Fused Deposition Modeling

Fused deposition modeling (FDM) is a 3D printing process by which a molten plastic is extruded through a heated nozzle to form an object one layer at a time [52]. While there exist a number of different 3D printing technologies, FDM is relatively inexpensive and there are a wide array of machines and materials available to consumers. Generally, a thermoplastic filament is fed to a moving print head by a drive gear at well-defined rates for the manufacture of an object on the print bed. Common materials used in FDM include poly (acrylonitrile butadiene styrene) (ABS), polylactic acid (PLA), polyamide (nylon), polyethylene tereph- thalate (PET), polycarbonate (PC), etc. The plastic filament must have a well-defined diameter (generally ±0.05 mm) in order to produce an object with good precision.

The general scheme for producing an object by FDM involves four parts: (1) computer modeling of the object, (2) conversion of the model to appropriate format, (3) generation of machine tool paths, and (4) transfer of tool paths to the machine for object production. The object can be modeled in any of a number of computer aided drafting (CAD) programs depending on their availability. For the work presented herein all objects were initially modeled in Autodesk Inventor (Autodesk, CA, USA). The 3D model is then converted to a file type that represents the surfaces of the object with polygons, typically this is accomplished by exporting the part to a suitable file format. The most common file type being stereolithography file format (.stl). The.stl file is then processed using a “slicing” software which divides the object into layers and generates tool paths, most often in the form of G-Code. Within the slicing engine, several parameters can be set, including infill percentages, extrusion width, speed, and layer height. Objects manufactured by FDM are very seldom fully filled with material, but rather a sparse infill and solid perimeters. This lessens total material consumption and printing time, as well as minimizes errors caused by diameter variation in the filament. The layer height determines the resolution of the final printed object in the Z-direction, that is, the axis orthogonal to the layers produced. After the slicer has been run, the G-Code commands are sent serially to the control electronics of the printer. From these commands, the printer generates a 3D object one layer at a time.

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