Investigation of formability of low carbon steel sheets by forming limit diagrams

Low carbon steel sheets have many applications in industries, especially in automotive parts, therefore it is necessary to study formability of these steel sheets. Forming limit diagram (FLD) is one of the strong pieces of equipment used to study the formability of sheet metals. In this study, FLDs have been determined experimentally for three grades ST12, ST14, and Interstitial free (IF) by conducting punch-stretching experiments using suitably designed and fabricated tools. Formability observed from FLDs has been correlated with mechanical properties and formability parameters like punch type, punch diameter, friction between punch and sheet, work hardening exponent (n) and plane-anisotropy (r) of the sheets. Results have indicated that forming strains in IF and ST14 steel sheets are higher than ST12 and higher nxr values and thickness are desirable to raise the forming strains. The sheet orientation can be effective and in addition, depends on the strain path Tor example, forming limit strains in 45 degrees angles with respect to the rolling direction are less than that for 0 degrees and 90 degrees within the right band of FLDs.