【作者】 许威；

【导师】 方洪渊；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2008， 博士

【摘要】 基于电磁感应原理,针对焊接热裂纹和焊接变形问题,提出了一种在焊接过程中基于电磁力作用(WTIEF)控制焊接应力应变的方法。该方法为非接触施力,可以避免焊缝表面损伤,从而降低对接头力学性能的破坏,特别是疲劳性能。另外,该方法还具有能量易于控制、设备更加柔性化等特点。文中借助ANSYS软件讨论了电磁线圈的形式、电磁力的作用特点、工件的塑性变形行为、装置和工艺参数对电磁力的影响。研制了随焊电磁冲击装置,采用与焊枪同轴放置的平面螺旋线圈+集磁器(FCC)的线圈形式实现了焊接热裂纹的随焊控制。实现了利用电磁力焊接变形的焊后控制,提出了动态屈服应力的概念,并确定了随焊控制焊接变形的最佳施力位置。文中讨论了电磁力及工件塑性变形模拟时的关键技术,对线圈磁场、放电电流进行了测量,验证了电路-电磁耦合有限元模型的正确性。通过搭建单次电磁冲击原理性装置,实现了对板材的单次电磁冲击实验,验证了电路-电磁-结构耦合有限元模型的正确性。系统分析了平面螺旋线圈电磁力的作用特性。研究发现,轴向力(垂直工件的力)在放电电流的第一半波时间内几乎始终垂直工件向下,且远大于径向力(平行工件的力),有利于对热态焊缝及近缝区金属的延展。当线圈置于合适位置时,径向力的分布同样有利于焊接热裂纹和焊接变形的控制。研究了温度对电磁力的影响及工件存在高斯温度分布时电磁力的作用特性。随着温度的升高,轴向力减小,径向力增大。工件存在高斯温度分布时,与室温条件相比,轴向力减小,最大作用点的径向位置外移;径向力增大,换向点的径向位置内移。进行了WTIEF鱼骨焊接试件热裂纹的控制实验。FCC感应器能够使磁场集中在小范围作用区,从而实现对高温区施力,但其存在一定能量损失。合理尺寸的FCC感应器与焊枪同轴放置时能够实现对脆性温度区间的挤压,从而使热裂纹得到控制。焊接裂纹率随电压和冲击频率的增加而减小。在平面螺旋线圈作用下工件在轴向力最大位置附近产生拉伸塑性应变,因此采用平面螺旋线圈能够实现焊接变形的焊后控制。在随焊控制焊接变形时,外力只需克服动态屈服应力(屈服强度与焊接应力的差值)即可使焊缝及近缝区金属产生塑性延展。外力作用的最佳位置为动态屈服应力的较小区域。本研究条件下,动态屈服应力所表现的特征为,距离熔池较近区域和距离熔池较远区域达到较小值,而其中间区域则存在一个较高的值。对于基于电磁力随焊控制焊接变形,尽管最大轴向电磁力受温度影响而有所减小,但最佳施力位置并未受到影响。分析了装置及工艺参数对电磁力的影响。研究发现,随着回路电阻、回路电感、线圈-工件间隙和板厚的增加,最大轴向力密度呈指数减小。线圈匝数和尺寸对电磁力的影响与回路电阻和回路电感相关。磁性材料所受的电磁力大于导电性好的材料。在线圈中心加入磁芯后,由于线圈尺寸和磁饱和的限制很难达到集中能量同时增大电磁力的目的。更多还原

【Abstract】 Based on electromagnetic (EM) induction law, a new method of controlling welding stress and strain during welding with trailing impact EM force (WTIEF) is put forward to control the welding hot crack and distortion. The mothod avoids surface flaws which reduce mechanical performances, especially fatigue strength, as the coil do not contact with weldment applying the electromagnetic force . Moreover, the following characteristics are also very attractive, such as easily controlled energy and flexibly operated equipment. In this thesis, the shape of EM coil, feature of EM force, plastic deformation history of workpiece and effect of processing parameters on EM force are studied in detail by means of ANSYS software. A EM impact equipment is developed. Welding hot crack is suppressed during welding with the actuator consisting of flat coil and coaxial concentrator (FCC),while control welding buckling distortion after welding is performed with EM force. A new concept, dynamic yielding stress, is first introduced. And the optimal applying force location is also determined while controlling welding distortion during welding.In the thesis, the key technology of simulation by finite element method is discussed; Electromagnetic-Circuit coupled finite element model is verified with the measurement results of magnetic field of coil and current in discharge circuit.The single EM impact experiment of metal sheet is carried out. And Electromagnetic-Circuit-Structure coupled finite element model is verified. The characteristic of EM force of plat coil is studied in detail. The results show the direction of axial (perpendicular to workpiece) EM force is always downward almost and is greater than radial (parallel to workpiece) EM force. These all improve ductility deformation of metal in weld and near weld. In addition, distribution of the radial EM force also facilitates controlling of welding hot crack and distortion when the position of the coil is appropriate. The effect of temperature on EM force and plastic deformation in workpiece under EM force is studied. When temperature increases, axial EM force is down and radial EM force is up. When temperature distribution agrees with Gauss distribution, axial EM force decreases and the location of maximum EM force moves outward along coil radius direction, while radial EM force increases and the change location of radial EM force direction moves inward along coil radius direction.The controlling welding hot crack with EM force during welding is completed. The FCC actuator concentrates magnetic field into small region and is able to apply EM force in high temperature region. But its drawback is loss of energy. EM force of FCC with right dimensions is capable of squeezing high temperature metal in BTR, so it can control welding hot crack. And the crack rate decreases with the increasing voltage and impactive frequency.As the tension plastic deformation occurs near location of maximum EM force of flat spiral coil, the flat coil is good to control welding distortion. To control welding distortion, EM force should equal to dynamic yield stress, i.e., difference between metal yield stress and welding yield stress. Thus, the optimal location of applying EM force is minimum location of dynamic yield stress. During welding of metal sheet, the location of the smaller dynamic yield stress is the area of short distance from weld pool and large distance from weld pool, and there is a region with the large dynamic yield stress between these. Although the axial EM force decreases a little for WTIEF because of weldment with temperature distribution, the optimal location of applying EM force does not change.The effect of processing parameters on EM force is analyzed. The results indicate that the maximum EM force density is decreased with increasing the circuit resistance, the inductance, the gap distance between coil and workpiece and the workpiece thickness. The effect of number of turns and dimension of coil on EM force is related to the circuit resistance and inductance. The bearing force for well magnetic material is larger than well electric material. In addition, it is difficult to increase EM force because of limitation of coil size and magnetic saturation when the magnetic core is inserted into coil.更多还原