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dc.contributor.authorBaringbing, Henry Ako M.W. Tampubolonnb_NO
dc.date.accessioned2014-12-19T12:27:10Z
dc.date.available2014-12-19T12:27:10Z
dc.date.created2011-09-25nb_NO
dc.date.issued2010nb_NO
dc.identifier443431nb_NO
dc.identifier.isbn978-82-471-2299-0nb_NO
dc.identifier.urihttp://hdl.handle.net/11250/241450
dc.description.abstractThe present thesis consists of two parts: Part 1 includes the Rotary Stretch-Bending (RSB) of profiles and Part 2 the mechanical calibration of crash-boxes. The main challenge in the present work is to control the dimensional variability of a bent profile and crash-box tube to meet tight dimensional accuracy during the assembly process. Thus, the research focuses on understanding basic bending theory using analytical solutions, developing an experimental test rig, developing a standard simulation procedure and using the Response Surface Method (RSM) as a statistical tool to determine factors that affect the dimensional accuracy for the RSB and calibration processes. Some companies have developed a calibration process, e.g. hydro-calibration, in order to achieve the necessary level of precision. This approach has led to considerable improvements in accuracy, but a serious drawback remains the high cost involved in the hydro-forming operation. These costs are attributed to both the high level of investment in hydro-forming equipment (presses, tooling, etc.) and the relatively high cycle time, though an attempt has been made to develop a more effective alternative. The new process uses mechanical calibration to reduce the dimensional variability of extruded tubes. For stretch-formed components used in the automotive industry, such as bumper beams, it is of primary importance to control the parameters that affect dimensional accuracy. In the first part, the focus is given to bent profiles produced by RSB. The variations in geometry and mechanical properties induced in extrusion and stretch forming lead to a subsequent dimensional inaccuracy in the final product. Tensile, compression and Lankford parameter tests were performed to determine the material parameters used in a constitutive model suited for Strong Texture Materials (STM 2003). Tensile and compression samples were taken at three different positions along AA7108-W extruded profiles to determine material parameters for the material model. In addition, the geometry was measured and statistically analyzed to study its impact on local cross-sectional distortions (sagging) and springback in the stretch-bending of a bumper beam. These full-scale experiments were combined with analytical and numerical simulations in order to quantify the impact of each basic parameter on product quality. It has been concluded that this methodology provides a means for systematically controlling product quality. For the second part, mechanical calibration of an aluminium tube section was investigated on both an experimental and numerical basis. A prototype die was made to validate the numerical and analytical calculations using extruded profiles in alloys AA6060-T1 and AA6063-T1. The geometry of each tube was carefully measured before and after forming to determine the dimensional accuracy achieved by calibration. The results show that the calibration process is an effective method for improving the dimensional accuracy of crash-box tubes, providing significant improvement in dimensional accuracy compared to that seen in extruded sections. The tests performed reveal that the numerical model predicts the observed behavior with a good accuracy  nb_NO
dc.languageengnb_NO
dc.publisherNorges teknisk-naturvitenskapelige universitet, Fakultet for ingeniørvitenskap og teknologi, Institutt for produktutvikling og materialernb_NO
dc.relation.ispartofseriesDoktoravhandlinger ved NTNU, 1503-8181; 2010:164nb_NO
dc.titleDimensional variability of formed aluminium extrusions : a study of rotary stretch-bending and mechanical calibration processesnb_NO
dc.typeDoctoral thesisnb_NO
dc.contributor.departmentNorges teknisk-naturvitenskapelige universitet, Fakultet for ingeniørvitenskap og teknologi, Institutt for produktutvikling og materialernb_NO
dc.description.degreePhD i produktutvikling og materialernb_NO
dc.description.degreePhD in Engineering Design and Materialsen_GB


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