The Effect of Heat Source Path on Thermal Evolution during Electro-Gas Welding of Thick Steel Plates

Abstract

In recent years, the shipbuilding industry has experienced a growing demand for tighter control and higher strength requirements in thick steel plate welding. Electro-gas welding (EGW) is a high heat input welding method, widely used to improve the welding efficiency of thick plates. Modelling the EGW process of thick steel plates has been challenging due to difficulties in accurately depicting the heat source path movement. An EGW experiment on 30 mm thickness E36 steel plates was conducted in this study. A semi-ellipsoid heat source model was implemented, and its movement was mathematically expressed using linear, sinusoidal, or oscillate-stop paths. The geometry of welding joints, process variables, and steel composition are taken from industrial scale experiments. The resulting thermal evolutions across all heat source-path approaches were verified against experimental observations. Practical industrial recommendations are provided and discussed in terms of the fusion quality for E36 steel plates with a heat input of 157 kJ/cm. It was found that the oscillate-stop heat path predicts thermal profile more accurately than the sinusoidal function and linear heat path for EGW welding of 30 mm thickness and above. The linear heat path approach is recommended for E36 steel plate thickness up to 20 mm, whereas maximum thickness up to 30 mm is appropriate for sinusoidal path, and maximum thickness up to 35 mm is appropriate for oscillate-stop path in EGW welding, assuming constant heat input.

Keywords: electro-gas welding; finite element analysis; heat source movement path; high heat input; thermal evolution.

Figure 1

The electro-gas welding (EGW). (a) The 3D schematic diagram of EGW equipment, (b) The 2D schematic diagram of EGW equipment, (c) Photographs of EGW equipment, (d) Photographs of experimentation.

Figure 2

Geometry of welded steel plate.

Figure 3

(a) Geometry and mesh of EGW model implemented in this study, (b) the transient temperature distribution simulated of steel plate at 520 s, (c) schematic diagram welding joint of pre-welding bevel, (d) welding joint of after-welding showing the fusion line.

Figure 4

Schematic diagram of the activation process of the weld metal.

Figure 5

Schematic diagram of heat source (semi-ellipsoid heat source).

Figure 6

Schematic diagram of heat source path. (a) linear heat source path, (b) sinusoidal path heat source, (c) oscillate-stop heat source path.

Figure 7

Sinusoidal heat source movement vs. time (t) for 30 mm, 35 mm and 40 mm thick steel plates.

Figure 8

Movement path of oscillate-stop for thickness of 30 mm, 35 mm and 40 mm.

Figure 9

Melt pool and fusion line of experiments and simulated welded joints of 30 mm thickness steel plates, (a) experimental weld joint, (b) modelling using linear path heat source, (c) modelling using sinusoidal path heat source, (d) modelling using oscillate-stop path heat source.

Figure 10

Calculated thermal profiles using three different heat source paths at different welding times of 340 s, 349 s and 357 s. (a) linear path (b) sinusoidal path, (c) oscillate-stop path.

Figure 11

Calculated thermal cycles at selected points in heat affect zones (HAZ), (a) position of selected points in HAZ, (b) thermal cycle curves using linear path, (c) thermal cycle curves using sinusoidal path, (d) thermal cycle curves using oscillate-stop path.

Figure 12

The simulated welding molten pool with three heat sauce paths. Linear heat source path model for 20 mm thickness (a), for 25 mm thickness (b); Sinusoidal path for 30 mm thickness (c), for 35 mm thickness (d); Oscillate-stop path for 35 mm thickness (e) and for 40 mm thickness (f).