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Finite element modelling of low stress no distortion welding

 

Low stress no distortion (LSND) welding in 304 stainless steel: improved numerical simulation and experimental validation

TWI Member Report Summary 813/2004

N Bagshaw

Background

Distortion in the form of buckling can occur in welded thin-walled structures. This is a concern for industries such as aerospace, automotive and ship building, as expensive re-work is carried out to rectify the problem. Low Stress No Distortion (LSND) is a welding technique which reduces residual stresses and hence distortion. The techniques used to achieve LSND involve thermal tensioning, heat sinking and mechanical restraint. Moving or stationary heat sources or cooling sources are applied to regions close to the weld. With each method there are several parameters that may be varied to optimise the effectiveness of LSND welding. For this reason LSND welds are difficult to achieve and, to the author's knowledge, LSND welds have not yet been automated for industrial applications. The work presented in this document, the second report of LSND numerical modelling, shows further validation of the modelling approach with experimental tests of fully penetrating TIG welds in stainless steel plates, where different welding speeds were explored using LSND conditions. The LSND technique involved a trailing cooling source of liquid CO 2 positioned behind the weld. A more rigorous modelling procedure was also developed and was used in studies of LSND optimisation and plate geometry effects.

Objectives

  • To validate finite element (FE) modelling approaches with experimental work for different welding speeds.
  • To optimise the distance between the LSND trailing cooling and the arc torch.
  • To investigate geometric effects on distortion in welded plates, where different widths and thickness were modelled with and without LSND conditions.

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