Defect Characteristics
Location is sidewall near square cup corners at die corner radius. Shape is inverted W-form with cross-hatching above it. Generally difficult to predict during design.
Formation Mechanism
Straight sides and corners deform unevenly. Thickness increases only at corners, concentrating blank holder pressure while promoting work hardening. Two load peaks form: first for drawing failure, second for wall failure. Later stage load shifts to corners causing wall issues.
Root Cause Analysis
Product Shape Related
Deep drawing needs depth reduction or alternative methods. Small corner radius needs value increase with careful grinding.
Stamping Conditions
Excessive holder pressure can be reduced if no wrinkling occurs. Poor lubrication indicator is part too hot when removed - reconsider oil selection. Improper blank shape can be fixed by changing shape. Positioning errors occur even with correct cut amount.
Die Issues
Rough surface needs grinding. Poor parallelism degrades with increased die height. Draw bead position needs weakening at corners.
Material Factors
Insufficient tensile strength needs better material. Excessive grain size needs reduced grain material.
Diagnostic Principles
Irregular pattern indicates material quality issue. Neat line indicates process or die problem. Material flow rule: excess wrinkles, insufficient fails. Regulate via holder pressure, draw beads, radii, or notches.
