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Additive Manufacturing 101-3: What is material extrusion?

(Image: 3D Hubs)

Material Extrusion (Image: 3D Hubs)

  Mechanical Design Engineer and Additive Manufacturing Ph.D. student

This is the fourth article in a series of original articles that will help you understand the origins of the technology that is commonly called 3D printing. First an introduction, followed by the seven main technologies categories (binder jetting, directed energy deposition, material extrusion, material jetting, powder bed fusion, sheet lamination, vat photopolymerization) and then a design philosophy for additive manufacturing.

Material Extrusion

ISO/ASTM definition: “material extrusion, —an additive manufacturing process in which material is selectively dispensed through a nozzle or orifice.”[1]

Material Extrusion can also be known as (in alphabetical order):

➢ Direct Ink Writing or DIW[2]

➢ Extrusion Freeform Fabrication or EFF[3]

➢ Fused Deposition Modeling‎ or FDM® (Stratasys Inc.)[4]

➢ Fused Filament Fabrication or FFF[5]

➢ Glass 3D Printing or G3DP[6]

➢ Liquid Deposition Modeling or LDM[7]

➢ Micropen Writing[8]

➢ Plastic Jet Printing or PJP (3D Systems Corporation)

➢ Robocasting or Robotic Deposition[9], [10]

In 1988, Scott Crump invented a new AM process based on candle wax and a hot glue gun while making a toy for his daughter in the kitchen. The next year he started the company Stratasys, which became one of the largest AM companies in the world. In 2005, in the United Kingdom, Adrian Bowyer at the University of Bath started the RepRap project[5] based on the technology that made Stratasys so successful. His goal was to be able to make use of expiring patents[4] that would make FFF available to everyone, and create an open source 3D printer that was capable of replicating rapidly (RepRap) itself, or at least make as many parts for itself as it could. This first open source printer was released in 2008 and inspired many companies to make their own versions based on the RepRap platform. One company, MakerBot, was founded in 2009 and later acquired by Stratasys in 2013. This open-source design along with the expired patents allowed hundreds of different printer designs and companies to emerge since then. This recent development has contributed to the public’s general awareness of AM technology, even though the core technology started over 30 years ago. Most desktop 3D printers in the world are of this type and are what most people think of when they think 3D printer.

Figure 1: Example of a material Extrusion system’s basic components[11]

The core principle of this technology is that any material that is in a semi-liquid or paste form can be pushed through a nozzle and used to draw the 2D cross-sections of a sliced 3D model. Similar to how a hot glue gun heats a rod of glue and the trigger selectively pushes the material through the nozzle, material extrusion works exactly the same way. The material that is extruded doesn’t need to be plastic or even heated. While the vast majority of these printers use a plastic like ABS (Acrylonitrile butadiene styrene) or PLA (Polylactic acid), any material that can be pushed through a nozzle (heated or not) and afterwards retain its shape can be used. Other examples include cement[12], chocolate[13], ceramic pastes or slurries[9], metal clays and metal filled plastics[14], ground-up and blended food[15], or even biocompatible organic cellular scaffolding gel[16]. The technology is scalable and is only limited by nozzle size and supporting machine structure. This supporting machine structure can take many different shapes such as a delta robot configuration or multi-jointed robot arms[17]. This printer structure can also be built using traditional scaffolding structures to create some of the largest printers in the world. Two examples are a 2014 Chinese built 12m x 12m x 12m printer in the city of Qingdao, and a 2016 12m tall delta printer in the Italian town of Massa Lombarda, both of which are large enough to print a small house. There are plans to build printers that move on a rail system enabling an almost infinite build length in one direction[18]. Multiple print heads can be installed on the same machine thus enabling multi-material printing, but there can be challenges with calibration between heads; thus, more than 2 heads on a machine is rare.The greatest advantage of this process is the extensive range of materials it can use. Almost all types of thermoplastics can be used, from the standard plastics like ABS to more engineering plastic grades like nylon, all the way up to advanced engineering plastics like polyether ether ketone also known as PEEK. These plastics have superior dimensional stability and can be used as actual end-use parts like in the Boeing 787 where many parts (mostly air ducting) are 3D printed from FDM processes. The mechanics of this type of printing are fairly simple and easy to modify especially due to the availability of open source designs; thus people have taken these principles to print anything that can fit into a syringe or that can be made into a filament.Some disadvantages are that this process is slow as only one nozzle operates at a time and the entire layer must be subdivided into actual tool paths to trace out the whole 2D slice. This tool path causes the fill factor to be less than 100% due to geometric constraints and nozzle diameter[19]. Parts generally have anisotropic material properties, and the same part can exhibit different strengths depending on how it was printed[19]. Layer heights are generally larger than other AM processes and are thus more visible and contribute to a higher surface roughness. Support materials and structures need to be used, otherwise, considerable sagging can occur depending on geometry. Removing these supports is either a manual and labour intensive process, or a process which requires dissolving and rinsing of parts in a chemical bath of some sort. Generally, only one material is used, with one main material and one support material being quite common. Anything more than one material and support is rare, it usually requires specialised print heads or specialised calibration techniques.

References

[1] “ISO/ASTM 52900:2015(en), Additive manufacturing — General principles — Terminology,” International Organization for Standardization (ISO), Geneva, Switzerland, 2015.

[2] Lewis J. A. and Gratson G. M., “Direct writing in three dimensions,” Materials Today, vol. 7, no. 7–8, pp. 32–39, Jul. 2004.

[3] Calvert P. D., Frechette J., and Souvignier C., “Gel mineralization as a Model for Bone Formation,” in MRS Proceedings, San Francisco, California, USA, 1998, vol. 520, pp. 305–401.

[4] Crump S. S., “Apparatus and method for creating three-dimensional objects,” U.S. Patent 5,121,329, 09-Jun-1992.

[5] Jones R., Haufe P., Sells E., Iravani P., Olliver V., Palmer C., and Bowyer A., “RepRap – the replicating rapid prototyper,” Robotica, vol. 29, no. 1, pp. 177–191, Jan. 2011.

[6] Klein J., Stern M., Franchin G., Kayser M., Inamura C., Dave S., Weaver J. C., Houk P., Colombo P., Yang M., and Oxman N., “Additive Manufacturing of Optically Transparent Glass,” 3D Printing and Additive Manufacturing, vol. 2, no. 3, pp. 92–105, Sep. 2015.

[7] Postiglione G., Natale G., Griffini G., Levi M., and Turri S., “Conductive 3D microstructures by direct 3D printing of polymer/carbon nanotube nanocomposites via liquid deposition modeling,” Composites Part A: Applied Science and Manufacturing, vol. 76, pp. 110–114, Sep. 2015.

[8] Morissette S. L., Lewis J. A., Clem P. G., Cesarano III J., and Dimos D. B., “Direct-Write Fabrication of Pb(Nb,Zr,Ti)O 3 Devices: Influence of Paste Rheology on Print Morphology and Component Properties,” Journal of the American Ceramic Society, vol. 84, no. 11, pp. 2462–2468, Nov. 2001.

[9] Cesarano III J., Segalman R., and Calvert P. D., “Robocasting provides moldless fabrication from slurry deposition,” Ceramic Industry, vol. 148, no. 4, Business News Publishing, Troy, Michigan, USA, pp. 94–100, 1998.

[10] Cesarano III J. and Calvert P. D., “Freeforming objects with low-binder slurry,” U.S. Patent 6,027,326, 22-Feb-2000.

[11] Gibson I., Rosen D. W., and Stucker B., Additive Manufacturing Technologies. Boston, MA: Springer US, 2010.

[12] Khoshnevis B., “Automated construction by contour crafting—related robotics and information technologies,” Automation in Construction, vol. 13, no. 1, pp. 5–19, Jan. 2004.

[13] Li P., Mellor S., Griffin J., Waelde C., Hao L., and Everson R., “Intellectual property and 3D printing: a case study on 3D chocolate printing,” Journal of Intellectual Property Law & Practice, vol. 9, no. 4, pp. 322–332, Apr. 2014.

[14] Nickels L., “Crowdfunding metallurgy,” Metal Powder Report, Nov. 2015.

[15] Periard D., Schaal N., Schaal M., Malone E., and Lipson H., “Printing Food,” in Proceedings of the 18th Solid Freeform Fabrication Symposium (SFF), Austin, Texas, USA, 2007, pp. 564–574.

[16] Mironov V., Boland T., Trusk T., Forgacs G., and Markwald R. R., “Organ printing: computer-aided jet-based 3D tissue engineering,” Trends in Biotechnology, vol. 21, no. 4, pp. 157–161, Apr. 2003.

[17] Song X., Pan Y., and Chen Y., “Development of a Low-Cost Parallel Kinematic Machine for Multidirectional Additive Manufacturing,” Journal of Manufacturing Science and Engineering, vol. 137, no. 2, p. 21005, Apr. 2015.

[18] Khoshnevis B., Bodiford M., Burks K., Ethridge E., Tucker D., Kim W., Toutanji H., and Fiske M., “Lunar Contour Crafting – A Novel Technique for ISRU-Based Habitat Development,” in 43rd American Institute of Aeronautics and Astronautics Aerospace Sciences Meeting and Exhibit, Reno, Nevada, USA, 2005, vol. 13(1), no. January, pp. 5–19.

[19] Bagsik A. and Schöoppner V., “Mechanical Properties of Fused Deposition Modeling Parts Manufactured with ULTEM 9085,” in Proceedings of the 69th Annual Technical Conference of the Society of Plastics Engineers 2011 (ANTEC 2011), Boston, Massachusetts, USA, 2011, pp. 1294–1298.