阅读说明：本技术 制造中空螺钉的方法 (Method for manufacturing hollow screw ) 是由 C·G·哈特 于 2015-07-07 设计创作，主要内容包括：本发明涉及制造中空螺钉的方法,其包括以下步骤：从大致平坦的金属材料形成浅杯,浅杯在其一端具有径向向外延伸的粗切凸缘；从浅杯挤出长形中空本体；将大致径向向外延伸的粗切凸缘夹持并弄平成螺钉头部的所需的尺寸和形状；退火以软化至少长形中空本体；将多个螺纹滚压至软化的长形中空本体的外部的至少一部分,由此将长形中空本体形成为大致平滑的杆部分和螺纹部分；和硬化中空螺钉。(The invention relates to a method for producing a hollow screw, comprising the following steps: forming a shallow cup from a generally planar metallic material, the shallow cup having a rough cut flange extending radially outwardly at one end thereof; extruding an elongated hollow body from a shallow cup; clamping and flattening the substantially radially outwardly extending rough cut flange to a desired size and shape of the screw head; annealing to soften at least the elongated hollow body; rolling the plurality of threads to at least a portion of the exterior of the softened elongated hollow body, thereby forming the elongated hollow body into a substantially smooth stem portion and a threaded portion; and hardening the hollow screw.)

1. A method of manufacturing a hollow screw comprising the steps of:

forming a shallow cup from a generally planar metallic material, the shallow cup having a rough cut flange extending radially outwardly at one end thereof;

extruding an elongated hollow body from a shallow cup;

clamping and flattening the substantially radially outwardly extending rough cut flange to a desired size and shape of the screw head;

annealing to soften at least the elongated hollow body;

rolling the plurality of threads to at least a portion of the exterior of the softened elongated hollow body, thereby forming the elongated hollow body into a substantially smooth stem portion and a threaded portion; and

the hollow screw is hardened.

2. The method of claim 1 including the step of stamping a generally circular blank from a flat coil of metal material including corrosion resistant a286 steel.

3. A method according to claim 1, including the step of redrawing the elongate hollow body into a stem portion and a redrawing portion, the redrawing portion having an outer diameter which is relatively narrower than the outer diameter of the stem portion.

4. The method of claim 1, including the step of applying internal splines or cross recesses to the screw head.

5. The method of claim 1, wherein the annealing step comprises: a step of heating the hollow screw at an elevated temperature of about 950-.

6. The method of claim 1 including the step of inserting a stabilizing pin into the elongated hollow body during the rolling step, the stabilizing pin having an outer diameter approximately the size of the inner diameter of the threaded portion of the elongated hollow body, the stabilizing pin supporting the peripheral wall thereof to prevent collapse during the rolling step.

7. The method as claimed in claim 1, wherein the hardening step includes the step of heat treating the hollow screw by precipitation hardening at a temperature of about 690-720 degrees celsius for about 16 hours.

8. The method of claim 1 wherein the hollow screw comprises a hardness of about 42 rockwell C and the thread comprises a strength of about 1200 and 1400MPa after the hardening step.

9. The method of claim 1, including the step of forming a rounded nose from one end of the elongated hollow body.

10. The method of claim 1, including the step of keying a recess formed in the bottom to the closed end of the elongated hollow body.

11. The method of claim 1, wherein the weight of the hollow screw is about 1/2 of the weight of a solid screw of sufficient thread strength.

12. A method of manufacturing a hollow screw comprising the steps of:

forming an elongated hollow body having a wall thickness of about 0.2 to about 0.7 millimeters from a substantially flat metallic material;

clamping and flattening one end of the elongated hollow body to the desired size and shape of the screw head;

annealing at a high temperature of about 950-;

rolling a plurality of threads to at least a portion of an exterior of the softened elongated hollow body; and

the hollow screw is hardened to a hardness of 42 rockwell C, wherein the threads comprise a strength of about 1200 and 1400 MPa.

13. The method of claim 12 including the step of stamping a generally circular blank from a flat coil of metal material including a corrosion resistant material, a286 steel.

14. A method according to claim 12, including the step of redrawing the elongate hollow body into a stem portion and a redrawing portion, the redrawing portion having an outer diameter which is relatively narrower than the outer diameter of the stem portion.

15. The method of claim 12 including the step of inserting a stabilizing pin into the elongated hollow body during the rolling step, the stabilizing pin having an outer diameter approximately the size of the inner diameter of the threaded portion of the elongated hollow body, the stabilizing pin supporting the peripheral wall to prevent collapse during the rolling step.

16. The method of claim 12, including the step of forming a nose rounded from one end of the elongated hollow body and keying a recess formed in the bottom into the nose.

17. A method of manufacturing a hollow screw comprising the steps of:

forming a shallow cup and a radially outwardly extending rough cut flange from a generally circular flat metallic material;

extruding an elongated hollow body from a shallow cup;

clamping and flattening the substantially radially outwardly extending rough cut flange to a desired size and shape of the screw head;

turning the screw head into a central curved dome with an outwardly extending skirt;

the center bending round top is reconstructed into a polygonal shape;

stamping the skirt into an integral gasket;

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 size of the inner diameter of the elongated hollow body, the stabilizing pin supporting the peripheral wall therein;

rolling a plurality of threads to at least a portion of an exterior of the softened elongated hollow body;

stamping the spline recess to the screw head; and

the hollow screw is hardened.

18. A method according to claim 17, including the step of redrawing the elongate hollow body into a stem portion and a redrawing portion, the redrawing portion having an outer diameter which is relatively narrower than the outer diameter of the stem portion.

19. The method of claim 17, comprising the steps of:

stamping a generally circular blank from a flat coil of corrosion resistant material comprising a286 steel, wherein the elongated hollow body comprises a wall thickness of about 0.2 to about 0.7 millimeters;

heating the hollow screw at a high temperature of about 950-; and

precipitation hardening the hollow screw at a temperature of about 690-720 degrees Celsius for about 16 hours, wherein after precipitation hardening the hollow screw comprises a hardness of about 42 Rockwell C and the thread comprises a strength of about 1200-1400 MPa.

20. The method of claim 17, including the step of inserting a washer on the elongated hollow body prior to the rolling step, the washer configured to float freely between the integral washer and the threads.

21. The method of claim 20, including the step of forming a rounded nose from one end of the elongated hollow body and keying the bottom-formed recess into the nose.

22. A method of manufacturing a hollow screw comprising the steps of:

forming a shallow cup from a generally planar metallic material, the shallow cup having a rough cut flange extending radially outwardly at one end thereof;

extruding an elongated hollow body from a shallow cup;

clamping and flattening the substantially radially outwardly extending rough cut flange to a desired size and shape of the screw head;

annealing to soften at least the elongated hollow body;

rolling the plurality of threads to at least a portion of the exterior of the softened elongated hollow body, thereby forming the elongated hollow body into a substantially smooth stem portion and a threaded portion;

inverting the screw head into a generally central curved dome having an outwardly extending skirt;

the center bending round top is reformed into an outer polygonal shape;

stamping the skirt into an integral gasket; and

the hollow screw is hardened.

23. The method of claim 22 including the step of stamping a generally circular blank from a flat coil of metal material including corrosion resistant a286 steel.

24. A method according to claim 22, including the step of redrawing the elongate hollow body into a stem portion and a redrawing portion, the redrawing portion having an outer diameter which is relatively narrower than the outer diameter of the stem portion.

25. The method of claim 22 including the step of forming the lock washer on the unitary washer in rotational relationship therewith.

26. The method of claim 22, including the step of applying internal splines or cross recesses to the screw head.

27. The method of claim 22, wherein the annealing step comprises: a step of heating the hollow screw at an elevated temperature of about 950-.

28. The method of claim 22 including the step of inserting a stabilizing pin into the elongated hollow body during the rolling step, the stabilizing pin having an outer diameter approximately the size of the inner diameter of the threaded portion of the elongated hollow body, the stabilizing pin supporting the peripheral wall thereof to prevent collapse during the rolling step.

29. The method as claimed in claim 22 wherein the hardening step includes the step of heat treating the hollow screw by precipitation hardening at a temperature of about 690-720 degrees celsius for about 16 hours.

30. The method of claim 22 wherein the hollow screw comprises a hardness of about 42 rockwell C and the thread comprises a strength of about 1200 and 1400MPa after the hardening step.

31. The method of claim 22, including the step of forming a rounded nose from one end of the elongated hollow body.

32. The method of claim 22, including the step of keying a recess formed in the bottom to the closed end of the elongated hollow body.

33. The method of claim 22, wherein the weight of the hollow screw is about 1/2 of the weight of a solid screw of sufficient thread strength.

34. A method of manufacturing a hollow screw comprising the steps of:

forming an elongated hollow body having a wall thickness of about 0.2 to about 0.7 millimeters from a substantially flat metallic material;

clamping and flattening one end of the elongated hollow body to the desired size and shape of the screw head;

inverting the screw head into a generally central curved dome having an outwardly extending skirt;

the center bending round top is reformed into an outer polygonal shape;

stamping the skirt into an integral gasket;

annealing at a high temperature of about 950-;

rolling a plurality of threads to at least a portion of an exterior of the softened elongated hollow body; and

the hollow screw is hardened to a hardness of 42 rockwell C, wherein the threads comprise a strength of about 1200 and 1400 MPa.

35. The method of claim 34 including the step of stamping a generally circular blank from a flat coil of metal material including the corrosion resistant material a286 steel.

36. A method according to claim 34, including the step of redrawing the elongate hollow body into a stem portion and a redrawing portion, the redrawing portion having an outer diameter which is relatively narrower than the outer diameter of the stem portion.

37. The method of claim 34 including the step of inserting a free formed washer over the elongated hollow body and bending its outer edge over the outer periphery of the unitary washer to at least partially clamp the unitary washer therein.

38. The method of claim 37, including the step of stamping the spline recess into the screw head.

39. The method of claim 34 including the step of inserting a stabilizing pin into the elongated hollow body during the rolling step, the stabilizing pin having an outer diameter approximately the size of the inner diameter of the threaded portion of the elongated hollow body, the stabilizing pin supporting the peripheral wall to prevent collapse during the rolling step.

40. The method of claim 34, including the step of forming a nose rounded from one end of the elongated hollow body and keying a recess formed in the bottom into the nose.

Technical Field

The present invention relates generally to a lightweight hollow metal stainless steel screw design, particularly for aerospace applications, and an associated method of manufacturing a hollow metal screw. The hollow metal screw is made by stamping from a generally circular sheet metal disc in one or more steps to form a hollow tubular head and screw shaft 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, and thus contributes to aircraft fuel economy.

Background

Screws are generally known in the art and tend to include a solid core over 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 the threaded hole socket without thread damage. However, CRES constitutes a heavier metal material and therefore does not contribute to aircraft fuel economy, particularly 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 the machinist to repeatedly install and remove the same screws without damaging the threads due to thread wear.

In the past, threaded screws included solid cores or hollow screws supported by a core insert of plastic or the like. Unfortunately, the plastic core insert adds at least some weight, whereby the screw still limits its 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 selected corrosion resistant metal material to provide a shaft wall thickness of 0.2 to 0.7 millimeters, then annealed to soften the metal material, then subsequently rolled by threads and then through a hardening step to provide a hollow metal screw having thread strength sufficient to withstand most aerospace applications, and to facilitate aircraft fuel economy by providing a hollow screw having corrosion resistant metal threads, wherein the hollow screw is about 50% of the weight of a solid core screw made of the same material. The present invention fulfills these needs and provides further advantages.

Disclosure of Invention

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

In another aspect of this embodiment, the unitary gasket may be formed from a flat blank of metal material and extending outwardly from the head. A lockwasher (captive washer) may be formed at least partially around the solid washer in a manner that allows the lockwasher to rotate freely relative to the solid washer, the head and the elongate hollow shaft. More specifically, the outer edge of the lockwasher may be directed upwardly and around the outer periphery of the unitary washer to attach the lockwasher adjacently around the unitary washer for clamping the unitary washer therein. In one embodiment, the lock washer may include a conductive material and have a thickness of about 0.15 to 0.30 millimeters.

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

In one embodiment, the resulting hollow screw may be made from a flat stock of metallic material including a corrosion resistant metallic material (e.g., a286 steel), wherein the elongated hollow shaft includes a wall thickness of about 0.2 to about 0.7 millimeters, while the threads have a strength of about 1200MPa to 1400MPa, and the weight of the hollow screw is about 1/2 of the weight of a solid screw of similar size and shape. Further, a nose may be formed at an end of the elongate hollow shaft opposite the head. In another aspect, the elongate hollow shaft may further include a cap on an end opposite the head, the cap configured to prevent fluid flow 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 elongate hollow shaft may include a shaft portion and a threaded portion having a plurality of threads thereon. Preferably, the thread has a strength of about 1200 to 1400 MPa. The threaded portion may be longer than the shank portion and the major diameter of the threads is greater than the diameter of the shank portion. Alternatively, the unitary gasket may be formed from a flat blank of metal material and have an increased horizontal surface area extending radially outwardly from the head. The lock washer may be positioned below the increased horizontal surface area and (optionally) have an outer rim that curves generally around the periphery of the unitary washer at least partially sandwiching the unitary washer therebetween. In another aspect of this embodiment, the wave washer can be sandwiched between the lockwasher and the enlarged horizontal surface area of the unitary washer. In either embodiment, the lock washer is free to rotate relative to the solid washer. To this end, a rotary drive mechanism, which is integrally formed from a flat blank of metal material and is connected to the head or the elongated hollow shaft, may be configured to facilitate fastening of the hollow screw by means of a thread and around the lock washer.

In one embodiment, the stem portion and the threaded portion of the elongate hollow shaft have a wall thickness of between about 0.2 to about 0.7 millimeters, and the lockwasher is made of an electrically conductive material having a thickness of about 0.15 to 0.30 millimeters. In another embodiment, the rotary drive mechanism may include an outer polygonal shape or an inner recess formed in the head from a flat blank of metal material, wherein the outer polygonal shape is hexagonal and the inner recess is a splined recess.

Alternatively, the rotary drive mechanism may include an internal recess stamped into the bottom of the elongate hollow shaft and stamped from a flat blank of metal material. In this embodiment, a nose may be formed at the 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 stock 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 of 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 millimeters may also be formed from a corrosion resistant flat stock metal material and extend from the head. The elongate hollow shaft preferably includes a shaft portion and a threaded portion having a plurality of threads thereon, wherein the threads have a strength of between about 1200MPa and 1400 MPa. The hollow screw may further comprise a rotational engagement mechanism, such as a polygonal shape or recess formed by the head or the elongated hollow shaft, and configured to allow fastening of the hollow screw by threading. Preferably, the rotary 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 further include an integral washer formed by the head and having an enlarged horizontal and generally rounded surface area extending radially outward from the head. The lock washer is then positioned adjacent the increased horizontal surface area with the outer rim bent generally about the outer periphery of the unitary washer to at least partially sandwich the unitary washer therein. The lock washer is free to rotate relative to the integral washer and screw body. In one embodiment, the lock washer may have a thickness of 0.15 to 0.30 mm and be made of a conductive material. Further, the elongate hollow shaft may include a capped and tapered nose portion having a splined recess therein and positioned at an end opposite the head portion. In this aspect, the head preferably comprises a rounded, flat or 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 radially outwardly extending rough cut flange at one end thereof, the shallow cup being formed from a generally flat metallic material, such as a generally circular blank stamped from a flat coil of corrosion resistant material such as a286 steel. An elongated and hollow body having a wall thickness of about 0.2 to about 0.7 millimeters can be extruded from a shallow cup. The rough cut flange, which extends generally radially outward, may then be trimmed and flattened to the desired size and shape of the screw head (e.g., flat or round head) as part of the clamping and flattening step. Next, the hollow screw may be annealed by heating the hollow screw at an elevated temperature of about 950-. Thereafter, the plurality of threads may be rolled onto at least a portion of the exterior of the softened elongated and hollow bodies to form the elongated and hollow bodies into substantially smooth shank and threaded portions, and then finally hardening the hollow screw in a final step by precipitation hardening at a temperature of about 690 and 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 thread may have a strength of about 1200 and 1400MPa, and is about 1/2 of the weight of a solid core screw with sufficient thread strength.

Additionally, the method may include redrawing the elongated hollow body into a stem portion and a redrawing portion having an outer diameter narrower than the outer diameter of the stem portion. Further, the screw head may be inverted into a generally central curved dome with an outwardly extending skirt, then reconfigured into an outer polygonal shape, and the skirt stamped into an integral washer. In addition, the free formed washer may be formed as a lock washer on a unitary washer. A spline or cross-shaped recess may be further stamped into the screw head as a rotational drive mechanism. During the rolling step, the stabilizing pin may be inserted into the elongated hollow body. The outer diameter of the stabilizing pin is preferably approximately the size of the inner diameter of the threaded portion of the elongated hollow body. Thus, the stabilizing pins provide support to the inner circumferential wall to prevent inward collapse during the rolling step. In other aspects of the method, a rounded nose may be formed from one end of the elongated hollow body and a recess formed in the bottom may be stamped into the closed end of the elongated hollow body.

In another embodiment of the method of manufacturing a hollow screw disclosed herein, the method steps may include forming an elongated hollow body having a wall thickness of about 0.2 to about 0.7 millimeters from a substantially flat metallic material. One end of the elongated hollow body is then clamped and flattened to the desired size and shape of the screw head. The hollow screw is then annealed at a high temperature of about 950-. 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 rockwell C hardness of about 42, wherein the threads have a strength of about 1200 and 1400 MPa.

The method may further comprise the steps of: stamping a generally circular blank from a flat roll blank of corrosion resistant material (e.g., a286 steel); the elongated hollow body is pulled into a rod part and a heavy-pulling part, and the outer diameter of the heavy-pulling part is narrower than the outer diameter of the rod part; inserting a stabilizing pin into the elongated hollow body; the threads are then rolled onto the exterior or outer surface of the elongated hollow body. As described above, the outer diameter of the stabilizing pin may be about the size of the inner diameter of the threaded portion of the elongated hollow body, so that the stabilizing pin may support its peripheral wall to prevent collapse when the threads are rolled.

In other aspects of the method, the screw head may be inverted into a generally central curved dome having an outwardly extending skirt. Next, the substantially central curved dome may be reconfigured into an outer polygonal shape (e.g., a hexagon). Thereafter, the skirt may be stamped into a unitary washer, wherein the freely formed washer inserted over the elongated hollow body may have an outer rim that is bent over an outer periphery of the unitary washer to at least partially sandwich the unitary washer therein. Furthermore, a rotary drive mechanism may be imparted to the hollow screw, for example by punching a threaded recess or a cross-shaped recess into the screw head or keying a recess formed in the bottom into the nose. In another aspect of the method, a rounded nose can be formed from one end of the elongated hollow body.

Another method for manufacturing a hollow screw may include: forming a shallow cup from a generally circular flat metal material and having a rough cutting flange extending radially outward at one end thereof, extruding an elongated and hollow body from the shallow cup, clamping and flattening the rough cutting flange extending radially outward to the desired size and shape of the screw head, inverting the screw head into a central curved dome having an outwardly extending skirt, reconfiguring the central curved dome into a polygonal shape, stamping the skirt into a unitary 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 generally sized to the inner diameter of the elongated hollow body to support the peripheral wall therein, rolling a plurality of threads to 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 stem portion and a redrawn portion having an outer diameter narrower than an outer diameter of the stem portion, stamping a generally circular blank from a flat roll of corrosion resistant material comprising a286 steel, wherein the elongated hollow body comprises a wall thickness of about 0.2 to about 0.7 millimeters. Further, the hollow screw may be heated at an elevated temperature of about 950-. Furthermore, a washer may be inserted over the elongated hollow body prior to the rolling step, which allows the washer to float freely between the integral washer and the threads. In addition, a circular nose may be formed from one end of the elongated hollow body and formed with a bottom-mounted recess as a rotational 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 lockwasher is formed at least partially around the radially outwardly extending flange, generally adjacent the first end, and is permitted to freely rotate relative to the nut when attached thereto, the lockwasher having an inner bore diameter larger than the internally threaded core to permit insertion of the threaded fastener. In this embodiment, the 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 the hollow nut comprises: a body having an internally threaded core with at least one end having a radially extending flange; a wave washer positioned substantially adjacent the at least one end; and a lockwasher formed at least partially around the radially outwardly extending flange and generally sandwiching the wave washer therebetween, wherein the lockwasher 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, which illustrate, by way of example, the principles of the invention.

Drawings

Detailed Description

As shown in the exemplary drawings, one embodiment of a hollow screw according to the present disclosure is generally indicated 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 portion 20; and a generally hollow interior, identified therein as hollow shaft 22, which may be capped at one end to prevent fluid flow through hollow shaft 22. In this embodiment, the hollow screw 10 further includes an integral washer 24, preferably generally formed by 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 free to rotate relative to the integral washer 24 to prevent the head 20 of the hollow screw 10, and in particular the integral washer 24, from embedding into an external mounting surface into which the hollow screw 10 may be inserted and used, such as in the case of aerospace applications. In this embodiment, the head 20 is in the shape of a hexagonal nut, and may be used alone or in combination with an internal recess 28 (e.g., a spline or cross recess or dimple) for the purpose of rotationally securing the hollow screw 10, in accordance with known tools and embodiments disclosed herein.

The resulting hollow screw 10 may comprise a lightweight structure that is easy to install, remove, and reinstall, and significantly contributes to the overall fuel economy of the aircraft. Furthermore, 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 variants such as shown in fig. 16 to 25 are generally shown in the flow chart of fig. 2, and more particularly with reference to fig. 3-15. The hollow screw 10 provides greater thread strength to resist wear when removed or reinstalled and is about 1/2 the weight of a solid screw.

With respect to the manufacturing process, fig. 2 is a flow chart illustrating a general process (200) for forming one or more variations of 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 be initially fed to a punch or the like (shown generally in fig. 3) to cut a plurality of circular blanks 32 with a punch 34. Each circular blank 32 is then stamped as part of step (204) into a shallow cup 38 of a selected size and shape using one or more structures that may use one or more stamping tools 36 of the type generally shown in fig. 4. The shallow cup 38 shown in fig. 4 includes a rough cut upper flange 40 extending generally radially outward and a shorter extruded cup body 42. The shallow cup 38 is then processed as part of the extrusion step (206) in fig. 5, wherein the extruded cup 42 is extended in one or more configurations by the 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, the size and shape of which of course depends 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 redraw step (208) is optional. As shown in more detail in fig. 6, step (208) includes redrawing the narrower or redrawn portion 48 from an otherwise uniform diameter elongate body 12 as shown in workpiece 46'. Step (208) substantially divides the elongate body 12 into two main portions, the smooth shaft portion 14 and the narrower and still smooth redraw portion 48, as shown in fig. 6. Whether step (208) is performed depends on whether the resulting outside diameter of the threads 18 of the threaded portion 16 is the same (fig. 22) or greater (fig. 23 and 24) relative to the smooth shaft portion 14, as described in more detail below. Although it is preferred that the entire elongate body 12 have a wall thickness of about 0.2 to about 0.7 millimeters, the outer diameter of the smooth shaft portion 14 may be different than the outer diameter of the redraw portion 48 (and ultimately the resulting thread 18).

The next clamping step (210) is compatible with both variants as described above, i.e. the workpiece 46 has an elongated shank 12 of constant diameter (not shown in fig. 7) or the workpiece 46' has an elongated shank 12 with a redraw portion 48 (shown in fig. 7). Generally, the subsequent steps (212) - (228) are also compatible with both workpieces 46, 46'. The only difference is with respect to the outer diameter of shaft portion 14 relative to threaded portion 16 and in particular threads 18, as shown and described in greater detail below with reference to fig. 22-24. In step (210), the head 20 is shown clamped and flattened. As shown in fig. 7, the rough-cut flange 40 may be trimmed to the overall desired size and shape by a single stamping tool 50, or by clamping the work pieces 46, 46 'in one step with one tool and stamping the work pieces 46, 46' in another step with another tool. Of course, the clamping and stamping steps may involve multiple forms. To do so, 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 roughened outer edge portion 52 cut away from the head portion 20 and discarded. The flat head 54 may be the same 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 configuration suitable for insertion into a workpiece 46' with the elongate body 12 having a stem portion 14 and a narrower redraw portion 48, but the tool blank 56 may be modified for use with tool blanks comprising a constant diameter to match the size and shape of a workpiece 46 having an elongate body 12 with a constant diameter, or any other such embodiment having various sizes, shapes and/or diameters.

As shown in the flow chart of fig. 2, the next step (212) is to invert the flat head 54 to form a generally inverted central curved dome 58, as generally shown in fig. 8. The overall size and shape of the curved dome 58 may be accomplished in one or more shaping as part of the inversion step (212), depending on the desired shape and size of the curved dome 58. Further, fig. 8 shows a generally outwardly extending skirt 60 formed at the bottom of the curved dome 58. The skirt 60 may be formed into the above-described unitary gasket 24 in a subsequent step or multiple forming as described herein, as briefly mentioned above. Similarly, this step (212) may be used with the workpieces 46, 46'.

The next step (214) is to optionally reconfigure the curved dome 58 into the outer polygonal shape 62 using a stamping tool 64 having an inverse size and shape, as shown in fig. 9. Similarly, step (214) may be accomplished in one or more forming depending on the size, shape, and desired application of the finished product. In the embodiment shown in fig. 9, the curved dome 58 is stamped into a standard polygonal shape 62 of a selected size and shape (e.g., hexagonal) for use with a hex wrench or the like. The curved dome 58 may be stamped into other keyed shapes or polygons as may be known in the art and adapted to be rotated by a standard key or the like. Of course, the polygonal shape 62 may be any shape or size known in the art to provide keyed rotation of the hollow screw 10 as well. Also as part of step (214), and as part of one or more forming, the outer skirt 60 may generally form the size and shape of the integral gasket 24, as shown herein with reference to fig. 1, 16, 17, and 20.

In addition to or in lieu of step (214), the fillet 28 may be formed as part of step (216). For example, FIG. 10 shows the head 20 being stamped by the spline stamp 66 forming its inner surface into the shape of the internally formed recess 28. In this embodiment, the female portion 28 is a spline recess sized and shaped to rotate with a standard spline or the like. 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 inner recess 28 (e.g., fig. 19 and 21), a combination of the outer polygonal shape 62 and the inner recess 28 (e.g., fig. 1, 16, 17, and 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 annealing 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-. The elongate body 12, including only the rod portion 14 in some embodiments, or in other embodiments the rod portion 14 and the redraw portion 48, may have a hardness of about 79 rockwell B at the end of the annealing step (218).

In this regard, as part of step (220), the threads 18 may be roll formed, as shown in FIG. 11. In one embodiment, as shown in fig. 11, the threads 18 are roll formed into the redrawn portion 48 of the elongate body 12 by at least one pair of thread rolling dies 68. However, step (220) may be performed with any number of rolling dies 68, such as three or more, as desired. Further, step (220) may include deploying stabilizing pin 70 into hollow shaft 22 during the rolling step (220) for stabilization therein and to prevent the peripheral wall of redraw portion 48 from collapsing into the interior of hollow shaft 22. In this regard, the outer diameter dimension of stabilization pin 70 is preferably substantially the same as the inner diameter of hollow shaft 22. Accordingly, threads 18 are preferably formed having the same wall thickness as shaft portion 14, i.e., about 0.2 to about 0.7 millimeters.

After rolling the threads 18 in step (220), the entire hollow screw 10 "" is precipitation hardened by heat treatment at elevated temperatures of approximately 690 and 720 degrees Celsius for approximately 16 hours during step (222) to provide a hollow screw 10 "" having a Rockwell hardness C of approximately 42. The strength of the threads 18 is on the order of about 1200 to about 1400 megapascals ("MPa"), preferably 1300 MPa, suitable for most aerospace applications. Thus, FIG. 11 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 "" may be fitted with an optional washer, such as the lock washer 26 (fig. 1), as shown in fig. 12 relative to step 224 in fig. 2. Here, a free-formed washer 72 having a bore 74 with a diameter slightly larger than the outer diameter of the thread 18 is slidable over the hollow screw 10 "" along the length of the elongate body 12 to the position shown in phantom in fig. 12. This configuration is now commensurate with the scope of the hollow screw 10' shown in fig. 17 and may be used as described herein. However, a potential disadvantage of this embodiment is that the free formed washer 72 may fall off the length of the elongate body 12.

Alternatively, the hollow screw 10' and the free formed washer 72 may be loaded together by another tool 76 into press fit engagement with the outer edge 78 of the free formed washer 72 turned up to fit more tightly with the integral washer 24. This embodiment is shown in relation to a hollow screw 10 as shown in figure 12. Here, the integrally formed head 20 and elongate body 12 are able to rotate relative to the now installed lockwasher 26. The mounting 224 of the outer edge 78 of the free formed washer 72 on the integral washer 24 of the head 20 may be performed in a conventional assembly press (shown generally in fig. 12) or similar process. The optional lock washer 26 may be thin, for example, on the order of about 0.15 to 0.3 millimeters, preferably 0.2 millimeters, and is desirably formed of an electrically conductive material, such as stainless steel or the like. The lock washer 26 is used in those environments where it is desirable to avoid the application of turning (torque) forces from a rotating associated accessory or the like to tension the hollow screw 10.

Fig. 13 is an alternative embodiment to those shown in fig. 11 and 12 and pertains to steps (220) and (224). Fig. 13 shows the hollow screw workpiece 80 formed as a result of the elimination of the redraw step (208), as described above. In this regard, the work-piece 80 comprises only a constant diameter elongate body 12 — the work-piece 80 otherwise does not include the narrower redraw portion 48. Here, the freely formed washer 72 is able to slide onto the elongate body 12 because the diameter of the bore 74 is slightly larger than the outer diameter of the elongate body 12. The workpiece 80' may then be passed through the same or substantially similar annealing step (218) and rolling step (220), as described above. However, in this embodiment, since the elongate body 12 is of constant diameter, the resulting threaded portion 16 includes a series of threads 18 having an outer diameter greater than the outer diameter of the stem portion 14 and preferably wider than the diameter of the bore 74 of the freely formed washer 72. Thus, the larger diameter threads 18 may capture the free formed washer 72 with the integral washer 24, for example as shown in fig. 17 and in more detail in the cross-sectional view of fig. 24. Here, because the outer diameter of the threaded portion 16 is enlarged during the rolling step (220) of the threads 18, the freely formed washer 72 may be free floating along the shank portion 14, but still remain captured between the integral washer 24 and the threads 18. This feature may prevent the freely formed washer 72 from sliding off the elongated body 12 of the hollow screw 10' in the event that the washer 72 is not mounted to the integral washer 24 as part of step (224).

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

In another aspect of the manufacturing method for making the various hollow screws disclosed herein, fig. 2 shows an additional and optional step (226) of deforming the threaded portion 16 to form the nose 82 thereon. This step (226) is more particularly illustrated in fig. 14, wherein the base 84 of the threaded portion 16 is inserted into a forming tool 86 having a generally tapered deformation bore 88 therein to generally reduce the diameter of the base 84 to the form illustrated with respect to the hollow screw 10 "" "and with respect to the hollow screw 10" in fig. 18. In one embodiment, a spline-keyed retention tool 90 may be inserted into the hollow shaft 22 to prevent it from rotating when the deformation bore 88 generally forms the nose 82, with the generally tapered feature shown in fig. 14 and 18 at the bottom 84 of the threaded portion 16. Of course, this step (226) may be used to form nose 82 on other embodiments, such as hollow screws 10, 10', 10 ""', shown in fig. 16, 17, and 19-21, respectively.

In another aspect of the manufacturing method for manufacturing one or more of the hollow screws disclosed herein, fig. 2 illustrates an additional optional step of stamping the bottom-formed recess 92 into, for example, the nose 82. The stamping process (228) is generally illustrated with reference to fig. 15. Accordingly, the bottom-formed recess 92 may be used in conjunction with or in place of the outer polygonal shape 62 or the inner recess 28 formed in the head portion 20. In this regard, various combinations of hollow screws may 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 forming recess 92 to allow for rotational tightening during installation and release during disassembly.

Fig. 16-21 illustrate various exemplary embodiments of hollow screws as disclosed herein. For example, fig. 16 shows an embodiment of a hollow screw 10 comprising an elongated body 12 having a shank portion 14 approximately equal in length to the threaded portion 16, with a flat bottom 84. The hollow screw 10 also includes an outer polygonal shape 62 formed from the head 20 with an internal recess 28 in the form of a splined recess formed therein (e.g., for use with a socket head cap screw or the like). Thus, the hollow screw 10 may be tightened with one of a socket wrench, a spline wrench, or a combination tool for simultaneous engagement with the polygonal shape 62 and the internal recess 28. The head 20 also includes an integral washer 24 having a lock washer 26 formed thereon.

Fig. 17 shows another embodiment of a hollow screw 10' in which the elongated body 12 is shorter than the hollow screw 10 shown in fig. 16. In the present embodiment, the threaded portion 16 is longer than the smooth shank portion 14. The freely formed washer 72 is captured by the threads 18 between the threaded portion 16 and the integral washer 24, as described above, and is shown more particularly in the cross-sectional view of fig. 24, for example. Similar to fig. 16, this embodiment also includes an outer polygonal shape 62 and an inner recess 28 in the form of a spline recess formed in the head 20, and the bottom 84 is unshaped or smooth. Thus, the hollow screw 10' may be tightened with one of a socket wrench, a spline wrench, or a combination tool for simultaneous engagement with the polygonal shape 62 and the internal recess 28.

Fig. 18 shows another alternative embodiment of hollow screw 10 "in which the threaded portion 16 is longer than the shaft portion 14, similar to the embodiment described above with respect to fig. 17. In the present embodiment, however, the head 20 is generally smooth or flat 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 "may be tightened with a spline wrench by engaging the bottom formed recess 92. Of course, however, the bottom-formed recess 92 may be formed at the bottom 84, whether or not in the nose 82 formed therein according to step (226). Similarly and alternatively, the nose 82 may 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) may be inserted into hollow shaft 22 to close off the interior from the surrounding environment, which may be particularly preferred in applications where hollow screw 10 "is subjected to airflow, such as outside of an aircraft (e.g., along the fuselage, wing, etc.).

Fig. 19 is another alternative embodiment of the hollow screw 10' ″ wherein the threaded portion 16 and the shaft portion 14 of the elongate body 12 are similar in size and structure as described above with reference to fig. 16. In this embodiment, the head 20 differs in that it includes a rounded surface 94, unlike the outer polygonal shape 62 described above. The rounded surface 94 may be formed on the stamping tool 64 of the opposite size and shape as part of step (214) rather than stamping the outer polygonal shape 62 thereon. In this embodiment, the hollow screw 10 "' includes an internal recess 28 configured to receive a form of phillips head screwdriver.

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

Fig. 21 shows yet another variation of the 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 the present embodiment, the hollow screw 10 "" 'includes a tapered head 20' that is designed to be flush with the outer mounting surface 96 as shown.

In addition, the head 20' is shown having an internal recess 28 configured for use with a phillips screwdriver or the like for a tight fitting therein.

Each of the features described above, of course, for example, the length of the elongate body 12, the length and diameter of the shank portion 14 and the threaded portion 16 including the threads 18, the size and shape of the head 20 (e.g., polygon 62, flat 54, circle 94, flush 20', etc.), the inclusion (e.g., fig. 16, 17, and 20) or exclusion (e.g., fig. 18, 19, and 21) of the integral washer 24, the inclusion (e.g., fig. 16) or exclusion (e.g., fig. 17-21) of the lockwasher 26, the inclusion (e.g., fig. 16, 17, 19, and 20) or exclusion (e.g., fig. 18 and 21) of the internal recess 28, the location and placement of the freely formed washer 72, the formation (e.g., fig. 18) of the nose 82 or the use of the flat bottom 84 (e.g., fig. 16, 17, and 19-21), and/or the bottom formed recess 92 (e.g., fig. 18) may be mixed and matched to one another in various embodiments. Although the present application discloses various examples of such combinations, the scope and content of the present application should not be so limited to the particular embodiments disclosed herein.

Fig. 22-24 more particularly illustrate the above embodiments with respect to 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 freely formed washer 72. The embodiment shown in fig. 22 is formed as a result of the redraw step (208). In this regard, the elongate body 12 is further formed in two parts, namely a first outer diameter of the first stem portion 14 is greater than the second narrower redraw portion 48 (fig. 6). As a result of the shaping, the inner diameter "A" of rod 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 about 1/2 the difference between distance "a" and distance "B". In other words, the outer diameter of rod portion 14 as measured by distance "C" is approximately the same as the outer diameter of the peak-to-peak distance of threads 18 as measured by distance "D" after the rolling step (220) is completed. Accordingly, the shank portion 14 and the threaded portion 16 have substantially the same outer diameter.

A slight difference between fig. 22 and 23 is that the elongate body 12 is not subjected to a redraw step (208) in the forming process. As a result, the elongate body 12, and in particular the hollow shaft 22, has a constant inner diameter, identified by distance "E". As a result, the thread rolling step (220) again causes outward deformation of the material along the threaded portion 16 to create the threads 18 therein. This will result in the threads 18 extending generally outwardly a distance greater than the outer diameter of the shank portion 14. This is best shown in fig. 24 and 25. In addition, this expanded diametrical distance may be used to capture and retain the free formed washer 72 because the diametrical distance of the bore 74 as measured by distance "F" in fig. 24 is smaller than the outer diameter of the thread 18, also indicated by distance "G" in fig. 24. Thus, in this embodiment, it is necessary to mount the free-formed washer 72 to the elongate body 12 prior to 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), so long as the diameter of the bore 74 is greater than the outer diameter "G" of the threads 18.

Fig. 25 shows another embodiment in which the hollow screw 10 includes a wave washer 98. In this embodiment, the wave washer 98 may be crimped or sandwiched between the solid washer 24 and the lock washer 26. The cross-sectional view of fig. 26 shows a cross-section along line 26-26 of fig. 25, with the lock washer 26 added to sandwich the wave washer 98 with the solid washer 24. The installation process is the same or similar to step (224), as described above, except for the sandwiched wave washer 98.

Similarly, the embodiments disclosed herein may be used to manufacture hollow nut 100 from flat stock of metallic or similar material, as shown in fig. 27 and 28. Fig. 27 illustrates an embodiment wherein the hollow nut 100 includes a comparable body 12' as one or more shaped components, as described herein. It is clear that the body 12' is shorter than the above-described elongated body 12, which is used as a nut, but the same basic forming process is applied. Further, the body 12 'may 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 (corresponding to the integral washer 24) made, for example, in comparable steps (210) and (212) for selectively installing the lock washer 26' in accordance with the above-described embodiment (e.g., comparable step (224)). Fig. 28 is a similar embodiment but including a wave washer 98 'crimped or sandwiched between the outwardly extending radial flange 104 and the lock washer 26' in a similar or comparable step (224). The nut 100 may also be subjected to 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 of the hollow screw and the method of its manufacture will be apparent to those skilled in the art. For example, either of the inner and outer polygonal shapes may be omitted, or both may be performed in a single stamping step. Alternatively, instead of the internal driving recess as described above, such as a cross or quincunx recess, other forms of standard driving recesses or polygonal recesses may be formed therein. The annealing and hardening steps may also vary. Accordingly, the invention is not limited by the foregoing description and drawings.