After analyzing the steps involved in rapid prototyping, let us move to an important rapid prototyping process: Fused Deposition Modeling (FDM).
Actually FDM is the second most widely used rapid prototyping technology. In it a plasitc filament is melted down and this melted plastic is sent to a nozzle. This nozzle extrudes the melted plasitc by moving in a plane. Due to simultaneous action of movement and extrusion a thin layer is formed. This melted plastic solidifies immediately. ABS is the most suitable plastic for this process. Sometimes a companion material is introduced to support the layer of melted plastic. This companion material also enhances the temperature bearing capacity and strength of the solidified layer. We can implement this method for the manufacture of small products also. Here is a brief review of procedural steps of FDM:
A CAD file is converted into .stl format. This file is sliced into layers. At the same time, tool path is programmed using SML language. Molten plastic is extruded out of a nozzle which is moving along the path programmed earlier. Another nozzle is used to extrude the companion material. Layers formed according to the inputted sliced model. These layers fused together to build up the 3D model of the design. After that companion material is removed, and the model is ready after removal from the fabrication platform.
Material Used in FDM process: Acrylonitrile Butadiene Styrene (ABS)
The chemical formula of this material is : C8H8 . C4H6 . C3H3N. This material is light and rigid. It is a synthetic monomer. The main advantage of ABS is that it combines the strength and rigidity of acrylonitrile and styrene with toughness of polybutadiene. Here are some advantages of FDM:
This process is speedy, safe, environment friendly, clean, simple, easy and cost effective. Also no material removal is required. On the other hand the disadvantage of this process is: poor strength in vertical direction, slow for big part and accuracy is low.
The major problem to FDM is that the 3-D files we found are not always transferable to sliced model.
FDM begins with a software process which processes an STL file (stereolithography file format), mathematically slicing and orienting the model for the build process. If required, support structures may be generated. The machine may dispense multiple materials to achieve different goals: For example, one may use one material to build up the model and use another as a soluble support structure, or one could use multiple colors of the same type of thermoplastic on the same model.
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.
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. There is typically a worm-drive that pushes the filament into the nozzle at a controlled rate.
The nozzle is heated to melt the material. The thermoplastics are heated past their glass transition temperature and are then deposited by an extrusion head.
The nozzle can be moved in both horizontal and vertical directions by a numerically controlled mechanism. The nozzle follows a tool-path controlled by a computer-aided manufacturing (CAM) software package, and the part is built from the bottom up, one layer at a time. Stepper motors or servo motors are typically employed to move the extrusion head. The mechanism used is often an X-Y-Z rectilinear design, although other mechanical designs such as deltabot have been employed.
Although as a printing technology FDM is very flexible, and it is capable of dealing with small overhangs by the support from lower layers, FDM generally has some restrictions on the slope of the overhang, and cannot produce unsupported stalactites.
Myriad materials are available, such as ABS, PLA, polycarbonate, polyamides, polystyrene, lignin, among many others, with different trade-offs between strength and temperature properties
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