Spherically curved layer (SCL) model for metal 3-D printing of overhangs

Abstract

Directed energy deposition (DED), equipped with 5-axis tool mechanism and no additional machining process, turned out to be able to deposit overhang/undercut features with no support directly on a part in multiple directions. When performing the deposition, two additional axes of rotating and tilting newly added to the working table where the part is typically fixed need to be precisely controlled using an advanced process management technique. The previous approach for slicing algorithm corresponding with multi-axis tool paths along the part and providing a simple stepwise two dimensional layering process of repetitive +/- 90 degree tilting of the base table can cause unavoidable process delay whenever the base table needs to be tilted for conforming the geometry of overhang/undercut features. Another clear and present barrier to the approach, in addition, is the physical interferences between the tool and the workpiece moving separately during the build. This study proposes a Spherically curved layer (SCL) model providing interference-free 5-axis tool-part movement, a continuous and synchronized interaction between the tool and the part each separately but precisely controlled while kept contacted together, for the build of overhangs. A methodological approach generating SCL information directly from an STL model, followed by the implementation onto various overhang problems as case studies using the proposed methodology, will be discussed in this paper.