点溶接の温度分布と酸化膜のBreakdownについて(第1報)

FH法と初期温度分布に影響する要因について

抄録

Several noteworthy investigations of temperature distribution in spot welding have been reported; especially, Greenwood calculated temperature distribution during spot welding taking into account the actual geometry involved, but neglecting the effect of contact resistance. Furthermore, he andothers measured experimentally temperature distribution in spot welding by metallographic method, and compared the results (it is possible to find temperature distributions of 730°C, 900°C, 1050°C and 1450°C by the metallographic method) with the results theoretically obtained. From this comparison it was generally concluded that in early stage of spot welding the calculated temperature distribution did not resemble the experimental one, but at a later stage this was reversed. On the other hand, the authors calculated temperature distribution in a one-dimensional model that simulated spot welding, replacing the effect of contact resistance intoa temperature rising part of band shape in initial stage of heating, and found that contribution to nugget formation originated in contact resistance might be almost neglected in thetime of nugget formation, compared with contribution originated in bulk electric resistance, in the case of spot welding thin sheets. Anyway, details of temperature rise in the initial stage of spot welding are unknown, and there is a complete lack of concrete information on how oxide layer between welded sheets begins to breakdown, and how subsequently the temperature in the welded part rises.
The authors developed a new measuring technique (FH-method) for temperature distribution in a two-dimensional model that simulated spot welding geometry at an earlier stage, by combination of the temperature indicator with high speed photography.
This technique makes it possible oflserve in detail, the breakdown of oxide layer between the sheets and the subsequent temperature rise, and therefore can give a valid means for making clear spot welding phenomena. In this report, authors study influences of the electrode force and the electrode shape on temperature patterns and factors which influence unsymmetry of the initial temperature distributions.