Improved Crimp-Joining of Aluminum Tubes onto Mandrels with Undulating Surfaces
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Date
2004
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Institut für Umformtechnik - Technische Universität Dortmund
Abstract
Over its history electromagnetic forming (EMF) has probably seen far and away more application in assembling tubes or rings onto (or into) nominally axisymmetric mating elements. The vast majority of these assemblies does not require any significant structural integrity or strength. However, a small fraction of these are designed and fabricated for mechanically-demanding applications. There are two key factors (which seem to be largely independent) that are key in the design and performance of a crimpedelectromagnetic tube joint. First is the state of residual stress that exists after the crimped joint is created. A natural interference fit seems to be a fairly general feature of EMF crimp joints. This interference gives a backlash-free joint that will not fret. The second key issue is the configuration of the joint. The fabrication of designed interlocking geometries is required to create a joint that maximizes mechanical strength while minimizing the electromagnetic energy and forces required to create it. Both of these issues will be considered here. Here we consider crimping onto textured surfaces such as screw threads and knurls. We show experimentally that approaches of this type can give joints that exceed the strength of the tube both in torsion and axial loading. Analysis methods based on coupling impact-indentation and break-before-strip criteria can be used to compare joints made in this way with those based on the more traditional large scale deformation of the tube. One of the advantages of forming onto 'textured' surfaces is that a number of small pulses (possibly generated by small and inexpensive capacitor banks) can be used to create a joint that has the strength of the parent tube, without any heat affected zones or distortion. Again, the natural interference fit developed by impact eliminates the potential for fretting.
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Keywords
aluminum, electro-impulse, joining, strength