FDM PROCESS IN DETAIL

FDM machines have build volume capacities ranging roughly from 288 cu. in. to 31K cu. in. (4719 cu. cm to 508K cu. cm). Material cartridges (a) supply plastic filament to the extrusion head (b). In the heated chamber (c), the head moves in the X- and Y-axes while liquefying and depositing material. The Z stage platen (d) moves down to give the part the third dimension.

Let’s take a closer look at the FDM process from start to finish.

 

1. CREATE BUILD FILE

  • In Catalyst or Insight software, open your CAD file (in STL format), and select a material, color and slice thickness.
  • Pick a build and support style to match your application’s requirements.
  • Select an orientation and then let the software do the rest. It sections the design into layers and creates toolpaths for both the part and its disposable support structures. Then it outputs a build file, which defines precise motion control paths.
  • Click print to send the build file to the 3D printer.


     

2. PREP MACHINE AND BUILD PART

  • Insert the part-material and the support-material cartridges; the system will automatically feed the material filament to the extrusion head.
  • Insert a base and close the chamber door. You are ready to build.
  • Select your job from the queue, and press the machine’s start button.
  • The 3D printer heats the build chamber and brings the plastic liquefier up to operating temperature.
  • The Z stage (platen) rises to its starting position, just a few thousandths of an inch (or tenths of a millimeter) from the material extrusion tips that protrude from the liquefier.
     
  • The 3D printer starts with a few layers of disposable “support material” to provide a foundation. Support material is also used to support features such as overhangs that would otherwise have nothing to rest upon. The extrusion head, which moves about an XY gantry, lays down a ribbon of material. After each layer is complete, the Z stage build platen lowers slightly to make way for the next layer.
     
  • The same process used for the support structure is used for the part, except it employs a different material – a thermoplastic, such as ABS or polycarbonate. When building a part, the extrusion head alternates between part-material and support-material extrusion tips.
     
  • Close-up of process: In the Fused Deposition Modeling process, each layer of molten plastic is deposited on top of the previous one and flattened slightly by the extrusion head. The layers instantly fuse to one another.
     

Extrusion Detail



The secret of FDM’s accuracy and precision is the coupling of material feed rates and extrusion head motion. Both are constantly changing to produce a flat ribbon of material that measures from 0.008 inch to 0.038 inch wide (0.20 mm to 0.97 mm) and as fine as 0.005 inch high (0.13 mm). On the highest performance FDM machines, part accuracy or tolerance reaches as high as 0.003 inch (0.08 mm), which rivals injection molding.

Drive wheels push the plastic filament into the hot liquefier section of the tip assembly. The pressure forces the plastic through a tiny orifice in the tip, which presses down to flatten the bead.

Meanwhile, the head accelerates and decelerates as it travels across the platen. As the head speed changes, the drive wheels adjust the material flow rate. The result is a precise ribbon width that adjusts as required to produce the part.

3. REMOVE SUPPORTS

  • When the 3D printer display reads “complete,” open the chamber door and remove the build tray.
  • Give the tray a twist to release the part. Now, you’re ready for the final step.
  • The supports have done their job, so it is time to remove them.
  • The removal depends on the support material type used:
     
  1. Soluble support material:
    This method uses an automated support-removal process in which the material is removed in a tank via an agitated waterbased detergent solution.

     
  2. Break Away support material:
    This is a manual removal process, in which you twist, break, and scrape support material from the part. A needle nose pliers and a pick are usually sufficient.
     
  • The FDM part is now ready for use.