Additive manufacturing or 3D printing will use digital manufacturing processes to produce light and strong parts without the need for special molds. In the past ten years, 3D printing has grown rapidly at an annual growth rate of over 20%, using metals and engineering polymers to print various parts such as aircraft parts, auto parts, medical and dental implants. Among them, selective laser sintering (SLS) is one of the most commonly used manufacturing processes. Lasers can be used to print micron-sized material powders into parts: the laser heats the particles to a certain temperature and then fuses them into a solid.
According to foreign media reports, James and Sally Scapa Professors Hod Lipson, Department of Innovation (Mechanical Engineering), Columbia University School of Engineering and Applied Science, said: “Additive manufacturing is the key to economic recovery, but the problem Yes, SLS technology can only print one material at a time: the entire part is made of one powder. So how many products are made of only one material? This limits the development of this process."
To solve this challenge, Lipson and his PhD student John Whitehead used their expertise in robotics to develop a new method to overcome the limitations of SLS technology. By inverting the laser and pointing it upward, the researchers developed a method that allows SLS technology to produce parts using multiple materials at the same time.
Generally speaking, selective laser sintering (SLS) technology uses a laser directed downward to heat the print bed to fuse material particles together. A solid print is printed from bottom to top. A layer of powder is uniformly placed on the printer, and a laser is used to selectively fuse some materials in this layer of powder. Then, the printer deposits a second layer of powder on the first layer, and the laser fuses the new material to the material of the previous layer, and this process continues until the part is completed.
If only one material is used when printing, the SLS process will work well. But using multiple materials in a single print is extremely challenging because once the powder layer is deposited on the print bed, it cannot be removed or replaced by another powder.
In addition, in a standard printer, because the materials placed on each layer are the same, the materials that are not fused together will make it difficult to see the object being printed until the printing cycle is over and the printed parts can be removed. . This also means that before the printing is completed, it is not always possible to find that the printing has failed, which will waste time and money.
The researchers decided to find a method that does not require a powder printing bed at all. They set up multiple transparent glass plates, each coated with a thin layer of different types of plastic powder. Then, place a printing platform above one of the powder surfaces and guide a laser beam from the bottom surface up through the bottom. According to the virtual blueprint, the process can selectively sinter some powder on the printing platform in a pre-programmed pattern. Then, the platform is lifted by the molten material and moved to another flat plate coated with a different powder, and the process is repeated. The whole process allows different materials to be combined into one layer or stacked together. At the same time, the old, used plates are constantly being filled with powder.
The researchers showed the prototype of its printed product, using thermoplastic polyurethane (TPU) powder with an average layer height of 43.6 microns to create a 50-layer thickness and 2.18 mm sample, and printed it with multi-material nylon and TPU with an average layer height of 71 microns part. This type of component not only proves the feasibility of the process, but also proves that a stronger and denser material can be created by squeezing a flat plate against the suspension part during the sintering process.
Now, researchers are still experimenting with metal powders and resins in order to directly make more types of mechanical, electrical and chemical components than those made with SLS systems.