The pushing overpowering the screw material with formation manner of the screw which has looseness stopping function and the tool screw thread

摘要

PROBLEM TO BE SOLVED: To form a screw which performs a locking function without fail.;SOLUTION: A female screw material is pressed by a tool thread of a cold forming tap 1 to cold-form a pair of projected ribs while the ribs are drawn near to become like one thread. The thread is formed releasing at least one of the projected ribs to a relief part 9 ranging from a thread angle changing point CP to the vicinity of a bottom of thread groove 6, while the point CP locates between a point of effective diameter d2 on both flank faces 7, 8 of the tool thread and a point of the maximum female screw inside diameter allowance D1m of a female screw to be formed engaging with the tool screw. The female screw forming method is characterized in that a portion with a smaller thread angle than the regular angle is formed on the projected rib constituting both flank faces of the thread from the thread angle changing point closer to the thread top than the effective diameter to the vicinity of the thread top.;COPYRIGHT: (C)2005,JPO&NCIPI