【作者】 陈丽萍；

【导师】 史玉升； 蔡道生；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2007， 硕士

【摘要】 SLA技术使用激光束进行截面区域加工,扫描系统需要作大量的扫描,所以扫描路径的选择就显得尤为重要。高效精确的扫描路径在减小翘曲变形,提高成形件精度和强度以及设备的制造效率,延长激光-振镜的使用寿命等方面有着重要的作用。本文详细分析了当前SLA系统中常用激光扫描路径的特点。针对快速成形系统中光栅式扫描在切片轮廓边界处逆转换向产生延时,振镜偏转额外消耗时间,提出了一种优选方向的光栅扫描方式,寻求扫描线与轮廓相交次数最少的方向进行扫描。这种扫描方式在保持原有成形精度基础上,能大幅度提高激光扫描效率,缩短成形时间,延长激光器使用寿命。但对任意多边形轮廓,要获得扫描线与轮廓相交次数最少的扫描方向,如果直接运用直线与多边形求交,计算量非常大。凸多边形与一条直线相交只有两个交点,那么一系列均匀间隔的平行直线与凸多边形求交,算法简单易实现。为此本文设计了将任意多边形等效变形为凸多边形的两种算法,不改变直线与多边形相交次数。文中对这种扫描方式的实现策略和方法进行了深入地分析和研究,运用二维图形变换实现了任意方向扫描路径数据的生成问题,将优选方向的光栅扫描方式集成到华中科技大学研发的HRPL系列快速成形系统中。通过强度、精度测试实验及效率对比实验,可以得出结论:本文开发的扫描方式在抗弯曲、抗拉伸强度与普通的平行X、Y方向的光栅扫描方式几乎一样,由于同属于光栅扫描,其精度效果属于同级别。而在成形效率上,对于截面长宽不等的情况有所提高,截面长宽尺寸或分组区域内长宽尺寸相差大的情况下效果相当明显。更多还原

【Abstract】 Laser is used to sinter the stereo lithography (SLA) parts. The scanning system needs to do plenty of scan, so scan method is very important to SLA process. Efficient scan method can minimize the parts’shrinkage, increase the precision and strength of the SLA parts, improve the fabrication productivity of the SLA machine, and increase of the laser-galvanometer’s service life.The character of the scan method currently used in SLA process is investigated in this dissertation. The number of switch-backs at the contour in the path is a major contributor to scanning time. We develop algorithms to pick the direction in which a zigzag path on a polygon will have the minimum number of switch-backs. These algorithms are adopted to generate a new scan method that selects the optimal direction for zigzag path based on section information. This new method can assure the strength of the parts, increase scanning efficiency, shorten fabrication time, increase of the laser service life.For general polygon, it’s too complicate to find the optimal direction. But for convex polygon, the problem is reduced. Therefore, two algorithms were proposed to convert an arbitrary polygon into a convex polygon with the same switch-backs.The path generation strategy was studied and the two-dimensional graphics trans-formation theory was used to produce final path data. The optimal direction scanning method was integrated to HRPL series system, which is developed by the Rapid Manufacturing Center of Huazhong University of Science and Technology.The results of the experiment indicate that the fabrication efficiency of SLA parts fabricated with the optimal direction scan method is improved and they have the same strength and precision effect as with other raster scan methods. The method show great effect dealing with polygons with slim characters.更多还原