What is a Forming Limit Diagram (FLD) and how is it used in stamping?

A Forming Limit Diagram plots major versus minor strain combinations that cause failure (necking) in sheet metal. It establishes a boundary between safe and failure regions for different strain paths (drawing, plane strain, stretch). FLD is used to: Evaluate part formability during die design, assess safety margins in CAE simulation, investigate splitting failures, and compare material formability. Strain is measured using circle grid analysis or digital image correlation. Factors affecting FLD include material grade, thickness, strain rate, and temperature. Process modifications to avoid failure include changing binder pressure, drawbead design, blank shape, or lubrication.