چكيده به لاتين
Nakazima’s biaxial stretch-forming test is the well-known method to create forming limit diagram (FLD) of sheet metals experimentally. The objective of this study is to present a method and apparatus for effectuating ultrasonic-assisted forming limit diagram. In this new method, ultrasonic vibration with high frequency are added to the movement of forming tool in a biaxial stretch-forming test. By superimposing ultrasonic vibration, the mechanical and microstructural properties of the investigated St14 steel sheet such as formability, Vickers hardness, and grain sizes were improved significantly. Moreover, microstructural observation alongside Micro-Vickers test have been performed on steel sheet. The conventional FLD as well as the new “Ultrasonic-Assisted Forming Limit Diagram” (UA-FLD) have been attained for St-14 steel sheet. The achived results indicated that applying ultrasonic vibrations with the amplitude of 15µm at the frequency of 20 kHz to the tool, would cause an impressive enhancement in forming limit diagram, a maximum of 28% increasment in hardness ,and 24% reduction in average grain size of the sheet.
Keywords: Ultrasonic-assisted sheet metal forming, Forming limit diagram, Biaxial stretch-forming, Micro-Vickers Hardness, Grain refinement.
