An alternating current (ac) pulsed metal inert gas (MIG) welding power source has been developed for welding thin sheets of aluminium alloys and the process features are investigated. Advantages such as high wire melting coefficient, low heat input, shallow penetration, and increased reinforcement height are obtained at high values of electrode negative ratio (ratio of electrode negative current integration to electrode negative plus electrode positive current integration over one pulse cycle). These features successfully counteract the problem of burnthrough in welding of thin sheet joints and greatly improve the bridging ability for wide gap joints. Thin sheet joints can be welded at high speed and with low distortion. By integrating the present welding power source with a welding robot, welding process and current waveform parameters can be defined by key operations in the teach pendant. It is possible to switch between welding processes such as ac pulsed MIG, direct current (dc) pulsed MIG, low frequency modulated ac pulsed MIG, and low frequency modulated dc pulsed MIG during a continuous welding run, so that the optimum welding process can always be selected.

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The binding isotherm of sodium dodecyl sulfate to amylose was potentiometrically investigated by using amyloses of various degrees of polymerization from 32 to 1100. From the Scatchard plots, the binding was found to be cooperative for the amyloses of DP≥76 and Langmuir type for those of DP≤57. By analogous experiments using a series of sodium alkyl sulfates, it was clarified that (1) eight carbon atoms of surfactant are required for the complexation and (2) more than twelve carbon atoms of surfactant are required for the cooperative binding. Thus, the amylose has an interrupted helical structure in solution and the cooperativity arises from the hydrophobic interaction between the surfactants included partly in the helic of amylose.

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