为减小激光沉积成形层温度梯度及制件残余应力,结合激光沉积成形金属薄壁件结构的特点,进行了分区环形扫描验证性实验,实验结果表明:采用分区环形扫描路径,可有效减小成形件的残余应力。提出了一种分区环形扫描路径生成算法。为避免扫描线过长引起的翘曲变形,结合激光沉积成形扫描线极限长度,提出了一种基于扫描线极限长度阈值内极值点搜索的分区算法,对独立轮廓组进行分区;针对薄壁件壁厚多变的结构特点,依据壁厚判断的扫描方式优选准则,采用中线扫描与环形扫描相结合的算法,生成分区自适应环形扫描路径;同时为避免扫描环间过渡区的过熔覆,采用端点偏置算法实现扫描环间的平滑过渡连接;最后为减小层面温度梯度和制件残余应力,提出一种基于四色定理的分区扫描顺序优化算法。

Based on the structural characteristics of laser deposition formed metal thin-wall workpieces, the confirmatory test of subarea annular scan is conducted to reduce the temperature gradient of laser deposition formed layers and the residual stress of workpieces. The experimental results show that the usage of subarea annular scan paths can reduce the residual stress of formed parts effectively. An algorithm for generating the subarea annular scan paths is proposed. First, in order to avoid warping deformation caused by the long line scan, a subarea algorithm based on the extreme point search within the scan line limit length threshold is proposed according to the scan line limit length of laser deposition forming, and used for partitioning the independent contour group. Then based on the structural characteristics of thickness-changeable thin-walled workpieces and according to the optimization criterion of wall-thickness, the midline scan and annular scan are combined as an algorithm for the generation of subarea adaptable annular scan paths. Meanwhile, in order to avoid the over-cladding of the transition zone between scan rings, the endpoint offset algorithm is adopted to achieve a smooth transition connection between scan rings. Finally, in order to reduce the temperature gradient of layer surface and the residual stress of workpieces, a sequential optimization algorithm for subarea scan is proposed based on the four-color theorem.