搅拌摩擦焊技术应用现状和发展趋势

文章对搅拌摩擦焊技术概况和技术特点进行了简要介绍,对搅拌摩擦焊技术在国内外的应用现状进行了分析,并预测了搅拌摩擦焊技术的发展趋势。文章认为,铝合金等轻金属连接是搅拌摩擦焊技术的主要应用领域。同时,在搅拌摩擦焊技术的基础上进行新技术（如表面改性、材料制备和搅拌摩擦点焊等）的开发,是该技术的一个很重要的发展趋势。     

搅拌摩擦焊材料流动的试验表征研究现状

搅拌摩擦焊作为一种较新的固相连接技术,在航空航天、高速列车、汽车、船舶等机械制造领域中具有广阔的应用前景。充分认识搅拌摩擦焊接过程中的塑性材料流动,对于深刻理解焊缝成形机理、优化焊接工艺具有重要的理论指导意义。综述了当前搅拌摩擦焊塑性材料流动的试验表征技术研究现状,重点分析了采用"点"、"线"、"面"和"体"形标记材料来研究塑性材料流动的优缺点。在此基础上,综述了搅拌摩擦焊缝成形机理的研究现状,探讨了关于材料流动的尚未有效解决的关键科学问题。     

搅拌摩擦焊中材料流动行为数值模拟的研究进展

搅拌摩擦焊是一种革命性的焊接技术。相比于熔化焊,搅拌摩擦焊在铝合金、镁合金等材料的焊接方面具有明显的优势。而搅拌摩擦焊过程中材料在熔化温度以下经历剧烈的塑性流动,这与传统焊接过程有着明显不同,因此非常有必要对搅拌摩擦焊过程中的材料流动行为进行研究。由于试验方法本身在空间与时间上的局限性,数值模拟成为研究搅拌摩擦焊过程中的材料流动行为的重要方法。分析搅拌摩擦焊过程中的物理过程,从数值方法、热源模型、边界摩擦模型、材料本构模型这四个方面介绍搅拌摩擦焊中材料流动行为的数值模拟的最新研究进展及相关应用。对当前搅拌摩擦焊材料流动模拟中存在的不足进行分析,提出未来研究中应关注的研究方向。     

搅拌摩擦焊的温度分析

在介绍一种新型固相连接技术-搅拌摩擦焊技术的基础上，重点分析了搅拌摩擦焊的工艺规范对温度的影响。搅拌摩擦焊的搅拌工艺规范对焊接不同区域的温度有较大的影响。     

搅拌摩擦焊工艺与机理的研究

搅拌摩擦焊（Friction Stir Welding，简称FSW）是一种利用高速旋转的搅拌头与工件磨擦产生的热量使被焊材料局部塑化的新型固相连接工艺。它可以对多种熔化焊接性差的有色金属等材料进行可靠的连接，而且连接工艺简单，有较好的工艺适应性。本文在总结搅拌摩擦焊研究成果的基础上，论述了搅拌摩擦焊的基本原理和特点，阐述了近年来国内外搅拌摩擦焊工艺参数、接头微观组织、焊接成形机理等方面的研究现状，并展望FSW的应用前景。     

先进的搅拌摩擦焊技术

搅拌摩擦焊(FSW)是英国焊接研究所20世纪90年代初发明并拥有专利权的一种固相塑性连接技术。目前,国内外研究较多的是各种铝及铝合金的搅拌摩擦焊。(1)搅拌摩擦焊原理及特点与常规摩擦焊一样,搅拌摩擦焊也是利用摩擦热作为焊接热源。不同之处在于,搅拌摩擦焊的焊接过程是由一个带有探针和轴肩的特殊形式的搅拌头来完成的,如附图所示。先将探针插入被焊接板     

铝合金搅拌摩擦焊技术研究

论述了搅拌摩擦焊的焊接方法、工艺过程和基本原理；通过大量的工艺参数优化，解决了焊缝中的孔洞问题，使ＬＦ６板材搅拌摩擦焊的焊缝达到与母材等强，ＬＹ１２焊后未经热处理，连接强度接近母材的８０（。由金相分析可以看出，搅拌摩擦焊属于固相连接，焊缝晶粒细小，无气孔、夹杂、裂纹等焊接缺陷。初步应力测试发现，搅拌摩擦焊焊缝比熔焊焊缝的残余应力低。试验研究结果表明，搅拌摩擦焊焊接过程稳定可靠，焊接接头性能良好，具有广泛的应用前景。     

搅拌摩擦焊在新能源汽车电池下壳体焊接工艺中的应用

介绍了搅拌摩擦焊的原理及优点、电池下壳体的结构、搅拌摩擦焊系统及生产工艺流程,针对搅拌摩擦焊技术在新能源汽车电池下壳体焊接工艺中的应用,利用机器人搅拌摩擦焊对焊接工艺参数及母材连接方式进行了试验研究,得到优化后的主轴转速S、焊接速度F、下压力P及工件连接方式,提高了焊缝融合度和接头稳定性,且焊接接头的抗拉强度均能达到母材标准抗拉强度的70％以上,表明该工艺方法在焊接速度、节能环保和产品质量等方面具有一定的优势.     

搅拌摩擦加工制备金属基复合材料的研究现状

搅拌摩擦加工技术是源于搅拌摩擦焊接技术的一种加工技术,目前已经被用于各种复合材料制备的研究中.本文主要介绍了搅拌摩擦加工技术制备复合材料的原理,概述了目前采用搅拌摩擦加工技术制备复合材料的研究进展,简要分析了搅拌摩擦加工制备复合材料的应用前景.     

轻质异种材料搅拌摩擦点焊技术研究进展

由于汽车工业轻量化的要求,轻质材料复合结构取代单一材料结构的方法受到社会各界的广泛关注。对于异种材料复合结构的连接,传统焊接方法具有一定的局限性。搅拌摩擦点焊技术作为一种绿色、高效、固相连接技术,在异种材料连接方面具有很大潜力,国内外学者针对异种材料搅拌摩擦点焊开展了大量研究。从铝-碳纤维增强热塑性树脂基复合材料、铝-铜和铝-钢三种复合结构搅拌摩擦点焊的研究现状出发,阐述了国内外科研人员在焊接工艺、微观组织演变以及接头力学性能等方面的研究成果,并展望了搅拌摩擦点焊技术现阶段亟待解决的热点问题以及发展趋势。     

Development of the technical capabilities needed to build and position a prepolarization coil for a magnetic resonance imaging magnet

An experiment to show that a magnetic resonance imaging (MRI) magnet could be assembled around a patient, and used as part of a prepolarization system in which substantial transient forces are applied to parts of it, is described. The paper describes the circumstances that develop as a result of the application of the large transient fields used in this type of study, and outlines the reason for the tolerances that are permissible on the alignment of the system components. It then describes a test rig used to evaluate how the various problems might be overcome, and reports on the performance achieved with this rig. On the basis of this work, it appears that a system could be developed that would allow the application of these methods in clinical MRI.     

三类电液施力系统的优化设计

本文介绍一种电液施力系统的优化设计理论。它包括：1、系统优化,将电液施力系统划分成跟踪型、保持型和正弦型三种,并分别给出了优化设计方法;2、元件优化,介绍选择伺服阀空载流量和油缸有效面积最佳值的P-Q计算尺;3、为消除强干扰、负载影响和交链影响,介绍了结构不变性原理;4、为探讨干扰力产生的过程及其与伺服阀予开口的关系,介绍了伺服阀的两种工作状态及其全局负载曲线。     

High-force magnetic tweezers with force feedback for biological applications

Magnetic micromanipulation using magnetic tweezers is a versatile biophysical technique and has been used for single-molecule unfolding, rheology measurements, and studies of force-regulated processes in living cells. This article describes an inexpensive magnetic tweezer setup for the application of precisely controlled forces up to 100 nN onto 5 microm magnetic beads. High precision of the force is achieved by a parametric force calibration method together with a real-time control of the magnetic tweezer position and current. High forces are achieved by bead-magnet distances of only a few micrometers. Applying such high forces can be used to characterize the local viscoelasticity of soft materials in the nonlinear regime, or to study force-regulated processes and mechanochemical signal transduction in living cells. The setup can be easily adapted to any inverted microscope.     

Type synthesis of two-degrees-of-freedom rotational parallel mechanism with two continuous rotational axes

The two-rotational-degrees-of-freedom(2R) parallel mechanism(PM) with two continuous rotational axes(CRAs) has a simple kinematic model. It is therefore easy to implement trajectory planning, parameter calibration, and motion control, which allows for a variety of application prospects. However, no systematic analysis on structural constraints of the 2R-PM with two CRAs has been performed, and there are only a few types of 2R-PM with two CRAs. Thus, a theory regarding the type synthesis of the 2R-PM with two CRAs is systematically established. First, combining the theories of reciprocal screw and space geometry, the spatial arrangement relationships of the constraint forces applied to the moving platform by the branches are explored, which give the 2R-PM two CRAs. The different distributions of the constraint forces in each branch are also studied. On the basis of the obtained structural constraints of branches, and considering the geometric relationships of constraint forces in each branch, the appropriate kinematic chains are constructed. Through the reasonable configuration of branch kinematic chains corresponding to every structural constraint, a series of new 2R-PMs with two CRAs are finally obtained.     

同轴K—H型行星减速器的研究

本文介绍了同轴Ｋ－Ｈ型少齿差行星减速器机构的结构组成和特点，并着重对其进行了受力分析和效率计算，结果表明，该机构的销轴和转壁的轴承受力小，且机构的效率高。     

Influence of liquid meniscus on surface forces

The condensation of water in the gaps between members of microelecromechanical systems and precision friction units is caused by the presence of water vapors in air. The formation of liquid meniscus induces an additional force and affects considerably other surface forces. Numerical simulation was used to determine the meniscus and Van der Waals forces depending on the distance between the bodies in contact. Theoretical dependencies are used when interpreting experimental data obtained with the contact adhesion meter. Different factors that affect surface interaction and the application of the proposed approach to micro-and nanotribology are discussed.     

Mechanical and dynamic characteristics of double and single beam cantilevers for MEMS manipulation

Micro and millimeter-scaled cantilever beams are commonly used to apply and measure microforce and manipulate micro-objects, biological cells, and tissues. In manipulating micro-objects and actuating micro-devices by cantilever beams, sudden application and release of forces are typical, and subject to static and dynamic modes of operation. Therefore, the cantilever’s mechanical behavior and vibration characteristics are vital since they are also used in force sensors and probes. The dynamic behavior of the double beam cantilever (DBC) in micro and millimeter-scaled is explored by varying the length without changing the stiffness and compared with the single beam cantilever (SBC). The dynamic attributes such as mode shape, natural frequency, resonance, and response under the impulse force and Coulomb friction are evaluated numerically. This study will assist in selecting the appropriate type and length of cantilevers in micro and millimeter-scale to manipulate micro-objects, biological cells and tissues, and use in MEMS sensors.

     

Adhesion characteristics of the snail foot under various surface conditions

Recently, there have been many studies on the adhesion mechanisms of various mollusca such as snails, clams and octopi. Understanding their magnitude and working force is advantageous for application in specially designed robotic systems. The adhesion mechanism in these animals is effectively generated by a complex biological system that is able to operate under various surface conditions. In this work, fundamental research was conducted to understand the adhesion mechanism of living snails. Pull-off and lateral forces were measured while the snail was adhered to various surfaces in order to investigate the effects of surface conditions such as surface energy, surface roughness and surface type on the adhesion or suction of the snail. In order to understand the relationship between suction and adhesion of the snail, pull-off and suction forces were simultaneously measured using a custom-built apparatus. The average adhesion and suction force was estimated to be 0.2 kgf and 0.44 kgf, respectively. It was found that the snail effectively used both capillary adhesion and suction mechanisms to attach to and move on the surface.     

Effects of surface forces and surface roughness on squeeze thin film of elastohydrodynamic lubricated spherical conjunction

The pure squeeze thin film elastohydrodynamic lubrication motion of circular contacts with effects of surface forces and surface roughness taken into account is explored under constant load conditions. The coupled transient stochastic Reynolds, elasticity deformation, the load balance, surface forces (hydrodynamic, solvation and van der Waals pressure) and lubricant rheology equations were solved simultaneously by using the finite difference method and the Gauss–Seidel iteration method. The simulation results reveal that the differences between radial type roughness and circular type roughness problems are apparent as the film thickness is thinner than 5 nm. The oscillation phenomena in pressure and film thickness come mainly from the action of solvation forces. The effects of surface forces become significant as the film thickness becomes thinner. The film thickness with circular type roughness is thicker than that with radial type roughness. Copyright © 2012 John Wiley & Sons, Ltd.