FDM 3D Printing
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FDM 3D Printing
Fused deposition modeling, or FDM 3D Printing, 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.
FDM is the same as fused filament fabrication (FFF), but the term “fused deposition modeling” and the abbreviated “FDM” were trademarked by Stratasys in 1991, creating the need for a second name. FDM is also known as fused filament fabrication (FFF), is an additive manufacturing process that falls within the category of material extrusion. In FDM, an object is built by selectively depositing melted material in a predetermined path, layer by layer. The materials used are thermoplastic polymers, which come in a filament form.
Fused Deposition Modeling
Many types of materials can be used with this techniques, including the most common thermoplastics, chocolate, pastes, and even “exotic” materials like metal- or wood-infused thermoplastic.
Widely accepted as the simplest way to achieve 3D printing, Fused deposition modeling is cheap and fairly efficient. FDM 3D printers dominate the 3D printing market, almost drowning out more expensive methods.
Variations in Design and Capability
The common theme with all of these variations is that a substance is being extruded through a nozzle onto a build plate and/or fusing through heat or material adhesion to a previous layer in specific patterns to create a shape, which is the basis of an FDM 3D printer.
Other variations in FDM 3D printing include the systems of movement for all 3 axes on a printer. The two main variations are Cartesian 3D printers — like the RepRap/Prusa i3 or the CoreXY designs — and delta 3D printers. Each has advantages over the others, but they all use the same general method of printing. For a comparison of designs, see this article.
- Warping is one of the most common defects in FDM. When extruded material cools during solidification, its dimensions decrease. Since different sections of the print cool at different rates, their dimensions also change at different speeds.
- Differential cooling causes the buildup of internal stresses that pull the underlying layer upward, causing it to warp , as shown in figure.
- Warping can be prevented through closer temperature monitoring of the FDM system (namely, of build platform and chamber) and increasing adhesion between the part and the build platform.
- Secure adhesion between the deposited layers is critical for an FDM part. When the molten thermoplastic is extruded through the nozzle, it is pressed against the previously printed layer. High temperature and pressure cause this layer to remelt and enable the new layer to bond with the previously printed part.
- Bond strength between the different layers is always lower than the base strength of the material. This means that FDM parts are inherently anisotropic: their strength in the z-axis is always smaller than their strength in the XY plane. For this reason, it is important to consider part orientation when designing parts for FDM 3D Printing .
- Because molten thermoplastic cannot be deposited on thin air, some geometries require support structures. Read this detailed article explaining the use of support structure.
- Support material might be difficult to remove, so it is often easier to design parts to minimize the need for supports.
- Support is usually printed in the same material as the part. Support materials that dissolve in liquid also exist, but they are used mainly in high-end desktop or industrial FDM 3D printers . Using dissolvable supports increases the overall cost of a print.
Infill and shell thickness
- To reduce print time and save on material, FDM parts are usually not printed solid. Instead, the outer perimeter—called the shell—is traced using several passes, and the interior—called the infill—is filled with an internal low-density structure.
- Infill and shell thickness greatly affect the part’s strength. For desktop FDM printers, the default setting is 20% infill density and 1mm in shell thickness, which provides a nice compromise of strength and speed for quick prints.
Advantages and Disadvantages
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. Check out this article for a list of the best cheap FDM machines.
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.
- 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.