超声-电弧复合焊接系统换能器优化设计

研究了超声-电弧复合焊接系统中超声换能器的优化设计方法.根据超声-电弧复合焊接系统工作条件确定了超声换能器整体形式和各部分材料.通过传统解析法推导了超声换能器整体谐振频率方程,求解各部分基础尺寸.利用有限元分析软件ANSYS对解析法设计的超声换能器结构进行了模态分析,研究了前后盖板尺寸对于超声换能器谐振频率的影响并优化...     

超声振动系统的数值仿真研究

旋转超声加工是加工硬脆性材料的一种很有效方法,而超声振动系统是其核心和关键。借助ANSYS对超声振动系统的超声换能器、变幅杆进行数值仿真,求出谐振频率、放大系数等重要参数,分析了变幅杆不同的过渡圆弧尺寸和外形结构对超声纵向振动性能参数的影响。     

微小孔加工超声电火花系统设计

在难切削材料的微小孔电火花加工中,电火花机床的电极丝一般由机床电主轴端部引入导向套中定位,基于此设计一种通孔式超声系统。所设计的指数过渡阶梯形变幅杆能将两种单一形变幅杆的优势结合起来,且便于电极丝的放入。结合所购置的超声发生器和换能器将此变幅杆的谐振频率设计为43 kHz,大端面设计为20 mm,小端面设计为12 mm。计算其余参数后使用ANSYS进行有限元分析、参数优化,并对加工后的超声系统进行阻抗分析试验,再安装于电火花机床上对不同材料进行微孔加工,观测入口形貌。计算与试验表明：仿真优化后的超声系统的频率与实际频率相差很小,稳定性较高;添加超声加工微孔,不论是加工效率还是孔的表面形貌,都比普通电火花加工质量好。试验结果验证了该超声系统符合初始设计要求。     

基于人工神经网络的超声加工振幅控制的研究

针对超声振动加工中,系统振幅随外界条件的变化而衰减的问题,提出了利用人工神经网络分析换能器的输入电流,以保证超声加工的振幅始终工作在最大值附近。通过人工神经网络训练数据,建立换能器输入电流与超声波发生器频率调整间的关系,达到实时调节超声波发生器频率使整个系统处于谐振的作用。最后,将此方案应用在功率超声珩磨加工中,通过换能器输入电流的稳定性和加工精度证明此方案的效果。     

大功率超声换能器的研制

研究了功率超声换能器的设计方法,依据超声换能器理论建立数学模型,确定了功率超声换能器的工程设计方法,得出功率超声换能器的设计特点及参数,这种功率超声换能器可推广应用。     

旋转超声加工非接触式供电匹配研究

为提高旋转超声加工非接触式供电的能量传递能力,建立了非接触式耦合器能量传递的互感模型,并基于该模型进行原、副边匹配网络的研究。对特定的感应耦合器,给出了几种不同的原、副边匹配网络设计方案,提供了对匹配参数设计的具体方法。通过实验,分别从电学性能和机械性能两方面来对旋转超声非接触式供电的电能传输效果进行评估,测试了功率传输能力和振幅情况。副边并联补偿电容可以有效提高能量传输能力和换能器振动效果,且在此基础上对其进行原边串联可调电感,达到更好的调谐效果和提高了非接触式电能传输系统的传输效率。     

功率超声珩磨单颗磨粒耦合颤振模型

颤振是功率超声珩磨中极易产生的一种动态强烈自激振动现象,是影响工件加工质量和机床加工效率的重要因素之一.在对功率超声珩磨机理研究的基础上,以单颗磨粒工件系统为研究对象,分别建立了功率超声珩磨系统的两自由度非线性耦合颤振物理模型及数学模型,并确定了其微分方程表达式,为进一步寻求抑制、消除颤振策略提供了理论依据.     

安装端面对换能器谐振性能的影响

在换能器的设计过程中,用来安装换能器的端面往往被设计者忽视.文章从半波长换能器的等效电路出发,利用机电类比方法,推导出带安装端面换能器四分之一波长振子的输入电导纳的表达式和频率方程,并讨论了安装端面对换能器谐振性能的影响:即随着安装端面长度和直径的减小,换能器的谐振频率下降,要使换能器处在最佳的谐振状态,应根据安装端面的尺寸相应调整前端盖长度;同时按照功率超声振动系统的原理和要求,设计了一套复合纵向换能振动装置,并依据研究结果设计制作了超声换能器,结果表明换能器在设计频率下工作正常,验证了设计的正确性.该研究结果为换能器优化设计和使用提供了理论依据.     

适合于微孔加工的半波长超声振动系统研究

基于变截面杆纵振方程和阻抗匹配理论，设计了振速易于稳定、重量轻、转动惯量小的半波长超声振动系统，该系统适合于d≤φ1mm的微孔加工。利用薄壳理论，在节面支撑处设计了阻尼器，以此产生径向弯曲变形来缓冲节面处的径向振动，使小孔在钻削过程中的振速易于稳定。同时，在振动系统的输出端采用滑移径向支撑来减少工具的悬伸量和增加钻削时的径向刚度。实践表明，以此设计进行的微孔超声加工取得了良好的效果。     

时间控制法应用于某航空精密型面零件的电火花加工试验研究

时间控制法电火花加工是一种新的电火花加工工艺.介绍时间控制法的原理,并研究其应用于精密型面浅"U"型槽的电火花加工工艺.重点分析运用时间控制方案来控制零件所需的高尺寸精度,同时分析了影响零件尺寸精度和表面粗糙度的因素.通过实验表明,采用时间控制法,选择合适电规准参数,注意加工过程中的要点因素,可加工出高尺寸精度和低表面粗糙度值的精密型面,为此类高精密零件的加工提供了一种有效的加工方法.     

超声振动辅助微塑性成形系统设计与开发

针对微塑性成形工艺过程对位移、力等参数精确控制的要求,分析了超声振动辅助成形系统的设计要点,提出了关键设计参数。超声振动辅助微塑性成形系统由机床本体系统、超声振动系统和伺服控制系统等主要单元组成。机床本体设计参考四柱液压机结构形式,采用两端固支梁和压杆的简化模型,计算得到主要结构尺寸,并用ABAQUS验证其刚度。通过选用匹配的超声发生器和换能器,满足成形过程中的超声振动要求,利用理想变截面杆纵振波动方程设计变幅杆结构,并用ABAQUS进行变幅杆模态分析,确保设计振幅满足要求。伺服控制系统采用可编程多轴控制器PMAC卡控制伺服电机,通过光栅尺和力传感器反馈实现高精度的位置及成形压力控制。通过测试证明在纯铜压缩试验中叠加超声振动,成形压力显著降低,成形精度达到4μm。     

超声检测过程的数值模拟

简要评述超声检测过程的数值模拟,探讨超声波声场的模拟、超声波和缺陷的相互作用、换能器－缺陷检测系统、超声波在材料和构件中的传播路径、探头设计和超声检测可靠性等。     

An Optimized Design of the Bearing in Machines for Ultrasonic Machining Processes

In high-power ultrasonic manufacturing processes, the design of the bearing of the components transmitting ultrasound is of particular importance, since the position of the nodal planes in the vibrating structure is altering as a consequence of changing coupling conditions during the process. A special bearing, which reduces the residual vibrations at the fixing ring by a system of several resonators, has been developed for the use in ultrasonic production processes, such as tube drawing and wire drawing but also drilling and welding. Since the transmitted longitudinal vibrations always involve radial components as well, the dynamic stiffness of the coupling on the interface between the components transferring energy and the components deleting vibration is very important. In the method described in this paper, an optimization of dynamic behavior is attained by stiffness-reduced coupling.     

超声相控阵技术的仿真试验

超声相控阵技术是一种先进的超声无损检测技术。超声相控阵技术通过对超声阵列换能器中各阵元进行精确延时控制,获得灵活可控的合成波束,并可随意控制聚焦点的位置。利用仿真相控阵合成聚焦技术的方法,搭建了一个16阵元、超声信号发射、接收和处理试验系统。利用该系统对缺陷试块进行了检测试验,试验结果与实际试块缺陷情况吻合。通过对试块缺陷的检测试验,对比聚焦与不聚焦的检测效果,证明了相控阵合成聚焦技术可以极大地提高检测的信噪比和灵敏度,验证了相控阵聚焦可以提高检测能力。     

Development of novel ultrasonic transducers for microelectronics packaging

Novel high-frequency ultrasonic transducers have been developed in order to provide faster, more repeatable and stronger microelectronics bonding technology, and fine-pitch packaging can be accomplished by these transducers. The analytical model of the transducer system is established on the basis of electromechanical equivalent circuitry theory, vibration theory and wave theory, which lays the foundation for determining the initial topological information of the ultrasonic transducer. By use of finite element method (FEM), the dynamic characteristics of components are investigated. The resonance frequency, vibration displacement nodes and rule of ultrasonic energy transmission are acquired by making modal and harmonic analysis. Through optimum design by considering the piezoelectric effect, the dimensions of ultrasonic transducer have been gained finally. The prototyped transducer is tested through the impedance analyzer and laser Doppler vibrometer, which proves remarkable resemblance with the theory and FEM. The experimental results also show that there are no undesirable vibration modes around the working frequency, thus it becomes convenient for the vibration control.     

Optimal design of EMAT transmitters

A three-part finite element model is developed that characterizes the ultrasonic pulse produced by an electromagnetic acoustic transducer (EMAT). The model represents several significant improvements over previously published works, as follows: (a) spatial inhomogeneities in the magnetic flux density are calculated and then incorporated in the determination of body forces, (b) an improved model of the electromagnetic induction phenomenon is formulated, allowing a more accurate evaluation of the ultrasonic pulse launched by an EMAT transmitter and (c) results from the model are compared directly with experimental measurements, yielding discrepancies of the order of 15% in the amplitude of the ultrasonic pulse. The new model is used to optimize the design of the EMAT system. In particular, a parametric study was conducted on the effects of varying an EMAT's magnet-to-coil width ratio. For the EMAT configuration considered, significant improvements can be achieved in the ultrasonic beam amplitude and profile by increasing the ratio to about 1.2; further increases in magnet dimensions yield only marginal improvements in the ultrasonic beam, at the cost of excessive EMAT size.     

Circumferential higher order guided wave modes for the detection and sizing of cracks and pinholes in pipe support regions

The non-dispersive propagation of ultrasonic guided wave higher order modes cluster (HOMC) traveling along the circumferential direction in a hollow cylinder and its interaction with defects in pipe support regions is reported. These circumferential guided waves were generated in mild steel (MS) pipe specimens containing artificially created axial notches (simulating axial cracks) and pinholes (simulating pinhole-like defects) of different sizes in order to simulate conditions such as cracking and corrosion under pipe supports. The characteristics of these guided waves were also studied as a function of parameters related to how they were generated; namely, using: (a) 2.25 MHz linear phased array transducer, (b) 2.25 MHz conventional circular transducer and (c) 1 MHz conventional circular transducer. These higher frequency modes were explored for their ability to detect and size defects. Because of access limitations to the pipe support region in actual field testing, the transducer was always placed at a fixed circumferential position and moved axially along the length of the pipe. The defect position along the circumference was ascertained from the time of flight while the defect size was estimated using the amplitude data. The signals obtained for all three transducer configurations are compared for their ability to locate, detect and size the above-mentioned defects. It was shown that at these relatively higher frequencies, the guided wave modes exhibit small dispersion and have the ability to provide improved imaging of small size defects throughout the cross-section of the pipe.