Page 41 - MetalForming November 2013

Tooling by Design
occurred during the stamping process. The strip is the equivalent of an eye- witness of a car accident. Like the wit- ness, the strip was physically present during the entire process, and experi- enced everything that occurred. It knows, for example, if:
• The material fed properly.
• The pilots accurately positioned the strip.
• Pitch length (the distance between pilot holes) grew or shrunk beyond spec.
• A stretch flange split due to a mis- matched cut.
• Extrusions split due to a burr.
• The die is hitting too hard or not hard enough.
• Deep-drawn features split due to restricted material flow or an incor- rect radius.
• The carrier design is appropriate.
• The die is hitting level in all sta- tions.
• Die timing is correct with the die fully loaded.
• Cutting clearances change with the die fully loaded, due to tipping moments.
Press shops also must monitor tool wear and fatigue—breakage not caused by a die crash—and implement pre- ventive-maintenance programs to avoid wear-related instability.
Finally, don’t overlook how changes in process temperature affect linear expansion of press members and die components. A press structure will change size as it warms to its normal operating temperature on a cold morn- ing, or when it cools during a long repair or lunch break. In-die process heat, due to friction, can change the charac- teristics of punches and die sections by altering their size and clearances. When the press structure and die com- ponents change shape, the parts that they produce surely will be affected.
Achieving consistent part quality relates directly to how well the stamp- ing process inputs are understood and, most importantly, how well they are controlled. MF

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