Abstract: Most of the existing offset algorithms were limited to simple graphics, which might not meet the complex structure requirements of real additive manufacturing parts. Therefore, a contour offset framework was proposed based on line segment topology. The types and formation mechanism of offset anomalies were studied, and the multi-loop processing algorithms such as line segment coincidence, (self) intersection, ring formation, ring reversal and ring failure were proposed to realize the processing of complex anomalies. The formation mechanism and influences of local sharp corners on the boundary were investigated, and the patching smoothing algorithm was proposed to optimize the angle of adjacent edges, almost eliminating the problems of singular sharp corners and void defects, and ensuring the stability of the algorithm. Using C++ language to write the algorithm program, compared with the results of the offset algorithm of the CGAL geometric graph library, the calculation speed of the contour offset method is faster, and the planned path is more in line with the machining geometric characteristics of the machining equipment. Compared with other scanning methods such as parallel line scanning and partition scanning, the total length of the present contour offset path is relatively lower and the overall scanning efficiency is higher.

Key words: selective laser melting, topological relation, offset anomaly, angular feature

摘要： 已有的偏置算法大多限于简单图形，远远达不到真实的增材制造零件的复杂结构要求，因此提出一种基于线段拓扑的轮廓偏置框架。研究了偏置异常的种类和形成机理，提出线段重合、（自）相交、成环、环反向、环失效等多环处理算法，实现了对复杂异常的处理；探究了边界上局部尖角的形成机理和影响，提出修补式光顺算法对邻边夹角进行了优化，基本消除了奇异尖角和空洞缺陷问题,保障了算法的稳定性。使用C++语言编写算法程序，与CGAL几何图形库的偏置算法结果相比，该轮廓偏置方法计算速度更快，且规划的路径更符合加工设备的加工几何特点；与平行线扫描和分区扫描等其他扫描方式进行对比，该轮廓偏置的规划路径总长度相对较小，扫描效率综合更高。

关键词: 选区激光熔化, 拓扑关系, 偏置异常, 尖角特征