This work created a manufacturing process and material system based on binder jetting Additive Manufacturing to process pure copper. In order to reduce the sintered part porosity and shape distortion during sintering, the powder bed voids were filled with smaller particles to improve the powder packing density. Through the investigation of a bimodal particle size powder bed and nanoparticle binders, this work aims to develop an understanding of (i) the relationship between printed part properties and powder bed particle size distribution, and (ii) the binder-powder interaction and printed primitive formation in binder jetting of metals.
Bimodal powder mixtures created by mixing a coarse powder with a finer powder were investigated. Compared to the parts printed with the monosized fine powder constituent, the use of a bimodal powder mixture improved the powder flowability and packing density, and therefore increased the green part density (8.2%), reduced the sintering shrinkage (6.4%), and increased the sintered density (4.0%).
The deposition of nanoparticles to the powder bed voids was achieved by three different metal binders: (i) a nanoparticles suspension in an existing organic binder, (ii) an inorganic nanosuspension, and (iii) a Metal-Organic-Decomposition ink. The use of nanoparticle binders improved the green part density and reduced the sintering shrinkage, which has led to an improved sintered density when high binder saturation ratios were used. A new binding mechanism based on sintering the jetted metal nanoparticles was demonstrated to be capable of (i) providing a permanent bonding for powders to improve the printed part structural integrity, and (ii) eliminating the need for organic adhesives to improve the printed part purity.
Finally, the binder-powder interaction was studied by an experimental approach based on sessile drop goniometry on a powder bed. The dynamic contact angle of binder wetting capillary pores was calculated based on the binder penetration time, and used to describe the powder permeability and understand the binder penetration depth. This gained understanding was then used to study how the nanoparticle solid loading in a binder affect the binder-powder interactions and the printed primitive size, which provided an understanding for determining material compatibility and printing parameters in binder jetting. / PHD / The binder jetting Additive Manufacturing (AM) process can be used to fabricate net-shape metal parts with complex geometries by selectively inkjet printing a liquid binding agent into a powder bed, followed by post-process sintering of the printed green parts. Motivated by the need to create highly efficient thermal management systems, this work has established a binder jetting manufacturing process chain for fabricating components made of pure copper, a conductive and optically reflective material that is challenging to be processed by laser-based AM systems. In order to improve the performance metrics (e.g., mechanical strength, electrical and thermal conductivity) of the printed copper parts, an overall strategy to improve powder bed packing density by filling the powder bed voids with fine particles was investigated. Through the use of a bimodal powder mixture and a nanoparticle binder, the sintered density and structural integrity of the printed parts were improved. Via the investigation of these novel material systems created for binder jetting of copper, (i) the gaps in understanding the relationship between printed part properties and powder bed particle size distribution were filled, and (ii) an experimental approach to characterize and understand the binder-powder interaction and printed primitive formation was created to guide the selection of printing parameters in binder jetting.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/95855 |
| Date | 01 June 2018 |
| Creators | Bai, Yun |
| Contributors | Mechanical Engineering, Williams, Christopher B., Diller, Thomas E., Lu, Peizhen, Suchicital, Carlos T. A., Zheng, Xiaoyu, Aning, Alexander O. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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