Improvement in formability of tailor welded blanks by application of counter pressure in biaxial stretch forming

The use of new manufacturing concepts and advanced materials is of major interest to manufacturers of automobile and aerospace parts to reduce weight and cost and improve part performance. Despite numerous benefits associated with the use of tailor welded blanks (TWBs), forming of TWBs is challenging due to a significant reduction of formability associated with these materials. The importance of hydro forming of sheets is increasing, especially in the case of materials with low formability. The present paper investigates formability of tailor welded blanks of extra low carbon steel sheets in hydro-mechanical stretch forming. The effect of counter pressure and friction between the punch and the blank on limiting dome height and strain distribution has been investigated. Weld line movement has also been studied. Though the counter pressure increases limiting dome height, it has been found that simultaneous application of counter pressure and lubrication leads to higher stretchability and greater uniformity of strain distribution. The process has also been simulated using finite element method and results have been compared with experimental data.