What Are the Problems of Metal Powders in SLS Prototyping？

SLS prototyping technology is a very young manufacturing field, and it is not perfect in many aspects. Three-dimensional parts manufactured generally have problems, such as low strength, low precision and poor surface quality. The SLS process involves many parameters (such as physical and chemical properties of the material, laser parameters, and sintering process parameters) that affect the sintering process, molding accuracy, and quality. During the forming process, due to various material factors and process factors, the sintered parts may cause various metallurgical defects (such as cracks, deformation, pores).

 

 

Effect of Powder Materials

Physical properties of powder materials, such as particle size, density, thermal expansion coefficient and fluidity, have an important impact on the formation of defects in parts. The particle size and density of powder not only affect the formation of defects in the moulded parts, but also have a significant impact on the accuracy and roughness of the moulded parts. The influence of powder expansion and solidification mechanism on sintering process can lead to the increase of porosity and the decrease of tensile strength.

 

 

Effect of Process Parameters

Laser and sintering process parameters, such as laser power, scanning speed, direction and spacing, sintering temperature, sintering time and layer thickness, will affect the bonding between layers, shrinkage deformation, warping deformation and even cracking of sintered bodies. The above parameters often influence each other in the forming process. For example, Yong Ak Song and other studies show that reducing scanning speed and spacing or increasing laser power can reduce the surface roughness, but the decrease of scanning spacing will lead to the increase of warpage.

 

Therefore, in the process of optimum design, it is necessary to consider the optimization of all parameters in order to get the most effective parameter group for improving the quality of the finished parts. The manufactured parts generally have some problems, such as low density, low strength and accuracy, mechanical and thermal properties can not meet the requirements of use. These mouldings can not be used directly as functional parts, and need post-processing (such as hot isostatic pressing, liquid phase sintering, high temperature sintering and melting immersion) before they can be put into practical use. In addition, due to the high temperature of SLS of metal powder, in order to prevent oxidation of metal powder, metal powder must be enclosed in a container filled with protective gas during sintering.

 

 

In the rapid prototyping technology, metal powder SLS prototyping technology is a hot spot of research. It is difficult to produce high strength parts by traditional cutting methods, and it is very important for the wider application of rapid prototyping technology to realize the direct sintering of parts with high melting point metals.  Looking forward to the future, the research direction of SLS prototyping technology in the field of metal materials should be sintering of unit system metal parts, sintering of multi-element alloy parts, laser sintering of advanced metal materials such as metal nano-materials, amorphous metal alloys and so on. And it is especially suitable for the molding of micro-components of cemented carbide materials. In addition, parts with functional gradients and structural gradients are sintered according to the specific function and economic requirements of the part. We believe that with the mastery of laser sintering metal powder forming mechanism, the acquisition of optimal sintering parameters for various metal materials, and the emergence of special rapid prototyping materials, the research and application of SLS prototyping technology will enter a new stage.