SLS manufacturing of metal parts, there are two methods, one is the indirect method, the polymer coated metal powder SLS; the second is the direct method, namely direct metal laser sintering (DirectMetalLaserSintering, DMLS).
Since the research of direct laser sintering of metal powders in Leuvne University of Chatofci in 1991, the direct sintering of metal powders by SLS process is one of the ultimate goals of rapid prototyping.
Compared with the indirect SLS technology, the most important advantage of DMLS process is the removal of expensive and time-consuming pretreatment and post-processing steps.
Characteristics of direct metal powder laser sintering (DMLS)
DMLS technology as a branch of SLS technology, the principle is basically the same.
But DMLS precise forming of metal parts with complicated shape is difficult, after all, is mainly because of the metal powder in DMLS "balling" effect and sintering deformation, balling phenomenon, is to make the molten metal surface and the surrounding medium surface melting system with minimum free energy, the interfacial tension of liquid metal with the surrounding medium, a phenomenon of changing surface shape of liquid metal to the surface of the sphere.
The ball will make the metal powder is melted to form a molten pool solidification not smooth, thus forming the porous parts, resulting in forming failure due to single component metal powder in liquid phase sintering stage the viscosity is relatively high, so the "balling" effect is particularly serious, and the diameter is often greater than the particle diameter, which will resulting in a large number of pore exist in sintered parts.
Therefore, the DMLS of single component metal powders has obvious process defects, and often requires subsequent processing, not real "direct sintering".
In order to overcome the single component metal powder DMLS in the "ball" phenomenon, and the resulting deformation and sintering process defects such as current density loose, generally through the use of different melting points of multi component metal powder or alloy powder used to achieve.
Multi component metal powder system is generally composed of high melting point metal, low melting point metal and some added elements mixed into the high melting point metal powder as matrix metal, can retain the solid core in DMLS; low melting point metal powder as binder, in DMLS melts into liquid phase, the liquid phase coating, wetting the bond and solid metal particles, in order to achieve densification.
The problem of direct metal powder laser sintering (DMLS)
As an important branch of SLS technology DMLS technology is still in the process of continuous development and improvement, the physical process and the sintering Sintering Densification Mechanism is still unclear, the laser sintering parameters of different metal powder system still need to explore, develop special powder and development have to be a breakthrough.
Therefore, mathematical and physical model to establish direct metal laser sintering process, sintering behavior and microstructure change of quantitative study of DMLS Sintering Densification Process, become one of the important content in the research of science and Engineering in powder metallurgy.
In DMLS, the physical properties of metal powders have important influence on the sintering quality. Under the same process parameters, the sintering effects of different powder systems are very different.
It is the most basic and important requirement of DMLS to grasp the physical properties of powder system and select the optimum technological parameters for it. A large number of studies have shown that the three key parameters affecting the quality of DMLS are sintering characteristics, paving characteristics and stability.