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Friction welding of pipe to plate: estimate of heat input and comparison with MAG welding

Welding is an efficient method for assembly of structures, although it faces the problem of welding deformation due to local heating of welds. Welding deformation is difficult to correct once welding has been completed, and it is therefore important to prevent its occurrence at the outset. Available methods used to prevent welding deformation include design of structures with few welds, application of welding jigs, implementation of deformation-reducing welding procedures, etc. Since welding deformation originates from local heat input to the metal, the adoption of low-heat input welding methods is also an important way of reducing welding deformation. Despite limits being set on the weld shape, friction welding as a solid-phase welding technique ranks as an important low-heat input welding method. Friction welding exploits the heat of friction between parts being welded. During friction welding, the maximum temperature of the weld interface is generally below the melting point of the parts being joined. Though friction welding is a relatively short-term welding process, it is regarded as being able to provide a lower heat input than alternative fusion welding processes, such as arc welding. In arc welding, the heat input per unit length can be readily calculated from the welding current, welding voltage, and welding speed. In friction welding, however, no general-purpose heat input calculation method is available, with only a handful of calculation methods having been previously proposed. 3 In friction welding, the weld line as used in arc welding is not defined, and the heat input per unit length therefore cannot be defined either. For these reasons, it is difficult to make any direct heat input comparison in friction welding and arc welding. When similar materials are being welded, it is accordingly unclear at what specific lower degree of heat input friction welding should be performed as compared with arc welding in order to avoid welding deformation. This study attempts to make a direct heat input comparison with arc welding through the weld line in arc welding being replaced by the pipe circumference in friction welding. This article describes an investigation of pipe to plate welding. Welding was performed by friction welding and MAG welding as a reference arc welding method. The amounts of deformation generated in the plate materials were compared. Through the pipe circumference being adopted as the weld line in arc welding, the heat input per unit length in friction welding is calculated to enable a direct heat input comparison with arc welding to be made.