Cold expansion of holes (cold working) is a fatigue enhancement technique which is used extensively on metallic aircraft components to enhance the fatigue performance of a structural assembly. This paper reports on a new cold expansion tool, developed by EADS Innovation Works. The tool provides a number of potential benefits over the conventionally employed Split Sleeve or Split Mandrel tools. The specific design of the tool enables the control of variable expansion levels which in turn can compensate for hole tolerances and wear entailed changes in tooling diameter thus ensuring the same level of cold expansion for each hole is maintained. Furthermore, the tool generates a more homogeneous strain distribution around the hole which can be used for an extended exploitation of a materials deformation behaviour. This may lead to an optimised and improved cold working of high strength anisotropic Aluminium alloys (e.g. 7xxx series alloys) using higher levels of applied expansion with a reduced risk of crack formation. There are also additional benefits associated with the tool compared with conventional cold working methods including potential reduced manufacturing costs and also the ability to cold work hybrid stacks in-situ (e.g. aluminium/cfrp) whereby only a portion of the hole requires cold expansion for fatigue life improvement (e.g. cold expand aluminium part of stack only).
The variable expansion process - a new cost efficient method for cold working fastener holes in aluminium aircraft structures
2009
10 Seiten, 8 Bilder
Aufsatz (Konferenz)
Englisch
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