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Additive Manufacturing Technologies: Rapid Prototyping to Direct Digital Manufacturing deals with various aspects of joining materials to form parts. Additive Manufacturing (AM) is an automated technique for direct conversion of 3D CAD data into physical objects using a variety of approaches. Manufacturers have been using these technologies in order to reduce development cycle times and get their products to the market quicker, more cost effectively, and with added value due to the incorporation of customizable features. Realizing the potential of AM applications, a large number of processes have been developed allowing the use of various materials ranging from plastics to metals for product development. Authors Ian Gibson, David W. Rosen and Brent Stucker explain these issues, as well as:

Providing a comprehensive overview of AM technologies plus descriptions of support technologies like software systems and post-processing approaches Discussing the wide variety of new and emerging applications like micro-scale AM, medical applications, direct write electronics and Direct Digital Manufacturing of end-use components Introducing systematic solutions for process selection and design for AM

Additive Manufacturing Technologies: Rapid Prototyping to Direct Digital Manufacturing is the perfect book for researchers, students, practicing engineers, entrepreneurs, and manufacturing industry professionals interested in additive manufacturing.

Inhaltsverzeichnis

Frontmatter

1. Introduction and Basic Principles

Abstract
The term Rapid Prototyping (or RP) is used in a variety of industries to describe a process for rapidly creating a system or part representation before final release or commercialization. In other words, the emphasis is on creating something quickly and that the output is a prototype or basis model from which further models and eventually the final product will be derived. Management consultants and software engineers both use the term Rapid Prototyping to describe a process of developing business and software solutions in a piecewise fashion that allows clients to test ideas and provide feedback during the development process. In a product development context, the term rapid prototyping was used widely to describe technologies which created physical prototypes directly from digital data. This text is about these technologies, first developed for prototyping, but now used for many more purposes.
Ian Gibson, David W. Rosen, Brent Stucker

2. Development of Additive Manufacturing Technology

Abstract
Additive Manufacturing (AM) technology came about as a result of developments in a variety of different technology sectors. Like with many manufacturing technologies, improvements in computing power and reduction in mass storage costs paved the way for processing the large amounts of data typical of modern 3D Computer-Aided Design (CAD) models within reasonable time frames. Nowadays, we have become quite accustomed to having powerful computers and other complex automated machines around us and sometimes it may be difficult for us to imagine how the pioneers struggled to develop the first AM machines.
This chapter highlights some of the key moments that catalogue the development of Additive Manufacturing technology. It will describe how the different technologies converged to a state where they could be integrated into AM machines. It will also discuss milestone AM technologies. Furthermore, we will discuss how the application of Additive Manufacturing has evolved to include greater functionality and embrace a wider range of applications beyond the initial intention of just prototyping.
Ian Gibson, David W. Rosen, Brent Stucker

3. Generalized Additive Manufacturing Process Chain

Abstract
Every product development process involving an Additive Manufacturing machine requires the operator to go through a set sequence of tasks. Easy-to-use “desktop” or “3D printing” machines emphasize the simplicity of this task sequence. These desktop machines are characterized by their low cost, simplicity of use, and ability to be placed in an office environment. For these machines each step is likely to have few options and require minimal effort. However, this also means that there are generally fewer choices, with perhaps a limited range of materials and other variables to experiment with. The larger and more versatile machines are more capable of being tuned to suit different user requirements and therefore are more difficult to operate, but with a wider variety of possible results and effects that may be put to good use by an experienced operator. Such machines also usually require more careful installation in workshop environments.
This chapter will take the reader through the different stages of the process that were described in much less detail in Chap.​ 1. Where possible, the different steps in the process will be described with reference to different processes and machines. The objective is to allow the reader to understand how these machines may differ and also to see how each task works and how it may be exploited to the benefit of higher quality results. As mentioned before, we will refer to eight key steps in the process sequence.
Ian Gibson, David W. Rosen, Brent Stucker

4. Photopolymerization Processes

Abstract
Photopolymerization processes make use of liquid, radiation curable resins, or photopolymers as their primary materials. Most photopolymers react to radiation in the ultraviolet (UV) range of wavelengths, but some visible light systems are used as well. Upon irradiation, these materials undergo a chemical reaction to become solid. This reaction is called photopolymerization, and is typically complex, involving many chemical participants.
Photopolymers were developed in the late 1960s and soon became widely applied in several commercial areas, most notably the coating and printing industry. Many of the glossy coatings on paper and cardboard, for example, are photopolymers. Additionally, photo-curable resins are used in dentistry, such as for sealing the top surfaces of teeth to fill in deep grooves and prevent cavities. In these applications, coatings are cured by radiation that blankets the resin without the need for patterning either the material or the radiation. This changed with the introduction of stereolithography.
Ian Gibson, David W. Rosen, Brent Stucker

5. Powder Bed Fusion Processes

Abstract
Powder bed fusion (PBF) processes were among the first commercialized AM processes. Developed at the University of Texas at Austin, USA, Selective Laser Sintering (SLS) was the first commercialized powder bed fusion process. Its basic method of operation is schematically shown in Fig. 5.1, and all other PBF processes modify this basic approach in one or more ways to enhance machine productivity, enable different materials to be processed, and/or to avoid specific patented features.
All PBF processes share a basic set of characteristics. These include one or more thermal sources for inducing fusion between powder particles, a method for controlling powder fusion to a prescribed region of each layer, and mechanisms for adding and smoothing powder layers.
Ian Gibson, David W. Rosen, Brent Stucker

6. Extrusion-Based Systems

Abstract
This chapter deals with AM technologies that use extrusion to form parts. These technologies can be visualized as similar to cake icing, in that material contained in a reservoir is forced out through a nozzle when pressure is applied. If the pressure remains constant, then the resulting extruded material (commonly referred to as “roads”) will flow at a constant rate and will remain a constant cross-sectional diameter. This diameter will remain constant if the travel of the nozzle across a depositing surface is also kept at a constant speed that corresponds to the flow rate. The material that is being extruded must be in a semi-solid state when it comes out of the nozzle. This material must fully solidify while remaining in that shape. Furthermore, the material must bond to material that has already been extruded so that a solid structure can result.
Since material is extruded, the AM machine must be capable of scanning in a horizontal plane as well as starting and stopping the flow of material while scanning. Once a layer is completed, the machine must index upwards, or move the part downwards, so that a further layer can be produced.
Ian Gibson, David W. Rosen, Brent Stucker

7. Printing Processes

Abstract
Printing technology has been extensively investigated, with the majority of that investigation historically based upon applications to the two-dimensional printing industry. Recently, however, it has spread to numerous new application areas, including electronics packaging, optics, and additive manufacturing. Some of these applications, in fact, have literally taken the technology into a new dimension. The employment of printing technologies in the creation of three-dimensional products has quickly become an extremely promising manufacturing practice, both widely studied and increasingly widely used.
This chapter will summarize the printing achievements made in the additive manufacturing industry and in academia. The development of printing as a process to fabricate 3D parts is summarized, followed by a survey of commercial polymer printing machines. Both direct part printing and binder printing technologies are introduced. Direct printing refers to processes where all of the part material is dispensed from a print head, while binder printing refers to a broad class of processes where binder or other additive is printed onto a powder bed which forms the bulk of the part. Some of the technical challenges of printing are introduced; material development for printing polymers, metals, and ceramics is investigated in some detail. From the topic of pure printing technologies, we move to the three-dimensional binder printing process, where binder is printed into a powder bed to form a part.
Ian Gibson, David W. Rosen, Brent Stucker

8. Sheet Lamination Processes

Abstract
One of the first commercialized (1991) additive manufacturing techniques was Laminated Object Manufacturing (LOM). LOM involved layer-by-layer lamination of paper material sheets, cut using a CO2 laser, each sheet representing one cross-sectional layer of the CAD model of the part. In LOM, the portion of the paper sheet which is not contained within the final part is sliced into cubes of material using a cross-hatch cutting operation. A schematic of the LOM process can be seen in Fig. 8.1.
A number of other processes have been developed based on sheet lamination involving other build materials and cutting strategies. Because of the construction principle, only the outer contours of the parts are cut, and the sheets can be either cut and then stacked or stacked and then cut. These processes can be further categorized based on the mechanism employed to achieve bonding between layers: (a) gluing or adhesive bonding, (b) thermal bonding processes, (c) clamping, and (d) ultrasonic welding. As the use of ultrasonic welding is relatively new, and is an area of considerable research interest, an extended discussion of this bonding approach is included at the end of this chapter.
Ian Gibson, David W. Rosen, Brent Stucker

9. Beam Deposition Processes

Abstract
Beam deposition (BD) processes enable the creation of parts by melting and deposition of material from powder or wire feedstock. Although this basic approach can work for polymers, ceramics, and metal matrix composites, it is predominantly used for metal powders. Thus, this technology is often referred to as “metal deposition” technology. To avoid limiting the readers’ understanding to just metal build materials, however, we will refer to this category of processes as beam deposition processes.
BD processes use some form of energy focused into a narrow region (a beam), which is used to heat a material that is being deposited. Unlike the powder bed fusion techniques discussed in Chap. 5, BD processes are NOT used to melt a material that is pre-laid in a powder bed but are used to melt materials as they are being deposited.
Ian Gibson, David W. Rosen, Brent Stucker

10. Direct Write Technologies

Abstract
The term “Direct Write” (DW) in its broadest sense can mean any technology which can create two- or three-dimensional functional structures directly onto flat or conformal surfaces in complex shapes, without any tooling or masks [1]. Although beam deposition, direct printing, extrusion-based and other AM processes fit this definition; for the purposes of distinguishing between the technologies discussed in this chapter and the technologies discussed elsewhere in this book, we will limit our definition of DW to those technologies which are designed to build freeform structures in dimensions of 5 mm or less, with feature resolution in one or more dimensions below 50 μm. This “small-scale” interpretation is how the term direct write is typically understood in the additive manufacturing community. Thus, for the purposes of this chapter, DW technologies are those processes which create meso, micro, and nano-scale structures using a freeform deposition tool.
Ian Gibson, David W. Rosen, Brent Stucker

11. Design for Additive Manufacturing

Abstract
Design for manufacture and assembly (DFM) has typically meant that designers should tailor their designs to eliminate manufacturing difficulties and minimize manufacturing, assembly, and logistics costs. However, the capabilities of additive manufacturing technologies provide an opportunity to rethink DFM to take advantage of the unique capabilities of these technologies. As we will cover in Chap. 14, several companies are now using AM technologies for production manufacturing. For example, Siemens, Phonak, Widex, and the other hearing aid manufacturers use selective laser sintering and stereolithography machines to produce hearing aid shells, Align Technology uses stereolithography to fabricate molds for producing clear dental braces (“aligners”), and Boeing and its suppliers use selective laser sintering to produce ducts and similar parts for F-18 fighter jets. For hearing aids and dental aligners, AM machines enable manufacturing of tens to hundreds of thousands of parts; where each part is uniquely customized based upon person-specific geometric data. In the case of aircraft components, AM technology enables low volume manufacturing, easy integration of design changes and, at least as importantly, piece part reductions to greatly simplify product assembly.
The unique capabilities of AM technologies enable new opportunities for customization, very significant improvements in product performance, multifunctionality, and lower overall manufacturing costs. These unique capabilities include: shape complexity, in that it is possible to build virtually any shape; hierarchical complexity, in that hierarchical multiscale structures can be designed and fabricated from the microstructure through geometric mesostructure (sizes in the millimeter range) to the part-scale macrostructure; material complexity, in that material can be processed one point, or one layer, at a time; and functional complexity, in that fully functional assemblies and mechanisms can be fabricated directly using AM processes. These capabilities will be expanded upon in Sect. 11.4.
Ian Gibson, David W. Rosen, Brent Stucker

12. Guidelines for Process Selection

Abstract
AM processes, like all materials processing, are constrained by material properties, speed, cost, and accuracy. The performance capabilities of materials and machines lag behind conventional manufacturing technology (e.g., injection molding machinery), although the lag is decreasing. Speed and cost, in terms of time to market, are where AM technology contributes, particularly for complex or customized geometries.
Ian Gibson, David W. Rosen, Brent Stucker

13. Software Issues for Additive Manufacturing

Abstract
It is clear that Additive Manufacturing would not exist without computers and would not have developed so far if it were not for the development of 3D solid modeling CAD. The quality, reliability, and ease of use of 3D CAD have meant that virtually any geometry can be modeled, and it has enhanced our ability to design. Some of the most impressive models made using AM are those that demonstrate the capacity to fabricate complex forms in a single stage without the need to assemble or to use secondary tooling. As mentioned in Chap. 1, the WYSIWYB (What You See Is What You Build) capability allows users to consider the design with fewer concerns over how it can be built.
Ian Gibson, David W. Rosen, Brent Stucker

14. Direct Digital Manufacturing

Abstract
Direct digital manufacturing (DDM) is the usage of additive manufacturing technologies for production or manufacturing of end-use components. DDM is also known as “Rapid Manufacturing;” and for the purposes of this discussion, the term rapid manufacturing, as commonly used in this field, is synonymous with DDM.
Ian Gibson, David W. Rosen, Brent Stucker

15. Medical Applications for Additive Manufacture

Abstract
Additive Manufacturing is coming into its third decade of commercial technological development. During that period, we have experienced a number of significant changes that has led to improvements in accuracy, better mechanical properties, a broader range of applications and reductions in costs of machines and the parts made by them. Also in previous chapters, we have seen that AM technologies can vary according to the following non-exclusive list of parameters:
Ian Gibson, David W. Rosen, Brent Stucker

16. Post-Processing

Abstract
The skill with which various AM practitioners perform post-processing is one of the most distinguishing characteristics between competing service providers. Companies which can efficiently and accurately post-process parts to a customer’s expectations can often charge a premium for their services; whereas, companies which compete primarily on price may sacrifice post-processing quality in order to reduce costs.
Ian Gibson, David W. Rosen, Brent Stucker

17. The Use of Multiple Materials in Additive Manufacturing

Abstract
Almost since the very beginning, experimenters have tried to use more than one material in Additive Manufacturing machines. In fact, multiple materials are a fundamental benefit to how some AM technologies work. The Laminated Object Manufacturing (LOM) process, for example, was one of the earliest AM technologies developed and required that sheet material (paper) be combined with a resin to bond the sheets together to form a composite object of paper and resin.
Ian Gibson, David W. Rosen, Brent Stucker

18. Business Opportunities and Future Directions

Abstract
The current approach for many manufacturing enterprises is to centralize product development, product production, and product distribution in a relatively few physical locations. These locations can decrease even further when companies off-shore product development, production, and/or distribution to other countries/companies to take advantage of lower resource, labor or overhead costs. The resulting concentration of employment leads to regions of disproportionately high underemployment and/or unemployment. As a result, nations can have regions of underpopulation with consequent national problems such as infrastructure being underutilized, and long-term territorial integrity being compromised [1].
Ian Gibson, David W. Rosen, Brent Stucker

Backmatter

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