Abstract
Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting. The range of polymers used in AM encompasses thermoplastics, thermosets, elastomers, hydrogels, functional polymers, polymer blends, composites, and biological systems. Aspects of polymer design, additives, and processing parameters as they relate to enhancing build speed and improving accuracy, functionality, surface finish, stability, mechanical properties, and porosity are addressed. Selected applications demonstrate how polymer-based AM is being exploited in lightweight engineering, architecture, food processing, optics, energy technology, dentistry, drug delivery, and personalized medicine. Unparalleled by metals and ceramics, polymer-based AM plays a key role in the emerging AM of advanced multifunctional and multimaterial systems including living biological systems as well as life-like synthetic systems.
Highlights
First introduced during the 1980s to serve the highly specialized needs of model making and rapid prototyping (RP), additive manufacturing (AM) alias 3D printing has emerged as a versatile technology platform for computerassisted design (CAD) and rapid manufacturing
At the beginning of the 21st century, additive manufacturing provides a versatile platform for computer-assisted design and manufacturing of advanced functional materials and unconventional material systems
In the 1990s, new AM techniques were developed, and engineers utilized these for rapid prototyping of principally tools and machine components
Summary
First introduced during the 1980s to serve the highly specialized needs of model making and rapid prototyping (RP), additive manufacturing (AM) alias 3D printing has emerged as a versatile technology platform for computerassisted design (CAD) and rapid manufacturing. The principle design of selective laser sintering (SLS, 3D Systems) and laser sintering (EOS) machines is very similar (Figure 32).[234] The building procedure consists of powder deposition, powder solidification, followed by the lowering of the build platform by one layer thickness. These three steps are repeated until the final layer of the manufactured part has been sintered. Throughout the described procedure, the process chamber is kept at an elevated temperature, a few degrees below the processed material’s softening point The aim of this measure is to decrease processing time and reduce the amount of thermally induced internal stresses and curl distortions developed during layered solidification. As photobased AM methods matured, formulators sought to provide resins that required a smaller dose of energy to reach gelation, which relate to faster writing speeds and “rapid” prototyping.[5,111] For SLA, the critical exposure Ec to cause gelation as measured in mJ cm−2 can be defined as
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