TWI Industrial Member Report Summary 503/1994
P C J Anderson
The depth of penetration of the weld bead has a direct influence on weld strength. Fatigue performance can be adversely affected by incomplete root fusion. For high integrity components, achieving the required weld mechanical and fatigue properties is critical. It is, therefore, essential that the required depth of fusion can be maintained and, for fully fused joints, that adequate root fusion can be assured.
Problems are frequently experienced in ensuring consistent penetration of the joint, due to minor variations in the composition of the parent material, the component dimensions, the joint fit-up or the surface condition of the component. In manual welding, the welder can adjust the welding parameters, or his technique, to compensate for some of the variations. In mechanised and automated welding, the welding parameters are normally fixed prior to welding. A sensor which observes the back of the weld and modifies the welding parameters to ensure consistent penetration is commercially available. However, the many applications, access to the back face of the weld is not possible.
There is a need for a sensor system to control accurately the weld bead penetration from the top-face, for mechanised and automated welding. To be widely applicable in the fabrication industry, the system should be able to accommodate:
- TIG, MIG and laser welding processes.
- Flat, vertical and overhead welding positions.
- Butt and fillet welds.
- A broad range of materials, including C-Mn steels, stainless steels and aluminium alloys.
- Full and partial penetration welds.
Ideally, the sensor should not make contact with the workpiece, or intrude into the welding area. Currently, there is no system commercially available which fulfills these criteria. Some sensors have been applied in specific applications, although these each have limitations to their capabilities.
To review the available literature on sensor systems for the top-face control of weld pool penetration in arc and laser welding, with a view to developing a commercial system for the top face control of weld penetration.