Method of Designing, Partitioning, and Printing 3d Objects with Specified Printing Direction

Although 3D objects to be printed may have “natural direction” or intended direction for printing, most 3D printing methods slice and print them horizontally. This causes staircase effect on the surface and prevents expression of the natural or intended direction; that is, the natural direction and the printing direction contradict. This paper proposes a methodology for direction-specified 3D printing and methods for designing, partitioning, and printing 3D objects with specified printing direction using a fused deposition modeling (FDM) printer. By using these methods, printed objects do not only have unnatural steps but also enables to express the direction explicitly. By developing and evaluating a set of methods based on this methodology, chained rings of an Olympic symbol are designed, partitioned, and printed by a delta-type 3D printer, which is cheaper but can move quick vertically. The rings were well designed and printed rings look well. Although there are still several unsolved problems including difficulty in deciding part partition points and weakness in the partition points, this methodology will probably enable new applications of 3D printing, such as 3D calligraphy. INTRODUCTION In additive manufacturing (AM) processes, two problems are caused by horizontally-layered printing. 3D printers print objects horizontally, i.e., layer by layer. A print head of a fused deposition modeling (FDM) printer almost never moves vertically except when it moves to the next layer. Problems that may be caused by this feature are as follow. The first problem is the staircase effect. That is, if the surface of objects is not horizontal, horizontally-layered printing generates non-smooth surface. The second problem is that the “strength” of printed objects is usually weaker than printed objects that were aligned horizontally. Moreover, horizontally-layered printing disables many possibilities of FDM printers that may be able to generate natural or intentional texture on the object surface (and potentially inside the object, which may be visible when the object is transparent). 3D printing can be used not only for rapid prototyping, in which the texture of the artistic impression of printed objects is not very important, but it can also be used for wider applications, such as printing figures or other artistic objects. For example, a printed object, such as hair or grass has natural directions, which are not usually horizontal, the natural direction contradicts with the printing direction. The printing direction is sometimes invisible in printed objects, but it is usually visible in printed objects unless it is intentionally erased, and it can be explicitly controlled. If the printing direction is consistent with the natural or intentional direction, the printed objects can explicitly express the direction and generate artistic texture. This paper proposes a methodology for printing 3D objects with specified printing direction by using an FMD method. This methodology was briefly summarized in a poster and a short note [2, 3]. This methodology is called the direction-specified 3D printing methodology. If the object to be printed has a natural direction, the direction may be detected by the printing system or software. However, the direction is not assumed to be natural in this methodology because it may be unable to decide a natural direction and it is considered to be sometimes useful to decide a direction intentionally. Therefore, the direction, i.e., the printing direction, is explicitly specified at design time in the proposed methodology. This methodology thus requires (1) a new representation of directed object models and (2) at least four new methods for modeling an object, partitioning the model, generating a toolpath, and printing the object. First, an object is modeled as a model with directions or a “vector field”, similar to a magnetic field; that is, each point in the model has a direction. Because this model is different from conventional CAD models and different methods for manufacturing are required, this paper proposes new methods for designing, tool-path generation, and printing methods. In conventional 3D printing, STL (Standard Triangulation Language or Stereo-Lithography) is used for the modeling language; however, because STL-based models are not directed models, STL cannot be used in this methodology