Preformed-hole-free connection method for thermoplastic resin-based composite material and metal material

Abstract

The invention discloses a prefabricated-hole-free connection method for a thermoplastic resin-based composite material and a metal material. A rivet tip end of a semi-hollow rivet is of a dip angle structure with an inclined inner cavity. Low-pressure penetration of the thermoplastic resin matrix composite upper-layer plate is achieved by means of high-speed rotation of the rivets, the bonding-riveting-welding prefabricated-hole-free composite connection technology is adopted, the problems of material damage, breakage, chipping and the like caused in the riveting process are solved, the sealing effect is achieved on a connection interface, and the corrosion resistance of a connection joint is improved.

Description

Technical Field

[0001] The present invention relates to a technology in the field of machining, specifically a method for connecting a thermoplastic resin-based composite material and a metal material without pre-drilled holes. Background Art

[0002] Existing riveting with pre-drilled holes requires additional hole-making processes, and the joint sealing performance and anti-electrochemical corrosion ability are poor; the impact force of riveting without pre-drilled holes is large, which is easy to damage the composite material. Mechanical locking depends on the plastic deformation ability of the rivet and the metal material, and the connection strength is insufficient, making it difficult to rivet metal materials with poor plasticity. The existing friction riveting technology for composite materials and aluminum alloys generates heat through rotational friction, and at the same time adjusts the rotational speed and axial feed speed of the rivet to achieve the optimal riveting and welding state value between the thermoplastic carbon fiber composite material plate and the aluminum alloy plate. However, the existing technology cannot avoid the damage and delamination of carbon fibers caused by rotational friction; rotational friction can only make the thermoplastic resin flow by heating, and the carbon fiber filaments of the base material have a large resistance to plastic flow and large deformation resistance, resulting in cracking and damage of the thermoplastic carbon fiber composite material. At the same time, the debris of the composite material is likely to exist at the contact interface between the rivet and the aluminum alloy, resulting in insufficient strength and even riveting failure. Summary of the Invention

[0003] Aiming at the problems that the existing riveting process is prone to damage, deformation and cracking of thermoplastic resin-based composite materials and metal materials, the present invention provides a method for connecting thermoplastic resin-based composite materials and metal materials without pre-drilled holes. By means of the high-speed rotation of the rivet, low-pressure penetration of the upper layer of the thermoplastic resin-based composite material is realized, and a non-pre-drilled hole composite connection technology of adhesion-riveting-welding is adopted to reduce problems such as material damage and fracture debris caused during the riveting process, form a sealing effect on the connection interface, and improve the corrosion resistance of the connection joint.

[0004] The present invention is realized through the following technical solutions:

[0005] The present invention relates to a semi-hollow rivet for connecting thermoplastic resin-based composite materials and metal materials without pre-drilled holes, and the tip of the rivet adopts an inclined inner cavity angle structure.

[0006] The tip of the rivet is provided with a cutting edge to ensure a good cutting effect on the thermoplastic resin-based composite material when the rivet rotates at a high speed, and at the same time promote the quick movement of the cut material into the inner cavity of the rivet, reducing the residual debris between the rivet and the thermoplastic resin-based composite material.

[0007] The length L of the semi-hollow rivet w and the thickness t of the thermoplastic resin-based composite material c and the thickness t of the metal material m satisfy: t c +α×tm <L w <t c +(α + β)×t m , where: α is the wear length, β is the riveting and welding depth, and 0.1 ≤ α ≤ 0.5, 0.05 ≤ β ≤ 0.1, so as to achieve the effect that the rivet penetrates the upper thermoplastic resin matrix composite material plate and friction-welds with the surface of the lower metal plate, and obtain good connection strength.

[0008] The semi-hollow rivet is made of the same material as the metal plate to be connected located below the thermoplastic resin matrix composite material.

[0009] The present invention relates to a composite connection method for forming a thermoplastic resin matrix composite material and a metal material, comprising the following steps:

[0010] 1) Conduct experiments on specific materials and rivets, set thermocouple sensors in the rivet body or in the metal material near the rivet hole to measure the contact interface temperature during the riveting process in real time. After measuring the temperature of the contact interface under different riveting process parameters, calibrate the loss factor η of the friction heat generation converted into temperature rise according to the calculated temperature rise and the actually measured temperature rise, and obtain the correlation calculation model between the process parameters and the contact interface temperature rise.

[0011] The so-called calibration means: The so-called adjustment means: By controlling the rivet feeding speed and the rivet rotation speed, the friction heat generation Q between the rivet and the metal material is made to be within a safe range, specifically: where: F f is the axial feeding force of the rotary drive shaft, M is the torque of the rotary drive shaft, V f is the rivet feeding speed, ω is the rivet rotation speed in the first stage of the process, Δt is the process time; η is the loss factor in the process of friction heat transfer, C 1 is the specific heat capacity of the thermoplastic composite material, m 1 is the mass of the thermoplastic composite material in the inner cavity of the rivet, C 2 is the specific heat capacity of the metal material, m 2 is the mass of the metal in the inner cavity of the rivet, ΔT is the temperature rise of the material in the inner cavity of the rivet; where: is the outer diameter of the rivet body, f is the feeding amount of the rivet. According to f and, t c the masses m 1 and m 2 of the thermoplastic composite material and the metal material in the inner cavity of the rivet can be determined; based on F f 、V f 、M, ω and Δt in the riveting process, the friction heat generation Q can be determined, and then C 1 and C2 Calculate the temperature rise ΔT caused by the riveting process. By measuring the actual temperature rise of the contact interface at different riveting stages through sensors and other means, the change curve of the loss factor η can be calibrated, thereby establishing a correlation calculation model between the riveting process parameters and the temperature rise, and ultimately achieving the control of the temperature of the rivet contact interface through the riveting process parameters.

[0012] Preferably, a software program for real-time temperature calculation is pre-written in the riveting equipment, so as to calculate the temperature rise of the contact interface according to the process parameters collected and output in real time, and adjust the feeding speed V of the rivet f and the rotational speed ω of the rivet, so that the temperature of the thermoplastic resin during the riveting process is within the range of the melting temperature and the cracking temperature.

[0013] 2) Process preparation: After the surfaces of the rivet and the metal plate are modified according to the set parameters by pulsed laser, the thermoplastic resin matrix composite plates to be joined are stacked on the metal material plate, and then the whole stack is placed on the support mechanism, and the workpiece to be joined is pressed by the blank holder;

[0014] For the said modification treatment, it is carried out on the lower surface of the rivet head, the outer wall of the nail body, the end of the nail body and the upper surface of the metal plate to improve the bonding strength between the rivet and the thermoplastic resin, and between the metal plate part and the thermoplastic resin, with the surface roughness reaching 1 - 5μm as the standard, and the surface roughness where: a and b are correlation coefficients, and the spot spacing of the same laser scanning line The parallel spacing of different laser scanning lines v l is the laser scanning speed, is the laser spot diameter, F l is the laser pulse frequency.

[0015] 3) Contact stage: The coaxial assembly of the rivet and the rotating drive spindle is realized through the card slot on the upper surface of the rivet cap. The rotating drive shaft performs axial feeding according to the set process parameters, makes the tip of the rivet body approach the upper surface of the thermoplastic resin matrix composite to be joined, and controls the interface temperature of the metal / thermoplastic resin matrix composite within the range of the melting temperature and the cracking temperature of the thermoplastic resin by adjusting the process parameters.

[0016] The melting temperature and cracking temperature of the thermoplastic resin of the materials used are obtained by, but not limited to, differential scanning calorimetry.

[0017] 4) Piercing stage: The rotating drive shaft drives the rivet to rotate at a set speed, and then makes the rivet perform axial movement according to the set feeding speed. When the tip of the rivet body pierces into the upper thermoplastic resin matrix composite, it is set that the rotating drive shaft completes the piercing stage with a constant axial feeding force;

[0018] In the described piercing stage, the maximum threshold value F of the axial feeding force f <0.8×A×σ p , and the maximum threshold value of the radial cutting force where: A is the contact area between the tip of the rivet and the thermoplastic resin matrix composite material, σ p is the interlaminar peel strength of the thermoplastic resin matrix composite material, M is the reaction torque received by the rotating drive shaft head, is the diameter of the tip of the rivet body, τ s is the shear strength of the carbon fiber filaments in the thermoplastic resin matrix composite material.

[0019] The interlaminar peel strength and shear strength are obtained by testing according to national test standards; the contact area is calculated from the geometric dimensions of the tip of the rivet, and then the maximum threshold values of the axial feeding force and radial cutting force in the piercing stage are determined. Among them: the maximum threshold value of the radial cutting force is obtained by back-calculation based on M and back-calculated.

[0020] 5) Friction stage: After the rivet pierces through the upper thermoplastic resin matrix composite material plate, the tip of the rivet body stirs and frictions with the lower metal plate. According to the set process parameters, the rotation speed and feeding speed of the rivet are controlled. After the rivet stops rotating and feeding, the tip of the rivet body completes solid-phase welding with the lower metal plate. And under the action of the axial feeding force, the rivet undergoes plastic deformation and expands outward, thus forming a mechanical locking riveting effect;

[0021] 6) Adhesion stage: The stirring and friction between the rivet and the lower metal plate generate heat. According to the process parameters of the rivet: the axial feeding force F f , torque M, feeding speed V f , rotation speed ω and process time Δt, after the frictional heat generation Q is calculated in real time, based on the masses m 1 and m 2 of the thermoplastic composite material and the metal material in the inner cavity of the rivet, as well as the specific heat capacities C 1 and C 2 of the two materials, and the pre-calibrated loss factor η, the temperature rise value at the interface is calculated by back-calculation, so as to obtain the interface temperature. By changing the feeding speed and / or rotation speed, etc., to control the interface temperature within the melting temperature and cracking temperature range, so that the thermoplastic resin is heated and melted and flows into the connection interface gap. After the rivet stops rotating, the downward pressure is continuously maintained, and the molten thermoplastic resin gradually cools to form an adhesive area;

[0022] 7) Process end: The rivet completes the connection process of the thermoplastic resin matrix composite material and the metal material. The rotating drive shaft is in a stopped rotating state, and then feeds backward to return to the original position. The blank holder is released and a composite connection joint is formed. Technical effects

[0023] In the present invention, a cutting edge is prepared at the tip of the rivet body, and the high-speed rotation of the rivet is utilized to achieve high cutting effect and low extrusion piercing of the thermoplastic resin matrix composite material; by controlling the torque and axial feeding force of the high-speed rotation of the rivet, the geometric structure size of the tip of the rivet body, etc., low-damage piercing of the thermoplastic resin matrix composite material is realized, avoiding delamination damage and splitting; under the action of the frictional heat generation between the rivet and the metal material, the thermoplastic resin is heated and melted, so as to fill the cutting section of the thermoplastic resin matrix composite material, and an adhesive effect is formed on the contact interface of the three of the rivet-thermoplastic resin matrix composite material-metal material. The interface temperature can be controlled between the melting temperature and the cracking temperature of the thermoplastic resin by the feeding speed, axial feeding force, rotation speed, torque of the rivet and the geometric size of the rivet body. Compared with the prior art, the present invention can realize low-damage piercing of the thermoplastic resin matrix composite material, and at the same time, the adhesive-riveting-welding composite connection effect can be realized through a single process, with high process efficiency, small riveting impact force, and reduced requirements for the structural load, stiffness and anti-wear of the riveting equipment. Description of the Drawings

[0024] Figure 1 is a semi-hollow rivet with a cutting edge;

[0025] Figure 2 is a schematic diagram of the present invention;

[0026] Figure 3 is a schematic diagram of laser modification;

[0027] Figure 4 is the rivet size and joint cross-sectional view adopted in the experiment;

[0028] Figure 5 is the single-lap shear test curve of the joint obtained under different process parameters. Detailed Embodiments

[0029] As Figure 1 shown, the semi-hollow rivet with a cutting edge adopted in this embodiment includes: a rivet head 101, an inclination structure 102 of the oblique inner cavity, a rivet shank 103 and a rivet inner cavity 104.

[0030] In this embodiment, the height H of the rivet head is 2 mm and the diameter is 10 mm, and the length L of the rivet body w is 5.8 mm, the height L of the rivet inner cavity n is 6.8 mm, the diameter of the rivet inner cavity is 4.9 mm, the outer diameter of the rivet body is 6.6 mm, the thickness t of the carbon fiber PEEK composite material c is 4.5 mm, and the thickness t of the stainless steel plate material m is 3 mm.

[0031] As Figure 2 shown, this embodiment is based on the above-mentioned connection method of thermoplastic resin-based composite materials and metal materials for semi-hollow rivets, and includes:

[0032] 1) Laser modification: Use a 10W infrared pulsed laser (wavelength 1064nm, pulse width 200ns, laser spot diameter is 50μm) pulsed laser to treat the surfaces of the rivet and the stainless steel plate. The pulse frequency F l used is 30Hz, the scanning speed v l is 1500mm / s, and the parallel spacing S c is 50μm. The initial surface roughness of the rivet is 0.24μm, and the surface roughness R a of the rivet obtained by laser treatment is 2.83μm. The initial surface roughness of the stainless steel plate is 0.18μm, and the surface roughness R a of the stainless steel plate obtained by laser treatment is 2.85μm.

[0033] 2) Process preparation: Place the carbon fiber PEEK composite material plates to be joined on the stainless steel plate, and then stack them as a whole on the support mechanism. Use a blank holding force of 50N to press the workpiece to be joined through the blank holder ring;

[0034] 3) Contact stage: Realize the coaxial assembly of the rivet and the rotating drive spindle through the upper surface slot of the semi-hollow rivet. The rotating drive shaft feeds axially at a rate of 3mm / s so that the tip of the rivet body approaches the upper surface of the carbon fiber PEEK composite material to be joined;

[0035] 4) Piercing stage: The rotating drive shaft drives the rivet to rotate at a high speed of 2400rpm, and then makes the rivet move axially at the set feed speed. When the tip of the rivet body pierces into the upper layer of carbon fiber PEEK composite material, set the axial feed force F f of the rotating drive shaft to be controlled not higher than 8kN to complete the piercing stage. The average torque M of the rotating drive shaft is 10Nm. This stage is mainly a cutting piercing process, with a small temperature rise. The temperature at the position near the rivet hole rises from ~20.3°C to ~30.7°C;

[0036] 5) Friction stage: After the rivet pierces through the upper layer of carbon fiber PEEK composite material plate, the tip of the rivet body stirs and frictions with the lower layer of stainless steel plate. Set the rotation speed of the rivet to 2400rpm and the feed speed to 8mm / s. At this time, the temperature on the upper surface of the carbon fiber PEEK composite material near the rivet hole rises to a maximum of ~352.4°C. After the rivet stops rotating and feeding, the tip of the rivet body completes solid-phase welding with the lower layer of stainless steel plate;

[0037] 6) Bonding stage: The heat generated by the friction stir between the rivet and the lower stainless steel plate causes the thermoplastic resin to heat up and melt, flowing into the gap at the connection interface of the stainless steel / carbon fiber PEEK composite material. After the rivet stops rotating, the downward pressure is maintained. The molten thermoplastic resin gradually cools to form a bonding area. The bonding area between the rivet head and the upper surface of the carbon fiber PEEK composite material is approximately a ring (outer diameter 10 mm, inner diameter 6.6 mm), the bonding area between the rivet body and the hole wall of the carbon fiber PEEK composite material is a cylindrical surface, and the bonding area between the carbon fiber PEEK composite material and the stainless steel is a ring (outer diameter 15.4 mm, inner diameter 8.5 mm); the rivet completes the connection process, the rotary drive shaft stops rotating, and then feeds backward to return to the original position. The blank holder is released, and the composite connection joint is formed, and the process ends.

[0038] As Figure 3 shown, different laser modification parameters can change the surface roughness of materials such as rivets and metal plates, thereby ensuring the improvement effect on the bonding strength between the rivet and the thermoplastic resin, and between the metal plate and the thermoplastic resin.

[0039] As Figure 4 shown, the semi-hollow rivet with a cutting edge used in the present invention can have a good cutting and piercing effect on the composite material, and cause the thermoplastic resin to heat up and melt to form a bonding interface between "the rivet and the composite material" and "the composite material and the metal plate"; at the same time, a good solid-phase welding interface is formed between the rivet and the lower metal plate under the action of friction stir.

[0040] As Figure 5 shown, improper parameter A results in too high interface temperature and causes thermal damage; parameter B has insufficient interface temperature between the rivet and the stainless steel substrate, resulting in slightly lower connection strength, mainly due to insufficient solid-phase welding degree and smaller bonding area; the optimized parameter C can form a good combination of bonding, riveting and welding, and the single-lap shear strength of the joint reaches 15.4 kN, with excellent performance.

[0041] In summary, for the joint obtained by the present invention for the carbon fiber PEEK composite material with a thickness of 4.5 mm and the stainless steel with a thickness of 3 mm, the maximum connection force under the single-lap shear test condition is 15.4 kN, which is 492% higher than 2.6 kN of the traditional self-piercing riveting joint, 59% higher than 9.7 kN of the pre-drilled blind riveting joint, and equivalent to the performance of 15.8 kN of the Hi-Lok bolt joint. The present invention omits the pre-drilling process, improves the connection efficiency, reduces the requirement for the axial feeding force of the connection equipment, introduces a bonding interface through frictional heat generation, improves the sealing and corrosion resistance of the connection joint. In addition, the presence of the bonding interface helps to improve the stress concentration at the connection interface.

[0042] The above specific embodiments can be locally adjusted in different ways by those skilled in the art without departing from the principles and purposes of the present invention. The protection scope of the present invention is subject to the claims and is not limited by the above specific embodiments. All implementation solutions within its scope are subject to the present invention.

Claims

1. A semi-hollow rivet for connecting thermoplastic resin-based composite materials and metal materials without prefabricated holes, characterized in that: The tip of the rivet adopts an angled structure that is oblique to the inner cavity; The rivet tip is provided with a cutting edge; The length L of the semi-hollow rivet w The thickness of thermoplastic resin matrix composite material c , metal material thickness t m Satisfy: t c +α×t m <L w <t c +(α+β)×t m , where: α is the wear length, β is the riveting depth.

2. The semi-hollow rivet for connection without prefabricated holes according to claim 1, characterized in that: The semi-hollow rivet is made of the same material as the metal sheet to be connected and located below the thermoplastic resin-based composite material.

3. The semi-hollow rivet for connection without prefabricated holes according to claim 1, characterized in that: The wear length and riveting depth respectively satisfy: 0.1≤α≤0.5, 0.05≤β≤0.

1.

4. A composite connection method of thermoplastic resin-based composite materials and metal materials based on the semi-hollow rivets without prefabricated holes as claimed in claim 1, 2 or 3, characterized in that: include: 1) Conduct experiments for specific materials and rivets: Set a thermocouple sensor in the rivet body or in the metal material near the rivet hole to measure the contact interface temperature in real time during the riveting process. After measuring the temperature of the contact interface under different riveting process parameters, calibrate the loss factor η of the friction heat converted into temperature rise based on the calculated temperature rise and the actual measured temperature rise, and obtain the correlation calculation model between the process parameters and the contact interface temperature rise; 2) Process preparation: After the surface of the rivet and the metal plate are modified by a pulse laser according to the set parameters, the thermoplastic resin-based composite material plate to be connected is stacked on the metal material plate, and the whole is stacked on the support mechanism, and the workpiece to be connected is pressed by a blank holder; 3) Contact stage: The rivet and the rotating drive spindle are coaxially assembled through the slot on the upper surface of the rivet cap, and the rotating drive spindle is axially fed according to the set process parameters, so that the tip of the rivet body is close to the upper surface of the thermoplastic resin-based composite material to be connected, and the interface temperature of the metal / thermoplastic resin-based composite material is controlled to be within the melting temperature and cracking temperature range of the thermoplastic resin by adjusting the process parameters; 4) Piercing stage: the rotating drive shaft drives the rivet to rotate at a set speed at a high speed, and then the rivet is moved axially at a set feed speed. When the tip of the rivet body penetrates into the upper layer of the thermoplastic resin-based composite material, the rotating drive shaft is set to complete the piercing stage with a constant axial feed force; 5) Friction stage: After the rivet pierces the upper thermoplastic resin-based composite material plate, the tip of the rivet body stirs and rubs with the lower metal plate. The rotation speed and feed speed of the rivet are controlled according to the set process parameters. After the rivet stops rotating and feeding, the tip of the rivet body and the lower metal plate complete solid phase welding, and the rivet undergoes plastic deformation and expands outward under the action of the axial feed force, thereby forming a mechanically locked riveting effect; 6) Bonding stage: The stirring friction between the rivet and the lower metal plate generates heat, according to the axial feed force F f , torque M, feed speed V f After the friction heat Q is obtained by real-time calculation based on the rotation speed ω and the process time Δt, the temperature rise value at the interface is obtained by reverse calculation based on the mass m1 and m2 of the thermoplastic composite material and the metal material in the rivet cavity, the specific heat capacities C1 and C2 of the two materials, and the pre-calibrated loss factor η, thereby obtaining the interface temperature; by changing the feed speed and / or the rotation speed to control the interface temperature to be within the melting temperature and cracking temperature range, the thermoplastic resin is melted by heat and flows into the connection interface gap, and the downward pressure is maintained after the rivet stops rotating, and the molten thermoplastic resin is gradually cooled to form a bonding area; 7) End of process: The rivet completes the connection process between the thermoplastic resin-based composite material and the metal material. The rotating drive shaft is stopped and then fed in the reverse direction and returns to its original position. The blank holder is released and a composite connection joint is formed.

5. The composite connection method according to claim 4, characterized in that: The calibration means: The adjustment means: by controlling the rivet feeding speed and the rivet rotation speed, the friction heat Q between the rivet and the metal material is within a safe range, specifically: Among them: F f is the axial feed force of the rotating drive shaft, M is the torque of the rotating drive shaft, V f is the rivet feed speed, ω is the rivet rotation speed in the first stage of the process, Δt is the process time, η is the loss factor in the friction heat transfer process, C1 is the specific heat capacity of the thermoplastic composite material, C2 is the specific heat capacity of the metal material, ΔT is the temperature rise of the rivet inner cavity material, and the mass of the rivet inner cavity thermoplastic composite material is The quality of the metal inside the rivet is the outer diameter of the rivet body, and f is the feed rate of the rivet; according to f and t c Determine the mass m1 and m2 of the thermoplastic composite material and the metal material in the rivet cavity; according to the F f 、V f , M, ω and Δt to determine the friction heat Q, and then calculate C1 and C2 to obtain the temperature rise ΔT caused by the riveting process. The actual temperature rise of the contact interface at different riveting stages is measured by sensing to calibrate the change curve of the loss factor η, so as to establish a correlation calculation model between the riveting process parameters and the temperature rise, and finally achieve the control of the rivet contact interface temperature by the riveting process parameters.

6. The composite connection method according to claim 4, characterized in that: The modification treatment is carried out on the lower surface of the rivet cover, the outer wall of the rivet body, the end of the rivet body and the upper surface of the metal plate to improve the bonding strength between the rivet and the thermoplastic resin, and between the metal plate and the thermoplastic resin, with the surface roughness reaching 1-5μm. Where: a and b are correlation coefficients, and the spot spacing of the same laser scanning line Parallel spacing of different laser scanning lines v l is the laser scanning speed, is the laser spot diameter, F l is the laser pulse frequency.

7. The composite connection method according to claim 4, characterized in that: In the piercing stage, the maximum threshold F of the axial feed force is f <0.8×A×σ p , the maximum threshold of radial cutting force Where: A is the contact area between the rivet tip and the thermoplastic resin matrix composite material, σ p is the interlaminar peel strength of the thermoplastic resin-based composite material, M is the reaction torque on the rotating drive shaft head, is the diameter of the rivet tip, τ s It is the shear strength of carbon fiber filaments in thermoplastic resin matrix composites.

8. The composite connection method according to claim 7, characterized in that: The interlayer peel strength and shear strength are obtained according to the national test standard test; the contact area is calculated by the geometric dimensions of the rivet tip, and then the maximum thresholds of the axial feed force and radial cutting force in the piercing stage are determined, wherein: the maximum threshold of the radial cutting force is based on M and Obtained by reverse push.

Images