Review Lecture - The need for new welding processes

Abstract

Fusion welding is the most important metal joining process because it permits the joining of thicker sections than by riveting or bolting and therefore the construction of much larger plant than could be produced by forging or casting. The joints are leak-proof and thus allow the production, transport and use of a broad spectrum of hazardous substances. There are problems in fusion welding arising from distortion, residual stresses, defects such as cracks and changes in the microstructure of the parent metal. The risk of failure from buckling is enhanced by distortion and residual stresses. Residual stresses may promote stress corrosion cracking and the presence of cracks may lead to catastrophic failure by brittle fracture. The growing public concern with the environment and safety at work has led to more stringent and more numerous requirements for quality assurance testing. At the same time research, whilst greatly enhancing our understanding of fusion welding, has also revealed the scientific complexity of the process with the result that more and more variables require to be controlled in production. To an increasing extent the remedy for the avoidance of one problem produces a different one so that no further progress can be expected from research in fusion welding along traditional lines and only the development of processes not requiring fusion, of which friction welding and diffusion bonding are examples, offer an escape route from this impasse.