Andrew J. Pascall

Light‐Directed Electrophoretic Deposition: A New Additive Manufacturing Technique for Arbitrarily Patterned 3D Composites

Dr. A. J. Pascall, Dr. F. Qian, Dr. M. A. Worsley, Dr. J. D. Kuntz Lawrence Livermore National Laboratory Livermore , CA 94550 , USA E-mail: pascall1@llnl.gov G. Wang, Prof. Y. Li Department of Chemistry and Biochemistry University of California Santa Cruz , CA 95064 , USA

Direct metal writing: Controlling the rheology through microstructure

Most metal additive manufacturing approaches are based on powder-bed melting techniques such as laser selective melting or electron beam melting, which often yield uncontrolled microstructures with defects (e.g., pores or microcracks) and residual stresses. Here, we introduce a proof-of-concept prototype of a 3D metal freeform fabrication process by direct writing of metallic alloys in the semi-solid regime. This process is achieved through controlling the particular microstructure and the rheological behavior of semi-solid alloy slurries, which demonstrate a well suited viscosity and a shear thinning property to retain the shape upon printing. The ability to control the microstructure through this method yields a flexible manufacturing route to fabricating 3D metal parts with full density and complex geometries.

Light Directed Electrophoretic Deposition for Additive Manufacturing: Spatially Localized Deposition Control with Photoconductive Counter Electrodes

Electrophoretic deposition (EPD) has traditionally been viewed as a thin film deposition technique for coating conductive surfaces. Recently, there have been reports of producing functional parts with EPD to near net shape, often containing gradients in material properties normal to the conductive deposition surface. By using reconfigurable electrode systems, a few researchers have gone beyond purely out-of-plane gradients and demonstrated gradients in material properties in the plane of the deposition electrode, a necessary condition for 3D additive manufacturing. In this work, we build upon a previously published technique called light directed electrophoretic deposition (LD-EPD) in which the deposition electrode is photoconductive and can be activated with light, leading to a patterned deposit. Here, we demonstrate that the LD-EPD technique can also lead to patterned deposits on any conductive surface by utilizing the photoconductive electrode as the counter electrode. This eliminates several issues with standard LD-EPD by allowing the potentially expensive photoconductive electrode to be reused, as well as mitigates post-processing material compatibility issues by allowing deposition on any conductive surface. We also detail the results of a finite element simulation of the deposition process in LD-EPD systems that captures key features seen experimentally in the final deposit.

Additive Micro-Manufacturing of Designer Materials

Material properties are governed by the chemical composition and spatial arrangement of constituent elements at multiple length scales. This fundamentally limits material properties with respect to each other creating trade-offs when selecting materials for a specific application. For example, strength and density are inherently linked so that, in general, the more dense the material, the stronger it is in bulk form. Other coupled material properties include thermal expansion and thermal conductivity, hardness and fracture toughness, strength and thermal expansion, etc. We are combining advanced microstructural design, using flexure and screw theory as well as topology optimization, with new additive micro- and nano-manufacturing techniques to create new material systems with previously unachievable property combinations. Our manufacturing techniques include Projection Microstereolithography (PμSL), Direct Ink Writing (DIW), and Electrophoretic Deposition (EPD). These processes are capable of reliably producing designed architectures that are highly three-dimensional, multi-scale, and often composed of multiple constituent materials.