Abstract
A novel soft variable polarity plasma arc has been proposed to solve the problems in horizontal welding of aluminium alloys (in 2G position). It is defined as an arc with reduced arc pressure while retaining the ability to maintain a stable keyhole. In this paper, its characteristics were studied and its influence on the stability of keyhole was investigated. The results indicate that it has been changed in the energy and pressure distribution compared with ordinary variable polarity plasma arc. It is beneficial for the stability of keyhole especially for the stability of keyhole shrinking process. The keyhole can be established easily. It can also improve the wetting and spreading of molten metal in weld pool. The reason for a stable keyhole is that the soft variable polarity plasma can provide a suitable heat input and a suitable arc pressure.
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