Waterjet and laser etching: the nonlinear inverse problem

In waterjet and laser milling, material is removed from a solid surface in a succession of layers to create a new shape, in a depth-controlled manner. The inverse problem consists of defining the control parameters, in particular, the two-dimensional beam path, to arrive at a prescribed freeform surface. Waterjet milling (WJM) and pulsed laser ablation (PLA) are studied in this paper, since a generic nonlinear material removal model is appropriate for both of these processes. The inverse problem is usually solved for this kind of process by simply controlling dwell time in proportion to the required depth of milling at a sequence of pixels on the surface. However, this approach is only valid when shallow surfaces are etched, since it does not take into account either the footprint of the beam or its overlapping on successive passes. A discrete adjoint algorithm is proposed in this paper to improve the solution. Nonlinear effects and non-straight passes are included in the optimization, ...在水射流铣削（waterjet milling）与激光铣削工艺中，通过逐层去除固体表面材料，以深度受控的方式加工出目标形状。所谓逆问题，即通过确定控制参数——尤其是二维光束路径——以加工出指定的自由曲面（freeform surface）。本文聚焦水射流铣削（waterjet milling, WJM）与脉冲激光烧蚀（pulsed laser ablation, PLA）两种工艺，因通用非线性材料去除模型可同时适配这两类加工过程。针对这类加工的逆问题，传统解法通常是将驻留时间与表面各像素点所需的铣削深度成正比控制以实现求解。但该方法仅适用于浅表层蚀刻场景，因未考虑光束光斑的尺寸效应，亦未兼顾加工路径间的重叠效应。本文提出一种离散伴随算法（discrete adjoint algorithm）以优化该求解过程，优化过程中已纳入非线性效应与非直线路径加工的影响……