Electron beam fuse deposition(EBFD)is a rapidly developed metal 3D printing technology in recent years.The EBFD technology was used to print 304 stainless steel materials.The effects of different accelerating voltages in the process of EBFD on the morphology,density,microstructure and mechanical properties of the forming products were compared.The results show that when the accelerating voltage is 50 kV,there are a few austenite grains in the microstructure.When the accelerating voltage is increased to 60 kV,the austenite grain boundary is completely formed,and the growth continues with the increase of the accelerating voltage.When the accelerating voltage is 60 kV,the comprehensive mechanical properties are the best,the anisotropy is the weakest,and the fracture is ductile fracture.
Air entrainment defect is a common type of defect in the casting process, which will seriously affect the quality of the casting. Numerical simulation technology can predict the occurrence of casting defects according to the evolution law of liquid metal in the process of fill ing and solidification. The simulation of air entrainment process is a hot and difficult issue in the field of numerical simulation. The evolution law of air entrainment and the tracking of induced bubbles in the process of metal filling are still lacking. So is the quantitative prediction of trained gas. In this paper, based on the numerical simulation software of Inte CAST, this paper proposes an algorithm for air entrainment search and tracking, which is used to develop a quantitative prediction system for air entrainment. The feasibility of the system is verified through the simulation calculation of the typical test pieces of the air entrainment and the prediction of air entrainment defects of the casting in the process of filling is obtained through the simulation calculation of the actual casting, which can provide a certain guiding role for the optimization of the process in the production practice.
In order to improve the reliability and stability of complex joints hybrid welding, this paper establishes an arc numerical analysis model, studies the T-joint high-frequency rotating laser-GMAW hybrid welding arc physical characteristics, and expounds the effects of laser rotation frequency along with rotation radius on arc plasma temperature, velocity, and metal vapor concentration field distribution. The research results show: the arc is more likely to start on the bottom plate and vertical plate surfaces, and the current density at the angle between the plates decreases significantly; temperature drops at the hybrid welding arc tail, the current effective distribution radius was reduced, and current density was more concentrated; the laser beam rotation frequency increases, the eruption speed of the metal vapor ejected from the keyhole decreases, while the meeting height of arc plasma and laser-induced metal vapor decreases; and, with an increase in rotation radius, the laser rotation speed increases accordingly. At the same rotation frequency, the injected metal vapor kinetic energy and rising height are reduced.
Mechanical vibration in the high-temperature forging production line often causes large forging thermal dimensional measurement error in the detection task, so a vibration point cloud compensation method based on an acceleration sensor is proposed in this study. First, the vibration signal is obtained through the built-in acceleration sensor in the laser camera. After the acceleration of the camera vibration is detected, the displacement of the camera in three directions is solved by secondary integration. Subsequently, the coordinate value of the corresponding point is obtained by the rotation matrix transformation so as to compensate and correct the point cloud deviation caused by the camera vibration. Finally, the forging point cloud is matched using the surface matching algorithm in Halcon. An automatic forging production line for wheel hubs has been built, and the key dimensions of high-temperature forging products have been measured online using the developed method. After the forging point cloud is compensated, the average measurement error of dimensions is reduced from ±0.9 mm to ±0.1 mm, and the standard deviation is reduced from 0.52 mm to 0.056 mm. Using the vibration point cloud compensation method based on the acceleration sensor, as well as using silica aerogel insulation, vibration structural parts, heat insulation and constant temperature, a blue-violet 3D laser camera, and other measures, the dimensional detection accuracy of high-temperature forgings in the forging production line can be improved, and the instability of dimensional detection can be reduced.
目的 实现工业金属导管数字化快速制造,提高导管制造质量,缩短装备研制周期.方法 采用基于知识工程驱动的三维数字化设计技术、人工智能技术、计算机仿真技术,开发导管数字化制造集成系统,该系统主要包括导管数字化制造子系统、拼装夹具数字化设计子系统和系统管理子系统,进行导管三维建模、工艺设计与仿真、拼装夹具设计和导管数字化检测,实现金属导管数字化快速制造.结果 实现了多种装备上千种不同类型导管的数字化快速制造,提高了生产效率,导管数模的利用率达 100％,导管试装合格率达 78％,制造周期缩短了 2 个月,生产成本显著降低.
The work aims to solve the problems of cracks,pores and other defects in 30CrMnSi during CO2 gas shielded welding due to poor weldability.A rigid restraint welding crack test was conducted to simulate the restraint of the base metal during the actual welding process of the rear box section of a certain aircraft,and the formation mechanism of the welding crack was determined according to the types and forms of welding cracks.At the same time,the porosity in the weld was analyzed.Cold cracks were easy to occur in the joint.Under high stress conditions,stress concentration occurred at the tip of the mi-cro-crack,and finally a cold crack penetrating the weld was formed under the effect of hydrogen.TIG welding with relatively concentrated energy density is considered to replace the original CO2 gas shielded welding,which is also conducive to reducing or eliminating porosity defects.The structural design and welding sequence can be optimized to reduce stress concentration,thereby reducing the effect of welding heat on crack sensitivity.At the same time,welding should be avoided at corners or posi-tions with poor welding accessibility,so as to effectively reduce porosity.
Selective laser melting(SLM)is the most accurate metal additive manufacturing process for manufacturing metal parts with complex geometric shapes.316L stainless steel has a face-centered cubic structure,which usually does not undergo a solid phase transition when cooling from the molten state to room temperature.Based on this property,316L stainless steel has become the most widely used metal material in SLM.Compared with the traditional process,although this process can produce high-density and high-performance parts,it can not avoid the appearance of holes,voids and other defects,as well as mechanical properties differences and the need for post-processing.In order to solve these problems,it is necessary to reveal the effect law of SLM manufacturing parameters on the performance.The research status of raw powder,process parameters and post-proc-essing of SLM-316L before and during the preparation process was reviewed.The effect mechanism of powder quality index and powder process on stainless steel parts was discussed.Secondly,the research status of the effect of laser input power,scan-ning speed and other process parameters on the performance of the parts was summarized.Finally,the effects of mechanical wear treatment,electrolytic polishing and other post-processing methods on the performance of the parts were briefly summa-rized.The academic point of view of predicting the mechanical properties of stainless steel forming parts by SLM affecting fac-tors is expounded,which provides some references for obtaining high quality parts and promoting the practical application of stainless steel materials.
The work aims to study the hot metal gas forming(HMGF)of B1800HS tube and explore the feasibility and laws of HMGF of characteristic variable diameter tube parts,so as to provide reference and support for further research on HMGF of ultra-high strength steel tube and the promotion of applications in engineering.ABAQUS finite element simulation analysis and experimental comparison were adopted to study the HMGF characteristics of 1 800 MPa ultra-high strength steel variable di-ameter tube.Through finite element analysis,the effects of temperature(700,800,900℃),pressurization rate(1,3,5 MPa/s),and bulging pressure(12,15,18 MPa)on the forming law of variable diameter tube were studied.The effect of sensitive pa-rameters on the size accuracy,strength distribution and thickness change of variable diameter tube sample was studied.Increas-ing the forming temperature,pressurization rate and bulging pressure could improve the clamping accuracy and tensile strength of variable diameter tube.At a forming temperature of 900℃,the tensile strength of the variable diameter tube could reach the level of 1 800 MPa,and the effect of the pressurization rate and bulging pressure was relatively small.The variable diameter tube was evenly distributed along the circumferential thickness,and the parts were free of obvious thickening and excessive thinning defects.The application of HMGF to 1 800 MPa variable diameter tube is feasible.By optimizing process parameters,the forming accuracy and strength of parts can be effectively improved,which provides basis and reference for the HMGF de-velopment of typical ultra-high strength steel tubes.
The work aims to study the CMT additive single channel forming quality and dimension prediction model for 5556 aluminum alloy under different parameters.The residual height,weld width,forming height,and forming width of the CMT additive sample section were measured by the vernier caliper and steel ruler.SPSS,Excel and Origin were used to estab-lish and verify the dimension prediction model.With the welding current increasing from 60 A to 140 A,the overall trend of re-sidual height and weld width of the monolayer single channel additive sample increased.The increase speed of the residual height was much smaller than that of the weld width.With the welding speed increasing from 300 mm/min to 1 100 mm/min,the weld width and residual height showed a declining trend.However,when the welding speed exceeded 700 mm/min,the change in weld width was relatively small.With the gas flow increasing from 10 L/min to 25 L/min,the change in residual height was relatively small,but the change in weld width was relatively large.With the welding speed increasing from 400 mm/min to 800 mm/min,the forming height and width of the multilayer single channel additive sample decreased.As the welding current changed from 90 A to 130 A and the interlayer residence time changed from 1 min to 5 min,the forming height and width increased.Based on the multilayer single channel additive experiment and the dimension prediction model,the weld-ing current was positively correlated with the width of the additive sample.The welding speed was negatively correlated with the width and height of the additive sample.The weld width of the monolayer single channel additive sample is mainly affected by the welding current.The residual height is mainly affected by the welding speed.Under the experimental conditions,the pa-rameters for the optimal forming quality of the monolayer single channel additive sample are welding current 100 A,welding speed 500 mm/min and gas flow 22.5 L/min.By comparing the forming width and forming height of multilayer single channel additive samples with the dimension prediction model under the same process parameters,it can be shown that the errors are both within 10%.
The work aims to investigate the change rule of martensite reverse transformation,microstructure evolution and mechanical properties of metastable austenitic stainless steel subject to cryogenic rolling at different annealing temperature.Firstly,the experimental raw material 304 austenitic stainless steel was subject to solution treatment at 1 050℃for 30 min.Then,the experimental steel was treated by cryogenic rolling under a total reduction of 65%and annealed at 600-750℃for 5 min.Finally,the microstructure and mechanical properties of the annealed steel were characterized and tested,and the micro-structure evolution and variation of mechanical properties during annealing were studied.After cryogenic rolling under a total reduction of 65%,all the austenite in the experimental steel structure could be transformed into martensite.With the increase of annealing temperature,the austenite content subject to reverse transformation increased,and the structure gradually changed from recovery structure to recrystallization structure.When the annealing temperature was 750℃,the grain size was about 420 nm.After annealing treatment,the hardness of the experimental steel decreased from 566.2HV10 under cryogenic rolling to 378.1HV10 with annealing treatment at 750℃,and the yield strength under cryogenic rolling was higher than that under solid solution.The excellent comprehensive mechanical properties of the experimental steel such as 896.5 MPa tensile strength,52.7%elongation and 47.2 GPa·%strong plastic volume were obtained after annealing at 750℃for 5 min.The submi-cron/nanometer microstructure with grain size<500 nm of the 304 austenitic stainless steel can be obtained by cryogenic rolling and annealing treatment.Comprehensive mechanical properties better than those under solid solution state can be obtained by annealing above 700℃.
The work aims to reveal the effect of welding parameters on the temperature field,displacement field,and stress field during the welding of TC4 thin plates.Based on the finite element(FEM)simulation method,Fortran language was used to define the welding heat sources and welding parameters,to simulate the TIG butt welding process of TC4 thin plates under dif-ferent welding parameters.The temperature field during the stable arc stage was a set of ellipses with the welding direction as the major axis,and there was a temperature gradient.As the welding speed increased,the peak value of the temperature field,the temperature gradient of the temperature field,the width and volume of the molten pool gradually decreased;while the impact of welding efficiency and welding current on the temperature field was exactly opposite to that of the welding speed.As the weld-ing speed increased,the maximum deformation of the thin plate gradually decreased,and the welding angular deformation and deflection deformation were gradually improved;while the effect of welding efficiency and welding current on the displacement field was exactly opposite to that of welding speed.During the stable arc stage,the residual stress at the weld position was ten-sile stress,with compressive stress on both sides.As the welding speed and welding current increased,the longitudinal residual tensile stress gradually increased,and the width of the high stress concentration zone at the weld gradually decreased;while the effect of welding efficiency on the stress field was exactly opposite to that of welding speed.Under high welding speed,medium welding efficiency,and low welding current parameters,a weld with a small pool volume and narrow pool width could be ob-tained,which was beneficial for reducing residual stress and deformation after welding.The above research results can provide certain theoretical guidance for the welding process of TC4 thin plates.
The work aims to explore the effect of electric pulse treatment(EPT)with different parameters on the tensile properties,microhardness,and microstructure of rolled 316L stainless steel.The rolled 316L stainless steel was used as the original sample,and the pulse current density flowing through the sample was adjusted.Then,the sample was treated with cur-rent of 130,170,190,260,310 A/mm2,respectively and the relationship between the pulse current density and the tensile prop-erties and microhardness of the sample was analyzed.The tensile strength and microhardness of rolled 316L stainless steel showed an increasing and then decreasing trend with the increase of pulse current density,in which the peak value was reached when the pulse current density was 170 A/mm2,and the tensile strength increased from 1 485 MPa to 1 625 MPa,and micro-hardness increased from 431HV to 473HV.The microstructure of the samples was analyzed by electron backscattering diffrac-tion,which showed that the grain size of the sample after electric pulse treatment decreased significantly compared with that of original sample,and the martensite content increased significantly compared with that of original sample.Electric pulse treat-ment could promote rapid homogenization of microstructure.Electric pulse treatment can achieve the uniform regulation of rolled 316L stainless steel microstructure in a short time,effectively improve the microstructure of rolled 316L stainless steel,reduce the rolled steel deformation weaving,and prompt the participation of austenite into martensite,so that the microstructure tends to stabilize.At the same time,it can make the rolled 316L stainless steel grain rapid refinement to achieve the effect of fine crystal strengthening,effectively improving the overall tensile strength and microhardness.
The work aims to investigate the effect of welding parameters on the macroscopic morphology of welded joints of PHS2000 hot stamping steel,to reduce welding defects with the double spot laser welding process and obtain welded joints with good morphology of PHS2000 hot stamping steel.The Trudisk 5000 dual spot laser from TRUMPF,Germany,was selected for laser welding of 2 000 MPa grade hot stamping steel.The front and back morphology and the cross-sectional welding pene-tration and depth of welded joints under different parameters were studied and analyzed with a metallurgical microscopy.Ex-perimental results showed that as the laser power from 3 500 W to 4 400 W,the welded joint was well formed,the penetration increased generally,the penetration to width ratio decreased generally.As the welding speed increased from 50 mm/min to 250 mm/min,the weld penetration and weld width basically decreased,the penetration-to-width ratio showed a decreasing trend in general.As the core raised,the formation of the back of the weld was deteriorated,and the penetration was ideal when the core was set to 55%-65%.The overall penetration-width ratio was in an ascending"W"shape.When the defocus amount was set to 0 mm,severe burn discoloration on the back of the weld and spatter on both sides of the weld were observed.However,as the defocus amount decreased to-4 mm,the burn damage was improved.In summary,this experiment reveals that the laser power and the core have significant influence on the formation of welded joints.The best forming effect of welded joint of 1.4 mm thick 2 000 MPa grade hot stamping steel are obtained with the dual spot laser welding technique when the laser power is 4 700 W,welding speed is 150 mm/min,core is 65%,and defocus amount is-2 mm.
SiC particle reinforced aluminum matrix composites are widely used in aerospace,electronics,medical and other fields due to their excellent properties such as high specific strength,high specific stiffness,high wear resistance,and high tem-perature stability.However,due to the high melting point and high hardness of SiC particles,as well as the interface reaction between silicon carbide reinforced particles and aluminum matrix,SiC aluminum matrix composites have problems such as poor processability and insufficient interfacial adhesion.It is no longer possible to meet the requirements for material performance in fields such as national defense and aerospace.Therefore,studying the ways to improve the interface between particles and ma-trix is of great scientific significance for improving the comprehensive performance of composite materials.In combination with existing research results at home and abroad,the interface strengthening mechanism,interface reaction characteristics,existing surface modification technology principles and numerical simulation development status of SiC reinforced particles and alumi-num matrix composites were summarized.The results showed that the performance improvement of reinforced particle alumi-num matrix composites after strengthening was limited after being treated with a single surface modification method.Therefore,how to adopt new methods to improve the performance of composite materials will become a hot research topic in the future,and the design of composite materials based on finite element numerical simulation methods is also an inevitable trend.Finally,in response to the limited improvement of single strengthening performance,the author proposes a flexible particle multimodal strengthening method based on surface modification,and looks forward to future research directions in response to existing technical difficulties,hoping to provide theoretical reference for the preparation of particle reinforced composite materials.
The work aims to improve the forming margin of automotive rear floor drawing part and optimize the forming parameters.Firstly,by setting the blank holding force as 807 kN,friction coefficient as 0.135,blank holder stroke as 205 mm,and forming force as 3 572 kN,the drawing process of the rear floor was numerically simulated based on Autoform software.Secondly,full-field grid strain measurement technique was used to measure the actual drawing part,and full-field forming mar-gin cloud image,forming limit diagram and thinning cloud image were obtained.Finally,the forming parameters of the drawing process were optimized by adjusting the blank holding force,the depth and radius of the draw bead.The potential risk areas of the forming margin were obtained by simulation and the maximum thinning rate of the parts was 24.10%and the full-field forming margin was less than 10%.The measurement results showed that the maximum forming margin was-9.29%.After the die radius of the risk area was polished,the maximum forming margin reached-10.65%.After comprehensive analysis of the measurement results and simulation results,with the blank holding force as 782 kN,the radius of draw bead B as 4.5 mm and the depth of draw bead B as 4.5 mm,the part without cracking and wrinkling defects was obtained,and the maximum forming margin was-14.33%,which met the needs of large-scale production.The numerical simulation combined with the full-field grid strain measurement technology can guide the die repair operation and forming parameters optimization,which can improve the commissioning efficiency of die.
The work aims to carry out finite element simulation analysis and experimental verification for the multi-process forming of a typical sheet metal part in aeroengine splash baffle.ABAQUS and DEFORM were adopted as simulation platforms.ABAQUS was used to simulate the first deep drawing and springback process.On the basis,the simulation results were im-ported into DEFORM as the initial state for annealing heat treatment.Then,the results after annealing were imported into ABAQUS for the second deep drawing and springback process.The data transfer process of the previous one was repeated for the next heat treatment and the third reshaping simulation.Meanwhile,the simulation and experiment results were compared af-ter each deep drawing process.The data transfer of geometric shape and physical field of the sheet metal part between the same and different software was achieved and the multi-pass continuous process simulation forming of sheet metal part was com-pleted.After the first deep drawing and unloading,the part had little springback,and the error between the simulated part ge-ometry and the experimental results was small.There was a large residual stress in the part after unloading,but it could be al-most eliminated by heat treatment,which enhanced the subsequent formability of the superalloy.After multi-process forming simulation,the cumulative error value of the geometric feature size increased slightly,while it was still within acceptable limits.The multi-process simulation forming including intermediate annealing can describe the experimental results well,prove the accuracy and effectiveness of the simulation results and provide scientific guidance for improving and optimizing the design and manufacture of sheet metal parts.
The work aims to optimize the welding parameters of 2 mm thick 304 stainless steel pipe and simulate the ther-mal stress field of the joint based on simulation software to solve the problem of inconvenient stress testing for thin-walled pipe joints.The 2 mm thick stainless steel pipe was welded by TIG technology,and the optimal welding parameters were obtained by optimizing the macro morphology,microstructure and microhardness of the joint.The numerical simulation was carried out by using double ellipsoid heat source and temperature-displacement coupling method combined with the optimal parameters.When the welding current was 150 A and the welding speed was 66 cm/min,the welded joint was completely penetrated and the front and back weld passes were uniform and dense,which was well formed.The upper and lower regions of the weld zone exhibited equiaxed crystal morphology,while the size of the lower region was slightly larger than that of the upper region.The columnar crystal structure appeared near the fusion line.The overall trend of the microhardness of the welded joint presented a"U"shape,in which the microhardness of the head-affected zone(197HV)was larger than that of the weld zone(162HV),and the micro-hardness near the fusion line was the lowest(145HV).The simulation results showed that the longitudinal residual stress gradu-ally transformed from compressive stress to tensile stress when transitioning from the base metal to the center of the weld seam.The transverse stress at the center of the weld seam bore compressive stress,and the stress value gradually approached 0 when transitioning to the base metal on both sides.The radial stress value in the thickness direction of the weld seam changed slightly,and the changing trend of simulated data was close to that of the measured data.
The work aims to investigate the effects of cooling medium and number of passes on the microstructure and me-chanical properties of pure copper by single and multi-pass friction stir processing(FSP)in air and water,respectively.T2 pure copper plates with a thickness of 3 mm were processed one to two passes in the air and one to four passes in the water.The mi-crostructure and mechanical properties of the processed samples were measured with an optical microscopy,a microhardness tester,a scanning electron microscope and a tensile tester.Compared with air friction stir processing,the surface quality of sam-ples after underwater friction stir processing was better.The grain size of the sample processed by friction stir in air was larger than that of the base metal.The grain size of the sample processed by friction stir under water(SFSP)could be effectively re-fined,and the grain size increased gradually with the increase of the number of processing passes.Among them,the grain size of pure copper processed by friction stir under water for one pass was the smallest(3.93 μm).The results of microhardness test and tensile test showed that the yield strength and hardness of the samples processed under water were higher than those in air,but the yield strength and hardness of the samples would decrease with the increase of the number of processing passes.The grain size of pure copper can be reduced and the mechanical properties of pure copper can be improved by underwater multi-pass fric-tion stir processing.
The work aims to develop an environmentally friendly water-based binder for the injection molding of 316L stainless steel,and explore the effect of water degreasing temperature on the removal rate of PEG.Different ratios of PEG/PMMA binders were prepared,and the appropriate binder ratio was determined by observing the morphology and SEM of the molded samples.The rheological properties of the complete molded green parts were tested.Finally,the green parts were degreased in a water bath,and their morphology was examined with SEM.Three types of feedstock with PEG contents of 76wt.%,79wt.%,and 82wt.%were successfully molded into complete green parts by injection.According to SEM observations,the 316L stainless steel powder was not covered evenly by the binders.At 160℃,the viscosity of all three binders was below 1 000 Pa·s,and the shear rate ranged from 102 to 105 s-1,meeting the requirements for injection molding.The removal rate of PEG from the green parts increased with the degreasing temperature.The removal of PEG resulted in the formation of numerous pores inside the green parts,which proved beneficial for subsequent debinding and presintering processes.The binder with a composition of 79wt.%PEG+19wt.%PMMA+5wt.%SA exhibits better fluidity in feeding compared with other compositions,making it suitable for injection molding.The resulting molded green parts have a complete morphology with fewer internal voids,and they retain their original shape without any external defects after degreasing.Degreasing the green parts at a water temperature of 60℃achieves the highest removal rate of PEG,with the PEG removal rate reaching 80%after 10 hours of de-greasing.
The work aims to make the integrated door inner panel with lightweight 5-series aluminum alloy material to meet the lightweight requirements of new energy vehicles.AutoForm numerical analysis software and CAE numerical simulation analysis technology were used to predict the forming difficulties and rebound trends of the parts in the process design stage.The depth of the integrated door inner panel was analyzed,and several plans to improve the formability of the parts were proposed.Rebound compensation was carried out on the mold surface based on the rebound results.Important links such as mold process-ing and debugging were controlled deeply.The forming problem in 9 areas of the part was solved successfully after analyzing and verifying.The depth of the aluminum alloy monolithic door inner panel that has been mass-produced was benchmarked,and a plan to reduce the depth of parts from 171 mm to 156 mm was proposed.The reasonable depth reference value of the alumi-num alloy integrated door inner panel was 150 mm after CAE analysis and verification.The theoretical rebound value of steel and aluminum was compared and analyzed,and the rebound value of aluminum alloy was calculated to be 2.6 times that of low carbon steel.A mold development system for forming and rebound controlling is formed by controlling the entire development process of the door inner panel.The correctness of the entire development plan is verified with the first sample.It ensures the development of the aluminum alloy integrated door inner panel successfully.
