The Manufacturing Process
Air bag production involves three different separate assemblies that combine to form the finished end product, the air bag module. The propellant must be manufactured, the inflator components must be assembled, and the air bag must be cut and sewn. Some manufacturers buy already-made components, such as air bags or initiators, and then just assemble the complete air bag module. The following description of the manufacturing process is for driver-side air bag module assembly. Passenger-side air bag module assemblies are produced slightly differently.
- The propellant consists of sodium azide mixed together with an oxidizer, a substance that helps the sodium azide to burn when ignited. The sodium azide is received from outside vendors and inspected to make sure it conforms to requirements. After inspection it is placed in a safe storage place until needed. At the same time, the oxidizer is received from outside vendors, inspected, and stored. Different manufacturers use different oxidizers.
- From storage, the sodium azide and the oxidizer are then carefully blended under sophisticated computerized process control. Because of the possibility of explosions, the powder processing takes place in isolated bunkers. In the event safety sensors detect a spark, high speed deluge systems will douse whole rooms with water. Production occurs in several redundant smaller facilities so that if an accident does occur, production will not be shut down, only decreased.
- After blending, the propellant mixture is sent to storage. Presses are then used to compress the propellant mixture into disk or pellet form.
- The inflator components, such as the metal canister, the filter assembly—stainless steel wire mesh with ceramic material inside—and initiator (or igniter) are received from outside vendors and inspected. The components are then assembled on a highly automated production line.
- The inflator sub-assembly is combined with the propellant and an initiator to form the inflator assembly. Laser welding (using CO2 gas) is used to join stainless steel inflator sub-assemblies, while friction inertial welding is used to join aluminum inflator sub-assemblies. Laser welding entails using laser beams to weld the assemblies together, while friction inertial welding involves rubbing two metals together until the surfaces become hot enough to join together.
- The inflator assembly is then tested and sent to storage until needed.
- The woven nylon air bag fabric is received from outside vendors and inspected for any material defects. The air bag fabric is then die cut to the proper shapes and sewn, internally and externally, to properly join the two sides. After the air bag is sewn, it is inflated and checked for any seam imperfections.
Final assembly of air bag module
- The air bag assembly is then mounted to the tested inflator assembly. Next, the air bag is folded, and the breakaway plastic horn pad cover is installed. Finally, the completed module assembly is inspected and tested.
- The module assemblies are packaged in boxes for shipment and then sent to customers.
The future for air bags looks extremely promising because there are many different applications possible, ranging from aircraft seating to motorcycle helmets. The air bags of the future will be more economical to produce and lighter in weight; will involve smaller, more integrated systems; and will use improved sensors.