【作者】 初红艳；

【导师】 费仁元； 陆辛；

【作者基本信息】 北京工业大学 ， 机械设计及理论， 2003， 博士

【摘要】 电磁成形是金属在强脉冲磁场中受力而发生塑性变形的一种高能高速的成形方法。其优点如下：成形时没有物理接触，可以在成形或装配操作前进行工件的抛光或研磨；成形过程中没有静态力，可以采用相对较轻的结构支撑模具；电磁脉冲载荷时间可以达到微秒的精度，强度可以电力控制达到很高的精度；成形过程不产生摩擦，不需要润滑剂，操作之后不需清理工件；成形速率高导致材料成形性的提高，对铝合金等强度高、成形性差的材料成形变得非常有利。采用电磁成形工艺进行铝合金件的成形，由其代替钢材用于汽车车体结构和其他零件的成形，可使汽车减重达30%，进而减少燃油消耗和温室气体CO2及其他有害气体的排放。因而电磁成形工艺应用于汽车领域是其重要的发展前景。本文的主要研究工作有：在对国内外发展状况进行调研的基础上，将平板件的电磁成形作为研究对象，采用理论分析、实验研究、有限元仿真等方法，探索影响成形质量的主要工艺因素，如脉冲电流频率，成形电压，模具，板料厚度等对成形的影响，获得进行平板件电磁成形工艺设计所需的成形线圈、成形设备电路参数、成形电压、模具等的设计方法，对于保证成形件的质量，推动其工业化应用具有重要的意义。将其应用于复合成形工艺（普通冲压成形+电磁成形），将使汽车车身铝合金件的复合成形成为非常有前途的新的工艺方法。本文从密绕导线平板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特点，并在此基础上提出了在平板件电磁成形时存在一个线圈的最小尺寸的概念，此时工件边缘处所受磁压强恰好为0。若线圈尺寸小于该尺寸，则工件边缘处所受磁压强垂直向上，不利于工件的变形。并分别用二分法和复合形法进行圆形线圈和椭圆线圈最小尺寸的计算。采用盒形模具和小孔模具，分别用圆形线圈和椭圆线圈进行板料的成形，得出了两种线圈的适用情况：对于长形工件，采用椭圆线圈要优于圆形线圈；对中心部位变形要求较高的工件，应尽可能采用圆形线圈。这对于电磁成形工艺设计时选择线圈形状、确定线圈尺寸具有一定的指导意义。本文详细讨论和阐述了平板件电磁自由成形及有模成形实验，根据实验结果分析了成形电压、模具、板料厚度等对变形的影响，初步得出了电磁成形时平板件的变形响应规律：对于自由成形，加载时间内板料的变形很小，大部分<WP=5>变形发生在加载结束后的惯性阶段；对于有模成形，板料与模具底部高速撞击后将产生反向运动，其结果是工件的底部形状可能为平的，也可能为内凹的。通过对实验结果的统计分析，得出了工件最大变形高度与成形电压之间为线性关系的结论，并且提出可以用二次多项式曲线来逼近工件的变形曲线。因此可以实现根据所需的工件最大变形高度来确定成形电压，并预知工件的近似变形曲线。从趋肤效应的角度出发，分析了最大变形高度与板料厚度的关系，得出在其他条件相同的情况下，板料厚度等于趋肤深度时，设备能量利用率最高，工件变形高度最大的结论。并分析了可以通过改变线圈导线的材料、规格、线圈的匝数、匝间距等来获得最高的设备能量利用率。这对于电磁成形工艺设计时线圈的设计有一定的指导意义。本文在若干合理简化的基础上用ANSYS/LS-DANA对电磁成形过程进行了有限元仿真，利用仿真结果分析了板料自由成形、有模成形时的变形模式，分析了脉冲电流频率对平板件电磁成形的影响：自由成形时，随脉冲电流频率的减小，工件的最大变形高度先是增大，然后减小，当脉冲电流频率减小到一定程度时，工件的最终变形程度差别不大；有模成形时，在凹模深度相同的情况下，脉冲电流频率越大，工件的反向变形程度越大，随脉冲电流频率的减小，工件底部的贴模情况逐渐变好，直至没有反向变形，工件底部为平的，而且当脉冲电流频率减小到一定程度时，工件的变形曲线趋于相同。文中还分析了载荷幅值对平板件电磁成形的影响：载荷幅值对板料的变形过程没有影响，但是会影响工件的最终变形程度。在其他条件相同的情况下，对于自由成形，载荷幅值越大，工件的变形程度越大；对于有模成形，加载时间较短时，载荷越大，工件的反向变形程度越大；加载时间中等时，工件底部内凹，载荷幅值越小，内凹程度越大，载荷幅值越大，工件侧壁靠模程度越高；加载时间较长时，工件底部近似为平的，载荷幅值越大，工件侧壁靠模程度越高。这对于电磁成形工艺设计时选择最佳的脉冲电流频率、载荷幅值以获得所需的变形曲线具有重要的意义。更多还原

【Abstract】 Electromagnetic forming is a new kind of forming method with high energy and high forming velocity, by which the metal is loaded under strong impulse magnetic field and deformed plastically. The advantages of the method are as follows. There is no physical contact during forming process, so the workpiece can be polished or grinded before forming or assembling. There is no static force exerted during forming, so relatively light frame structure can be used for die supporting. Magnetic impulse pressure time can be in the order of microsecond, and the intensity of electromagnetic impulse pressure can be controlled electrically to very high precision. There is no friction during forming, so lubricant is not necessary, and cleaning of workpiece after operation is also not necessary. Material with high strength and bad formability, such as aluminum alloy can be used since material’s formability can be increased under high forming velocity. Forming sheet metal of aluminum alloy using electromagnetic forming method, and substituting it for steel to use for body structure and other parts of automobile, can decrease the weight of the automobile 30 percent. It, in turn, can decrease the oil assumption and exhausts. It will be more and more important for electromagnetic forming process to apply in automobile field.The main research of this dissertation is as follows. Based on investigation of the development status of the area in China and oversea countries, electromagnetic forming of sheet metal was selected as main research work. Theory analysis, experiment research and finite element simulation were carried out to study the process factors with strong affect to the forming quality, such as impulse current frequency, forming voltage, mould design, sheet thickness, and so on. Therefore the design methods of forming coil, circuit parameters of forming equipment, forming voltage and the mould, which are necessary for the electromagnetic forming process design, were acquired. It is important for the quality insurance of the workpiece and the promoting of its application in industry. And the application of sheet metal electromagnetic forming in combined forming process (conventional drawing + electromagnetic forming) can promote the application of combined forming of aluminum alloy parts of automobile body.<WP=7>In the dissertation, the distribution of magnetic induction intensity induced by intense winding conductor plane coil was deduced, and the distribution of the electromagnetic pressure on the sheet metal was analyzed. On this basis, minimum size of the coil was proposed so that electromagnetic pressure at the edge of the sheet was zero. If coil size is smaller than the minimum size, the direction of electromagnetic pressure at the edge of the sheet will be upward, and it is disadvantageous to the deformation of the sheet. The dichotomy method and complex method were used for the calculation of the minimum size of circular coil and elliptic coil. Using box die and hole die, the experimental research to sheet forming with circular coil and elliptic coil were carried out, and the suitable cases of the application of the two kinds of coil were acquired. For the long workpiece, elliptic coil is more suitable than circular coil. For the workpiece that has much demand for the deformation of its center area, circular coil should be selected. All of these are important for coil shape selection and coil size calculation during electromagnetic forming process design.In the dissertation, sheet metal electromagnetic free forming and die forming experiments were discussed in detail. And based on the experiments, the affect of forming voltage, die structure, and sheet thickness to deformation was analyzed, and the deformation process of sheet metal electromagnetic forming was preliminarily acquired. For free forming, deformation during loading time is small, and most of the deformation happens during the inertia stage. For die forming, the sheet moves toward the opposite direction after its impact with the bottom of the d更多还原