Session: 03-04-01: Emerging Materials Technology I

Paper Number: 107356

107356 - Fabricating Machine Elements Using Hydrogel-Infused Additive Manufacturing 

Additive manufacturing (AM) of metals can enable rapid development of functional parts with complex geometries, with potential applications in the aerospace, automotive, and biomedical fields. Typical metal additive manufacturing techniques are based on expensive laser melting or sintering processes limiting the development and use of these products. These traditional metal additive manufactured components are often highly anisotropic. Furthermore, few additive manufacturing techniques focus on high temperature materials, ceramics, and fabrication of machine elements. 

Hydrogel-Infusion Additive Manufacturing (HIAM) is a novel process with potential applications in high performance metal and ceramic devices and components. The HIAM process involves 3D printing a polymer structure from a polyethylene oxide (PEO) photo-resin using vat polymerization. This polymer structure is then immersed in a metal salt precursor solution. The salt water solution swells the hydrogel scaffold, allowing the ionized metal ions to bond to the Oxygen sites on the PEO repeat unit of the polymer. The sample is subsequently calcined by heating it in the presence of air to combust the polymer and oxidize the metal ions, leaving a metal oxide that takes the same functional structure as the original polymer, albeit a smaller size given the loss of polymer mass. Metal oxides thus produced may be reduced in the presence of forming gas (95% N2/5% H2) to give a metal product that maintains the complex as-printed architecture. This technique enables architected features with microscale resolution by use of a single photoresin simply by varying post-processing conditions. HIAM has been shown to be successful in producing octet lattice micro-structures consisting of nickel, iron, copper, and copper-nickel alloys among other metals. 

As a first step, this paper outlines an attempt to fabricate springs out of silver metal using Hydrogel Infused Additive Manufacturing. Silver nitrate is infused into an additively manufactured polymer spring structure. Based on the Ellingham Diagram shown in Figure 3, Silver Oxide (AgO) is readily reduced to silver metal under calcination temperatures of 500°C used in this study. Hence it is possible to fabricate machine elements and components made of silver metal in a single step. XRD analysis of the springs confirm the presence of low microstrain (8.40E-7 ± 2.78E-9) crystalline Silver with average crystallite size of 514.95 ± 5.32 Å and lattice parameter of 4.09 ± 5.23E-5 Å. Thermal analyses such as Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC) elucidate the mass loss and reactions that occur during the furnace processing. DSC kinetic analysis demonstrates a consistent combustion-reduction reaction with constant activation energy. TGA shows consistent water loss from dehydration  and evaporation, followed by significant mass loss during the direct formation of silver through combustion. The study’s standard and larger compression springs have a coil diameter of 2.5 mm and 5 mm, a wire diameter of 0.75 mm and 1 mm, and a stiffness of ~20 N/mm and ~2 N/mm, respectively, as measured using a Dynamic Mechanical Analyzer (DMA). HIAM fabricated springs show consistency of part stiffness following compaction under cyclic loading.

Presenting Author: Anil Saigal Tufts University

Presenting Author Biography: Anil Saigal is Professor of Mechanical Engineering at Tufts University. He received his Ph.D from Georgia Istitute of Technology. He is a Fellow of ASME.

Authors:

Anil Saigal Tufts University
Seneca Jackson Velling California Institute of Technology
Akash Dhawan California Institute of Technology
Maria Azcona Baez California Institute of Technology
Miguel Nocum California Institute of Technology
Julia R. Greer California Institute of Technology