METHOD FOR FORMING MULTI-START HELICAL RIFFLES Russian patent published in 2008 - IPC B21C37/20 B21J5/12 B21K21/06 

FIELD: plastic working of metal, possibly forming on inner surface of tubular blanks with bottom multi-stat helical riffles of mutually opposite directions at manufacturing fragmentation type envelope of ammunition.

SUBSTANCE: riffles form grid of rhombic protrusions. In order to form such riffles, tubular blank is reduced by two successive operations. At each operation tubular blank and punch with helical protrusions are together pulled through sizing die. Each operation is realized at least during two transitions while punches whose length is multiply less that length of blank are used. Common pulling through of blank and punch during first transition of each reduction operation is realized while punch rests upon bottom of blank. Between transitions at each reduction operation punch is unscrewed from blank with formed helical riffles for forming between punch and blank band of engagement of helical protrusions of punch and helical riffles of blank. Said band is used at next reduction transition for resting punch and for providing desired direction of formed helical riffles.

EFFECT: enlarged functional and manufacturing possibilities of method.

5 dwg