Date of this Version
G. Madireddy, 2018. Modeling Residual Stress Development in Hybrid Processing by Additive Manufacturing and Laser Shock Peening, Masters Thesis.
The term “hybrid” has been widely applied to many areas of manufacturing. Naturally, that term has found a home in additive manufacturing as well. Hybrid additive manufacturing or hybrid-AM has been used to describe multi-material printing, combined machines (e.g., deposition printing and milling machine center), and combined processes (e.g., printing and interlayer laser re-melting). The capabilities afforded by hybrid-AM are rewriting the design rules for materials and adding a new dimension in the design for additive manufacturing paradigm. This work focuses on hybrid-AM processes, which are defined as the use of additive manufacturing (AM) with one or more secondary processes or energy sources that are fully coupled and synergistically affect part quality, functionality, and/or process performance. Secondary processes and energy sources include subtractive and transformative manufacturing technologies, such as machining, re-melting, peening, rolling, and friction stir processing. Of particular interest to this research is combining additive manufacturing with laser shock peening (LSP) in a cyclic process chain to print 3D mechanical properties. Additive manufacturing of metals often results in parts with unfavorable mechanical properties. Laser shock peening is a high strain rate mechanical surface treatment that hammers a work piece and induces favorable mechanical properties. Peening strain hardens a surface and imparts compressive residual stresses improving the mechanical properties of the material. The overarching objective of this work is to investigate the role LSP has on layer-by-layer processing of 3D printed metals. As a first study in this field, this thesis primarily focuses on the following: (1) defining hybrid-AM in relation to hybrid manufacturing and classifying hybrid-AM processes and (2) modeling hybrid-AM by LSP to understand the role of hybrid process parameters on temporal and spatial residual stress development. A finite element model was developed to help understand thermal and mechanical cancellation of residual stress when cyclically coupling printing and peening. Results indicate layer peening frequency is a critical process parameter and highly interdependent on the heat generated by the printing laser source. Optimum hybrid process conditions were found to exists that favorably enhance mechanical properties. With this demonstration, hybrid-AM has ushered in the next evolutionary step in additive manufacturing and has the potential to profoundly change the way high value metal goods are manufactured.
Advisor: Michael P. Sealy