Microstructure and forming mechanism of metals subjected to ultrasonic vibration plastic forming: A mini review

Compared with traditional plastic forming,ultrasonic vibration plastic forming has the advantages of reducing the forming force and improving the surface quality of the workpiece.This technology has a very broad application prospect in industrial manufactur-ing.Researchers have conducted extensive research on the ultrasonic vibration plastic forming of metals and laid a deep foundation for the development of this field.In this review,metals were classified according to their crystal structures.The effects of ultrasonic vibration on the microstructure of face-centered cubic,body-centered cubic,and hexagonal close-packed metals during plastic forming and the mech-anism underlying ultrasonic vibration forming were reviewed.The main challenges and future research direction of the ultrasonic vibra-tion plastic forming of metals were also discussed.

Design and analysis of longitudinal–flexural hybrid transducer for ultrasonic peen forming

Ultrasonic peen forming(UPF)is an emerging technology that exhibits great superiority in both its flexible operating modes and the deep residual stress that it produces compared with conventional plastic forming methods.Although ultrasonic transducers with longitudinal vibration have been widely studied,they have seldom been incorporated into UPF devices for machining in confined spaces.To meet the requirements of this type of machining,a sandwich-type piezoelectric transducer with coupled longitudinal-flexural vibrational modes is proposed.The basic structure of the transducer is designed to obtain large vibrational amplitudes in both modes.Experimental results obtained with a prototype device demonstrate the feasibility of the proposed transducer.The measured vibrational amplitude for the working face in the longitudinal vibrational mode is 1.0μm,and electrical matching increases this amplitude by 40%.The flexural vibration characteristics of the same prototype transducer are also tested and are found to be slightly smaller than those of longitudinal mode.The resultant working strokes of the UPF impact pins reach 1.7 mm and 1.2 mm in the longitudinal and flexural modes,respectively.The forming capability of the prototype has been evaluated via 15-min machining on standard 2024-T351 aluminum plates.After UPF,an improved surface morphology with lower surface roughness is obtained.The aluminum plate test piece has an apparent upper deformation with an arc height of 0.64 mm.The measured peak value of the compressive residual stress is around 250 MPa,appearing at a depth of 100μm.The proposed longitudinal-flexural hybrid transducer thus provides a high-performance tool for plate peen forming in confined spaces.

A Review on Ultrasonic-Assisted Forming:Mechanism,Model,and Process

Compared with conventional forming processes,ultrasonic-assisted forming technology with a high frequency and small amplitude can significantly improve the forming quality of materials.Owing to the advantages of reduced forming force,improved surface quality,avoidance of forming defects,and strengthened surface structure,ultrasonic-assisted forming technology has been applied to increasingly advanced forming processes,such as incremental forming,spinning,and micro-forming.However,in the ultrasonic-assisted forming process,there are multiple ultrasonic mechanisms,such as the volume effect and surface effect.The explanation of the effect of ultrasonic vibration(UV)on plastic deformation remains controversial,hindering the development of related technologies.Recently,many researchers have proposed many new theories and technologies for ultrasonic-assisted forming.To summarize these developments,systematic discussions on mechanisms,theoretical models,and forming performances are provided in this review.On this basis,the limitations of the current study are discussed.In addition,an outlook for ultrasonic-assisted forming is proposed:efficient and stable UV systems,difficulty forming components with complex geometry,explanation of the in-depth mechanism,a systematic theoretical prediction model,and multi-field-coupling energy-assisted forming are considered to be hot spots in future studies.The present review enhances existing knowledge of ultrasonic-assisted forming,and facilitates a fast reference for related researchers.

Theoretical Modeling and Surface Roughness Prediction of Microtextured Surfaces in Ultrasonic Vibration-Assisted Milling

Textured surfaces with certain micro/nano structures have been proven to possess some advanced functions,such as reducing friction,improving wear and increasing wettability.Accurate prediction of micro/nano surface textures is of great significance for the design,fabrication and application of functional textured surfaces.In this paper,based on the kinematic analysis of cutter teeth,the discretization of ultrasonic machining process,transformation method of coordinate systems and the cubic spline data interpolation,an integrated theoretical model was established to characterize the distribution and geometric features of micro textures on the surfaces machined by different types of ultrasonic vibration-assisted milling(UVAM).Based on the theoretical model,the effect of key process parameters(vibration directions,vibration dimensions,cutting parameters and vibration parameters)on tool trajectories and microtextured surface morphology in UVAM is investigated.Besides,the effect of phase difference on the elliptical shape in 2D/3D ultrasonic elliptical vibration-assisted milling(UEVAM)was analyzed.Compared to conventional numerical models,the method of the cubic spline data interpolation is applied to the simulation of microtextured surface morphology in UVAM,which is more suitable for characterizing the morphological features of microtextured surfaces than traditional methods due to the presence of numerous micro textures.The prediction of surface roughness indicates that the magnitude of ultrasonic amplitude in z-direction should be strictly limited in 1D rotary UVAM,2D and 3D UEVAM due to the unfavorable effect of axial ultrasonic vibration on the surface quality.This study can provide theoretical guidance for the design and fabrication of microtextured surfaces in UVAM.

Plastic deformation of magnesium alloy with different forming parameters during ultrasonic vibration-assisted single-point incremental forming

The research of forming parameters on the ultrasonic vibration single-point incremental forming of magnesium alloy plastic deformation can provide a theoretical basis for the establishment of the forming parameters.According to the forming characteristics of magnesium alloy sheet,a new method of ultrasonic vibration-as sis ted single-point incremental forming was proposed.The influence of forming parameters on the plastic deformation of magnesium alloy was studied by finite element simulation and experimentation.The influence of vibration frequency,amplitude,friction coefficient,and tool head size on stress and thinning rate of magnesium alloy during ultrasonic vibration-as sis ted single-point asymptotic forming was studied.The results show that the vibration frequency of 20 kHz and forming tool radius of about 5 mm are beneficial for plastic deformation magnesium alloy in ultrasonic vibration-assisted single-point incremental forming.With vibration amplitude increasing,the maximum shear stress tends to decrease as a whole,but at the amplitude of 0.16 mm,the thinning rate is large and fracture occurs easily.With friction coefficient increasing,the maximum shear stress tends to increase,and there is a good linear relationship between the maximum thinning rate and the friction coefficient.

Ultrasonic constitutive model and its application in ultrasonic vibration-assisted milling Ti3Al intermetallics

Ultrasonic vibration-assisted technology is widely utilized in the performance research and manufacturing process of metallic materials owing to its advantages of introducing highfrequency acoustic systems. However, the acoustic plasticity constitutive model and potential mechanism, involving Ti3Al intermetallic compounds, have not yet been clarified. Therefore, the Ultrasonic-K-M hybrid acoustic constitutive model of Ti3Al was established by considering the stress superposition, acoustic thermal softening, acoustic softening and acoustic residual hardening effects according to the dislocation density evolution theory and crystal plasticity theory. Meanwhile, the mechanical behavior of ultrasonic vibration-assisted tension(UVAT) and microstructure of ultrasonic vibration-assisted milling(UVAM) for Ti3Al was investigated. Dislocation density to be overcome from initial deformation to failure of Ti3Al was calculated in UVAT and was verified in UVAM. The results indicated that the Ultrasonic-K-M model showed a good agreement with the experimental data. There was an obviously softening phenomenon after introducing the ultrasonic energy field in the Ti3Al whole deformation region, and the degree of softening was positively correlated with amplitude. Furthermore, the maximum reduction ratio in yield strength of Ti3Al was16 % and the maximum reduction value in ultimate tensile strength was 206.91 MPa. The elongation rose first and then fell as amplitude enlarged, but only as the vibration was applied in the whole deformation region, the elongation was always greater than 14.58 %. In addition, The UVAM process significantly reduced the dislocation density increment to be overcome for Ti3Al material removal by 1.37 times, and promoted dislocation motion and cancellation to make twisted dislocations evolve into parallel dislocations. As the amplitude increased to 4 μm, the depth of the disturbed area of the plastic deformation layer increased by a maximum of 2.5 times.

钛合金温度/超声复合能场辅助成形及应用

基于材料在温度场下高温软化效应和超声能场下体积效应与表面效应,提出了钛合金温度/超声复合能场辅助成形方法,期望利用超声振动能场进一步提高钛合金钣金件热成形变形能力和成形质量,或者在相同成形质量下降低钛合金热成形温度。介绍了温度/超声复合能场辅助成形原理与装置,分析了复合能场对钛合金板材力学性能、微观组织以及钛合金板与模具间摩擦的影响。在此基础上,将该方法应用到钛合金弯曲及复杂弯边件的成形中,并对成形质量及成形性能进行了分析。最后对复合能场辅助成形过程存在的问题及发展趋势进行了总结与展望。

Vibration characteristics and machining performance of a novel perforated ultrasonic vibration platform in the grinding of particulate-reinforced titanium matrix composites

Ultrasonic vibration-assisted grinding(UVAG)is an advanced hybrid process for the precision machining of difficult-to-cut materials.The resonator is a critical part of the UVAG system.Its performance considerably influences the vibration amplitude and resonant frequency.In this work,a novel perforated ultrasonic vibration platform resonator was developed for UVAG.The holes were evenly arranged at the top and side surfaces of the vibration platform to improve the vibration characteristics.A modified apparent elasticity method(AEM)was proposed to reveal the influence of holes on the vibration mode.The performance of the vibration platform was evaluated by the vibration tests and UVAG experiments of particulate-reinforced titanium matrix composites.Results indicate that the reasonable distribution of holes helps improve the resonant frequency and vibration mode.The modified AEM,the finite element method,and the vibration tests show a high degree of consistency for developing the perforated ultrasonic vibration platform with a maximum frequency error of 3%.The employment of ultrasonic vibration reduces the grinding force by 36%at most,thereby decreasing the machined surface defects,such as voids,cracks,and burnout.

Ultrasonic vibration-assisted machining:principle,design and application

Ultrasonic vibration-assisted （UVA） machining is a process which makes use of a micro-scale high frequency vibration applied to a cutting tool to improve the material removal effectiveness. Its principle is to make the tool-workpiece interaction a microscopically non-monotonic process to facilitate chip separation and to reduce machining forces. It can also reduce the deformation zone in a workpiece under machining, thereby improving the surface integrity of a component machined. There are several types of UVA machining processes, differentiated by the directions of the vibrations introduced relative to the cutting direction. Applications of UVA machining to a wide range of workpiece materials have shown that the process can considerably improve machining performance. This paper aims to provide a comprehensive discussion and review about some key aspects of UVA machining such as cutting kinematics and dynamics, effect of workpiece materials and wear of cutting tools, involving a wide range of workpiece materials including metal alloys, ceramics, amorphous and composite materials. Some aspects for further investigation are also outlined at the end.

A METHOD OF PREPARING SPHERICAL NANO-CRYSTAL CELLULOSE WITH MIXED CRYSTALLINE FORMS OF CELLULOSE Ⅰ AND Ⅱ

A new kind of nano-crysta cellulose (NCC) prepared from natural cotton fiber has been obtained by the method ofacid hydrolysis. Compared to most other nanophase materials that derive from inorganic materials, our products are preparedfrom natural cotton fibers. The products are of spherical shape with mixed crystal forms of cellulose I and II. The preparationconditions determine the properties of the products. Prior treatment is a critical procedure. The properties of the products arealso strongly affected by such conditions as the kinds of acids used, the ratio of the acid mixture, the acid concentration, theultrasonic agitation time and hydrolysis temperature. The number average molecular weight of NCC is determined by gelpermeation chromatography (GPC). The particle size and shape were determined by transmission electron microscopy(TEM). X-ray diffraction was used to detect the crystallinity and average crystallite size of the panicle.

Thermomechanical coupling effect on characteristics of oxide film during ultrasonic vibration-assisted ELID grinding ZTA ceramics

Ultrasonic vibration-assisted ELID(UVA-ELID)grinding is utilized as a novel and highly efficient processing method for hard and brittle materials such as ceramics.In this study,the UVA-ELID grinding ZTA ceramics is employed to investigate the influence of thermomechanical loading on the characteristics of oxide film.Based on the fracture mechanics of material,the model of internal stress for oxide film damage is proposed.The thermomechanical loading is composed of mechanical force and the thermal stress generating from grinding temperature.The theoretical model is established for the mechanical force,thermal stress and internal stress respectively.Then the finite element analysis method is used to simulate the theoretical model.The mechanical force and grinding temperature is measured during the actual grinding test.During the grinding process,the effect of grinding wheel speed and grinding depth on the thermomechanical force and the characteristics of oxide film is analyzed.Compared with the conventional ELID(CELID)grinding,the mechanical force decreased by 25.6%and 22.4%with the increase of grinding wheel speed and grinding depth respectively,and the grinding temperature declined by 10.7%and12.8%during the UVA-ELID grinding.The thermal stress in the latter decreased by 16.3%and20.8%respectively,and internal stress reduced by 12.3%and 15.6%.It was experimentally found that the topographies of oxide layer on the surface of the wheel and the machined surface in the latter was better than that in the former.The results indicate that the action of ultrasonic vibration establish a significant effect on the processing.Subsequently,it should be well considered for future reference when processing the ZTA ceramics.

The influence of ultrasonic vibration on parts properties during incremental sheet forming

The integration of ultrasonic vibration into sheet forming process can significantly reduce the forming force and bring benefits including the enhancement of surface quality,the enhancement of formability and the reduction of spring-back.However,the influencing mechanisms of the high-frequency vibration on parts properties during the incremental sheet forming(ISF)process are not well known,preventing a more efficient forming system.This paper comprehensively investigates the effects of different process parameters(vibration amplitude,step-down size,rotation speed and forming angle)on the micro-hardness,minimum thickness,forming limit and residual stress of the formed parts.First,a series of truncated pyramids were formed with an experimental platform designed for the ultrasonic-assisted incremental sheet forming.Then,microhardness tests,minimum thickness measurements and residual stress tests were performed for the formed parts.The results showed that the surface micro-hardness of the formed part was reduced since the vibration stress induced by the ultrasonic vibration within the material which eliminated the original internal stress.The superimposed University,Beijing 100083,People’s Republic of China ultrasonic vibration can effectively uniform the residual stress and thickness distribution,arid improve the forming limit in the case of the small deformation rate.In addition,through the tensile fracture analysis of the formed part,it is shown that the elongation of material is improved and the elastic modulus and hardening index are decreased.The findings of the present work lay the foundation for a better integration of the ultrasonic vibration system into the incremental sheet forming process.

WC Particle High Speed Steel Composites Manufactured by Ultrasonic Spray Forming

The process of manufacturing high speed steel matrix composites reinforced by WC particles was studied. The changes in microstructures and mechanical properties of composites with WC particles were also investigated. The results show that increasing the deposition height can significantly enhance the bending strength and hardness of the alloy, and that the fishbone like carbide ledeburite structure gradually diminishes as the WC particles content increases. It was discovered that the hardness of the composites increases due to the increase of pointlike carbide ledeburite, accompanying the breaking of the fishbone like and the net like carbides. However, the bending strength deteriorates due to excessive WC particles increasing the brittle interfacial phase.

超声振动辅助微挤压成形界面摩擦特性研究

基于超声振动辅助微挤压成形过程摩擦特性表征需求,将超声振动辅助双杯挤压实验拆分为超声振动辅助正杯挤压和反杯挤压两个部分。通过超声振动辅助T2紫铜正杯挤压和反杯挤压的对比成形实验研究了不同超声振动模式辅助微挤压成形过程中试样-模具型腔间的界面摩擦特性,并提出一种量化评价新方法来评估超声振动辅助微挤压成形试样-模具型腔间摩擦应力及摩擦因数的变化规律。结果表明,微挤压成形应力降低值和试样-模具型腔间的摩擦应力降低值都随着超声振幅的增大而增大,且随着工具超声振动、工具-工件复合超声振动和工件超声振动的不同超声振动模式顺序依次增大。

超声振动辅助塑性成形及形性预测研究进展

随着微机电系统等领域的快速发展,对零件成形精度与性能的要求日益增加。超声振动辅助塑性成形是一种典型的能场辅助塑性成形工艺,相比于传统塑性成形工艺,具有流动应力低、材料成形能力高、界面摩擦少、成形质量较好等优势,被广泛应用于难成形材料加工、微成形、复杂构件成形等塑性成形过程。然而,由于不同塑性成形工艺中金属的变形行为特性存在较大差异,对塑性成形质量与成形性能进行预测有利于实现成形过程的形性协同控制。介绍了超声振动辅助塑性成形在体积成形工艺(镦粗、挤压、拉拔等)与板料成形工艺(拉伸、拉深、渐进成形、冲压等)中的应用及发展概况,讨论了超声振动对材料塑性变形过程中宏观表现与微观演化的影响。在已有研究基础上,重点分析了超声振动辅助塑性成形过程中成形能力预测(流动应力、成形极限等方面)和成形性能预测(表面性能、力学性能、微观组织等方面)的研究进展,为金属零部件成形高质量形性调控提供理论参考,并展望了超声辅助塑性成形工艺的发展趋势。

面向超声喷丸的纵弯复合换能器设计与分析

为解决当前超声喷丸枪在狭小空间内难以加工壁板的问题,设计了一种纵弯复合模态的夹心式压电超声喷丸换能器.采用COMSOL仿真软件,对换能器进行模态分析,计算得到纵振和弯振的谐振频率,并改变尺寸使换能器在2种模态下均呈现较大的振幅.采用多普勒测振仪对换能器工作端面扫频,纵振与弯振振幅分别为1.0和0.8μm,经匹配后振幅各增长了40%和50%.利用激光位移传感器测得2种模态下撞针振幅均可到达1.2 mm.同时,对2024-T351铝合金板件进行了超声喷丸成形试验,并采用X射线法对喷丸后板件中的残余应力进行了检测.超声喷丸成形试验和残余应力检测表明,板件喷丸后发生不同程度的变形,且板件中的残余压应力最大可达250 MPa,验证了纵弯复合换能器的有效性.

裂缝形式对泡沫混凝土声参量影响的试验研究

首先对126个配合比相同的泡沫混凝土试块进行抗压试验,并统计分析了经抗压试验后、未完全破损的泡沫混凝土试块的裂缝形式;然后通过超声检测试验研究了不同裂缝形式对泡沫混凝土试块声参量的影响规律.研究表明,比较有代表性的泡沫混凝土裂缝形式为宽度2 mm、角度不超过30°、相对位置主要集中在试块中间区域的单条裂缝;泡沫混凝土试块的声速、波幅、主频均随着裂缝数量的增加而减小;随着裂缝长度的增加,泡沫混凝土试块的声速逐渐下降,波幅、主频的变化范围及其最大值均随之减小;裂缝长度一定时,随着裂缝宽度的增加,泡沫混凝土试块的声速呈线性下降的趋势,波幅则呈先快速减小后缓慢减小的趋势,裂缝宽度对泡沫混凝土试块的主频没有明显影响;随着裂缝角度的增加,泡沫混凝土试块的声速、波幅和主频均呈先增加、后减小、再增加的趋势;裂缝相对位置对泡沫混凝土试块的声速和主频的影响均不是很大,但当裂缝相对位置从超声发声端移向超声接收端时,泡沫混凝土试块的波幅逐渐增大;随着荷载裂缝发展,泡沫混凝土试块的声速、波幅在加载前期均变化不大,在加载后期则均迅速减小,且终止加载时5组试块的波幅大小与试块的破坏程度呈负相关关系.

钛合金超声振动辅助弯曲成形的有限元分析及成形装置关键部件的强度校核

在金属材料塑性成形过程中,超声振动能够有效降低材料成形力,提高成形性能,在钛合金这类难加工材料的成形制造中有着广阔应用前景。为了探究超声振动对钛合金塑性成形的影响,设计一套超声振动辅助成形装置来进行钛合金成形试验。为验证装置设计是否能够满足材料成形试验的要求,需要进行强度校核。本研究以其关键部件即装置支架为研究对象,采用有限元仿真软件ABAQUS对钛合金板V形弯曲成形过程进行分析,得到典型工作状态下弯曲力和凸模位移之间的关系以及设备的最大工作载荷,进而对装置支架进行静力学分析,得到装置支架在加载状态下的应力分布和整体变形情况。研究结果表明:装置支架的整体设计能满足超声振动辅助成形试验的强度和刚度需求。

声塑性机制及其在塑性加工中的应用

超声振动作为一种能量输入被广泛应用于各类塑性成形工艺中,目前研究普遍认为,超声振动叠加在金属塑性变形上可显著降低成形载荷,称之为声塑性,主要作用机制包括体积效应和表面效应。分别对目前已有的考虑体积效应和表面效应的理论模型的研究进展进行了综述,在此基础上,从超声辅助工艺原理、利用声塑性机制的侧重点以及超声辅助塑性成形装置的改进3个方面介绍了搅拌摩擦焊、滚压、旋压以及微成形等领域采用超声振动辅助塑性成形工艺的发展现状,并提出了未来主要的研究思路。

激光立体成形和超声冲击混合制造Ti60合金的显微组织和性能

采用激光立体成形(LSF)和超声冲击处理(UIT)混合制造的方法,通过逐层强化表面,改善Ti60合金的结构和性能。采用SEM、TEM和XRD分析并比较UIT前后LSF处理Ti60样品的显微组织、力学性能和阻燃性能。结果表明,UIT后LSF处理Ti60合金的晶粒得到细化,冶金缺陷减少。同时,UIT后沉积层严重变形,并在表面形成纳米晶体。此外,沉积层表面显微硬度提高,残余应力由拉应力变为压应力。烧蚀坑面积减少了21%,Mo,Nb和Zr元素的比例增加。综上所述,LSF和UIT的混合制造可以改善LSF处理Ti60样品的显微组织和性能。