Melt deposition modeling (FDM) or melt filament manufacturing (FFF) is an additive manufacturing process, which belongs to the material extrusion series. In FDM, objects are constructed by selectively depositing melted materials layer by layer in the predetermined path. The material used is thermoplastic polymer, filamentous. FDM is the most widely used 3D printing technology, which represents the world 's largest 3D printer installation foundation, and is usually the first technology people contact. FDM technology has been widely used in the product development and design process of household appliances, communications, electronics, automobiles, medicine, construction, toys and other fields, such as product appearance evaluation, scheme selection, assembly inspection, function test, user-like ordering, pre-die checking design of plastic parts, and small-batch production.
Working principle of FDM printer manufacturing process
1. First, a roll of thermoplastic filament is loaded into a 3D printer. Once the nozzle reaches the required temperature, filaments are fed into the extrusion head and melted in the nozzle.
2. The extrusion head is connected to a three-axis system allowing it to move in X, Y and Z directions. The melted material is extruded into fine lines and deposited layer by layer in a predetermined position, where it is cooled and solidified. Sometimes, the cooling of the material is accelerated by using a cooling fan mounted on the extruder head.
3. To fill a region, multiple passes are required. After the # layer is completed, build the platform to move downward ( or in other machine settings, the extrusion head moves upward ) and deposit a new layer. Repeat this process until the parts are completed.
Features of FDM Printing
1. Warpage
Warpage is one of the most common defects in FDM3D printer. When the extruded material is cooled during solidification, its size will decrease. Since different parts of the printed parts are cooled at different speeds, their sizes will also change at different speeds. Differential cooling will lead to internal stress accumulation, pull the bottom up, and lead to warping. From a technical point of view, the warping platform and cavity can be prevented by monitoring the temperature of the FDM system more closely, and the adhesion between the parts and the building platform can be increased. Can reduce the probability of warping : Large flat area (rectangle) is easier to warp, should be avoided as much as possible. Thin prominent features ( think fork ) are also easy to warp. In this case, warping can be avoided by adding some sacrificial materials to the edge of thin features (e. g., 200 - micron rectangular ) to increase the area of contact platform. Tip angle is easier to warp than round, so adding round angle in your design is a good way. Different materials are more prone to warpage : ABS is usually more sensitive to warpage than PLA or PETG because of its higher glass transition temperature and relatively higher thermal expansion coefficient.
2. Support structure
The supporting structure is crucial for creating a geometric figure with drape in FDM. Melted thermoplastics cannot be deposited in thin air. Therefore, some geometric shapes need support structures. The surface quality printed on the supporting parts is usually lower than the rest of the parts. For this reason, it is suggested that the design of parts can minimize the need for support.
3. Filling and shell thickness
FDM parts are usually not printed entity to reduce printing time and save material. Internal filling has an internal low density structure called filling. Filling and shell thickness have great influence on the strength of parts. For desktop FDM3D printers, the default setting is 25 % filling density and 1 mm shell thickness, which is a good trade-off between fast printing strength and speed.
The advantages and limitations of FDM
Advantages
1. FDM is the most cost-effective way to produce customized thermoplastic parts and prototypes.
2. Due to the high availability of this technology, the delivery time of FDM is very short.
3. A variety of thermoplastic materials can be selected for prototype production and some non-commercial applications.
Limitations
1. Compared with other 3D printing technologies, FDM3D printing technology has the lowest dimensional accuracy and resolution, so it is not suitable for parts with complex details.
2. FDM3D printing parts may have visible layers, so post-processing is needed to obtain smooth surfaces.
3. Layer adhesion mechanism makes FDM components have inherent anisotropy.
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