电磁优化激光熔化沉积的应力场研究

发布时间：2018-08-25 16:58

【摘要】：激光熔化沉积技术借助大功率激光技术及CAD/CAM技术可以实现复杂结构金属零部件的快速无模近成形,不仅能大幅缩减产品开发周期还能最大程度上节约原材料。然而由于缺乏规范的工艺标准,成形件常出现内部孔隙、裂纹等缺陷,严重制约了其在更广泛领域的应用。交变磁场能在其附近导体内产生感应电磁力,使导体发生塑性变形。这一原理已被广泛应用在金属成形领域。本文借鉴电磁成形的工艺技术,旨在利用感生的电磁力使工件产生塑性变形,抵消工件因冷却收缩产生的拉伸应变,从而达到降低残余应力幅值,抑制热裂纹生长的目的。主要完成工作如下:(1)从理论方面系统分析了激光熔化沉积残余应力产生的机理以及电磁优化激光熔化沉积的机理,包括降低残余应力和细化枝晶组织的机理。(2)基于ANSYS平台,模拟了电磁辅助激光熔化沉积过程。研究了单一激光熔化沉积的残余应力在时间和空间上的分布,并分析了固定电磁力对残余应力的影响以及不同电磁力大小的影响规律。(3)搭建试验装置,并开展了激光熔化沉积单道单层试验,制备了金相样件,对制造件内部晶粒组织进行了观察分析。(4)在激光熔化沉积单道单层的基础上,进行了多道多层试验。使用X射线衍射法测量工件表面残余应力,并结合电解腐蚀的方法对深度方向的残余应力进行了测量。本文通过APDL编程语言实现了温度场、应力场和电磁场的三场耦合。利用该仿真模型不仅研究了残余应力的分布情况,而且分析了电磁场对残余应力的影响规律,仿真结果与后期试验取得了较好的一致性,为后期进一步的工艺研究奠定了基础。
[Abstract]:Laser melting deposition technology can realize the rapid formability of metal parts with complex structure by means of high power laser technology and CAD/CAM technology. It can not only greatly reduce the product development cycle but also save the raw materials to the greatest extent. However, due to the lack of standard process standards, defects such as internal pores and cracks often occur in forming parts, which seriously restrict its application in a wider field. The alternating magnetic field can produce inductive electromagnetic force in the nearby conductor, which causes plastic deformation of the conductor. This principle has been widely used in the field of metal forming. Using the technology of electromagnetic forming for reference, the purpose of this paper is to make use of the induced electromagnetic force to make the workpiece produce plastic deformation, to counteract the tensile strain caused by cooling shrinkage of the workpiece, so as to reduce the amplitude of residual stress and restrain the growth of hot crack. The main works are as follows: (1) the mechanism of laser melt deposition residual stress and the mechanism of electromagnetic optimization of laser melting deposition are analyzed theoretically, including the mechanism of reducing residual stress and refining dendrite structure. (2) based on ANSYS platform, The electromagnetic assisted laser melting deposition process was simulated. The distribution of residual stress in time and space of single laser melting deposition is studied, and the influence of fixed electromagnetic force on residual stress and the influence of different electromagnetic force are analyzed. (3) A test device is built. The single channel single layer experiment of laser melting deposition was carried out and the metallographic sample was prepared. The grain structure in the fabrication part was observed and analyzed. (4) on the basis of laser melting deposition single channel monolayer, multichannel and multilayer tests were carried out. The residual stress of workpiece surface was measured by X-ray diffraction method and the residual stress in depth direction was measured by electrolytic corrosion method. In this paper, the coupling of temperature field, stress field and electromagnetic field is realized by APDL programming language. The simulation model is used not only to study the distribution of residual stress, but also to analyze the influence of electromagnetic field on residual stress. The simulation results are in good agreement with the later test results, which lays a foundation for further technological research in the later stage.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG665

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