Welding and joining in the new Defence Materials Technology Centre
By Professor John Norrish*, University of Wollongong
The Defence Materials Technology Centre (DMTC) was established in May 2008 following the Federal Government’s announcement it would establish technology development joint ventures called Defence Future Capability Technology Centres (DFCTCs), to combine expertise and resources from defence industries and research providers.
Operational funding of approximately $86 million is drawn from several sources including a $30 million contribution from the Federal Government and a combined $9 million from the state governments of Victoria, Queensland and New South Wales. Collaborative industry and research sector partners provide the balance.
The overall aim of DMTC is to develop and deliver advanced materials/manufacturing technology that will be incorporated into future defence industry products and services; it covers applications in land, marine and air platforms. It is also an important objective of the government to sustain Defence manufacturing and support capability in Australia.
Welding and joining play a key role in the fabrication of all defence platforms and in an attempt to progressively improve performance, capability and availability it is likely that new challenges will arise in the joining technology area.
In particular, higher strength materials and lighter weight structures are likely to be used. As the strength of the materials increase, 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 manufacture in Australia mean 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 increases in speed, 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 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; and
- 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 the land vehicles such as the various armoured personnel carriers manufactured by Thales in Bendigo.
The research, which is based at the UOW involves a team which includes 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. In order 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. In order 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 off-line programming may extend the application of such techniques to more specialised short runs.
The team are therefore evaluating off-line 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 UOW 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 multi-disciplinary 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.
*Prof Norrish is a Director of DMTC Ltd
This article first appeared in the Australasian Welding Journal (Vol 54, Third Quarter, 2009) published by the Welding Technology Institute of Australia. Visit www.wtia.com.au
Posted by DMTC on September 15th, 2009