3D printing technology is actually a collection of rapid prototyping technologies, all of which are based on the principle of layered manufacturing. The rapid prototyping machine forms the cross-sectional shape of the workpiece by scanning in the X-Y plane, while intermittently displacing the layer thickness in the Z coordinate, ultimately forming a three-dimensional object. Currently, the rapid prototyping technologies available in the market include 3DP technology, FDM (Fused Deposition Modeling), SLA (Stereolithography), SLS (Selective Laser Sintering), DLP (Digital Light Processing), and UV (Ultraviolet) curing technology.
3DP Technology: 3DP stands for Three Dimensional Printing. This is the true 3D printing! This technology is very similar to flat printing, and even uses a print head similar to that of a flatbed printer. Like SLS, the raw material for this technology is also powder. A typical 3DP printer has two chambers. As shown in the figure above, the left is the powder storage tank, and the right is the forming tank. During printing, the left chamber rises by one layer (usually 0.1mm), and the right chamber descends by one layer. The powder roller transfers powder from the storage tank to the forming tank, laying down a thickness of 0.1mm of powder. The printer head applies a liquid onto the powder according to computer data. (In a flat printer, the Y-axis moves the paper, while in 3DP, the Y-axis moves the print head.) The liquid is either an adhesive or water (used to activate the powdered adhesive).
FDM (Fused Deposition Modeling): FDM is a technology that melts filamentous thermoplastic materials, while a three-dimensional nozzle, under computer control, selectively deposits the material onto the worktable based on the cross-sectional contour information, quickly cooling to form one layer of cross-section. After one layer is formed, the machine’s worktable descends by one height (i.e., the layer thickness) and forms the next layer until the entire solid shape is created. This technology has a variety of forming materials, produces high-strength and high-precision parts, and is mainly suitable for forming small plastic parts.
SLA (Stereolithography): SLA uses lasers to selectively cause liquid photosensitive resin that needs to be formed to undergo polymerization to harden, thus shaping the object. There are two main types of SLA: one represented by Objet, which prints from the bottom up, and the other represented by FormLabs, which prints from the top down.
SLS (Selective Laser Sintering): SLS is similar to SLA in that it uses lasers. However, unlike SLA, SLS does not use liquid photosensitive resin but rather powder. The energy from the laser heats the powder and causes it to undergo a sintering reaction with adjacent powder particles, bonding them together.
DLP (Digital Light Processing): DLP technology is quite similar to SLA, but it uses a high-resolution digital light processor (DLP) projector to cure liquid photopolymer layer by layer. Because each layer is cured using a slide-like projection, it is faster than SLA technology. This technology offers high forming precision and can match the durability of injection-molded plastic parts in terms of material properties, detail, and surface finish.
UV (Ultraviolet) Curing Technology: UV curing technology is similar to SLA, but it uses UV light to expose liquid photosensitive resin, stacking layers from the bottom up without generating noise during the process. It offers the highest precision among similar technologies and is typically used in industries requiring high precision, such as jewelry and mobile phone casing.
Each type of additive manufacturing technology has its unique principles, but they mainly aim to create a layer of material based on computer data and then build upon that layer, layer by layer, until the entire three-dimensional model is formed.
The main feature is that the complexity of the finished structure is almost unlimited. Currently, it is mainly used in the aerospace industry, automotive industry, professional design (product design and architectural model making), and surgery (customized orthodontic braces, dentures, hearing aids), etc.
