叶轮零件的五轴数控制造质量与关键技术研究

叶轮叶面的制造质量直接影响其运行的效率、性能、流体动力稳定性、工作可靠性和使用寿命等.从具体叶轮零件结构与工艺性分析人手,通过叶轮叶面的三维建模和加工程序调试、仿真分析与刀具轨迹验证,研究叶轮数控加工策略和加工关键技术.经过分析叶轮零件的加工质量,明确了控制插补弦长、插补周期和进给速度、刀轨残留误差,可以控制五轴数控加工的误差,保证制造质量.以叶面造型的轴向截线为加工依据,解决了刀具切削间隔的计算和刀路轨迹的求解,并进行了仿真分析.实践证明:采用五轴数控加工中心对叶面进行截面法加工,避免了加工干涉,容易实现曲面间的光滑走刀,提高了叶片的加工效率和质量,降低了加工成本.     

铣削机器人去除锻件裂纹的轨迹规划研究

针对铣削机器人去除锻件裂纹的问题,进行了相关轨迹规划插补算法的研究。首先,将离散的裂纹轨迹型值点用三次B样条曲线插值,拟合的曲线就是机器人末端执行器的运动路径。其次,提出了梯形速度控制算法,将裂纹路径按照速度敏感点进行分段,确定出每段曲线的加速段、匀速段、减速段的进给速度,进而利用泰勒展开式确定出每个采样周期的插补参数;同时,用三次B样条曲线插补形成各坐标轴的运动增量。最后,建立机器人运动学模型,将笛卡尔空间的插补数据映射到机器人关节空间,在分析机器人各关节位移、速度、加速度的基础上证明了这种插补算法在实际应用中的可行性。     

基于UG和Vericut的开式整体叶轮加工仿真

为降低整体叶轮类零件最终抛光工序的劳动强度、提高加工效率,切削加工工序有很高的尺寸精度要求,文章以提高切削加工仿真尺寸精度为目的,以UG为平台进行了叶轮零件的建模及加工轨迹规划,在Vericut软件中构建了DMU50五轴数控机床的加工仿真环境。将数控加工仿真与刀具路径轨迹规划结合研究,通过仿真检查结果反复修正刀路轨迹,最后设计生成的刀具路径轨迹在仿真加工中残留在0.15mm以内,过切在0.10以内,有效的降低了抛光工序加工余量,可以减少抛光工序工作量,提高抛光效率,降低由于抛光余量大造成烧伤的危险。     

六自由度机器人的运动学分析及码垛轨迹规划

现如今生产过程中的码垛场景多为专用的四自由度码垛机器人,通用性和灵活性较差。为提高码垛过程中机器人的通用性和灵活性,实现六自由度串联机器人的码垛,根据改进D-H法,在UR5机器人各关节末端建立固连坐标系,推导出UR5的正运动学变换矩阵及逆运动学各关节表达式。使用梯形速度控制,确定了码垛过程中直线轨迹部分的运动规律,得到了码垛过程中圆弧轨迹部分的坐标转换关系及机器人末端运动过程。在空间中规划出码垛时机器人末端轨迹,并进行仿真。绘制了各关节运动曲线,表明机器人在码垛过程中轨迹平滑,运行平稳,对六自由度串联机器人的码垛研究具有参考意义。     

基于运动学的机器人轨迹规划研究

针对6自由度关节机器人轨迹规划问题,建立机器人的运动学方程,采用虚拟样机仿真的方法计算机器人各关节角速度和角加速度随时间变化的数据,同时采用拟合算法对数据进行轨迹化处理。建立了关节机器人实验平台,将关节空间轨迹规划参数运用到机器人上,使用激光跟踪仪测量机器人末端轨迹数据,通过机器人末端位置稳定时间和位置超调量来评估轨迹规划的有效性,实验结果表明:该方法所得轨迹平滑可控,可实现机器人按规划运行要求。     

基于ADAMS的六自由度串联机器人运动学仿真研究

借助ADAMS仿真软件建立了六自由度串联机器人的虚拟样机模型,对其运动学问题进行了仿真研究。通过对末端执行器添加点驱动,设置期望轨迹参数方程,仿真测量得到各个关节角度变化的曲线,通过对曲线的拟合,最终得到运动学逆解。利用六个关节的运动驱动,仿真得到机器人末端执行器的位移与速度曲线,其变化平稳,无突变现象。通过在ADAMS平台上进行仿真,可直观的了解到机器人运动过程中的各连杆、各关节及末端执行器的运行状态,为机器人轨迹规划、动力学分析及离线编程、物理样机实验等提供依据。     

基于焊接机器人的关节空间轨迹规划方法

针对"昆山一号"机器人关节空间运动的实际需求,结合机器人实时轨迹插补算法,提出了关节空间轨迹规划方法.运用离线编程软件仿真得到机器人末端运行轨迹,路径平稳连续.通过MATLAB 仿真得到机器人各个关节角度变化曲线和关节速度变化曲线,关节角度曲线平滑连续,关节速度曲线合理无突变.关节空间规划方法也可以应用在由变位机、导轨和机器人组成的多轴系统中,运行轨迹连续稳定,速度曲线满足工艺要求.该方法应用于"昆山一号"焊接机器人中,满足焊接实时调速和实时调整轨迹的需要.规划结果表明关节空间规划方法是合理正确的.     

铣削大理石切削参数对PCD刀具磨损的影响

目的探索PCD刀具磨损机理,以延长刀具使用寿命。方法设计正交试验,研究不同加工参数切削大理石对刀具磨损的影响情况。分析主轴转速、进给速度与切削深度对PCD刀具磨损量的影响规律,以优化切削参数来减小刀具磨损量。根据经验公式,建立单位时间刀具磨损量和固定行程磨损量模型。通过对试验过程刀具振动情况记录,结合刀具实际磨损情况,给出了刀具磨损等级。结果主轴转速的提高可以减少刀具磨损量,进给速度的增大会加剧刀具磨损,而切削深度小于1 mm时,其对刀具磨损量的影响很小,但切削深度大于1 mm时,继续增大切削深度会使刀具快速磨损。利用预测模型能够很好地对刀具磨损情况进行预判,根据磨损等级,得出刀具与机床发生共振时磨损最为严重,在刀具表面产生了明显的犁沟、磨损以及金刚石颗粒脱落。结论在实际加工中,通过提高主轴转速、降低进给速度以及减小切削深度有助于增强刀具的耐用度,避开共振切削参数可以有效降低刀具磨损,主轴转速、进给速度、切削深度分别为12000r/min、500 mm/min、0.5 mm时的切削效果较佳,有最小的刀具磨损量。     

基于NURBS算法的工业机器人轨迹规划研究

轨迹规划是工业机器人研究领域的重要内容之一。为解决使用直线与圆弧逼近不规则曲线方法带来较大误差的问题,提出使用NURBS拟合自由曲线,并使用S形速度曲线来控制机器人末端的运动速度和加速度,使各个插补点的位置、速度和加速度能够连续,将之反推到关节空间可以得到各个关节的角度、角速度和角加速度。最后以IRB2600工业机器人为仿真本体,通过MATLAB仿真证明:NURBS和S形速度曲线相结合的方法可以得到在关节空间连续、平稳的运行轨迹、速度曲线、加速度曲线,减弱了因各关节角度、角速度、角加速度突变带来的冲击影响,优化了机器人运行轨迹。     

五轴联动加工中进给速度的控制算法

目的研究刀具进给速度平稳性对五轴联动加工中复杂自由曲面表面粗糙度、轮廓精度的影响。方法首先对五轴联动机床运动过程中的空间线性插补原理进行了分析,推导出插补周期内各轴的分解速度数学模型。根据数控系统中不同的速度指令方式以及刀具在空间的实际运动距离,分端铣和侧铣两种情况,分别建立了刀具空间运动的实际速度计算模型,然后根据机床各轴的最高速度及加速度约束条件,对各轴分速度、分加速度进行校核处理,最终求得刀具实际的合成速度。最后,基于后置处理技术,用开发的专用后置处理软件进行刀位源代码后置处理,采用某叶轮试件进行了验证,并对实验结果进行了分析。结果在复杂曲面加工中,稳定的表面进给速度会获得较高的表面质量及轮廓精度,曲面曲率变化越大,速度变化对加工质量的影响越大。在同等条件下切削,刀具采用恒表面速度与采用恒进给速度相比,获得的叶片进出汽边轮廓误差值由0.1 mm减小为0.04 mm。结论在五轴联动加工中,越稳定的表面进给速度,越能获得较高的表面质量和轮廓精度,对于曲率变化较大的复杂曲面,需要严格控制刀具的进给速度,尽量获得稳定的表面速度以减少过切值,从而提高零件表面质量。     

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.     

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.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

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.