Effect of powder specifications on additive manufacturing processes for aerospace parts
Lee, Rennie Xin Mei
Date of Issue2017
School of Mechanical and Aerospace Engineering
Additive manufacturing (AM) processes (including Powder-Bed, Powder-Blown and HPCS), use powders as the feedstock to manufacture the parts layer by layer or for repairing & remanufacturing. However, the full benefits of AM are not yet utilised widely across industries as there is a lack of specific standardized methods for characterizing both feedstock power and the mechanical properties of finished parts. The final outcome of the finished part quality is affected by properties and behaviors of the powder during the production process. Therefore, it is essential to be able to confidently select powders to ensure that the quality of parts produced are of acceptable standard. Powder Dynamic behavior is a consequence of the combined effects of many factors including powder characteristics like size distribution, morphology, density and porosity. Most of the conventional methods test powder in static state however, in the AM process most of the time the powder will be moving around. In this report, various conventional and newer methods were used for powder characterization and to quantify and qualify both the static and dynamic powder behaviors. The objective is to identify the most suitable and reliable way to correlate powder characterization to the dynamic behaviors occurring during the different AM processes. Experiments were undertaken on 7 different IN718 powder for HPCS (10-30µm), Powder-Bed (20-50µm) & Powder-Blown (50-100µm). Mainly focused on comparing the powder characterization and key behaviors (like flowability, packing density and cohesiveness) by correlating them to the actual AM processes and between the different methods of qualifying and quantifying both static and dynamic behaviors. Particle size is the most reliable indicator affecting powder behavior. The larger particle size and regular morphology powders are more stable and predictable in their behavior for the tests. Although, the finer powder particles produced a more randomized and erratic powder behaviors in the tests, it generally shows that the flowability of the powder improves greatly when fluidization /aeration is introduced. The result allowed a more in-depth understanding of powder interactions and their behaviors with the different characterization methods. These powder characterization methods are suitable to be used to characterized and better understand the powder behavior during the AM processes. Newer methods help improve the description of powder behavior complementing the conventional method. Hence serving as an input for future works in coming up with a more robust and standardized characterization methods for various specific additive manufacturing processes by understanding their powder characteristics coupled with their interactions and behaviors under a particular processing environment.
Final Year Project (FYP)
Nanyang Technological University