Polishing of metal 3D printed parts with complex geometry

Parts produced with metal additive manufacturing often suffer from a poor surface finish. Surface finishing techniques are effective to improve the quality of 3D printed surfaces, however they have as downsides that they also slightly change the geometry of the part, in an unpredictable way. This effect on the geometrical features of complex parts has received little attention. In this research, we illustrate a method to visualize the impact of surface finishing techniques on geometrical features, as well as their effectiveness on parts with high shape-complexity, by using centrifugal disk finishing as a case study. We designed and 3D printed test parts with different features using selective laser melting, which were coated with a blue metal lacquer prior to polishing. After polishing, the blue lacquer was eroded away from the spots that were easily reached by the polishing process, yet had remained on the surfaces that could not be reached by the process. We used measurements of material removal and image processing of the remaining blue lacquer on the surfaces to analyze these effects. Using this method, we were able to derive a number of specific design guidelines that can be incorporated while designing metal AM parts for centrifugal disk finishing. We suggest that this visualization method can be applied to different polishing methods to gain insight into their influence, as well as being used as an aid in the design process.

采用金属增材制造（Metal Additive Manufacturing）生产的零件往往存在表面光洁度不佳的问题。表面处理工艺可有效改善3D打印表面的质量，但该类工艺存在显著弊端：会以不可预知的方式小幅改变零件的几何形状。目前针对复杂零件几何特征受此类工艺影响的研究尚未得到足够关注。本研究以离心圆盘抛光（Centrifugal Disk Finishing）为案例，提出了一种可可视化表面处理工艺对几何特征的影响，以及其在高形状复杂度零件上的应用效果的研究方法。我们采用选择性激光熔化（Selective Laser Melting，SLM）工艺设计并3D打印了带有不同特征的测试零件，并在抛光前为其喷涂了蓝色金属漆。抛光完成后，抛光工艺可触及区域的蓝色金属漆会被侵蚀去除，而无法被触及的表面则仍保留该漆层。我们通过测量材料去除量，并对表面残留的蓝色金属漆进行图像处理，以此分析上述影响。通过该方法，我们推导得到了一系列可用于适配离心圆盘抛光工艺的金属增材制造零件设计准则。我们认为，该可视化方法可推广应用至其他抛光工艺，以深入理解其对零件的影响，同时也可作为零件设计过程中的辅助工具。