FDM is Fused Deposition Modeling. This 3D printing technology was successfully developed by American scholar Scott Crump in 1988. In general, FDM uses high temperature to melt the material into a liquid state, extrude it through the print head and then solidify it, and finally arrange it in a three-dimensional space to form a three-dimensional object.
The technical principle of FDM rapid prototyping technology:
The FDM mechanical system mainly includes five parts: nozzle, wire feeding mechanism, motion mechanism, heating studio and workbench (as shown in the figure below). The materials used in the fused deposition process are divided into two parts: one is the molding material and the other is the support material.
The low melting point filamentary material is melted into liquid through the extrusion head of the heater, and the molten thermoplastic material is extruded through the nozzle. The extrusion head accurately moves along the contour of each section of the part to extrude semi-fluid thermoplastic The material is deposited and solidified into an accurate thin layer of the actual part, which covers the built part and solidifies rapidly within 1/10s. Each time a layer of molding is completed, the worktable is lowered by one layer, and the sprinkler heads to the next layer of cross-section. The scanning spinneret is repeatedly deposited layer by layer until the last layer, which is stacked layer by layer from bottom to top to form a solid model or part.
In FDM forming, each layer is stacked on the upper layer, and the upper layer plays the role of positioning and supporting the current layer. As the height increases, the area and shape of the layer contour will change. When the shape changes greatly, the upper layer contour cannot provide sufficient positioning and support for the current layer, which requires the design of some auxiliary structures – ” Support” to ensure the smooth realization of the forming process. The supports can be built with the same material. Now, two nozzles are generally used for independent heating. One is used to spray the model material to make parts, and the other is used to spray the support material for support. The characteristics of the two materials are different, and it is quite easy to remove the support after production. . The wire feeding mechanism conveys the raw materials for the nozzle, and the wire feeding is required to be stable and reliable. The wire feeding mechanism and the nozzle adopt a combination of push and pull to ensure stable and reliable wire feeding and avoid wire breakage or accumulation.
The advantages of FDM rapid prototyping process:
- (1) Low cost. The fused deposition modeling technology replaces the laser with a liquefier, and the equipment cost is low; in addition, the utilization efficiency of raw materials is high and there is no pollution of poisonous gas or chemical substances, which greatly reduces the molding cost.
- (2) The use of water-soluble support materials makes it simple and easy to remove the stent structure, and can quickly build complex inner cavities, hollow parts and assembled structural parts that are formed in one time.
- (3) The raw materials are provided in the form of reel wire, which is easy to handle and quick to replace.
- (4) A variety of materials can be selected, such as engineering plastics ABS, PC, PPS and medical ABS of various colors.
- (5) There is no chemical change in the raw materials during the molding process, and the warping deformation of the parts is small.
- (6) Prototype parts formed with wax can be directly used for investment casting.
- (7) The FDM 3d printing? system is non-toxic and does not produce odor, dust, noise and other pollution. There is no need to spend money to establish and maintain a dedicated space, which is suitable for use in an office design environment.
- (8) The material has excellent strength and toughness, and can be assembled for functional testing.
Disadvantages of FDM rapid prototyping process:
- (1) There are obvious stripes on the surface of the prototype.
- (2) The strength in the direction perpendicular to the section is small.
- (3) Need to design and manufacture supporting structures.
- (4) The molding speed is relatively slow, which is not suitable for building large parts.
- (5) Raw materials are expensive.
- (6) The nozzle is prone to blockage, which is inconvenient to maintain.
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