平板件电磁成形时线圈最小尺寸的计算

成形线圈是平板件电磁成形的一个关键部件。从平板加工线圈的磁感应强度分布入手，分析了平板件上的电磁力分布，确定在成形特定尺寸的工件时，存在一个线圈的最小尺寸，并通过二分法和复合形法分别对圆形线圈和椭圆形线圈的最小尺寸进行了计算。     

基于方形骨架的宽频雷击电流传感器理论研究与实验

通过对国家标准中标准雷击电流波形特性进行准确检测的要求,设计了方形和圆形2种结构参数不同的罗氏线圈。在深入分析和计算线圈测量原理的基础上,结合测量的动态特性进行了仿真和实验研究,可知方形和圆形骨架的罗氏线圈测得的电流频率范围分别为50Hz~394MHz和743Hz~394MHz,线圈骨架方形和圆形所测得的灵敏度分别为117mV/kA和111.3mV/kA,根据实际测试结果显示,所设计的2种线圈可测量各类快速变化的大幅值雷击电流,并具有较好的灵敏度和线性度。同时,对这2种结构形式不同的线圈设计的参数进行对比分析得知,方形骨架线圈比圆形骨架的测量误差小,方形骨架所测得的电流频率更宽。     

临床应用方形与圆形亥姆霍兹线圈对比研究

为了实现胶囊机器人临床应用,需要设计一种大尺寸的三轴亥姆霍兹线圈,根据圆形和方形亥姆霍兹线圈的结构与物理特性,建立满足人体容纳空间的三轴亥姆霍兹线圈电磁模型,分析了空间磁场的均匀度。以总视在功率为目标函数,通过序列二次规划法对方形和圆形线圈结构参量进行优化和对比,研究结果表明:在中心磁感应强度、内部有效容纳空间和通入交流电流相同时,方形线圈总视在功率最低、均匀度更高,易于装配,总体性能更好。     

电磁冲击加载平板线圈的有限元分析

电磁冲击加载中,成形线圈是电能转化为磁场能的载体,使毛坯产生塑性变形的关键部件。介绍了平板线圈电磁驱动基本原理,通过ANSYS多物理场模拟平板线圈的简化模型,系统研究了线圈几何参数对轴向电磁力的影响;探讨了线圈驱动下驱动片上所受轴向电磁力分布规律及线圈参数对成形设备能量利用率的影响。仿真结果显示:随线圈匝数增加电磁力呈指数增加,随匝间距的增加呈指数减少,随起点距呈近似指数减小;轴向电磁力在线圈距中心轴2/3区域达到最大值;减小电感值有利于提高成形效率。     

异形件两道次拉深试验与有限元模拟

塑性成形领域中对钣金件非对称零件的两道次拉深成形一直是个难题。以非对称形件为研究对象,采用数值模拟和试验相结合的方法进行了研究。试验中采用网格法研究了两道次拉深后得到的成形件局部应变分布和第二道次成形件的壁厚变化。数值模拟中采用两道次连续成形的方法进行了仿真分析,根据仿真结果分析了成形性、应力、应变分布等,同时得到了对应试验结果仿真结果,并将试验结果和仿真结果进行了对比。结果表明,多道次有限元模拟中厚度变化与试验相差较小,可以通过有限元模拟预测多道次成形件厚度;多道次有限元模拟中应变分布与试验相差较小,可以通过有限元模拟预测多道次成形件成形性;采用多道次连续成形方法可以解决多道次成形中不同道次间材料属性变化难处理的问题。     

布风器形式对船舶会议室内气流分布影响的数值模拟

会议室内环境质量的优劣直接影响开会人员的工作效率。为分析布风器形式对会议室室内气流环境的影响。以某船舶会议室作为研究对象,以计算流体力学方法和传热学为基础,应用AIRPAK商用软件对会议室采用方形平板、圆形平板等4种布风器送风时的室内气流分布进行模拟。通过温度场、速度场、通风效率等的比较分析说明,孔板形布风器送风的温度场、速度场分布较均匀,热舒适性较好,平板形布风器送风的能量利用率高且除污效果较好。     

汽车发电机磁极精锻成形三维有限元模拟和工艺优化

简述了汽车发电机磁极几种典型成形工艺。基于Abaqus通用有限元软件,应用三维刚粘塑性有限元显式算法对磁极精锻成形过程进行了模拟分析,得出了变形中材料的流动状态和等效塑性应变分布规律。根据有限元模拟分析结果对磁极精锻成形工艺参数、模具结构进行了优化设计,并进行了磁极精锻成形工艺试验。试验验证了有限元模拟分析结果,并精锻成形出合格的汽车发电机磁极产品。     

平板件电磁成形用线圈的设计

通过对线圈产生的磁感应强度的推导，并结合实验结果分析，得出线圈形状选择时遵循的原则：长形工件采用椭圆形线圈要优于圆形线圈，中心部位变形要求较高的工件应尽可能采用圆形线圈。通过对平板件上电磁力分布特点的分析，确定在成形特定尺寸的工件时，存在一个最小线圈尺寸，若线圈最外圈尺寸小于该尺寸，则工件边缘部分所受磁场力垂直向上，不利于工件的变形。从设备能量利用率的角度进行分析，得出在设备能量相同的情况下，板料厚度等于趋肤深度时，设备能量利用率最高，板料变形程度最大。在设备电容确定的情况下，可以通过改变线圈导线的材料、规格、线圈的匝数、匝间距等获得最高的设备能量利用率．     

不同夹芯复合材料夹层结构的剪切破坏行为

对蜂窝和泡沫夹芯的复合材料夹层结构通过夹具用拉伸试验模拟剪切破坏行为,分析了试验载荷-应变曲线及失效模式,得出应变场分布情况及失效原因,并分别对不同夹层结构的剪切行为进行了有限元模拟。结果表明:夹层结构的失效模式均为沿加载方向的屈曲破坏,并且在中间区域与边界区域之间的区属于纯剪应力区;夹芯材料的横向剪切模量直接影响了复合材料夹层结构的屈曲破坏载荷和失效模式:有限元分析的屈曲模态与试验失效模式较为吻合。     

X-cor夹层结构剪切强度的有限元分析

利用有限元软件分析了X-cor夹层结构的剪切强度及失效机理,提出了失效判据和材料刚度退化规则,明确了X-cor夹层结构的失效过程和模式;根据失效判据,采用有限元模型中发生刚度退化的单元及其分布模拟失效类型及扩展路径,说明了X-cor夹层结构的剪切失效机理。结果表明:在剪切载荷下,树脂区首先失效,然后是Z-pin拔出面板、Z-pin被剪断及Z-pin屈曲多重失效模式并存;有限元分析结果与试验数值吻合较好,说明了失效判据和刚度退化规则选择的有效性。     

Electromagnetic blank restrainer in sheet metal forming processes

Electromagnetic blank restrainer (EMBR) is a new technology that was recently developed to control material movement in sheet metal forming processes. Magnetic attraction on the ferrous sheet metal is the intrinsic property of EMBR. Such magnetic force is quantified using Maxwell's stress tensor to assess the feasibility of EMBR in the sheet metal forming process. The 3D finite element analysis (FEA) of an electromagnetic system is conducted to determine the distribution of magnetic flux density on contacting surfaces of the sheet metal. The distribution is then used to estimate the magnetic force. Experiments have been conducted to measure the magnetic force and compare with results from the FEA. Biaxial-loading apparatus has been built to measure restraining forces on the sheet metal with blankholder, drawbead, and EMBR. All the restraining forces are put together in a chart to see where each method stands with respect to one another. In order to evaluate the quality of forming with each method, an experimental die has been built. The die forms a channel in a single stroke and provides a direct indication of how each restraining method controls blank movement in the die. The real advantage of EMBR lies in the effectiveness of force control and its flexible location in a sheet metal forming die. To prove this, a prototype has been built in a tryout die where house appliance panel is formed with blankholder and EMBR. EMBRs are locally installed in the die and actively controlled during the forming process. The part formed with EMBR shows a significant improvement in the forming quality. At the end of this paper, two immediate impacts that EMBR can bring to the sheet metal forming industry are also discussed.     

Comparison of plastic strains on AA5052 by single point incremental forming process using digital image processing

In this study, a surface based strain measurement was used to determine the formability of the sheet metal. A strain measurement may employ manual calculation of plastic strains based on the reference circle and the deformed circle. The manual calculation method has a greater margin of error in the practical applications. In this paper, an attempt has been made to compare the formability by implementing three different theoretical approaches: Namely conventional method, least square method and digital based strain measurements. As the sheet metal was formed by a single point incremental process the etched circles get deformed into elliptical shapes approximately, image acquisition has been done before and after forming. The plastic strains of the deformed circle grids are calculated based on the nondeformed reference. The coordinates of the deformed circles are measured by various image processing steps. Finally the strains obtained from the deformed circle are used to plot the forming limit diagram. To evaluate the accuracy of the system, the conventional, least square and digital based method of prediction of the forming limit diagram was compared. Conventional method and least square method have marginal error when compared with digital based processing method. Measurement of strain based on image processing agrees well and can be used to improve the accuracy and to reduce the measurement error in prediction of forming limit diagram.

     

正方形亥姆霍兹线圈的磁场均匀性

利用三个正方形亥姆霍兹线圈构建三维匀强磁场,并分析其匀强磁场区域特性。将正方形亥姆霍兹线圈视为四段载流导线,采取分段计算然后矢量叠加的方法,分析正方形亥姆霍兹线圈轴线上和空间磁场强度及其均匀性,及其仿真数据结果。最后得到正方形亥姆霍兹线圈三维匀强磁场的结构模型及相关数据分析,证明了三维亥姆霍兹线圈产生的磁场满足匀强磁场要求。     

Viscous pressure bulging of aluminium alloy sheet at warm temperatures

Improving the formability of aluminium alloy sheet metal by using warm or elevated temperature has become a valid approach. In this paper, viscous pressure bulging (VPB) at warm temperature is proposed. The coupled thermo-mechanical finite element method and experimental method were used to investigate the VPB of aluminium alloy AA3003 at warm temperature. The temperature distributions of sheet metal and viscous medium were analyzed for non-isothermal VPB. The influence of forming temperature on thickness distribution, forming load and failure location of sheet metal were investigated. Research results show the temperature gradient field in sheet metal forms when the initial temperature of viscous medium is lower than that of sheet metal. The formability and failure location of sheet metal changes with initial temperature of viscous medium.     

Failure in single point incremental forming

This paper revisits the formability limits of single point incremental forming (SPIF) in the light of fundamental concepts of plasticity and ductile fracture mechanics. The paper has a twofold objective of investigating the limiting strain pairs at fracture in parts showing and not showing signs of necking before cracking and of demonstrating that failure by fracture occurs by tension in crack opening mode I. The overall methodology is based on the combination of circle grid analysis, measurement of the ‘gauge length’ strains at fracture and determination of fracture toughness from experimental tests performed with truncated conical SPIF parts and double edge notched test specimens loaded in tension. The work is performed in aluminium AA1050-H111 and is a step towards comprehension of the circumstances under which failure will occur in SPIF. It is shown that fracture strain pairs of truncated conical parts, fracture forming limit lines (FFLs) determined from conventional sheet formability tests and fracture toughness in crack opening mode I can be merged to create a new understanding of plastic flow and failure by fracture above the onset of necking.     

Fault tolerant control of magnetic bearings with force invariance

A magnetic bearing even with multiple coil failure can produce the same decoupled magnetic forces as those before failure if the lemaining coil currents are properly redistributed This faulttolerant, force invariance control can be achieved with simply leplacing the distribution matrix with the appiopnate one shortly after coils fail, without modifying feedback control law The distribution gain matrix that satisfies the necessary constraint conditions of decoupling linearized magnetic foices is determined with the Lagrange Multiplier optimization method     

铝合金磁脉冲辅助板材冲压技术研究进展

铝合金板材室温下的成形性较差,但在高速变形条件下成形极限大幅提高。为了促进铝合金板材在汽车制造、航空航天及3G领域的应用,需要开发先进的板材成形技术。磁脉冲辅助板材冲压成形技术（EMAS）通过在普通冲压模具中嵌入线圈,能有效控制和改善变形板料的应变分布。针对这些问题,重点介绍和讨论了EMAS技术的国内外研发现状,阐明了开展该技术研究的必要性和重要意义。     

双重拉深筋力能特性的实验研究

以双重拉深筋中最常见的双圆筋为对象，设计了专门的实验装置。通过大量实验，对拉深筋的阻力、压筋力和夹持力与其高度及各圆角半径间的关系进行了系统的研究。研究表明，拉深筋的阻力、压筋力和夹持力主要受其高度的影响，而拉深筋圆角半径的影响相对较弱；内侧拉深筋高度对拉深筋阻力的影响大于对压筋力与夹持力的影响，外侧拉深筋则相反，对压筋力与夹持力的影响较大。同时对双拉深筋与单拉深筋的力能特点进行了对比，指出双拉深筋的阻力可达到单筋的2倍以上，而压筋力和夹持力则明显大于单筋的2倍。提出了双拉深筋的设计调整原则。给出了双拉深筋的高度和圆角半径的合理取值范围。     

盒形件固体颗粒介质板材成形工艺研究

固体颗粒介质板材成形工艺是采用固体颗粒微珠代替刚性凸(凹)模(或弹性体、液体)的作用对板材拉深成形的新工艺。选用非金属固体颗粒介质——GM颗粒作为研究对象,以固体颗粒介质在高应力水平下的体积压缩试验和摩擦强度试验为基础,应用散体力学理论中扩展的Drucker-Prager线性模型构建固体颗粒介质有限元材料模型。以具有非轴对称性的方盒形件为代表,进行固体颗粒介质成形工艺的有限元模拟,研究成形过程中板材的流动特征和壁厚分布规律。工艺试验成功得到方盒形零件,将加载曲线、成形过程变形特征和壁厚分布曲线与数值模拟结果比对较为吻合。分析表明,采用以散体力学为基础建立的固体颗粒介质材料模型进行工艺模拟,能够得到与试验较为接近的变形特征和力能参数,可以应用于制定工艺方案的依据,为该技术在板材成形中的应用起到指导和借鉴作用。