Now that you’ve (hopefully) read Part 1, and know the history of 3D printing and how it got started, its time to cover the basics of 3D printing.
3D printing is a type of what is called “additive manufacturing”. This process involves slowly adding more material to the object until it is complete. This is different than subtractive manufacturing (e.g. machining) where you remove unwanted material until you have the object/shape you desire.
Now that we have a broad idea of how 3D printers work, we can get more detailed. As mentioned in Part 1, a 3D printer doesn’t actually print objects in three dimensions at the same time. It instead prints “slices” of objects in two dimensions, and stacks each of these slices on top of one another until the object is completed. It may seem obvious at this point, but the four things that are always needed to 3D print are: A file in the proper format, a slicer, a printer and material.
A 3D-printable File
Prior to printing a 3D object, you need to create a full model of that object. These models are created using Computer Aided Design (CAD) software where the user can model the entire object (part and/or assembly) in three dimensions. Here at PAI, we are partial to a program called Solidworks, but just about any CAD program is capable of creating 3D-printable files.
CAD file for the Sandman Doppler housing
After the model is created, it needs to then be converted into a stereolithography (*.stl) file so that it can move to the next step in preparation for printing. The way this works is that the surfaces of the 3D model created in the CAD program are “translated” into tessellated (cover a surface with repeated uses of the same shape) triangles that approximate the same shape. The resolution (or number of triangles) can be adjusted within the CAD program when preparing the *.stl file. An interesting note: this file type was originally created by 3D Systems (remember them?) when they developed the first 3D printer. It has since retroactively been called a “Standard Tessellation Language” or “Standard Triangle Language” file.
The surface of this model being approximated by differing numbers of triangles (via solidworks.com)
This is basically what a slicer does...
Okay, now that you have your *.stl file, you need one more step before everything is ready to print. As previously mentioned, the printer is actually printing 2D slices of the object on top of one another until the full object is created. The way the printer knows what each slice looks like is by processing the *.stl file with a slicing program. In the program, you can usually tweak various settings for the final product including: wall layers, ceiling/floor layers, infill percentage, and infill pattern. Changing each of these setting has a different effect on the final product. For example, changing the number of wall or ceiling/floor layers will change the quality/appearance of the final part, and different infill patterns each offer various different advantages or disadvantages. Generally, each of the 3D printer companies has their own slicer that is designed to work specifically with their printers. Once the object has been sliced, the slicer outputs a(nother!) different file with specific instructions for the printer that tell it which motors need to activate when and for how long in order to move the printer into the correct position for printing. This is generally what is known as a gcode file.
Once your file is ready, you need to select with material you will use to print. Each material has different advantages and disadvantages, and we will cover all the different materials in a future edition of the Deep Dive. Suffice to say that 3D printable material comes in three main different forms: filament, resin, and powder. Generally, filaments are heated to a prescribed temperature (melted) then the printer uses the now melted filament to create each layer, resins are cured by various forms of light, and powders are fused together using high powered lasers.
3D printing filaments (via tobuya3dprinter.com)
Liquid resin (via indiamart.com)
Powdered metal (via 3dprint.com)
Alright, the only thing left is to load the gcode onto the printer and start the print! Based on the slices that the slicer determined, the printer will, layer by layer, create your part! It's like MAGIC.
Next time, we'll go further in depth on the various 3D printing technologies and why you might want to use one technology over another.
Check out this cool timelapse video of some 3D prints in action!