电磁冲击增强激光熔化沉积的电磁力数值模拟

发布时间：2019-01-05 04:47

【摘要】：激光熔化沉积(laser melting deposition,LMD)在航空航天、医疗器械等领域具有广泛的应用前景。但由于该技术本身所固有的骤热、骤冷特点,沉积件内部大多存在残余应力、气孔等微观缺陷,制约了零件的推广和应用。为此,本文提出电磁冲击增强金属激光熔化沉积技术方法,以期通过电磁力对熔池附近高温沉积层施加冲击,起到在线降低制件内部残余应力、减少孔隙等缺陷的作用。本文以激光熔化沉积铁基粉末、316L不锈钢基板为例进行该方法的研究,具体研究内容如下:(1)研究电磁冲击增强激光熔化沉积的理论基础,包括对沉积层所受电磁力的推导分析,激光熔化沉积残余应力的产生及控制方法研究,以及电磁冲击消减激光熔化沉积制件内残余应力的机理的初步分析。(2)运用有限元技术获得了平面螺旋线圈作用下沉积层内感应电磁力的时间、空间分布特性以及不同电参数及几何参数下内电磁力的分布规律,确定线圈施力区域,提出集磁器线圈,并对其进行优化设计。从仿真结果得出,集磁器上表面半径与励磁线圈半径相同,下表面与内孔半径较小时更适合电磁冲击增强激光熔化沉积试验。此外,电流强度较高时,电磁力更大,更有利于冲击效果。(3)根据仿真参数搭建电磁冲击增强激光熔化沉积装置并完成不同励磁电流下的单道、多层多道沉积件制作,并与常规制件进行对比。(4)对制件微观组织、孔隙、残余应力等方面进行分析,结果表明:电磁场的施加有利于制件晶粒细化,显微硬度增加、孔隙数量和平均尺寸的下降,沉积层显微组织一次枝晶间距由5μm降低至3.2μm,内部残余应力最大降低49%。
[Abstract]:Laser melt deposition (laser melting deposition,LMD) has been widely used in aerospace, medical equipment and other fields. However, due to the inherent characteristics of sudden heat and sudden cooling, the microcosmic defects such as residual stress, porosity and so on exist in the deposition parts, which restrict the popularization and application of the parts. In this paper, a method of electromagnetic shock enhanced laser melting deposition of metals is proposed in this paper. It is expected that the electromagnetic force will exert an impact on the high temperature deposit near the molten pool, which can reduce the internal residual stress of the parts and reduce the defects such as pores on line. In this paper, the method of laser melting deposition of iron-based powder and 316L stainless steel substrate is studied. The main contents are as follows: (1) the theoretical basis of electromagnetic shock enhanced laser melting deposition is studied. Including the derivation and analysis of electromagnetic force, the generation and control of residual stress in laser melt deposition. The mechanism of reducing residual stress in laser melted deposition parts by electromagnetic shock is analyzed. (2) the time of inductive electromagnetic force in the deposit layer under the action of planar spiral coil is obtained by using finite element technique. According to the spatial distribution characteristics and the distribution law of electromagnetic force in different electric and geometric parameters, the force region of the coil is determined, and the magnetic collector coil is proposed and optimized. From the simulation results, it is concluded that the upper surface radius of the collector is the same as that of the excitation coil, and the radius of the lower surface and the inner hole is more suitable for the electromagnetic shock enhanced laser melting deposition test. In addition, when the current intensity is high, the electromagnetic force is larger, which is more favorable to the impact effect. (3) according to the simulation parameters, the electromagnetic shock enhancement laser melting deposition device is built and the single channel, multi-layer and multi-channel deposition parts are made under different excitation current. And compared with the conventional parts. (4) the microstructure, pore and residual stress of the parts are analyzed. The results show that the application of electromagnetic field is beneficial to the grain refinement and the increase of microhardness of the parts. With the decrease of the number of pores and the average size, the primary dendritic spacing of the deposited layer decreases from 5 渭 m to 3.2 渭 m, and the internal residual stress decreases by 49%.
【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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