Sheet metal forming tools

Claim 1

A TOOL FOR FORMING SHEET METAL COMPRISING TWO DIE MEMBERS, ONE OF SAID DIE MEMBERS HAVING A CHANNEL-LIKE RECESS HAVING AN ENTRANCE END AND AN EXIT END AND DEFINED BY A BOTTOM SURFACE AND TWO HELICAL SIDE SURFACES, SAID HELICAL SIDE SURFACES STARTING AT THE ENTRANCE END OF SAID CHANNEL FROM A PLANE COINCIDING WITH THE BOTTOM SURFACE AND CONVERGING TOWARDS THE EXIT END OF THE CHANNEL, THE OTHER DIE MEMBER HAVING A RIB-SHAPED BODY PORTION EFFECTIVE TO PRESS THE SHEET METAL INTO SAID CHANNEL WHEN RELATIVE MOVEMENT IS IMPARTED TO ONE OF SAID DIE MEMBERS TO IMPART RELATIVE MOVEMENT TO EACH OTHER AND THE SHEET METAL TO BE FORMED IS ADVANCED STEPWISE LONGITUDINALLY THROUGH SAID CHANNEL, SAID BODY PORTION HAVING A PLANE WORKING SURFACE CONFORMING TO THE BOTTOM SURFACE OF SAID CHANNEL AND HAVING TWO SIDE SURFACES JOINING THE WORKING SURFACE ALONG STRAIGHT LINE EDGES OF THE BODY PORTION, SAID BODY PORTION HAVING AT LEAST AT THE EXIT END OF THE TOOL A CROSS-SECTIONAL CONFIGURATION COINCIDING WITH THE CROSSSECTION OF THE CHANNEL AT THE EXIT END THEREOF, AND HAVING ALONG THE REMAINDER OF ITS LENGTH A CROSS-SECTIONAL WIDTH LESS THAN THAT OF THE CHANNEL THEREBY TO LEAVE IN OPERATION A FREE CLEARANCE BETWEEN THE SIDE SURFACES OF THE RIB-SHAPED BODY PORTION AND OPPOSING SIDE SURFACES OF THE CHANNEL IN A TERMINAL OPERATIVE POSITION OF A WORKING STROKE OF THE DIE MEMBERS, SAID CLEARANCE CONVERGING TOWARDS THE EXIT END OF THE TOOL, WHEREBY SAID SHEET IS SHAPED PROGRESSIVELY SOLELY BY ITS BEING BENT ABOUT SAID STRAIGHT LINE OF THE RIB-SHAPED BODY PORTION.