关键词: 成形极限, 成形性能, 焊管, 液压成形, 预测模型

Abstract: Welded tubes have been widely used to manufacture tube hydroformed parts in the automotive industry. The non-uniform plastic deformation is caused by the weld zone, thus the accuracy evaluation for necking or fracture of seamed tube hydroforming is a problem which catches much concern in engineering. Based on metallographic analysis and microhardness testing methods, the structure and the forming characteristics of electrical resistance welding (ERW) welded tube are analyzed. A novel theoretical method is developed to predict the forming limit diagram (FLD) for welded tube hydroforming considering the unique features of seamed tube hydroforming. Based on this theoretical method, a new prediction model for forming limit of welded tube hydrforming is proposed using Swift hardening equation and Hill yield criterion. The FLD for welded tube hydroforming can be calculated after ascertaining the properties of welded tube, comprised of weld zone metal and base metal. Based on this prediction model, the FLD for an ERW welded tube of QSTE340 is calculated by programming. Good correlation between the theoretical predicting result and experimental data is indicated, and prove the validity and reliability of this theoretical model.

Key words: Formability, Forming limit, Hydroforming, Prediction model, Welded tube