Weld Modelling
The finite element method is routinely used at TWI to predict the temperature distribution resulting from welding procedures. This information is then used to predict residual stresses and distortion, and therefore allow the process to be optimised. Recent applications have included simulations of arc, laser, and electron beam welding.
Case studies:
Pipe Girth Weld
A pipe girth weld problem can be analysed using an axisymmetric model. Initially a thermal analysis is carried out to determine the temperature distribution history associated with the addition of each pass. Fig 1 shows the temperature distribution at the start of the second pass of a three pass weld.
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Fig.1. Temperature distribution after deposition of the second pass of a three-pass weld |
A subsequent mechanical analysis uses the temperatures predicted in the thermal analysis to calculate the residual stresses and distortion resulting from the heat input during the welding. Validation of modelling results is of great importance, and TWI's laboratories are well equipped to confirm modelling results. Figs 2 & 3 show the axial and hoop residual stress distributions after the completion of the multipass pipe girth weld and following cooling to room temperature.
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Fig.2. Predicted axial distribution of residual stress |
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Fig.3. Predicted hoop distribution of residual stress |
SDPS - Structural Distortion Prediction System
There is a long-standing need for better prediction and control of weld distortion, as rectification can greatly increase fabrication costs. Finite element analysis is being used as part of a system that will allow the prediction of the accumulation of distortion during the assembly of a complex welded structure.
Validation of the SDPS is being carried out using a test structure relevant to the aerospace industry.
In principle, the method is applicable to any welded structure.
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Fig.4. Prediction of the distortion in a complex welded structure |
Laser welding of plastics
The optimisation of laser welding parameters for joining plastic components was carried out as part of TWI's Core Research Programme. Using finite element analysis, the weld quality can be efficiently predicted for a range of laser speeds and powers on different plastics. The pigments in the thermoplastic polymers are chosen so one part of the joint transmits laser light, while the other part absorbs it, leading to melting and the formation of a weld. This is shown in Fig.5, where all the red material has been predicted to melt and form a weld.
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Fig.5. Prediction of welded region following laser welding of plastic components |
To find out more about how TWI could benefit your company, please contact us at fea@twi.co.uk
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