Sintered metal technology is divided into three categories. Let's briefly analyze it,
1. Compact sintered metal
Guo Zuoxing of Jilin University used this method to conduct experimental research on FeCu, Fe C and other alloys. It is found that compact laser sintering has a completely different densification phenomenon from conventional sintering. The microstructure after laser sintering varies with the cooling mode. Fine pearlite is obtained by air cooling and martensite and granular are obtained after quenching.
Compact sintered metal is that two kinds of metal powders with high and low melting points are pre pressed into sheet blanks, and laser sintering is carried out with appropriate process parameters. The metal with low melting point melts and flows into the pores of particles with high melting point, so that the powder particles with high melting point are rearranged to obtain samples with high density.
2. Laser sintered metal
The University of Texas in Austin conducted SLS forming research on metal powder without polymer binder, such as CuSn NiSn bronze nickel powder composite powder, and successfully manufactured metal parts. In recent years, they have studied the laser sintering of single metal powder and successfully manufactured metal parts of Inconel625 superalloy and ti6a 14 alloy for F1 fighter and aim9 missile. American aviation materials company has successfully developed advanced laser rapid prototyping technology for Qin alloy components. At present, the Institute of metals, Chinese Academy of Sciences and Northwest University of technology are committed to the research on Laser Rapid Prototyping of high melting point metals. Nanjing University of Aeronautics and Astronautics has also carried out research in this regard. The sintering forming test is carried out with Ni based alloy mixed with copper powder, and the metal parts with large angle inverted cone shape are successfully manufactured.
The technology of manufacturing parts by laser direct sintered metal is not very mature. At present, more research is the mixed sintering of two kinds of metal powder, 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 binds the high melting point metal powder together. Because the sintered metal components have low strength, they need post-treatment to achieve high strength.
3. Mixed sintered metal and binder
This process is relatively mature, and has been able to manufacture metal parts, which have been used in practice. Nanjing University of Aeronautics and Astronautics uses metal powder as the base material (iron powder), adds an appropriate amount of drying agent, sinters and forms the prototype, and then carries out subsequent treatment, including burning out binder, high-temperature roasting, metal infiltration (such as copper infiltration), and finally produces EDM electrode. The electrode is used to machine the three-dimensional mold cavity on the EDM machine tool.
Firstly, the metal powder and a certain binder are mixed evenly in a certain proportion, and the mixed powder is selectively scanned with a laser beam. The action of the laser melts the binder in the mixed powder and binds the metal powder together to form the green body of metal parts. Then the green body of metal parts is properly post treated, such as secondary sintering, to further improve the strength and other mechanical properties of metal parts.