Types of 3D powder printing: melting, sintering, “powder-bed” technology
Due to active development of 3D printing, modern market has a wide range of 3D devices that are able to recreate physical objects using digital models and applying various materials and methods. Additive manufacturing technology can be roughly divided into several groups:
- extrusion printing (FDM, MJM);
- stereolithography (SLA);
- lamination (LOM);
- powder printing (3DP, SLS, DMLS, SLM).
Let’s take a look at the last one. There are several main methods of powder printing: inkjet three dimensional printing (3DP), also known as powder-bed technology, laser sintering technologies (SLS and DMLS), selective laser melting technology (SLM). In each case, printed object is formed by different methods.
Three dimensional printing
This type of additive technology was developed almost 25 years ago. Of course, the technology was improved greatly since then.
Principle: An inkjet print head moves across a bed of powder, selectively depositing binding material, adhering model layers, so that printed objet is formed layer by layer. Besides, particles of each layer are bound both to the previous and the next one.
Materials: 3DP printers are compatible with gypsum plaster, sand, plastics, metal powders.
Application: Strength of models printed using this method depends on binding material type. However, it is not enough for printing functional prototypes of mechanical parts. 3DP printers are used for printing souvenirs, models, jewelry and other products with complicated structure, which are not exposed to stresses. In addition, various types of the technology are used in bioprinting, pastry printing etc.
Laser sintering technology
Unlike the previous method, laser sintering allows stronger full metal products to be created. The technology was developed in 1980s. However, its active development and application started in 2014, when the last patent expired, and the method became open to public.
There are two main types of the technology: Selective laser sintering (SLS) and Direct metal laser sintering (DMLS), where machines with extremely powerful laser emitters are used.
Principle: layer-by-layer sintering of powder particles is performed with the help of carbon dioxide lasers of various powers. SLS method applies powders with special additives, while DMLS allows additives-free metal particles to be sintered. During the printing process, lasers draw model outlines on powder bed and when the ‘scanning’ is over, the powder bed is lowered by one layer thickness, and a new layer of material is applied on its top.
Materials: this method is applied for various polymers, metals and alloys, as well as for composite materials and sand mixtures.
Application: initially, the technology was utilized for prototype creation, since it allowed complicated, yet strong and durable parts to be manufactured within a short period of time. Currently, SLS and DMLS methods are used for small volume manufacturing of end products. Often such 3D printers are used for printing works of art and jewelry.
Selective Laser Melting
This method appeared only early this century, and it is often referred to a type of laser sintering. However, it is not quite correct, since material is not sintered, but rather completely melted and fused, and as the result highly strong and uniform objects are formed. It is SLM technology that is capable of creating structural parts for engines and rockets, since they are able to resist heavy loads.
Principle: powder is distributed onto a substrate plate, usually metal, a chamber is filled with special inert gases, and then a high power laser fused material selectively. After that, the table is lowered and another layer is distributed. An interesting fact is that laser beam is directed in axis with the help of mirrors.
Materials: the most widely used materials are metals and various alloys.
Application: using SLM technology, it is possible to create full metal homogeneous objects with thin baffles, holes and other complicated structural parts. The method is used for the creation of details, which can not be built applying other techniques. Besides, the quality of the product is so high, that it doesn’t require additional post processing. That’s why SLM printers became an integral tool in the aerospace and automotive industries. It is also widely used in medicine and production sector.
One of the main advantages of the listed above printing methods is that they do not require the creation of support structures and at the same time allow high-quality and high-resolution products of various shape to be created. In addition, the technologies economize material: powder that wasn’t used during printing can be re-used later. The disadvantage is quite high price of quality printing stations.