Intro
13%
Cavity design and stress concentration: radii, draft, flash land, gates
Where forge dies actually crack and the geometric rules that move the failure point: minimum radii at stressed corners, draft angles by cavity depth, flash land and gutter dimensions, and gate placement that does not dump metal into a corner.
A closed-die forge shop puts an H13 connecting-rod cavity into production with R 1.5 mm at the base of a 22 mm rib. The die runs 4,200 cycles and cracks through the corner. The shop sends it back to the heat treater, who confirms 47 HRC and rejects the warranty claim. The next die out of the same heat treat lot, with the radius opened to R 3 mm on rev B, runs 95,000 cycles before the corner shows the first heat-check craze. The heat treat was fine. The geometry was the failure.
This lesson covers the radii, draft, flash, and gate decisions that decide where a forge die will crack before the cavity is cut.