混流装配线的规划设计与仿真研究

混流装配线可以在同一条线上可装配几种不同类型的产品.本文主要研究混流装配线的负荷平衡以及投产排序优化的问题.阐述了混流装配线负荷平衡的分类、目标函数及求解算法,并建立了三种排序的目标函数:最小化工作站的闲置与超载时间、保持均匀的零部件消耗速率.根据某汽车装配线的实际情况,在eM-Power数字化工厂软件的基础上二次开发装配线的仿真模型并进行了生产评估.     

基于JIT的多车间混流装配计划排序问题

为使JIT生产模式下多车间混流装配线敏捷、高效地运行,研究了具有供需关系的多车间混流装配线计划排序问题。以JIT车间混流装配线上车型切换次数、关键件型号切换次数、车身喷涂颜色变化和违反选装件的选装频率次数最少为优化目标,采用加权平均法建立了多目标优化数学模型。针对遗传算法容易陷入局部最优和提前收敛的问题,提出了求解多车间混流装配计划排序的自适应遗传算法。通过交叉概率和变异概率的自适应调整、局部寻优和保优策略,提高了算法的寻优能力。最后通过算例验证了算法的有效性。     

基于改进NSGA-Ⅱ算法求解混流装配线平衡问题

针对混流制造系统装配线平衡和物料配送车辆路径优化问题,从优化目标、影响因素和约束条件等方面,建立了以装配线平衡最小均衡系统、物料小车最短行驶距离和最小车辆利用率最大为优化目标的多目标混流装配线模型。根据问题的具体情况,设计了一种基于生态进化策略的NSGA-Ⅱ算法,该算法定义了一种环境自检算子用于检测环境是否变化,主体种群与选择后经过交叉、变异后面对环境变化的种群进行竞争,迭代过程中种群内捕食与被捕食的竞争以促进种群多样性及不断提高生存力,算法采用0~1编码,通过具体混流装配系统中实例验证了所建模型和算法的有效性。     

面向混流生产线排序问题的改进回溯搜索算法

针对产品工艺的复杂性和多样性导致的混流生产线生产效率低下的问题,建立各个工作站零件利用率最大化和总体均衡化的函数模型,提出了一种基于改进多个目标回溯搜索算法的混流生产线排序方法,利用多权重下的最优个体精英历史种群引导当前种群进化,以提高全部搜索能力的收敛速度。将该算法应用于装配线排序问题上,为混流生产车间的作业排序提供有效的依据;同时将多目标回溯搜索算法与遗传算法、回溯搜索算法进行对比,结果表明改进的回溯搜索算法在混流生产线排序问题上的优越性。     

双阀燃油喷射系统多次喷射特性优化试验研究

针对双阀燃油喷射系统凸轮轴型线工作段灵活的选取方式对燃油喷射过程和平均循环喷油量等影响较大的问题，以预喷开启压力、主喷开启压力、主喷峰值压力和平均循环喷油量为评价指标，选择正交试验和极差分析方法，进行多次喷射特性试验研究，获得不同评价指标影响的主次因素和最优组合方案。以喷射压力和循环喷油量等为综合评价指标，依据综合平衡方法获得多评价指标综合平衡方案，分别为供油正时156°CaA,预喷正时161°CaA,主喷正时177°CaA,凸轮转速500 r/min。以综合平衡优化方案为基础，利用平均试验法研究预主喷间隔时间变化对平均循环喷油量的影响，获得平均循环喷油量非线性波动规律，并验证了主喷开启压力变化与其一致的特征。     

基于改进MULTIMOORA方法的PCCP焊接工艺参数优选

焊接作为预应力钢筒混凝土管(prestressed concrete cylinder pipe, PCCP)钢筒加工的主要技术,焊接工艺控制参数直接影响焊缝质量,进而影响PCCP应用性能. 故确定PCCP钢筒最优焊接工艺参数尤为重要,基于现场采集数据和改进MULTIMOORA方法,以焊缝特征指标为评价依据,对螺旋焊接工艺进行综合优选. 首先获取并整理各指标数据,将各指标转化为多属性决策问题,通过评价指标数据,定义权重因子用来分配优先级,量化指标,根据优化原则对方案进行排序,过程采用OWA算子和熵权法消除主观评价值中极端值影响,得到指标综合权重,进行决策排序优选,最后利用占优理论对焊接控制工艺技术参数进行最终评价. 结果表明,PCCP钢筒最优焊接工艺参数为焊接电流340 A、电弧电压为24 V、焊接速度为10.81 mm/s,以期为PCCP钢筒焊接工艺提供技术参考.     

数控机床进给系统动态特性评价研究

为更加全面准确地评价数控机床进给系统的动态性能,建立了进给系统动态性能的评价指标体系。从抗振性和瞬态响应性能两个方面确定评价指标,应用模糊层次分析法建立直觉模糊偏好关系矩阵,并依据实际工况建立了隶属度函数,从而得到评价矩阵。以MCH63数控机床为对象进行应用评价研究,结果表明该机床进给系统动态特性综合性能良好,并指出可通过对固有频率性能指标进行优化从而提高进给系统的整体性能。分析表明,该方法能够有效评价进给系统动态性能。     

一种新型混流器的动态配气系统设计

在实际的动态配气系统中,为了快速得到浓度可控的气体,通常需要设计特殊结构的混流器以实现多种气体的混流,达到混流的目的。针对上述问题,设计了一种新型的混流器,并对传统的动态配气气路进行了改进。通过控制系统反馈的数据设计实验验证了混流器的混流效果。     

基于GA&SA的混流装配线平衡系统的研究与实现

在对柔性生产环境下的多品种混流装配线设计问题进行分析的基础上,结合4种不同型号的保险杠的装配工艺,提出结合当量节拍、可变装配站与固定工作站的设计技术,设计以装配线过载和闲置成本最低为目标的投产排序模型,并开发一个面向对象的投产排序系统,运用SA&GA混合算法对模型进行求解,得出最佳投产排序解决方案。     

基于SGRASP-LP算法的混流装配线排序问题

针对实际混流装配线上工作站工作过载过大、无效时间过长导致的装配线运行效率低下问题,在保留基本模型约束条件的基础上引入"保持生产混合"和"作业自主中断"两个约束条件,建立以"最小化工作过载和无效时间"为目标的混流装配线排序问题优化模型。在基本GRASP算法的初始解构造阶段增加阈值参数选择机制,并将改进后的GRASP算法与线性规划方法结合,设计了模型的SGRASP-LP求解算法。以某汽车企业的底盘装配线为例,将SGRASP-LP算法分别与GRASP算法和企业解决该类问题常用的MILP算法相比较。结果表明,SGRASP-LP算法运算速度更快,所求方案更优,是解决相关排序问题的有效算法。     

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).     

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.     

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.     

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.