Design method and manufacturing method of anti-fatigue lightweight cylindrical fastener and fastener

Abstract

The invention provides an anti-fatigue lightweight cylindrical fastener design method, a manufacturing method and a fastener. The anti-fatigue lightweight cylindrical fastener design method comprises the following steps that a cylindrical cavity is formed in the cylindrical fastener; the cylindrical cavity and the cylindrical fastener are coaxially arranged; and determining the value range of the sectional area of the cylindrical cavity according to the screw pitch of the bolt and the nominal diameter of the bolt. The anti-fatigue bolt has the beneficial effects that compared with a common bolt, the anti-fatigue performance of the fastener is improved, compared with a thin-rod bolt, the anti-bending performance is improved, the mass of the fastener is reduced, and an aviation aircraft obtains higher load.

Description

Technical Field

[0001] The invention belongs to the technical field of fasteners, and in particular relates to a design method and a manufacturing method of a fatigue-resistant lightweight columnar fastener and the fastener. Background Art

[0002] Fasteners are basic components, numbering in the tens of thousands and classified into groups. They play an important role in "connecting structures and systems". The quality of fasteners directly affects the life and reliability of equipment. In the fields of aviation and aerospace, fastening connection systems are often subjected to severe vibration loads during service. Fasteners, as key supporting connectors, are often prone to fatigue failure under external excitation dynamic load environments, resulting in equipment failures. Their concealment and suddenness can easily lead to major accidents.

[0003] As high-end equipment such as large launch vehicles and aircraft engines show a development trend of extreme service conditions and ultra-long service life, extreme environments and diversified connections have an impact on the fatigue reliability of bolts. Solid bolts have low flexibility, resulting in poor fatigue resistance. Although thin-rod bolts increase the flexibility of bolts by reducing the cross-sectional area of ​​the light rod area and reducing the stiffness of the bolts, the diameter of the light rod becomes thinner, so although the flexibility is improved, the bending and torsional strength of the fasteners have decreased to a large extent.

[0004] The current fasteners have the following problems in the application of aviation and other fields: First, although MJ threaded fasteners (which have a larger tooth root radius and a lower stress concentration factor than metric threads) are currently used to improve the fatigue resistance of fasteners, they still cannot meet the fatigue resistance requirements of existing equipment connection systems. Failures caused by fastener fatigue failure still occur from time to time. Among existing products, although thin-rod bolts can improve fatigue resistance, their bending, torsion, flexure, and knocking strengths have decreased significantly, which is a fatal shortcoming for the aerospace service environment. Second, lightweighting is also of great significance to the aviation field. Reducing the weight of an aircraft can increase the weight of the onboard objects. Compared with other fasteners such as high-strength rivets, threaded fasteners are the heaviest products among various fasteners in the same usage scenarios, and the degree of lightweighting is low. Therefore, other connection forms are widely used in non-critical structural connections of high-end equipment to replace bolt fasteners, but threaded fasteners are still widely used in critical structures. The lightweighting of fasteners is a major problem that needs to be solved urgently for weight-sensitive fields such as aerospace; third, the heat treatment performance of metal materials is usually affected by temperature, heating rate, and cooling rate. Due to the solid structural characteristics of the fasteners, the core temperature and temperature change rate of larger-sized fasteners during heat treatment are different from other parts, resulting in the material properties closer to the center axis after heat treatment often having some differences from the external material properties, and even affecting the final quality of the product. Summary of the invention

[0005] In view of this, the present invention aims to provide a design method, a manufacturing method and a fastener for a fatigue-resistant lightweight cylindrical fastener, in order to solve at least one of the above-mentioned technical problems.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A first aspect of the present invention provides a method for designing a fatigue-resistant lightweight cylindrical fastener, comprising the following steps:

[0008] A cylindrical cavity is provided in the cylindrical fastener;

[0009] The cylindrical cavity is coaxially arranged with the cylindrical fastener;

[0010] The value range of the cross-sectional area of ​​the cylindrical cavity is determined according to the limit utilization factor of the bolt, the current utilization factor of the bolt and the nominal diameter of the bolt.

[0011] Further, the columnar fastener is one of a bolt, a screw, and a stud screw;

[0012] The bolt utilization ratio value is obtained by subtracting the current utilization coefficient of the bolt from the limit utilization coefficient of the bolt and dividing it by the current utilization coefficient of the bolt;

[0013] The cylindrical cavity is a cylindrical cavity;

[0014] The ratio of the cross-sectional area of ​​the cylindrical cavity to the cross-sectional area of ​​the stud is the cross-sectional area reduction rate, and the available ratio of the bolt is the same as the maximum cross-sectional area reduction rate;

[0015] The maximum cross-sectional area of ​​the cylindrical cavity is taken as the product of the maximum cross-sectional area reduction rate and the cross-sectional area of ​​the stud.

[0016] Further, the length of the cylindrical cavity is determined according to the total length of the screw rod of the bolt and the pitch of the bolt;

[0017] The cylindrical cavity is processed by drilling, and the processing size needs to be an integer, so the diameter of the cylindrical cavity is rounded down at the maximum possible value point.

[0018] Further, the bolt comprises a bolt head, and the cylindrical cavity is provided with an opening on the end surface of the bolt head;

[0019] The length of the cylindrical cavity is the total length of the bolt minus the first specified multiple of the bolt pitch.

[0020] Further, the bolt comprises a bolt head, and the cylindrical cavity is provided with an opening on the end face of the stud;

[0021] The length of the cylindrical cavity is equal to the length of the screw minus the second specified multiple of the pitch value;

[0022] And the length of the cylindrical cavity is not less than the sum of the thread length and the third specified multiple of the pitch value.

[0023] Furthermore, if the bolts with a higher diameter are used to replace the solid bolts, the formula for determining the value range of the cylindrical cavity diameter is as follows:

[0024]

[0025] Among them, d s，HBolt The equivalent diameter of a bolt that is one diameter higher than a solid bolt, d s，Bolt is the equivalent diameter of a solid bolt.

[0026] Further, the bolt comprises a bolt head, and the cylindrical cavity is provided with an opening on the end surface of the bolt head;

[0027] When the thickness of the connected part is unknown, the length of the cylindrical cavity is the total length of the bolt minus the first specified multiple of the bolt pitch;

[0028] When the thickness of the connected part is determined, the length of the cylindrical cavity shall not be less than the sum of the thickness of the bolt head, the thickness of the connected part, and the fourth specified multiple of the pitch value;

[0029] And the length of the cylindrical cavity is not greater than the sum of the thickness of the bolt head, the thickness of the connected part, and the fifth specified multiple of the pitch value.

[0030] Furthermore, when the bolt is a stud bolt and a through-hole stud bolt with a higher diameter specification is used to replace the solid stud bolt, the diameter calculation formula of the cylindrical cavity of the through-hole stud bolt is as follows:

[0031]

[0032] Among them, d 2，HBolt The mid-diameter of a stud that is one diameter higher than a solid stud, d 2，Bolt It is the mid-diameter of a solid stud.

[0033] A second aspect of the present invention provides a fatigue-resistant lightweight columnar fastener, which is designed and manufactured using the design method described in the first aspect.

[0034] The third aspect of the present invention provides a method for manufacturing the fatigue-resistant lightweight cylindrical fastener as described in the second aspect, which is manufactured by the following steps:

[0035] S1. Drill a cylindrical cavity in the bolt by punching;

[0036] S2. Heat treat the punched bolts.

[0037] Or produced by the following steps:

[0038] A1. Heat treat the bolts;

[0039] A2. Drill a cylindrical cavity into the heat-treated bolt by punching.

[0040] Compared with the prior art, the fatigue-resistant lightweight cylindrical fastener and the manufacturing and using method thereof described in the present invention have the following beneficial effects:

[0041] (1) The present invention discloses a method for designing a fatigue-resistant lightweight cylindrical fastener. Compared with ordinary bolts, the fasteners manufactured by this method have improved fatigue resistance, compared with thin-rod bolts, improved bending resistance, and reduced mass of the fasteners, thereby enabling aircraft to obtain a higher load-bearing capacity.

[0042] (2) The fatigue-resistant lightweight cylindrical fastener manufacturing method described in the present invention improves the uniformity of the material compared to ordinary solid bolts, thereby improving the consistency of the bolts and ensuring product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0044] Figure 1 This is a schematic diagram of the cross-sectional structure of a bolt according to the first embodiment of the present invention;

[0045] Figure 2 This is a schematic diagram of the cross-sectional structure of the double-headed screw described in Example 1 of the present invention;

[0046] Figure 3 This is a schematic diagram of the cross-sectional structure of a bolt according to the second embodiment of the present invention;

[0047] Figure 4 This is a schematic diagram of the cross-sectional structure of the bolt described in Example 3 of the present invention. DETAILED DESCRIPTION

[0048] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0049] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0050] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0051] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0052] Embodiment 1:

[0053] like Figure 1 , 2 As shown, a method for designing a fatigue-resistant lightweight cylindrical fastener includes the following steps: a cylindrical cavity is provided in the bolt; the cylindrical cavity is arranged coaxially with the screw rod; the range of the cross-sectional area of ​​the cylindrical cavity is determined according to the limit utilization coefficient of the bolt, the current utilization coefficient of the bolt and the nominal diameter of the bolt; the length of the cylindrical cavity is determined according to the total length of the screw rod of the bolt and the pitch of the bolt.

[0054] The columnar cavity may be a cylindrical cavity or a polygonal columnar cavity.

[0055] The cylindrical fastener is one of a bolt, a screw, and a stud screw;

[0056] The formula for determining the range of values ​​for the cylindrical cavity diameter based on the bolt pitch and the bolt nominal diameter is as follows:

[0057]

[0058] Among them, d hbis the diameter of the cylindrical cavity, d is the nominal diameter of the bolt, and p is the pitch of the bolt.

[0059] The derivation process of the above formula is as follows:

[0060] The bolt utilization ratio value is obtained by subtracting the current utilization coefficient of the bolt from the limit utilization coefficient of the bolt and dividing it by the current utilization coefficient of the bolt;

[0061] The ratio of the cross-sectional area of ​​the cylindrical cavity to the cross-sectional area of ​​the stud is the cross-sectional area reduction rate, and the available ratio of the bolt is the same as the maximum cross-sectional area reduction rate;

[0062] The maximum cross-sectional area of ​​the cylindrical cavity is taken as the product of the maximum cross-sectional area reduction rate and the cross-sectional area of ​​the stud;

[0063] The maximum diameter of the cylindrical cavity is calculated based on the maximum cross-sectional area.

[0064] In order to ensure that the preload force and connection stiffness of the fatigue-resistant lightweight cylindrical fastener are consistent with those of the solid bolt, in this embodiment, the maximum assembly utilization factor of the national standard bolt is 80%, the recommended utilization factor of the European design guide is 90%, the limit utilization factor does not exceed 95%, the difference between the limit utilization factor and the maximum assembly utilization factor of the national standard bolt is 80%, and the available ratio is 15% / 80%=3 / 16;

[0065]

[0066] Substitute it into:

[0067]

[0068] When the fastener is a bolt, the cylindrical cavity is provided with openings on the end faces of the bolt head and the stud, that is, the cylindrical cavity is a through hole.

[0069] The cylindrical cavity is processed by drilling, and the processing size needs to be an integer, so the diameter of the cylindrical cavity is rounded down at the maximum possible value point.

[0070] The diameter of the cylindrical cavity is d hb , the other parameters are bolt head opposite side length s, bolt head height k, bolt head bearing surface diameter d w , screw length l, thread length b, bolt nominal diameter d, except for the cylindrical cavity diameter, the other parameters of fatigue-resistant lightweight cylindrical fasteners are consistent with ordinary metric bolts and can be obtained through the mechanical design manual or the corresponding current bolt standards.

[0071] Embodiment 2:

[0072] like Figure 3As shown, a design method for a fatigue-resistant lightweight cylindrical fastener is provided, wherein a cylindrical cavity is provided in a bolt; the cylindrical cavity is arranged coaxially with the screw rod; the value range of the cross-sectional area of ​​the cylindrical cavity is determined according to the pitch of the bolt and the nominal diameter of the bolt; and the length of the cylindrical cavity is determined according to the total length of the screw rod of the bolt and the pitch of the bolt.

[0073] The bolt comprises a bolt head, and the cylindrical cavity is provided with an opening on the end face of the bolt head, that is, the cylindrical cavity is a groove opened on the end face of the bolt head;

[0074] The method for determining the diameter of the cylindrical cavity in this embodiment is the same as the method for determining the diameter in the first embodiment.

[0075] The length of the cylindrical cavity is the total length of the bolt minus the first specified multiple of the bolt pitch.

[0076] The formula is as follows:

[0077] l hb,I = l + k - a1P;

[0078] a1 is the first specified multiple and its value range is 1-6.

[0079] When the thickness of the connected parts is uncertain, the length setting of the cylindrical cavity fully considers the misalignment between the maximum stress concentration point of the thread teeth and the end face of the bottom end of the cylindrical cavity, thereby ensuring the fatigue life of the bolt; and the length of the blind hole should exceed the thread engagement area to ensure a higher flexibility improvement.

[0080] Embodiment three:

[0081] like Figure 4 As shown, a design method for a fatigue-resistant lightweight cylindrical fastener is provided, wherein a cylindrical cavity is provided in a bolt; the cylindrical cavity is arranged coaxially with the screw rod; the value range of the cross-sectional area of ​​the cylindrical cavity is determined according to the pitch of the bolt and the nominal diameter of the bolt; and the length of the cylindrical cavity is determined according to the total length of the screw rod of the bolt and the pitch of the bolt.

[0082] The bolt comprises a bolt head, and the cylindrical cavity is provided with an opening on the end face of the stud, that is, the cylindrical cavity is a groove opened on the end face of the stud;

[0083] The method for determining the diameter of the cylindrical cavity in this embodiment is the same as the method for determining the diameter in the first embodiment.

[0084] The length of the cylindrical cavity is equal to the length of the screw rod minus the second specified multiple of the pitch value; and the length of the cylindrical cavity is not less than the sum of the thread length and the third specified multiple of the pitch value.

[0085] The formula is as follows:

[0086] l hb,II =l-a2P&lhb,II ≥ b + a3P;

[0087] a2 is the second specified multiple and its value range is 1-6, and a3 is the third specified multiple and its value range is 1-6.

[0088] The length of the cylindrical cavity of the bolt, whose cylindrical cavity is a groove opened on the end face of the stud, shall not exceed the total length of the screw rod, and the bolt head-screw rod connection and the thread-plain rod connection are both weak positions and failure-prone fracture surfaces of the bolt. The end face of the blind hole shall be staggered with the support surface step by a certain pitch to ensure that the performance of the weak position is not negatively affected.

[0089] Beneficial effects:

[0090] Compared with ordinary solid bolts, the fatigue resistance of fasteners is improved and the fatigue life is increased. The following is the verification process:

[0091] Since the bolt load calculation method is relatively complicated, this article uses a relatively simple sinusoidal alternating axial external load as an example to conduct a qualitative analysis of the load amplitude (the calculation idea comes from the "VDI 2230 Part I System Calculation of High-Strength Bolted Connections" published by the German Engineers Association, which is the most authoritative bolt connection design calculation guide recognized worldwide). Assuming that the maximum value of the axial external load is FAmax and the minimum value is FAmin, the bolt load amplitude calculation method is:

[0092] F Bolt =φ(F Amax -F Amin );

[0093] Where φ is the load distribution coefficient.

[0094] For the axial external load of coaxial clamping, the load distribution coefficient φ of the bolt can be calculated through the deformation coordination relationship of the bolted connection structure.

[0095] The bolt load distribution coefficient φ is defined as the bolt additional load F SA With external load F A The ratio of, that is:

[0096]

[0097] From the deformation coordination relationship diagram, it can be seen that the axial elongation f of the bolt SA Axial compression of the connected parts f PA Equal, according to Hooke's law, we have:

[0098] F SA =f SA K S ;

[0099] FPA =f PA K P ;

[0100] Therefore, satisfaction;

[0101]

[0102] In the formula, K S is the spring constant of the bolt, K P is the spring constant of the connected component.

[0103] The flexibility is defined as the inverse of the spring constant:

[0104]

[0105] F PA =F A -F SA

[0106] So we can get:

[0107]

[0108] In the formula, δ s is the flexibility of the bolt, δ P The flexibility of the connected parts.

[0109] According to the definition of load distribution coefficient φ, the calculation formula can be finally obtained:

[0110]

[0111] Since the change of the bolt will not affect the flexibility of the connected parts P , so there is no need to give δ P The calculation method only needs to know δ here P is a constant. Bolt flexibility δ S The calculation idea is to divide the bolt into multiple cylinders and calculate them separately. Since the calculation formula is complicated, the specific calculation content is not given here. Under the same specifications and dimensions, the relationship between the flexibility of the hollow bolt and the flexibility of the ordinary bolt is:

[0112] δ S,HB >δ S ;

[0113] Therefore, the load distribution coefficient relationship between hollow bolts and ordinary bolts is;

[0114] φ HB <φ;

[0115] Finally, it can be known that the load amplitude relationship between hollow bolts and ordinary bolts under the same alternating external load is;

[0116] F Bolt,HB <F Bolt ;

[0117] The fatigue load amplitude is positively correlated with the fatigue performance, so the fatigue performance of hollow bolts is better than that of ordinary bolts.

[0118] Compared with ordinary thin-rod bolts, the bending resistance is improved;

[0119] Compared with the thin-rod bolt (of the same cross-sectional area), the present invention has significantly improved properties such as bending resistance, torsion resistance, flexural resistance, and knock resistance. Taking the M12×1.75 thin-rod bolt and the hollow bolt of the present invention of the same cross-sectional area as an example, the difference in the bending resistance of the bare rod part of the two is calculated:

[0120] The calculation formula of the bending section coefficient of the hollow circle is:

[0121]

[0122] Where, d is the outer diameter of the hollow bolt polished rod area, that is, the nominal diameter; d hb It is the inner diameter of the hollow bolt polished rod area.

[0123] The calculation formula for the bending section coefficient of a solid circle is:

[0124]

[0125] The calculation formula for the shank diameter of a thin-shank bolt is:

[0126] d2=d-0.6495P

[0127] Where d is the nominal diameter and P is the pitch of the bolt.

[0128] According to the formula, the diameter of the M12×1.75 thin-stem bolt is 10.8634mm and the cross-sectional area is 92.6871mm2

[0129] The hollow bolt with the same diameter as the thin-shank bolt is equivalent to an outer diameter of d = 12 mm and an inner diameter of d hb =5.0978mm.

[0130] Therefore, the bending section coefficient of the rod of the M12×1.75 thin-rod bolt is W=125.8627mm3, and the bending section coefficient of the hollow bolt is W=151.0778mm3, and the bending resistance is improved by 20.03%.

[0131] The mass is reduced compared to ordinary solid bolts;

[0132] The effect of reducing weight by removing material is obvious. Due to the variety of bolt specifications, the weight reduction effect of hollow bolts is not easy to calculate accurately. We can simply estimate the bolts as cylinders, that is,

[0133]

[0134] Where Δw is the weight difference between a hollow bolt and an ordinary solid bolt of the same specification, and w is the weight of an ordinary solid bolt.

[0135] Embodiment 4:

[0136] A design method for fatigue-resistant lightweight cylindrical fasteners uses fatigue-resistant lightweight cylindrical fasteners of the same diameter to replace solid bolts. The fatigue-resistant lightweight cylindrical fasteners used have the same nominal diameter and other specifications as the solid bolts in the existing structural design. This replacement method is suitable for scenarios where the requirements for improving the fatigue performance of bolts are not high, but the requirements for lightweight are high. Under the same specifications, the static strength of the fatigue-resistant lightweight cylindrical fasteners is reduced, the fatigue performance is slightly improved, and the weight is reduced by about 8% to 15%.

[0137] Fatigue-resistant lightweight cylindrical fasteners have the same preload as ordinary solid bolts and can be installed using torque control.

[0138] If a bolt with a higher diameter is used to replace a solid bolt, the formula for determining the range of the cylindrical cavity diameter is as follows:

[0139]

[0140] Among them, d s，HBolt The equivalent diameter of a bolt that is one diameter higher than a solid bolt, d s，Bolt is the equivalent diameter of a solid bolt.

[0141] The fatigue-resistant lightweight cylindrical fasteners used are one level higher in nominal diameter than the existing solid bolts. For example, if M12×1.75 metric bolts are used in the existing structure, M14×1.75 fatigue-resistant lightweight cylindrical fasteners are used as replacements. This replacement method can significantly improve the fatigue performance and stiffness of the connection structure without improving the quality of the structure. It is suitable for expandable hole structures, high requirements for fatigue performance improvement, and no requirements for lightweight.

[0142] If the same preload force as that of the existing solid bolts is used, the preload force is low for the fatigue-resistant lightweight cylindrical fasteners of a higher specification, the utilization rate of the bolts is low, and the effect of improving the connection performance cannot be achieved. If the installation torque of the solid bolts of the same specification as the fatigue-resistant lightweight cylindrical fasteners is used, since the ultimate static load of this situation is not considered when calculating the aperture, it is very likely that the fatigue-resistant lightweight cylindrical fasteners will exceed the yield limit during installation, resulting in over-tightening of the bolts. Therefore, the most reasonable way is to ensure that the utilization rate of the fatigue-resistant lightweight cylindrical fasteners after replacement is consistent with the utilization rate of the solid bolts before replacement, which not only increases the preload force, improves the structural stiffness and connection performance, but also ensures that the bolts do not have insufficient static bearing capacity during service.

[0143] If torque-controlled installation is adopted, the method of accurately calculating the installation torque of fatigue-resistant lightweight cylindrical fasteners is relatively complicated. In order to ensure that the data is easily available, the installation torque value rule of fatigue-resistant lightweight cylindrical fasteners can be obtained by estimation. When other parameters are completely consistent, the preload force and the equivalent stress cross-sectional area of ​​the bolt can be regarded as a proportional relationship, and the preload force and the torque are also proportional. Therefore, the installation torque value rule of fatigue-resistant lightweight cylindrical fasteners is:

[0144]

[0145] Where, T HBolt Installation torque for fatigue-resistant lightweight cylindrical fasteners, T Bolt The installation torque of ordinary solid bolts of the same specification can be obtained by consulting the Mechanical Design Manual, VDI2230 Guide or other standards and guidelines of the same type. S，HBolt is the equivalent cross-sectional diameter of the fatigue-resistant lightweight cylindrical fastener, d S，Bolt is the equivalent cross-sectional diameter of a common solid bolt of the next lower specification, d 2，HBolt is the mid-diameter of the fatigue-resistant lightweight cylindrical fastener, d 2，Bolt This is the mid-diameter of a common solid bolt of the next lower specification. This estimation method has an error of about 5% compared to the accurate calculation of the torque value.

[0146] The bolt comprises a bolt head, and the cylindrical cavity is provided with an opening on the end surface of the bolt head;

[0147] When the thickness of the connected member is unknown, the length of the cylindrical cavity is the total length of the bolt minus the first specified multiple of the bolt pitch (such as in Example 1);

[0148] When the thickness of the connected part is determined, the length of the cylindrical cavity shall not be less than the sum of the thickness of the bolt head, the thickness of the connected part, and the fourth specified multiple of the pitch value;

[0149] And the length of the cylindrical cavity is not greater than the sum of the thickness of the bolt head, the thickness of the connected part, and the fifth specified multiple of the pitch value. The groove length calculation formula in the second embodiment is as follows:

[0150] When the thickness of the connected part is determined (thickness L r +L ue ), due to the uneven load distribution in the thread meshing area, the first few teeth bear most of the external load. After the core rod material of the first few teeth is removed, the load distribution in the entire meshing area of ​​the thread will be more uniform, which will reduce the stress concentration factor at the bottom of the thread teeth and have a positive effect on the connection performance.

[0151] k+l r +l ue +2P≤l hb,I ≤k+l r +l ue +3P;

[0152] Among them, L r is the length of the polished rod (Lr = 0 for full thread), L ue For non-engaged threads.

[0153] When the bolt is the stud bolt of the first embodiment, and a through-hole stud bolt with a higher diameter specification is used to replace the solid stud bolt, the diameter calculation formula of the cylindrical cavity of the through-hole stud bolt is as follows:

[0154]

[0155] Among them, d 2，HBolt The mid-diameter of a stud that is one diameter higher than a solid stud, d 2，Bolt It is the median diameter of the solid stud. The cylindrical cavity is processed by drilling, and the actual processing size needs to be an integer. Since the performance redundancy is large enough, it can be rounded up or rounded off.

[0156] Embodiment five:

[0157] A fatigue-resistant lightweight columnar fastener is designed and manufactured through embodiments 1 to 4.

[0158] Embodiment six:

[0159] A method for manufacturing the fatigue-resistant lightweight cylindrical fastener of the fifth embodiment comprises the following steps:

[0160] S1. Drill a cylindrical cavity in the bolt by punching;

[0161] S2. Heat treat the punched bolts.

[0162] The presence of the core hole of the fastener increases the heated area of ​​the parts during heat treatment, and the path of heat conduction inside the metal is also shorter. According to the following Fourier law of heat conduction, when the thermal conductivity remains unchanged (i.e. the same metal material), the heat transfer area increases, the temperature gradient increases, and ultimately the heat flux density increases. For the heat treatment process, improving the consistency of the temperature and temperature change rate of different parts can improve the heat treatment performance.

[0163] Embodiment seven:

[0164] A method for manufacturing the fatigue-resistant lightweight cylindrical fastener of the fifth embodiment comprises the following steps:

[0165] A1. Heat treat the bolts;

[0166] A2. Drill a cylindrical cavity into the heat-treated bolt by punching.

[0167] Although there is no essential improvement on the heat treatment performance, by removing the poor performance structure in the structure, the uniformity of the fastener material is also improved, avoiding product problems caused by tissue defects.

[0168] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

[0169] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A design method for a fatigue-resistant lightweight cylindrical fastener, characterized in that: The following steps are involved: A cylindrical cavity is provided in the cylindrical fastener; The cylindrical cavity is coaxially arranged with the cylindrical fastener; The value range of the cross-sectional area of ​​the cylindrical cavity is determined according to the limit utilization factor of the bolt, the current utilization factor of the bolt and the nominal diameter of the bolt.

2. The method for designing a fatigue-resistant lightweight cylindrical fastener according to claim 1, characterized in that: The cylindrical fastener is one of a bolt, a screw, and a stud screw; The bolt utilization ratio value is obtained by subtracting the current utilization coefficient of the bolt from the limit utilization coefficient of the bolt and dividing it by the current utilization coefficient of the bolt; The cylindrical cavity is a cylindrical cavity; The ratio of the cross-sectional area of ​​the cylindrical cavity to the cross-sectional area of ​​the stud is the cross-sectional area reduction rate, and the available ratio of the bolt is the same as the maximum cross-sectional area reduction rate; The maximum cross-sectional area of ​​the cylindrical cavity is taken as the product of the maximum cross-sectional area reduction rate and the cross-sectional area of ​​the stud.

3. The method for designing a fatigue-resistant lightweight cylindrical fastener according to claim 2, characterized in that: The length of the cylindrical cavity is determined according to the total length of the bolt and the pitch of the bolt; The cylindrical cavity is processed by drilling, and the processing size needs to be an integer, so the diameter of the cylindrical cavity is rounded down at the maximum possible value point.

4. The method for designing a fatigue-resistant lightweight cylindrical fastener according to claim 3, characterized in that: The bolt comprises a bolt head, and the cylindrical cavity is provided with an opening on the end surface of the bolt head; The length of the cylindrical cavity is the total length of the bolt minus the first specified multiple of the bolt pitch.

5. The method for designing a fatigue-resistant lightweight cylindrical fastener according to claim 3, characterized in that: The bolt comprises a bolt head, and a cylindrical cavity is provided with an opening on the end face of the stud; The length of the cylindrical cavity is equal to the length of the screw minus the second specified multiple of the pitch value; And the length of the cylindrical cavity is not less than the sum of the thread length and the third specified multiple of the pitch value.

6. The method for designing a fatigue-resistant lightweight cylindrical fastener according to claim 3, characterized in that: If the bolt with a higher diameter specification is used to replace the solid bolt, the formula for determining the range of values ​​of the cylindrical cavity diameter is as follows: Among them, d s，HBolt The equivalent diameter of a bolt that is one diameter higher than a solid bolt, d s，Bolt is the equivalent diameter of a solid bolt.

7. The method for designing a fatigue-resistant lightweight cylindrical fastener according to claim 3, characterized in that: The bolt comprises a bolt head, and the cylindrical cavity is provided with an opening on the end surface of the bolt head; When the thickness of the connected part is unknown, the length of the cylindrical cavity is the total length of the bolt minus the first specified multiple of the bolt pitch; When the thickness of the connected part is determined, the length of the cylindrical cavity shall not be less than the sum of the thickness of the bolt head, the thickness of the connected part, and the fourth specified multiple of the pitch value; And the length of the cylindrical cavity is not greater than the sum of the thickness of the bolt head, the thickness of the connected part, and the fifth specified multiple of the pitch value.

8. The method for designing a fatigue-resistant lightweight cylindrical fastener according to claim 2, characterized in that: When the fastener is a stud, and a through-hole stud with a higher diameter specification is used to replace the solid stud, the formula for calculating the diameter of the cylindrical cavity of the through-hole stud is as follows: Among them, d 2，HBolt The mid-diameter of a stud that is one diameter higher than a solid stud, d 2，Bolt It is the mid-diameter of a solid stud.

9. A fatigue-resistant lightweight cylindrical fastener, characterized in that: The fastener is designed and manufactured using the design method described in any one of claims 1-8.

10. A method for manufacturing the fatigue-resistant lightweight columnar fastener according to claim 9, characterized in that: Made by the following steps: S1. Drill a cylindrical cavity in the bolt by punching; S2. Heat treat the punched bolts. Or produced by the following steps: A1. Heat treat the bolts; A2. Drill a cylindrical cavity into the heat-treated bolt by punching.

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