| Major diameter correcting re-roll thread rolling die -> Monitor Keywords |
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Major diameter correcting re-roll thread rolling dieRelated Patent Categories: Metal Deforming, By Use Of Tool Acting During Relative Rotation Between Tool And Work About Internal Center (e.g., Gyrating Or Rotating Tool), During Rotation Of Work, Using Non-cylindrical Rotating Tool, Having Helical GrooveMajor diameter correcting re-roll thread rolling die description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060169015, Major diameter correcting re-roll thread rolling die. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED PATENT APPLICATION [0001] This application claims priority to commonly owned U.S. Provisional Patent Application Ser. No. 60/648,325; filed Jan. 28, 2005; entitled "Major Diameter Correcting Re-Roll Thread Rolling Die," by Michael A. Garver; which is hereby incorporated by reference herein for all purposes. TECHNICAL FIELD [0002] The present disclosure relates to fastener thread manufacturing dies, more particularly, to a major diameter correcting re-roll thread rolling die. BACKGROUND [0003] Referring to FIG. 1, in thread manufacturing today, threads are normally applied to externally threaded products such as bolts and machine screws by a process where the threads are formed by pressing dies 102, onto which the shape of the finished thread 104 has been impregnated into a cylindrical member 106. [0004] Referring to now FIG. 2, the metal of the cylindrical member 106 is progressively displaced by the pressing dies 102 as the cylindrical member 106 is rotated in a direction 208 between opposing faces of the dies 102a and 102b having proper shapes for forming the threads on the cylindrical member 106, similar to the action of rolling a pencil between one's hands as they are pressed together. [0005] Referring to now FIGS. 3A, 3B and 3C, in order to accomplish this, the shape machined into the dies 102 is a series of parallel grooves 310, cut diagonally across the face of the die 102. Each groove 310 has two flat sides 312a and 312b, each of these sides angled at approximately thirty degrees, such that the included angle between the two sides 312a and 312b of the grooves 310 is approximately sixty degrees. At the bottom of each of the grooves 310 is a flat surface 314, perpendicular to the plane forming the center of the groove 310, and intersecting each angled side 312a and 312b at approximately a thirty degree angle. [0006] Referring now also to FIGS. 4A, 4B and 5, when the metal of the cylindrical member 106, e.g., "work piece," to be threaded is pressed into the grooves 310, the cylindrical member 106 metal is displaced so as to fill the grooves 310 in the die 102. Depending on the pressure exerted, the cylindrical member 106, e.g., bolt or machine screw, may either partially fill the die groove 310 (represented by 416 of FIG. 4A) or completely fill the die groove (represented by 418 of FIG. 4B). If the pressure is great enough, the resulting shape of the work piece threads, e.g., 418, may have a shape substantially matching the shape of the groove 310 cut in the die 102. This may result in an external thread profile having two flanks 520a and 520b (FIG. 5) and a flat peak or "crest" 522 (FIG. 5). [0007] Referring to FIG. 6, as pressure is reduced, the sharp corners of the die 102 tend not to fill completely with metal. Rather than being "packed" into a sharp corner, the metal of the work piece 106 may flow naturally in an area where the corners had been. The thread profile may then appear to have a radius where the sharp corners had been, e.g., 624 shown in FIG. 6. As pressure continues to be reduced this natural flow eventually forms what appears to be a completely curved surface on the peak of the thread 418, linking both flanks and forming the "crest" 624 of the thread 418. Further reducing pressure may result in a curved surface degrading into a "ragged" appearing crest (726 of FIG. 7), then eventually, with lower pressure and because of lack of metal, the flanks 520a and 520b may themselves begin to degrade. Typically, standard externally threaded fasteners may tend to have some variant of these shapes on the crest of the threads. [0008] In fastener manufacture, production processes for both dies and threads have significant inherent variations. Because of these variations, it is very uncommon in the thread rolling process to completely fill the corners of the die groove as first discussed above and shown in FIG. 4B. What is more common, are various degrees of corner fill depending upon the tolerances of the cylindrical work piece 106 and dies 102, and the amount of pressure applied during actual production thereof. [0009] Due to this phenomenon, die manufacturing specifications are such that it is assumed the that the normal result of the rolling process will not be a thread profile with sharp corners, e.g., crest 522 of FIG. 5, but some variant of the crest shape discussed above and shown in FIGS. 6 and 7. The most common shape seen in commerce today is the "fully radiused" crest 624 shown in FIG. 6. [0010] In order to allow this condition, commonly known as "underfill" of the die, the depth of the flat bottom of the groove in the die is normally made deeper than expected. Thus, there is "extra" room in the die, so that any metal forming the curved crest seen on the resulting thread profile 828 of the work piece shown in FIG. 8, exceeds the metal required to obtain the minimum flank height of the thread profile represented by 830 of FIG. 8. This, therefore, insures that the thread flanks 520a and 520b are high enough to meet minimum thread strength characteristics while allowing for excess metal flow. [0011] Thread rolling die specifications, therefore, are set up not to match the desired shape, but to exceed the specified envelope of the minimum height of the actual thread profile, as designated in ISO and other thread standard specifications, incorporated by reference herein for all purposes. Minimum flank height and thread strength required by the specification thereby may be maintained. [0012] Referring to now to FIG. 9, depicted is a comparison of an M8.times.1.25 6 g external thread tolerance envelope (on the right) and the accompanying die dimension envelope (on the left). Note that the die envelope shows the desired die tolerances 932, shown solid black, along with the permissible die movement allowed by thread pitch diameter tolerances 934. The thread envelop is shown with its entire permissible major, minor and pitch diameter variations shaded and represented as 936. Note that the peak of the die specification, when adjusted to maximum pitch diameter may significantly exceed the maximum permissible major diameter of the thread. [0013] The threads formed thusly, therefore tend to have a major diameter (for practicality, measured across the rounded crests of the threads) that is larger than expected for a thread of that pitch diameter. These threads also have smaller flank height than expected for such a major diameter. It, in fact, means that external threads produced with dies made to present day die specifications can, within the permissible range of pitch diameters, exceed the permissible major diameter of the thread, while having flank heights that are within specification. This potentially leads to internal/external thread interference in use. This often leads manufacturers to make their fasteners to the low end of the pitch diameter range, in order that the measured major diameter does not exceed the maximum specification. It also means that threads produced deliberately to the low end of the pitch range to allow for thick plating on the surface of the thread, potentially have flank height below that required for minimum strength requirements. SUMMARY [0014] Therefore, there is a need for a method of and apparatus for manufacturing threads that do not ultimately result in an undesirable rounded crest, thus allowing thread major diameters to be made to the specified diameter, with sharp flank-crest interfaces and no excess metal beyond said diameter, while not significantly affecting the current thread manufacturing process. Such a method of and apparatus for manufacturing threads would guarantee intended thread strength characteristics across the entire range of possible thread and die dimensional envelopes, thus allowing threads to be deliberately manufactured to the lower end of the pitch diameter range to permit painting and/or plating of the fastener and also allow interfaces with painted internal threads. [0015] According to a specific example embodiment of the present disclosure, an apparatus for rolling threads on a cylindrical work piece and having major diameter thread crest correction may comprise a first die set for rolling threads on a cylindrical work piece, wherein the first die set has thread forming grooves at a first depth; and a second die set for re-rolling the threads on the cylindrical work piece, wherein the second die set has thread forming grooves at a second depth, wherein the second depth is less than the first depth. The second die set thread forming grooves may reshape a crest of the threads on the cylindrical work piece to a desired height. The second die set thread forming grooves may reshape a crest of the threads on the cylindrical work piece to a desire shape. The second die set thread forming grooves may reshape a crest of the threads on the cylindrical work piece to a substantially flat peak. [0016] According to another specific example embodiment of the present disclosure, an apparatus for rolling threads on a cylindrical work piece and having major diameter thread crest correction may comprise a die set for rolling threads on a cylindrical work piece, wherein the die set has a first portion with thread forming grooves at a first depth, and a second portion with thread forming grooves at a second depth, wherein the second depth is less than the first depth; wherein during thread rolling on the cylindrical work piece in the first portion of the die set the thread crests are at substantially the first depth, and during thread rolling on the cylindrical work piece in the second portion of the die set the thread crests are at substantially the second depth. The second portion with thread forming grooves at the second depth may reshape a crest of the threads on the cylindrical work piece to a desired height. The second portion with thread forming grooves at the second depth may reshape a crest of the threads on the cylindrical work piece to a desired shape. The second portion with thread forming grooves at the second depth may reshape a crest of the threads on the cylindrical work piece to a substantially flat peak. [0017] According to yet another specific example embodiment of the present disclosure, an apparatus for rolling threads on a cylindrical work piece and having major diameter thread crest correction may comprise a die set for rolling threads on a cylindrical work piece, wherein the die set comprises a plurality of portions having progressively smaller groove depths, whereby during thread rolling the cylindrical work piece has thread crest heights at substantially the groove depths of each of the plurality of portions of the die set and at the end of thread rolling has a thread crest height at substantially a groove depth of a last one of the plurality of portions of the die set. The thread forming grooves of the last one of the plurality of portions of the die set are at a depth and shape whereby the crest of the threads on the cylindrical work piece are reshaped to a desired height. The thread forming grooves of the last one of the plurality of portions of the die set are at a depth and shape whereby the crest of the threads on the cylindrical work piece are reshaped to a desired shape. The thread forming grooves of the last one of the plurality of portions of the die set are at a depth and shape whereby the crest of the threads on the cylindrical work piece are reshaped to a substantially flat peak. [0018] According to still another specific example embodiment of the present disclosure, a method for rolling threads on a cylindrical work piece and for correcting a major diameter thread crest may comprise the steps of rolling threads on a cylindrical work piece with a first die set, wherein the first die set has thread forming grooves at a first depth; and re-rolling the threads on the cylindrical work piece with a second die set, wherein the second die set has thread forming grooves at a second depth, wherein the second depth is less than the first depth. The step of re-rolling the threads on the cylindrical work piece with the second die set may include the step of reshaping a crest of the threads on the cylindrical work piece to a desired height. The step of re-rolling the threads on the cylindrical work piece with the second die set may include the step of reshaping a crest of the threads on the cylindrical work piece to a desired shape. The step of re-rolling the threads on the cylindrical work piece with the second die set may include the step of reshaping a crest of the threads on the cylindrical work piece to a substantially flat peak. [0019] According to another specific example embodiment of the present disclosure, a method for rolling threads on a cylindrical work piece and for correcting a major diameter thread crest may comprise rolling threads on a cylindrical work piece with a die set, wherein the die set comprises a first portion with thread forming grooves at a first depth, and a second portion with thread forming grooves at a second depth, wherein the second depth is less than the first depth; wherein during the step of rolling threads in the first portion of the die set the cylindrical work piece has thread crests at substantially the first depth and during the step of rolling threads in the second portion of the die set the cylindrical work piece has thread crests at substantially the second depth. The step of rolling threads in the second portion of the die set may include the step of reshaping a crest of the threads on the cylindrical work piece to a desired height. The step of rolling threads in the second portion of the die set may include the step of reshaping a crest of the threads on the cylindrical work piece to a desired shape. The step of rolling threads in the second portion of the die set may include the step of reshaping a crest of the threads on the cylindrical work piece to a substantially flat peak. [0020] According to yet another specific example embodiment of the present disclosure, a method for rolling threads on a cylindrical work piece and for correcting major diameter thread crests may comprise the steps of rolling threads on a cylindrical work piece with a die set, wherein the die set comprises a plurality of portions with thread forming grooves at progressively smaller depths; wherein during the step of rolling threads on the cylindrical work piece the threads are formed to a desired shape. The step of rolling threads may include the step of reshaping a crest of the threads to a desired height. The step of rolling threads may include the step of reshaping a crest of the threads to a substantially flat peak. Continue reading about Major diameter correcting re-roll thread rolling die... Full patent description for Major diameter correcting re-roll thread rolling die Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Major diameter correcting re-roll thread rolling die patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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