Wrinkle-free metal shells and the production thereof from flat metal sheets

Claim 1

IN THE PRODUCTION OF SHELLS FROM FLAT SHEET METAL BLANKS THROUGH THE USE OF A PUNCH, A DIE AND AN ASSOCIATED GAUGE PLATE, THE METHOD OF EQUALIZING AND MINIMIZING THE STRESSES IN THE BLANK WHICH COMPRISES PLACING A BLANK WITH ITS BORDER PORTIONS BETWEEN THE GAUGE PLATE AND THE DIE FACE, SETTING THE GAUGE PLATE AND DIE FACE IN SUBSTANTIAL BUT NON-CLAMPING CONTACT WITH OPPOSITE FACES OF THE BLANK, AND HOLDING SAID GUAGE PLATE AND DIE FACE IMMOVABLE IN SUCH SET RELATION WHILE THE PUNCH IS OPERATED THROUGH ITS FORMING STROKE WHEREBY ALL FRICTIONAL RESTRAINING FORCES EXERTED ON THE BORDER PORTIONS OF THE BLANK ARE CREATED SOLELY BY METAL FLOW IN THE BORDER PORTIONS OF THE BLANK IN RESPONSE TO FORCES APPLIED TO THE BLANK BY THE PUNCH IN ITS FORMING STROKE AND THE METAL OF THE BLANK IS RE-ORIENTED TO PRODUCE A SHELL WITH A SMOOTH FLANGE AND SMOOTH WALLS OF A THICKNESS NOT LESS THAN THE ORIGINAL BLANK THICKNESS.