Thermoformable Shell for Repeatable Thermoforming Donghyeon Ko Myeongseong Kim Woohun Lee donghyeon.ko@kaist.ac.kr pluto6944@kaist.ac.kr woohun.lee@kaist.ac.kr KAIST KAIST KAIST Daejeon, South Korea Daejeon, South Korea Daejeon, South Korea Figure 1: Repeatable thermoforming with TF-Shell ABSTRACT We propose a thermoformable shell called TF-Shell that allows re- peatable thermoforming. Due to the low thermal conductivity of typical printing materials like polylactic acid (PLA), thermoforming 3D printed objects is largely limited. Through embedding TF-Shell, users can thermoform target parts in diverse ways. Moreover, the deformed structures can be restored by reheating. In this demo, we introduce the TF-Shell and demonstrate four thermoforming be- haviors with the TF-Shell embedded fgure. With our approach, we envision bringing the value of hands-on craft to digital fabrication. CCS CONCEPTS · Human-centered computing → Human computer interac- tion (HCI). KEYWORDS 3D printing; thermoforming; metamaterial; self-repair ACM Reference Format: Donghyeon Ko, Myeongseong Kim, and Woohun Lee. 2022. Thermoformable Shell for Repeatable Thermoforming. In The Adjunct Publication of the 35th Annual ACM Symposium on User Interface Software and Technology (UIST ’22 Adjunct), October 29-November 2, 2022, Bend, OR, USA. ACM, New York, NY, USA, 3 pages. https://doi.org/10.1145/3526114.3558632 1 INTRODUCTION Although the automation of 3D printing is convenient and precise, users should fabricate 3D objects through virtual modeling. Heat Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for proft or commercial advantage and that copies bear this notice and the full citation on the frst page. Copyrights for third-party components of this work must be honored. For all other uses, contact the owner/author(s). UIST ’22 Adjunct, October 29-November 2, 2022, Bend, OR, USA can be used to soften rigid prints to manually deform them. How- ever, due to the low thermal conductivity of typical FDM printed materials, thermoforming is limited to the deformation thin parts or surface fnishing processes such as smoothing. The use of ther- moforming in 3D printing can be beneftial because it enables the application of appropriate digital and tangible methods. Users can develop the design while feeling the objects’ size or proportions. The fabrication process can be fexible with an additional iteration point, i.e., modifcation after printing [4, 6, 16]. To facilitate thermoforming, researchers have suggested diverse approaches such as a custom printer to use functional materials [16] or inserting heating elements to heat from the inside [4]. Dis- tinctively, Ko et al. [6] suggested modifying internal structures that pass hot air, so users can deeply and locally heat the printed ob- jects. However, this approach also has several limitations. First, it is difcult for users to carefully control the speed and temperature of the hot air. Additionally, global heating or the heating of large objects is not feasible. Above all, iterative thermoforming is almost impossible as the structures collapse by heating, and it is difcult to restore to their original shape. We propose a thermoformable shell called TF-Shell. Like TF-Cells [6], our structure allows the thermoforming of printed objects while addressing the aformentioned issues. Moreover, by applying shape memory, the shell can be restored after reheating, which supports design iterations. As illustrated in Figure 1, if users embed the TF- Shell to target parts and print, they can thermoform with hot air or hot water. Upon reheating, they can restore their original shape and keep iterating thermoforming. In this demon, we frst introduce the principle of the TF-Shell, and demonstrate thermoforming and restoration through the structure. 2 THERMOFORMABLE SHELL © 2022 Copyright held by the owner/author(s). We aimed to use two characteristics of polylactic acid (PLA), which ACM ISBN 978-1-4503-9321-8/22/10. https://doi.org/10.1145/3526114.3558632 is one of the most widely used flament materials. First, PLA has