Abstract
This chapter builds new knowledge for design engineers adopting fused deposition modeling (FDM) technology as an end manufacturing process, rather than simply as a prototyping process. Based on research into 2.5D printing and its use in real-world additive manufacturing situations, a study featuring 111 test pieces across the range of 0.4-4.0mm in thickness were analyzed in increments of 0.1mm to understand how these attributes affect the quality and print time of the parts and isolate specific dimensions which are optimized for the FDM process. The results revealed optimized zones where the outer wall, inner wall/s, and/or infill are produced as continuous extrusions significantly faster to print than thicknesses falling outside of optimized zones. As a result, a quick reference graph and several equations are presented based on fundamental FDM principles, allowing design engineers to implement optimized wall dimensions in computer-aided design (CAD) rather than leaving print optimization to technicians and manufacturers in the final process parameters.
TopIntroduction
As a range of technologies, additive manufacturing (AM), also known as 3D printing, has been the subject of research for several decades. A considerable body of knowledge has been built on the topic across disciplines and there are many publications focusing on processes, materials and applications. Research-based guidelines have been developed to provide designers and engineers with core principles to consider when adopting AM processes; for example Gibson, Rosen and Stucker’s (2015) ‘Additive Manufacturing Technologies’ textbook, as well as books by Lipson and Kurman (2013) and Redwood, Schöffer and Garret (2017). However, as AM shifts from a predominantly prototyping technology, known as rapid prototyping (RP), towards an end-use manufacturing technology (Campbell, Bourell, & Gibson, 2012; Gibson et al., 2015), further guidance is needed for designers to understand how to design specifically for end-use production appropriate to the specific AM technology. Designers need to be aware of the constraints and opportunities of individual AM processes, just as they would when designing for traditional manufacturing technologies. For example, designing for injection molding requires a thorough understanding of draft angles, part-lines and appropriate wall thicknesses, which can vary between injection molding machines and individual molds. These constraints influence the design decisions made throughout product development, and ultimately impact the final form and function. Likewise, there are constraints when designing for additive manufacturing.
Design for additive manufacturing (DfAM) is emerging as an interdisciplinary field of research to address these constraints, helping design engineers effectively adopt AM through the development of more specific methodologies and discourse. This chapter builds on recent DfAM guidelines (Kumke, Watschke, & Vietor, 2016; Pradel, Zhu, Bibb, & Moultrie, 2018; Thompson et al., 2016), focusing specifically on research into the relationship between computer-aided design (CAD) geometry and stereolithography (STL, also known as Standard Triangulation Language) files for part thicknesses in the range of 0.4-4.0mm. Furthermore, it identifies the relationship between such thin geometry and the quality and speed of 3D printing, providing design engineers with specific settings to optimize a design for fused deposition modeling (FDM) as the end manufacturing process. Thin test pieces in 0.1mm increments are analyzed using Cura software from Ultimaker, alongside three printed wall thicknesses (also called the shell) related to nozzle diameter, and graphed alongside three STL export settings (fine, medium and coarse). The vast data set is presented in a visual quick-reference graph with optimal dimensions for FDM printing with the most common Ø0.4mm nozzle highlighted, allowing design engineers to implement settings for maximum printing speed and accuracy, or calculate them using the provided equations for other nozzle diameters. This is particularly important when part designs may only consist of a small number of layers, often described as a 2.5D print (Galbally & Satta, 2016; Zhu, Dancu, & Zhao, 2016), with an increasing range of projects being manufactured using 2.5D printing. The value of this research and experimental study is that it allows designers to significantly improve the final manufacturability of a thin part design, prior to a technician or manufacturer modifying process parameters which are often outside the control of the designer.
Key Terms in this Chapter
2.5D Printing: The use of 3D printing to produce a relatively simple geometric form which can be described in a single orthogonal drawing and extruded in a single axis.
Infill: Within the perimeter wall thickness describing a part, infill is the material used to fill the interior space of a part, and can range from empty (0%) to solid (100%) and gradients in between where infill patterns are used to create solid and hollow zones within a part.
3D Printing (Additive Manufacturing): A digital fabrication technology that allows the production of an object by adding material layer-by-layer in three dimensions.
Computer-Aided Design (CAD): The use of computer systems to assist in the creation, modification, analysis or optimization of a design in 2D or 3D.
Wall Thickness: Within the context of slicing, this is the thickness of the perimeter of a part, directly proportional to the nozzle diameter e.g. a wall thickness of 0.8mm requires two passes with a 0.4mm nozzle, or a single pass with a 0.8mm nozzle. It may also be called the shell thickness.
Fused Deposition Modeling (FDM) or Fused Filament Fabrication (FFF): The most common form of extrusion-based 3D printing technology that works similar to a hot glue gun; plastic filament is fed through a heating element, where it softens and is extruded through a small nozzle, which can move in 3D space to deposit the plastic layer-by-layer as it builds up an object.
STL File: Originally short for Stereolithography file and now often described as a Standard Triangulation Language file, this is the native 3D file type exported from CAD software and imported into a slicing program linked to a 3D printer. A STL file is a mesh made up of triangles describing the exterior surface of an object.
Slicing: The process of converting a three-dimensional STL file into layer-by-layer information that can be 3D printed.