Additive Manufacturing of TPU and Hybrid TPU-PLA Formwork for Custom Repetitive Precast Concrete

Abstract Concrete is a building material with excellent structural and architectural qualities that could be molded into any shape. However, it is responsible for approximately 8% of the world’s total greenhouse gas emissions. Therefore, material consumption must be reduced during the design and construction of concrete structures. To achieve this, designers could employ approaches that allow achieving more with less, such as designing structural geometries that use material where it is needed and removing it from elsewhere. In addition, efficient concrete construction methods are a major focus of research in architecture, civil engineering, and material sciences. One area of investigation is the direct digital fabrication of concrete, or three-dimensional concrete printing (3DCP), and another is the indirect digital fabrication by three-dimensional printed formworks (3DPFs). Focusing on 3DPFs, many projects have investigated them using multiple approaches, such as stay-in-place, in situ, or disposable strategies. A number of these approaches are incompatible with economies of scale. Mass production and modular, reusable assemblies currently dominate the market to cut costs, with reusable 3DPFs largely underrepresented in current research. This research presents a case study for a new manufacturing workflow for the design and fabrication of precast facade panels. Structural topology optimization (TO) designs facade panels with optimized material distribution according to the panel’s connection to a substructure. Then, flexible thermoplastic polyurethane (TPU) molds are additively manufactured and repeatedly cast. This research demonstrates a proof-of-concept for additively manufactured TPU molds for the repeatable casting of concrete when accommodating undercuts in complex cast geometries. In addition, it investigates a hybrid molding approach that uses a TPU–polylactic acid (PLA) two-part mold. This research is novel because the use of additively manufactured flexible molds made from TPU for the repeatable casting of geometries is in its early stages. In addition, to the best of the author’s knowledge, no previous study has looked into creating hybrid molds with TPU and PLA filaments. This research is pioneering because it addresses material savings during the design phase with TO; and during the fabrication phase by creating reusable 3DPFs.