An automated, remotely controllable apparatus has been developed for resistance welding for hermetic sealing of pyrotechnic devices, as a substitute for special-purpose welding equipment that is no longer commercially available. Hermetic sealing of a pyrotechnic device involves a sequence of closely spaced, precise, spot welds made with low heat to minimize the potential of ignition. For safety, the welding must be performed under remote control. The apparatus includes a rotary table with a chuck, in which is mounted a fixture that holds the pyrotechnic device to be welded. The rotary table is programmed to step through appropriate angular increments (e.g., 360° in 1° increments). After each increment, a switch is closed to actuate a solenoid valve to extend a pneumatic cylinder to drive a welding head toward the pyrotechnic device. A spring-loaded electrode in the welding head is forced into contact with the pyrotechnic device with increasing force until a switch closes at a preset contact force, triggering a pulse of welding current through the welding electrode and workpiece with a return path through the welding fixture. The welding head is then retracted, the rotary table steps through the next increment, and the foregoing process is repeated.
This work was done by Todd J. Hinkel, Carl W. Hohmann, Richard J. Dean, Scott C. Hacker, and Douglas W. Harrington of Johnson Space Center.