Fused deposition modeling, or FDM, is a method of additive manufacturing where layers of materials are fused together in a pattern to create an object. The material is usually melted just past its glass transition temperature, and then extruded in a pattern next to or on top of previous extrusions, creating an object layer by layer. In layman’s terms, a typical FDM 3D printer takes a plastic filament and squeezes it through a hot end, melting it and then depositing it in layers on the print bed. These layers are fused together, building up throughout the print, and eventually they will form the finished part. Process of FDM FDM begins with a software process, developed byStratasys, which processes an STL file (stereolithography file format) in minutes, mathematically slicing and orienting the model for the build process. If required, support structures are automatically generated. The machine dispenses two materials – one for the model and one for a disposable support structure.

The thermoplastics are liquefied and deposited by an extrusion head, which follows a tool-path defined by the CAD file. The materials are deposited in layers as fine as 0.04 mm (0.0016") thick, and the part is built from the bottom up - one layer at a time. 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 the flow on and off. 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 manufacturing (CAM) software package. The model or part is produced by extruding small beads of thermoplastic material to form layers as the material hardens immediately after extrusion from the nozzle. Stepper motors or servo motor are typically employed to move the extrusion head.

Several materials are available with different trade-offs between strength and temperature properties. As well as acrylonitrile butadiene styrene (ABS) polymer, polycarbonates, polycaprolactone, polyphenylsulfones and waxes. A "water-soluble" material can be used for making temporary supports while manufacturing is in progress, this soluble support material is quickly dissolved with specialized mechanical agitation equipment utilizing a precisely heated sodium hydroxide solution.

Advantages

• One of the biggest advantages of FDM 3D printing is scalability. It can be easily scaled to any size. This is because the only constraint in the size of a build area is the movement of each gantry - make the gantry rails longer and the build area can be made larger. Of course, there are a few minor issues, and at a certain point the cost is no longer offset by the benefits, but no other printer design is capable of being scaled as easily with as few issues as FDM.
• One of the more obvious benefits of having an easily-scalable design is the cost-to-size ratio. FDM printers are continually being made bigger and less expensive, due to low part costs and the simple designs involved. Other styles of printer cost many times more per unit area of build volume, simply because they are difficult to scale up and the key components are still quite expensive.
• Another advantage is material flexibility. On any FDM printer, a wide variety of thermoplastic materials and exotic filaments can be printed with relatively few upgrades and modifications, something that cannot be said of other styles where a material must be a resin or fine powder.

Disadvantages

One of the most often referenced downsides of FDM 3D printing is part quality or detail. Because the material must be extruded in layers, and has a certain thickness predefined by the nozzle, high detail prints are hard to achieve and often require lots of post-processing to acquire a professional, finished look. Another downside of the layers in FDM printing is that they create and inherent weak point in the print where each layer is joined, making prints less sturdy and unsuitable for certain applications.