The 7 Key Zones of the FLD Chart in AutoForm Software

In the automotive industry, Computer-Aided Engineering (CAE) plays a critical role in the product development process. One of the most advanced CAE tools for sheet metal forming simulation is AutoForm, which helps engineers predict and prevent defects such as cracking, wrinkling, and excessive thinning through finite element analysis (FEA).

A core feature of AutoForm is the Forming Limit Diagram (FLD)—a powerful tool used for evaluating the forming limits of sheet metal. The FLD divides the strain states of the material into seven color-coded zones, allowing engineers to visually assess the risk level of part failure during the forming process.

Let’s dive into the seven FLD zones and what they indicate:

1. Crack Zone (Red)

Located above the Forming Limit Curve (FLC), this zone signals that the material has surpassed its forming limit and is highly likely to crack. Any point falling into this red zone indicates immediate failure and requires urgent modification to tooling, material, or process.

2. Risk of Crack Zone (Yellow)

This zone lies just below the crack zone and represents a high-risk region. Though the material hasn’t yet cracked, it is operating close to its limit. Preventive action is recommended—either adjust forming parameters or change material properties to keep strain levels out of this danger zone.

3. Excessive Thinning Zone (Orange)

Excessive thinning means the sheet metal’s thickness has been reduced beyond an acceptable threshold, compromising the structural integrity and durability of the part. This is often caused by over-stretching in localized areas and should be avoided for safety-critical components.

4. Safe Zone (Green)

This is the ideal forming condition. Parts that fall in this zone are within the optimal strain range, meaning they are unlikely to crack, wrinkle, or thin excessively. This is the target zone for all critical product areas.

5. Insufficient Stretching Zone (Gray)

When sheet metal does not experience sufficient stretching, it may not fully conform to the desired shape. AutoForm flags these regions in gray. While sometimes acceptable in non-functional areas like flange or trimming zones, they should be minimized in product surfaces to maintain dimensional accuracy.

6. Wrinkle Tendency Zone (Blue)

This zone suggests a risk of wrinkling. While not a failure yet, wrinkles may form if certain conditions persist. Engineering judgment, supported by wrinkle height metrics and forming experience, is essential to manage this risk.

7. Wrinkle Zone (Purple)

Once material enters the wrinkle zone, visible wrinkling has occurred. This compromises both aesthetics and function. Engineers must revise die designs or modify draw bead layouts to eliminate or control wrinkles.

Why FLD Matters in Automotive CAE Analysis?

By leveraging FLD diagrams within AutoForm, engineers can simulate and predict forming issues in the early design stages. This helps:

·Eliminate trial-and-error during tooling development

·Recuce time and production costs

·Improve quality and repeatability in mass production

Real-World Application Analysis

Below is an example FLD chart from an actual component simulation. Can you identify if this part is at risk of cracking or wrinkling? Are the majority of strain points in the green zone, or are there areas of concern?

Feel free to share your analysis in the comments—we’d love to hear your interpretation!