Thread rolling dies and process for forming same

Details Thread rolling dies and process for forming same Thread rolling dies and process for forming same

2000-07-31

2001-12-04

Crane, Daniel C. (Department: 3725)

Metal deforming

Tool and/or tool holder

Tool-comprising die plate having ribs and/or grooves

C072S088000

Reexamination Certificate

active

06324887

ABSTRACT:

BACKGROUND OF THE INVENTION
I. Field of the Invention
This invention relates to dies for forming the helical threads on a metal fastener and, in particular, to thread rolling dies which prevent laps and discontinuities in the thread form during manufacture of the fastener.
II. Description of the Prior Art
Thread rolling dies have been used for many years to form the helical threads on a fastener which allows it to be threadably received within an aperture. In typical manufacturing, the fastener blank is formed to the desired length and diameter. The blank has a substantially smooth outer circumference. In order to form the threads in the blank, the blank is positioned between a pair of grooved dies. While one of the dies is kept stationary, the other die is moved longitudinally thereby rolling the blank along the dies. The grooves of the dies form the desired threads in the shank of the fastener as it moves across the dies. The grooves of the die are formed according to the desired depth and angle of the finished threads. In addition, the rolling dies must be configured to the diameter of the fastener blank.
While the use of standard thread rolling dies to form the threads works well for most fastener manufacturing, the use of such dies for fasteners causes laps in the thread form resulting in considerable scrap. The fastener blank can slip between the dies causing defective threads. The known thread rolling die geometry has been an obstacle to the mass production of lap free fasteners. Accordingly, a thread-rolling technique and a process of configuring thread dies which would produce defect-free threads while maintaining mass production rates is desired.
SUMMARY OF THE PRESENT INVENTION
The present invention overcomes the disadvantages of the prior known thread rolling dies by providing a method of designing and constructing thread rolling dies which produce lap-free threads in fastener blanks.
The thread rolling dies of the present invention generally include a pair of cooperating die members, one of which will be stationary as the other moves longitudinally relative thereto. As the die moves relative to the stationary die, the fastener blank will be rolled therebetween causing the metal to flow so as to form a thread having a shape determined by the profile of the lands and grooves machined in the opposing faces of the dies.
The geometry of the dies varies over the length of the die to gradually create the desired thread configuration. The starting end of the die has a roll-up ramp which includes shallower grooves to initially press the metal blank. The roll-up ramp gradually alters the groove angle from a relatively shallow angle up to the desired angle and depth thereby gradually forming the thread. A dwell section at the finish groove configuration follows the roll-up section such that a stable and well-defined thread form is created. The dwell section is followed by a rolloff section wherein the grooves ramp down to release the fastener.
The dies are designed to optimize lap-free production of the threaded fasteners. In contrast to prior known design methods for thread rolling dies, the sections of the die are calculated beginning at the back end of the die, in accordance with the diameter of the fastener blank. First, an appropriate roll-off section is calculated. Thereafter, the length of the dwell section with full depth grooves is calculated so that at least two complete rotations of the fastener occur across this section. This creates the stable and delved thread form. Finally, the roll-up ramp length is calculated providing the gradual formation of the thread. The constructed thread rolling dies eliminate laps and discontinuities in the thread form, particularly laps below the pitch line.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawing, in which like reference characters refer to like parts throughout the views and in which:


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