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Recent developments in replica optics techniques originally conceived by U. S. Army Engineer Research and Development Laboratories are of significance to the electroforming industry. Basically the replica process is a simple and low-cost method to produce high-quality replicas of complex surfaces. The completed mirror consists of a protected aluminum reflecting surface bonded to an epoxy backing. However, many military and commercial applications have requirements which eliminate the use of plastic as a backing material. The foremost limiting factor is high-temperature operation which affects the dimensional stability of epoxy reflectors. In these cases, a more durable material such as copper or nickel is a necessity for the backing. That portion of the replica process of interest to electroforming is the step allowing fabrication of many inexpensive epoxy molds from one glass master. Optically precise epoxy molds can be fabricated for various configurations as long as the maximum included angle by line in the surface is no greater than 180 deg. Thus, such surfaces as parabolas, ellipses, prisms, or complex combinations of these can be readily replicated. These recent developments with epoxy molds permit quantity fabrication of high-quality metallic reflectors. The low cost of the epoxy molds allows purchase of additional molds, thereby permitting increased production rates. In addition, the lightweight epoxy offers ease of handling and less danger of breakage during handling or separation. Separation of the metallic reflector from the mold is normally achieved by thermal expansion. With glass, this is a critical operation, whereas with epoxy it is routine.
Schwenk, M. F.
Varo, Inc., Garland, Tex.