Additive manufacturing (AM) processes have advanced rapidly over the last three decades to the point where they have the potential to fundamentally change the way complex parts will be designed and fabricated in the future. Additive methods leverage the ability to join metal particles or molten droplets in a layer-by-layer fashion, allowing for efficient use of raw materials, to minimize waste, and enable cost effective production. Among the existing metal AM techniques available in the literature, the laser induced forward transfer (LIFT) technique is one of the notable methods well suited for three-dimensional (3D) printing of metal structures at the microscale. In the technique, a metallic donor thin film is locally melted by a pulsed laser, and small molten droplets liberated from the film are re-deposited on a target substrate in a layer-by-layer fashion in order to print a 3D object. The minimum feature size of the printed object is limited by a combination of the size of the metal droplets ejected from the donor film and the poor landing accuracy of droplets on the target substrate. In this project, the droplet size and landing accuracy achievable in the LIFT technique will be controlled through the use of patterned micron sized apertures in the donor. The aperture provides two functionalities, (1) the aperture size will control the droplet size, and (2) the aspect ratio will facilitate the formation of vertical liquid jets that promote highly directional ejection of single droplets from the apex of the jet. The objective of this project is to study the hydrodynamics of the liquid jet growth through the donor film aperture, and the ejection of the droplets from the apex of the jet. Specifically, multi-physics (laser heating and fluid dynamics) based numerical models are developed to investigate the transient heating and jetting hydrodynamics of liquid jets from high aspect ratio apertures in the donor film material. Furthermore, the modeling work is complimented with experimental results in patterned copper donor films, where transfer of micron sized single and multiple droplets are demonstrated. The modeling work facilitated the understanding of laser heating and molten metal hydrodynamics under different conditions, laser fluence, donor film thickness, flow velocity, and surface. The aperture based LIFT approach has the potential to enable voxel-by-voxel printing of metal micro- and nanostructures, which can open up new opportunities to fabricate complex nanostructures comprised of inhomogeneous properties, and 3D anisotropic structures with spatially varying properties.

Creator

• Zhang, Li

DOI

• https://doi.org/10.21985/n2-mgt2-zv87

Subject

• Mechanics
• Mechanical engineering
• Civil engineering

Language

• en

Alternate Identifier

• etdadmin_upload_618185
• http://dissertations.umi.com/northwestern:14414

Keyword

• Hydrodynamic
• Thermal
• Laser Induced Forward Transfer
• Aperture

Date created

• 2018-01-01

Resource type

• Dissertation

Rights statement

• In Copyright