Ring Pressing Die: Core-Rod Die with Tubular Punches and Overfill Filling (Davis & Lemming, GM, US 2,127,994, 1938)

The die set for pressing metal or other powder into rings (bushings, ring cores). A die with a round cavity has a fixed core rod standing up through its middle, so the cavity is ring-shaped; a tube-shaped lower plunger slides up and down round the core rod, and a tube-shaped upper punch comes down to press. Filling is the trick: the lower plunger drops past the pressing point under a shaking shoe of powder, then rises a little to push the surplus back, so every ring gets the same charge with no trapped air. Result: a die that presses powder into rings of even weight and density, ejected flush with the die top. Source: J. H. Davis and J. C. Lemming (General Motors), US 2,127,994 (1938). Unknown: steels, sizes, clearances, pressure. Picture: the patent drawing.