3D Printing Explained
How does a virtual image on a computer program get turned into a real life object using a 3D printer?
The process is not as complex as you might imagine. There are many types of printers, but we will focus on the Fused Deposition Modeling (that extrudes plastic) as that is the most common. Let’s start our journey of discovery from step 1.
There are many Computer Assisted Design (CAD) programs. These allow the user to visually design and modify a part or an object. Some examples of design software programs are Blender, SolidWorks and AutoCAD.
These programs allow the user to create and export models. For most 3D printing, the files used are .stl (stereolithograpy). The CAD program takes the image and models it as a series of interlocking, small triangles.
Once in this file format, it can be uploaded into a slicer. This is the gateway program between the computer and the printer. The slicer takes the .stl file and recreates the object in such a way that it can be virtually “sliced” for building. Each layer of the model is broken down according to the printing conditions, such as layer height, infill (how much material, if any is inside the model), printing speed, and other factors. Once the printing parameters have been set, the slicer creates a gcode file (more on this later), which can be saved or sent directly to the printer.
A typical printer creates objects by heating plastic past the melting point, pushing the melted plastic through a nozzle (extrusion) at a certain location, and letting it cool.
In order to do this, the printer needs to be able to move in the x, y, and z directions, move the filament, heat the extruder, and ensure that the temperature is consistent.
The movement aspect is fairly simple. For each axis, there is a stepper motor. A stepper motor is a very precise motor that moves a specific distance when given a voltage. This allows some printers to create models with layer heights under 60 micrometers!
Another stepper motor allows for movement of the filament of plastic string that is heated and molded. The actual extruder has a nozzle (usually about 0.4mm) where the heated plastic comes out and is deposited. It has a heating apparatus, and is cooled by a fan. The temperature is measured (most commonly) through an electronic device that changes its resistive properties depending on the heat to which it is exposed.
All of this is controlled by a central processing computational unit that is able to communicate with both the computer and control the physical machine.
When put together, the printer is able to move in such a way that it can deposit hot plastic at the necessary location, at a certain speed, such that a physical model is created.
Other types of printers use different methods; some use lasers to harden a goo-like resin. Others use lasers to melt metals and alloys.
The total picture should be coming together now. In order to tie the computer programs to the actual printing, we need to understand gcode and the firmware. Gcode are direct instructions for moving the motors, heating the nozzle, and performing the tasks required to print. Gcode has lines that tell the printer “move in x direction 3 mm” “Heat to 210 degrees” or “Extrude 5mm of material”.
For the 3D printer, the firmware is responsible for understanding the G-Code sent by the slicer and translating it to the stepper drivers. These control the motors, temperature, flow, acceleration, speed, and other aspects necessary to successfully print.