厚大构件磁再约束高能等离子弧类激光切割工艺机理

There is urgent need of high quality, high efficiency and fine cutting technology for thick workpieces in the large equipment manufacturing industries such as the marine and offshore engineering construction，the nuclear power plant construction and the petro-chemical pressure vessel manufacturing engineering, and so on. From the basic principles of plasma formation and plasma cutting technology, a novel magnetic field confined high energy laser plasma cutting technology with additional longitudinal and cross magnetic field effects is proposed based on the interaction between the arc plasma and the magnetic field. Considering the new characteristics of magnetic field confined high-energy laser plasma arc behavior and the dynamic removal process of the molten metal, a three dimensional transient turbulent mathematical model based on the Prandtl mixing-length theory and the MHD theory, in which unit the confined magnetic field, the laser plasma and the workpiece, is established. Through the combination of the numerical simulation and process experiment research, the heat transfer characteristic and the flow characteristic of the laser plasma jet as well as the flow mechanism of the molten metal are explored, and the effects of the optimized matching relation between the confined magnetic field parameters and the cutting process parameters on the forming quality of cut mouth are revealed. The Internal mechanism of the homogeneous movements of the cathode arc spots and the expansion of the arc root under the confined magnetic field effect is illustrated, and the way to improve the electrode erosion behavior under the condition of the thick workpiece cutting process is obtained. The above research can deeply reveal the process mechanism of the proposed magnetic field confined high energy laser plasma cutting technology which can be used to optimize the control of the dynamic forming process of the cut mouth, promote the deep integration of the technology and equipment, and improve the cutting process effect for the thick workpieces.

针对海工船舶、核电能源、石化容器等装备制造业对厚大构件优质、高效、精细热切割的迫切需求，从切割等离子弧形成及其基础工艺原理出发，基于电弧等离子体与磁场的可作用性，提出了纵横向交叉磁场再约束高能等离子弧类激光切割新工艺。综合考虑磁再约束等离子弧射流新特性以及厚板熔融金属动态去除过程，建立基于Prandtl混合长度理论和MHD效应的再约束磁场-等离子弧-工件全局相统一的三维瞬态湍流数学模型；将计算模拟和实验研究相结合，深入探索磁再约束等离子弧射流与工件的相互作用以及熔融金属流动与去除机制，揭示再约束磁场参数与切割工艺参数的优化匹配关系及其对切口成形质量的影响规律；探索再约束磁场驱动作用下的阴极电弧斑点运动与弧根扩展规律，掌握改善阴极局部烧蚀行为的新方法。项目研究可深入揭示磁再约束等离子弧类激光切割新工艺的物理本质，实现厚板类激光切割工艺质量的预测与优化，提高厚大构件等离子弧热切割的质量和效率。

针对海工船舶、核电能源、石化容器等装备制造业对厚大构件优质、高效、精细热切割的迫切需求，开展了厚大构件磁再约束高能等离子弧类激光切割工艺机理研究。项目优化设计了机器人等离子弧切割系统及其磁再约束装置，搭建了厚大构件磁再约束高能等离子弧类激光切割实验平台；在此基础上，采用高速摄像等实验手段分析了在磁再约束条件下等离子弧射流形态的变化规律，获得了磁再约束等离子弧切割工艺的基础数据。建立了磁再约束装置和等离子切割电弧的物理模型和数学模型，并采用Ansys和Maxwell等有限元及电磁仿真软件对磁约束等离子切割弧进行了联合仿真，分析并探索了磁约束方式的变化、磁场的调节对等离子电弧的温度场、压力场及其流动场的变化产生影响的机制。进一步明确了外加纵向磁场对等离子弧射流具有良好的收缩作用，可增加等离子弧的电流密度，强化等离子体中各种粒子的碰撞效果，显著改变阳极等离子弧的压力，会直接影响等离子弧切割工艺效果。项目将理论分析与实验研究相结合，较系统地揭示了磁再约束等离子弧类激光切割新工艺的物理本质，为优化等离子切割工艺、改善等离子弧切割效果提供了理论依据和技术支撑。