SBIR-STTR Award

The split-sleeve process is a standard life enhancement procedure. Advances in material science are producing new materials (e.g., 7050 and 2297) that are replacing legacy alloys (2024 and 7075). However, coldwork technology has not kept up with material advances. Coldworking the new aluminum alloys, particularly in the short-transverse grain orientation, with the split-sleeve process creates cracks at holes. The split-mandrel process is a simpler, faster, more cost effective coldworking process. Process tooling and life-enhancement results are similar to those of the split-sleeve process. More important, the process is currently being used to successfully coldwork 7050 and similar alloys, in the short-transverse orientation. Similar behavior to split-sleeve coldworking between the two materials indicates that split-mandrel coldworking should effectively coldwork 2297 and other high strength aluminum alloys. West Coast Industries proposes the first comprehensive process characterization of the split-mandrel process. During Phase I, Air Force and industry expectations will be determined, process parameters will be developed, a large quantity of holes will be coldworked and examined for the presence of holes, and modifications for computer models will be developed to differentiate between the two coldworking processes.

Keywords:
Life Enhancement, Coldwork Technology, Coldworking, Split-Sleeve, Split-Mandrel, Shear Cracking, Residual Stress, Crack Growth

New high-strength materials such as 7050 and 2297 aluminum are providing considerable life enhancement while production innovations allow components to be produced from single billets. This results in fastener holes that are normal to the short-transverse grain orientation, leading to problems with established coldworking procedures. Coldworking fastener holes is a common fatigue life enhancement process in the aerospace industry. However the established split-sleeve coldwork process produces cracks in new high-strength aluminum applications, and therefore cannot be used with the new materials. The Air Force is currently searching for a new coldworking process; West Coast Industries proposed to advance the split mandrel coldwork system. The process is similar to the legacy split sleeve system, but it can coldwork newer aluminum alloys without causing cracks. Phase I findings proved the feasibility of the split mandrel process for this application by successfully coldworking approximately 1,000 holes without any identified cracks. Using Phase I results as a foundation, Phase II efforts will optimize the process specification and create new and redesigned process tooling. At the end of a successful Phase II project, WCI will present the Air Force with a complete and thorough coldwork procedure.

Keywords:
Coldwork, Cold Expansion, Split Sleeve, Split Mand