Method for laser-assisted riveting of composite and metal materials in a ring

Abstract

A laser-assisted rivet-free riveting method of composite and metal materials, first, the composite material is stacked on the metal material to complete the laser ring cutting of the composite material through the annular laser to form regular through holes; then the connecting plate is pre-tightened by pressing the concave die; under the forming force of the convex die upward movement, the metal material is plastically deformed and rivet-free riveting is formed at the hole cutting part of the composite material; the waste cutting is collected under the condition of not completely opening the riveting die by opening the concave die outer cylinder in sections. The present application utilizes the difference in the absorption capacity of resin-based composite and metal materials for specific laser waveband laser energy, realizes the continuous process of laser cutting composite and metal material plastic deformation, and further realizes the rivet-free riveting of composite and metal materials without pre-punching, which is suitable for the connection of composite and metal materials with different resin materials as the matrix, and the connection head can have a certain tensile strength.

Description

Technical Field

[0001] This invention relates to a technology in the field of joining dissimilar sheet materials, specifically a method for ring-shaped laser-assisted rivetless riveting of thermoplastic or thermosetting resin-based composite materials and metal materials. Background Technology

[0002] Thin-plate joining of composite materials and metallic materials is widely used in the automotive, rail transportation, and aerospace industries. However, due to differences in electrical resistance, melting point, and thermal conductivity between dissimilar materials, a homogeneous weld nugget cannot be formed during welding, thus hindering effective and safe connections. Currently, mechanical joining methods are predominantly used for connecting dissimilar materials. Among these, rivetless joining has become the most economical mechanical joining process due to its advantages such as the absence of fasteners, no workpiece surface damage, and good fatigue resistance and sealing properties of the joint. However, the application of traditional rivetless joining is limited by the insufficient plastic deformation capacity of carbon fiber composites.

[0003] Existing technologies for laser-assisted joining of thermoplastic composites and lightweight alloys involve processing corresponding feature patterns on one side of the connecting plates, assembling the two, and then using a oscillating laser to scan the surface of the lightweight alloy plate. Under pressure, a highly strong riveted structure is formed between the thermoplastic composite and the lightweight alloy. However, the cost of preparing the feature patterns on the plate surface is high, making this technology unsuitable for mass commercial production.

[0004] Existing laser-heated rivetless riveting technology utilizes pre-embedded fiber optic tubes within the riveting punch and die. Before riveting, the forming area of ​​the riveting material is heated by laser, enhancing material properties and preventing brittle materials from cracking or fracturing during the riveting process. It also reduces the material's resistance to plastic deformation, allowing for sufficient deformation of the sheet metal during forming and improving connection quality. However, this heat-softening-assisted rivetless riveting method is only suitable for thermoplastic composites. When joining thermosetting composites, heat softening cannot improve the composite's plastic deformation capacity. Summary of the Invention

[0005] This invention addresses the problems of complex and difficult positioning processes in existing rivetless riveting with pre-drilled holes, as well as the inability of heat-assisted rivetless riveting to connect thermosetting composite materials. It proposes a ring-shaped laser-assisted rivetless riveting method for composite materials and metal materials. Utilizing the difference in absorption capacity of resin-based composite materials and metal materials for specific laser wavelengths, this method enables individual laser cutting of the composite material while it is stacked, thereby achieving rivetless riveting of the metal material and the perforated composite material in a continuous process. This invention is applicable to the connection of composite materials with different resin matrixes and metal materials, and the joint can possess a certain tensile strength.

[0006] This invention is achieved through the following technical solution:

[0007] This invention relates to a method for ring-shaped laser-assisted rivetless joining of composite materials and metal materials. First, the composite material is stacked on the metal material and the composite material is laser-cut into a ring shape by a ring laser to form regular through holes. Then, the connecting plates are pre-tightened by pressing down the die. Under the forming force of the upward movement of the punch, the metal material is plastically deformed and forms a rivetless joint with the cut hole of the composite material. After the connection is completed, the outer cylinder is moved by opening the die to form a side opening, thereby completing the collection of cutting waste. Finally, the die is fully opened and the connecting plates are removed.

[0008] The metal material is a metal that is easily plastically deformed, and its thickness is t. 13 =0.5-5.0mm; the composite material is carbon fiber or glass fiber with thermoplastic or thermosetting resin as the matrix, and its thickness t 12 =0.5-5.0mm. No surface pretreatment is required on the sheet material before connection.

[0009] The laser circumferential cutting method uses a biconical lens to disperse a point laser beam into a ring-shaped laser beam, wherein the width of the ring-shaped spot is less than or equal to 0.3 mm, the diameter of the ring-shaped spot is less than or equal to 10 mm, and the laser source power P = at 12 -b, a=120W / mm; b=40W.

[0010] The laser circumferential cutting process, wherein the highest temperature T of the composite material satisfies: et 12 +140℃ <T<et 12 +190℃, e=30℃ / mm, if the circumferential cutting is qualified, riveting can proceed; if the maximum temperature exceeds the range, the circumferential cutting is unqualified and the process ends.

[0011] The rivetless riveting method described above achieves the switching between cutting and riveting stations through the slide rail at the end of the die.

[0012] The sheet metal pre-tightening is achieved by applying downward pressure through the outer cylinder of the die, connecting the pre-tightened sheet metal between the outer cylinder of the die and the pressure ring. The pre-tightening pressure is q·(t) 12 +t 13 ), q=0.125mm / MPa.

[0013] The aforementioned rivetless connection, punch diameter The diameter of the hole is β, and the bevel angle is 2°-10°.

[0014] In the aforementioned rivetless joint, when the punch moves towards the metal material and applies an upward forming force, the metal material undergoes plastic deformation towards the die under the punch pressure. The resulting composite scrap is ejected by the deformed metal material, and its height is limited by the die's reverse ejection position: the die's reverse ejection distance d = t 12±0.4mm. When the composite scrap comes into contact with the die ejector, they jointly provide support for the metal material. Under the combined action of the forming force and the support force, the metal material is thinned to 20% at the bottom. 13 -50%t 13 This leads to radial flow of the material.

[0015] The aforementioned waste collection refers to the following: after riveting is completed, the spring cylinder inside the die is depressurized, and the outer cylinder of the die is moved upward by the spring tension to form an opening, through which the waste is collected.

[0016] Technical effect

[0017] The laser-assisted rivetless riveting technology proposed in this invention is suitable for joining composite materials made of metal to thermoplastic or thermosetting matrices, and specifically solves the problem that thermosetting resin-based composite materials cannot be thermally softened to improve riveting performance. Compared with thermal softening-assisted riveting, it reduces process time by 70%-85%. A ring-shaped laser beam can cut the composite material without damaging the metal surface. The residual heat generated by the laser ring-cutting of the composite material can, to some extent, improve the plastic deformation capacity of the metal material and enhance the connection quality. Compared with existing rivetless riveting technologies based on thermal softening, this invention utilizes a ring-shaped laser beam to directly cut composite materials stacked with metal, overcoming the limitations of the composite matrix material on rivetless riveting, and is suitable for both thermoplastic and thermosetting composite materials. After the connection is completed, the outer cylinder of the die is opened in sections to collect the cutting waste. Attached Figure Description

[0018] Figure 1 A cross-sectional diagram of a laser-assisted rivetless joint mold (laser cutting station) designed to eliminate the need for positioning and facilitate the collection of cutting waste.

[0019] Figure 2 A cross-sectional diagram of a laser-assisted rivetless riveting mold (rivetless riveting station) designed for positioning-free operation and convenient collection of cutting waste.

[0020] Figure 3 This is a schematic diagram showing the riveting state of the outer cylinder of the die.

[0021] Figure 4 This is a schematic diagram showing the material discharge state of the outer cylinder of the die.

[0022] Figure 5 A schematic diagram of the laser-assisted rivetless joining process.

[0023] Figure 6 This is a schematic diagram showing the dimensions of a rivetless joint mold and laser cutting.

[0024] Figure 7 A schematic diagram of a laser-assisted rivetless connector (the bottom of the metal material is higher than the bottom surface of the composite material);

[0025] Figure 8 A schematic diagram of a laser-assisted rivetless connector (the bottom of the metal material is aligned with the bottom surface of the composite material);

[0026] Figure 9 A schematic diagram of a laser-assisted rivetless connector (the bottom of the metal material is lower than the bottom surface of the composite material);

[0027] In the figure: 1. Outer cylinder of the die cavity, 101. Fixed outer cylinder, 102. Moving outer cylinder, 2. Die cavity counter-rotating, 3. First support block, 4. Spring cylinder, 5. Second support block, 6. Box cover plate, 7. Second slider, 8. Die cavity box, 9. Laser, 10. First slider, 11. Slide rail, 12. Composite material, 121. Composite material waste, 122. Bottom end of composite material, 123. Composite material through hole, 13. Metal material, 131. Connecting head neck, 132. Bottom of connecting head, 14. Punch, 15. Pressure ring, 16. Thermistor;

[0028] Figure 10 Images of laser-cut holes and composite waste samples generated from laser cutting of composite materials;

[0029] Figure 11 This is a cross-sectional view of the cut opening of a through-hole in a composite material;

[0030] Figure 12 The results show the surface temperature acquisition of the metal material during the laser cutting process. a) Schematic diagram of temperature change in the overlapping area of ​​the metal material; b) Temperature cloud map acquired by the thermal imager at t = 2 s.

[0031] Figure 13 This is a cross-sectional view of the joint between rivetless metal materials and composite materials. Detailed Implementation

[0032] like Figure 1 and Figure 2 As shown, this embodiment relates to an integrated laser-assisted rivetless riveting device, which includes: a cutting mechanism and a die mold hung in sequence, and a punch mechanism arranged opposite to each other. The die mold includes: a die outer cylinder 1, a counter-pushing mechanism and a second support block 5 arranged in sequence from bottom to top; the punch mechanism includes: a pressure ring 15 and a punch 14 disposed in the center of the ring, which faces the counter-pushing mechanism.

[0033] The hanging is achieved through a guide rail and two sliders 7 and 10 movably mounted on it, wherein the cutting mechanism and the die are respectively connected to the sliders, and the station conversion is achieved through an external drive device.

[0034] The anti-top mechanism includes: a die anti-top 2, a spring cylinder 4 and a first support block 3 disposed outside it, wherein: the die anti-top 2 is disposed in the inner hole of the first support block 3 and extends into the inner cavity of the die outer cylinder 1 without protruding from the die outer cylinder 1.

[0035] The outer cylinder 1 of the concave mold has a two-section structure, including a fixed outer cylinder 101 and a movable outer cylinder 102, wherein: the fixed outer cylinder 101 is connected to the first support block 3 of the anti-top mechanism, and the movable outer cylinder 102 is connected to the spring cylinder 4.

[0036] The outer cylinder 1 of the concave mold and the first support block 3 have concentric through holes of the same size.

[0037] The external part of the die is provided with a die box 8 and a box cover plate 6, wherein: the die outer cylinder 1 is placed inside the bottom of the die box 8, and the bottom of the die outer cylinder 1 protrudes from the bottom of the die box 8 through the bottom through hole; the upper surfaces of the die counter-top 2, the first support block 3 and the spring cylinder 4 are flush and connected to the second support block 5.

[0038] To ensure riveting quality, the position d of the lower surface of the die ejector 2 from the composite material 12 is adjusted by using die ejectors 2 of different lengths. Specifically, d = t 12 ±k, where: t 12 Based on the thickness of composite material 12, k is the interlocking value, which is 0.4 mm in this embodiment.

[0039] like Figure 5 As shown, the cutting mechanism is implemented by a laser 9, which disperses the point laser into a ring laser beam 91 through optical refraction.

[0040] The laser is preferably a CO2 laser with an output power P = P = 120 W / mm·t 12 -40W, for example, thickness t 12 The recommended power for composite materials with a thickness of 2mm is 200W.

[0041] The diameter of the punch 14 is D = 3 mm, and the bevel angle is β = 2°.

[0042] The thermistor 16 integrated in the pressure ring 15 is used to detect the surface temperature T of the metal material 13 and to define the process window for laser cutting of the composite material.

[0043] This embodiment relates to an integrated laser-assisted rivetless riveting method based on the above-mentioned device, including the following steps:

[0044] 1) Place the composite material 12 and the metal material 13 in the riveting station in a reasonable order;

[0045] 2) The laser 9 is moved to a position coaxial with the punch 14, emitting a ring-shaped laser beam 91 to complete the cutting of the composite material 12. During the laser cutting process, the laser beam 9 remains perpendicular to the surface of the composite material 12. The width of the ring-shaped spot is less than or equal to 0.3 mm, and the diameter of the ring-shaped spot is less than or equal to 10 mm. The laser beam can locally vaporize the composite material to achieve the cutting process. Figure 6 As shown, the angle α between the formed cut surface and the composite material plate surface satisfies: 120°>α>60° and also satisfies: 30℃ / mm·t 12 +140℃ <T<30℃ / mm·t 12 +190℃. If T>300℃, the specific situation needs to be checked before proceeding with the riveting process.

[0046] 3) The laser 9 and the riveting die exchange positions, the die presses down synchronously, and the outer cylinder 1 of the die applies a pre-tightening force to achieve pre-tightening of the connecting plate between the pressure ring 15 and the outer cylinder 1 of the die. Specifically, during the riveting process, the composite material 12 is placed at the die end and the metal material 13 is placed at the punch end. After the connection process begins, the outer cylinder 1 of the die applies downward pressure to the connecting plate, while the pressure ring 15 provides support force to pre-tighten the connecting plate. The pre-tightening pressure is set to 0.5MPa.

[0047] 4) The punch 14 applies an upward forming force, and under the action of the forming force, the metal material 13 is stretched into the composite material through hole 123. At the same time, the composite material scrap 121 is ejected upward. After the composite material scrap 121 contacts the die ejector 2, the composite material scrap 121 stops moving upward.

[0048] like Figure 3 As shown, in order to ensure the pre-tightening effect, during the riveting process, the cylinder spring 4 is in a pressurized state, and the moving outer cylinder 102 and the fixed outer cylinder 101 are at the same height.

[0049] 5) Due to the supporting effect of the die's reverse ejection, the stretched metal material is subjected to opposing compression from the composite scrap 10 and the punch 6 at the bottom. The bottom 13 of the metal material is upsetting due to compression, and the neck 11 of the metal material forms a tight fit with the through hole 15 of the composite material.

[0050] 6) Connection complete and reliable.

[0051] 7) such as Figure 4 As shown, the movable outer cylinder 102 opens, and the composite waste 121 is discharged. The cylinder spring 4 is in the depressurized state, and the movable outer cylinder 102 moves vertically upward by the spring tension to form an opening on the side of the die cavity. This opening allows for the collection of cutting waste without opening the die cavity as a whole. After the discharge process is completed, the cylinder spring 4 re-enters the pressurized state.

[0052] 8) Close the outer cylinder 102, open the upper mold, and remove the connecting material.

[0053] Based on specific practical experiments, using plate thickness t 12 =2mm thermoplastic carbon fiber composite plate CF-PA66 and plate thickness t 13 An experiment was conducted on a 2mm thick five-series aluminum alloy rolling plate AA5182. At the riveting station, the outer cylinder 1 of the die and the die back 2 were on top, the punch 6 and the pressure ring 7 were on the bottom, the composite material 12 was placed at the die end, and the metal material 13 was placed at the punch end. Neither of them required any surface pretreatment.

[0054] The anti-ejection depth d of the die is set to 2.1 mm, the distance between the laser 9 and the upper surface of the composite material 12 is 5 mm, and the power of the laser 9 is set to 350 W (60%), the frequency to 9 kHz, and the diameter to 5 mm. The annular laser beam 91 is always perpendicular to the surface of the composite material 12 and vaporizes the composite material 12, forming a composite through hole 123 in the composite material 12 and producing a complete sheet-like composite waste 121. The result is as follows: Figure 10 As shown, its cut surface is regular with no exposed fibers, and the heat-affected zone is small. The results are as follows... Figure 11 As shown.

[0055] During the laser cutting of the composite material, the temperature of the overlapping area of ​​the metal material rises rapidly, reaching a maximum temperature of 264℃ within 0.4 seconds. The laser cutting lasts for 2.0 seconds, during which the temperature of the overlapping area of ​​the metal material remains above 200℃. The results are as follows... Figure 12 As shown.

[0056] Further, the outer cylinder of the die 1 and the die ejector 2 are initially pressed down synchronously at a rapid speed of 50 mm / s. As they approach the connecting material, the speed is reduced to 20 mm / s for a slow, synchronous downward press until they are fully in contact with the surface of the composite material 12. A pre-tightening pressure of 2 MPa is applied to the outer cylinder of the die. The timing of the punch 14's activation is determined by the temperature measured by the thermistor 16 within the pressure ring 15: when the measured temperature drops by 5%, the punch 14 begins to feed upwards at a speed of 30 mm / s to apply forming force. Under the combined compression of the punch 14 and the composite material scrap 121, the bottom 132 of the metal material is thinned to 20% of the original plate thickness. This thinning of the metal material results in a certain amount of radial material flow, thus forming a tight fit at the riveting joint, such as... Figure 13 As shown.

[0057] When the thickness of the composite material is close to that of the metal material, the bottom of the metal material after plastic deformation may be lower than the bottom surface of the composite material, such as... Figure 9 As shown or aligned with the bottom surface of the composite material, such as Figure 8As shown, the plastically deformed metal material forms a tight fit with the composite material; when the thickness of the metal material is much greater than the thickness of the composite material, the plastically deformed metal material may be higher than the bottom surface of the composite material, such as... Figure 7 As shown, the metal material above the bottom surface of the composite material can undergo greater radial deformation due to the forming force, thereby forming a greater mechanical engagement.

[0058] When the cylinder spring is in the depressurized state, the moving outer cylinder moves vertically upwards by the spring tension to form the opening on the side of the die. Figure 4 As shown, the movable outer cylinder 102 opens, and the composite waste 121 is discharged. The movable outer cylinder 102 closes, the upper mold opens, and the cutting waste can be collected through its opening without opening the entire concave mold. After the discharge process is completed, the cylinder spring re-enters the pressurized state.

[0059] When joining identical metal materials and composite materials without rivets, the laser-assisted rivetless joining process proposed in this paper offers advantages over existing rivetless joining methods, including shorter connection time, elimination of material pretreatment, and applicability to various composite material types. The thermal effect generated by laser cutting effectively heats the metal materials being joined. Especially when joining aluminum alloys, the resulting temperature softens aged aluminum alloys and high-strength aluminum alloys, improving their plastic deformation capacity. Specific data are shown in the table below:

[0060]

[0061] Compared with existing technologies, this invention utilizes the difference in absorption capacity of resin-based composite materials and metal materials for laser energy in specific laser bands to achieve a continuous process of plastic deformation in laser cutting of composite and metal materials, thereby realizing rivetless riveting of composite and metal materials without pre-drilled holes. The laser 9 can emit a ring beam to achieve circumferential cutting of composite materials, and the slide rail 11 can achieve precise positioning of the riveting die to ensure connection quality. After riveting, the outer cylinder 1 of the concave die can be opened in sections, thereby enabling the collection of composite material cutting waste without fully opening the riveting die, avoiding the impact of composite materials on other results and the environment.

[0062] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for ring-shaped laser-assisted rivetless joining of composite materials and metal materials, characterized in that, First, the composite material is stacked on the metal material and laser circumferential cutting is performed on the composite material using a ring laser to form regular through holes; then, the connecting plates are pre-tightened by pressing down the concave die; under the forming force of the upward movement of the punch, the metal material undergoes plastic deformation and forms a rivetless joint with the cut hole of the composite material; The cavity mold includes: a cavity outer cylinder, a counter-ejection mechanism, and a second support block arranged sequentially from bottom to top; the punch mechanism includes: a pressure ring and a punch disposed at the center of its interior, the punch facing the counter-ejection mechanism. The anti-ejection mechanism includes: a die anti-ejection mechanism and a spring cylinder and a first support block disposed outside thereon, wherein: the die anti-ejection mechanism is disposed in the inner hole of the first support block and extends into the inner cavity of the die outer cylinder but does not protrude from the die outer cylinder; The outer cylinder of the die is a two-section structure, including a fixed outer cylinder and a movable outer cylinder, wherein: the fixed outer cylinder is connected to the first support block of the anti-jacking mechanism, and the movable outer cylinder is connected to the spring cylinder; The outer cylinder of the die and the first support block have concentric through holes of the same size; The external part of the die cavity is provided with a die cavity box and a box cover plate, wherein: the outer cylinder of the die cavity is placed inside the bottom of the die cavity box, and the bottom of the outer cylinder of the die cavity protrudes from the bottom of the die cavity box through the bottom through hole; the upper surfaces of the die cavity top, the first support block and the spring cylinder are flush and connected to the second support block.

2. The annular laser-assisted rivetless joining method for composite materials and metal materials according to claim 1, characterized in that, The metal material is a metal that is easily plastically deformed, and its thickness is t. 13 =0.5-5.0mm; the composite material is carbon fiber or glass fiber with thermoplastic or thermosetting resin as the matrix, and its thickness t 12 =0.5-5.0mm.

3. The annular laser-assisted rivetless joining method for composite materials and metal materials according to claim 1, characterized in that, The aforementioned laser ring cutting disperses a point laser beam into a ring-shaped laser beam using optical principles. The width of the ring-shaped laser spot is less than or equal to 0.3 mm, the diameter of the ring-shaped laser spot is less than or equal to 10 mm, and the laser source power P = at. 12 -b, a = 120W / mm; b = 40W; The laser circumferential cutting process, wherein the highest temperature T of the composite material satisfies: et 12 +140℃ < T < et 12 +190℃, e = 30℃ / mm, if the circumferential cutting is qualified, riveting can proceed; if the maximum temperature exceeds the range, the circumferential cutting is unqualified and the process ends.

4. The annular laser-assisted rivetless riveting method for composite materials and metal materials according to any one of claims 1-3, characterized in that, The connecting plates are pre-tightened, and the pre-tightening pressure is q·(t) 12 +t 13 ), q = 0.125 mm / MPa.

5. The annular laser-assisted rivetless joining method for composite materials and metal materials according to claim 4, characterized in that, When the punch moves toward the metal material and applies an upward forming force, the metal material undergoes plastic deformation toward the die under the punch pressure. The resulting composite scrap is ejected by the deformed metal material, and its height is limited by the die's ejection position: the die ejection distance d = t. 12 ±0.4mm, when the composite waste comes into contact with the die ejector, they jointly provide support for the metal material. Under the combined action of the forming force and the support force, the metal material is thinned to 20%t at the bottom. 13 -50%t 13 This leads to radial flow of the material.

6. The annular laser-assisted rivetless joining method for composite materials and metal materials according to claim 1, characterized in that, The diameter of the punch , The diameter of the hole is β, and the bevel angle is β = 2°-10°.

7. The annular laser-assisted rivetless joining method for composite materials and metal materials according to claim 1, characterized in that, After riveting is completed, the spring cylinder inside the die is depressurized, and the spring tension causes the outer cylinder of the die to slide upward to form an opening, through which the cutting waste is recycled.

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