Originally given as a Tech Enrichment Lecture, the information presented below is a general overview of 3-D printing.
What is 3-D Printing?
3-D Printing is a form of Additive Manufacturing, which means that material is added to create a figure. This is done by building up the material one layer at a time, as each layer is made of molten filament.
This differs from reductive manufacturing, where material is removed to create a figure (example: Laser Cutting, Mill or Lathe).
Why is 3-D Printing useful?
3-D printing is primarily used for Rapid Prototyping, experimentation, and simply just to build things for the sake of building things.
Rapid Prototyping is a term used to describe when you are testing designs to see what works in a very short time frame using rather rudimentary or simple methods. Then, you typically order the final design in a more sustainable material – whether it’s getting metal cut/bent/welded/extruded, printing it in a higher quality, or other more-permanent solutions.
How does 3-D Printing work?
The two common filaments are PLA (Polylactic Acid) and ABS (Acrylonitrile Butadiene Styrene). Both have their pros and cons, so be sure to research for your purpose. In the CSE labs, we use PLA only due to the fumes that are emitted when ABS printing.
The 3-D Printing Extruder is comprised of multiple segments working together. The filament is pulled from the spool via 2 gears (Extruder Drive), feeding it into the upper section of the extruder. Here, a fan and heatsink keep the filament cooled down so that it does not prematurely melt and clog up. In the lower section, a heating element superheats the filament to around 200°C (392°F) such that the filament is now semi-molten. At this point, the filament is pushed down and out of the nozzle into a ~0.2mm wide stream onto the build plate.
The build plate is typically heated to 60-70°C (140-158°F), which is enough to let the filament solidify, while still being warm enough that the tackiness of the material is retained, to keep it in-place on the plate.
Build plates can either be glass or metal, smooth or textured, and varies by manufacturer.
Shown here is the first layer of an object. Note that the outline and interior curved surfaces are done first, then the flat surface is filled in with diagonals.
The Creation and Building Process
There are 2 ways to source an object:
1. You can build it yourself using any of the many CAD software available
2. You can download a model from an online repository, likely built by somebody else in CAD
Either way, you will need the model to be in an STL format. If you download from a repository, the file will likely be provided. If you build the model yourself in CAD, there should be an Export or Save As function which has STL as an option.
STL stands for STereoLithography, which loosely translates as “To create selectively as viewed from two merged perspectives”.
You will then import the STL model into a slicer, which is the software that converts a visual model into machine code. The output machine code is a GCode file, short for Geometric Code. The GCode file is then uploaded to the printer.
What is Slicing?
As mentioned above, Slicing is the process of converting a visual model into machine code for the {X, Y, Z} extruder movements.
Slicing Software parameters can be divided into two categories: Printer-specific and Object-specific.
Slicing – Printer Specific Settings
All 3-D printers are slightly different. Even 2 printers of the same brand and model next to each other can have very minute differences.
Printer-specific profiles account for travel limits, the number of extruders, and how the GCode file is formatted.
Slicing – Object Specific Settings
The object-specific parameters are much more detailed and have direct outcomes on model quality and strength.
- Layer Height
Generally speaking, the 0.2mm layer height is sufficient for most builds. - Wall and Solid Layer count
More Walls and more Solid Layers will make a model stronger. Additionally, having more than 2 Solid Layers will make the interior infill structure less visual to the outside. - Print and Travel speed
Speed and Accuracy are a trade-off. While the nature of Stepper control is very accurate, the filament does not make sudden directional changes as well as the extruder itself is capable. As a result, a high travel speed around rounded corners on small parts will heavily rely on build plate adhesion to come out as desired. As such, it is highly suggestible to use slow travel speeds on smaller and more intricate parts. - Infill Parameters
Infill density and pattern type have a direct outcome in the texture and strength of a finished product. A hollow model will crush easily, while certain patterns may better support shear or pressing loads better. As a trade-off, more infill means a longer build time and more filament used. - Support Parameters
Support generally has 3 settings: None, Only against build plate, or Everywhere. Support is used when overhangs are in play – so that there is a horizontal surface, or elevated build plate if you will, to support the overhangs so that the filament of the first few layers does not sag down.
Like infill, there are multiple patterns available for support. However, since Support is intended to be removed, there’s not exactly much reason to pick any pattern over another. Typically, Zig-Zag is used, with the “Connect zig-zags” option unchecked for easier removal from the final model. - Adhesion Parameters
There are 4 possible adhesion options, but only 2 are significant. None and Skirt are effectively the same, as Skirt just draws a big circle around the part, and does not touch the part itself.
Brim adds one layer of material around the outside of the model to increase the footprint of the part as it interfaces with the buildplate. This helps keep the model in-place on the build plate, and can help keep a part attached in the case of a warped bed, uneven heating issues, or if the extruder is moving too fast around small or intricate parts.
Raft takes Brim to another level, by adding several layers of material and support structure between the model and the build plate. This further counteracts a warped bed or uneven heating issues.
Industry Applications
3-D printing has many applications in industry. Some examples are:
- Rapid Prototyping
Making sure things work with cheap, expensible material before ordering thousands of dollars of metal fabrication - Replacement Parts
Sometimes the parts you need aren’t available when or where you need them. Being able to print them as your own need can pay for a printer over time. - Problem Solving
Sometimes, you can solve a construction problem or conflict-of-space problem – usually followed by Rapid Prototyping mentioned above. - Making Molds for Composite Materials
Making parts out of Carbon Fiber or Fiberglass requires a mold. Traditionally, those molds have been made out of hand-carved wood. Now, they can be 3-D printed, which saves time and can make more complex shapes. - There is a large international movement pursuing 3-D printing in the Civil Engineering field – specifically building 3-D printed houses/structures.
