As the strength of the materials increases, the weldability issues can dictate whether the fabrication is feasible and what procedural constraints are imposed. In addition, the requirement for improved productivity and sustainable manufacturing in Australia means that advanced welding processes and manufacturing technologies must be evaluated. Weldability and process technology are inextricably linked; for example, high thermal intensity processes such as laser welding allow significant speed increases, reduction of heat input and lower distortion, but the risk of hydrogen-assisted cold cracking (HACC) in high-strength steels may be increased. By the same token, the use of high preheat levels to combat HACC may damage heat-affected zone properties and can be counter-productive when robotic welding is employed. As a result, some of the key welding research areas which are being tackled within the DMTC program are:
- The weldability and subsequent performance of high-strength structural steels for ships
- The weldability and performance of existing and alternative armour materials
- Advanced welding processes for improved productivity
- Lean automation of air platforms
- Lean automation and robotic welding for land and marine platforms
- Welding, repair and reclamation of marine components
A good example of the coordinated approach to these issues is the investigation of future armour requirements and manufacturing technology for land vehicles such as the various armoured personnel carriers manufactured by Thales in Bendigo. The research, which is based at the University of ÌìÃÀ´«Ã½, involves a team including Thales, DSTO, ANSTO, Bluescope Steel and Bisalloy. The armour materials currently used include quenched and tempered steels, and welding technologies are integral to defining and improving the ballistic and blast protection offered to operational personnel. To determine the limits of weldability of these and potentially higher grade steels, it is necessary to understand the basic metallurgy and the effects of welding thermal cycles in candidate welding processes.
The research team is therefore conducting basic studies to assess the transformation behaviour of the materials. This involves welding trials to establish actual thermal cycles and thermo-mechanical simulation. A Gleeble 3500 thermo-mechanical simulator is being employed to explore the effect of the complete range of welding variables on the material properties. To understand the likely effect of welding, the transformation behaviour of the candidate steels needs to be mapped, and dilatometric studies are underway to produce this basic data. In parallel and conjunction with these weldability studies, various high productivity process options, such as laser-GMAW hybrid and tandem GMAW techniques, are being evaluated. Whilst conventional robotic welding of long production runs is well established and Thales has already embarked on robotic welding implementation, recent developments in lean manufacturing and offline programming may extend the application of such techniques to more specialised short runs. The team are therefore evaluating offline programming, simulation and integrated design and production techniques for the land platforms as well as marine structures. This activity also involves the construction of a technology demonstration cell at the University of ÌìÃÀ´«Ã½, incorporating state-of-the-art welding and robotic hardware and associated software.
Similar studies are in hand for marine and air platforms with an emphasis on addressing future defence capability needs. Although specifically aimed at defence, the research is also expected to have spin-offs in other manufacturing applications.
It is important to recognise that the research is multidisciplinary and a holistic approach is essential to ensure that practical solutions which balance the weldability, productivity and performance are achieved. The collaborative model involving a range of research and industry partners is the ideal way to meet these goals.
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