3D打印机送丝机构和喷嘴协同优化研究

为提高3D打印机出丝的连续性与稳定性，提出送丝机构和喷嘴协同优化方法，克服了已有的打印机喷嘴和送丝机构单独优化而忽略两者之间耦合效应的不足。以喷嘴加热段长度、散热段长度、出口长度、送丝速度为优化参数，以喷嘴截面平均速度和平均温度为优化目标，设计正交试验，进行流体仿真。为快速得到最优方案，基于神经网络与NSGA-Ⅱ算法进行优化分析，结果表明：加热段长度为6 mm、散热段长度为4 mm、出口长度为0.7 mm、送丝速度为4.5 mm/s时，最大喷嘴截面平均速度为78 mm/s，最大平均温度为208.39 ℃，最大平均速度提高2.6%，最大平均温度提高1.22%。以最佳工艺参数组合进行流体仿真验证，结果表明：喷嘴截面平均速度与温度确实明显提高。     

FDM型3D打印机喷嘴多目标优化设计北大核心

分析传统桌面级熔融沉积成型(FDM型)3D打印机喷嘴的结构特点,选择喷嘴流道直径、收缩角与喷嘴温度作为试验变量,进行正交仿真试验。分析喷嘴熔体压力场、速度场、黏度场、温度场以及剪切速率场的分布状态。以稳定的出口截面速度、较低的流道熔体黏度以及较高的出口压力作为提高喷嘴打印精度与确保打印过程顺畅的优化目标。通过极差分析,确定三因素分别作用下每个优化指标的变化规律,并基于遗传算法求解多目标优化问题。结果表明:出口速度方差的最显著影响因素为流道直径,流道熔体黏度与出口压力两指标的最显著影响因素为喷嘴温度;综合考量,喷嘴流道直径为1 mm、收缩角为30°且在200~210℃工作时,能够实现较优指标的聚丙烯熔体打印。     

熔融沉积技术喷嘴结构尺寸优化研究

针对熔融沉积技术成型过程中丝材堵塞喷嘴现象，提出对喷嘴结构尺寸优化的思路。通过喷嘴出口截面温度场仿真，结合散热长度、出口长度及收敛角3个因素进行正交试验分析，得到喷嘴最佳结构尺寸组合。对比喷嘴优化前后实际打印过程及制件的表面质量、三维尺寸精度，结果表明：优化后的喷嘴能明显提高制件精度，同时可有效降低丝材堵塞发生的概率。     

数控车床高压冷却喷嘴的优化设计

为了研究高压冷却喷嘴结构参数对流体射流的影响,文章针对高压冷却系统的执行部件锥形喷嘴的收缩角、入口直径与出口直径的比值两个主要因素进行了结构参数的优化设计。采用计算流体动力学的分析软件Fluent对喷嘴的流场进行了数值模拟,通过仿真研究和分析对比其喷嘴流场的特性曲线获取了喷嘴的优化参数。基于Mixture多相流模型理论对其优化后的喷嘴进行了外部流场的气液两相模拟实验和车削断屑实验。研究结果表明:随着收缩角的增大,喷嘴射流的动压值先增大后减小,在α=25°时动压力达到了最大值;距喷嘴出口60 mm处截面上的径向速度随着距离的增加而下降,在α=25°时截面上的径向速度变化幅度最小;当喷嘴的直径比C_d=3时,射流初始段的轴向速度达到最大值,能产生更好的断屑效果。     

FDM 3D打印机喷嘴流场分析与结构优化

通过田口方法和有限体积法研究了喷嘴结构对熔融沉积型(FDM,Fused Deposition Modeling)3D打印机出口速度稳定性的影响,试验研究在喷嘴收敛角、过渡圆弧半径、整流段长度三个因素的水平组合下进行,利用ANSYS Fluent软件对喷嘴流场进行仿真,得出喷嘴内流场的速度变化云图、出口速度和出口速度方差,并对喷嘴结构进行优化设计。结果表明,收敛角、过渡圆弧半径、整流段长度以及它们之间的交互作用是影响丝料出口速度稳定性的重要因素。通过实验验证,在满足加工条件的情况下,收敛角越小,过渡圆弧半径越大,喷嘴出口速度越稳定。     

FDM 3D打印机喷头温度场分析与结构优化

针对熔融沉积型(FDM,Fused Deposition Modeling)3D打印机喷头系统在打印过程中存在打印材料提前软化和打印成型件不能及时冷却,引起打印精度差的问题,设计了一种高效简易的3D打印机喷头冷却装置。通过ANSYS fluent软件对结构优化前后的喷头和打印材料进行了热学仿真分析,得到结构优化前后喷头温度云图和打印材料的温度云图、应变云图的模拟数据。并通过实验测量出结构优化前后打印成型件的误差。结果表明:结构优化后喷头的冷却装置能够有效改善打印材料提前软化的现象,打印的成型件能够及时冷却,打印精度得到提高。     

重油催化裂化进料雾化喷嘴出口结构对喷嘴性能的影响研究

采用Fluent软件,基于欧拉-欧拉方法的VOF多相流模型对喷嘴的内部流场进行仿真分析,研究喷嘴出口段结构参数对喷嘴性能的影响;在确定喷嘴出口段最优结构的基础上,应用基于欧拉-拉格朗日方法的DPM模型对喷嘴的外部雾化射流区域进行了雾化状态分析,并探究了喷嘴的雾化机制.结果表明:出口锥角θ=51°时喷嘴的性能最优,平均速度为101.19 m/s,湍流强度为2141.1％,达到最大值;出口长度L2=20 mm时喷嘴的性能最优,速度为101.03 m/s,湍流强度为2121％;出口直径d2=25 mm时喷嘴性能最优,平均速度为101.49 m/s,湍流强度为2101％,且出口直径d2对喷嘴的雾化性能影响最大.并根据优化后的结构尺寸进行了5:1比例缩小的实验,对喷嘴内部液相流动状态呈四点分布进行了验证,同时喷嘴外部雾化液滴分布锥角与仿真结果误差为3.81％,雾化液滴粒径最大误差为3.67％.     

基于FDM的3D打印参数优化实验研究

以熔融沉积制造技术中常用的基体材料PLA作为对象,通过3D打印实验,对打印过程中的因素参数进行优化实验研究。利用单因素实验法和正交实验法,以打印时间和打印尺寸误差为实验指标,选取层厚、打印速度和喷嘴温度三个主要因素展开实验。实验结果表明,层厚为0.3mm,打印速度为20mm/s,喷嘴温度为200℃时,可以在保证打印质量的情况下获得最短打印时间。对打印效率影响程度由大到小依次是层厚,打印速度,喷嘴温度,并进一步通过实验验证。     

基于FLUENT模拟的熔融沉积快速成型喷头工艺参数研究

喷头是熔融沉积快速成型工艺最重要的部件之一。对喷头结构进行介绍,分析出喷头几种重要的工艺参数,进行有限元理论分析,建立喷头三维模型,用FLUENT软件对喷嘴直径为0.2、0.5、0.7 mm时的喷头结构进行分析。分析其温度场、速度场、压力场,找到不同送丝速度下的挤丝速度、压力损失、喷嘴处温度之间关系。仿真分析结果表明:在成型过程中选择合适的工艺参数,可以防止材料在喷头内堵塞,提高成形表面的表面品质。     

PEEK的3D打印参数优化及铣削试验研究

以医学中常用到的PEEK材料作为研究对象,通过3D打印试验,对打印过程中的因素参数进行优化试验研究。利用正交试验法,以打印尺寸误差为试验指标,选取层厚、打印速度和喷嘴温度三个主要因素展开优化试验。铣削试验是利用电主轴对打印模型进行表面加工,选取合适的铣削参数展开试验。试验结果表明:层厚为0.3mm,打印速度为15mm/s,喷嘴温度为360℃时,可以获得最佳的打印质量;在此基础上进行铣削可以提高表面精度,并进一步通过试验验证。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.