What is forming limit diagram?

Forming Limit Diagram (FLD) is a graphical representation which shows the limits of strains that a sheet metal material can withstand before it fails during a forming process such as bending or stamping. It is also known as a Forming Limit Curve (FLC). The FLD is plotted between two axes, the major strain (ε1) and minor strain (ε2). The major and minor strains are plotted as orthogonal axes to reveal the formability properties of the material.

The FLD indicates the limiting values of the strains and the corresponding stress states, beyond which the material would fail during a forming process. The forming limit diagram is an important tool used in the design of sheet metal components for automotive and aerospace applications. It helps in predicting the formability, and therefore the final shapes, of various sheet metal components.

The FLD testing is carried out in specialized machines that analyze the material's failure when subjected to various forming conditions. The results are then plotted on the FLD graph. The FLD graph is then used to determine and optimize the forming conditions such as the amount of deformation, yield strength, and the tool's radius, among other factors.

In general, FLDs are used to predict the maximum strain that a given sheet metal can handle without cracking. FLDs are helpful in the design process of automotive frames and other components so that manufacturers can improve the strength and durability of their products while also reducing the weight of the final product.