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Low Temperature Fusion Welding
Low Temperature Fusion Welding enables lightweight and ultra-lightweight mirrors destined for space-based imaging systems to retain the same properties and temporal stability of conventional fusion-welded mirrors at one-third the weight. Low temperature fusion uses a combination of heat and pressure to fuse a thin plate of low-expansion glass to one or both sides of a glass core structure that has been lightweighted by waterjet cutting. Developed in the mid 1990s, the process welds the two surfaces at the molecular level, creating a virtually seamless joint. The mirror is then ready for processing and figuring. Fusion vs Bonding Low Temperature Fusion Welding advances a proven bonding process known as FRIT® Bonding. Developed by Corning Inc., FRIT® bonding requires a glass ceramic adhesive to bond the core and faceplate under high temperature. Lightweighted mirror blanks are produced using this process. By contrast, Low Temperature Fusion Welding uses no adhesive to weld the core and faceplate. The process relies on low heat to soften the core structure and plates, and pressure to squeeze and hold the two glass surfaces together until they bond over a prescribed period. Fusion Benefits By eliminating adhesives, fusion bonding produces seamless welds in ULE® glass mirror blanks that are as strong as FRIT-bonded interfaces. The process maintains the mechanical integrity of precisely defined mirror structures, and further reduces the distortions normally associated with conventional fusion processes. |
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