(For more resources related to this topic, see here.)
How a 3D printer works
A 3D printer needs to take a description of a three-dimensional object and turn it into a physical object. Like Blender, a 3D printer uses values along the X, Y, and Z axes to determine the shape of an object. But where Blender sees an object as perhaps cylinders, spheres, cubes, or edges and faces, a 3D printer is all about layers and perimeters.
First, a slicing program opens the object file that you made and it slices the object into vertical layers as seen in the following screenshot:
Then, each layer is printed out one by one in a growing stack as seen in the following screenshot:
But you can get a better idea of how these layers stack up if you can see it interactively. I have provided an interactive illustration that allows you to see the dragon slice by slice. Scrolling through the frames, you can see how the walls of the dragon's body are built:
- Open up 4597OS_01_LayersDisplay.blendin your download packet. Examine the thickness of the body at each layer.
- Press Alt + A to play the animation. Press Esc to stop playing it.
- You can also drag the current time indicator in the timeline back and forth to look at individual frames, or use the right and left arrow keys.
Note how the dragon starts as a series of islands. Look at the dragon's hands. The fingers start off floating in space until they are joined to the arms.
The exact method a 3D printer uses to print a layer varies. Some printers work like a pencil, drawing an outline of the shape on that layer and then filling in the shape with cross-hatching. Look at the left side of the preceding screenshot again.
The printer would first outline the tail, then fill it in. Next, it would move to one haunch, outline it, and fill it in, and then the other. And finally, it would outline and fill each foot. You can get a better idea of how this happens with this 3D printer's hot end simulator. The hot end is the printer's nozzle where the 3D printing material is extruded.
Other printers may use a print head much like an inkjet printer. The print head moves across the printing bed and deposits material where needed.
Types of 3D printers
So what kinds of printers are there? How do they print and how are they different? The terminology is still a bit confusing. The American Society for Testing and Materials (ASTM International) recently came up with the following categories:
- Material extrusion is also known as Molten Polymer Deposition (MPD), Fused Deposition Modeling (FDM), or Fused Filament Fabrication (FFF); these extrude a gooey material out in layers to build up the proper shape. This is the class of printers that includes most hobbyist 3D printers. They work like the simulator you just used. These can use plastic, metal wire, wax, sugar, frosting, chocolate, cookie dough pasta, pizza, and even corn chips.
- Material jetting is also known as photopolymer jetting. Like an inkjet, this printer squirts liquid photopolymers at the right moment, which are cured immediately with ultraviolet light, layer by layer. The object being built is supported by a layer of gel that is also applied by the print head, so overhang is not a problem.
- Binder jetting uses a two part system. A thin layer of composite material is spread across the print bed. Then, an inkjet-like printing head sprays a binder fluid and possibly colored ink, which combine with the composite material to produce solid colored and sometimes textured objects. This can be plastic, gypsum, or metals, such as copper, tungsten, bronze, and stainless steel. For metals, a second step is needed to make them solid. The binder is removed and metal is infused where the binder used to be.
- Sheet lamination printers may use materials, such as paper or metal, and will color, cut out, and glue layers together into objects.
- Vat photopolymerization is also called Stereolithography (SLA). Photopolymerization printers use light to cure liquid material into the right shape. This process uses resins, wax, or liquid plastics for the material. It may use a laser or a high resolution DLP video projector similar to one you would hook up to your computer to give a PowerPoint presentation.
- Powder bed fusion is also known as Granular Materials Binding. These printers use a laser or heat to fuse layers of powder into the right shape. These can use metal, ceramic, gypsum, or plastic powder. There are several subtypes of powder bed fusion printers.
- Selective Laser Sintering (SLS) is used with thermoplastics, wax, and ceramic powders. A thin coat of powder is spread across the printing bed. Then, the printing head prints the layer by fusing selected areas with the laser. The printing bed then drops down. Another coat of powder is added and the laser prints the next layer.
- Selective heat sintering (SHS) uses heat instead of a laser and can be used with thermoplastic powder.
- Direct Metal Laser Sintering (DMLS) or Selective Laser Melting (SLM) is a subcategory of selective laser sintering. The laser beam melts the metal and makes solid parts with metal alloys like aluminum, iron, stainless steel, maraging steel, nickel, chromium, cobalt, and titanium alloys. In theory, it can be used with most alloys.
- Directed energy deposition, also known as Electron Beam Melting (EBM), is similar to SLS, but uses an electron beam instead of a laser. The high heat generated by the electron beam allows use of pure metal powder such as titanium alloys, and can make high-detail, high-strength objects that do not need any postmanufacturing heat treatment.
Question: Earlier, I mentioned a company named Made In Space, which is making a 3D printer to be used in zero gravity. What kind of printer is it making?
- Directed energy deposition
- Vat photopolymerization
- Material extrusion
- Powder bed fusion
Answer: Option 3, material extrusion is correct. Extruding a material avoids liquid or powder floating around in zero gravity.
Basic parts of a 3D printer
As you have observed, there are a wide variety of 3D printers. But there are some parts they all have in common.
The printing bed is what the 3D object is built upon.
The printing head holds the laser, the printing jet, or the hot end of the extruder.
And then there are controls to position the printing bed and the printing head in relation to each other; one control for the X dimension, one for the Y dimension, and one for the Z dimension.
There are no hard and fast rules for which controls the printing bed and printing head have. The Cube printing head is controlled in the X dimension only and the printing bed is controlled in the Y and Z dimensions, whereas the MendelMaxPro puts X and Z controls on the printer head and controls the printing bed only in the Y dimension.
How is a 3D printer controlled?
Generally, the answer is stepper motors. Stepper motors are motors that move in small discrete angles of rotation instead of spinning like most regular motors. This allows you to make definite, easily repeatable motions. It is also one reason why there are minimum sizes on the detail that you can make. A 3D printer can't make detail smaller than one step of the stepper motor.
Then, through wires, drums, gears, and threaded rods, the motion of the stepper motor is scaled to fit the medium that the printer uses. A hobbyist printer that uses a filament of the ABS or PLA plastic that feeds off of a reel will provide the kind of detail that those plastics can support. A high-end stereolithography printer may get much finer detail.
The next graphic is a diagram of the insides of a stepper motor. The rotor is in the center. It rotates and is attached to a shaft that pokes out of the motor. The stators are attached to the outer shell of the motor. They are wrapped with copper wire and an electrical current is run through the wire to give each stator a negative charge, a positive charge, or no charge as indicated in the next graphic. In the graphic, red represents a positive charge, the blue is a negative charge, and the grey has no charge.
The rotor in the center has 50 teeth. The stators around the outside have a total of 48 teeth. It's this imbalance in the number of teeth that allow the stepper motor's rotor to walk around step-by-step.
The positive charge of the rotor is attracted to the stator teeth that are negatively charged. In the following screenshot, you can see that the rotor teeth aren't well aligned with the uncharged stator that is counter-clockwise from the blue stator. To do a single step, the stepper motor controller changes the negative charge from the blue stator in the following screenshot to the stator just counter-clockwise to it. Then, the teeth in the rotor try to align with that stator. So, the rotor moves just a little, a step. To continue moving more steps, the stator with the negative charge keeps moving to the next stator, as follows:
The stepper motor is then attached to a control belt or a shaft with a screw thread to give the printer precise control of the print head and the printing bed. There may be one or more stepper motors controlling a single axis.
In this article, we covered the fundamentals of how a 3D printer works and the different kinds of printers that there are. And you discovered that 3D printers can handle a wide variety of materials from wood, to plastic, to titanium. We also covered how to control a 3D printer by a stepper motor.
Resources for Article:
- Introduction to the Editing Operators in Blender: A Sequel [Article]
- Getting Started with Blender’s Particle System [Article]
- Blender 3D: Interview with Allan Brito [Article]