IIW White Paper

4 Needs and challenges in welding and joining technologies

aspects of products fully integrate themselves with processes of fabrication excellence. Therefore, one of the major scientific challenges is to integrate welding & joining processes with the knowledge of welding mechanics into the design process to ensure high performance welded structures . Complex and ever increasing requirements of welded products include energy saving both in material use and fabrication while providing long and safe service life with almost no inspection and repair. This situation will require to use significantly more dissimilar materials (in combination with a multi-material design approach) to make innovative products. Breakthroughs in the technology for joining dissimilar materials could lead to new manufacturing strategies that could reduce costs, improve productivity, and open up new markets for welded structures and components. The use of high energy density welding processes, such as laser beam with advanced materials and design considerations can tackle various future challenges. Scientific analysis of joint features, properties and predictions of performance will remain, however, as one of the long-term challenges. Development of methods to expand capabilities of laser beam technology for surface modifications, create “ barriers” against crack initiation and growth, property gradient (e.g. to improve fatigue performance via crack growth retardation) and for forming with better understanding of local metallurgical and mechanical evolutions with predictions of weld lifetime and performance. Tailoring the local properties of the weld joints to meet the quality and performance requirements of the product should integrate design guidelines (including local engineering), materials science and mechanics based modelling and automated testing. Engineers should possess the ability to design a high performance product and its manufacturing process on the computer before production even begins. Development of intelligent weldments containing embedded sensors combined with real-time defect sensing techniques and laser based seam-tracking systems will provide new opportunities and challenges which need to be tackled within fundamental research activities. Here, real-time defect sensing techniques with their new developments are expected to validate joining processing while determining the fitness-for- service. This requires strong team work and interaction of designer, fabricator and end-user. Fitness-for-service analysis of welded structures is highly developed; however, they mostly use stress-based approaches. There is a need to develop “strain-based” fitness-for-service analysis procedures particularly for welded pipelines where welded pipe undergoes high plastic straining during the fabrication or service. A strategy for this challenge is to establish a task force of the IIWWorking Units of X and XI to generate a Best Practice Document and/or guidelines for better assessment of weld fitness-for-service and life expectancy. Basic research is needed to develop alloys (base metal and filler wire) for the laser beam welding process to enable high strength aluminum alloys to be welded with minimal material property degradation. This will have a major impact on the quality and performance of welds of aircraft structures while promoting welding as a key engineering process for metallic airframes. Joining of metal to carbon reinforced composite materials of the critical components of aerospace structures with durable and damage tolerant design should also be considered as one of the major challenges of the future. Furthermore, rethinking of the aerospace design and manufacturing processes to incorporate advanced welding processes will depend on the comprehensive scientific understanding of the welding processes and structural performance predictions of welded components. A better understanding of post-weld heat treatment (PWHT) is needed in terms of property (microstructures, residual stresses etc.) evolution of the weld metal and HAZ of original and repair welds. For this, the development of a capability to simulate thermal, mechanical and metallurgical changes caused by PWHT and the integration of information with overall system models should be considered as a challenge.

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Through Optimum Use and Innovation of Welding and Joining Technologies

Improving Global Quality of Life