Abstract
Nowadays, to increase of sheet hydroforming’s precision and effectiveness, new processes can be combined with it such as ultrasonic vibration. Even synchronic use of these two methods was studied in some metal forming processes such as tube hydroforming, but it has not been studied in sheet hydroforming. Therefore, the aim of this research is the experimental study of St14 sheet hydroforming with the assistance of ultrasonic vibration. For this purpose, ultrasonic vibration (with 20 kHz frequency and 4 μm amplitude) was applied radially to the punch of a hydro-mechanical deep drawing die. Then, process parameters consisting of LDR, maximum height, forming force, safe working zone, and thickness distribution were determined and compared in four states conventional deep drawing (CDD), hydroforming deep drawing (HDD), ultrasonic vibration assistance deep drawing (UDD) and ultrasonic vibration assistance hydroforming deep drawing (UHDD). Results indicate that applying ultrasonic vibration into the sheet hydroforming process increases LDR by12.5% and the maximum height of the cups by 35% compared to conventional deep drawing, decreases forming force by 8% and develops a safe working zone. Also, it effectively reduced thickness distribution by 18% and decreased sheet thinning in critical sections by 16%. Therefore, it is possible to see the positive effects of ultrasonic vibration on sheet hydroforming process. This situation can be justified from two macroscopic (ultrasonic lubrication) and microscopic aspects (acoustic softening).
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