Influence of Welding Current on Formation of Weld Bead in TIG Welding for Joining Thin Plates

In this paper, a new (novel) welding technology has been applied to join 0.1 mm thin plates. An initial study on the influence of welding current on the welding properties for stainless steel SUS304 plates is discussed in this paper. The weld bead appearance on both top surface and bottom surface was observed by microscope to indicate the change of weld bead size and welding defects. The results showed that by utilizing a constricted nozzle, a good weld bead is found out when the arc length is too short (0.3 mm), welding speed is very high (3000 mm min-1) and base metal is very thin (0.1 mm) with suitable welding conditions.

Development of a LASER Welding Apparatus and a Method for an Inner-Strap Welding of a Spacer Grid Assembly for a PWR Fuel Assembly

A spacer grid assembly, which is an interconnected array of slotted grid straps welded at the intersections to form an egg crate structure, is one of the core structural components for the nuclear fuel assemblies of a Pressurized light Water Reactor (PWR). The commercial spacer grid assembly is spot-welded at the crossing points of the intersections by a TIG welding, LASER beam welding or Electron beam welding method. In this study, a LASER beam welding apparatus and a method for an inner strap welding has been proposed to obtain a longer and finer weld line and a smaller weld bead size for a spacer grid assembly for a PWR fuel assembly. Also a rapid welding and excellent weld quality have been achieved by the proposed welding apparatus and method.

Semiadaptive Synergic-Fill Welding Tractor for Ship Unit Erection

At most U.S. shipyards, the bottleneck for improving productivity is unit fabrication and ship erection. Fit-up during unit, super-unit, and ship erection is difficult, resulting in variable gap and mismatch, which promote defects and repair. A semiadaptive synergic-fill welding tractor was developed for improving the productivity of seam welds during erection. The tractor has many features that advanced robots have but is simple to use because it relies on operator pass planning instead of robotic path preplanning. The "synergic-fill" welding concept was developed to maximize the deployment of robust welding procedures. This was a new control process for making changes to weld bead size during fabrication using one knob. The synergic-fill welding concept was developed for flux-cored arc welding of DH36 steels for horizontal erection seams. These seams have a range of gap and require a range of weld bead sizes to uniformly fill the weld seam. Welding parameters that ensured a constant base metal dilution were optimized and programmed into the synergic control. In addition, the welding tractor was developed with a laser seam tracking vision sensor and adaptive-fill control. The new control allows the operator to intervene during welding and toggle the adaptive features on and off. A special four-axis tractor was developed to permit cross-seam and torch height control for seam tracking while oscillating the welding torch. The laser sensor was integrated with modular fixturing to permit welding with either angled or transverse oscillation. The adaptive control algorithm varied the weld size from the synergic-fill starting point that was selected by the operator. The weld bead was made proportionally larger or smaller as the joint width became larger or smaller within the process capability range. A semiadaptive control algorithm was developed for the horizontal welding application. The process was not completely automatic. The operator, who plans the position of the welding torch for each weld bead in a layer, applies the process. Further, he made weld bead size decisions based on the joint width. Once the welding system was started, it tracked the bead location as the groove width changed, controlled the torch height, and can adaptively vary bead size relative to joint width. This flexible technology will minimize the susceptibility to defects during erection welding.

Numerical methods to predict failure during the in-service welding of gas pipelines

It is evident that numerical methods have a useful role in the assessment of welding conditions for the safe in-service welding of high-pressure gas pipelines. No published work has considered the direct calculation of burn-through using a combination of thermal and stress analysis. Using empirical relationships between welding process parameters and weld bead size and shape is an appropriate way of defining the weldment geometry and the heat-source coordinates. With this approach, adequate agreement between predicted weld penetration, weld cooling times and heat-affected zone hardness has been made. Following the prediction of a thermal field a full thermo-elastic plastic model can be used to predict the conditions likely to cause burn-through. In this paper two significant research aspects of in-service welding have been addressed, as follows: 1 A new mathematical description of a heat source to represent the common in-service welding process, i.e. vertically up and vertically down manual metal arc welding with hydrogen controlled electrodes has been formed and has given good correlation with experiment and field welds. 2 Preliminary burn-through modelling of in-service welding using non-linear thermal-stress numerical methods has given encouraging results.