蓄能缸体薄壁件的车削变形问题研究

薄壁件由于刚度较弱,容易产生变形,所以给车削加工带来一定困难,精度不容易得到保证。本文以蓄能缸体的加工为例,对薄壁件的车削变形问题进行分析,并提出了一些解决这些问题的方法。     

浅谈薄壁类零件高效铣削加工方式

航空零部件具有结构复杂、壁薄、精度要求高和制造工艺性差等特点,在切削力作用下极易产生变形而引起表面误差,严重影响加工精度,是近年来航空制造技术中比较突出的问题之一。该文通过理论研究总结并对现场典型薄壁零件加工效果分析论证,对工件装夹、定位方法、工艺加工方法、刀具路径优化进行探讨,寻找薄壁类零件高效铣削加工方式。     

深孔薄壁锥形件冷加工工艺研究

通过对锥形件产品的研制,论证了采用复合挤压、变薄拉伸和扩锥挤压相结合的工艺方法是加工深孔薄壁锥形件的可靠工艺方法,得出了变薄拉伸加工中加工率不应处于临界加工率状态的结论.     

筒形薄壁件内型面加工用柔性夹具设计

筒形薄壁件在军民品生产中占有极大的比例,针对简形薄壁件内型面加工中的变形和振动问题,设计了一种柔性夹具,以提高薄壁件在加工过程中的刚性,减小或消除加工过程中的零件变形和切削振动,从而提高零件加工质量。     

U型截面薄壁件测量精度优化方法研究

为提高三坐标测量机在测量一种U型截面薄壁件时的测量精度,分别从温度和测量力两方面研究精度优化方法。基于物体热膨胀效应的原子热振动原理分析铝合金材料的热膨胀影响因素,将温度影响引入测量能力评估算法,得到可实施温度补偿的边界条件,利用Minitab对变温测量实验数据进行分析并拟合出该薄壁件在径向方向上的热膨胀函数,实现在温度边界范围内对测量结果进行精度优化;针对RDS XXT测头系统的内部构造,通过对测头结构进行力学分析并建立采点触发力学模型,确定该测头系统的采点触发模式为力矩触发,利用材料力学理论分析力矩触发模式下的被测件形变机理。测力及测量截面位置交叉测量实验结果表明:测杆长度越长,测力越小,且越靠近工件底部,测量误差越小,测量精度越高。     

环形薄壁件加工中的胀紧减振夹具设计

薄壁零件在军民品生产中应用日益广泛,针对薄壁件加工中的变形与振动问题,本文介绍了一种利用聚氨脂橡胶件做为减振和胀紧零件的胀环,改善环形薄壁件在加工过程中的刚性,减小或消除加工过程中的切削振动,从而提高零件加工质量和精度。     

圆锥形薄壁件成形过程及性能的数值模拟

采用了ANSYS有限元分析软件对圆锥形薄壁件成形过程进行了数值模拟,分析了冲压过程中两类失效形式产生的原因,并提出了相应的解决办法.     

SLM成形薄壁件尺寸偏差预测与控制研究

目的 针对选区激光熔化成形薄壁件过程中存在的变形较大、精度低等问题,通过获得最优工艺参数区间来减小薄壁件的变形。方法 利用有限元软件分析薄壁件成形过程中温度场和应力场的演化规律;建立形变量预测模型并进行试验验证,研究工艺参数对薄壁件尺寸偏差的影响,得到激光功率、扫描速度与形变量之间的关系,实现对形变量的预测和控制。结果 随着扫描层数的增加,熔池的最高温度和热影响区也随之增大,等温线越密集,温度梯度越大,最终趋于稳定;薄壁件成形过程中,出现两侧壁边缘向内倾斜、上侧边缘出现内凹的现象,薄壁件的最大应力随层数的增加而减小,最大热应力主要分布在薄壁件底层的两端;形变量随激光功率的增大而增大,随扫描速度的增大而减小,薄壁件的形变量最小约为0.02 mm;试验验证所建立的数学模型误差在10%左右,误差较小,可以对形变量进行良好的预测和控制。结论 激光功率100~200 W、扫描速度800~1 000 mm/s为最优参数区间;降低能量密度可以有效降低薄壁件形变量,提高其精度。     

铝合金薄壁框架件加工变形的应力分布研究

7075航空铝合金薄壁框架件加工变形的预测是构件形变控制领域的技术难题,掌握铝合金薄壁框架件上的加工应力分布对预测构件变形有着重要的作用.本文运用弹性力学理论,在实验基础上,利用层削法和X射线衍射应力测试技术,建立了薄壁框架件的应力与弯曲变形的力学模型.模型反映了加工应力和初始应力对构件实际变形的影响机制,在此基础上,再通过数学解析方法,以这两种应力场分布为主变量,构建了薄壁框架构件应力与变形的函数,完成了对构件最大变形挠度的计算.通过比较实验所测构件变形值与计算得到的变形结果发现:构件实际测量最大变形量基本处于数学解析函数计算变形区间内,数据偏差在20~50μm.研究结果表明:在已知初始应力、结构尺寸、加工参数条件下,解析函数能有效地预测出薄壁框架件加工后的变形,可为薄壁构件加工变形控制提供工艺指导.     

激光选区熔化成形薄壁件研究进展

激光选区熔化是一种可以实现近净成形的数字化制造技术,能够制造传统工艺不能生产的复杂薄壁件,被认为是未来制造业的主导方向,应用前景广阔。综述了激光选区熔化成形薄壁件的研究现状,针对于激光选区熔化成形薄壁件成形质量较差、力学性能偏低等问题,重点介绍了工艺参数、热处理工艺以及壁厚等因素对激光选区熔化成形件微观组织、缺陷、成形质量及力学性能的影响,其中成形壁厚存在阈值,随着壁厚增加,薄壁孔隙先增加后减小,力学性能呈相反趋势。最后总结了薄壁件激光选区熔化成形存在的问题及未来的研究方向。     

Versatile waveguide-coupled optofluidic devices based on liquid core optical ring resonators

A versatile waveguide-coupled optofluidic device using the liquid core optical ring resonator (LCORR) that can be operated with liquid of any refractive index (RI) is theoretically analyzed and experimentally demonstrated. The results confirm the confinement of resonant modes for all sample RIs, and reveal that confined modes in a high-RI core are excited by an external waveguide by resonant tunneling through the LCORR wall. It is further found that a thin wall must be used for effective interaction between the core mode and the waveguide. The results have important applications in optofluidic devices, including sensors, microfluidic lasers, and nonlinear optics.     

An algorithm for a combined acoustic signal receiver

It is proposed sorting the instantaneous values of oscillatory velocity and acoustic pressure using the criterion of the similarity with signals in a plane wave using a combined acoustic-signal receiver. Part of the received instantaneous values are rejected, the Poynting vectors are calculated and their angular selection is carried out. Modeling showed that the algorithm enables two sources, separated by 2° in all, to be resolved even if their mean levels differ by 6 dB. __________ Translated from Izmeritel’naya Tekhnika, No. 10, pp. 59–62, October, 2007.     

Definition of Instantaneous Dielectric Loss Factor and Digital Algorithm for Online Monitoring

Among the digital algorithms currently available for online monitoring of the dielectric loss factor of power apparatus, there are unavoidable limitations, such as that most of them must strictly meet the synchronous sampling criterion simultaneously with a precondition that the power frequency must be invariable in the sampling periods. This paper presents a unique definition and a corresponding digital algorithm of the instantaneous dielectric loss factor. The theoretical basis of the algorithm is also deduced. In a nonstationary signal environment where power frequencies are randomly variable, the algorithm can accurately track the instantaneous frequency of power signals, recursively calculate the parameters of parallel equivalent circuit, and, finally, figure out the waveform of the instantaneous dielectric loss factor. Simulations and experimental results show that the proposed algorithm renders good application performance without being affected by the limitations incurred from synchronous sampling and harmonics.      

Measurement of lifetime of nonequilibrium charge carriers in single-crystal silicon

An equation of continuity describing decay of nonequilibrium charge carriers after illumination of semiconducting silicon by a long duration pulse of light with wavelength of 1.06 µm is solved by numerical methods in a one-dimensional approximation. It is shown that, when the volume recombination lifetime of minority carriers is 500 µs and higher, the known formula for “thin” samples 1/τ_eff = 1/τ _V + 2s/d cannot be used to evaluate the effective lifetime of thin plates (10 µm or above). Estimations of the range of variation of excess density in which the instantaneous lifetime achieves saturation are carried out; this takes place in the second part of the relaxation curve if the wafer thickness does not exceed three diffusion lengths of minority carriers. It is demonstrated that the formula scaled to an infinite recombination rate is applicable for thicknesses of the sample within the range from one to five diffusion lengths. For higher thicknesses, it is necessary to apply corrections taking into account the dependence of instantaneous lifetime on the excess density of nonequilibrium charge carriers.     

Determination of global failure pressure for tubes with two parallel cracks

The 40% of wall thickness criterion, which has been used as a plugging rule is applicable only to a single cracked steam generator tubes. In the previous studies performed by the authors, several failure prediction models were introduced to estimate the plastic collapse pressures of steam generator tubes containing two adjacent parallel axial through‐wall cracks. These models were applied preliminarily for thin plates with two parallel through‐wall cracks and the crack opening displacement (COD) base model was selected as the optimum one. The objective of this study is to verify the applicability of the proposed failure prediction model for real steam generator tubes with two parallel axial through‐wall cracks. For this purpose, a series of plastic collapse tests and finite element analyses have been carried out for the steam generator tubes with two machined parallel axial through‐wall cracks. Thereby, it was proven that the proposed failure prediction model can be used for estimating the global failure pressure quite well. Also, interaction effects between two adjacent cracks were assessed through additional finite element analyses to investigate the effect on the global failure behaviour.     

Copper and platinum thermal resistance converters for temperature measurements to 200°C

Copper and platinum resistance thermal converters are compared by the criterion of minimum theoretically attainable error when they function as part of transducers with optimized parameters. Translated from Izmeritel'naya Tekhnika, No. 4, pp. 30–32, April, 1997.     

利用反射式衍射光栅进行瞬态应变测量

介绍了利用反射式衍射光栅进行瞬态应变测量的方法,在一维细长杆中,通过测量杆未端的绝对速度,就可以算出动态应变和应变灵敏度系数K,文章对该方法进行了理论计算和实验结果分析,给出了结论和进一步研究方向。     

Ti-6Al-4V熔模精密铸造充型及凝固过程计算机模拟

应用自行开发的基于微机上运行的铸件凝固 /充型计算机模拟软件 ,对Ti-6Al-4V钛合金薄壁件精密铸造的充型及凝固传热过程进行了模拟分析 .应用自行安装的多通道钨铼热电耦温度数据计算机采集、分析系统 ,测定了该钛合金起吊接头精密铸件的凝固冷却曲线 ,获取了该合金有关的凝固参数 .对包括上述零件在内的钛合金薄壁件精密铸造的充型过程及凝固传热的温度分布进行了数值模拟 ,模拟计算与实测结果合理吻合 .基于该研究可对其精密铸造工艺进行优化设计 .     

水土围压爆破拆除混凝土薄壁池体

从常见的钢筋混凝土薄壁池体的爆破拆除工程出发 ,指出了水压爆破和钻眼爆破法的缺陷 ,提出了更适合于薄壁池体拆除的新方法———水土围压爆破 ;同时对如何确定爆破参数进行了较详尽的论述。通过工程实例 ,进一步证明了该方法的可行性。     

机枪内膛壁面瞬态温度的测试

借助专门研制的盲孔测温传感器和瞬态信号采集系统,测量得到距14．5mm机枪身管内壁一定厚度处（xp层等温面）各时刻的温度值．建立单发射击时身管壁瞬态导热的数理模型．以实验测定的xp层的温度一时间函数为已知条件,采用分析解法得到定解问题的解析解．最终可求出身管内壁各时刻的温度值．