SPRING

FIELD OF THE DISCLOSURE

[0001] This disclosure relates to flexure components and, more particularly, to a 3D printed, additively manufactured, elliptical bifurcating torsion spring.

BACKGROUND

[0002] Spring assemblies are used in a wide variety of applications, some with more constraints than others . Some applications require a force exerted via a spring/flexure in a confined space. Conventional torsion springs do not fit in tight spaces, and need to be tuned to specific requirements, so flexures are used. Typical torsion springs are round, and exhibit hysteresis inherent to an assembly of springs rubbing against the rotating spring arm. One example of an application with such constraints is the deployment of wings/control surfaces on precision guided munitions. Here, reliability, weight, parts count, and cost are paramount.

[0003] What is needed, therefore, is a device, system and method with improved Size Weight Power and Cost (SWaP-C) necessary for better performing springs and flexures for a reliable, light-weight, decreased partcount, low-hysteresis flexure system for constrained spaces. SUMMARY

[0004] An embodiment provides a flexure device comprising at least one elliptical bifurcating torsion spring comprising a bifurcated legs section supported by the base; a bifurcated elliptical torsion spring section contiguous with the bifurcated legs section; a single upper section contiguous with the elliptical torsion spring section, the single upper section comprising a connection component; and wherein the at least one elliptical bifurcating torsion spring is printed as an integral part by an additive manufacturing process. In embodiments, the bifurcated torsion spring is configured to maintain a balance while being torqued. In other embodiments, a material of the device comprises Ti6A14V. In subsequent embodiments the device comprises a 3D printed spring flexure comprising a plurality of the elliptical bifurcating torsion springs. For additional embodiments the device comprises an assembly comprising eight the elliptical bifurcating torsion springs. In another embodiment a stiffness-spring rate of the device comprises varying cross-sectional diameters by the 3D additive manufacturing printing. For a following embodiment, a tensile stiffness of the device is between about 14.7 and about 18.2 Msi. In subsequent embodiments a tensile stiffness of the device is about 18.2 Msi. In additional embodiments a near-linear force versus displacement of the device the device is between about 0 and 19 pounds and -0.2 to +0.4 inches deflection, respectively. In included embodiments a near-linear force versus displacement of the device the device is between about 0 and 27 pounds and about -0.2 to +0.25 inches deflection, respectively. In yet further embodiments the device comprises a wing-deployment mechanism. In related embodiments proportionate lengths of the sections comprise the elliptical torsion spring section is approximately equal to the single upper section; the connection component comprises approximately one-half of the single upper section; the bifurcated legs section is approximately one-half of the bifurcated elliptical torsion spring section. For further embodiments, a diameter of the base section is approximately 2.5 inches; and a height of spring flexure elements is approximately 2.5 inches. In ensuing embodiments an average spring hysteresis is less than about 0.01 lb. -in. [0005] Another embodiment provides an additive manufacturing method for 3D printing an elliptical bifurcating torsion flexure device comprising printing a base section; printing a bifurcated legs section supported by the base; printing a bifurcated elliptical torsion spring section contiguous with the bifurcated legs section; and printing a single upper section contiguous with the elliptical torsion spring section, the single upper section comprising a connection component; whereby at least one elliptical bifurcating torsion spring is printed as one part by the 3D printing additive manufacturing process ; and wherein the bifurcation maintains consistent balance while being torqued. For yet further embodiments, a stiffness-spring rate is determined at least partly by varying a cross sectional diameter by the 3D printing. For more embodiments a stiffness-spring rate is determined at least partly by varying a cross sectional diameter by the 3D printing wherein a cross sectional diameter of the bifurcated elliptical torsion spring section is 0.08 to 0.25 inch. Continued embodiments include a stiffness-spring rate determined at least partly by varying a cross sectional diameter by the 3D printing; wherein a cross sectional diameter of the bifurcated legs section is 0.08 to 0.25 inch. For additional embodiments a stiffness-spring rate is determined at least partly by varying a cross sectional diameter by the 3D printing; wherein a cross sectional diameter of the single upper section is 0.08 to 0.25 inch.

[0006] A yet further embodiment provides a 3D additively manufactured elliptical bifurcating torsion flexure assembly system comprising a base section; eight elliptical bifurcating torsion springs, each comprising a bifurcated legs section supported by the base; a bifurcated elliptical torsion spring section contiguous with the bifurcated legs section; and a single upper section contiguous with the elliptical torsion spring section, the single upper section comprising a connection component; wherein a material of the device comprises Hot Isostatic Pressing (HIP) heat-treated Ti6A14V; wherein a diameter of the base section is approximately 2.5 inches; wherein a height of spring flexure elements is approximately 2.5 inches ; wherein a cross sectional diameter of the elliptical torsion spring section is 0.08 to 0.25 inches; wherein a cross sectional diameter of the bifurcated legs section is 0.08 to 0.25 inches; wherein a cross sectional diameter of the single upper section is 0.08 to 0.25 inches; wherein the elliptical bifurcating torsion flexure assembly is printed as one part by a 3D additive manufacturing process ; and wherein the bifurcation maintains consistent balance while being torqued.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 depicts an application environment for an embodiment.

[0008] Figure 2 depicts a single spring flexure element configured in accordance with an embodiment.

[0009] Figure 3 depicts spring grooves and wing surfaces configured in accordance with an embodiment.

[0010] Figure 4 depicts a 3D printed titanium spring flexure assembly configured in accordance with an embodiment.

[0011] Figure 5 depicts mechanical analysis results in accordance with an embodiment.

[0012] Figure 6 is a graph comparing average force-displacement curves for deployment of wings at the wingtip configured in accordance with an embodiment.

[0013] Figure 7 depicts a test configuration of a torsion spring assembly configured in accordance with an embodiment.

[0014] Figure 8 is a graph comparing spring-only average forcedisplacement curves configured in accordance with an embodiment.

[0015] These and other features of the present embodiments will be understood better by reading the following detailed description, taken together with the figures herein described. The accompanying drawings are not intended to be drawn to scale. For purposes of clarity, not every component may be labeled in every drawing. DETAILED DESCRIPTION

[0016] The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been selected principally for readability and instructional purposes, and not to limit in any way the scope of the inventive subject matter. The invention is susceptible of many embodiments. What follows is illustrative, but not exhaustive, of the scope of the invention.

[0017] Embodiments apply to any custom spring/flexure application where typical torsion spring assemblies need to be specifically tuned to achieve optimal stiffness, force/deflection profile, and weight while reducing part count and eliminating hysteresis inherent to spring assemblies. The deployment of wings/control surfaces is one example. In embodiments, the spring assembly is the component that pushes the wings through the protective wing slot seals for deployment and therefore proper flight. Therefore, the spring assembly is a mission critical component. 3D printed titanium spring embodiments remove friction and hysteresis, providing reliable and repeatable actuating performance. Being 3D printed, the torsion spring can be tuned to specific stiffness with varying cross sectional diameters and custom load paths. By utilizing Additive Manufacturing (AM), embodiments increase performance, decrease weight 67%, decrease part count from 75 to 2, and decrease cost.

[0018] The new shape of this spring flexure can be used in areas where there is confined space. As mentioned, typical torsion springs are round, whereas embodiments are elliptical and bifurcating (dividing in two to keep consistent balance while being torqued or preloaded). Embodiments are printed as one part, and remove hysteresis inherent to an assembly of springs rubbing against the rotating spring arm. Applications include any scenario that needs a force exerted via a spring/flexure in a tall, narrow space.

[0019] FIG. 1 depicts an embodiment in an operational environment 100. View of projectile shows four wings 105 deployed by torsion spring embodiments. In applications involving precision guided munitions, wings, canards, flaperons, and related members are used to guide the munition and in some examples are deployed by a spring member such that the member is stowed until deployed.

[0020] FIG. 2 depicts a single device embodiment 200. Device 200 elements comprise a base 205; a pair of bifurcated legs 210, bifurcated elliptical torsion spring section 215, a single upper-section 220 and connection component 225. Bifurcating components (dividing in two) maintains consistent balance while being torqued, so the spring arm only rotates about the correct axis, and minimizes rotation in the other two orthogonal axes. Application embodiment dimensions in one example include a cross sectional diameter of the bifurcated legs of 0.08 to 0.25 inch; a cross sectional diameter of the elliptical spring section of 0.08 to 0.25 inch; and a cross sectional diameter of the single upper section of 0.08 to 0.25 inch. Dimensions of the spring assembly in this example are roughly 2.5 inches in base diameter, and the spring flexure elements are roughly 2.5 inches tall. Fig. 2 shows the coils ‘merging’ to a single unit on the lower half of the coil. The merge is located midway up the ellipse to be away from the bottom where the maximum stress is, so there is no stress concentration at the merge point. In embodiments, the base is integral with the precision guided kit.

[0021] For embodiments, Ti6AlV4 was chosen because of its modulus (stiffness) and its high strength to fit the force/deflection profile. However, in embodiments, a different force/deflection profile employs a different material such as 316 Stainless Steel, 17-4 PH Stainless Steel, Aluminum AlSilOMg, or other tool steels to dial in the stiffness for the application. Embodiment temperature requirements were tested at -40C to 60C based on program requirements, other embodiments can be tuned for any temperature range. Embodiments of this spring are made with the Direct Metal Laser Melting (DMLM) process. Other embodiments are made with Electron Beam Melting (another powder bed fusion process) and binder jetting. For embodiments, the elliptical shape is determined by the space requirements of the application. With differently shaped spaces, the geometry can be customized to fit in any volume, provided it can achieve the same stiffness. [0022] FIG 3 shows spring engagement 300 with the wing body surfaces. In embodiments the spring heads 305 are custom designed to contact the wing 310 in the appropriate place with grooves that keep the wing contained as it is being deployed. This feature can be printed to contact any type of surface. Additive manufacturing enables custom contact methods for different applications. For embodiments, the wings are held in place by a spring plunger, independent of the spring. Once the spring plunger is moved, the springs are free to push the wings through the wing slot seals.

[0023] FIG. 4 depicts a spring assembly 400. Assembly 400 comprises eight individual torsion springs 405 on base 410. In embodiments, these are printed all as one metal part, with a bonded EMI gasket 415 around the base which makes it an assembly of two parts. For embodiments, the metal part is designed to be 3d printed, needing minimal support structure.

[0024] FIG. 5 depicts mechanical analysis results 500 for an initial single spring embodiment 505, and then merged spring assembly 510. It shows the maturation of the spring flexure design and the design/analysis iterations performed to tune the stiffness to the particular application. Single spring design embodiments comprise initial single spring design 515, intermediate single spring design (two views) 520, and single spring final design 525. Initial single spring design 515 comprises a circular spring section. Intermediate single spring design 520 comprises an elliptical spring section. Single spring final design 525 comprises an oval spring section. Merged spring assembly 510 comprises four individual spring flexure pairs designed to make contact with the missile wings and deploy properly. Thirty design iterations are presented in the test results. Curves are Tip Deflection 530; VM Stress 535; Ti6A14V Yield Stress 540; and Deflection Goal 545. Stress data is given in psi (Von Mises Stress). Tip deflection 530 ranges from about 0.19 to about 0.5 inches. VM Stress 535 ranges from about 112,500 psi to about 230,000 psi. Ti6A14V Yield Stress 540 is about 150,000 psi. The Deflection Goal 545 is 0.5 inches. Merged spring assembly iteration 28 achieved the tip deflection goal of 0.5 inch.

[0025] FIG. 6 is a graph 600 comparing average force-displacement curves at the wingtip. Displayed are Baseline 605, and Rev B 610. As can be seen, average force in pounds load versus position in inches progresses from the most-variable. The Rev B 3D printed spring flexure design embodiment shows tuning for the exact application, and tracks the force/deflection curve of the baseline design, while exhibiting less hysteresis.

[0026] FIG. 7 depicts a test configuration 700 of a torsion spring assembly embodiment. Eight torsion springs are shown in an encasement 705 supporting the 3D printed spring flexure assembly 710.

[0027] FIG. 8 is a graph 800 comparing spring-only average forcedisplacement curves . Displayed are B aseline 805 and latest Rev B design 810. As can be seen, average force in pounds load versus position in inches is contrasted between the most-variable Baseline 805 and the least-variable Rev B 810. Rev B 810 exhibits a very-near-linear force versus displacement between about 0 and 37 pounds and about -0.2 to +0.25 inches.

[0028] The foregoing description of the embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of this disclosure. It is intended that the scope of the present disclosure be limited not by this detailed description, but rather by the claims appended hereto.

[0029] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the scope of the disclosure. Although operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results.

[0030] Each and every page of this submission, and all contents thereon, however characterized, identified, or numbered, is considered a substantive part of this application for all purposes, irrespective of form or placement within the application. This specification is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of this disclosure. Other and various embodiments will be readily apparent to those skilled in the art, from this description, figures, and the claims that follow. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.