Generally speak, 3D printing is a process of making three dimensional solid objects from a digital file.
3D printing technology appeared in the mid-1990s. However, it is still a novel forming technology nowadays which is integrating computer-aided design, numerical control, laser, new materials, and other advanced technologies.
Different from the traditional “removal” processing method, the complex three-dimensional workpiece is formed through the layer-by-layer superposition method.
“The creation of a 3D printed object is achieved using additive processes. In an additive process an object is created by laying down successive layers of material until the object is created. Each of these layers can be seen as a thinly sliced cross-section of the object.
3D printing is the opposite of subtractive manufacturing which is cutting out / hollowing out a piece of metal or plastic with for instance a milling machine.
3D printing enables you to produce complex shapes using less material than traditional manufacturing methods.“
——a brief intro from 3dprinting.com
The core theory of 3d printing is Photocuring and Laminated Object Manufacturing.
The working principle of 3D printing is basically the same as that of ordinary printing: The printer is equipped with “printing materials” such as liquid or powder. After connecting with the computer, the “printing materials” are superimposed layer by layer through computer control, and finally, the blueprint on the computer is turned into a physical object.
How Does 3D Printing Work?
“It all starts with a 3D model. You can opt to create one from the ground up or download it from a 3D library.
We often recommend beginners to start with Tinkercad (a 3D Software). Tinkercad is free and works in your browser, you don’t have to install it on your computer. Tinkercad offers beginner lessons and has a built-in feature to export your model as a printable file e.g .STL or .OBJ.
Now that you have a printable file, the next step is to prepare it for your 3D printer. This is called slicing.
Slicing basically means slicing up a 3D model into hundreds or thousands of layers and is done with slicing software.
When your file is sliced, it’s ready for your 3D printer. Feeding the file to your printer can be done via USB, SD or Wi-Fi. Your sliced file is now ready to be 3D printed layer by layer.“
——Guidance from 3dprinting.com
The printer reads the information of the cross-section from the file, prints these cross-sections layer by layer with liquid, powder or sheet materials, and then binds the cross-sections of each layer in various ways to create a solid piece.
The characteristic of this technology is that it can make objects in almost any shape.
According to the working principle, 3D printing includes the following four categories:
Extrusion deposition; Particle sintering; Laminated Manufacturing and Photoetching.
Extrusion Deposition is to “squeeze” the printing material from the nozzle in the form of mobile or semi-mobile, and stack it to the requested position to complete the material manufacturing.
One of the core technologies of this method is Fused Deposition Modeling (FDM), which was developed by S. Scott Crump in the 1980s and commercialized by Stratasys in 1990.
The available materials include most thermoplastic plastics, some metals and eutectic alloy systems, as well as melting edible materials such as chocolate.
The printing process of melt deposition molding: extrude the molten material through the nozzle like squeezing toothpaste, and then stack it at the required position in order. After one layer is completed, solidify the layer, and then print the next one.
The disadvantages: it can not print the hollow structure directly, and the selection of materials is limited.
In addition, another similar technology can be regarded as the development of melt deposition molding, which is Powder Bed and Inkjet Head 3D Printing. This technology extends the available materials to gypsum, clay, sand and even cement.
Particle sintering method: A layer of material is laid at the specified position, melted and sintered by laser or electron beam. Repeat the process on the second layer and continue. The object is stacked layer by layer.
Particle Sintering can be subdivided into Selective Laser Sintering (SLS), Direct Metal Laser Sintering (DMLS), Electron Beam Melting (EBM), etc.
Powder particles are sintered into blocks by laser. Thermoplastic, metal powder and ceramic powder can be produced by selective laser sintering.
The sintering process is difficult to control, which means the surface of the product produced by this method is not smooth enough and needed to be reprocessed and polished. However, the advantage of this method is that most metal products can be manufactured in a strong stucture. It is more friendly to metals.
Another variant of Selective Laser Sintering is called Selective Laser Melting (SLM), which was developed by Germany in 1995. It is not much different from Selective Laser Sintering, but Selective Laser Melting can be used to produce finer parts. Now it is mainly used in the manufacture of metal components.
Generally speaking, the particle sintering method is relatively simple and the equipment is not as complex as the Extrusion Deposition, but it requires the sintering and forming ability of materials.
The core idea of Laminated Manufacturing is to turn a 3D object into 2D planes layer by layer, complete each layer first, then stack all these layers into one product.
The main technology of this method is called Laminated Object Manufacturing (LOM). It continuously transports the sheet materials through the processing platform, cuts the material on the platform by laser, blade, needle…then stack or bind the shaped materials on the other side for compression molding. This technique can carry out continuous production. The cost on equipment and manufacturing are very low, so it is suitable for large-scale production.
The inspiration of Photoetching comes from the manufacturing method of integrated circuits: firstly, apply a layer of photosensitive resin on the copper-clad laminate, then print the circuit pattern on the resin surface like taking photos through light. Wash off the uncured resin, and corrode the exposed copper plate with acid. For 3D printing, this process is copied in the third dimension, and then manufactured layer by layer.
The most representative technique of this method is Stereolithography Apparatus (abbreviated as SL, STL or SLA).
Recently, with the progress of technology, Photoetching has some new development as well. For example Digital Light Processing (DLP), it utilizes a more controllable light source and finer-controlled platform to achieve higher accuracy. It makes it’s possible to produce super tiny and delicate products by 3D printing.
You can click 3dprinting.com for more detailed infomation:
The American Society for Testing and Materials (ASTM), developed a set of standards that classify additive manufacturing processes into 7 categories. These are:
- Vat Photopolymerisation
- Stereolithography (SLA)
- Digital Light Processing (DLP)
- Continuous Liquid Interface Production (CLIP)
- Material Jetting
- Binder Jetting
- Material Extrusion
- Fused Deposition Modeling (FDM)
- Fused Filament Fabrication (FFF)
- Powder Bed Fusion
- Multi Jet Fusion (MJF)
- Selective Laser Sintering (SLS)
- Direct Metal Laser Sintering (DMLS)
- Sheet Lamination
- Directed Energy Deposition
——Detailed intro on 3dprinting.com
Bibliography:
- Author: Chen Shikai, Cheng Chen. 《The Great Printing》. Published by Posts and Telecom Press, 2014.6.
- Author: Xia Zhengnong, Chen Zhili. 《Da Ci Hai: materials and science volume》, published by Shanghai Dictionary Publishing House on December, 2015.
- What is 3D printing? 3D PRINTING.COM. https://3dprinting.com/what-is-3d-printing/
