At present, the main rapid prototyping technologies in the market are FDM, LMD, SLA, SLS, SLM and so on.
Fused Deposition Molding(FDM)
Fused deposition moulding technology, also known as fuse deposition moulding technology, is one of the most widely used 3D printing technology. As shown in the figure above, the FDM heating head heats the hot melting material (ABS resin, nylon, wax, etc.) to a critical state, making it present a semi-fluid state, and then the heating head moves along the two-dimensional geometric trajectory determined by CAD under the control of software. At the same time, the nozzle extrudes the semi-flowing material, and the material solidifies instantaneously to form a thin layer with contour shape. Thin layers accumulate layer by layer, and finally print out the designed three-dimensional objects.
Laser Molding Deposition(LMD)
Laser molding deposition technology is that the cladding material is directly fed into the laser, and the material is melted and deposited under the irradiation of high-energy laser. Molding materials are usually fed in the form of powder, which can be divided into coaxial powder feeding and lateral powder feeding. At present, the powder used in laser cladding deposition mainly includes titanium alloy, aluminum alloy, stainless steel and other powder materials. Its forming schematic diagram is shown above.
Stereo lithography Apparatus technology is the earliest developed rapid prototyping technology. It is also one of the most thorough, mature and widely used rapid prototyping technologies. Stereo lithography Apparatus technology mainly uses photosensitive resins as materials, and selectively makes the liquid photosensitive resins which need to be moulded react with ultraviolet light or other light sources. It hardens, solidifies layer by layer, and finally obtains the complete product. Its schematic diagram is as follows:
The general steps of UV curing include:
Firstly, a three-dimensional solid model is designed by CAD. The model is sliced by discrete program, and the scanning path is designed. The generated data will accurately control the movement of laser scanner and elevator.
Laser beams are irradiated on the surface of liquid photosensitive resin through a scanner controlled by a numerical control device according to the designed scanning path, which solidifies a layer of resin in a specific area of the surface and generates a section of the part when the layer is processed.
When the lifting platform falls a certain distance, the solidified layer is covered with another layer of liquid resin, and then the second layer is scanned. The second solidified layer is firmly bonded to the first solidified layer, so that the layers are superimposed to form a three-dimensional workpiece prototype.
After removing the prototype from the resin, the final curing is carried out, and then the required products are obtained by polishing, electroplating, painting or coloring.
Selective Laser Sintering(SLS)
SLS technology is a kind of material-adding manufacturing technology using high-power laser (such as carbon dioxide laser). It combines very small material particles into clusters to form the required three-dimensional shape. Its basic principle is similar to that of photo-curing technology, but the raw materials are different. Photo-curing technology uses photosensitive resin, while selective laser sintering uses metal alloy powder and other materials.
Selective Laser Melting(SLM)
The selective laser melting technology is similar to the photo-curing technology. The principle is as shown in the figure. Before the laser beam starts scanning, the horizontal scraper first scrapes the metal powder onto the substrate of the processing room. Then the laser beam will selectively melt the powder on the substrate according to the profile information of the current layer, and process the profile of the current layer. Then the platform can be lifted and lowered to a distance of the thickness of the layer, and the horizontal scraping can be done. The plate is coated with metal powder on the current layer that has been processed, and the equipment is transferred to the next layer for processing, so that the layer processing is completed until the whole part is processed. The whole process is carried out in a gas-protected processing room to avoid metal reacting with other gases at high temperatures.