SHEET METAL STAMPING & FORMING PREPRESS

Sheet Metal Deep Drawing Tooling & Flat Blank Vector Guide

Deep drawing is a metal forming process wherein a flat sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. In automotive, aerospace, and consumer appliance stamping (Schuler, AIDA, Minster presses), accurate blank sizing and draw ratio calibration are essential to prevent flange wrinkling, excessive wall thinning, and sidewall tearing.

1. Surface Area Conservation & Blank Sizing

During deep drawing, sheet metal undergoes radial tensile stress and circumferential compressive stress, but overall volumetric surface area remains essentially constant. For a cylindrical flat-bottom shell with diameter $d$, depth $h$, and punch corner radius $r_c$, the blank diameter $D$ is derived from:

D = sqrt(d^2 + 4*d*h - 0.86*r_c*d)

To account for non-uniform material flow and planar anisotropy (earing due to rolling grain direction), add a $3\% - 5\%$ radial trim allowance to ensure post-draw pinch trimming yields a clean, perpendicular rim edge.

2. Draw Ratio Limits (LDR) Across Metal Alloys

3. Flat Blank DXF CAM Prepress Checklist

• Continuous Tangent Contours: Ensure blank perimeter DXF consists of 100% closed, continuous G02/G03 polyline entities without overlapping micro-segments.
• Grain Orientation Markers: Include engraved or low-power laser etched grain direction ticks ($0^\circ, 45^\circ, 90^\circ$) to align blank nesting with the sheet rolling axis.
• Draw Bead Position Geometry: For rectangular or asymmetrical draw dies, include exact draw bead centerlines in a distinct CAD layer (COLOR: RED, LAYER: DRAW_BEADS) for CNC die milling.