How to Sinter Metal Powders in SLS Prototyping？

Rapid prototyping (RP) technology is an advanced manufacturing technology developed in the 1990s. It is a key common technology serving the development of new products for manufacturing enterprises. Selective laser sintering (SLS prototyping) is a method of selectively layering solid powder by laser and superimposing the solidified layer formed by sintering to produce the required shape parts. Compared with rapid prototyping (RP) methods, the most outstanding advantage of SLS is that it uses a wide range of forming materials. Theoretically, any powder material that can form interatomic bonding after heating can be used as SLS forming material. The materials that can be successfully processed by SLS include paraffin, polymer, metal, ceramic powder and their composite powder materials. SLS is more and more widely used because of its many kinds of forming materials, material saving, wide distribution of forming parts performance, suitable for various purposes.

 

Laser Sintering of Mental Powder and Binder

First, the metal powder and a certain binder are uniformly mixed in a certain ratio, and the mixed powder is selectively scanned by a laser beam, and the action of the laser melts the binder in the mixed powder and bonds the metal powder together to form the green body of metal parts. The metal part blank is then subjected to appropriate post-treatment, such as secondary sintering to further improve the strength and other mechanical properties of the metal part. This process is relatively mature and has been able to manufacture metal parts and is used in practice. Nanjing University of Aeronautics and Astronautics uses metal powder as matrix material (iron powder), adding appropriate amount of binder, sintering and forming prototype parts, and subsequent treatment, including burning loss of binder, high temperature roasting, metal infiltration and other processes, finally produces EDM electrodes. Using this electrode, three-dimensional die cavity can be machined on EDM machine tool.

 

 

Laser Sintering of Mental Powder

The process of laser direct sintering of metal powder to make parts is not very mature. More research is done on the mixing and sintering of two kinds of metal powders, one of which has a lower melting point and the other has a higher melting point. Laser sintering melts the low melting point powder, and the molten metal bonds the high melting point metal powder together. Due to the low strength of the sintered parts, post-treatment is required to achieve higher strength. At the University of Texas at Austin, SLS prototyping forming of metal powders without polymer binders such as CuSn NiSn bronze nickel powder composite powder was carried out, and metal parts were successfully fabricated. They studied the laser sintering of a single metal powder and successfully fabricated the metal parts of the NCONEL625 superalloy and Ti6A 14 alloy for the F1 fighter and the AIM9 missile. The Institute of Metals of the Chinese Academy of Sciences and Xi'an Jiaotong University are working on laser rapid prototyping of high-melting-point metals. Nanjing University of Aeronautics and Astronautics has also studied this field. The sintering experiments of Ni-based alloy copper powder mixtures have been carried out, and the metal parts with large angle and inverted cone shape have been successfully manufactured.

 

 

Laser Sintering of Powder Compact

Metal powder compact sintering is to pre-press two kinds of metal powders with high and low melting points into thin sheet blanks. Laser sintering is carried out with appropriate technological parameters. The metal with low melting points melts and flows into the pore space of the particles with high melting points, so that the powder particles with high melting points are rearranged and the samples with high density are obtained. Guo Zuoxing of Jilin University used this method to study FeCu, Fe C and other alloys. It was found that compact laser sintering has a completely different densification phenomenon from conventional sintering. The structure of compact laser sintering varies with the cooling mode. Fine pearlite can be obtained by air cooling, and martensite and granular can be obtained by quenching.

 

 

SLS prototyping plays a positive role in promoting product innovation, shortening the development cycle of new products and improving product competitiveness. Since the advent of this technology, it has been widely used in the manufacturing industry of developed countries, resulting in a new technology field.