送粉多道搭接激光熔覆温度场的数值模拟

运用ANSYS有限元分析软件,对送粉式多道搭接激光熔覆过程的温度场进行了数值模拟。考虑到材料热物性的非线性特征以及对流换热的边界条件,建立了三维有限元模型;送粉过程及熔覆单元的生长过程采用"生死单元法"来实现。结果表明:在多道搭接激光熔覆过程中,先凝固的熔覆道对后续搭接熔覆道有预热作用,两者之间存在一个初始温度差;在熔覆层中,搭接区的温度高于其它区域,存在重熔现象;熔覆层每道熔池节点的热循环曲线呈现周期性变化且基本相似;熔覆层易出现端部效应问题;熔覆层中上部温度梯度沿激光扫面方向水平分布,下部与扫描方向垂直分布,在基体与熔覆层交界处温度梯度出现突变和最大值,是裂纹高发区。     

The significance of deposition point standoff variations in multiple-layer coaxial laser cladding (coaxial cladding standoff effects)

Direct laser deposition (DLD) is an additive manufacturing process that builds up a part layer-by-layer by fusing metal powder to a solid substrate. A coaxial laser and powder delivery head is commonly used, and here a critical process variable is the standoff distance between the nozzle and the material deposition point. This contribution investigates the role of this variable and the effect that it has on the final part geometry. The experimental results show that good layer consistency can, in fact, be obtained with no movement of the substrate between layers for more than 20 layers, or 10 mm under tested conditions, and that poorer results are obtained by regular movement of the substrate by a badly chosen constant amount. A theoretical analysis of the situation establishes a method to estimate melt pool size using an analytically calculated temperature near the heat source. Based on this, simple heat and mass flow models are established to allow some of the results to be explained.     

多点渐进成形工艺数值模拟及实验对比

针对成形大尺寸船板需要大设备的问题,以多点渐进成形方法为研究对象,该方法既有单点渐进成形的由局部变形累计成总体变形的特点,又有多点成形模具自由重构的特点。采用数值模拟法仿真了4种不同的成形工艺产生的成形效果,同时展开了相同工况的实验研究,将实验结果在三维扫描仪下进行测量,然后对比验证了数值模拟的仿真结果。研究结果表明:对于双曲率船板而言,两侧多点同步驱动的成形方案比一侧先调整好位置、另外一侧再依次驱动的方案要优越,成形路径对成形效果的影响不太明显,压头的驱动方式对成形力的历史变化影响显著。     

Optimization of the shape of nozzles for coaxial laser cladding

The results of mathematical modelling of the flows of powder in nozzles for coaxial laser cladding are presented. The modelling results are used to determine the optimum geometrical parameters of the nozzle used for the construction of appropriate technological equipment. Calculations are carried out to determine the optimum values of the flow rate of powder, the size of powder particles, the geometry of the powder flow and the distance from the outlet of the nozzle to the surface of the components. The resultant values were used in the development of technological processes of cladding with powders of different composition.     

Warpage of injection-molded thermoplastics parts: Numerical simulation and experimental validation

A mathematical model and the integrated simulation program for predicting part warpage, which arises during injection molding of thermoplastic polymers, were developed. To build the model, the finite element method (FEM) was used and the theory of shells, represented as an assembly of flat elements formed by combining the constant strain triangular element and the discrete Kirchhoff triangular element, was applied. This shell theory is well suited for thin injection molded products of complex shape. Furthermore, in this work, experimental research on flat plates was performed to study the effect of the plastic material, the mold structure, and certain key processing parameters on warpage. The investigated processing parameters include injection pressure, packing pressure, injection time, packing time, cooling time, and melting temperature. Different examples were presented to examine the developed simulation software, and results predicted from the simulation program were verified in the above experiments and showed reasonable accuracy compared with experiment data.     

Numerical simulation and experimental validation of slag entrainment during tundish draining

Abstract

During continuous steel casting slag entrainment from the tundish into the mould has to be avoided. Since slag entrainment most likely occurs at low tundish levels, this paper focuses on the behaviour of the steel phase and the covering liquid slag during tundish draining. The process of slag entrainment is modelled both numerically by a volume of fluid (VOF) approach and physically by corresponding water-oil experiments. Thereby, the influence of a centric stopper and additional inserts on the critical suction level is studied. With help of the numerical model these results are subsequently extrapolated to real plant applications with steel and slag as liquid phases. The numerical simulations have been proven to reasonably depict the onset of slag entrainment during tundish draining and their results agree with corresponding experiments.     

预热对激光熔覆陶瓷涂层温度场和应力场影响

采用SYSWELD软件建立激光熔覆Ni-WC-Cr3C2涂层的热应力分析的有限元模型,通过熔池形貌对比验证模型的可靠性。利用建立的模型,进一步分析陶瓷涂层冷却阶段温度梯度和应力场的变化规律及基板预热对温度梯度和应力分布的影响。结果表明,激光熔覆处理是经历了快速加热、快速冷却的过程,陶瓷涂层内呈拉应力状态,极易沿垂直扫描方向发生脆性开裂。基板预热可以显著降低陶瓷涂层的冷却速度,且预热温度越高,冷却速度降低越明显,涂层内应力也随之降低。预热350℃及以上可以有效抑制裂纹产生。     

Numerical simulation of temperature field during selective laser sintering of polymer-coated molybdenum powder

The technology of length-alterable line-scanning laser sintering was introduced. Based on the research of laser heating property, powder thermal physics parameters and laser sintering process, a numerical model of the temperature field during length-alterable line-scanning and laser sintering of polymer-coated molybdenum powder was presented. Finite element method （FEM） was used to simulate the temperature field during laser sintering process. In order to verify the simulated results, a measuring system was developed to study the laser sintering temperature field. Infrared meter was introduced to measure the surface temperature of sintering powder; the temperature of its inside part was measured by thermocouple. The measured results were compared with the numerical simulation results; the conformity between them is good and the relative error is less than 5%.     

Numerical simulation study on monoblock casting process of ultra-slender structural components and experimental validation

Substrate, a typical ultra-slender aluminum alloy structural components with a large aspect ratio and complex internal structure, was traditionally manufactured by re-assembly and sub-welding. In order to realize the monoblock casting of the substrate, the Pro/E software was utilized to carry out three-dimensional (3D) modeling of the substrate casting, and the filling and solidification processes were calculated, as well as the location and types of casting defects were predicted by the casting simulation software Anycasting. Results of the filling process simulation show that the metal liquid is distributed into each gap runner evenly and smoothly. There is no serious vortex phenomenon in the mold cavity, and the trajectory of the virtual particles is clear. Results of the solidification process simulation show that shrinkage cavities mainly appear at the junction of gap runners and the rail surface of the substrate. The average deformation is 0.6 mm in X direction, 3.8 mm in Y direction, and 8.2 mm in Z direction. Based on the simulation results, the casting process of the substrate was optimized, and qualified castings were successfully produced, which will provide a reference for the casting process design of other ultra-slender aluminum alloy structural components.     

Numerical simulation and experimental validation on fabrication of nickel-based superalloy Kagome lattice sandwich structures

Nickel-based superalloy lattice sandwich structures present higher stiffness,higher strength and higher temperature resistance in comparison with other metals.In this study,the Kagome unit was adopted to design the lattice sandwich structure and ProCAST software was used to simulate the filling and solidification processes of the nickel-based superalloy.Grain morphology and sizes of the nickel-based superalloy lattice sandwich structures were simulated by using of cellular automaton coupled with finite element model(CAFE),and indirect additive manufacture combining with investment casting were carried out to fabricate the nickel-based superalloy lattice sandwich structures.The calculated grain morphology and sizes are in good agreement with the experimental results.The grains are mainly equiaxed with an average size of about 500µm.The simulated results also show that the superheat of melting and the mold preheated temperature have significant influence on the grain size of the Kagome lattice sandwich structures,lower superheat of melting and mold preheated temperatures are encouraged to obtain the fine grains while assuring the integrity of the Kagome lattice sandwich structures for industrial application.     

Comparison of coaxial and off-axis nozzle configurations in one step process laser cladding on aluminum substrate

Laser cladding of aluminum bronze alloy has been studied in order to increase the wear resistance of aluminum parts. Aiming a more productive and controlled process, this study analyzes the blown powder process, with two possibilities of blowing configurations that are off-axis and coaxial nozzle, and process parameters, such as axial motion speed, mass flow and power modulation. Dilution, catchment efficiency and hardness were analyzed for the used process parameters and nozzle configurations.     

Study of an annular laser beam based axially-fed powder cladding process

An annular laser beam based powder cladding head, which enables an axial powder feeding and variation of the laser beam intensity distribution (LBID) on the workpiece surface is presented. The influence of typical LBIDs, including Ring, Tophat(?), Tophat(+), and Gaussian-like, on a cladding process has been characterized based on the process and melt pool visualization, powder catchment efficiency, clad layer geometry, and porosity. The results showed that the most stable process without plasma formation but with low dilution and porosity of the clad layer can be achieved within the range from a Ring to a Tophat(?) LBID. Additionally, axial powder feeding results in a high powder catchment efficiency above 80%.     

薄板激光冲击强化残余应力场的数值模拟与试验

激光冲击强化会在材料表面形成深度达到1 mm的残余压应力,而对于厚度小于1 mm的薄板,由于冲击时应力波的反射和叠加,其残余应力场的分布肯定不同于厚板。文章采用4种冲击方式(单面冲击、底面约束情况下的单面冲击、双面非同时冲击以及双面同时对冲)对2024铝合金薄板(厚度为1 mm)进行激光冲击强化,并应用有限元软件ANSYS/LS-DYNA对其进行数值模拟,系统分析经过4种不同的冲击方式,得到薄板的变形以及残余应力的分布情况。结果表明,双面同时对冲方式能够使薄板两面都产生很大的残余压应力,而且不会出现弯曲变形,是理想的冲击方式。     

激光熔覆F305粉加WC的界面组织与性能

在球墨铸铁基体上进行送粉激光熔覆,通过改变扫描速度和送粉速率获得不同条件下的熔覆层,并对其进行显微组织观察与性能测试,从而得出工艺参数对熔覆层组织、性能的影响规律,并结合凝固理论探讨了熔覆层显微组织和性能不均匀性的产生原因.     

Numerical simulation in powder compaction of metallurgy component

1Introduction Forming multi-level component in die compaction,the density is more or less inhomogeneous depending onthe part geometry,the tool design and the frictionbetween powder and die wall[1?3].The productdistortions are result of inhomogeneous densi…     

Ti掺杂对Cr-Fe合金粉激光熔覆层组织与性能的影响

采用CO2激光加工机,在Q235钢基体表面预涂覆加入不同Ti含量(1%~4%)的高碳Cr-Fe合金粉,制备熔覆涂层。采用OM、XRD及硬度测试、耐磨测试、腐蚀性能测试等手段,研究了Ti掺杂对涂层组织性能的影响。结果表明,加入Ti减小了熔覆涂层初生碳化物尺寸,使组织均匀细化,物相为α-Fe、CrFe、(Cr,Fe)7C3、Cr7C3、TiC和Cr23C6。当加入Ti量为2%时,涂层表面平均硬度达到最高917.8 HV0.2,磨损率为0.491 mg·mm-2,自腐蚀电流密度最小,为517.6μA·cm-2。     

Computer simulation and experimental validation of stretch flanging

The axisymmetric stretch flanging process is a common secondary operation in sheet metal stamping. The process is characterized by a uniaxial state of stress at the edge of the flange. An approximate analysis, based on the assumption that the state of stress throughout the flange is mainly uniaxial, is used to model the stretch flanging (second step) process. The approximation is derived from the total strain membrane theory of plasticity which incorporates strain hardening and normal anisotropy of the material. Under such conditions, flangeability is controlled by the tensile elongation of the metal and is limited by localized necking or fracture of the flanged edge. The analysis includes a stretching limit criterion to determine the flanging limit of the material. The influence of prestretching (first step) on flangeability is modeled using the membrane shell theory with axisymmetric deformation to solve the contact condition in stretch forming. Inputs to the model are a desired flange profile, material properties, and sheet thickness. The output includes the feasibility of the flanging operation, any requirements for prestretching and the size of the trim radius needed to successfully flange the profile. The model is verified by experimental results.     

工艺参数对送粉式激光熔覆组织及性能的影响

通过对不同规范参数情况下激光熔覆过程的研究分析,讨论了在熔覆过程中不同激光粉匹配条件对熔覆层尺寸、熔覆层组织及性能的影响,从而确定其影响规律。     

一种新型四代镍基粉末高温合金挤压过程数值模拟及试验验证

采用正交设计与有限元模拟相结合的方法对热等静压态的一种新型四代镍基粉末高温合金包覆挤压工艺进行了优化设计,分析了坯料初始温度、挤压速度、模具模角等关键参数对挤压棒材的应变、温度分布及成形载荷的影响.结果表明:随着挤压速度、模角的增大,挤压棒材的温度、应变及挤压载荷升高;随坯料初始温度的升高,挤压棒材温度升高,挤压载荷降...