Multi-wire submerged arc welding: a study of secondary process parameters

Abstract

Abstract:The goal of this thesis is to investigate the effect of secondary process parameters on the geometry of the weld bead in multi-wire submerged arc welding. Bead-on-plate welding experiments will be conducted using 3, 4 and 5 wires. The parameters being varied will be the wire stick out, the angles of the torches and the spacing in between. Primary process parameters like voltage, current and welding speed will be kept constant. Penetration, bead width and height, percentage dilution, HAZ, weld penetration shape factor and weld reinforcement shape factor will be measured and evaluated. Fewer experiments will be needed because of the use of a design of experiments approach, namely a fractional factorial design. This will allow to determine the significance of each single parameter and their mutual interaction with respect to weld bead shape.Keywords: Multi-wire; Submerged arc welding; Design of experiments; Secondary parameters; Fractional factorial INTRODUCTIONMulti-wire submerged arc welding (SAW) is a high deposition rate process that is frequently used for piping and offshore applications. It is capable of joining thick steel plates or pipes in a fully automated process at high speed, which makes it economically very interesting to use for relatively large production series. Typically process parameters are set using rules of thumb and optimised through trial and error. Once good parameters are found, they are kept constant for the entire batch. In a previous master thesis the effect of primary process parameters (voltage, current, welding speed) on the geometrical quality of plate butt welds has been experimentally evaluated [3]. This study will focus on the effect of secondary process parameters on the geometrical weld quality. First, a short description of the multi-wire SAW process is given followed by a discussion of primary and secondary process parameters. Next, the experimental approach designed to evaluate the effects of secondary process parameters is elaborated. MULTI-WIRE SUBMERGED ARC WELDING Process descriptionSubmerged arc welding is a form of arc welding in which the weld pool is shielded by a mineral weld flux. This flux protects the weld pool from atmospheric influences, provides alloying elements to the weld pool and has several other properties that influence the weld [4]. The arc is formed within the flux and causes the continuously fed wire electrode to melt off and dilute with the molten base material. Because the arc is submerged, the heat loss is minimum resulting in a thermal efficiency as high as 95% [5]. No eye protection is needed [4][5][6][7][8], but this also implies that no visual monitoring can be done during welding [8]. This causes the need for automation [2,4]. To increase productivity, multiple wires can be fed into the same weld pool (see Figure 1). Every single wire can have different settings, which gives each of them a specific role. The first wire has specific settings to cause a deep penetration [6,8,9], the other wires have a more filling function. This makes...