金属零件激光-CMT电弧复合增材制造工艺与机理研究

In order to break through the limitations of the precision in arc additive manufacturing and the efficiency in laser additive manufacturing, a new technique, laser-CMT (Cold Metal Transfer, a new arc technique) hybrid additive manufacturing is developed. It not only has precise energy controlling and high deposition efficiency of the arc, but also has excellent process stability at high speed by the assistance of laser-arc interaction. It would increase the energy input efficiency of arc addictive manufacturing by both increasing the wire feeding speed and the scanning speed, and would make it possible to manufacture large metallic structures with high efficiency and high precision..The possible new phenomena, new principles and new scientific findings in this new technique would be studied in detail by combining the process experiments and the theoretical analysis. Firstly, the effects of laser-arc interaction on the process characterizations (such as arc burning, droplet transfer, material depositing amount, melt flow in molten pool, etc.) would be observed and discussed. The methods to quantify the process stability would be developed to reveal the laser-arc interaction in hybrid additive manufacturing, as well as the stabilization mechanism. Secondly, the finite element numeric simulation of the molten pool would be established to discuss the effects of laser-arc interaction and multi-layer heat accumulation on the heat and mass transfer in molten pool. In addition, the strain behavior, the microstructure evolution and the mechanical properties of the deposited parts would be discussed. Some interesting relationships among the parameter, microstructure, stress and the mechanical properties would be built. .On the basis of above-mentioned results, the mechanism to harmonically control the deposition efficiency, manufacturing precision, microstructure characterization and mechanical properties would be found out, as well as and the empirical principle. The results would provide an alternatives for manufacturing large metallic structures with high quality, and develop significant theories for additive manufacturing and laser hybrid processing.

为解决单一激光增材制造效率偏低，单一电弧增材制造精度偏低的技术瓶颈，实现大型金属构件的高效率、高精度快速制造，本项目基于能量精确可控的冷金属过渡（CMT）弧焊工艺和激光-电弧复合焊接技术，提出开发激光-CMT复合增材制造新工艺，并围绕其中的新现象、新原理和新科学问题开展研究。项目将重点探讨复合增材制造中的激光-电弧相互作用机理，及其对工艺过程主要物理行为（电弧燃烧、熔滴过渡、材料沉积数量、熔池流动过程等）的影响规律，构建复合增材过程稳定性的定量分析方法，揭示工艺过程的稳定增强机制和关键因素；其次，以实验检测和有限元数值分析相结合的方法揭示热源叠加效应和多层多道热累加效应对熔池温度场、传热传质过程、应力应变，以及组织演变和力学行为的影响机理，确立沉积效率-成形精度-组织性能的平衡调控原则。研究成果不仅能提供一种新的高效高质增材制造方法，还能丰富增材制造和激光复合加工的基础理论。

本项目围绕激光-电弧复合增材制造（Laser-arc Hybrid Additive Manufacturing，LHAM）关键科学问题开展了系统研究，明晰了激光-电弧相互作用对工艺稳定性的增强机理，及其对熔滴过渡和制件组织性能的影响机制，基于数值模拟对LHAM热-流场进行了可视化探讨，确立了沉积效率-精度-组织性能平衡调控原则，完成了预期目标。主要研究结果如下：.（1）在优化的工艺参数下，LHAM单丝沉积效率可达6.8kg/h，是当前单丝CMT电弧增材制造（CMT-AM）的2倍，在同样的沉积效率下（3kg/h），LHAM成形精度优于CMT-AM，其侧壁粗糙度从CMT-AM的203μm降低至52μm；.（2）基于响应面法和多目标优化模拟，确定了LHAM平均层高、层宽和粗糙度的二次回归模型和优化范围，拟合度分别为0.882、0.831、0.907，能够对制件成形参数进行准确预测；.（3）研究发现CMT-AM在高速条件下，原有的冷金属过渡方式会转变为多种过渡方式并存的不稳定状态，但是LHAM能够通过激光对电弧的吸引压缩效应成功抑制弧根跳跃，进而加速熔滴脱离，使得熔滴过渡重新进入平稳的冷金属过渡模式；.（4）构建了三维瞬态数值模型，研究了LHAM热-流场多尺度时空演变过程，采用独创Restart分段模拟方法，可提升计算效率50%。熔池动力学结果表明多层热累积效应会降低熔池峰值流速，增加熔池不完全对流传热倾向和沉积高度的不一致性，是造成高沉积效率下增材制造成形失稳坍塌的主要原因；.（5）揭示了工艺参数对LHAM组织性能的影响规律。LHAM最大抗拉强度可达600MPa，比CMT-AM提高70 MPa，各向异性可降低至0.5%。分析认为细晶区占比增加和气孔抑制是抗拉强度提升的主要原因；光束扫描行为降低{110}<100>高斯织构含量是各向异性降低的主要机理。

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