What is Rapid Prototyping?

Sandwich
Flat multi layer composite design consisting of two high-strength outer layers and a light, thick inner layer; this design provides a high surface moment of inertia and great stiffness.

Saran®
A trademark for a thermoplastic copolymer of vinylidene chloride and usually small amounts of vinyl chloride or acrylonitrile often used for packaging.

Saturated compounds
Organic compounds which do not contain double or triple bonds and thus cannot add on elements or compounds.

Secondary Operations
Manual or machine-based operations which must be carried out on a part fabricated by a rapid prototyping system before use. Secondary operations may include, post curing, support-removal, sanding, machining, etc. secondary process Any one of a large number of processes such as rubber molding. Sprayform, EcoTool, etc., that utilize a rapid prototyping-fabricated part as pattern to create a final tool or part.

Sealing point
Time at which the molding compound inside the sprue has become solid enough to prevent any further flow.

Secondary valence forces
Intermolecular forces with a very limited range of a few nanometers, e.g. hydrogen bonds. self-extinguishing Ability of a burning plastic to extinguish itself without external influence.

Selective Laser Sintering (SLS)
A rapid prototyping technology in which powders are fused laser fused layerwise by a laser. The technology produces accurate parts and models in engineering polymers, metals and polymer-coated sand for casting applications. Speed is similar to stereolithography, but material selection is wider. [Also referred to as "selective laser sintering in rapid prototyping"]

shear strength (interlaminar)
Property defined as the force sufficient to cause a rupture within the area subjected to shear divided by the area subjected to shear.

Shrinkage, Cast Bar
Refers to the linear component of the shrinkage of a material during cure. Involves the casting of material to be tested into a properly released, standard configuration mold exactly 10" long and measuring the shrinkage after full cure. [Also referred to as ASTM D2566]

Silicone
One of the family of polymeric materials in which the recurring chemical group contains silicon and oxygen atoms as links in the main chain. At present these compounds are derived from silica (sand) and methyl chloride. The various forms obtainable are characterized by their resistance to heat and low coefficients of thermal expansion.Silicones are used in the following applications: (a) greases for lubrication, (b) rubber-like sheeting for gaskets, etc. (c) heat-stable fluids and compounds for waterproofing, insulating, etc., (d) thermosetting insulating varnishes and resins for both coating and laminating.

Silk
The soft lustrous fiber obtained as a polymeric filament from the cocoon of the silk worm.

Softening temperature (ST)
Temperature at which amorphous parts of a thermoplast melt.

Solution
Homogeneous mixture of two or more components, for example, gas dissolved in gas or liquid, or a solid in a liquid.

Solvent
Any chemical substance that dissolves another to form a solution.

Sonotrode
Welding tool used in ultrasonic welding to transmit vibrations to the plastics part being welded.

Solid Freeform Fabrication (SFF)
A synonym for rapid prototyping. The term is more precise and wider in scope, and somewhat favored by the academic community. A variant is freeform fabrication (FFF).

Specific Gravity
The density (mass per unit volume) of any material divided by the density of water at a standard temperature, usually 4 deg. C. Since water's density is nearly 1.00 g/cc, density in g/cc and specific gravity are numerically nearly equal. [Also referred to as ASTM D1475]

Specific Heat
The amount of heat required to raise a specified mass by one unit of a specified temperature.

Specific Volume
Specific volume is calculated from the materials' density, and is the cubic inches of volume a pound of the material will occuply. [Also referred to as ASTM D792]

Spiral Development
An iterative process for developing a defined set of capabilities within one increment. This process provides the opportunity for interaction between the user, tester,and developer. In this process, the requirements are refined through experimentation and risk management, there is continuous feedback, and the user is provided the best possible capability within the increment. Each increment may include a number of spirals. Spiral development implements evolutionary acquisition. ~ Taken from a memorandum f understanding written by US Undersecretary of Defense for Acquisition, Technology, and Logistics, E.C. Aldridge, Jr. in 2002.

Sprue Bush
Part of an injection mold that lies against the nozzle of the injection unit and through which the molding compound flows into the mold. stabilizers Chemical additives that make a plastic more resistant to certain influences (e.g., UV radiation, heat, oxidation, weathering).

Semifinished Product
Intermediate product made of plastic (e.g., pipes and sheets), which will be further processed (reshaped) to form a finished product. setting temperature The temperature to which a liquid resin, and adhesive, or products or assemblies involving either must be heated in order to set them. shear strength (1) The ability of a material to withstand shear stress. (2) The stress at which a material fails in shear.

Solid Ground Curing (SGC)
This photopolymer-based technology was provided by Cubital. The company has been dissolved, but the process may still be available from a very few companies. A xerographically-generated mask is used to cure an entire layer of photopolymer at one time. It offers good accuracy coupled with high throughput, but is considered quite expensive.

Solid Model
A CAD model that is defined by the volume of an object, not by its surfaces.

Stairstepping
A type of inaccuracy, as well as a visual appearance artifact It refers to the stepped appearance of the edges of a part, a consequence of additive fabricating a part in layers of necesarily finite thickness.

Starch
Polysaccharide made in plants to store glucose. stress crack External or internal crack in a plastic caused by tensile stresses. The development of such cracks is frequently accelerated by the environment to which the plastic is exposed. The stresses which cause cracking may be present internally or externally or may be combinations of these stresses. The appearance of a network of fine cracks is called crazing.

STEP
A follow-on to the IGES neutral file exchange format. The acronym stands for Standard for the Exchange of Product Model Data.

Stereolithography (SL) (SLA)
A rapid prototyping process that fabricates a part layerwise by hardening a photopolymer with a guided laser beam. Stereolithography is frequently used as a general term for "rapid prototyping," but this is neither precise nor correct.

Stereolithography (SLA)
The stereolithography process uses a CAD model to guide a laser through a polymer solution. The laser hardens the solution within the boundary of the part, one thin layer at a time, to produce a real, three-dimensional mockup. [Also referred to as "stereolithography" "sla prototyping" "stereolithography prototypes" "stereolithography rapid prototyping" "prototype stereolithography" "QuickCast stereolithography"] more...

STEP
Standard for the Exchange of Product Model Data - a neutral format for exchanging CAD data between software programs.

STL
A polygonal model file format used in RP to define the geometry of the part to be made. STL files are created by CAD programs by translating their native or neutral files into the STL format. The STL file defines the coordinates of numerous triangular facets that approximate the shape of an object or part. subtractive machining The fabrication of a part by removing material from a stock shape of material. The stock shape may be a prismatic solid, cylinder, plate, etc. The removal of material may by cutting, turning, electro-discharge or other means. Common machinery such as millers, lathes and drills are subtractive tools. Also known as Standard Tessellation Language.

Stratasys
Stratasys, Inc. is a leading manufacturer of in-office rapid prototyping and manufacturing systems for automotive, aerospace, industrial, recreational, electronic, medical and consumer product OEMs. View resin datasheets: Transparent FullCure720 | VeroBlue FullCure840 | TangoGray FullCure950.

Stress
A basic engineering quantity, stress is defined as force per unit area.

Stress Strain Diagram
The stress-strain diagram is a plot of the stress on y-axis versus the strain on the x-axis. The data is often obtained from a uniaxial tension test although this is not the only test possible. The axes must be labeled with the appropriate units for stress. Strain is dimensionless

Stress Strain Properties
Some plastics have high modulus and tensile strength but low elongation. Most rubbers, have high elongation but low modulus and tensile strength. Polyurethane elastomers have high modulus, high tensile strength and high elongation. This combination imparts toughness and durability to the part.

Support Structure
Many rapid prototyping machines need a means to hold in place unsupported geometries during fabrication, such as the top of a part in the shape of the letter "T." These supports are usually calculated and added to the part by the system's software and may be formed of the same material as the part, or from a different material entirely. Support structures are either mechanically removed or dissolved away in secondary operations before the part can be used.

Styrofoam®
A trademark for a polystyrene foam product having exceptional insulating properties.

Surface Model
A CAD model of an object that is defined by its bounding surfaces.

Synthesis
Formation of chemical compounds from the basic elements or basic chemicals with a simpler structure ("synthesis" is derived from the Greek word for "put together"). synthetic polymer Man-made polymer.