Richardson, R. and Stewart, T., "Composites Assembly and Fastening Automating Grip Length Measurements to Generate a True As-Built Kit List," SAE Int. J. Aerosp. 5(1):97-100, 2012, doi:10.4271/2012-01-1889.
With composite skins and structures, the exact thickness of a part stack is indeterminate, and thus the fastener grip length for any particular hole cannot be known with certainty, from engineering data alone. A common practice on the assembly line is to provide “overs and unders” - that is, one or two grips lengths above and below the expected fastener length. Unless all of the fasteners are kept line-side which slows production operations, pre-kitted fasteners will require a tremendous amount of return-to-stock. Test fitting every fastener before sealant application and/or delivering 200-400% more fasteners than are needed for the task are not a good value for production.This paper will discuss the development processes and production applications of making fast, accurate stack thickness measurements that are correlated to each particular hole, creating the as-built kit list, and then delivering the kitted fasteners to the production line in the order that they will be installed. With every fastener location known to have the exact grip length required for its as-built condition, production line workers can stay strictly focused on value-added work. The ability to grip up to 40 fastener locations per minute allows the technician to move at an increased rate during the measurement process. By simplifying the installation and semi-automating the measurement, the assembly process can see immediate improvements.