HK1233578B - Hollow metal screw and method of making - Google Patents

Description

Hollow metal screw and manufacturing method thereof

Technical Field

The present invention generally relates to a lightweight hollow stainless steel metal screw design, particularly for aerospace applications, and an associated method for manufacturing the hollow metal screw. The hollow metal screw is formed by stamping from a generally circular sheet metal disc in one or more steps to form a hollow tubular head and shank having a wall thickness of 0.2 to 0.7 mm. The shank is then annealed to soften the shank for thread rolling, after which the hollow metal screw is sufficiently hardened to meet aerospace thread strength requirements in a screw that is lighter than a similarly sized solid screw, thereby contributing to aircraft fuel economy.

Background Art

Screws are generally known in the art and tend to include a solid core rod onto which is rolled to form a set of threads having a specified pitch and length. Generally, high strength corrosion resistant steel (CRES) material is preferred as the screw material because the threads of the hardened CRES can be repeatedly reinstalled into a threaded hole socket without thread damage. However, CRES constitutes a relatively heavy metal material and therefore does not contribute to aircraft fuel economy, especially when a typical aircraft includes thousands of such screws. Attempts to use lighter weight metals, such as solid core aluminum or titanium screws, have been limited in the ability of a mechanic to repeatedly install and remove the same screw without damaging the threads due to thread galling.

In the past, threaded screws included either a solid core or a hollow screw supported by a core insert of plastic, etc. Unfortunately, the plastic core insert added at least some weight, thereby still limiting the screw's contribution to aircraft fuel economy.

The present invention comprises an improved hollow corrosion-resistant metal screw wherein the screw is stamped from a generally circular disk of a selected corrosion-resistant metal material to provide a shank wall thickness of 0.2 to 0.7 mm, subsequently annealed to soften the metal material, then subsequently thread rolled and then hardened to provide a hollow metal screw having thread strength sufficient to withstand most aerospace applications, and contributes to aircraft fuel economy by providing a hollow screw having corrosion-resistant metal threads that is approximately 50% the weight of a solid core screw made of the same material. The present invention satisfies these needs and provides further advantages.

Summary of the Invention

One embodiment of the hollow screw disclosed herein includes a head and an elongated hollow shaft extending from its entirety and formed by a flat blank of a metal material. The elongated hollow shaft includes a rod portion and a threaded portion having a plurality of threads thereon. The rotary drive mechanism can be formed integrally from a flat blank of a metal material and coupled with the head or the elongated hollow shaft, and configured to facilitate tightening the hollow screw by thread. In one embodiment, the rotary drive mechanism is a polygonal shape formed from a flat blank of a metal material, wherein the polygonal shape may include an external polygonal shape (e.g., a hexagonal shape). Alternatively, the rotary drive mechanism may include an internal recess (e.g., a spline or a cross-shaped recess) formed by the head. This recess may be formed as a flat head or a round head.

In another aspect of this embodiment, the integral washer can be formed from a flat blank of a metal material and extend outwardly from the head. A captive washer can be at least partially formed around the integral washer in a manner that allows the captive washer to rotate freely relative to the integral washer, the head, and the elongated hollow shaft. More specifically, the outer edge of the captive washer can be upward and around the outer periphery of the integral washer to attach the captive washer adjacently around the integral washer for clamping the integral washer therein. In one embodiment, the captive washer can include a conductive material and have a thickness of approximately 0.15 to 0.30 mm.

In other aspects of this embodiment, the hollow screw can include an elongated hollow body having a constant diameter. In this embodiment, the outer diameter of the threads is larger than the outer diameter of the smoother shank portion. Here, when added before rolling the threads, the free-floating washer can slide along the shank portion and be captured between the integral washer and the threaded portion. Alternatively, the elongated hollow body can be formed from a shank portion having a first diameter that is relatively larger than a second, smaller diameter, redrawn portion, wherein the threads are imparted to the redrawn portion during the rolling step.

In one embodiment, the resulting hollow screw can be made from a flat stock of a metallic material, including a corrosion-resistant metallic material (e.g., A286 steel), wherein the elongated hollow shaft comprises a wall thickness of approximately 0.2 to approximately 0.7 mm, the threads have a strength of approximately 1200 MPa to 1400 MPa, and the weight of the hollow screw is approximately 1/2 the weight of a solid screw of similar size and shape. Furthermore, a nose can be formed at the end of the elongated hollow shaft opposite the head. In another aspect, the elongated hollow shaft can further include a cap at the end opposite the head, the cap being configured to prevent fluid from flowing through the body of the hollow screw.

In another embodiment, a hollow screw as disclosed herein may include a head formed from a flat blank of metal material and an elongated hollow shaft formed from the flat blank of metal material and extending integrally from the head. In one embodiment, the elongated hollow shaft may include a shank portion and a threaded portion having a plurality of threads thereon. Preferably, the threads have a strength of approximately 1200 MPa to 1400 MPa. The threaded portion may be longer than the shank portion, and the major diameter of the threads may be greater than the diameter of the shank portion. Alternatively, an integral washer may be formed from a flat blank of metal material and have an increased horizontal surface area extending radially outward from the head. A locking washer may be positioned below the increased horizontal surface area and (optionally) have an outer edge that curves approximately around the periphery of the integral washer, at least partially sandwiching the integral washer therebetween. In another aspect of this embodiment, a wave washer may be sandwiched between the locking washer and the increased horizontal surface area of the integral washer. In either embodiment, the locking washer is free to rotate relative to the integral washer. To this end, a rotary drive mechanism integrally formed from a flat blank of metal material and connected to the head or elongated hollow shaft may be configured to facilitate tightening of the hollow screw via the threads and surrounding lock washers.

In one embodiment, the shank portion and the threaded portion of the elongated hollow shaft have a wall thickness of between about 0.2 and about 0.7 millimeters, and the lock washer is made of a conductive material having a thickness of about 0.15 to 0.30 millimeters. In another embodiment, the rotary drive mechanism can include an external polygonal shape or an internal recess formed in the head from a flat blank of metal material, wherein the external polygonal shape is a hexagon and the internal recess is a spline recess.

Alternatively, the rotary drive mechanism may include an internal recess stamped into the base of the elongated hollow shaft and from a flat blank of metal material. In this embodiment, a nose may be formed at this end, particularly when the head is rounded or flat. Here, the elongated hollow shaft has a cap to prevent flow through the body of the hollow screw. Preferably, the flat blank of metal material is a corrosion-resistant metal material, such as A286 steel.

In another embodiment, a hollow screw as disclosed herein may include a head formed from a corrosion-resistant flat stock metal material, such as A286 steel. An elongated hollow shaft having a wall thickness of about 0.2 to about 0.7 mm may also be formed from a corrosion-resistant flat stock metal material and extend from the head. The elongated hollow shaft preferably includes a rod portion and a threaded portion having a plurality of threads thereon, wherein the threads have a strength between about 1200 MPa and 1400 MPa. The hollow screw may also include a rotational engagement mechanism, such as a polygonal shape or recess formed by the head or the elongated hollow shaft, and configured to allow the hollow screw to be tightened by threads. Preferably, the rotational engagement mechanism is also formed from a corrosion-resistant flat stock metal material and may include a hexagonal head or a splined recess.

In another aspect of this embodiment, the hollow screw may also include an integral washer formed by the head and having an enlarged horizontal and generally circular surface area extending radially outward from the head. The lock washer is then positioned adjacent to the enlarged horizontal surface area, wherein the outer edge is bent roughly around the outer periphery of the integral washer to at least partially clamp the integral washer therein. The lock washer is able to rotate freely relative to the integral washer and the screw body. In one embodiment, the lock washer can have a thickness of 0.15 to 0.30 mm and be made of conductive material. In addition, the elongated hollow shaft may include a capped and tapered nose having a spline recess and positioned at the end opposite to the head. In this aspect, the head preferably includes a round head, a flat head or a tapered head, rather than a polygonal head similar to the hexagonal head described above.

A method for manufacturing a hollow screw as disclosed herein includes a step for forming a shallow cup having a rough-cut flange extending radially outward at one end thereof, the shallow cup being formed from a generally flat metal material, such as a generally circular blank stamped from a flat coil of a corrosion-resistant material such as A286 steel. An elongated, hollow body having a wall thickness of about 0.2 to about 0.7 mm can be extruded from the shallow cup. Then, as part of a clamping and flattening step, the roughly radially outward extending rough-cut flange can be trimmed and flattened to the desired size and shape of the screw head (e.g., a flat head or a round head). Next, the hollow screw can be annealed by heating the hollow screw at an elevated temperature of about 950-980 degrees Celsius for about 1 hour to soften at least the elongated hollow body to a Rockwell hardness of about 79. Thereafter, a plurality of threads may be rolled onto at least a portion of the exterior of the softened elongated and hollow body, thereby forming the elongated and hollow body into a substantially smooth shank portion and a threaded portion, and then in a final step, the hollow screw may be final hardened by precipitation hardening at a temperature of about 690-720 degrees Celsius for about 16 hours. In one embodiment, the hollow screw may have a final hardness of about 42 Rockwell C, and the threads may have a strength of about 1200-1400 MPa and be about 1/2 the weight of a solid core screw having sufficient thread strength.

In addition, the method may include redrawing the elongated hollow body into a rod portion and a redraw portion, the outer diameter of the redraw portion being narrower than the outer diameter of the rod portion. In addition, the screw head can be inverted into a roughly central curved dome with an outwardly extending skirt, and then reconstructed into an external polygonal shape, and the skirt punched into an integral washer. In addition, the freely formed washer can be formed as a lock washer on the integral washer. Splines or cross-shaped recesses can be further punched into the screw head as a rotational drive mechanism. During the rolling step, a stabilizing pin can be inserted into the elongated hollow body. The outer diameter of the stabilizing pin is preferably approximately the same size as the inner diameter of the threaded portion of the elongated hollow body. Thus, the stabilizing pin provides support for the inner circumferential wall to prevent it from collapsing inward during the rolling step. In other aspects of the method, a circular nose can be formed from one end of the elongated hollow body, and a recess formed at the bottom can be punched into the closed end of the elongated hollow body.

In another embodiment of the method for manufacturing a hollow screw disclosed herein, the method steps may include forming an elongated hollow body having a wall thickness of approximately 0.2 to approximately 0.7 mm from a generally flat metal material. One end of the elongated hollow body is then clamped and flattened into the desired size and shape of the screw head. The hollow screw is then annealed at an elevated temperature of approximately 950-980°C for approximately 1 hour to soften the elongated hollow body and the screw head. Next, a plurality of threads are rolled onto at least a portion of the exterior of the softened elongated hollow body, and the hollow screw is finally hardened to a hardness of approximately 42 Rockwell C, with the threads having a strength of approximately 1200–1400 MPa.

The method may further include the steps of: stamping a generally circular blank from a flat roll blank of a corrosion-resistant material (e.g., A286 steel); redrawing the elongated hollow body into a rod portion and a redraw portion having an outer diameter narrower than the outer diameter of the rod portion; inserting a stabilizing pin into the elongated hollow body; and rolling the threads onto the exterior or outer surface of the elongated hollow body. As described above, the outer diameter of the stabilizing pin may be approximately the same size as the inner diameter of the threaded portion of the elongated hollow body, so that the stabilizing pin can support the peripheral wall thereof to prevent collapse when the threads are rolled.

In other aspects of the method, the screw head can be inverted into a roughly central curved dome with an outwardly extending skirt. Next, the roughly central curved dome can be reconfigured into an outer polygonal shape (e.g., a hexagon). Thereafter, the skirt can be stamped into an integral washer, wherein the free-formed washer inserted into the elongated hollow body can have an outer edge that is curved on the periphery of the integral washer to at least partially clamp the integral washer therein. In addition, a rotary drive mechanism can be imparted to the hollow screw, for example by stamping a threaded recess or a cross-shaped recess into the screw head or typing a recess formed at the bottom into the nose. In another aspect of the method, a circular nose can be formed from one end of the elongated hollow body.

Another method for making a hollow screw may include: forming a shallow cup from a generally circular, flat metal material and having a rough-cut flange extending radially outward at one end thereof, extruding an elongated, hollow body from the shallow cup, clamping and flattening the rough-cut flange extending radially outward to a desired size and shape for the screw head, inverting the screw head into a centrally curved dome with an outwardly extending skirt, reshaping the centrally curved dome into a polygonal shape, stamping the skirt into an integral washer, annealing to soften at least the elongated, hollow body, inserting a stabilizing pin into the elongated, hollow body, the stabilizing pin having an outer diameter approximately the same size as the inner diameter of the elongated, hollow body to support a peripheral wall therein, rolling a plurality of threads into at least a portion of the exterior of the softened, elongated, hollow body after the inserting step, stamping a spline recess into the screw head, and hardening the hollow screw.

Additionally, the method may include redrawing the elongated hollow body into a rod portion and a redraw portion having an outer diameter narrower than the outer diameter of the rod portion, stamping a generally circular blank from a flat coil of a corrosion-resistant material including A286 steel, wherein the elongated hollow body comprises a wall thickness of approximately 0.2 to approximately 0.7 millimeters. Furthermore, the hollow screw may be heated at an elevated temperature of approximately 950-980 degrees Celsius for approximately one hour and precipitation hardened at a temperature of approximately 690-720 degrees Celsius for approximately 16 hours, wherein the threads of the hollow screw have a hardness of approximately 42 Rockwell C after the precipitation hardening step and the threads comprise a strength of approximately 1200-1400 MPa. Furthermore, prior to the rolling step, a washer may be inserted into the elongated hollow body, allowing the washer to float freely between the integral washer and the threads. Additionally, a circular nose may be formed from one end of the elongated hollow body and formed with a recessed portion for mounting as a base for the rotary drive mechanism.

In another aspect of the embodiments disclosed herein, a hollow nut may include a body having an internally threaded core and a first end having a radially outwardly extending flange. A lock washer is formed at least partially around the radially outwardly extending flange, generally adjacent to the first end, and allows free rotation relative to the nut when attached thereto, the lock washer having an inner bore diameter larger than the internally threaded core to allow insertion of a threaded fastener. In this embodiment, a wave washer may also be sandwiched between the lock washer and the first end having the radially outwardly extending flange. Preferably, the body is formed from a flat blank of metal material.

Another embodiment of a hollow nut includes: a body having an internally threaded core, at least one end of the internal core having a radially extending flange; a wave washer positioned substantially adjacent the at least one end; and a lock washer formed at least partially around the radially outwardly extending flange and generally sandwiching the wave washer therebetween, wherein the lock washer is freely rotatable relative to the wave washer and the radially extending flange.

Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In these drawings:

FIG1 is a perspective view of one embodiment of a hollow screw as disclosed herein;

FIG2 is a flow chart showing a series of process steps for making hollow screws such as those shown in FIG1 , 16-21 and 25 ;

FIG3 is a fragmentary perspective view illustrating an initial cutting step in which a generally circular and flat blank is cut from a flat stock of metal material;

FIG4 is a partial perspective view of a circular blank being stamped into the shape of a shallow cup having a generally rough cut flange and an extruded cup body;

5 is a partial perspective view showing the extrusion step of forming an elongated hollow body having a wall thickness on the order of about 0.2 to 0.7 mm;

6 is a partial perspective view showing the redrawing step of forming a reduced diameter or redrawn portion at the lower end of the elongated body;

FIG7 is a partial perspective view showing the clamping and flattening steps of trimming and flattening the head;

FIG8 is a partial perspective view showing the inversion step of forming a dome-shaped head with an unfinished skirt protruding downward;

FIG9 is a partial perspective view showing the reconstruction step of forming a hexagonal head and an integral washer;

FIG10 is a fragmentary perspective view similar to FIG9 showing a stamping step for forming an internal drive recess;

FIG11 is a partial perspective view showing a thread rolling process;

12 is a partial perspective view showing the installation step, in which the lock washer is stamped onto the integral washer of the hollow screw head;

FIG13 is a fragmentary perspective view similar to FIG12 showing an alternative installation step for stamping the lock washer to the integral washer;

FIG14 is a partial perspective view showing a deformation step, with one end of the threaded hollow screw rounded into a tapered nose;

15 is a partial perspective view showing the step of punching a recess formed in the inner bottom of the nose;

FIG16 is a partial cross-sectional perspective view of the hollow screw of FIG1;

FIG17 is a perspective view, partially in section, of an alternative hollow screw having an elongated body shorter than that of FIG16, a threaded portion larger than the smooth shaft portion, and a freely formed washer thereon;

FIG18 is a perspective view, partially cut away, of another hollow screw having a flat head, a rounded nose, and a recess stamped into the interior bottom thereof;

FIG19 is a perspective view, partially cut away, of an alternative hollow screw similar to that of FIGS. 16 and 17 , showing a substantially circular head in place of a hexagonal head;

FIG20 is a partial cutaway perspective view of another alternative embodiment of a hollow screw similar to FIG1 , FIG16 and FIG17 , showing a separate integral washer;

21 is a partial cutaway perspective view of another embodiment of a hollow screw including a flat head that mounts flush with a surface according to embodiments disclosed herein;

FIG22 is a cross-sectional view of one embodiment of a hollow screw having threads formed into a narrower redraw portion;

FIG23 is a cross-sectional view of another embodiment of a hollow screw having threads formed into an elongated body of constant diameter;

FIG24 is another cross-sectional view similar to FIG23 showing the locking placement of the free-form washer between the integral washer and the threads;

FIG25 is a perspective view of the hollow screw of FIG1 , further comprising a wave washer;

FIG26 is a cross-sectional view taken about line 26-26 in FIG25 with a lock washer added, illustrating the clamping relationship of the wave washer between the integral washer and the lock washer;

FIG27 is a diagram showing an alternative embodiment of a lock washer mounted to a nut; and

28 is an embodiment similar to FIG. 27 showing the wave washer sandwiched between the nut and the collar washer.

DETAILED DESCRIPTION

As shown in the exemplary drawings, one embodiment of a hollow screw according to the present disclosure is generally designated by reference numeral 10 in FIG. 1 . As shown in FIG. 1 , this embodiment of the hollow screw 10 includes an elongated body 12 (e.g., made of a corrosion-resistant metal or steel material) having a smooth shank portion 14 and a threaded portion 16 having a plurality of threads 18 thereon; a head 20; and a generally hollow interior, designated therein as a hollow shaft 22, which may be capped at one end to prevent fluid from flowing through the hollow shaft 22. In this embodiment, the hollow screw 10 also includes an integral washer 24, preferably generally formed from a portion of the head 20, and a lock washer 26, which is optionally added to the hollow screw 10 during the stamping step, as described in more detail below. The lock washer 26 is freely rotatable relative to the integral washer 24 to prevent the head 20 of the hollow screw 10, and in particular the integral washer 24, from becoming lodged in an external mounting surface into which the hollow screw 10 may be inserted and used, such as in aerospace applications. In this embodiment, the head 20 is in the shape of a hexagonal nut and can be used alone or in combination with an internal recess 28 (such as a spline or cross-shaped recess or depression) for the purpose of rotationally tightening the hollow screw 10 according to known tools and embodiments disclosed herein.

The resulting hollow screw 10 can include a lightweight structure that is easy to install, remove, and reinstall, and significantly contributes to the overall fuel economy of the aircraft. In addition, the threaded portion 16, and in particular the threads 18, are preferably able to meet most aerospace strength requirements in an acceptable manner. To this end, the hollow screw 10 and the associated method steps for manufacturing the screw 10 and its variations, such as those shown in Figures 16 to 25, are generally shown in the flow chart of Figure 2, and more specifically with reference to Figures 3-15. The hollow screw 10 provides greater thread strength to resist wear during removal or reinstallation, and is approximately 1/2 the weight of a solid screw.

With respect to the manufacturing process, FIG2 is a flow chart illustrating a general process (200) for forming one or more variations of the hollow screw 10 as disclosed herein. For example, in a first step (202), a flat strip of stainless steel stock 30 (e.g., A286 corrosion-resistant steel, etc.) may initially be fed to a punch press, etc. (generally shown in FIG3 ) to cut a plurality of circular blanks 32 using a punch 34. Each circular blank 32 is then punched into a shallow cup 38 of a selected size and shape as part of step (204) using one or more structures, which may utilize one or more punching tools 36 of the type generally shown in FIG4 . The shallow cup 38 shown in FIG4 includes a roughly cut upper flange 40 extending generally radially outward and a shorter extruded cup 42. The shallow cup 38 is then processed as part of an extrusion step (206) in FIG5 , wherein the extruded cup 42 is extended in one or more structures by an extrusion tool 44 to the approximate size and shape of the elongated body 12 of the final hollow screw 10. Of course, the extrusion step (206) may use one or more extrusion tools 44, whose size and shape will of course depend on the final size and shape characteristics of the hollow screw 10 and as part of one or more structures to obtain the desired workpiece 46 suitable for the next step (208).

In this regard, the subsequent redrawing step (208) is optional. As shown in more detail in Figure 6, step (208) includes redrawing the narrower or redrawn portion 48 from the otherwise uniform diameter elongated body 12 as shown in the workpiece 46'. Step (208) essentially divides the elongated body 12 into two main parts, the smooth shaft portion 14 and the narrower and still smooth redrawn portion 48, as shown in Figure 6. Whether step (208) is performed depends on whether the outer diameter of the threads 18 of the resulting threaded portion 16 is the same (Figure 22) or larger (Figures 23 and 24) relative to the smooth shaft portion 14, as described in more detail below. Although it is preferred that the entire elongated body 12 has a wall thickness of about 0.2 to about 0.7 mm, the outer diameter of the smooth shaft portion 14 can be different from the outer diameter of the redrawn portion 48 (and the resulting threads 18).

The next clamping step (210) is compatible with both variants as described above, i.e., the workpiece 46 having an elongated rod 12 of constant diameter (not shown in FIG. 7 ) or the workpiece 46 ′ having an elongated rod 12 with a redraw portion 48 (shown in FIG. 7 ). In general, the subsequent steps (212)-(228) are also compatible with both workpieces 46 , 46 ′. The only difference is with respect to the outer diameter of the rod portion 14 relative to the threaded portion 16 and, in particular, the threads 18 , as shown and described in more detail below with reference to FIG. 22-24 . In step (210), the head 20 is shown as being clamped and flattened. As shown in FIG. 7 , the rough-cut flange 40 can be trimmed to the overall desired size and shape by a single punching tool 50, or by clamping the workpieces 46 , 46 ′ in one step with one tool and punching the workpieces 46 , 46 ′ in another step with another tool. Of course, the clamping and punching steps can involve multiple forming steps. To this end, either way, the rough cut flange 40 is cut away from the head 20, and the head 20 is stamped into a generally flat head 54. FIG. 7 shows the rough outer edge portion 52 cut away from the head 20 and discarded. The flat head 54 can be the same as or substantially similar to the flat head 54 shown in the final hollow screw 10″ of FIG. 18. The tool blank 56 below is shown having a shape and structure suitable for insertion into a workpiece 46′ having an elongated body 12 with a shank portion 14 and a narrower redraw portion 48, but the tool blank 56 can be modified to include a constant diameter tool blank to match the size and shape of a workpiece 46 having an elongated body 12 of a constant diameter, or any other such embodiment having various sizes, shapes and/or diameters.

As shown in the flowchart of FIG2 , the next step (212) is to invert the flat head 54 to form a generally inverted central curved dome 58, as generally shown in FIG8 . The overall size and shape of the curved dome 58 can be achieved in one or more forming steps as part of the inversion step (212), depending on the desired shape and size of the curved dome 58. In addition, FIG8 shows a generally outwardly extending skirt 60 formed at the bottom of the curved dome 58. The skirt 60 can be formed into the above-mentioned integral gasket 24 in a subsequent step or multiple forming steps as described herein, as briefly mentioned above. Similarly, this step (212) can be used with the workpieces 46, 46 '.

The next step (214) is to use a punching tool 64 of opposite size and shape to optionally reshape the curved dome 58 into an outer polygonal shape 62, as shown in FIG9 . Similarly, step (214) can be completed in one or more forming steps, depending on the size, shape, and desired application of the finished product. In the embodiment shown in FIG9 , the curved dome 58 is punched into a standard polygonal shape 62 of a selected size and shape (e.g., hexagonal) for use with a hexagonal wrench or the like. However, the curved dome 58 can be punched into other keyed shapes or polygons, as can be known in the art, and suitable for rotation by a standard key or the like. Of course, the polygonal shape 62 can be any shape or size known in the art to provide keyed rotation of the hollow screw 10 . Also as part of step (214), and as part of one or more forming steps, the outer skirt 60 can be generally formed into the size and shape of the integral washer 24 , as shown herein with reference to FIG1 , 16 , 17 , and 20 .

In addition to or in lieu of step (214), as part of step (216), an internal recess 28 may be formed. For example, FIG. 10 shows the head 20 being stamped by a spline die 66 to form its inner surface into the shape of the internally formed recess 28. In this embodiment, the internal recess 28 is the size and shape of a spline recess, suitable for rotation by a standard spline, etc. Of course, the internal recess 28 may be any shape or size known in the art to provide keyed rotation of the hollow screw 10. The hollow screw may include only the outer polygonal shape 62 (e.g., FIG. 25), only the internal recess 28 (e.g., FIG. 19 and 21), a combination of the outer polygonal shape 62 and the internal recess 28 (e.g., FIG. 1, FIG. 16, FIG. 17, and FIG. 20), or none of the above (e.g., FIG. 18), as described in more detail below.

In one embodiment, the next step (218) may be to anneal the now formed hollow screw workpiece to soften the corrosion-resistant steel for thread rolling. In one embodiment, the annealing step (218) may be performed in a heat treatment at an elevated temperature of about 950-980 degrees Celsius for about one hour. The elongated body 12, which in some embodiments includes only the shank portion 14 or in other embodiments includes the shank portion 14 and the redraw portion 48, may have a hardness of about 79 Rockwell B at the end of the annealing step (218).

At this point, as part of step (220), the threads 18 can be roll-formed, as shown in Figure 11. In one embodiment, as shown in Figure 11, the threads 18 are roll-formed into the heavy draw portion 48 of the elongated body 12 by at least one pair of thread rolling dies 68. However, step (220) can be performed with any number of rolling dies 68, such as three or more, as desired. In addition, step (220) can include deploying a stabilizing pin 70 into the hollow shaft 22 during the rolling step (220) for stabilizing and preventing the peripheral wall of the heavy draw portion 48 from collapsing into the interior of the hollow shaft 22. In this regard, the outer diameter of the stabilizing pin 70 is preferably approximately the same size as the inner diameter of the hollow shaft 22. Therefore, the formed threads 18 preferably have the same wall thickness as the shank portion 14, i.e., about 0.2 to about 0.7 mm.

After rolling the threads 18 in step (220), the entire hollow screw 10"" is precipitation hardened by heat treatment at an elevated temperature of about 690-720 degrees Celsius for about 16 hours during step (222) to provide a hollow screw 10"" having a Rockwell hardness of about 42. The strength of the threads 18 is on the order of about 1200 megapascals ("MPa") to about 1400 MPa, preferably 1300 MPa, which is suitable for most aerospace applications. Thus, FIG11 shows one embodiment of a finished stainless steel hollow screw 10"" (FIG. 20) ready for use.

Although, in another alternative embodiment, the hollow screw 10"" can be installed with an optional washer, such as the lock washer 26 (Figure 1), as shown in Figure 12 relative to step (224) in Figure 2. Here, a free-formed washer 72 having a hole 74 whose diameter is slightly larger than the outer diameter of the threads 18 is able to be slid over the hollow screw 10"" along the length of the elongated body 12 to the position shown in dashed lines in Figure 12. This configuration is now commensurate with the scope of the hollow screw 10' shown in Figure 17 and can be used as described herein. However, a potential disadvantage of this embodiment is that the free-formed washer 72 can fall off the length of the elongated body 12.

Alternatively, the hollow screw 10' and the free-formed washer 72 can be loaded together by another tool 76 to a press-fit engagement, wherein the outer edge 78 of the free-formed washer 72 is turned upward to fit more tightly with the integral washer 24. This embodiment is shown in relation to the hollow screw 10 shown in Figure 12. Here, the integrally formed head 20 and elongated body 12 are able to rotate relative to the now installed lock washer 26. The installation (224) of the outer edge 78 of the free-formed washer 72 on the integral washer 24 of the head 20 can be carried out in a conventional assembly press (generally shown in Figure 12) or similar process. The optional lock washer 26 can be relatively thin, for example, on the order of about 0.15 to 0.3 mm, preferably on the order of 0.2 mm, and is ideally formed of a conductive material such as stainless steel or the like. The lock washer 26 is used in those environments where it is desired to avoid tensioning the hollow screw 10 by applying rotational (torque) forces from rotating associated accessories or the like.

FIG13 is an alternative embodiment to those shown in FIG11 and 12 and relates to steps (220) and (224). FIG13 shows a hollow screw workpiece 80 formed as a result of excluding the redraw step (208), as described above. In this regard, the workpiece 80 comprises only the constant diameter elongated body 12 - the workpiece 80 otherwise does not include the narrower redraw portion 48. Here, the free-formed washer 72 is able to slide onto the elongated body 12 because the diameter of the hole 74 is slightly larger than the outer diameter of the elongated body 12. The workpiece 80' can then pass through the same or substantially similar annealing steps (218) and rolling steps (220), as described above. However, in this embodiment, because the elongated body 12 is of constant diameter, the resulting threaded portion 16 comprises a series of threads 18 having an outer diameter that is larger than the outer diameter of the shank portion 14 and preferably wider than the diameter of the hole 74 of the free-formed washer 72. Thus, the larger diameter threads 18 can capture the free-formed washer 72 with the integral washer 24, as shown, for example, in FIG17 and in more detail in the cross-sectional view of FIG24. Here, because the outer diameter of the threaded portion 16 is enlarged during the rolling step (220) of the threads 18, the free-formed washer 72 can float freely along the shank portion 14, yet remain captured between the integral washer 24 and the threads 18. This feature can prevent the free-formed washer 72 from sliding off the elongated body 12 of the hollow screw 10' if the washer 72 is not mounted to the integral washer 24 as part of step (224).

Alternatively, step (224) may be performed on the workpiece 80' whereby, prior to steps (218)-(222), the outer edge 78 of the free-formed washer 72 is rolled and rolled onto the integral washer 24 substantially in accordance with step (224). The workpiece 80" is then subjected to the same or substantially similar annealing step (218) and rolling step (220) as described above. However, as described above, since the elongated body 12 is of constant diameter, the resulting threaded portion 16 includes a series of threads 18 having an outer diameter that is greater than the outer diameter of the shank portion 14 and preferably wider than the diameter of the bore 74 of the free-formed washer 72. Thus, if the lock washer 26 happens to be driven off the integral washer 24, the larger diameter threads 18 can prevent the lock washer 26 from sliding off the elongated body 12.

In another aspect of the manufacturing method for making the various hollow screws disclosed herein, FIG2 shows an additional and optional step (226) of deforming the threaded portion 16 to form a nose 82 thereon. This step (226) is more particularly shown in FIG14 , wherein the bottom 84 of the threaded portion 16 is inserted into a forming tool 86 having a generally tapered deformation hole 88 therein to generally reduce the diameter of the bottom 84 to the form shown with respect to the hollow screw 10″″” and with respect to the hollow screw 10″ in FIG18 . In one embodiment, a spline keyed retaining tool 90 may be inserted into the hollow shaft 22 to prevent it from rotating when the deformation hole 88 generally forms the nose 82, having the generally tapered features shown in FIG14 and FIG18 at the bottom 84 of the threaded portion 16. Of course, this step (226) can be used to form the nose 82 on other embodiments, such as the cannulated screws 10, 10', 10'", 10", 10'" shown in Figures 16, 17, and 19-21, respectively.

In another aspect of the manufacturing method for manufacturing one or more hollow screws disclosed herein, FIG2 illustrates an additional optional step of stamping a bottom-formed recess 92 into, for example, the nose 82. This stamping process (228) is generally illustrated with reference to FIG15. Thus, the bottom-formed recess 92 can be used in conjunction with or in place of the outer polygonal shape 62 or the inner recess 28 formed in the head 20. In this regard, various combinations of hollow screws can include one or more of the outer polygonal shape 62, the inner recess 28, and/or the bottom-formed recess 92, or any combination thereof. However, it is preferred that any such hollow screw include at least one of the outer polygonal shape 62, the inner recess 28, or the bottom-formed recess 92 to allow for rotational tightening during installation and release during removal.

Figures 16-21 illustrate various exemplary embodiments of hollow screws as disclosed herein. For example, Figure 16 illustrates an embodiment of a hollow screw 10 comprising an elongated body 12 having a shank portion 14 approximately the same length as a threaded portion 16 and having a flat bottom 84. The hollow screw 10 also includes an outer polygonal shape 62 having an inner recess 28 formed therein in the form of a splined recess formed therein from the head 20 (e.g., for use with a hexagon socket screw or the like). Thus, the hollow screw 10 can be tightened using an hexagonal wrench, a spline wrench, or a combination tool for simultaneously engaging the polygonal shape 62 and the inner recess 28. The head 20 also includes an integral washer 24 with a lock washer 26 formed thereon.

FIG17 shows another embodiment of a hollow screw 10 ′, in which the elongated body 12 is shorter than the hollow screw 10 shown in FIG16 . In this embodiment, the threaded portion 16 is longer than the smooth shank portion 14 . A freely formed washer 72 is captured by the threads 18 between the threaded portion 16 and the integral washer 24 , as described above and more particularly shown in the cross-sectional view of FIG24 , for example. Similar to FIG16 , this embodiment also includes an outer polygonal shape 62 and an inner recess 28 in the form of a splined recess formed in the head 20 , and the bottom 84 is unformed or smooth. Thus, the hollow screw 10 ′ can be tightened using an Allen wrench, a spline wrench, or a combination tool for simultaneously engaging the polygonal shape 62 and the inner recess 28 .

FIG18 shows another alternative embodiment of a hollow screw 10″ in which the threaded portion 16 is longer than the shank portion 14, similar to the embodiment shown above with respect to FIG17. However, in this embodiment, the head 20 is generally smooth or flat head 54 and otherwise does not include the outer polygonal shape 62 or the inner recess 28. Instead, the hollow screw 10″ includes a bottom-formed recess 92 formed generally in the nose 82. In this embodiment, the hollow screw 10" can be tightened with a spline wrench by engaging the bottom-formed recess 92. However, of course, the bottom-formed recess 92 can be formed at the bottom 84 regardless of whether the nose 82 is formed therein according to step (226). Similarly and alternatively, the nose 82 can be formed at the bottom 84 without the bottom-formed recess 92. This embodiment is particularly advantageous for flush mounting of the flat head 54 to a surrounding mounting surface (not shown). A cap (also not shown) can be inserted into the hollow shaft 22 to seal the interior from the surrounding environment, which may be particularly preferred in such applications, that is, where the hollow screw 10" is subjected to airflow, such as on the outside of an aircraft (e.g., along the fuselage, wings, etc.).

Figure 19 is another alternative embodiment of the hollow screw 10'" in which the threaded portion 16 and the shank portion 14 of the elongated body 12 are similar in size and structure as described above with reference to Figure 16. In this embodiment, the head 20 differs in that it includes a rounded surface 94, which is different from the outer polygonal shape 62 described above. Instead of stamping the outer polygonal shape 62 thereon, the rounded surface 94 can be formed thereon as part of step (214) using a stamping tool 64 of the opposite size and shape. In this embodiment, the hollow screw 10'" includes an inner recess 28 configured to receive a cross-head screwdriver.

FIG. 20 shows another alternative embodiment of a hollow screw 10 ″″, similar to FIG. 16 , except for the lock washer 26 .

21 shows yet another variation of a hollow screw 10""' comprising a hollow shaft 22 formed by an elongated body 12 having a smooth shank portion 14 and a longer threaded portion 16. In this embodiment, the hollow screw 10""' includes a tapered head 20' designed to lie flush with an outer mounting surface 96 as shown.

Additionally, the head 20' is shown as having an internal recess 28 configured for use with a Phillips screwdriver or the like for a tightening fit therein.

Of course, each of the features described above, such as the length of the elongated body 12, the length and diameter of the stem portion 14 and the threaded portion 16 including the threads 18, the size and shape of the head 20 (e.g., polygonal 62, flat 54, round 94, flush 20', etc.), the inclusion (e.g., Figures 16, 17 and 20) or exclusion (e.g., Figures 18, 19 and 21) of an integral washer 24, the inclusion (e.g., Figure 16) or exclusion (e.g., Figures 17-21) of a lock washer 26, the inclusion (e.g., Figures 16, 17, 19 and 20) or exclusion (e.g., Figures 18 and 21) of an internal recess 28, the location and placement of the free-formed washer 72, the shaping of the nose 82 (e.g., Figure 18) or the use of a flat bottom 84 (e.g., Figures 16, 17 and 19-21) and/or the bottom-formed recess 92 (e.g., Figure 18) can be mixed and matched with each other in various different embodiments. Although this application discloses various examples of these combinations, the scope and content of this application should not be so limited to only those specific embodiments disclosed herein.

22-24 illustrate in more detail the above-described embodiment, involving the different diameter sizes of the shaft portion 14 relative to the threaded portion 16 and the diameter size of the bore 74 of the free-formed washer 72. The embodiment shown in FIG. 22 is formed as a result of the redrawing step (208). In this regard, the elongated body 12 is further formed into two sections, namely, a first shaft portion 14 having a first outer diameter that is larger than a second, narrower redraw portion 48 (FIG. 6). As a result of the forming, the inner diameter "A" of the shaft portion 14 is wider than the inner diameter "B" of the subsequently formed redraw portion 48. When the threads 18 are added as part of the rolling step (220), the outer material of the redraw portion 48 is deformed outwardly by approximately 1/2 of the difference between distance "A" and distance "B". In other words, the outer diameter of the shaft portion 14, as measured by distance "C", is approximately the same as the outer diameter of the peak-to-peak distance of the threads 18, as measured by distance "D", after the rolling step (220) is completed. Thus, the shaft portion 14 and the threaded portion 16 have substantially the same outer diameter.

A slight difference between Figures 22 and 23 is that the elongated body 12 is not subjected to the redrawing step (208) during the forming process. As a result, the elongated body 12, and specifically the hollow shaft 22, has a constant inner diameter, indicated by the distance "E". As a result, the thread rolling step (220) again causes the material along the threaded portion 16 to deform outward to produce the threads 18 therein. This will cause the threads 18 to extend generally outward a distance greater than the outer diameter of the shaft portion 14. This is best illustrated in Figures 24 and 25. In addition, this extended diameter distance can be used to capture and retain the free-formed washer 72 because the diameter distance of the hole 74, as measured by the distance "F" in Figure 24, is smaller than the outer diameter of the threads 18, also indicated by the distance "G" in Figure 24. Therefore, in this embodiment, it is necessary to attach the free-formed washer 72 to the elongated body 12 before performing the rolling step (220), as described above. Of course, however, a free-formed washer of another size may be attached after the rolling step ( 220 ) as long as the diameter of the hole 74 is larger than the outer diameter “G” of the threads 18 .

FIG25 shows another embodiment in which the hollow screw 10 includes a wave washer 98. In this embodiment, the wave washer 98 can be crimped or sandwiched between the integral washer 24 and the lock washer 26. The cross-sectional view of FIG26 shows a cross-section along line 26-26 of FIG25, with the lock washer 26 added to sandwich the wave washer 98 with the integral washer 24. The installation process is the same or similar to step (224), as described above, except that the wave washer 98 is sandwiched in between.

Similarly, the embodiments disclosed herein can be used to manufacture a hollow nut 100 from a flat stock of metal or similar material, as shown in Figures 27 and 28. Figure 27 shows an embodiment in which the hollow nut 100 includes a comparable body 12' as one or more formed parts, as described herein. It is obvious that the body 12' is shorter than the elongated body 12 described above for use as a nut, but the same basic forming process is applied. In addition, the body 12' can include a set of female or internal threads 102 by threading the body 12' using methods known in the art. Similar to the above, the hollow nut 100 also includes a generally outwardly extending radial flange 104 (equivalent to the integral washer 24), which is made according to, for example, comparable steps (210) and (212) for optional installation of a lock washer 26' according to the above embodiments (e.g., comparable step (224)). FIG28 is a similar embodiment, but includes a wave washer 98' crimped or clamped between the outwardly extending radial flange 104 and the lock washer 26' in a similar or comparable step (224). The nut 100 may also undergo a comparable annealing step (218) to soften the nut 100 to form the internal threads 102, and a comparable hardening step (222) to ensure rigidity and longevity.

Various further modifications and improvements to the hollow screw and its method of manufacture will be readily apparent to those skilled in the art. For example, either the inner or outer polygonal shape can be omitted, or both can be formed in a single stamping step. Alternatively, instead of the internal drive recess, such as a cross or plum blossom recess, other standard drive recesses or polygonal recesses can be formed. The annealing and hardening steps can also vary. Therefore, the present invention is not limited by the foregoing description and accompanying drawings.

Claims (15)

1. A hollow screw, comprising: A head formed from a flat raw material of metallic material; An elongated hollow shaft includes a cap configured to prevent fluid from flowing through the hollow screw. The elongated hollow shaft is formed from a flat raw material of metallic material and extends integrally from the head. The elongated hollow shaft includes a rod portion and a threaded portion having multiple threads thereon. The skirt, formed from the flat raw material of the metal material, extends downward and outward from the head and forms an integral washer having an enlarged horizontal surface area that terminates at a radially outwardly extending flange; An anti-loosening washer, positioned below the enlarged horizontal surface area and having an outer edge curved generally around the periphery of the integral washer, at least partially clamps the integral washer therein, the anti-loosening washer being able to rotate freely relative to the integral washer; and A rotary drive mechanism is integrally formed from the flat raw material of the metal material and connected to at least a portion of the elongated hollow shaft or the head, and is configured to facilitate the tightening of the hollow screw by thread. 2. The hollow screw according to claim 1, wherein the elongated hollow shaft has a wall thickness between 0.2 and 0.7 mm. 3. The hollow screw according to claim 1, wherein the thickness of the anti-loosening washer is 0.15 to 0.30 mm. 4. The hollow screw according to claim 1, wherein the anti-loosening washer comprises a conductive material. 5. The hollow screw of claim 1, comprising a free-floating washer that is slidable along the shank portion and is captured between the integral washer and the plurality of threads, wherein the outer diameter of the threaded portion is larger than the outer diameter of the shank portion. 6. The hollow screw according to claim 1, wherein the rotary drive mechanism comprises a polygonal shape formed from the flat raw material of the metallic material. 7. The hollow screw according to claim 6, wherein the rotary drive mechanism includes the polygonal shape and a recess formed from the head. 8. The hollow screw according to claim 7, wherein the polygonal shape includes a hexagon and the recess includes a spline recess. 9. The hollow screw according to claim 1, wherein the flat raw material of the metal material includes a corrosion-resistant metal material. 10. The hollow screw according to claim 9, wherein the corrosion-resistant metal material comprises A286 steel. 11. The hollow screw according to claim 1, wherein the thread has a strength of 1200 MPa to 1400 MPa. 12. The hollow screw according to claim 1, comprising a nose formed at one end of an elongated hollow shaft opposite to the head. 13. The hollow screw according to claim 1, wherein the head comprises a round head or a flat head. 14. The hollow screw according to claim 1, wherein the elongated hollow shaft includes a cap to prevent fluid from flowing through the interior of the hollow screw. 15. The hollow screw according to claim 1, wherein the mass of the hollow screw is approximately half the mass of a solid screw of similar size and shape.