Question:
Explain the path generation in FDM, LOM process.
Answer:
Both FDM and LOM processes rely on a crucial step called path generation (also known as tool path generation or slicing) to convert a 3D model into instructions for the machine. While the goal is the same—to guide the machine to build the part layer by layer—the specifics of how the path is created and used are fundamentally different.
Path Generation in FDM
In FDM, path generation is a pre-processing step where a 3D CAD model (usually in an STL file format) is sliced into thin horizontal layers. For each layer, the software generates a trajectory for the nozzle to follow. The path consists of two main components:
Perimeters (or Contours): These are the outermost lines that define the boundaries of the part for a given layer. The nozzle traces these lines to create the external walls.
Infill: After the perimeters are laid down, the software generates a pattern to fill the interior of the part. Common infill patterns include zigzag, honeycomb, or grid. The density of the infill (e.g., 20% vs. 100%) is also determined at this stage and dictates the final part's strength and weight.
The completed path for each layer is then converted into G-code, a machine language that the printer's controller can interpret. The G-code instructs the nozzle's movement in the X, Y, and Z axes, the extrusion rate, and temperature settings.
Path Generation in LOM
In LOM, path generation is simpler because the material is not extruded; it is cut. The software slices the 3D model into layers, but instead of creating paths for infill, it generates two distinct paths for each layer:
Cutting Path: This is the outline of the part's cross-section for the current layer. The laser or blade follows this path to precisely cut the part's shape from the sheet of material.
Hatching Path: This path is a grid or crisscross pattern that the laser or blade cuts into the waste material surrounding the part. This cross-hatching makes it easier to manually break away the excess material (a process called "decubing") once the entire object is finished. The laser doesn't cut completely through the previous layer when hatching to ensure the waste material remains attached and provides support.