A lightweight fastener mountable with standard hexagonal drive tools

Abstract

The invention is a fastener (1) comprising a shaft (30) and a head (10). The novelty of the invention is in order to be assembled with standard hexagonal driving tools (40) and to reduce weight, the head (10) comprises at least two contact regions (11), each including at least one of a loosening contact surface (112) and a tightening contact surface (111), and the number of tightening contact surfaces (111) is greater than the number of loosening contact surfaces (112).

Description

[0001] A LIGHTWEIGHT FASTENER MOUNTABLE WITH STANDARD HEXAGONAL DRIVE TOOLS

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a fastener with lightweight, which can be assembled using standard driving tools.

[0004] BACKGROUND OF THE INVENTION

[0005] Fasteners are mechanical components used to hold different parts together. They are widely used in many industrial fields, particularly in the automotive and construction sectors.

[0006] In order to apply tightening during the assembly of the parts, an axial rotation process is performed by applying torque to the external or internal driving surfaces of the head of the fastener, using a suitable wrench, socket, or special driving tool. The space caused by the tolerances between the contact surfaces of the tightening tools used for external and internal drive forms results in torque transmission occurring through smaller contact areas compared to the main contact area during the axial rotation in tightening and loosening processes.

[0007] The space resulting from the tolerances between the tightening tools used with the external and internal drive forms leads to torque transmission during axial rotation for tightening and loosening purposes being made through smaller contact areas compared to the main contact area on the contacting driving surfaces. The non-contacting areas on the surfaces do not have any other functionality and remain inactive under tightening and loosening conditions. The material located in these regions causes the fastener to have excess weight, leading to an additional increase in the weight due to the fastener. In weight reduction studies on fasteners, new designs are generally created by removing nonfunctional parts, and efforts are made to remove the inactive material from the head of the fastener. This situation involves design constraints and limits the weight reduction rate to around 25%. In weight reduction studies, it is also possible for the head to be damaged in such a way that it loses its original geometry due to deformation caused by the torque applied through the tightening tool, resulting in the loss of rigidity and integrity of the head. Additionally, although the rate of weight reduction achieved through special head designs tailored for use with special driving tools may increase, the fact that tightening and loosening operations can only be performed with said special driving tool causes longer procurement processes and additional costs. In other words, in weight-reduced fasteners that can be driven with standard tightening tools, the reduction in weight is limited, and fasteners designed for special driving tools lead to different issues.

[0008] In the state of the art, U.S. patent application number US2011116895A1 discloses a fastener with a threaded body having a longitudinal axis and a head in the form of a head with hexagonal flange or non-flanged head, modified to be usable with standard drivers. These modifications result in the formation of lugs providing contact in three or four regions corresponding to multiples of sixty degrees on the head form in the tightening and loosening direction, and concave curved surfaces connecting adjacent lugs. These head forms are referred to as 3-lobed and 4-lobed shapes. Additionally, to reduce the amount of material used in the fastener, an inward recess has been formed in the central portion of the head.

[0009] Another U.S. application of US20160223005A1 , relates to head forms provided for different fasteners that can undergo repeated tightening and loosening using standard tightening tools. In the designs presented in this application, there are hexagonal forms with weak zones designed as symmetrically mirrored circular recesses on each of the six sides. By placing these recess forms at an angle on the head, an attempt has been made to provide a prevention against unauthorized loosening and removal.

[0010] PCT application of WO8302983 discloses head forms for fasteners based on the principle that the outwardly -curved regions, where the tightening and loosening surfaces meet each other, located on a circle concentric with the axis of the fastener. In the forms disclosed in the invention, it is proposed that the internal angle between two adjacent torque application surfaces is alternately smaller and larger than 180°, such that the connection points between them are alternately located on an outer and an inner tangential circle. These fasteners require the use of special drivers having the same geometry as the head form.

[0011] In the assembly conditions of fasteners, reaching the required clamp force during for tightening and the release of the clamp force for loosening are provided through the driving contact regions on the head form of the fastener. Here, during tightening and loosening, the axial rotational force resulting from the torque applied by the appropriate wrench or socket to the driving contact surfaces on the head of the bolt is transmitted to the fastener. In the known state of the art, head forms of fasteners generally consist of repeated geometries of extensions or lobes in the form of symmetrical mirroring. These head designs ensure that the driving surfaces on the head are contacted by the tightening tool from an equal number of points in both tightening and loosening directions, providing equal contact area in both directions. However, the torque applied for tightening, which is required to achieve the necessary clamping load during assembly, is higher than the torque required for loosening due to elastic interactions and frictional conditions between the assembly parts and the fasteners.

[0012] In assembly conditions of fasteners, axial rotational forces resulting from the torque applied for tightening and loosening may cause a stripping problem due to insufficient driving contact surfaces, leading to localized plastic deformation in the regions contacted by the driving tool. When the stripping problem occurs, the axial rotational force required to tighten or loosen the fastener cannot be transmitted by the driving tool to the fastener, and the desired clamping load cannot be achieved. Consequently, the assembly operation cannot be properly completed.

[0013] To avoid the stripping problem known in the state of the art, customized driving tools for the fastener, which has a form matching the head of fastener and provide a higher ratio of driving contact area, or alternatively, the head height is increased to provide sufficient driving contact area. However, this leads to additional material usage.

[0014] In studies aimed at weight reduction, it is generally achieved by forming inward recesses in the center of the head form in known shapes such as cylindrical or spherical, or by creating inward cavities with a certain wall thickness preserved at the outer edges of the head form. Although weight reduction is achieved by designing internal driving sections in the head for the tightening and loosening of the fastener, the level of weight reduction achieved remains limited due to the size and tolerance ranges of the tools to be used.

[0015] As a result, all the abovementioned problems have made it necessary to make an improvement in the relevant technical field.

[0016] SUMMARY OF THE INVENTION The present invention relates to a lightweight fastener, which aims to eliminate the above- mentioned disadvantages and to introduce new advantages to the relevant technical field.

[0017] An object of the invention is to provide a fastener that enables connections in which the desired torque and / or clamping load can be achieved during assembly without encountering the stripping problem, thus allowing for effective fastening.

[0018] Another object of the invention is to provide a fastener that can be used with conventional wrenches having a standard hexagonal head portion, without requiring a special driving tool for tightening and loosening operations under assembly conditions.

[0019] Another object of the invention is to provide a fastener having a specially designed head form that differs from conventional fasteners and serves the use of lightweight and high- strength components, which is one of today’s industrial trends.

[0020] Another object of the invention is to provide a fastener in which torque transmission is performed through a greater number of driving contact points in the tightening direction than in the loosening direction, unlike the known state of the art where tightening and loosening torques are transmitted through an equal number of contact points and contact areas.

[0021] Another object of the invention is to provide a solution to the stripping problem, which occurs when the contact areas affected by the axial rotational force generated by the tightening and loosening torques are insufficient, negatively affecting the assembly performance. A fastener is provided which ensures sufficient driving contact areas through fewer contact points compared to conventional fasteners with hexagonal heads, without encountering the stripping problem.

[0022] Another object of the invention is to provide a lightweight fastener, in which, unlike conventional fasteners with hexagonal head portions, the head form is designed without symmetric mirroring, and in which the contact regions are interconnected by concave arcs, resulting in a significant reduction in the material of the head form.

[0023] Another object of the invention is to prevent damage to the head form in a way that would cause the loss of the driving geometry, which may occur due to deformation resulting from material reduction in the head form during tightening and loosening operations. Thus, by preserving the rigidity of the head form, the recess formed at the center of the head is carried out with reference to the characteristic main boundaries of the head form, unlike conventional recess shapes. Accordingly, a fastener is provided having a head form with a prismatic and axially asymmetric groove, achieving significantly higher weight reduction.

[0024] Another object of the invention is to provide a fastener that is suitable for forming production methods applied within the scope of cold forging processes.

[0025] The present invention relates to a fastener comprising a shaft and a head in order to achieve all the objectives mentioned above and those that will emerge from the detailed description below. Accordingly, the novelty of the invention is that, for assembly with standard hexagonal drive tools and for weight reduction, the mentioned head comprises at least two contact regions, each including at least one of a loosening contact surface and a tightening contact surface, and the number of tightening contact surfaces is greater than the number of loosening contact surfaces. Thus, while preserving the strength of the fastener and retaining the head form that does not require special driving tools, substantial weight reduction and cost savings can be achieved.

[0026] In one possible embodiment of the invention, the number of contact regions is four. Thus, optimal contact for torque transmission is achieved without reducing strength, while the weight of the fastener is reduced.

[0027] In one possible embodiment of the invention, only two of the contact regions include tightening contact surfaces. In addition, the other two contact regions include both a tightening contact surface and a loosening contact surface. Thus, material that would otherwise be used to form tightening contact surfaces is saved and the weight is reduced.

[0028] In one possible embodiment of the invention, the number of tightening contact surfaces is four. Thus, a larger contact area is provided during tightening, increasing torque efficiency.

[0029] In one possible embodiment of the invention, the number of loosening contact surfaces is two. Thus, the loosening operation is performed with fewer surfaces, reducing head weight and providing material savings.

[0030] In one possible embodiment of the invention, the head includes at least one groove of asymmetric prismatic form. Thus, while the amount of material is reduced, head stiffness is preserved and weight savings are obtained. In one possible embodiment of the invention, the head includes at least one cavity formed by material removal. Thus, unnecessary material is removed, lightening the fastener.

[0031] In one possible embodiment of the invention, comprises between the contact regions, a first curvature, a second curvature, a third curvature, and a fourth curvature, such that their radii decrease successively. Thus, maximum material removal, and therefore weight reduction, is achieved without adversely affecting the strength of the fastener.

[0032] In one possible embodiment of the invention, the first, second, third, and fourth curvatures are concave arcs. Thus, cavities can be formed without changing strength and the weight is reduced. In addition, since the amount of material used is decreases, costs are also reduced.

[0033] In one possible embodiment of the invention, at least one flange is provided between the head and the shaft. Thus, slippage and loosening during assembly are prevented, increasing the robustness of the connection.

[0034] BRIEF DESCRIPTION OF THE FIGURES

[0035] Figure 1 illustrates a representative isometric view of the fastener according to the invention.

[0036] Figure 2 illustrates a top view showing the head portion of the fastener according to the invention.

[0037] Figure 3 illustrates a side view of the fastener according to the invention.

[0038] Figure 4 illustrates another representative isometric view of the fastener according to the invention.

[0039] Figure 5 illustrates a representative isometric view of the fastener according to the invention from a different angle.

[0040] Figure 6 illustrates a representative isometric view of the fastener according to the invention from another different angle. Figure 7 illustrates a representative isometric view of the fastener according to the invention and the driving tool that can engage with the fastener via the head.

[0041] Figure 8 illustrates a front view of the fastener according to the invention engaged with the driving tool.

[0042] Figure 9 illustrates the A-A cross-section of the head portion of the fastener engaged with the driving tool in the tightening direction.

[0043] Figure 10 illustrates the A-A cross-section of the head portion of the fastener engaged with the driving tool in the loosening direction.

[0044] DETAILED DESCRIPTION OF THE INVENTION

[0045] In this detailed description, the fastener (1) of the invention is explained solely with nonlimiting examples, for the purpose of better understanding the subject.

[0046] Figure 1 illustrates a representative isometric view of the fastener (1 ) according to the invention. The present invention relates to a next-generation fastener (1) having a specially developed head (10) form, designed to overcome the above-mentioned disadvantages of the known state of the art and to correspond to the industrial trend of using lightweight and high-strength components in fasteners (1 ).

[0047] The fastener (1) consists of at least one head (10) and at least one shaft (30). It may also comprise at least one flange (20). The fastener (1) is essentially a bolt. However, in alternative embodiments, the fastener (1) may be any externally threaded fastener, such as a screw.

[0048] The head (10) is positioned above the flange (20), and the circumference of the flange (20) has a larger diameter than the head (10), similar to conventional hexagonal flanged fasteners (1). Additionally, with respect to the flange (20), a flange angle in the region on the head (10) is between 3° and 10°, preferably between 5° and 7°. Moreover, the flange angle in the region on the head (10) and the flange (20) is lower than the flange angle of conventional hexagonal flanged fasteners (1). In this way, an optimal flange (20) angle value has been determined to enable easy adjustment of the head (10) height, providing ease of the production in the cold forming process. The head (10) has an asymmetric form. That is, it is formed without symmetric mirroring. The phrase “formed without symmetric mirroring” means that the geometry of the head (10) is not mirrored symmetrically on both sides but is designed in a different structure. In other words, the head (10) form of the invention is asymmetric. This head (10) design aims to reduce the amount of material used in the head (10) region and to optimize the torque-out resistance of the fastener (1).

[0049] The head (10) comprises at least two contact regions (11) which allow a driving tool (40) to apply torque to the fastener (1). In the preferred embodiment, the number of contact regions (11 ) is four. The contact regions (11 ) are formed so as not to be deformed under the axial rotational force. The driving tool (40) applies torque to the head (10) through the contact regions (11), thereby rotating the fastener (1 ) in a tightening direction (I) or in a loosening direction (II). The driving tool (40) may be a standard wrench.

[0050] The contact regions (11 ) include at least one tightening contact surface (111), that contacts the surfaces of the driving tool (40), i.e. a standard hexagonal wrench, and enables the axial rotational force generated by the torque applied in the tightening direction (I) through the driving tool (40) to be transmitted to the fastener (1 ). In the preferred embodiment, a tightening contact surface (111) is located in each contact region (11), resulting in four tightening contact surfaces (111) in total.

[0051] The dimensional measurements of the tightening contact surfaces (111) are determined according to meet the strength values of the grade 12.9 with the highest strength of the fastener defined in the main fastener standard “ISO 898-1 - Mechanical properties of fasteners made of carbon steel and alloy steel — Part 1 : Bolts, screws and studs with specified property classes — Coarse thread and fine pitch thread” and the sufficient contact areas providing the minimum breaking torques given in “ISO 898-7 - Mechanical properties of fasteners — Part 7: Torsional test and minimum torques for bolts and screws with nominal diameters 1 mm to 10 mm”.

[0052] In order to achieve the clamping load, which is one of the most important parameters affecting the performance of fasteners (1) under assembly conditions, the magnitude of the axial rotational force generated at the contact regions (11) by applying torque during the tightening process is crucial. The contact regions (11 ) on the head (10) are optimized to provide resistance against stripping in the contact regions (11 ) even when axial rotational forces generated at the highest torque values, which may cause the fastener (1) to lose functionality, are applied during tightening. The tightening torque applied to achieve the clamping load required for the assembly of the fasteners (1) is higher than the loosening torque required to release the fastener (1 ), due to the elastic interactions between the assembly components and the fasteners (1), as well as frictional conditions. Therefore, a smaller number of contact surfaces in the loosening direction (II), compared to those in the tightening direction (I), is sufficient to transmit the loosening torque to the fastener (1) for loosening.

[0053] In the contact region (11 ), there is at least one loosening contact surface (112) that contacts the surfaces of the standard hexagonal wrench used to transmit the axial rotational force created by the torque applied in the loosening direction to the fastener (1 ).ln line with the above paragraph, the number of loosening contact surfaces (112) in the preferred embodiment is two. In other words, while two out of the four contact regions (11) on the head (10) include loosening contact surfaces (112), each contact region (11) includes a tightening contact surface (111 ). Thus, during loosening, the fastener (1 ) can be safely removed from the assembly area without experiencing stripping-related problems. The loosening contact surfaces (112) are located on opposite contact regions (11). That is, the loosening contact surfaces (112) are placed on opposite diagonal contact regions (11) to transmit the axial rotational force in the loosening direction (II) equally to the driving surfaces. In the preferred embodiment, there are two tightening contact surfaces (111 ) between the two loosening contact surfaces (112). In this way, the forces applied to the fastener (1 ) are transmitted in a more balanced and stable manner, preventing possible stripping on the head (10).

[0054] When the head (10) is viewed from the top perspective as shown in Figure 2, the weight has been reduced by removing material from the areas of the head (10) that do not contact the wrench, in a way that does not affect the assembly performance of the fastener (1 ), that is, by creating cavities in the head (10). These recesses are cavities (16) bounded by concave arcs between the two contact surfaces (11)

[0055] The height of the cavities (16) is equal to the height of the wrench engagement on the fastener (1) according to the invention. As shown in Figure 9, the cavity (16) is formed between the head (10) and the driving tool (40) after the tool is attached to the head (10). To clarify further, the cavity (16) is formed by removing material in such a way that it does not cause the loss of the rigidity and strength of the head (10), and it serves to reduce the weight of the head (10) of the fastener (1 ). As a result of the formed cavities (16), the head (10) comprises, in sequence, a first curvature (12), a second curvature (13), a third curvature (14), and a fourth curvature (15), which provide the asymmetric form of the head. That is, the four contact regions (11 ) are respectively connected to one another by the first curvature (12), second curvature (13), third curvature (14), and fourth curvature (15). Accordingly, the curvatures (by curvatures it means, the first curvature (12), the second curvature (13), the third curvature (14), and the fourth curvature (15)) are located between the contact regions (11). These curvatures are in the form of concave arcs and have radius. Since there are four curvatures, there are four cavities (16). As a result, unlike the state of the art, the contact regions (11) are not connected by straight lines but by curvatures. In order to reduce material use in the head (10), material is removed from the head (10) to form the cavities (16). As shown in Figure 2, the radius of the curvatures decreases from the first curvature (12) to the fourth curvature (15), resulting in a non-symmetrical head (10) form. The gradual decrease in the radius values of the curvatures provides a balance between material usage and the rigidity of the fastener (1). Thus, while reducing the weight of the fastener (1), structural integrity is maintained, and optimal material usage is ensured.

[0056] At the center of the head (10), taking the geometric center as reference, at least one groove (17) is formed, which is asymmetric, not created by symmetric mirroring, and located within the boundaries of the main geometric form of the head (10), in a rectangular form (similar to prismatic geometry). The inclusion of the groove (17) in the design, the targeted weight reduction amount in the fastener (1) provides at least a 30% weight reduction advantage compared to the weight of conventional hexagonal flanged fastener heads.

[0057] Considering the outline of the recess shape, transitions are made with concave arcs to avoid sharp edges. In addition, the material amount between the cavities (16) and the groove (17), which defines the inner and outer boundaries of the head (10) geometry, is optimized to prevent the stripping problem during tightening and loosening operations. The depth of the cavity (16) and the groove (17) is determined according to the desired metric of the fastener (1) to achieve the highest possible material savings from the weight of the head (10).

[0058] The dimensions of the head (10) form of the fastener (1) can be revised according to the preferred wrench width for different metrics. To increase the usability of the fastener (1), each geometric feature and dimension of the head (10) form has been proportioned according to a specific coefficient based on the wrench width. The flange (20) diameter of the fastener (1 ) is determined according to the desired area of the bearing surface beneath the head (10). Thus, by reducing the risk of loosening of the fastener (1), the reliability of the connection is increased.

[0059] The characteristic form of the head (10) of the fastener (1) according to the invention is determined to be compatible with the forming techniques applied in the cold forging process, which is the main manufacturing method of fasteners (1). Thus, lightweight fasteners (1) can be quickly and easily produced in large volumes where needed.

[0060] In light of all the above, the invention operates as follows: Due to elastic interactions between the assembly parts and fasteners (1 ), and frictional conditions, the tightening torque required to achieve the clamping load for assembly is higher than the loosening torque required to loosen the fastener (1). Therefore, only two of the four contact regions (11 ) on the head (10) comprise loosening contact surfaces (112) (see Figure 10). Consequently, the contact regions (11 ) located on the left and right in Figure 9 comprise only tightening contact surfaces (111 ), contributing to material reduction in the fastener (1). In addition, the head (10) comprises four cavities (16) in the parts connecting the contact regions (11 ) to each other in a way that does not reduce durability. These cavities (16) form the first curvature (12), second curvature (13), third curvature (14), and fourth curvature (15), respectively. Due to these cavities (16), material is reduced and weight is reduced.

[0061] Finally, the asymmetrical prismatic groove (17) located at the center of the head (10) (essentially another cavity) also enables material reduction while preserving rigidity and strength. During assembly, the driving tool (40) is rotated in the tightening direction (I), applying force to the tightening contact surfaces (111 ) shown in Figure 9, and in the loosening direction (II), applying force to the loosening contact surfaces (112) shown in Figure 10, thus allowing tightening and loosening operations to be performed.

[0062] Therefore, unlike conventional recess forms, the fastener (1 ) according to the invention comprises a prismatic, axially non-symmetric recess shape groove (17), cavities (16), four contact regions (11), with only two of them the loosening contact surfaces (112), all designed with reference to the characteristic main boundaries of the head (10) form. This allows for significantly higher weight reduction without compromising the strength of the fastener (1). As a result, by eliminating unnecessary material used in the head, the weight of the head is reduced by at least 30%, and costs are decreased due to the use of less raw material. In conclusion, a fastener is provided that can be assembled with standard hexagonal driving tools, has high strength, and significantly reduced weight.

[0063] The protection scope of the invention is specified in the appended claims and cannot be limited to the description made for illustrative purposes in this detailed description. Likewise, it is clear that a person skilled in the art can present similar embodiments in the light of the above descriptions without departing from the main theme of the invention.

[0064] REFERENCE NUMBERS THAT GIVEN IN THE FIGURE

[0065] 1 Fastener

[0066] 10 Head

[0067] 11 Contact Region

[0068] 111 Tightening Contact Surface

[0069] 112 Loosening Contact Surface

[0070] 12 First Curvature

[0071] 13 Second Curvature

[0072] 14 Third Curvature

[0073] 15 Fourth Curvature

[0074] 16 Cavity

[0075] 17 Groove

[0076] 20 Flange

[0077] 30 Shaft

[0078] 40 Driving Tool

[0079] (I) Tightening Direction

[0080] (II) Loosening Direction

Claims

CLAIMS1. A fastener (1) comprising a shaft (30) and a head (10), characterized in that, in order to be assembled with standard hexagonal driving tools (40) and to reduce weight, the head (10) comprises at least two contact regions (11), each including at least one of a loosening contact surface (112) and a tightening contact surface (111 ), and the number of tightening contact surfaces (111) is greater than the number of loosening contact surfaces (112).

2. The fastener (1) according to claim 1 , characterized in that the number of contact regions (11) is four.

3. The fastener (1) according to claim 1 , characterized in that two of the contact regions (11 ) comprise only a tightening contact surface (111).

4. The fastener (1) according to claim 1 , characterized in that two of the contact regions (11 ) comprise both a tightening contact surface (111 ) and a loosening contact surface (112).

5. The fastener (1) according to claim 1 , characterized in that the number of tightening contact surfaces (111) is four.

6. The fastener (1) according to claim 1 , characterized in that the number of loosening contact surfaces (112) is two.

7. The fastener (1 ) according to claim 1 , characterized in that the head (10) comprises at least one groove (17) in an asymmetric, prismatic form.

8. The fastener (1 ) according to claim 1 , characterized in that it comprises a first curvature (12), a second curvature (13), a third curvature (14), and a fourth curvature (15) arranged sequentially between the contact regions (11 ), wherein the radius of each curvature decreases progressively.

9. The fastener (1 ) according to claim 8, characterized in that at least one of the first curvature (12), the second curvature (13), the third curvature (14), and the fourth curvature (15) is a concave arc.

10. The fastener (1) according to claim 8, characterized in that it comprises at least one cavity (16) formed by removing material from between the driving tool (40) and the first curvature (12), the second curvature (13), the third curvature (14), and the fourth curvature (15) after the driving tool (40) is attached to the head (10).

11. The fastener (1 ) according to claim 1 , characterized in that at least one flange (20) is provided between the head (10) and the shaft (30).

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