Vacuum Stress Relieve of Tomahawk Encasements at Solar Atmospheres Inc

Solar Atmospheres, Souderton, PA, specializes in vacuum heat treating and has the capability of processing extraordinary large loads of metal parts or assemblies.  One current example is the stress relieving of Tomahawk missile housings.  Stress relieving has a slow heating and cooling cycle to reduce stresses in fabricated or machined metal.

The processing is done at the company’s Souderton location in a 12′ long, VFS HL 84 furnace.  This spring, Solar will be adding a 24′ long vacuum furnace to process even larger loads at the company’s second location in Hermitage, PA.

The 12′ long furnace chamber working parameters enables 24 of the (48″ OAL x 15″ OD) weldments, with a combined net weight of 11,900 lbs., to be stress relieved in one furnace cycle.  The electron beam welded assemblies are composed of two titanium alloy forgings manufactured by Defense Research Inc.

These housings are utilized in submarine and surface ship launched missiles as replacements for nuclear type housings.  A smaller version of the Tomahawk housing, also stressed relieved, is used in another Navy stand-off weapon, the SLAM ER missile, and manufactured by Boeing Co.

An advantage of vacuum heat treating is precise temperature processing.  Critical to the process is the utilization of part thermocouples to accurately read material temperatures.  This is particularly true in large furnaces where temperature uniformity is a greater challenge. Therefore, to stress relieve the housings three “dummy” blocks are strategically placed in the furnace with imbedded part thermocouples to accurately monitor and control the cycle.

The housing load has a hold time of 4 hours at 1400°F with a total cycle time of 18 hours.  The load is cooled in argon.  The housings, having been processed in hard vacuum (10-5 torr), are bright and clean when removed from the furnace.  All processes are done in conformity with MIL-H-81200B specifications.