Distortion, and its adverse affects on dimensional accuracy, is a leading cost driver in manufacturing of large welded structures. Considerable costs are incurred prior to manufacturing for both design analysis and fixturing, as well as in post manufacturing repair techniques. Several forms of distortion including angular distortion, longitudinal bowing, transverse and longitudinal shrinkage, and buckling distortion, have been a major issue in the fabrication of welded structures. It is important to predict distortion during the design stage and to develop distortion control methods during the manufacturing stage. However, with the limitation of computational power, it takes days or weeks to analyze a large and complicated welded structure.
To reduce the computational time, EWI has developed and validated two distortion modeling methods, mapping plastic strain and lump-pass modeling. The mapping plastic-strain method requires two kinds of models, local models and a global model. The local models are analyzed to predict plastic strains and the global model is analyzed by mapping the plastic strains to predict distortions. The lump-pass modeling method includes two kinds of analyses: a thermal analysis and a thermomechanical analysis. The thermal analysis is conducted to predict temperature history. The thermomechanical analysis is performed to predict distortion by inputting the predicted temperature history.
EWI has been able to demonstrate the effeteness of these distortion prediction methods on analyzing large welded structures by reducing the computational time from weeks and days to hours and minutes.
EWI will present the distortion modeling methods in SNAME Annual Meeting & Expo 2010 which is held in Seattle, Washington on Nov. 3-5, 2010.