Experimental Investigation of Multi-stage Deep Drawing of IN718 Sheet at Elevated Temperature

Abstract

IN718 is a nickel-based super alloy that retains its mechanical properties at elevated temperatures and hence has numerous applications in the aerospace industry. In this study, deep drawing of IN718 sheet at elevated temperatures (700-1000°C) has been investigated experimentally. Initially, stress-strain response with failure strain at different temperatures was evaluated by uniaxial tensile tests along different orientations. Subsequently, hot deep drawing and re-drawing tools were designed and fabricated. A circle-grid marked circular blank of 3mm thickness was used in the first draw to form a circular cup followed by re-drawing (2nd draw). The major and minor diameter of the circular grid on the blank after the deep drawing was used to examine the strain distribution in the drawn cup and further used to calculate the thickness strain. These deep drawing operations were carried out at different temperatures with a constant blank holding force. Further, the deep drawing force at different temperatures was examined. The effect of the test temperatures during hot deep drawing and the process parameters on the variation of the thickness strain over the surface of the drawn cup has been studied. Finally, the major and minor strains are plotted in Keeler and Arcelor V9 forming limit curve to examine the formability of IN718 sheets at elevated temperature.