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Contour Crafting is a mega scale layered fabrication process which builds large scale three-dimensional parts by depositing paste materials layer by layer at unprecedented speed and with superior surface quality. This paper presents an overview of related research activities and the progress aimed at extending the technology to construction of residential housing units and civil structures.

Purpose -The purpose of this paper is to present a mask-image-projection-based stereolithography (MIP-SL) process that can combine two base materials with various concentrations and structures to produce a solid object with desired material characteristics. Stereolithography is an additive manufacturing process in which liquid photopolymer resin is cross-linked and converted to solid. The fabrication of digital material requires frequent resin changes during the building process. The process presented in this paper attempts to address the related challenges in achieving such fabrication capability. Design/methodology/approach -A two-channel system design is presented for the multi-material MIP-SL process. In such a design, a coated thick film and linear motions in two axes are used to reduce the separation force of a cured layer. The material cleaning approach to thoroughly remove resin residue on built surfaces is presented for the developed process. Based on a developed testbed, experimental studies were conducted to verify the effectiveness of the presented process on digital material fabrication. Findings -The proposed two-channel system can reduce the separation force of a cured layer by an order of magnitude in the bottom-up projection system. The developed two-stage cleaning approach can effectively remove resin residue on built surfaces. Several multi-material designs have been fabricated to highlight the capability of the developed MIP-SL process. Research limitations/implications -A proof-of-concept testbed has been developed. Its building speed and accuracy can be further improved.The tests were limited to the same type of liquid resins. In addition, the removal of trapped air is a challenge in the presented process. Originality/value -This paper presents a novel and a pioneering approach towards digital material fabrication based on the stereolithography process. This research contributes to the additive manufacturing development by significantly expanding the selection of base materials in fabricating solid objects with desired material characteristics.

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