The effects of AC and DC on cooling rate, solute distribution and nugget shape after solidification, which are responsible for microstructure of the fusion zone, during resistance spot welding are realistically and extensively investigated. The finite difference method is used to predict transport variables in workpieces and electrodes during heating, melting, cooling and freezing periods. The model accounts for electromagnetic force, heat generations at the electrode-workpiece interface and faying surface between workpieces, and dynamic electrical resistance including bulk resistance and contact resistances at the faying surface and electrode-wokpiece interfaces, which are function of hardness, temperature, electrode force, and surface condition. The computed results show that in contrast to DC, using AC readily produces the nugget in an ellipse shape. Deficit and excess of solute content occur in a thin layer around the boundary and interior of the nugget, respectively.
The effects of dynamic electrical resistance subject to AC (Alternative current) on transport variables, cooling rate, solute distribution and nugget shape after solidification during resistance spot welding are realistically and extensively investigated. The model accounts for electromagnetic force, heat generation and contact resistances at the faying surface and electrode-workpiece interfaces and bulk resistance in workpieces. Contact resistance are comprised of constriction and film resistances, which are functions of hardness, temperature, electrode force and surface condition. The computed results show that the weld nugget readily occurs by increasing constriction resistance and Curie temperature. High Curie temperature enhances convection and solute mixing, and readily melts through the workpiece surface near the electrode edge. Aside from finding the significant effect of Curie temperature on resistance spot welding, this study indicates that any mean (For example, adjusting solute content) to reduce Curie temperature can be a new way to control weld quality.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0719110-125755 |
| Date | 19 July 2010 |
| Creators | Wu, Tzong-Huei |
| Contributors | Lee,Ming-San, Chen,Han-Taw, Hsiao,Fei-Bin, Jang,Jin-Yuh, Chien,Chi-Hui, Hsieh,Shou-Shing, Wei,Peng-Sheng |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0719110-125755 |
| Rights | restricted, Copyright information available at source archive |
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