Parting layer

Stereolithography builds plastic parts layer by layer by passing a laser beam (guided by a three-dimensional image) on the surface of a pool of liquid photopolymer. This photopolymer quickly solidifies where the laser beam strikes the surface of the liquid. Once one layer is completely traced, the part is lowered a small distance into the pool, allowing new liquid to cover the completed layer, and then a second layer is traced on top of the first. The layers bond and eventually form a complete, three-dimensional object after many such layers have been formed. A schematic diagram of this process is shown in Figure 6.26. 

A) An edge dislocation in a metal. The shaded atoms indicate Ihe extra part-layer of atoms. (B) The crystal grain under stress. (C) Motion of the dislocation to the right different atoms (shaded) now constitute the dislocation. (D) The dislocation has reached the edge of the grain, forming a step by motion of the dislocation the upper part of the crystal has moved to the left relative to the lower part. 

SILICON CARBIDE FIBERS. There are two forms of SiC fibers, neither of which is available commercially. One consists of a pyrolytic deposit (CVD) of SiC on an electrically conductive, usually carbon, continuous filament. Fiber diameter is about 140 fim. This technology has been used to make filaments with both graded and layered structures, including surface layers of carbon which provide a toughness-enhancing parting layer in composites having a brittle matrix (sdicon nitride, for example). 

The release agent layer is used in ultrathin, printed wiring boards to facilitate removal of the carrier film fi om the very ultra thin metal layer. In order to avoid the problem of picking, which results in incomplete transfer of the very ultra thin metal foil to the substrate under lamination, the release agent layer is designed to peel at the interface between the parting layer and film carrier. The parting layer is... 

FIGURE 3 ZCorp 3D printed layer. Glue is printed inside the blue contours of the part layer. Color figure available online at http /Avww.nap.edu/catalog.php record id=13274. 

Vacuum deposition processes can be used to form freestanding structures by depositing the film on an appropriately shaped mandrel. On the mandrel there is either a parting layer , such as evaporated NaCl, or the surfaces may be non-adhering, such as copper on the oxide on stainless steel. This technique is used to fabricate thin-walled structures and windows. In some cases, the mandrel must be dissolved to release the deposited form. 

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