SLS technology is a widely used technology in the high-end manufacturing field, May be the most far-reaching 3D Printing technology. Originally proposed by C.R. Dechard, a graduate student at the University of Texas.and It was successfully developed in 1989. With this core technology,He formed a company named DTM,Since then DTM has been a major leader in SLS technology.Until 2001,the company was fully acquired by 3D Systems.
For decades, researchers at DTM, University of Texas, have done a lot of research in the SLS field,And in the equipment development, process and materials research and development has achieved fruitful results.
Today,Alunar share the SLS technology in the field of 3D printing knowledge from the following five parts:
Part 1: SLS 3D Printing Technology Principle
Selective laser sintering (Selective, Laser, Sintering, SLS) technology was invented by C.R. Dechard of University of Texas-Austin,The basic principle of high temperature sintering of powder materials under laser irradiation is mainly studied,Precise positioning is achieved by computer controlled light source positioning device,Then layer by layer sintering, accumulation molding.
The working process of SLS is similar to that of 3DP,Are based on the powder bed,The difference is that 3DP is used to bind powder by spraying binders,While SLS is sintered with infrared laser powder.
Lay a layer of powder material with the powder roller first,By printing the thermostat in the device, it is heated to just below a certain temperature of the burning point of the powder,The laser beam is then irradiated on the powder layer,To cause the irradiated powder to rise above the melting point,Sintering is carried out and bonded with the formed parts.
When sintering is completed on one level,The print platform drops a layer of height,The powder laying system lays new powder materials for the printing platform,The control laser beam is then re irradiated for sintering,So cycle, layer by layer, until the completion of the entire three-dimensional object printing.
SLS process principle
Laser sintering technology is one of the most complicated, highest condition, highest equipment and material cost 3D printing technology, but it is also the most far-reaching technology for 3D printing technology development. In theory, any powder material after heating can form a bond between the atoms can be used as a molding material, SLS has been mature at present, used in SLS equipment to print materials mainly include paraffin, nylon, metal, ceramic powders and their composite materials.
Part 2: SLS Advantages & Technical Limitations
SLS Technical Advantage:
1.Wide range of materials available.
Materials to be used include nylon, polystyrene and other polymers, iron, titanium, alloy and other metals, ceramics, coated sand ,etc.
2.High molding efficiency.
Because SLS technology does not completely melt the powder, but only sintering it, so the manufacturing speed.
3.Material utilization rate is high.
Non sintered materials can be reused, less material waste and lower cost.
4.Without Any Support.
Since the sintered powder can support the cavity and cantilever part of the model, it is not necessary to design the supporting structures in the same way as the FDM and SLA processes, which can directly produce prototypes and parts with complicated shapes;
5.Wide range of applications.
Because of the diversity of forming materials, different molding materials can be used to make sintered parts of different uses, which can be used in the design of prototype models, moulds, dies, investment casting, casting shells and cores, etc.
SLS technology limitations:
1.Raw material prices and procurement maintenance costs are higher.
2.Mechanical performance is insufficient. The principle of SLS forming metal parts is a low melting point powder bonded high melting powder, resulting in parts of the high porosity and poor mechanical properties, especially the elongation rate is very low, very few can be directly applied to the manufacturing of metallic functional parts.
3.More complex auxiliary process is needed. Because the material difference between SLS with larger, more complex and sometimes aided process needs, such as the need for a long time on the pretreatment of raw material (heating), which need to be finished after the completion of the surface cleaning powder,etc.
Part 3: SLS Core Technology Materials Sintering
1.Sintering of Metal Powders
There are three kinds of metal powders used for SLS sintering: single metal powder, metal powder, metal powder and organic powder. Correspondingly, SLS technology has three main ways of forming metal parts:
1).Sintering of Single Metal Powders
For example, iron powder, iron powder is preheated to a certain temperature, and then laser beam scanning, sintering. The sintered parts are treated by hot isostatic pressing, and the relative density of the final parts can reach 99.9%.
2).Sintering of Metal Mixed Powders
It is mainly a mixture of two metals, one of which has a lower melting point and the other has a high melting point. For example, a mixture of bronze powder and nickel powder. The metal mixture is preheated to a certain temperature. The laser is then scanned to fuse the low melting point metal powder (such as bronze powder) so that the refractory nickel powder is bonded together. The relative density of the final part can reach 82% when the sintered parts are treated by liquid phase sintering.
3).Mixture of Metal Powder and Organic Binder Powder
The metal powder and organic binder powder mixed in certain proportion, the laser beam scanning after the organic adhesive melting, organic binder melting metal powder together (such as copper and organic glass powder). The sintered parts are treated by high temperature subsequent treatment, on the one hand, the organic binder is removed. On the other hand, the mechanical strength and heat resistance of the parts are improved.
2.Sintering of Ceramic Powder
Compared with metal composite materials, ceramic powder materials have higher hardness and higher working temperature, and can also be used for copying high temperature mold. Because of the high melting point of ceramic powders, it is necessary to add low melting point adhesives to the ceramic powders when sintering the ceramic powders by SLS process. In laser sintering, the binder is melted first, and then the ceramic powder is bonded and formed by melting adhesive. Finally, the performance of the ceramic parts is improved by post-processing.
At present, the main raw materials used for pure ceramic powder are SiC and the binder has three kinds of inorganic binders, organic binders and metal binders. Because the original process of middle density powder layer is low, so the density of the products is low, it is used for manufacturing casting shell.
3.Sintering of Polymer Materials
Materials used in polymeric materials include polycarbonate (PC), polystyrene powder (PS), ABS, Niron (PA), Niron and glass fiber mixtures, waxes, etc.. Low temperature forming polymer material, the laser power required for sintering, high melt viscosity, no metal powder is difficult to overcome the "balling" effect, therefore, polymer powder is the most widely used and most successful applications of SLS materials.
Nylon material is widely used in SLS 3D printing field because of its high strength, good wear resistance and easy processing. At the same time, nylon, carbon fiber and other materials can be added into the nylon material to improve the mechanical properties, wear resistance, dimensional stability and thermal deformation resistance of the nylon.
Part 4: SLS Print Material Purchase
1.Metal Powder Material
At present, SLS inventor Dechard set up the United States DTM company's products, commercial metal powder products have the following:
The material composition of 1080 carbon steel metal powder and polymer materials, polymer coated uniformly on the surface of particles, forming a density density of 55% steel, strength up to 2.8 MPa, the metal infiltration can be copper, can also be bronze, this material is mainly used to manufacture injection mold.
The sintering parts fully dense, reach Aluminum Alloy strength and hardness, capable of machining, welding, heat treatment and surface treatment, can be used as injection molding plastic injection mold, the life span can reach 100 thousand pieces / vice, can also be used to manufacture of die casting die for Al, Mg, Zn etc. non-ferrous metal parts, die-casting die life can reach 200 ~ 500 / vice.
The matrix material for copper powder, bonding agent for polyamide (Polyamide), the characteristic is not two times after sintering, molding can be used for injection molding of plastic, life is 100 to 400 pieces / vice.
In addition, there are German EOS launched DirectSteel (mixed oil, other metal powder, steel powder) and other materials.
2.SLS Polymer Material
At present, commercialized SLS polymer powder materials mainly have:
1).DuraForm PA (nylon powder, DTM USA)
Which has excellent thermal stability and chemical stability.
2).DuraForm GF (nylon powder with glass beads, DTM, USA)
It has excellent thermal stability, chemical stability and high dimensional accuracy.
3).Polycarbonate (polycarbonate powder, American DTM Corporation)
Which has good thermal stability and can be used for precision casting.
4).CastForm (polystyrene powder, American DTM company)
Need to be treated with casting wax to improve the strength and surface roughness of parts, and can be used in wax free manufacturing process.
5).Somos 201 (elastomer polymer powder, DSM, Somos)
Similar to its rubber products, has very high flexibility.
Part 5: SLS 3D Printing Application
Specifically, the application of SLS can be broadly summarized into six aspects.
The SLS process enables rapid manufacturing of models, thus shortening the time from design to finish, enabling customers to see prototypes of the end product more quickly and visually.
2.Preparation and Development of New Materials
Some new powder particles can be developed by using SLS technology to strengthen the strength of composites.
3.Small batch, Special Parts Manufacturing Process
When it comes to manufacturing requirements of small quantities and special parts, it is often more expensive to manufacture by traditional methods, and the SLS process can solve this problem quickly and effectively, thus reducing costs.
4.Fast Tooling and Tool Manufacturing
At present, with the improvement of technological level, some parts manufactured by SLS can be directly used as moulds.
The use of 3D scanning technology, without drawing and CAD model under the conditions of processing in accordance with the original parts by using SLS technology, according to the final part constructed CAD model prototype, so as to realize the application of reverse engineering.
6.Application in Medicine
Because the parts made by SLS process have a certain porosity, they can be used in artificial bone making. It has been proved by clinical research that the artificial bone has good biocompatibility.