Microstructural Analysis of Sheet Hydroforming Process Assisted by Ultrasonic Vibration on Punch Radial in a Hydro-Mechanical Deep Drawing Die

Abstract

Today, the use of sheet hydroforming methods in the conventional deep drawing process has significantly improved the formability of the sheet. However, due to the limitations of the sheet hydroforming process, new methods can be used in combination with it, such as ultrasonic-vibration-assisted forming. Many of the mechanical effects of ultrasonic vibration in the metal forming process are due to the metallurgical and structural impacts of the material, so to find the cause of the observed events, one must look at the microstructural interactions of materials. Therefore, the process of St14 sheet hydroforming with the assistance of ultrasonic vibration is investigated microstructurally in this paper. For this purpose, during the hydroforming drawing process, ultrasonic vibration was radially applied to the punch in a hydro-mechanical deep drawing die. Then the process parameters, including thickness, equivalent strain, grain size, and rotation at a selected point of the cross-section of the sample parts are compared in four modes of conventional deep drawing (CDD), hydroforming deep drawing (HDD), deep drawing assisted by ultrasonic vibration (UDD), and hydroforming deep drawing assisted by ultrasonic vibration (UHDD). Results showed that the application of ultrasonic vibrations in the sheet hydroforming process led to a significant reduction in thickness strain (as well as equivalent strain), increased grain length, and reduced rotation. This implies the positive impact of ultrasonic vibrations in the flow of materials is due to the reduction of friction and facilitates the movement of dislocations.