Rapid Prototyping Flashcards
What is rapid prototyping?
Rapid prototyping (RP) is a family of fabrication methods to make engineering prototypes in minimum possible lead times based on a computer-aided design (CAD) model of the item.
What are the two basic categories of rapid prototyping?
(1) material removal processes
(2) material addition processes
Give an overview of material removal processes?
The material removal process involves machining, primarily milling and drilling, using a dedicated Computer Numerical Control (CNC) machine. The starting material is often a solid block of wax, which is very easy to machine, and the part and chips can be melted and re-solidified for reuse when the current prototype is no longer needed.
What are the standard starting materials in material addition processes?
(1) liquid monomers that are cured layer by layer into solid polymers, (2) powders that are aggregated and bonded layer by layer, and (3) solid sheets that are laminated to create the solid part.
What are the three steps of preparing the control instructions for a RP process.
1) Geometric modelling
2) Tessellation of the geometric model
3) Slicing of the model into layers
What is geometric modelling?
This consists of modeling the component on a CAD system to define its enclosed volume. Solid modeling is the preferred technique because it provides a complete and unambiguous mathematical representation of the geometry. For rapid prototyping, the important issue is to distinguish the interior (mass) of the part from its exterior, and solid modeling provides for this distinction
What is tessellation?
In this step, the CAD model is converted into a format that approximates its surfaces by triangles or polygons, with their vertices arranged to distinguish the object’s interior from its exterior. The common tessellation format used in rapid prototyping is STL, which has become the de facto standard input format for nearly all RP systems
What happens in the third step of the computer modelling process?
The model in STL file format is sliced into closely spaced parallel horizontal layers. These layers are subsequently used by the RP system to construct the physical model. By convention, the layers are formed in the x-y plane orientation, and the layering procedure occurs in the z-axis direction. For each layer, a curving path is generated, called the STI file, which is the path that will be followed by the RP system to cure (or otherwise solidify) the layer.
What is Stereolithography(STL)?
A process for fabricating a solid plastic part out of a photosensitive liquid polymer using a directed laser beam to solidify the polymer. Part fabrication is accomplished as a series of layers, in which one layer is added onto the previous layer to gradually build the desired three dimensional geometry.
What are the two basic components of a stereolithography apparatus?
(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 x-y direction.
How does stereolithography work?
Initially the platformed is positioned just below the surface of the liquid polymer, The laser beam follows a path defined by the STI file, the polymer solidifies where the laser strikes. The platform is moved down corresponding to layer thickness and the process repeats multiple times to form a part. Before each new layer is cured, a wiper blade is passed over the viscous liquid resin to ensure that its level is the same throughout the surface. After all of the layers have been formed, the photopolymer is about 95% cured. The piece is therefore “baked” in a fluorescent oven to completely solidify the polymer.
What is typical layer thickness in Stereolithography?
Each layer is 0.076 to 0.50mm thick.
What type of laser is used in stereolithography?
Polymerization occurs upon exposure to ultraviolet light produced by helium-cadmium or argon ion lasers.
What is fused-deposition modelling ( FDM )
Fused-deposition modeling (FDM) is an RP process in which a filament of polymer is extruded onto the existing part surface from a workhead to complete each new layer. The workhead is controlled in the x-y plane during each layer and then moves up by a distance equal to one layer in the z-direction.
