Self-thread forming threaded fasteners and method and apparatus for making the same

Claim 1

Method of rolling a thread of a self-threading screw comprising a rear shank portion having a circular cross section and a front end portion having a cross section of arcuate, lobular shape of reduced thickness including a tapered portion and in which a blank having the above described cross sections is rolled between two opposed thread forming dies, the invention being characterized in: a. applying thread-forming pressures simultaneously to said shank and tapered portions; and b. applying intermittent deflecting pressures to said front end portion to vary periodically the distance from the axis of said front end portion to said dies by bending said front end portion while maintaining at least a substantial extent of the axis of said shank portion substantially equally spaced from said opposed dies during the application of said thread-forming and deflecting pressures such that only a portion of said blank that includes said front end portion is deflected by said deflecting pressures.

Claim 5

A method of making a self-thread forming threaded fastener having a main shank section of circular cross sectional shape and a thread-forming work-entering section of lobular cross sectional shape, said method comprising: rolling a blank having a cylindrical shank section of circular cross section, the front extremity of said blank being of lobular, arcuate, cross section of lesser diametrical width than said shank section and a tapered transition section between said shank and said extremity between a pair of thread-rolling dies each having a first die portion with die ridges and grooves for forming a substantially straight thread overlying the shank portion of said blank, a second die portion immediately adjacent said first die portion with ridges and grooves for forming a tapered thread overlying said transition section of said blank as a continuation of the thread on said sHank section, and a third die portion having a substantially unridged surface, applying thread-forming pressures simultaneously to said shank and said transition sections, and during said rolling operation causing said third die portions to engage the lobular extremity of said die blank and intermittently bend said extremity and said tapered transition section first away from one die and then away from the other while maintaining at least a substantial portion of the central axis of said shank section equally spaced from said dies, whereby the thread formed on said transition section is of arcuate lobular cross sectional shape.

Claim 6

A method of making a self-thread forming threaded fastener having a main shank section of circular cross sectional shape and a thread-forming work-entering section of lobular cross sectional shape, said method comprising: rolling a blank having a cylindrical shank section of circular cross section, the front extremity of said blank being of lobular, arcuate, cross section of lesser diametrical width than said shank section and a tapered transition section between said shank and said extremity between a pair of thread-rolling dies each having a first die portion with die ridges and grooves for forming a substantially straight thread overlying the shank portion of said blank, a second die portion immediately adjacent said first die portion with ridges and grooves for forming a tapered thread overlying said transition section of said blank as a continuation of the thread on said sHank section, and a third die portion having a substantially unridged surface, applying thread-forming pressures simultaneously to said shank and said transition sections, and during said rolling operation causing said third die portions to engage the lobular extremity of said die blank and intermittently bend said extremity and said tapered transition section first away from one die and then away from the other while maintaining at least a substantial portion of the central axis of said shank section equally spaced from said dies, whereby the thread formed on said transition section is of arcuate lobular cross sectional shape.

Claim 9

The method of making a self-thread forming threaded fastener comprising the steps of: a. forming a blank with a cylindrical shank section of circular cross sectional shape, and a forward end section with cross sections in the shape of an arcuate, equilateral triangle including arcuate sides merging with intermediate arcuate lobes; b. rolling said blank between a pair of thread-rolling dies, each having a first ridged die surface portion for forming substantially complete threads on said shank section, a second ridged die surface portion having progressively wider, truncated ridges separated by grooves of progressively diminishing depth in the direction toward one edge of said die portion and defining a substantially flat die portion along said edge, the crests of all of said ridges and said substantially flat die portion extending in a straight line transversely of each said die; c. and during said rolling operation engaging said lobular end section of said blank with said flat die edge portions for deflecting the axis of at least said end section alternately toward first one and then the other of said dies during each revolution of said blank while maintaining at least a substantial portion of the axis of said shank section equally spaced from said dies, thereby forming a tapered thread on said end section having a substantially fully developed, sharp crest of arcuate, triangular pitch surface configuration.

Claim 10

The method of making a self-thread forming threaded fastener comprising the steps of: a. forming a blank with a cylindrical shank section of circular cross sectional shape, and a forward end section with cross sections in the shape of an arcuate, equilateral triangle including arcuate sides merging with intermediate arcuate lobes; b. rolling said blank between a pair of thread-rolling dies, each having a first ridged die surface portion for forming substantially complete threads on said shank section, a second ridged die surface portion having progressively wider, truncated ridges separated by grooves of progressively diminishing depth in the direction toward one edge of said die portion and defining a substantially flat die portion along said edge, the crests of all of said ridges and said substantially flat die portion extending in a straight line transversely of each said die; c. and during said rolling operation engaging said lobular end section of said blank with said flat die edge portions for deflecting the axis of at least said end section alternately toward first one and then the other of said dies during each revolution of said blank while maintaining at least a substantial portion of the axis of said shank section equally spaced from said dies, thereby forming a tapered thread on said end section having a substantially fully developed, sharp crest of arcuate, triangular pitch surface configuration.

Claim 15

The method of making a self-thread forming threaded fastener comprising the steps of: a. forming a blank with a cylindrical shank section of circular cross sectional shape, and forming an end portion on said blank adjacent said shank section of arcuate equilateral, triangular shape including arcuate sides merging with intermediate, arcuate lobes; b. providing a pair of cooperating thread-rolling dies each with a first ridged die surface portion for forming substantially uniform threads on said shank section and providing a second ridged die surface portion adjacent said first portion having progressively truncated ridges of increasing width separated by grooves of progressively diminishing depth in a direction toward one edge of said die, the crests of the truncated ridges being in a substantially straight line when viewed in profile transverse to the longitudinal directions thereof, whereby the die portion adjacent said edge is substantially smooth and lying in the same surface transversely of the die as that defined by said ridges; c. and rolling said blank between said dies causing said substantially smooth edge portions of said dies to engage said lobular end portion of said blank thereby bending the axis of at least said end portion and a portion of said shank section immediately adjacent said lobular end portion alternately first toward one and then toward the other of said dies during each revolution of said blank forming a tapered thread on said end portion of said blank with a lobular pitch surface configuration, and simultaneously forming the uniform threads on said shank section while maintaining at least a substantial extent of the axis of said shank section equally spaced from said dies.

Claim 16

The method of making a self-thread forming threaded fastener comprising the steps of: a. forming a blank with a cylindrical shank section of circular cross sectional shape, and forming an end portion on said blank adjacent said shank section of arcuate equilateral, triangular shape including arcuate sides merging with intermediate, arcuate lobes; b. providing a pair of cooperating thread-rolling dies each with a first ridged die surface portion for forming substantially uniform threads on said shank section and providing a second ridged die surface portion adjacent said first portion having progressively truncated ridges of increasing width separated by grooves of progressively diminishing depth in a direction toward one edge of said die, the crests of the truncated ridges being in a substantially straight line when viewed in profile transverse to the longitudinal directions thereof, whereby the die portion adjacent said edge is substantially smooth and lying in the same surface transversely of the die as that defined by said ridges; c. and rolling said blank between said dies causing said substantially smooth edge portions of said dies to engage said lobular end portion of said blank thereby bending the axis of at least said end portion and a portion of said shank section immediately adjacent said lobular end portion alternately first toward one and then toward the other of said dies during each revolution of said blank forming a tapered thread on said end portion of said blank with a lobular pitch surface configuration, and simultaneously forming the uniform threads on said shank section while maintaining at least a substantial extent of the axis of said shank section equally spaced from said dies.

Claim 20

A method of rolling the thread of a self-threading screw from a blank having a rear shank portion of circular cross section and front end portion having a cross section of arcuate, lobular shape of reduced thickness and including a tapered portion, said method including rolling the blank between opposed thread rolling dies that apply thread-forming pressure simultaneously to said rear shank portion and said tapered portion to form a thread thereon, and applying intermittent deflecting pressures to said front end portion during the thread rolling to bend the same relative to the axis of said rear shank portion and thereby periodically vary the distance of the axis of said front end portion to said dies.

Claim 21

A method of rolling the thread of a self-threading screw from a blank having a rear shank portion of circular cross section and front end portion having a cross section of arcuate, lobular shape of reduced thickness and including a tapered portion, said method including rolling the blank between opposed thread rolling dies that apply thread-forming pressure simultaneously to said rear shank portion and said tapered portion to form a thread thereon, and applying intermittent deflecting pressures to said front end portion during the thread rolling to bend the same relative to the axis of said rear shank portion and thereby periodically vary the distance of the axis of said front end portion to said dies.