Automated Apparatus for Welding to Seal Pyrotechnic Devices

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.