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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 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, 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.


[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.

Additive Manufacturing 101-2: What is directed energy deposition?

(Image: 3D Hubs)

Directed Energy Deposition (Image: 3D Hubs)

  Mechanical Design Engineer and Additive Manufacturing Ph.D. student

This is the third 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, and then a design philosophy for additive manufacturing.

Directed Energy Deposition

ISO/ASTM definition: “directed energy deposition, —an additive manufacturing process in which focused thermal energy is used to fuse materials by melting as they are being deposited. “Focused thermal energy” means that an energy source (e.g., laser, electron beam, or plasma arc) is focused to melt the materials being deposited.”[1]

Directed Energy Deposition or DED can also be known as (in alphabetical order):

➢   3D Laser Cladding[2]

➢   Cold Gas Dynamic Spray[3]*

➢   Cold Spray[4]*

➢   Direct Laser Deposition or DLD[5]

➢   Direct Laser Fabrication[5]

➢   Direct Metal Deposition or DMD® (DM3D Technology, LLC)[5]

➢   Directed Light Fabrication or DLF[5]

➢   Electron Beam Additive Manufacturing or EBAM ™ (Sciaky, Inc.)

➢   Electron Beam Freeform Fabrication or EBF3[6]

➢   Focused Ion Beam Direct Writing or FIBDW[7]

➢   Metal Powder Application or MPA (Hermle Maschinenbau GmbH)

➢   Laser Chemical Vapor Deposition or LCVD[8]

➢   Laser Consolidation or LC [9]

➢   Laser Deposition Welding[10]

➢   Laser Engineered Net Shaping or LENS® (Sandia National Labs)[5], [11]

➢   Laser Metal/Melting Deposition or LMD[5]

➢   Laser Powder Forming[12]

➢   Laser Rapid Forming[5]

➢   Powder Fusion Welding[13]

➢   Shape Welding[14]

➢   Shape Deposition Manufacturing or SDM[15]

➢   Three-Dimensional Welding[16]

➢   Wire Arc Additive Manufacturing or WAAM[17]

*An additive manufacturing process in which kinetic energy is used to fuse materials by plastic deformation as they are being deposited. “Kinetic energy” means the energy contained by the material that is being deposited at high velocity and is released at the time the material contacts a solid surface.

From 1994-1997 in New Mexico USA, Sandia National Laboratories developed a new AM technology which they called LENS. It differed quite a bit from all other AM technologies at the time and spawned a number of similar processes like DMD, which was commercialized in 2002 by POM Group based in Michigan USA. These other processes use many different names in an attempt to differentiate themselves; DLD, LC, LMD, DLF and more, but can be understood the same as LENS. LCVD is a completely different process from LENS and has its origins in the 1980s, but it wasn’t used to build actual 3D parts until the early 1990s. Three-dimensional welding has its roots in 1960s Germany where parts were built up using welders, but it wasn’t specifically used in AM until in the 1990s[14]. In 2002, engineers at NASA developed a system that uses electron beams and solid wire feedstock to create parts that could potentially be made in space without gravity called EBF3. Since 2013 researchers have been investigating the use of cold spray techniques in AM as an alternative to thermally based fusion methods.


Figure 1: Example of a directed energy deposition system’s basic components, LENS (top) and EBF3 (below)[18]

Directed energy deposition processes look very different between each method, but the premise is the same in each case. First, there is a focused area of intense energy, usually a thermal energy source like a laser, electron beam, or TIG welding torch. A feedstock material is introduced into that intense energy area causing it to bond to the surrounding material. This feedstock can be introduced either through blowing powder into that area like with the LENS or cold spray process, by pushing a solid wire into that area like with EBF3 and WAAM, or by introducing a special gas into the build chamber like with LCVD or FIBDW. The bonding mechanism varies in each process as well. In LENS and related methods, the powder enters into a melted pool of material and initially sticks to it and then melts to join the melt pool which will then cool and solidify. With EBF3 and WAAM, the wire melts and binds to the previous layers and then cools and solidifies. With LCVD and FIBDW, either a laser or an ion beam heats a spot on the build surface to a high enough temperature to thermally decompose a halide gas compound. This special gas then deposits half of itself onto the build surface, while the other half combines with a reducing chemical in the air like hydrogen to form a secondary gas compound. With the cold spray process, material is deposited at very high velocities onto the build surface and then plastically deforms and bonds onto the part.

Several different processes fall into this category, so advantages depend on the process. With the powder blowing method, powders can be changed or mixed mid-build thus creating multiple materials in a build, even creating a gradient between two different materials in the same build. This can also occur in LCVD or FIBDW by evacuating the build chamber from one gas, and putting in a different one thus making multiple materials possible. LENS type processes are able to aid in the repair of damaged parts that normally could not have been repaired using traditional methods. It can roughly add material to the damaged areas which are then cleaned up and machined to tolerance afterwards. Some of these processes like EBF3 and WAAM can also be used to develop near net shape parts that can then be machined to final tolerance without the traditional waste associated with subtractive manufacturing from a solid block. Some of these processes can also be used in space without the need for gravity like EBF3 and cold spray.

Again disadvantages range between processes. All of these processes require material to be deposited one spot at a time, and cannot do entire layers all at one time; tool paths are needed to complete each layer. Consequently build speeds are limited and somewhat slow. LCVD is especially slow due to the decomposition process and limited material deposited by it. These processes do not lend themselves to create support structures, so certain geometries with overhangs may not be created. Resolutions are generally very low and have a rough surface finish that may need post-processing like machining to get tight tolerances.


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

[2]    Murphy M. L., Steen W. M., and Lee C., “The Rapid Manufacture of Metallic Components by Laser Surface Cladding,” in Proceedings of the Laser Assisted Net Shape Engineering Conference (LANE’94), Erlangen, Germany, 1994, vol. 2, pp. 803–814.

[3]    Sova A., Grigoriev S., Okunkova A., and Smurov I., “Potential of cold gas dynamic spray as additive manufacturing technology,” The International Journal of Advanced Manufacturing Technology, vol. 69, no. 9–12, pp. 2269–2278, Dec. 2013.

[4]    Lupoi R. and O’Neill W., “Deposition of metallic coatings on polymer surfaces using cold spray,” Surface and Coatings Technology, vol. 205, no. 7, pp. 2167–2173, Dec. 2010.

[5]    Gu D. D., Meiners W., Wissenbach K., and Poprawe R., “Laser additive manufacturing of metallic components: materials, processes and mechanisms,” International Materials Reviews, vol. 57, no. 3, pp. 133–164, May 2012.

[6]    Taminger K. M. and Hafley R. A., “Electron Beam Freeform Fabrication for Cost Effective Near-Net Shape Manufacturing,” in Specialists’ Meeting on Cost Effective Manufacture via Net Shape Processing (NATO/RTO AVT-139), Amsterdam, The Netherlands, 2006, p. 16:1-10.

[7]    Matsui S., Kaito T., Fujita J., Komuro M., Kanda K., and Haruyama Y., “Three-dimensional nanostructure fabrication by focused-ion-beam chemical vapor deposition,” Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, vol. 18, pp. 3181–3184, 2000.

[8]    Williams K., Maxwell J., Larsson K., and Boman M., “Freeform fabrication of functional microsolenoids, electromagnets and helical springs using high-pressure laser chemical vapor deposition,” in Proceedings of the 12th IEEE International Conference on Micro Electro Mechanical Systems (MEMS ’99), Orlando, Florida, USA, 1999, pp. 232–237.

[9]    Xue L. and Islam M. U., “Laser Consolidation – A Novel One-Step Manufacturing Process for Making Net-Shape Functional Components,” in Specialists’ Meeting on Cost Effective Manufacture via Net Shape Processing (NATO/RTO AVT-139), Amsterdam, The Netherlands, 2006, p. 15:1-14.

[10]  Kaierle S., Barroi A., Noelke C., Hermsdorf J., Overmeyer L., and Haferkamp H., “Review on Laser Deposition Welding: From Micro to Macro,” Physics Procedia, vol. 39, pp. 336–345, 2012.

[11]  Griffith M. L., Keicher D. M., Atwood C. L., Romero J. A., Smugeresky J. E., Harwell L. D., and Greene D. L., “Free Form Fabrication of Metallic Components Using Laser Engineered Net Shaping (LENS),” in Proceedings of the 7th Solid Freeform Fabrication Symposium (SFF), Austin, Texas, USA, 1996, pp. 125–132.

[12]  Liu Q., Leu M. C., and Schmitt S. M., “Rapid prototyping in dentistry: technology and application,” The International Journal of Advanced Manufacturing Technology, vol. 29, no. 3–4, pp. 317–335, Jun. 2006.

[13]  Bohrer M., Basalka H., Birner W., Emiljanow K., Goede M., and Czerner S., “Turbine blade repair with laser powder fusion welding and shape recognition,” in Proceedings of the 2002 International Conference on Metal Powder Deposition for Rapid Manufacturing, San Antonio, Texas, USA, 2002, pp. 142–150.

[14]  Dickens P. M., Pridham M. S., Cobb R. C., Gibson I., and Dixon G., “Rapid Prototyping Using 3D Welding,” in Proceedings of the 3rd Solid Freeform Fabrication Symposium (SFF), Austin, Texas, USA, 1992, pp. 280–290.

[15]  Fessler J., Nickel A., Link G., Prinz F., and Fussell P., “Functional gradient metallic prototypes through shape deposition manufacturing,” in Proceedings of the 8th Solid Freeform Fabrication Symposium (SFF), Austin, Texas, USA, 1997, pp. 521–528.

[16]  Spencer J. D., Dickens P. M., and Wykes C. M., “Rapid prototyping of metal parts by three-dimensional welding,” Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, vol. 212, no. 3, pp. 175–182, Jan. 1998.

[17]  Wang F., Williams S., Colegrove P., and Antonysamy A. a., “Microstructure and Mechanical Properties of Wire and Arc Additive Manufactured Ti-6Al-4V,” Metallurgical and Materials Transactions A, vol. 44, no. 2, pp. 968–977, Feb. 2013.

[18]  Frazier W. E., “Metal Additive Manufacturing: A Review,” Journal of Materials Engineering and Performance, vol. 23, no. 6, pp. 1917–1928, Jun. 2014.