National Shipbuilding Research Program. Evaluation of the Usability and Benefits of Twist Wire GMAW and FACW Narrow Gap Welding.

摘要

Butt welding of thick plates with narrow gap fit-ups in lieu of conventional U-groove and V-bevel angles is recognized as one approach to reducing the time and cost of welding in shipbuilding. The use of multiple twisted filler wires as electrodes is found to overcome some of the problems of lack of side wall fusion and slag entrapment associated with single wire arc welding of narrow gap butt welds. To date there are numerous articles written which show a tremendous potential cost savings of various narrow gap welding processes including twist wire welding. These articles very adequately address other important productivity factors such as a comparison of reduced joint geometry, arc time, deposition rate and mechanical properties. No attempt is made in this report to verify or duplicate these issues. The main objectives of this project are: (a) Identify known problems which have caused other narrow gap processes to be nonproductive as well as new problems unique to the twist wire process or the shipbuilding industry; (b) Identify the welding conditions that cause these problems so that the operating range which provides defect free welds can be identified. (c) Once the operating range is known, evaluate whether this range will be adequate to provide cost effective welds in the non-optimum conditions found in the shipbuilding industry. The problems causing narrow gap processes to fail are: (a) Solidification cracking (b) Lack of sidewall fusion (c) Lack of fusion between two weld beads (d) Undercut of the sidewall (e) Equipment problems.