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AssigneeResearch Engineering & Manufacturing, Inc.
InventorHerman G. Muenchinger
Estimating the term…
A thread-forming screw has a work-entering section for forming a thread in a workpiece and a work-holding section adjacent thereto. Both sections are of an arcuate, polygonal lobular configuration in cross-section. The amount of lobulation on the holding section is considerably less than the lobulation on the work-entering section, which is of such magnitude as to insure effective thread-forming at low torque. The lobulation on the holding section is preferably just sufficient to effect a locking action with the thread of the workpiece and also to improve the stripping torque of the screw from the workpiece. The work-entering end of the fastener also has a pilot thread of about one turn and with a uniform width over 360.degree. and sized approximately the same as the pilot hole in the workpiece to prevent cocking of the fastener as it is initially inserted into the pilot hole. Thread-rolling dies for forming the fastener have a die section with grooves of equal depth to roll the pilot thread.
A thread-forming fastener having a work-entering section and a work-holding section, each section having more than one thread turn, a continuous roll thread on both said work-entering and work-holding sections, the thread formation on said work-entering section being tapered and having a pitch cross section in the form of a generally arcuate polygon with an odd number of arcuate sides merging gradually with intermediate thread-swaging lobes, the thread formation on said work-holding section also having a pitch cross section in the form of a generally arcuate polygon with an odd number of arcuate sides merging gradually with intermediate lobes, the number of sides and lobes in said holding section being respectively the same as the number of sides and lobes in said work-entering section, the radii of curvature of the sides in each section being substantially greater than the radii of curvature of the lobes in that section, and the lobulation in the holding section being substantially less than the lobulation in said work-entering section, said lobulation being defined as the maximum distance from the crest of the thread at an arcuate side to the circle that inscribes the crests of the thread at the adjacent lobes, the lobulation in said work-entering end being sufficient to provide a low torque thread-forming action in a workpiece, the lobulation in the holding section being a sufficient departure from a circular configuration to enhance in the holding section thread a locking action and an increase in the stripping torque when threaded into such workpiece, and a pilot thread section on said work-entering section intermediate the larger end of the tapered thread formation and the work-entering tip of the fastener for aligning the axis of the fastener with the axis of a hole in a workpiece when the pilot thread is inserted therein, said pilot thread section having a crest cross section of substantially uniform width throughout 360.degree. and extending for at least approximately one thread turn.
A thread-forming fastener having a work-entering section and a work-holding section, each section having more than one thread turn, a continuous roll thread on both said work-entering and work-holding sections, the thread formation on said work-entering section being tapered and having a pitch cross section in the form of a generally arcuate polygon with an odd number of arcuate sides merging gradually with intermediate thread-swaging lobes, the thread formation on said work-holding section also having a pitch cross section in the form of a generally arcuate polygon with an odd number of arcuate sides merging gradually with intermediate lobes, the number of sides and lobes in said holding section being respectively the same as the number of sides and lobes in said work-entering section, the radii of curvature of the sides in each section being substantially greater than the radii of curvature of the lobes in that section, and the lobulation in the holding section being substantially less than the lobulation in said work-entering section, said lobulation being defined as the maximum distance from the crest of the thread at an arcuate side to the circle that inscribes the crests of the thread at the adjacent lobes, the lobulation in said work-entering end being sufficient to provide a low-torque thread-forming action in a workpiece, the lobulation in the holding section being a sufficient departure from a circular configuration to enhance in the holding section thread a locking action and an increase in the stripping torque when threaded into such workpiece, the lobulation in each section being substantially a function of the diameter of the stress area of the fastener, said stress area being defined as the area of a circle whose diameter is the mean of the pitch diameter and the root diameter of the thread, which root diameter is measured at the point of maximum root diameter at a lobe in said holding section, and in which the range of lobulation of the work-entering section is as follows:
A thread-rolling die for forming a self-threading fastener having a holding section and a work-entering section, said work-entering section having a tapered thread-swaging thread formation and a non-tapered pilot thread formation between the larger end of said thread-swaging formation and an adjacent work-entering tip of the fastener, said pilot thread formation being of uniform width throughout 360.degree. and extending axially at least approximately one thread turn;
Dependencies are inferred from the claim text.