A rivetless flat bottom riveting method for pre-preparing an S-shaped structure cavity of a lower plate

Abstract

The present application belongs to the field of metal stamping, and relates to rivetless riveting technology, and discloses a rivetless flat-bottom riveting method for a lower plate with a prefabricated S-shaped structure cavity, aiming to solve the problems in traditional rivetless riveting, such as excessive deformation of the plate material leading to failure and fracture of the formed joint, difficulty in controlling the self-locking size of the neck thickness, and the joint protruding after forming affecting the appearance, etc. The present application adopts a lower plate with a prefabricated S-shaped structure cavity; when riveting, the punch contacts the upper plate, causing plastic deformation and lateral flow of the upper plate, until the prefabricated S-shaped structure cavity of the lower plate is completely filled, and finally a rivetless riveting joint is formed; meanwhile, a formula for the relationship between the S-shaped structure feature of the lower plate and the thickness and material performance of the upper plate is established, so as to optimize the joint forming quality by adjusting and controlling the prefabricated S-shaped structure cavity feature of the lower plate. The present application can adjust and control the forming appearance of the rivetless riveting joint, reduce the joint forming stress, and ensure the flatness of the joint surface.

Description

Technical Field

[0001] This invention belongs to the field of metal stamping and relates to rivetless riveting technology, specifically a rivetless flat-bottom riveting method for a prefabricated S-shaped cavity in the lower plate. Background Technology

[0002] With the profound upgrading of my country's high-end equipment manufacturing industry, fields such as aerospace, rail transportation, and new energy heavy equipment are developing towards high load-bearing capacity, lightweight, long lifespan, and high reliability, placing higher demands on the lightweighting, connection strength, and service stability of high-end equipment components. In traditional high-end equipment manufacturing, equipment structures often use single-metal materials, and connection processes are mainly based on traditional methods such as welding and riveting. These methods suffer from problems such as excessive weight and insufficient adaptability to connection conditions, making it difficult to meet the service requirements of high-end equipment under extreme loads and complex environments. Therefore, achieving efficient lightweighting and weight reduction of equipment has become a crucial technical problem that urgently needs to be solved in the field of high-end equipment manufacturing, and it is also a key path to support the performance upgrading and high-quality development of my country's high-end equipment.

[0003] In current high-end equipment manufacturing, lightweighting primarily involves structural lightweighting, material lightweighting, and process lightweighting. High-strength steel, aluminum alloys, titanium alloys, and carbon fiber are widely used in high-end equipment manufacturing, including fuselage structures, railcar bodies, new energy equipment shells, and precision machine tool frames. Reliable connection of dissimilar materials is a key aspect of lightweighting processes in high-end equipment manufacturing. Rivetless riveting, as a method of joining dissimilar materials, utilizes the plastic flow of the sheet metal to form a self-locking structure. It offers advantages such as no rivets required, low cost, simple process and operation, and no pollution, making it highly promising for lightweight manufacturing of high-end equipment. Traditional rivetless riveting methods mainly rely on the joint plastic deformation of upper and lower plates to form a mechanically self-locking structure for connection. However, due to the difference in plastic deformation capacity between dissimilar plates, forming defects such as neck fracture are easily caused, resulting in a decrease in the static strength and fatigue life of the joint, which cannot meet the load-bearing requirements under complex working conditions. At the same time, the shape and size of the self-locking structure are affected by molds and process parameters, making it impossible to achieve quantitative control of joint forming. Furthermore, existing rivetless riveting methods generally suffer from protruding riveted joints, which damages the surface flatness of the plates.

[0004] Therefore, it is urgent to develop a new type of rivetless flat-bottom riveting method to break through the technical limitations of traditional processes, solve problems such as unstable forming quality of dissimilar materials, uncontrollable self-locking dimensions, and uneven joint surfaces, and provide reliable technical support for the high-quality lightweight manufacturing and safe service of high-end equipment. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a rivetless flat-bottom riveting method using a prefabricated S-shaped cavity in the lower plate. By prefabricating the S-shaped cavity in the lower plate, a formula is established to relate the S-shaped structural characteristics of the lower plate to the thickness and material properties of the upper plate, thereby effectively solving the aforementioned technical problems in existing processes. This invention effectively avoids the risk of neck breakage caused by plate deformation during the riveting process, reduces reliance on riveting molds, meets the requirements for high-strength plate connections, and produces a smooth joint surface after forming.

[0006] The technical solution adopted by this invention to solve the technical problem is as follows:

[0007] This invention relates to a rivetless flat riveting method for a prefabricated neck-thickness self-locking structure on a lower plate, applicable to high-end equipment manufacturing. The lower plate has a pre-formed, un-holeed cavity, and the cavity wall is machined into an S-shape. During riveting, a punch presses the upper plate into the S-shaped cavity of the lower plate, forcing the upper plate to undergo plastic deformation and lateral flow until it completely fills the prefabricated S-shaped cavity of the lower plate, thus completing the connection. After the joint is formed, the surface of the upper plate is flush with the original plate surface, resulting in a flat-bottomed riveted joint without protrusions.

[0008] First, a lower plate with an S-shaped cavity is prepared. The cavity sidewalls are S-shaped and can be manufactured using one or more processes such as 3D printing and CNC machining. The cavity sidewalls have an S-shaped self-locking geometric feature. Second, preparations are made before riveting. The upper plate is stacked on top of the lower plate with the pre-made S-shaped cavity. Both plates are placed together in the lower die, ensuring that the punch is aligned with the geometric center of the S-shaped cavity. Then, the pressure ring moves down to press and fix the upper and lower plates onto the lower die, completing the plate positioning. Next, stamping is performed. The punch moves downward and contacts the upper plate. The axial force applied by the punch drives the upper plate to undergo plastic deformation and flow downward, gradually filling the S-shaped cavity of the lower plate. During the forming process, the lower plate undergoes a small amount of controllable plastic deformation, making the upper and lower plates fit more tightly and improving the joint forming quality. After the plate completely fills the cavity, the punch position is kept fixed for pressure holding to prevent the plate from springing back. Finally, the punch and pressure ring move upward synchronously, returning to the initial position, and the rivetless flat-bottom riveting is completed.

[0009] Furthermore, to ensure that the upper plate does not crack when plastic deformation flows into the S-shaped cavity and can form an effective mechanical self-locking mechanism, this invention proposes a formula relating the S-shaped structural features of the lower plate to the thickness and material properties of the upper plate:

[0010] ,

[0011] in, The self-locking value is the value of the side wall of the S-shaped cavity in the lower plate. This represents the initial thickness of the upper plate; The neck characteristic thickness of the sidewall of the S-shaped cavity in the lower plate; The plastic flow coefficient of the upper plate material is taken in the range of [value range missing]. ; The tensile strength of the upper plate material; The yield strength of the material on the upper plate.

[0012] Furthermore, to prevent the bottom of the upper plate from becoming too thin after forming, this invention introduces a formula to constrain the relationship between the thickness parameters of the lower plate, ensuring good joint forming quality:

[0013] ,

[0014] in, The thickness of the lower plate; The depth of the S-shaped cavity; The depth coefficient of the S-shaped cavity, with a value range of [value missing]. ; The minimum residual safety thickness at the bottom of the S-shaped cavity of the lower plate (satisfying) ).

[0015] Furthermore, the present invention can be based on the minimum residual safety thickness. Adjust the depth of the punch downwards The residual thickness at the bottom of the self-locking structure is satisfied. Under the premise of structural safety, Satisfying the formula:

[0016] .

[0017] Furthermore, the present invention can achieve [a certain level of] yield strength. ,tensile strength Reliable connection of high-strength, difficult-to-form high-strength plates with poor plastic deformation capabilities, such as high-strength steel and 3D-printed high-strength alloys.

[0018] The formula of this invention provides guidance for the selection of plate thickness and the processing of characteristic parameters of prefabricated S-shaped structural cavities in lightweight connections, ensuring good service performance of the joint after forming.

[0019] The beneficial effects of this invention are as follows: This invention provides a rivetless flat-bottom riveting method for a prefabricated S-shaped cavity in the lower plate. It proposes a method using a lower plate with an S-shaped cavity feature, where a punch fills the S-shaped cavity of the lower plate, forming a mechanical self-locking mechanism. A formula is introduced to relate the S-shaped cavity feature of the lower plate to the thickness and material properties of the upper plate. This formula allows for the control of the geometric parameters of the S-shaped cavity in the lower plate, thereby controlling the joint's forming morphology. Since the S-shaped cavity feature of the lower plate is prefabricated, the punch only needs to overcome the plastic deformation resistance of the upper plate during riveting, effectively reducing radial friction of material flow and joint forming stress, thus reducing joint forming defects. Furthermore, the rivetless riveted joint formed by this invention is flat and without protrusions, ensuring an aesthetically pleasing appearance after forming. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of a rivetless flat-bottom riveting method for a prefabricated S-shaped cavity in the lower plate according to the present invention.

[0021] Figure 2 This is a cross-sectional view of the rivetless flat riveting joint after forming, which is a rivetless flat bottom riveting method for prefabricated S-shaped cavity of lower plate according to the present invention.

[0022] Figure 3 This is a schematic diagram of the S-shaped structure cavity and the calculation parameters of the upper and lower plate structures in the rivetless flat-bottom riveting method of the prefabricated S-shaped structure cavity of the lower plate according to the present invention.

[0023] Among them, 1. punch, 2. pressure ring, 3. upper plate, 4. lower plate, 5. lower die; The self-locking value is the value of the side wall of the S-shaped cavity in the lower plate. This represents the initial thickness of the upper plate; The thickness of the lower plate; The neck characteristic thickness of the sidewall of the S-shaped cavity in the lower plate; This refers to the depth of the punch press; The depth of the S-shaped cavity; This is the minimum residual safety thickness at the bottom of the S-shaped cavity of the lower plate; This refers to the residual thickness of the upper plate left at the bottom of the self-locking structure after stamping. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings.

[0025] Example 1: Dissimilar material connection of the main reinforcing frame of a helicopter fuselage.

[0026] This embodiment is applied to the load-bearing structural components of the main reinforcing frame of a helicopter fuselage, mainly addressing the requirements for lightweight and highly reliable connections in heavy-duty load-bearing components of aviation. The specific method is as follows:

[0027] Material selection: The thickness of the upper plate is selected as follows: DC04 high-grade deep-drawing cold-rolled low-carbon steel sheet, yield strength ,tensile strength The thickness of the lower plate is selected as follows: DP785 ultra-high strength duplex steel plate.

[0028] Self-locking value calculation: Set the expected thickness of the neck feature of the S-shaped structure cavity. Flow coefficient According to the invention, the S-shaped cavity self-locking value With upper plate thickness Relationship formula:

[0029] ,

[0030] Substitute into the calculation of this embodiment:

[0031] ,

[0032] Calculation of opening depth and residual thickness: To address the failure issue caused by the reduction in the load-bearing cross-section of the lower plate after stamping, a formula relating the lower plate thickness parameters is introduced: Taking the cavity depth coefficient as 0.7, the depth of the S-shaped cavity is calculated by substituting the parameters:

[0033] ,

[0034] The minimum residual safety thickness at the bottom of the lower plate self-locking cavity is calculated using the formula. :

[0035] ,

[0036] Verify the thickness condition at the bottom of the connector:

[0037] It meets structural safety requirements.

[0038] Set the residual thickness of the upper plate (satisfy (Requirements), calculate the punch depth :

[0039] .

[0040] Operating steps: First, the DP785 ultra-high strength duplex steel lower plate is CNC machined to produce an S-shaped self-locking cavity with a single-sided width of approximately 0.344mm and a cavity machining depth of 1.137mm. A layer of agricultural machinery-specific structural adhesive is uniformly applied to the interface between the DC04 high-grade deep-drawing cold-rolled low-carbon steel upper plate and the DP785 ultra-high strength duplex steel lower plate to enhance the joint's sealing and corrosion resistance. In this embodiment, the structural adhesive used is Henkel Loctite 9466 high-toughness toughened epoxy resin. Riveting begins with the pressure ring moving down to press and fix the upper and lower plates onto the lower die. The punch moves down to contact the upper plate, causing it to plastically deform and flow laterally under the pressure of the punch, gradually filling the pre-made S-shaped self-locking cavity of the lower plate. After the upper plate material completely fills the S-shaped cavity, the punch position is maintained for 10 seconds to eliminate plate springback. Finally, the punch and pressure ring are simultaneously lifted and reset to complete the riveting process.

[0041] Example 2: Corrosion-resistant thin plate connection for rail transit.

[0042] This embodiment is applied to the connection of corrosion-resistant thin plates in rail transit. Considering the characteristics of equipment operating in a complex, humid, and corrosive environment for extended periods, a combination of corrosion-resistant materials is used while meeting strength requirements. The specific method is as follows:

[0043] Material selection: The thickness of the upper plate is selected as follows: For 6061 aluminum alloy plate, yield strength ,tensile strength The thickness of the lower plate is selected as follows: The Ti-6Al-4V titanium alloy material is processed into titanium alloy plates using 3D printing technology.

[0044] Parameter settings: Set the characteristic thickness of the neck of the S-shaped cavity. Flow coefficient .

[0045] Example calculation:

[0046] ,

[0047] Substitute the parameters in this embodiment for calculation:

[0048] ,

[0049] Taking a cavity depth coefficient of 0.75, calculate the cavity depth of the S-shaped structure:

[0050] ,

[0051] Calculate the minimum residual safety thickness at the bottom of the lower plate self-locking cavity. :

[0052] ,

[0053] Verify the thickness condition at the bottom of the connector:

[0054] It meets structural safety requirements.

[0055] Set the residual thickness of the upper plate (satisfy (Requirements), calculate the punch depth :

[0056] .

[0057] Operating steps: First, using Ti-6Al-4V titanium alloy material, the titanium alloy lower plate is 3D printed to produce an S-shaped cavity with a single-sided self-locking value of 0.146mm. The cavity machining depth is controlled to 1.299mm. When riveting begins, the pressure ring moves down to fix the upper and lower plates on the lower mold. The punch moves down to contact the upper plate. Under the action of the punch, the upper plate undergoes plastic flow and fills the pre-made S-shaped self-locking cavity of the lower plate. After forming, the punch position is kept still, and the pressure holding time is 8 seconds. Finally, the punch and pressure ring move up back to the starting position to form a rivetless flat-bottom riveted joint.

[0058] This invention is not limited to the specific details of the exemplary embodiments described above. Other forms may be used to implement this invention without departing from its core ideas or essential characteristics. Therefore, these embodiments are merely examples and not intended to limit the scope of the invention. The scope of this invention is defined by the appended claims and covers all modifications falling within the equivalent scope of the claims.

[0059] Furthermore, although this specification describes embodiments, not every embodiment corresponds to only one independent technical solution. This descriptive method is merely for clarity, and those skilled in the art should consider the specification as a whole, combining it with the technical solutions in each embodiment to form other understandable implementation methods.

Claims

1. A rivetless flat-bottom riveting method for a prefabricated S-shaped cavity in a lower plate, characterized in that, The method is used to achieve a rivetless connection between the upper and lower plates, and includes the following steps: Step S1: Prepare a lower plate (4) with an S-shaped cavity; the S-shaped cavity of the lower plate (4) is a closed cavity with S-shaped sidewalls and a depth of [missing information]. The total thickness of the lower plate (4) The depth of the S-shaped cavity The following relationship exists: ， Among them, the The depth coefficient of the S-shaped cavity, with a value range of [value missing]. ; The minimum residual safety thickness at the bottom of the S-shaped cavity of the lower plate (4) must meet the following requirements. To prevent the bottom plate (4) from failing due to bottom fracture; The formula relating the S-shaped cavity features in the lower plate (4) to the thickness and material properties of the upper plate (3) is as follows: ， Among them, the The self-locking value of the side wall of the S-shaped cavity of the lower plate (4); The initial thickness of the upper plate (3); The neck characteristic thickness of the S-shaped cavity sidewall of the lower plate (4); The plastic flow coefficient of the material of the upper plate (3) is given, and its value range is: ; The tensile strength of the material of the upper plate (3); The yield strength of the material of the upper plate (3); Step S2: Preparation before riveting; Place the upper plate (3) and the lower plate (4) of the prefabricated S-shaped cavity on the lower mold (5), with the upper plate (3) placed on the lower plate (4), so that the punch (1) is aligned with the geometric center of the prefabricated S-shaped cavity, the pressure ring (2) moves down, and fix the upper plate (3) and the lower plate (4) on the lower mold (5), and position the upper plate (3) and the lower plate (4); Step S3: Initial forming by stamping; the punch (1) moves down to contact the upper plate (3); the punch (1) presses down, causing the upper plate (3) to undergo plastic deformation and flow downwards into the S-shaped cavity of the lower plate (4); the depth of the punch (1) pressing down is ; Step S4: Joint forming and pressure holding; Under the combined action of the S-shaped structure cavity of the punch (1) and the lower plate (4), the upper plate (3) flows into and fills the S-shaped structure cavity of the lower plate (4) to form a mechanical self-locking structure, and after forming, the punch (1) remains stationary to hold pressure; Step S5: After riveting is completed, the punch (1) and the pressure ring (2) move upwards and return to the starting position.

2. The rivetless flat-bottom riveting method for a prefabricated S-shaped cavity in a lower plate according to claim 1, characterized in that, In step S1, the S-shaped cavity is prepared by 3D printing or CNC machining; the sidewall of the S-shaped cavity is prefabricated and has the geometric features of an S-shaped self-locking structure.

3. The rivetless flat-bottom riveting method for a prefabricated S-shaped cavity in a lower plate according to claim 1, characterized in that, In step S3, the depth of the punch (1) pressing down satisfy: ,in, The depth of the S-shaped cavity of the lower plate (4); This refers to the residual thickness of the upper plate (3) remaining at the bottom of the self-locking structure after stamping, and .

4. The rivetless flat-bottom riveting method for a prefabricated S-shaped cavity in a lower plate according to claim 1, characterized in that, A structural adhesive is applied between the upper plate (3) and the lower plate (4) to form a hybrid connection.

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