Quick prediction of the folding defect in transitional region during isothermal local loading forming of titanium alloy large-scale rib-web component based on folding index

Forming quality of transitional region determines the performance of titanium alloy large-scale rib-web component under isothermal local loading forming. As folding defect is the most sensitive defect in transitional region, its prediction is very critical to the precision shape forming in isothermal local loading forming. In this paper, a quick prediction model for the folding defect in transitional region was established to replace the traditional defect prediction method by time-consuming FE simulation. First of all, the FE model of local eigen model of transitional region during local loading forming of large-scale rib-web component was established and validated by physical experiment. Then, an adaptive folding index was proposed to measure the possibility and severity of folding defect based on the mechanism that there exists a local increase of strain rate when a folding tends to appear. Availability of the adaptive folding index was checked by large numbers of uniform experiments designed by the space-filling Maximin Latin hypercube designs (maximin LHDs). Furthermore, a judging criterion for folding defect based on the folding index was developed and validated by random samples. Subsequently, the folding index was correlated with the geometrical characteristic parameters of transitional region model by RSM model, through which the folding index can be predicted quickly without the time-consuming FE simulation. Finally, a quick prediction model was established for folding defect judgment under various geometrical parameters by combination of the RSM model for folding index and proposed judging criterion. Prediction results are quite consistent with the results of FE simulation and experiment. The folding prediction model can greatly facilitate the design space exploration and engineering design thereby providing guideline to the precision shape forming. Besides, the adaptive folding index and corresponding judging criteria for folding defect put forward in this work have reference significance to the study on folding defect in other forging processes.