基于直流电源的短电弧铣削加工性能研究

为了探究直流短电弧铣削加工性能,分别以管状镀铜石墨为工具电极,45钢作为工件材料,分析电压、电极转速、加工深度对电极损耗率、材料去除率(MRR)和表面质量的影响规律。试验结果表明:增大电压可以有效提高MRR,但会降低工件表面质量;提高电极转速不仅能够改善工件表面质量,同时还能获得较高MRR;加大铣削深度能够大大提高MRR,但切深过大会使铣削变得困难,当铣削速度不能满足进给率时,会出现撞刀现象,工具电极断裂从而产生台阶面,严重影响工件表面成型质量。     

内外冲液组合式的短电弧铣削加工间隙流场仿真

为进一步改善短电弧铣削加工间隙排屑情况,采用内外冲液组合式,通过Fluent对其进行仿真分析,得到了流场压力、速度和蚀除颗粒分布规律。分析不同冲液方式、冲液压力和电极转速对极间间隙流场特性的影响规律,并进行单因素试验。以MRR、TWR为评价指标,找出短电弧铣削加工性能的最佳参数。     

侧铣式高速电弧放电加工工艺研究

侧铣式高速电弧放电加工利用电极侧面放电蚀除工件材料,能加工复杂的型腔、沟槽及直纹面等。为了探索这种新型电弧放电加工的工艺特性,探讨了峰值电流、脉宽和冲液压力等条件对工件材料去除率和相对电极损耗率的影响。实验结果表明:提高冲液压力和峰值电流均能增大工件材料去除率;相对电极损耗率随冲液压力的提高而增大,随峰值电流的提高而减小。在一定范围内,工件材料去除率随脉宽的提高而增大,相对电极损耗率随脉宽的提高而减小。     

单晶SiC基片的磁流变化学复合抛光

基于芬顿反应的磁流变化学复合抛光加工原理,对单晶SiC基片进行磁流变化学复合抛光试验,研究工艺参数对其抛光效果的影响。结果表明：随着金刚石磨粒粒径的增大,材料去除率先增大后减小,而表面粗糙度先减小后增大;随着磨粒质量分数的增大,材料去除率增大,而表面粗糙度先减小后增大;当羰基铁粉质量分数增大时,材料去除率增大,而表面粗糙度呈先减小后增大的趋势;随着氧化剂质量分数增大,材料去除率先增大后减小,而表面粗糙度呈现先减小后增大的趋势;加工间隙对材料去除率的影响较大,加工间隙为1.0 mm时,加工表面质量较好;随着工件转速和抛光盘转速增大,材料去除率均先增大后减小,表面粗糙度均先减小后增大。获得的优化的工艺参数为：磨粒粒径,1.0μm;磨粒质量分数,5%;羰基铁粉质量分数,25%;过氧化氢质量分数,5%;加工间隙,1.0 mm;工件转速,500 r/min;抛光盘转速,20 r/min。采用优化的工艺参数对表面粗糙度约为40.00 nm的单晶SiC进行加工,获得表面粗糙度为0.10 nm以下的光滑表面。     

钛合金结构件磁流变电解复合抛光试验研究

目的 针对钛合金结构件高质高效抛光需求，提出了磁流变电解复合抛光新方法，探究不同抛光参数对钛合金表面质量的影响，以实现钛合金构件的高质高效抛光。方法 深入探究了加工电压、加工间隙、电解质质量分数和抛光转速等参数对钛合金抛光表面粗糙度以及粗糙度变化率的影响，分析了不同抛光参数下的钛合金表面形貌变化，验证了磁流变电解复合抛光钛合金的可行性。结果 随着电解液中Na NO3质量分数的提高，钛合金表面粗糙度先减小后增大，质量分数为1.0%～2.5%时，得到了优于单磁流变抛光加工的抛光效果。不同加工电压下的表面粗糙度对比结果表明，在加工电压为0.1 V时，钛合金加工后表面粗糙度达到最小，而后随着加工电压的增大，加工区域表面粗糙度呈现增大趋势；随着加工间隙的增大，钛合金抛光表面粗糙度呈现先减小后增大的趋势；随着抛光工具转速增大，钛合金加工后表面粗糙度先减小后增大。相比于单一的磁流变抛光，磁流变电解复合抛光钛合金90 min，可使表面粗糙度从初始323 nm降低至15nm，加工效率提高了62.5%。结论 磁流变电解复合抛光工艺能够用于钛合金人工关节假体高效高质量的抛光。     

不同电极材料的短电弧铣削加工效率研究

短电弧铣削加工是一种新型的放电加工,它进一步提高了放电加工效率。论述了短电弧加工材料去除机制、去离子原则和热现象,分析了余热对材料去除率(MRR)的影响。研究了短电弧铣削加工效率的主要指标——MRR,在不同工具、工件电极的材料组合下,分析峰值电流、脉冲时间、脉冲间隔、进给速度、气压等工艺因素对MRR的影响规律。实验表明:不同电极材料组合的MRR存在差异;在大多数放电条件下,石墨电极和45碳钢工件获得较高的MRR,而紫铜电极和镍基高温合金GH4169工件获得较低的MRR。     

超声振动滚压加工参数对TC4钛合金表面质量的影响

通过超声振动滚压加工正交试验,研究主轴转速、进给速度、静压力和加工次数对TC4钛合金表面质量的影响,并将材料的表面粗糙度、显微硬度及残余应力作为其表面质量的评价指标。试验结果表明:超声振动滚压加工工艺能降低TC4钛合金表面粗糙度,大幅度提高显微硬度,在表面引入残余压应力;合适的主轴转速、进给速度及加工次数使表面粗糙度达到最佳效果,一定范围内,表面粗糙度随着静压力的增大而减小;主轴转速对材料表面显微硬度影响较小,显微硬度随着进给速度的增大而减小,随着静压力及加工次数的增大而增大;主轴转速对材料表面残余应力有无规律的影响,材料表面的残余应力值随着进给速度的增大而减小,随着静压力及加工次数的增大而增大。     

振动辅助液中喷气电火花加工性能研究

提出了振动辅助液中喷气电火花加工方法。该方法通过工件机械振动改善了极间的放电状态,降低了短路率。通过实验研究了机械振动的频率和振幅对液中喷气电火花加工性能的影响,研究了振动辅助作用下电加工参数、气体压力、工具电极转速对加工性能的影响。结果表明,工件的机械振动可有效提高液中喷气电火花加工的材料去除率,改善加工表面质量,而电极损耗几乎为零。     

超声辅助电解磨削GH625微小孔工艺研究

超声振动辅助电解磨削加工技术是一种以超声振动作为辅助、电解磨削为主要加工方式实现零件精加工的新型加工技术.为获得更高表面质量的管电极微孔,首先利用单因素法对GH625材料进行管电极打孔,初步得到最小平均锥度0.043°的微小孔,然后通过正交试验研究脉冲电压、电解液浓度、主轴进给速度、阴极转速对加工微小孔锥度和表面质量的...     

高速电弧放电加工的多孔电极制备

高速电弧放电加工是利用流体动力断弧机制实现对电弧的有效控制从而去除材料的。流体动力断弧机制的实现依赖于高速的极间流场动力,该动力需由多孔电极的强制内冲液提供。首先阐明了选择石墨作为多孔电极材料的原因;其次,完成了集成CAD、CAE(主要是CFD)和CAM的多孔电极设计、仿真及制造的软件模块,这些模块能依据加工工件的特征快速、高效地完成对应多孔电极的制备;最后,为了验证制备的一系列多孔电极的电弧加工能力,对典型工件包括具有复杂3D型腔的零件进行了加工实验。结果表明:基于多孔电极的高速电弧放电加工能实现很高的材料去除率(MRR14 000 mm3/min)和较低的工具损耗率(TWR1%),故特别适用于以难切削材料的大余量去除为主的粗加工。     

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.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。