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Fused deposition modeling, which is often referred to by its initials FDM, is a type of rapid prototyping or rapid manufacturing (RP) technology commonly used within engineering design. The technology was developed by S. Scott Crump in the late 1980s and was commercialized in 1990. The FDM technology is marketed commercially by Stratasys Inc.

Like most other RP processes (such as 3D Printing and stereolithography) FDM works on an "additive" principle by laying down material in layers. A plastic filament or metal wire is unwound from a coil and supplies material to an extrusion nozzle which can turn on and off the flow. The nozzle is heated to melt the material and can be moved in both horizontal and vertical directions by a numerically controlled mechanism, directly controlled by a Computer Aided Design software package. In a similar manner to stereolithography, the model is built up from layers as the plastic hardens immediately after extrusion from the nozzle.

Several materials are available with different trade-offs between strength and temperature. As well as Acrylonitrile butadiene styrene (ABS) polymer, the FDM technology can also be used with polycarbonates, polycaprolactone, polyphenylsulfones and waxes. A "water-soluble" material can be used for making temporary supports while manufacturing is in progress. Marketed under the name WaterWorks™ by Stratasys this soluble support material is actually dissolved in a heated sodium hydroxide solution with the assistance of ultrasonic agitation.

Most available commercial printers using FDM technology utilize positioning systems employing either stepper or servo motors to move the extrusion head.

As of 2004 FDM is the best-selling rapid prototyping technology.^[1]

FDM systems include the FDM Titan, FDM Vantage, FDM Maxum and Prodigy Plus. FDM uses production-grade thermoplastics, such as ABS, ABSi, polyphenylsulfone (PPSF) and polycarbonate (PC), including PC-ABS. Because of the material properties, FDM parts typically withstand functional testing and have high heat resistance. Some companies have sterilized PPSF for medical applications, however material manufacturer Stratasys does not advertise that PPSF is sterilizable.

The FDM process does not yield very high detail, so FDM prototypes are mostly used for functional testing or as a final product, not as display models.

Main article: RepRap Project

Mk II fused deposition extruder (created by Dr. Adrian Bowyer).

FDM was taken into the world of open source hardware with the creation of the Mk 2 FDM^[2] extruder late in 2005 by Dr. Adrian Bowyer, project manager of the RepRap Project, at the University of Bath in the UK.

Mk 2.1 FDM extruder (created by Dr. Adrian Bowyer and modified by Dr. Forrest Higgs).

The Mk 2 represents a major advance in FDM technology in that it can build 3D objects in a room temperature environment. While the Mk 2 was designed to extrude polycaprolactone, a low melting point plastic, it was recently demonstrated that a modified version of the Mk 2 with a different extruder barrel could successfully extrude Acrylonitrile butadiene styrene (ABS), high density polyethylene (HDPE) and homopolypropylene (HPP), all engineering plastics with much higher melting points, at production rates.^[3] This modified Mk 2 is currently being tested on the Clanking Replicator Project's^[4] bootstrap, open source hardware self-replicating 3D printer Tommelise.

RepRap's prototype self-replicating FDM 3D printer, Zaphod, has recently created a full set of the plastic parts needed to make its own FDM extruder from polycapralactone.^[5] This self-replicated FDM extruder is currently being tested.

• The Rapid Prototyping Home Page
• Castle Island Castle Island's worldwide guide to rapid prototyping
• Stratasys
• The RepRap Project: Creating wealth without money...
• The Clanking Replicator Project: Bootstrap your own self-replicating, rapid prototyping machine