Purpose–The precast concrete slab track(PST)has advantages of fewer maintenance frequencies,better smooth rides and structural stability,which has been widely applied in urban rail transit.Precise positioning of prec...Purpose–The precast concrete slab track(PST)has advantages of fewer maintenance frequencies,better smooth rides and structural stability,which has been widely applied in urban rail transit.Precise positioning of precast concrete slab(PCS)is vital for keeping the initial track regularity.However,the cast-in-place process of the self-compacting concrete(SCC)filling layer generally causes a large deformation of PCS due to the water-hammer effect of flowing SCC,even cracking of PCS.Currently,the buoyancy characteristic and influencing factors of PCS during the SCC casting process have not been thoroughly studied in urban rail transit.Design/methodology/approach–In this work,a Computational Fluid Dynamics(CFD)model is established to calculate the buoyancy of PCS caused by the flowing SCC.The main influencing factors,including the inlet speed and flowability of SCC,have been analyzed and discussed.A new structural optimization scheme has been proposed for PST to reduce the buoyancy caused by the flowing SCC.Findings–The simulation and field test results showed that the buoyancy and deformation of PCS decreased obviously after adopting the new scheme.Originality/value–The findings of this study can provide guidance for the control of the deformation of PCS during the SCC construction process.展开更多
基金supported by the National Sci-ence and Technology Major Project of China(No.J2019-VI-0004-0117)the National Natural Science Foundation of China(Nos.52071205 and 51821001)+2 种基金the Aeronautical Science Fund of China(No.2023Z053057003)the Science and Technology Commission of Shanghai Municipality,China(No.23ZR1428800)the Shanghai Industrial Collaborative Innovation Project(No.XTCX-KJ-2022-41).
文摘Counter-gravity casting(CGC)is a widely adopted material processing technique in metals due to its notable benefits,including enhanced filling behavior,reduced defect occurrence,and elevated mechani-cal properties.It plays a pivotal role in fabricating intricate,high-quality components.After its inception in the early 1900s,various CGC processes have emerged,such as low-pressure,counter-pressure,vac-uum suction,and adjusted pressure casting,which are explored in this discourse with an eye toward further advancements.Despite CGC’s superiority over traditional gravity casting and other manufacturing methodologies,specific issues and constraints persist within CGC.This paper endeavors to provide a com-prehensive overview of the historical progression of CGC,its recent developments,and the associated re-search aspects,encompassing topics like filling processes,solidification,microstructural transformations,and the resultant mechanical properties of the fabricated products.Additionally,this paper offers insights into the future challenges and opportunities of CGC.
基金financially supported by the National Natural Science Foundation of China(No.51375391)the Xi’an Municipal Science and Technology Bureau in China(No.CX12180(5))
文摘To investigate the influence of Centrifugal Counter-gravity Casting(C3) process on the solidification microstructure and mechanical properties of the casting, A357 aluminum alloy samples were produced by different process conditions under C3. The results show that C3 has better feeding capacity compared with the vacuum suction casting; and that the mechanical vibration and the convection of melts formed at the centrifugal rotation stage suppress the growth of dendrites, subsequently resulting in the refinement of grains and the improvement of mechanical properties, density and hardness. A finer grain and higher strength can be obtained in the A357 alloy by increasing centrifugal radius and rotational speed. However, casting defects will appear near the rotational axis and the mechanical properties will decrease once the rotational speed exceeds 150 r·min-1.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.3102014JCQ01026)the Program of Introducing Talents of Discipline to Universities(Grant No.B08040)
文摘The cast Ti-6Al-4V alloy bars with different section sizes were fabricated by investment casting at counter-gravity condition with the mold temperatures of 300 ℃ and 650 ℃, respectively. The microstructure of the alloy was observed by means of OM and SEM, and the effect of mold temperature and casting dimension on tensile properties was studied. Results show that equiaxed grains are obtained regardless of the casting dimension. 13 grain size tends to increase with an increase in mold temperature. Hot isostatic pressing of the alloy was carried out for tensile properties＇ comparison. Room temperature tensile test results show that Ti-6Al-4V alloy produced via counter-gravity casting has good balance of strength and ductility after hot isostatic pressing （HIP）. The alloy shows higher ductility due to the elimination of porosity. In both cast and HIP status, the tensile strength is inclined to decrease with an increase in mold temperature, while the ductility is prone to slightly increase. Both the strength and ductility tend to decrease with an increase in the casting dimension.
基金supported by the National Natural Science Foundation of China (Grant No. 5186504)the University Science Foundation for Young Science and Technology Talents in Inner Mongolia Autonomous Region of China (Grant No. NJYT22078)+2 种基金the Basic Scientific Research Expenses Program of Universities directly under Inner Mongolia Autonomous Region (Grant No. JY20220059)the Inner Mongolia Autonomous Region ‘Grassland Talent’ project Young Innovative Talent Training Program Level ⅠBasic Research Expenses of Universities directly under the Inner Mongolia Autonomous Region (Grant No. ZTY2023040)。
文摘To develop a suitable production process for fiber reinforced investment casting shell mold,three methods were studied:the traditional method(M_(1)),the method of adding fiber into silica sol with mechanical stirring and ultrasonic agitation(M_(2)),and the method of adding fiber into slurry with mechanical stirring and ultrasonic agitation for durations of 3,15,30,and 45 min(M_(3)).The bending strength,high-temperature self-load deformation,and thermal conductivity of the shell molds were investigated.The results reveal that the enhancement of fiber dispersion through ultrasonic agitation improves the comprehensive performance of the shell molds.The maximum green bending strength of the shell mold by M_(2) reaches 3.29 MPa,which is 29% higher than that of the shell mold prepared by M_(1).Moreover,the high-temperature self-load deformation of the shell mold is reduced from 0.62% to 0.44%.In addition,simultaneous ultrasonic agitation and mechanical stirring effectively shorten the slurry preparation time while maintaining comparable levels of fiber dispersion.With the process M_(3)-45 min,the fillers are uniformly dispersed in the slurry,and the fired bending strength and the high-temperature self-load deformation reach 6.25 MPa and 0.41%,respectively.Therefore,the proposed ultrasonic agitation route is promising for the fabrication of fiber-reinforced shell molds with excellent fibers dispersion.
基金supported by the Key R&D Projects in Heilongjiang Province(GA23A901)。
文摘Al-Si-Cu-Mg alloy demonstrates a significant age-hardening effect,with its mechanical properties tunable by optimizing the aging parameters.To enhance this effect,the as-cast Al-8.5Si-2Cu-0.9Mg alloy was subjected to either single-stage aging at temperatures of 150℃,175℃,200℃,and 225℃for 0.5 h to 20 h;or double-stage aging:involving a first-stage aging treatment at 120℃for 1 h,3 h,5 h,or 7 h,followed by a second-stage aging treatment at 175℃ for 0.5 h to 20 h.The microstructure and mechanical properties were evaluated for samples aged at 175℃/7 h,175℃/10 h,120℃/5 h+175℃/5 h,and 120℃/5 h+175℃/8 h.XRD analysis reveals that the as-cast Al-8.5Si-2Cu-0.9Mg alloy consists of theα-Al,Si,θ-Al_(2)Cu,and Q-Al_(5)Cu_(2)Mg_8Si_6phases.The aging kinetics exhibit a double-peak behavior in both single-stage and double-stage aging processes.Under single-stage aging at 175℃/x h and double-stage aging(120℃/5 h+175℃/x h),the precipitates'size at the first peak is smaller than that at the second peak.Compared with single-stage aging(175℃/7 h),double-stage aging(120℃/5 h+175℃/5 h)produces a finer precipitate in the alloy.Theoretical calculations indicate that the number density and nucleation rate of both the Al_(5)Cu_(2)Mg_8Si_6 and Al_(2)Cu phases are higher during the double-stage aging(120℃/5 h+175℃/5 h)than those during the single-stage aging(175℃/7 h).Additionally,tensile tests at both room temperature and 250℃demonstrate that double-stage aging(120℃/5 h+175℃/5 h)significantly improves the mechanical properties of the alloy compared to single-stage aging(175℃/7 h),suggesting that double-stage aging is more effective for enhancing mechanical properties for this alloy.
基金financially supported by the National Natural Science Foundation of China(No.52303063)Hubei Provincial Department of Education Guided Scientific Research Project(No.B2024056)。
文摘Airless tires are essential for enhancing the safety,reliability,and convenience of maintenance of electric bicycles.Polyurethane(PU)is considered a promising candidate for such applications owing to its versatile properties.However,their use is limited by insufficient heat resistance and excessive dynamic heat generation under cyclic loading.In this study,star-shaped trifunctional polypropylene glycerol(PPG3)was incorporated into conventional poly(tetramethylene glycol)(PTMG)and 4,4'-methylenediphenyl diisocyanate(MDI)-based systems to construct microporous star-shaped casting polyurethanes(SCPU),with water serving as a green foaming agent.Unlike conventional small-molecule trifunctional crosslinkers that create junctions within hard segment domains,PPG3 introduces long flexible arms between the hard segments,anchoring the crosslinking points at its molecular core.The large steric hindrance of PPG3 effectively suppresses soft segment crystallization and lowers the degree of microphase separation,whereas the crosslinked network restricts chain mobility,thereby reducing dynamic heat generation.These structural features also enhance the heat resistance,yielding a softening temperature of 183℃,which is 30.9%higher than that of polyurethane without PPG3.When applied to airless tires by casting SCPU into rubber treads,the fabricated hybrid airless tires achieved a rolling distance of over 3000 km under a load of 65 kg at 25km/h without structural failure,satisfying practical performance requirements.This strategy offers a simple,solvent-free,and environmentally friendly process,underscoring the potential of SCPU for scalable production of high-performance airless tires.
基金financially supported by the Natural Science Foundation of Liaoning Province of China(2022-MS-109)the Key Research and Development Program of Liaoning Province(2023JH2/101800045)the Ministry of Science and Technology of the Peoples Republic of China(ZZ2021006).
文摘The Cu-12Fe alloy has attracted significant attention due to its excellent electrical conductivity and electromagnetic shielding capability,high strength,cost-effectiveness,and recyclability.In the present work,the Cu-12Fe alloy strip with the thickness of 2.4 mm was successfully produced by twin-roll strip casting.The microstructure and properties of the Cu-12Fe alloy were tailored by cold rolling and aging treatment.The tensile strength of the as-cast strip is approximately 328 MPa and its elongation is 25%.The Fe phase randomly dispersed in the matrix,and the average size of Fe-rich phase is 2μm.Besides,enrichment of Fe phase is observed in the central layer of the strip,results in the formation of the“sandwich structure”.Moreover,the as-cast strip of Cu-12Fe was directly cold-rolled from 2.4 to 0.12 mm.The directly cold-rolled sample after aging at 450℃for 16 h(ProcessⅠ)shows excellent electrical conductivity of 69.5%IACS,the tensile strength and elongation are 513 MPa and 3.8%,the saturation magnetic flux density is 20.1 emu·g^(-1),and the coercive force is 25.2 Oe.In ProcessⅡ,the as-cast strip firstly cold-rolled to 1.2 mm,then aged at 500℃for 1.5 h,followed by cold rolling to 0.12 mm,finally aged at 450℃for 16 h.The sample after ProcessⅡshows the electrical conductivity of 66.3%IACS,the tensile strength of 533 MPa,an elongation of 3.5%,saturation magnetic flux density of 21.4 emu·g^(-1),and the coercive force of 22.3 Oe.
基金supported by the National Natural Science Foundation of China(Nos.52422408 and 52171031)the Liaoning Xingliao Talents-Top-notch Young Talents Project(No.XLYC2203064)+1 种基金the Excellent Youth Fund of Liaoning Natural Science Foundation(No.2023JH3/10200001)the Fundamental Research Funds for the Central Universities(No.N2425004).
文摘The transient phenomena of re-oxidation and slag entrapment occurring in the tundish during the ladle change-over process have been proven detrimental to clean steel production.Therefore,an unsteady three-phase turbulence model,coupling velocity,temperature,and phase field was established to study the effect of the ladle shroud immersion depth on the slag eye formation,slag entrainment,slag dragging,air dragging,and flow characteristics during the ladle change-over process of a two-strand tundish.The results showed that reducing the immersion depth decreases the high-velocity region area under the slag layer in the quasi-steady process.During the emptying stage,as the molten bath level gradually decreases,the outlet temperature exhibits a trend of initially decreasing and subsequently increasing across all three shroud immersion depths.However,under a 210 mm shroud immersion depth,molten slag and air are dragged into the shroud,forming slag droplets and causing significant fluctuations,with a maximum scalar velocity of 0.0764 m/s at the monitoring point.In the filling stage,air and molten slag are dragged into the molten bath,forming bubbles and slag droplets at an immersion depth of 210 mm.Bubbles are observed within the molten slag layer,which can readily cause an emulsification phenomenon,making it easier to be dragged as slag droplets.Additionally,the slag eye area measured under 210 mm immersion depth at 45 s is 0.303 m^(2),while the maximum scalar velocity of 2.4259 m/s is detected at 12 s.At an immersion depth of 360 mm,the average area of the slag eye is minimized to 0.06268 m2,with corresponding variances of 0.006753,representing the optimal immersion depth.
基金supported by the National Natural Science Foundation of China(No.52274318).
文摘A full-sectional microstructure characterization method was developed to investigate the formation of coarse slag rims during the continuous casting of hypo-peritectic steel.The cross-sectional microstructural analysis of typical slag rims for two highly crystalline powders revealed that their formation was primarily driven by the solidification of the liquid slag.Distinct differences were observed in the microstructures of slag rims from the two powders.Powder A(characterized by a higher breaking temperature and viscosity)displayed alternating lamellar microstructures of coarse and fine phases,with the coarse phases composed of akermanite-gehlenite transition phases.In contrast,powder B(with a lower breaking temperature and viscosity)predominantly comprised regular akermanite-gehlenite crystals interspersed with a certain amount of glassy phases.Numerical simulations of a three-phase fluid flow coupled with heat transfer indicate that slag rim formation correlates with mold oscillation.Solidification of the liquid slag at the slag rim front predominantly occurs during the negative stroke of the mold oscillation.The average heating rate during the ascending stage of the mold reaches approximately 100 K·s^(−1),whereas the average cooling rate during the descending stage attains 400 K·s^(−1).This temperature variation leads to the formation of lamellar microstructures,whereas the ascending stage promotes the formation of coarse structures and thicker slag rims.Based on the powder properties,two distinct formation pathways exist for highly crystalline mold powders.For the powders with a higher breaking temperature,higher viscosity,and narrower solidification range(powder A),coarse microstructures and thicker slag rims were preferentially formed.For powders with lower breaking temperature and viscosity and wider solidification ranges(powder B),the liquid slag resisted rapid solidification,and the extended mushy zone allowed the partial liquid slag to persist at the slag rim front,promoting the formation of a thin slag rim.This study enhances the understanding of slag rim formation in highly crystalline mold powders and provides critical insights into the control of longitudinal surface cracks in hypo-peritectic steel.
基金funded by Multimedia University,Cyberjaya,Selangor,Malaysia(Grant Number:PostDoc(MMUI/240029)).
文摘Manual inspection of onba earing casting defects is not realistic and unreliable,particularly in the case of some micro-level anomalies which lead to major defects on a large scale.To address these challenges,we propose BearFusionNet,an attention-based deep learning architecture with multi-stream,which merges both DenseNet201 and MobileNetV2 for feature extraction with a classification head inspired by VGG19.This hybrid design,figuratively beaming from one layer to another,extracts the enormity of representations on different scales,backed by a prepreprocessing pipeline that brings defect saliency to the fore through contrast adjustment,denoising,and edge detection.The use of multi-head self-attention enhances feature fusion,enabling the model to capture both large and small spatial features.BearFusionNet achieves an accuracy of 99.66%and Cohen’s kappa score of 0.9929 in Kaggle’s Real-life Industrial Casting Defects dataset.Both McNemar’s and Wilcoxon signed-rank statistical tests,as well as fivefold cross-validation,are employed to assess the robustness of our proposed model.To interpret the model,we adopt Grad-Cam visualizations,which are the state of the art standard.Furthermore,we deploy BearFusionNet as a webbased system for near real-time inference(5-6 s per prediction),which enables the quickest yet accurate detection with visual explanations.Overall,BearFusionNet is an interpretable,accurate,and deployable solution that can automatically detect casting defects,leading to significant advances in the innovative industrial environment.
基金the National Key Research and Development Program of China(Grant No.2022YFB3404201)the National Natural Science Foundation of China(Grant Nos.52175335,52405342)+1 种基金the Natural Science Foundation Joint Foundation of Liaoning province(Grant No.2023-B SB A-108)the Fundamental Research Funds for the Central Universities(Grant No.N2402005)。
文摘The effects of the high pressure die casting(HPDC)processes on porosity,microstructure,and mechanical properties of heat-treatment-free aluminum silicon(Al-Si)alloys have long been a focal point in automotive die-casting research.In this work,the combined effect of shot sleeve materials and slow shot speeds on porosity,microstructure and mechanical properties of a newly designed HPDC Al-Si alloy was investigated.Results show that employing a ceramic shot sleeve or increasing the slow shot speed significantly reduces both the average size and area fraction of externally solidified crystals(ESCs),as well as the average pore size and volume fraction.When the slow shot speed is increased from 0.05 m·s^(-1)to 0.1 m·s^(-1),the pore volume fraction decreases by 10.2%in steel-shot-sleeve samples,compared to a substantial 67.1%reduction in ceramic-shot-sleeve samples.At a slow shot speed of 0.1 m·s^(-1),castings produced with a ceramic shot sleeve exhibit superior mechanical properties:8.3%higher yield strength,17.4%greater tensile strength,and an 81.4%improvement in elongation,relative to those from a steel shot sleeve.These findings provide valuable insights for minimizing porosity and coarse ESCs in die castings,offering promising potential for broader industrial applications.
基金financially supported by the National Key Research and Development Program of China (2022YFB3706802)。
文摘Automation and intelligence have become the primary trends in the design of investment casting processes.However,the design of gating and riser systems still lacks precise quantitative evaluation criteria.Numerical simulation plays a significant role in quantitatively evaluating current processes and making targeted improvements,but its limitations lie in the inability to dynamically reflect the formation outcomes of castings under varying process conditions,making real-time adjustments to gating and riser designs challenging.In this study,an automated design model for gating and riser systems based on integrated parametric 3D modeling-simulation framework is proposed,which enhances the flexibility and usability of evaluating the casting process by simulation.Firstly,geometric feature extraction technology is employed to obtain the geometric information of the target casting.Based on this information,an automated design framework for gating and riser systems is established,incorporating multiple structural parameters for real-time process control.Subsequently,the simulation results for various structural parameters are analyzed,and the influence of these parameters on casting formation is thoroughly investigated.Finally,the optimal design scheme is generated and validated through experimental verification.Simulation analysis and experimental results show that using a larger gate neck(24 mm in side length) and external risers promotes a more uniform temperature distribution and a more stable flow state,effectively eliminating shrinkage cavities and enhancing process yield by 15%.
基金support from the National Natural Science Foundation of China(Grant Nos.52174313 and 52304350)thank all members of the Hebei High Quality Steel Continuous Casting Engineering Technology Research Center at North China University of Science and Technology,Tangshan,China.
文摘The flow behavior of molten steel in the thin slab mold under high casting speed conditions was investigated,with a focus on the multi-mode continuous casting and rolling mold.A steel-slag two-phase flow model was established using large eddy simulation,the volume of fluid,and magnetohydrodynamics methods through numerical simulation.The maximum flow velocity and wave height at the steel-slag interface within the mold are critical evaluation criteria for analyzing asymmetric flow under varying casting speeds and electromagnetic braking.The results indicate that the asymmetric flows within the mold do not occur synchronously.The severity of the asymmetric flow correlates with the velocity difference across the steel-slag interface.A greater biased flow prolongs the time required to revert to a steady state.When the magnetic field intensity is set to 0.24 T and the magnetic pole position is at 390 mm from the steel-slag interface,this configuration can reduce the velocity of the steel-slag interface,thereby mitigating the asymmetric flow.Additionally,it can diminish the velocity,impact depth,and impact intensity on the narrow face of the jet,thus improving the distribution of velocity and turbulent kinetic energy within the mold.This configuration prolongs the time required for the steel-slag interface to transition from a stable state to its maximum velocity and shortens the time for the interface to return to stability from an unstable state.Moreover,it ensures the positional stability of the steel-slag interface,confining its position within−3 mm.
基金supported by the National Natural Science Foundation of China(No.52474396 and 52175284)the National Key Research and Development Program of China(Grant No.2022YFB3404201)。
文摘In order to investigate the effect of die wall thickness on morphologies of defect band,a stepped mold with a wall thickness of 5 mm,4 mm,3 mm,2 mm,and 1 mm was designed to carry out high pressure die casting experiments with AlSi10 MgMn alloy.For castings with wall thickness of 2-4 mm,the ratio of the mean defect band width(w)and mean grain size(d)in the defect band(w/d)ranges 7-18,while it increases to 24.47 for the 5 mm-thick casting.This difference is related with the filling speed and the distribution of externally solidified crystals(ESCs).The mold flow analysis indicates that the filling speed decreases from 25.41 m·s^(-1)to 11.07 m·s^(-1)when wall thickness increases from 2 mm to 5 mm.Due to the decreasing filling speed along the wall thickness,ESCs gradually diffuse from the center to the defect band,which keep the shear strength in the defect band at a high-level during filling.Meanwhile,the shear strength generated during the filling also decreases as the shear rate drops.Finally,the defect bands in the 5 mm-thick region become widen and indistinct,and the porosity is as high as 5.25%.
基金Project (51074185) supported by the National Natural Science Foundation of ChinaProjects (CX2009B037, CX2010B120) supported by Doctor Innovative Program of Hunan Province, China
文摘A novel counter-gravity infiltration casting device and corresponding fabricating process for producing open-celled aluminum foams were presented. The experimental results show that defects such as insufficient or excessive infiltrating can hardly be found in the foam samples prepared by counter-gravity infiltration casting. The foam materials exhibit excellent mechanical properties. The void content strongly affects the mechanical properties of aluminum foams. The yield stress and plateau stress significantly increase with the decrease of void content. Raising pre-heating temperature and increasing packing pressure are effective to lower the void content in aluminum foams.
基金National Natural Science Foundation of China(52201054,52175368)National Science and Technology Major Projects(J2019-VI-0018-0133)+2 种基金Liaoning Provincial Science and Technology Program(2023-BS-019,2023-MS-020)National Key R&D Program of China(2021YFB3700401)Key Specialized Research and Development Break-Through-Unveiling and Commanding the Special Project Program in Liaoning Province(2021JH15)。
文摘The impact of casting defects on the weldability of K4951 superalloy was investigated using tungsten inert gas(TIG)welding.The as-cast K4951 superalloy samples with prefabricated U-shaped grooves of varying depths and widths were TIG welded,and the microstructures,cracks morphology,and precipitated phases were analyzed using optical microscope,scanning electron microscope,transmission electron microscope,and energy dispersive X-ray spectrometer.The results reveal that the dimensions of casting defects significantly affect the weldability of K4951.Deep defects(greater than 2 mm)lead to rapid crack propagation,while wider defects can moderate the propagation process of cracks.Elemental segregation and the formation of precipitated phases,such as MC carbides,are observed in the fusion zone,contributing to welding cracks.An optimal groove aspect ratio(depth-to-width)between 0.2 and 0.5 minimizes crack formation tendency and enhances tensile strength,resulting in a mixed brittle-ductile fracture mode of joint after high-temperature tensile testing.
基金the financial support of the Natural Science Foundation of Hubei Province,China (Grant No.2022CFB770)。
文摘In the foundry industries,process design has traditionally relied on manuals and complex theoretical calculations.With the advent of 3D design in casting,computer-aided design(CAD)has been applied to integrate the features of casting process,thereby expanding the scope of design options.These technologies use parametric model design techniques for rapid component creation and use databases to access standard process parameters and design specifications.However,3D models are currently still created through inputting or calling parameters,which requires numerous verifications through calculations to ensure the design rationality.This process may be significantly slowed down due to repetitive modifications and extended design time.As a result,there are increasingly urgent demands for a real-time verification mechanism to address this issue.Therefore,this study proposed a novel closed-loop model and software development method that integrated contextual design with real-time verification,dynamically verifying relevant rules for designing 3D casting components.Additionally,the study analyzed three typical closed-loop scenarios of agile design in an independent developed intelligent casting process system.It is believed that foundry industries can potentially benefit from favorably reduced design cycles to yield an enhanced competitive product market.
文摘In this work,the influences of surface layer slurry at different temperatures(10℃,14℃,18℃,22℃)on wax patterns deformation,shrinkage,slurry coating characteristics,and the surface quality of the casting were investigated by using a single factor variable method.The surface morphologies of the shell molds produced by different temperatures of the surface(first)layer slurries were observed via electron microscopy.Furthermore,the microscopic composition of these shell molds was obtained by EDS,and the osmotic effect of the slurry on the wax patterns at different temperatures was also assessed by the PZ-200 Contact Angle detector.The forming reasons for the surface cracks and holes of thick and large ZTC4 titanium alloy by investment casting were analyzed.The experimental results show that the surface of the shell molds prepared by the surface layer slurry with a low temperature exhibits noticeable damage,which is mainly due to the poor coating performance and the serious expansion and contraction of wax pattern at low temperatures.The second layer shell material(SiO_(2),Al_(2)O_(3))immerses into the crack area of the surface layer,contacts and reacts with the molten titanium to form surface cracks and holes in the castings.With the increase of the temperature of surface layer slurry,the damage to the shell surface tends to weaken,and the composition of the shell molds'surface becomes more uniform with less impurities.The results show that the surface layer slurry at 22℃is evenly coated on the surface of the wax patterns with appropriate thickness,and there is no surface shell mold rupture caused by sliding slurry after sand leaching.The surface layer slurry temperature is consistent with the wax pattern temperature and the workshop temperature,so there is no damage of the surface layer shell caused by expansion and contraction.Therefore,the shell mold prepared by the surface layer slurry at this temperature has good integrity,isolating the contact between the low inert shell material and the titanium liquid effectively,and the ZTC4 titanium alloy cylinder casting prepared by this shell mold is smooth,without cracks and holes.
基金supported by the National Natural Science Foundation of China(No.52474355)the Liaoning Province Science and Technology Plan Joint Program(Key Research and Development Program Project),China(Nos.2022JH25/10200003 and 2023JH2/101800058).
文摘The application of liquid core reduction(LCR)technology in thin slab continuous casting can refine the internal microstruc-tures of slabs and improve their production efficiency.To avoid crack risks caused by large deformation during the LCR process and to minimize the thickness of the slab in bending segments,the maximum theoretical reduction amount and the corresponding reduction scheme for the LCR process must be determined.With SPA-H weathering steel as a specific research steel grade,the distributions of tem-perature and deformation fields of a slab with the LCR process were analyzed using a three-dimensional thermal-mechanical finite ele-ment model.High-temperature tensile tests were designed to determine the critical strain of corner crack propagation and intermediate crack initiation with various strain rates and temperatures,and a prediction model of the critical strain for two typical cracks,combining the effects of strain rate and temperature,was proposed by incorporating the Zener-Hollomon parameter.The crack risks with different LCR schemes were calculated using the crack risk prediction model,and the maximum theoretical reduction amount for the SPA-H slab with a transverse section of 145 mm×1600 mm was 41.8 mm,with corresponding reduction amounts for Segment 0 to Segment 4 of 15.8,7.3,6.5,6.4,and 5.8 mm,respectively.
文摘Purpose–The precast concrete slab track(PST)has advantages of fewer maintenance frequencies,better smooth rides and structural stability,which has been widely applied in urban rail transit.Precise positioning of precast concrete slab(PCS)is vital for keeping the initial track regularity.However,the cast-in-place process of the self-compacting concrete(SCC)filling layer generally causes a large deformation of PCS due to the water-hammer effect of flowing SCC,even cracking of PCS.Currently,the buoyancy characteristic and influencing factors of PCS during the SCC casting process have not been thoroughly studied in urban rail transit.Design/methodology/approach–In this work,a Computational Fluid Dynamics(CFD)model is established to calculate the buoyancy of PCS caused by the flowing SCC.The main influencing factors,including the inlet speed and flowability of SCC,have been analyzed and discussed.A new structural optimization scheme has been proposed for PST to reduce the buoyancy caused by the flowing SCC.Findings–The simulation and field test results showed that the buoyancy and deformation of PCS decreased obviously after adopting the new scheme.Originality/value–The findings of this study can provide guidance for the control of the deformation of PCS during the SCC construction process.
