Abstract :
Sheet metal forming is defined as the ability of metal to deform plastically (deformation by Stretching or drawing) or changing the shape of the sheet into a new desirable shape with out necking or crack . To control the operation of sheet metal forming with out failure. A diagram is used in which the range accepted , failure and critical deformation range are shown . This diagram is known as the Forming limit diagram. It is considered as one of the important tool to determine the formability of sheet metals. Every sheet metal has its own forming limit diagram which determines its formability, strain limit and the forming regions. These diagrams can be assessed using theoretical and experimental approaches, In this paper, the FLD is determined using different yield criteria Hill1948, Hosford1979 and modified Hosford 1985. It is shown that the determination of forming limit curve using the modified Hosford 1985 criterion with the (M-K) analysis , gave the best results compared with the other used criteria .Using this criterion gave the closest forming limit curve to that obtained experimentally, but with different criterion index for different alloy . The value of the index (a=6) gave the best results for brass, while (a=8) gave the best results for aluminum alloy and mild steel.