British Aerospace, Airbus Ltd., Chester, UK manufactures the main wing box assembly for all current Airbus programs. Titanium interference fasteners are used in large numbers throughout these aircraft structures. On the lower wing skin of the A320 alone there are approximately 11,000 of this fastener type. Currently, the majority of these fasteners are manually installed using pneumatic or hydraulic tooling. British Aerospace engineers recognized the significant potential which automation offers to reduce these current labor intensive installation methods. Electroimpact proposed extending Low Voltage Electromagnetic Riveter (LVER) technology to the automatic installation of these interference fasteners as well as rivets. Close liaison between Airbus and Electroimpact engineers resulted in the development of an automated LVER based lockbolt installation system, which is currently undergoing evaluation.
Over the past five years, Low Voltage Electromagnetic Riveting (LVER) has been gaining acceptance in the aerospace industry. LVER heads are impulse devices, which derive their power from the discharge of a bank of capacitors through a pancake coil. (1) LVER units are currently in production installing rivets in five major aircraft programs around the world. Besides rivets, the other primary type of fastener used in aircraft manufacture is the titanium interference bolt. Recent developments in LVER technology, have increased the reliability and quality of a complete LVER bolt installation system. An adjustable shock absorbing hardstop in the bolt driving head allows precise control of the point at which the driver stops at the end of the installation stroke. Other developments include innovative tooling for collar feeding and swaging. A compliant swaging die has been developed which will self-align to the bolt eliminating alignment problems between the opposing heads.
The quality of the LVER bolted joint has been evaluated relative to currently used installation methods. Results from joint preload, ultimate tensile strength and fatigue tests are presented. These results indicate the quality of the LVER installed lockbolt is comparable to methods currently employed in the aerospace industry.