Since the inception of rapid prototyping, rapid manufacturing of metal parts has become a remarkable research [1-3]. Including selective laser sintering (Selective Laser Sintering, referred to as SLS) technology for rapid metal parts can be manufactured much attention. So far, people mainly focused on two kinds of high melting point metal powder or metal powder blend to mix a binder, with a smaller laser power sintering of metal parts [4-5], while the use of high-power direct laser sintering of metal powder forming small metal pieces. This article is based on the work of previous studies [6-7], starting from the analysis of sintering phenomena and clarify the direct laser sintering of metal powder, the basic characteristics of the process, to further explore the basic law of the sintering process, the people directly using high-power laser sintering metal powder forming metal parts have a more complete and clear understanding.
The SLS process by slicing a CAD model of the software division, the formation of a number of books the layer plane. Sintering, the first device with shop shop pink powder, then the geometry of the laser according to aspects of the material selectively scanning the powder melting and bonding material on the lower, manganese powder but not laser scanning sintered powder is as part of the support body. After the completion of a layer of sintering, drop a slice thickness of the table, re-paved powder, sintering, repeat this process until the entire sintered parts.
After melting the metal powder to form the shape of the pool depends on three different substances in gas, liquid, solid three-phase contact situation, it can be said to depend on the interfacial tension between the exposure to substances. In the three-phase intersection of the liquid particles, set its end in disappointment for the physical point of force f1; by the force of the liquid particle f2; solid particles by the force of f3. f1, f2, f3, respectively, point to the gas, liquid, solid three-phase internal, shown in Figure 2. f1, f2, f3 force the size of the pool depends on the direction of the location. In the powder on the pool, as loose powder is, boron powder the gap between the particles, their combined force smaller, making the f1, f2, f3 total force F point to the liquid inside, as shown in Figure 2 (a) shown, liquid surface and solid - liquid interface obtuse angle, this time, the interfacial tension will reduce the spherical surface, pool shape is spherical. Under such conditions, the sintering, the bath flow in multiple directions under the influence of couple, bonding around the powder, and form a spherical pool. With the move to the next laser melting zone, making the powder has adhesive around the pool cooling and solidification speed. If the laser-molten zone under the action of the next does not have enough powder material (where the powder has been due to previous melt adhesive area to go), you can not form a new pool. Only after moving to a certain distance, only enough powder material is melted to form a new pool, silicon powder so that repeat to form a new sphere. Therefore, sintering line is composed by a bunch of balls. In the matrix part of the pool, because the force of the solid particles f3, and made the f1, f2, f3 total force F? Point to solid, as shown in Figure 2 (b) shown, liquid and solid - liquid interface angle an acute angle, interfacial tension will surface open along the solid surface, the shape of molten pool in the vertical scanning direction is a fan shape appeared, and in the pool along the scan direction is continuous, it is difficult to form a single sphere. Shape of the pool is the matrix determined by the depth of melting, the greater the depth of the matrix melt, the greater the pool of ellipticity, the better sintering.
In the laser sintering process, the role of the metal bath of fluid forces on the main unit body force and surface forces. The volume force main difference is the temperature inside the pool (? Τ) and the concentration difference (? C) caused by buoyancy, metal powder supplier and surface forces mainly pool surface temperature difference (? Τ) and the concentration difference (? C) caused the surface tension difference, because sintering using small spot (d = 1mm), the surface tension of molten pool in the accounts for the main role in this case, the role of volume force can be ignored. Source:http://www.mhcmp.com