Engineering Prototyping

Engineering prototyping is a group of manufacture techniques to make designing models in least conceivable lead times based on a computer aided design (CAD) model of the thing. The customary strategy for manufacturing a model part is machining, which can require significant lead times up to several weeks, sometimes longer, depending on part complexity, difficulty in ordering materials, and scheduling production equipment. A number of rapid prototyping techniques are now available that allow a part to be produced in hours or days rather than weeks, given that a computer model of the part has been generated on a CAD system. 

A virtual prototype, which is a computer model of the part design on a CAD system, may not be adequate for the designer to visualize the part. It certainly is not sufficient to conduct real physical tests on the part, although it is possible to perform simulated tests by finite element analysis or other methods. Using one of the available technologies, a solid physical part can be created in a relatively short time (hours if the company possesses the Prototyping equipment or days if the part fabrication must be contracted to an outside company specializing in Prototyping). The designer will thus visually examine and physically feel the half and start to perform tests and experiments to assess its deserves and short coming.

Engineering prototyping methods:
-Liquid based prototyping methods.
-Solid based prototyping methods.
-Powder based prototyping methods.

1-Liquid based prototyping 

-Stereolithography

Stereolithography (SL/SLA) is the oldest prototyping process. There are different types of liquid photopolymers used as material which hardens while exposed to the UV light of specific wavelength and intensity. Solidification of layers occurs under the influence of laser beams. Produced part is placed on the platform. After one layer becomes solid under the influence of laser beams, the platform moves down and the solidification of the next layer starts. As all layers become solid, the remaining liquid material is drained, the product is cleaned, and if necessary, additionally processed for obtaining adequate surface quality.The stereolithography apparatus consists of (1) a platform that can be moved vertically inside a vessel containing the photosensitive polymer, and (2) a laser whose beam can be controlled in the - direction. At the start of the process, the platform is positioned vertically near the surface of the liquid photopolymer, and a laser beam is directed through a curing path that comprises an area corresponding to the base (bottom layer) of the part.

 Solid Ground Curing
Like stereolithography, solid ground curing (SGC) works by curing a photosensitive polymer layer by layer to create a solid model based on CAD geometric data. Instead of using a scanning laser beam to accomplish the curing of a given layer, the entire layer is exposed to an ultraviolet light source through a mask that is positioned above the surface of the liquid polymer. The hardening process takes 2 to 3 seconds for each layer. SGC systems are sold under the name Soldier system.
2- Solid based prototyping methods
Laminated-Object Manufacturing
Laminated-object manufacturing produces a solid physical model by stacking layers of sheet stock that are each cut to an outline corresponding to the cross-sectional shape of a CAD model that has been sliced into layers. The layers are bonded one on top of the previous one before cutting. After cutting, the excess material in the layer remains in place to support the part during building. Starting material in LOM can be virtually any material in sheet stock form, such as paper, plastic, cellulose,metals, or fiber-reinforced materials.

Fused-Deposition Modeling
Fused-deposition modeling (FDM) is an prototyping method process within which a filament of wax or chemical compound is extruded onto the prevailing half surface from a workhead to complete every new layer. The workhead is controlled within the x-y plane throughout every layer and so moves up by a distance up to one layer within the z direction. The starting material is a solid filament with fed from a spool into the workhead that heats the material to about 0.5 before extruding it onto the part surface. The extrudate is solidified and cold welded to the cooler part surface in about 0.1 second. The part is fabricated from the base up, using a layer-by-layer procedure similar to other Prototypes methods.

3- Powder based prototyping methods

Three-dimensional printing (3DP) Like all processes for prototyping, this one also starts with the CAD model, which is divided into layers by a special algorithm. Various powder materials are used for making models by this method. Precise roller mechanism is used for application of powder materials in thin layers. After the layer of powder material is applied to the surface, the ink-jet head applies the binder, with the aim to selectively connect the powder particles. The platform is then lowered, and new layer of powder and binder is applied. Application of layers is repeated until the model is completed, which is followed by removal of material residues and surface finishing. In order to achieve adequate mechanical properties, the model can be infiltrated by other material (low viscosity epoxy and cyanoacrylate resins, as determined by slicing the CAD geometric model into layers. The binder holds the powders along to make the solid half, whereas the unbonded powders stay loose to be removed later. While the loose powders are in place during the build process, they provide support for overhanging and fragile features of the part. To additional strengthen the part, a sintering step is applied to bond the individual powders.



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