电弧增材成形中熔积层表面形貌对电弧形态影响的仿真

Simulation of the influences of surface topography of deposited layer on arc shape and state in arc based additive forming

电弧增材成形常采用单道多层或多道搭接的熔积方式,不同的熔积方式下对应的熔积层表面形貌不同,从而影响电弧的形态及其传热传质过程.本文建立了纯氩保护电弧增材成形的电弧磁流体动力学三维数值模型,以及不同表面形貌的熔积层模型,并在保持阳极与阴极之间距离和熔积电流不变的条件下,通过模拟计算获得增材成形特有的单道和多道搭接熔积条件下的不同表面形貌对应的电弧形态以及相应的温度场、流场、电流密度、电磁力、电弧压力分布.数值模拟结果表明:平面基板上起弧情况下电弧中心具有较高的温度、速度、电流密度以及压强;单道多层熔积情况下熔积层数对电弧的各个参量影响较小;多道搭接熔积情况下电弧呈非对称分布,电弧中心温度较前两者低,电流密度、电磁力和电弧压强的分布偏向熔积层一侧.

The stacking deposition and the overlapping deposition are usually employed in arc based additive forming process,which will result in different surface topographies of deposited layer. Consequently, the shape and state, heat and mass transfer of electric arc will be affected by the surface topography of deposited layer. A three-dimensional numerical model of electric arc based on magnetic fluid dynamics, local thermodynamic equilibrium and optical thin assumption for arc based additive forming process with pure argon shielding gas is presented. Simultaneously, four kinds of deposited layer model with different surface topographies are established, which are the deposited layer model of planar substrate,namely the substrate without weld bead, deposited layer model of single-pass single-layer, deposited layer model of single-pass two-layers, and deposited layer model of overlapping. The numerical calculation is performed on condition that deposition current and the distance between the electrodes are constant. And the simulation results include the profile of electric arc, corresponding temperature field, flow field, current density, electromagnetic force, and the arc pressure distribution. The temperature field of planar substrate accords well with other researcher＇s experimental result,and the profiles of electric arc are in good agreement with images captured by high-speed camera. Surface topography of deposited layer plays a decisive role in determining the profile of electric arc under the same process conditions. The comparison of evolvement among the distributions on specified paths shows that the electric arc of planar substrate has higher temperature, velocity, current density and pressure in the arc center, arising from completely symmetrical deposition layer model and smaller contact area between the arc and the substrate; the number of layers of single-pass multi-layer deposited layer has little influence on various parameters of electric arc, but because the deposited layer height changes, the temperature and pressure on the outside of deposited layer have small deviation; asymmetric arc profile will form when the overlapping deposition is performed. There is a relatively low temperature in the arc center,resulting from larger contact area between the arc and the surface of deposited layer. In addition, the distributions of current density, electromagnetic force and pressure deflect to the deposited layer. The above conclusions can provide a theoretical basis for basic research and process decision of arc based additive forming, and it can also provide the parameters for the subsequent weld pool dynamics and metal transfer simulation.