Technology-Specific Elements
Flowcharts 2.1,2.2, and 2.3 are basic algorithms of a standardized type. These algorithms need to be optimized to avoid errors and customize them to fit a specific method. Many refinements can be used to speed up the cutting cycle by reducing duplication, for example. Most AM systems need components designed using support structures. Supports are usually a loose-woven lattice pattern of material placed below the area to be supported. Such a lattice pattern may be a plain square pattern or something more complex like a hexagonal or even a fractal grid. In addition, the lattice could be connected to a part with a tapered area that could be more convenient to remove when compared to thicker connecting edges.
The identification of the regions to be assisted can be made by evaluating the angle of the standard triangle. Those normals that point downward at some previously specified minimum angle will need help. Those triangles that are sloping above that angle will not need support. The supports are extended until they converge either with the base platform or with another upward-facing surface of the portion. Supports attaching to the surface facing upward can also have a taper that allows quick removal. The method that would usually be used would be to stretch the supports from the entire build platform and eliminate any supports that do not overlap with the component at a minimum angle or less (see Figure 2.6).
Support structures could be generated directly as STL models and can be implemented into the already mentioned slicing algorithms. However, they are more likely to be directly created by the proprietary algorithm in the slicing process. Other processing specifications that would rely on different AM technologies include:
Raster scanning: Although many systems will use basic raster scans for each sheet, there are alternatives. Some systems use a switchable raster scan, scan in the X direction of the XY plane for a single layer, and then move to the Y direction for alternate layers. Many systems subdivide the filling area into smaller square regions and use switchable raster scans between squares.
Patterned vector scanning: The material extrusion technology requires a filling pattern to be produced within the enclosed boundary. This is done by using vectors generated using a patterning strategy. In the case of a particular layer, the pattern would be determined by choosing a specific angle for the vectors to travel. The fill is then a zigzag pattern in the direction defined by this angle. Once a zigzag has reached its end, further zigzag fills may be needed to complete a layer (see Figure 2.7 for an example of a zigzag scan pattern).
Hatching patterns: Sheet lamination processes, such as the Helisys LOM and the Solid Center system from Kira, involve material surrounding the part to be hatched with a pattern that enables it to be de-coated once the part has been completed (see Figure 2.8).
FIGURE 2.8 Hatching pattern for LOM-based (sheet lamination) processes. Note the outer hatch pattern that results in cubes that will be separated from the solid component during post-processing.
