变齿距铣刀高速微铣削的动态特性及稳定性研究（英文）

在高速微铣削加工过程中,提高生产效率和零件质量的需求日益强烈,这使得机床一直在系统的动态稳定性极限附近工作,而机床颤振的存在是限制微铣削加工生产率的主要障碍。基于颤振稳定性的准确预测,能采取一些措施来提高动态稳定性极限,例如通过改变铣刀结构。提出了数值分析与铣削实验相结合的方法,采用变齿距微铣刀来研究铣削加工的动态特性和稳定性。另外提出了采用时域仿真的输出力来表征加工稳定性的新方法,采用变齿距铣刀可以非常有效地提高某些速度范围的颤振稳定性。对于选定刀具的加工,这种方法可以用于加工优化,或在设计阶段预测刀具新型结构的性能。     

变螺旋铣刀结构设计与优化对铣削稳定性的影响

颤振是限制铣削生产率和影响工件加工质量的重要因素之一,稳定性图表和变螺旋铣刀结构设计是目前常用的抑制铣削颤振的方法。结合铣削过程中的稳定性极限三维叶瓣图对变螺旋铣刀结构进行设计优化,进而得到变螺旋铣刀最优螺旋角变量和齿距角变量。首先建立变螺旋铣刀铣削过程的动力学模型,结合仿真分析获得颤振稳定性三维叶瓣图,得到最大稳定性切削深度对应的最优螺旋角变量和齿距角变量值分别为1°和8.1°。实验结果可知,相较于常规结构铣刀,优化得到的变螺旋铣刀能够显著提高铣削稳定性极限、提高表面质量,为抑制铣削过程中颤振的变螺旋铣刀结构设计提供了理论基础。     

微细铣削加工再生颤振的研究(英文)

微细铣削是利用微铣刀在高转速下加工复杂三维结构的制造技术。再生型颤振能引起刀具的严重磨损,降低零件的加工质量,是微细铣削加工面临的主要挑战之一。铣削加工过程中切削系数和系统动态特性的多变影响颤振稳定性。针对该问题,建立了考虑再生效应的微铣削动态铣削力模型和颤振稳定域解析模型,通过模态试验获得机床 - 刀具系统的频响函数,综合使用铣削稳定性判据进行数值分析,获得了颤振稳定域解析解。最后进行了颤振稳定性加工实验,验证了建立的颤振系统动力学模型和颤振解析模型的正确性。     

利用颤振抑制和力控制方式提高钛基叶轮铣削生产率和质量

燃气轮机叶轮铣削中,使用较大的轴向切削深度时,产生严重的颤振和较大的切削力.在这类极大柔性零件的铣削中,使用变齿距铣刀可遏止颤振的产生.介绍了一种设计变齿距铣刀的新方法.由于刀具方向和切削深度的变化,在5轴铣削加工切削力连续改变.可使用自适应力控制或铣削力模型,使其保持为固定大小,可明显缩短加工周期.试验证明了上述两种方法的优点.     

一种快速的变螺旋铣刀铣削稳定性预测方法

变螺旋铣刀铣削作为一种有效的颤振控制策略,已经受到了广泛关注。由于在建立的变螺旋铣刀铣削动力学方程中,出现了由铣刀变螺旋特性引发的系统变时滞相,而现有方法无法求解该问题。针对该问题,提出了对刀具进行轴向离散,而后将每个离散后的变螺旋刀具单元,近似模拟成变齿距刀具,从而完成变时滞微分方程向多时滞微分方程的转化。通过与前人研究工作作比较以及模型验证与分析可知,所提出的方法具有良好的预测变螺旋铣刀铣削稳定性的能力,更高的计算精度、收敛效率和计算效率。     

铣刀的力学和动力学广义建模

本文介绍工业上使用最多的立铣和镶齿铣刀的广义数学模型.立铣刀的几何形状用环绕刀体参量外形的螺旋槽建模.镶齿铣刀的刀刃几何,用每一刀片的局部坐标系定义,并用刀具总坐标系在刀体上对其定位和定向.对两种情况用数学表达了刀刃的坐标.使用铣削时的纯运动学,包括刀具和工件两者的结构振动,估计每一切削点处的切屑厚度.用沿与工件接触的每一切削刃或刀齿积分处理,可预断出任意立铣刀和镶齿铣刀的切削力、振动、表面粗糙度及颤振稳定性图.对螺旋锥球头、大圆孤立铣刀和镶片铣刀,预断和测量出的切削力、表面粗糙度和稳定性图,为提出的广义立铣分析的有效性作了说明.集成到先进切削加工模拟程序中的算法,可用于铣削加工中的工艺计划,以避免颤振、扭矩和功率极限约束及尺寸形成误差.     

MDH80加工中心铣削稳定性研究

为了提高发动机缸体与缸盖结合面的表面加工质量,研究了铣削加工过程中的颤振稳定性问题。进行了刀具—主轴锤击模态试验和铣削力仿真实验,获得了所用刀具的低阶模态参数及铣削力系数。构建了铣削颤振的稳定性叶瓣图,用于指导切削参数的选择和优化。通过该方法可以选取合适的主轴转速和切削深度,避免加工过程中颤振的发生,提高工件表面的加工精度,并对加工刀具及机床本身有保护作用,可提高其使用寿命。     

基于RBF神经网络的花岗岩加工铣削力预测研究

以花岗岩铣削加工中金刚石铣刀为研究对象,对直接导致刀具断裂影响加工效能的关键因素——铣削力进行了研究。针对花岗岩加工铣削力理论公式在实际应用中的局限性,提出了一种采用实验法和神经网络预测相结合的方法。利用实验获得神经网络铣削力预测的建模样本和验证样本以及刀具的断裂极限,利用RBF神经网络对花岗岩加工的铣削力进行了建模预测,通过实验数据验证了该模型的准确性,通过该模型预测获得优选的加工参数,并进行了应用。结果表明该方法有效地提高了刀具的加工效能。     

影响铣削颤振稳定性的因素与规律分析

应用Altintas切削颤振理论实现了铣削颤振的预测,并对影响铣削稳定性的机床系统因素进行了分析。研究发现,稳定性叶瓣图会受到机床的主轴-刀具系统模态参数影响,尤其是模态刚度、阻尼比和固有频率。另外,通过系统动刚度相同的条件下不同的阻尼比和模态刚度组合对铣削稳定性的影响分析发现,模态刚度对系统稳定性的影响要大于阻尼比的影响程度。分别对影响铣削加工稳定性的刀具参数、工件材料特性以及切削参数等因素及其对铣削稳定性的影响规律进行了分析。结果显示:减小刀具齿数、刀具螺旋角和刀具悬伸量,并增大刀具直径对于改善切削颤振有益;具有较小切向切削力系数和径向切削力系数的材料更容易实现稳定切削;减小铣削宽度,并采用顺铣方式,系统的临界切深更大。     

铣削加工颤振稳定域影响参数研究及优化

建立圆柱形铣刀铣削加工动态切削数学模型,采用一种解析法计算并绘制稳定域图,获取加工稳定性随工艺参数变化的规律。分析系统参数对铣削加工颤振稳定特性的影响,提高固有频率、增大系统刚度和阻尼有助于提高系统加工稳定性。基于动态变化的稳定域图及共振功率半频带频率,提出一种铣削稳定性约束下铣削参数优化模型,获取最大加工效率下的主轴转速、径向进给量及轴向进给量参数的最优值。开发铣削稳定性分析仿真软件,实现铣削颤振稳定域分析、共振区域分析、铣削参数优化等功能。将复杂设计分析过程工程实用化,具有工程应用价值。该方法同样可推广到磨削、车削的颤振分析。     

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.