Prediction of weld distortion takes many forms, including basic rules-of-thumb, simple shrinkage models, and thermal elastic/plastic finite element analysis of various degrees of complexity. Use of an appropriate level of simulation is a powerful and cost-effective way of reducing costs and increasing the quality of welded structures.
Mitigation of distortion during fabrication or repair of welded structures is a significant cost for industry. The total cost for a ship has been estimated at £2-3M. Practical assessment of alternative joining strategies (welding speed and power, weld sequencing, clamping etc) is prohibitively expensive, or impossible for some repair applications. Computer simulation of distortion is therefore an essential tool to reduce costs, increase quality and improve safety.
TWI has over 40 years of experience in simulating welding processes. With access to a range of industry standard commercial software, as well as bespoke in-house code, we can predict distortion due to a wide selection of welding processes, including arc, friction stir, laser, and electron beam. In addition the effects of other processes, including post-weld heat treatment and proof testing can be simulated.
Working closely with TWI's process groups provides numerical modellers with detailed insights into the welding processes, together with clear guidance about process changes to minimise distortion. This proximity also allows rapid and cost-effective assessment and validation of simulations via welding trials, including the use of state-of-the-art measurement equipment.
TWI collaborated with the Ministry of Defence and BVT Surface Fleet (now BAE Systems Surface Ships) to optimise the assembly process for a ship panel. A typical bulkhead panel was chosen, approximately 10m wide and 5m high, containing 194 welds totalling over 100m in length. Advanced techniques used by TWI enabled this complex panel to be analysed much more quickly than was previously possible. The predictive model of a standard assembly process was validated with distortion measurements made by BVT. The model was then modified to assess several different assembly strategies. Following introduction of the optimised process, weld distortion in subsequent production panels was significantly reduced.
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