Numerical and Experimental Investigation of Unsteady-State Material-Laser Interactions with Application to Laser Cutting Process

小行星9500181 该项目的目的是提高非稳态条件下的材料激光相互作用的知识。 选择激光切割工艺进行研究是因为非稳态条件对材料-激光相互作用的影响在激光切割工艺中比其他类似工艺（如激光焊接）更明显。 具体目标是：（1）提高对材料-激光相互作用的几何效应的认识，（2）理解使用可变工艺参数来抵消非稳态材料-激光相互作用的有害影响的机制，（3）探索一般振荡现象的本质，特别是在激光切割过程中的条纹形成，（4）扩大提高工艺再现性所需的技术基础，消除试错的需要，并在非稳态条件下优化工艺。 该项目将开发一个瞬态三维模型，包括熔融液体层、固体工件和气体射流的耦合连续性、动量和能量方程。 液体/固体将被建模为一个单一的域，具有用于相变的多孔性公式。 采用基于控制容积的有限差分算法，对流项采用幂律格式，压力修正算法求解方程组。 通过引入微扰，对熔融层的不稳定性进行了数值研究。 该模型可以准确地预测切缝的几何形状、能量传输和熔体流动。 该模型将被用来研究各种非稳态现象，如上文所述，计算机数控（CNC）插值的影响，和非稳态条件下的优化策略。 氧气辅助二氧化碳激光切割低碳钢将成为研究的重点。 将在各种非稳态条件下进行实验研究，包括边界侵入、转弯、轮廓切割和可变工艺参数。 将使用的实验技术包括高速拍摄，以调查切割前的流动性和条纹的形成;近焦高温计和热电偶，以调查切割前的温度和工件温度分布在非稳态条件下。 激光器的聚焦热传递能力使其成为在非常选定的局部区域改性材料的理想选择。 这种高能量浓度的输送也给连续控制非稳态过程带来了困难。 该项目中开发的预测模型成功演示了受控激光切割，这将对材料加工行业中激光的使用产生重大影响。

9500181 Yao This project is aimed at advancing knowledge of material-laser interactions under unsteady state conditions. The laser cutting process has been chosen for investigation because the effects of unsteady state conditions on material-laser interactions are more pronounced in the laser cutting process than other similar processes like laser welding. Specific objectives are (1) advance knowledge of geometric effects on material-laser interactions, (2) understand the mechanism of using variable process parameters to offset the detrimental effects of unsteady-state material-laser interactions, (3) explore the nature of oscillatory phenomena in general and striation formation in particular in the laser cutting process, (4) expand the technology base necessary for improving process reproducibility, eliminating the needs for trial-and-error, and optimizing the process under unsteady state conditions. The project will develop a transient three-dimensional model embracing the coupled continuity, momentum and energy equations for the molten liquid layer, solid workpiece and gas jet. The liquid/solid will be modeled as a single domain with an enthalpy-porosity formulation for the phase change. A control-volume based finite-difference algorithm with power-law scheme for convective terms and pressure correction algorithm will be used to solve the equations. Instability of the molten layer will be numerically studied by introducing perturbations. The model can accurately predict the kerf geometry, energy transport and melt flow. The model will be used to investigate various unsteady state phenomena as mentioned above, the effects of Computer Numerical Control (CNC) interpolations, and optimization strategies under unsteady state conditions. Oxygen assist carbon dioxide laser cutting of mild steel will be the focus. Experimental investigation under various unsteady state conditions will be undertaken, including boundary encroachment, cornering, contour cuts and variable process parameters. Experimental techniques to be used include high speed filming to investigate cutting front mobility and striation formation; close focus pyrometer and thermocouples to investigate cutting front temperature and workpiece temperature distribution under unsteady state conditions. Focused heat delivery capability of lasers makes it ideal for modifying materials in a very selected local zones. Delivery of such high energy concentration also poses difficulties in continuously controlling the unsteady process. Successful demonstration of controlled laser cutting as a result of the predictive model developed in this project will significantly impact the use of lasers in materials processing industries.