The majority of spot welds in a wide range of sheet metal products e.g. automotive body in white structures and general engineering applications involve the joining of two or more dissimilar sheet thickness. Research to date has concentrated on the welding of two similar thicknesses. Work was therefore carried out to determine the differences in the heat patterns developed in two and three thickness welding and the effect on initial melting and weld nugget growth. Metallographic examination of partially completed welds, temperature profiles determined using thermal imaging techniques and measurement of the dynamic resistance at the electrode-sheet and sheet-sheet interfaces were used for this purpose. In addition, an FE model of the process has been developed to study the effect of contact characteristics and temperature dependent material properties on weld formation. The heat produced from the electrode-sheet and sheet-sheet interfaces as a result of current flow is conducted into the bulk of the material being welded leading to the thermal runaway cycle of increasing temperature/resistivity which aids the development of a weld nugget. This effect is considered essential to the process. Whilst the above accounts for heat generation, the end result in terms of weld nugget geometry can be markedly influenced by the extent of heat abstraction through the water-cooled electrodes and along the sheet thickness. The cooling effect can be the determining factor whether a weld nugget is formed. The results presented in this thesis indicate that cooling effects need to be given greater emphasis when developing a model to account for all the various factors of weld growth than has been given in the past.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:637360 |
| Date | January 2000 |
| Creators | Hutchings, C. L. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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