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Research and development of a new thixotropic metal 3D printing system
Dissertation   Open access

Research and development of a new thixotropic metal 3D printing system

Jie Xu
Doctor of Philosophy (Ph.D.), Drexel University
Jun 2024
DOI:
https://doi.org/10.17918/00010510
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Xu_Jie_202413.29 MBDownloadView
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Abstract

Metal 3D print process control Metal 3D printing system design Metal additive manufacturing Substrate adhesion Zinc aluminum alloy
Metal Additive Manufacturing (MAM) has rapidly advanced in modern manufacturing. Nonetheless, many limitations still need to be resolved in current powder-based MAM processes, such as sophisticated devices, health risks, low build rates, and unsuitability for printing biodegradable metal alloys like zinc and magnesium. Direct Metal Writing (DMW) and metal Fuse Filament Fabrication (FFF) are two extrusion-based MAM technologies that have emerged recently to address these limitations. However, research gaps persist in DMW and metal FFF, such as poor dimensional and geometrical resolution for DMW and complicated post-processes for metal FFF. This study proposes, designs, and validates a new Thixotropic Metal 3D Printing System based on theoretical thixotropy studies. Four research tasks were identified in this research: 1) fine-globular-grain metal filament generation, 2) new Thixotropic Metal 3D Printing System development, 3) substrate adhesion mechanism development and printability test, and 4) two-dimensional and three-dimensional geometry Print. In the first task, a refined grain structure was obtained through fast heating and quick quenching heat treatment. This result is a step forward in improving thixotropic metal 3D printing resolution since a smaller nozzle can be used with finer grain size. In the second task, an innovative Thixotropic Metal 3D Printing System was developed based on thixotropy theory. This system integrates a novel extrusion system, a flexible inert gas protection system, a creative substrate system using a reliable substrate adhesion mechanism, a robust metallic wire feeding system, and an XYZ moving platform. This innovative system can print Zn85-Al15 alloy and aims to print other biodegradable metallic materials, such as Zn-Mg alloy. In the third task, the substrate adhesion mechanism was studied, and the corresponding adhesion strength was analyzed. Results proved the effectiveness of the hot-coating substrate adhesion mechanism. In the fourth task, printability test results showcased the poor resolution of DMW, while thixotropic MAM demonstrated the ability to print geometries with higher resolution. The 2D surface print results show that XY and XZ surfaces can be printed with filament-to-filament and layer-to-layer adhesions without loss of resolution. For 3D geometrical prints, multi-layer square blocks, cylinders, and scaffolds were printed with good resolution and sufficient interlayer adhesion. Results in the fourth task validated the hypothesis that thixotropic ME can address existing research gaps. Overall, this research successfully addressed four pressing tasks in MAM. The potential impact of the innovative Thixotropic Metal 3D Printing System on the field is not just significant but transformative. Feasibility studies and process controls have demonstrated the system's capabilities, paving the way for future research in printing Zn-Mg biodegradable implants. This represents a significant advancement in the field, offering an optimistic outlook for the future of MAM.

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