Recent technological advancement in the field of manufacturing has led to the development of additive manufacturing technologies with the ability to print high density three-dimensional and complex geometries. Unfortunately, most of the manufacturing industries have not embraced the idea due to the limited process reliability and quality issues. Therefore, there is a great need to develop metal additive technologies with proper process documentation to ensure proper part selection and product quality. Recent studies have shown that the challenge can to be addressed by thorough investigation and understanding of the fundamental physics involved in the laser powder bed fusion. Alternatively, evaporation exhibits a significant influence on the manufacturing processes involving the use of laser. Unfortunately, the generation of sparks in laser powder bed fusion results in pool instability and poor quality of the products. As such, mechanisms of spatter generations have recently attracted significant attention of researchers.
To this end, Baihang University researchers: Hang Zheng and Prof. Lihui Lang in collaboration with Huaixue Li and Shuili Gong at AVIC Manufacturing Technology Institute and Dr. Yulong Ge at Tsinghua University investigated the formation and evolution of vapor plume and spatter generation under various scan speeds. In particular, they designed single track experiments for 304 stainless steel formation so as to further investigate the process stability and the melting tracks in an attempt to uncover the correlation between them. Their research work is currently published in the research journal, Journal of Manufacturing Processes.
In brief, the team of authors commenced their experimental work by understating the fundamental physics involved in the laser powder bed fusion. Consequently, they designed experiments on both powder bed and bare substrate to visualize and investigate the influence of powder particles on the process stability and spatter ejection as well as the relationship between the plume stability, melt morphologies, scan speeds and spatter generation on the track level.
“we investigated the plume behavior, especially its stability, by superimposing the frames from one track into one picture. Namely, that is how we realized the track-level analysis. It is not a big challenge in image processing, but it is indeed the one of the foundations of our research. We believe the superimposed pictures are useful in 3D printing and we sincerely hope this method can attract more attention.” Said first author, Hang Zheng in a statement to Advances in Engineering.
The authors observed that the process stability and plume behavior were significantly influenced by scan speeds. In addition, it was noted that during the single-track formation, the relationship between the process stability and the spatter generation was well established as compared to that between the spatter generation and the energy input. Furthermore, the coupling of the melting pool and vapor flux observed at the beginning of the track formation led to a significantly unique droplet spatter.
In summary, the study was the first to successfully investigate plume mechanisms under different scan speeds in which it was concluded that spatter generation was mainly as a result of powder particles. In general, the scientists elucidated that the process instability was due to the powder bed and thus was eliminated when the laser spots lefts the powder bed. As such, careful selection of the desired scan speed, the stability of the laser powder bed fusion process can be effectively controlled. Therefore, the study will advance understating of the dynamics physics involved in laser powder bed fusion thus resulting in high-quality products.
Zheng, H., Li, H., Lang, L., Gong, S., & Ge, Y. (2018). Effects of scan speed on vapor plume behavior and spatter generation in laser powder bed fusion additive manufacturing. Journal of Manufacturing Processes, 36, 60-67.Go To Journal of Manufacturing Processes