METHOD OF STRETCHING SHEET BLANKS Russian patent published in 1996 - IPC

FIELD: metal pressure forming. SUBSTANCE: method comprises steps of stretching until a close fitting of a blank over a punch; at stretching providing treatment by a pulse electric current of a central portion of the blank along its width for convex parts in accordance with a stretching-over angle Ψ_ax, in an axial direction, equal to Ψ_ax = (0,5...0,6) Ψ_f, and boundary portions of the blank along its width for concave parts in accordance with a stretching- over angle Ψi1

, in the axial direction, equal to Ψi1=(1-(0,4...0,5))Ψ_f,, where Ψ_f - a final stretching-over angle in the axial direction. EFFECT: enhanced accuracy and equal-strength of parts, being made; a possibility of making a casing by one transition instead of two or more transitions, including also intermediate heat treatment operations according to a well known methods; increased quality of casings, lowered manufacturing costs. 1 cl, 6 dwg, 2 tbl