From 3D Models to 3D Prints: an Overview of the Processing Pipeline <s> Printing-aware modelling <s> Geometric modeling and the physical validity of shapes are traditionally considered independently. This makes creating aesthetically pleasing yet physically valid models challenging. We propose an interactive design framework for efficient and intuitive exploration of geometrically and physically valid shapes. During any geometric editing operation, the proposed system continuously visualizes the valid range of the parameter being edited. When one or more constraints are violated after an operation, the system generates multiple suggestions involving both discrete and continuous changes to restore validity. Each suggestion also comes with an editing mode that simultaneously adjusts multiple parameters in a coordinated way to maintain validity. Thus, while the user focuses on the aesthetic aspects of the design, our computational design framework helps to achieve physical realizability by providing active guidance to the user. We demonstrate our framework on plank-based furniture design with nail-joint and frictional constraints. We use our system to design a range of examples, conduct a user study, and also fabricate a physical prototype to test the validity and usefulness of the system. <s> BIB001 </s> From 3D Models to 3D Prints: an Overview of the Processing Pipeline <s> Printing-aware modelling <s> Abstract In layer-based additive manufacturing (AM), supporting structures need to be inserted to support the overhanging regions. The adding of supporting structures slows down the speed of fabrication and introduces artifacts onto the finished surface. We present an orientation-driven shape optimizer to slim down the supporting structures used in single material-based AM. The optimizer can be employed as a tool to help designers to optimize the original model to achieve a more self-supported shape, which can be used as a reference for their further design. The model to be optimized is first enclosed in a volumetric mesh, which is employed as the domain of computation. The optimizer is driven by the operations of reorientation taken on tetrahedra with ‘facing-down’ surface facets. We formulate the demand on minimizing shape variation as global rigidity energy. The local optimization problem for determining a minimal rotation is analyzed on the Gauss sphere, which leads to a closed-form solution. Moreover, we also extend our approach to create the functions of controlling the deformation and searching for optimal printing directions. <s> BIB002
In Section 3 we have presented a number of techniques that, given an input shape, aim to find the best possible way to 3D print it so as to match one or a combination of the targets listed in Section 2. In this section we approach the same problem from a different perspective: how can I design a shape that, if 3D printed, will satisfy the quality, cost or mechanical requirements that I would like to satisfy? The key observation is that, in many cases, tiny changes on the design would make a big difference in terms of AM. Although shape design is out of the scope of this survey, we would like to give the reader a brief overview of this topic, to emphasize that most of the problems that the process plan aims to solve, can also be tackled at design time. We believe that future software will couple modeling and process planning more tightly in order to guide the user towards shape the can be fabricated more reliably. Design to reduce supports. Support structures impact on AM in many ways (material, removal effort, surface artifacts,...). Two interesting recent works attempt to reduce supports at the design stage. In BIB002 the shape is modified to make it more selfsustainable and, thus, require a minor amount of external supports. In  the authors propose three basic 3D sculpting operations (trim, preserve and grow) to produce shapes that can be printed without supports structures. In general, supports are one of the most difficult and penalizing issues for AM, and more research effort is required at all stages (modeling, planning, materials and machines) to alleviate their detrimental impact. Design to ensure structural soundness. Often, it is discovered only after fabrication that a printed shape will not be able to sustain its own weight or will be too fragile. Stava et al. [SVB * 12] proposed not only to predict fragilities in a part, but also proposed an algorithm to reinforce the shape by means of local operations such as hollowing, thickening ans strut insertion. Although not in the context of AM, Umetani et al. BIB001 proposed a design tool for furniture that suggests changes based on structural strength prediction. This type of feedback and automated suggestions during design could enable a widespread adoption of AM, allowing anyone to model a shape while the algorithm verifies the design and suggests fixes. Industry. People operating in industrial design have been creating shapes to be fabricated with subtractive techniques for decades. Nowadays AM poses new challenges for designer, which have to think of new good principles that fit a different manufacturing paradigm. Printing-aware design is often used in literature to refer to attempts to go in this direction. We point the reader to [HPE16, TMV * 16, SAZ15] and references therein for inspiring discussions on this topic.