CN114918361B

CN114918361B - Low-frequency auxiliary self-piercing riveting device and riveting method using same

Info

Publication number: CN114918361B
Application number: CN202210631532.XA
Authority: CN
Inventors: 林军; 邵聪; 李姣; 刘雨晴; 管延锦; 王硕; 李卓裔
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2022-06-06
Filing date: 2022-06-06
Publication date: 2023-08-22
Anticipated expiration: 2042-06-06
Also published as: CN114918361A

Abstract

The invention relates to the technical field of mechanical connection, and provides a low-frequency auxiliary self-piercing riveting device and a riveting method using the same. Comprising the following steps: the device comprises a low-frequency vibration generating device, a hydraulic cylinder, a matched blank holder and a female die; the output end of the hydraulic cylinder is sequentially connected with a force sensor and a punch, and the punch enters the blank holder to drive the semi-hollow rivet to move up and down to be close to or far away from the female die; low frequency vibrations are accompanied during the up and down movement of the punch and semi-hollow rivet. The invention has the beneficial effects that: the semi-hollow rivet is accompanied by low-frequency vibration during working, the downward force of the punch is reduced during punching the upper plate, meanwhile, the damage to fibers in the upper plate is reduced due to friction, and the mechanical property of the riveting joint is improved; the lower plate material is softened when the lower plate is pierced, the deformation of the lower plate is promoted, the cracking of the lower plate material in the riveting process is effectively prevented, the plate material is favorably filled in the female die, and the punch pressing force is also reduced.

Description

Low-frequency auxiliary self-piercing riveting device and riveting method using same

Technical Field

The invention relates to the technical field of mechanical connection, in particular to a low-frequency auxiliary self-piercing riveting device and a riveting method using the same.

Background

The self-punching riveting is to pierce the upper plate with a semi-hollow rivet at room temperature and then pierce the lower plate to generate plastic deformation so as to expand the nail angle, thereby forming a mechanical inner locking structure and realizing plate connection. The riveting joint has the technical characteristics of no need of prefabricated holes, high connection efficiency, good reliability and the like, has good sealing property, high strength and high fatigue property, is widely applied to vehicle body manufacturing and is gradually popularized to the aerospace field.

In the self-piercing riveting process of the carbon fiber composite material and the light alloy such as aluminum, magnesium and titanium, which are important ways for light weight of modern automobiles, rail transit and aerospace aircrafts, the carbon fiber composite material has higher brittleness, and in the self-piercing riveting process, rivet legs can pierce through a carbon fiber plate to cause damages such as fiber breakage, matrix cracking, interlayer separation and the like in the composite plate, so that the connection strength and the service life of a riveting member are seriously reduced; meanwhile, with the improvement of the strength of the bottom layer light alloy sheet, the alloy rivet with the strength matched with the bottom layer light alloy sheet is required to be used, so that the rivet legs are easy to generate microcracks under the restraint of the high-strength plate, difficult to expand and deform outwards and incapable of driving the sheet to generate enough plastic deformation to form high-quality mechanical interlocking

In order to solve the problems, two riveting processes of hot self-piercing riveting and electromagnetic self-piercing riveting exist at present. However, the heat input and the electromagnetic high-speed impact load can cause internal damage of the composite material, and residual tensile stress is easily generated around the nail holes due to uneven temperature distribution, so that the fatigue life of the joint is reduced.

Therefore, there is a need to improve the existing riveting process and develop a riveting method that can avoid material damage, improve material plasticity, and form good joint quality.

Disclosure of Invention

The invention aims to provide a low-frequency auxiliary self-piercing riveting device and a riveting method using the same, so as to solve the technical problems in the prior art.

In order to achieve the above purpose, the invention adopts the following technical scheme: a low frequency assist self-piercing riveting device comprising: the device comprises a low-frequency vibration generating device, a hydraulic cylinder, a matched blank holder and a female die; the output end of the hydraulic cylinder is sequentially connected with a force sensor and a punch, and the punch enters the blank holder to drive the semi-hollow rivet to move up and down to be close to or far away from the female die; low frequency vibrations are accompanied during the up and down movement of the punch and semi-hollow rivet.

In an alternative embodiment, the riveting device further comprises a servo valve for controlling the hydraulic cylinder to work, a displacement sensor for measuring the moving distance of the hydraulic cylinder and a pressure gauge for displaying the force of the force sensor.

On the other hand, the invention also provides a riveting method using the low-frequency auxiliary self-piercing riveting device, which comprises the following steps:

s1, assembling an upper plate and a lower plate which need to be riveted, and fully contacting the upper plate and the lower plate;

s2, placing the upper plate and the lower plate which are assembled above the female die;

s3, placing the blank holder above the upper plate, and simultaneously compacting the surface of the upper plate;

s4, placing the semi-hollow rivet in the blank holder, and enabling the semi-hollow rivet to be in contact with the upper surface of the upper plate;

s5, the hydraulic cylinder works, the punch is driven to move downwards and vibrate with low frequency, the semi-hollow rivet is driven to penetrate through the upper plate, and then the semi-hollow rivet penetrates into the lower plate, so that the lower plate is deformed until the female die is completely filled;

s6, stopping the punch from moving after the female die is completely filled, and staying for a period of time;

and S7, the punch leaves the semi-hollow rivet to return upwards, the blank holder and the female die are removed, the punch moves upwards to a designated position, and the riveting process is completed.

In an alternative embodiment, in S5, the movement speed of the punch is 1-10mm/min, and the time for penetrating the upper plate is 2-10S.

In an alternative embodiment, in S6, the punch residence time is 5-10 seconds.

In an alternative embodiment, the upper plate is a composite plate, and the composite plate comprises a resin matrix consisting of a thermoplastic resin matrix or a thermosetting resin matrix and a reinforcing phase; the reinforcing phase is one or more of carbon fiber, glass fiber or aramid fiber; the thermoplastic resin base is one or more of polyamide, polyacetyl imine, polyether-ether-ketone and polystyrene, and the thermosetting resin base is epoxy resin or phenolic resin.

In an alternative embodiment, the lower plate is a light alloy plate, and the light alloy plate is a high-strength aluminum alloy, a magnesium alloy or a titanium alloy.

In an alternative embodiment, in S5, the vibration frequency of the low-frequency vibration is 0-50Hz, the vibration amplitude is 0-0.3mm, and the vibration direction is up-down vibration.

In an alternative embodiment, the force sensor is connected with the punch through a bolt connection mode.

The invention has the beneficial effects that:

(1) In the riveting method, longitudinal low-frequency vibration is accompanied when the semi-hollow rivet pierces the upper plate, so that the downward force of the punch is reduced, the damage to fibers in the upper plate is reduced due to friction, and the mechanical property of the riveting joint is improved. Meanwhile, the semi-hollow rivet penetrates through the lower plate and is accompanied by longitudinal low-frequency vibration, so that the material of the lower plate is softened, the deformation of the lower plate is promoted, the lower plate material is effectively prevented from cracking in the riveting process, the lower plate material is favorably filled in the female die, and meanwhile, the punch pressing force is reduced.

(2) The low-frequency vibration generating device in the device is an electrohydraulic vibration exciter assisted by a servo press, has stable work and lower cost, is easy to realize automation, and can not generate the phenomenon that ultrasonic vibration cannot normally vibrate under the action of a large load.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic overall structure of a low-frequency auxiliary self-piercing riveting device according to an embodiment of the invention.

Fig. 2 is a schematic diagram of a riveting process of a low-frequency auxiliary self-piercing riveting device according to an embodiment of the invention.

Wherein, the reference numerals in the figures are as follows: the device comprises a servo valve 1, a hydraulic cylinder 2, a force sensor 3, a punch 4, a blank holder 5, a semi-hollow rivet 6, an upper plate 7, a lower plate 8 and a female die 9.

Detailed Description

In order to make the technical problems, technical schemes and beneficial effects to be solved more clear, the invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.

It will be understood that when an element is referred to as being "mounted" or "disposed" on another element, it can be directly or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly or indirectly connected to the other element. The directions or positions indicated by the terms "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are directions or positions based on the drawings, and are merely for convenience of description and are not to be construed as limiting the present technical solution. The terms "first," "second," and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features. The meaning of "a plurality of" is two or more, unless specifically defined otherwise.

Referring to fig. 1-2, an object of the present embodiment is to provide a low frequency auxiliary self-piercing riveting device, which includes: the low-frequency vibration generating device, the hydraulic cylinder 2, the blank holder 5 and the female die 9 which are matched for use, preferably, the low-frequency vibration generating device is an electrohydraulic vibration exciter assisted by a servo press, the working is stable, the cost is low, the automation is easy to realize, and meanwhile, the phenomenon that ultrasonic vibration cannot normally start under the action of a large load does not occur. The output end of the hydraulic cylinder is sequentially connected with a force sensor 3 and a punch 4, and the force sensor 3 is connected with the punch 4 in a bolt connection mode. The punch 4 enters the blank holder 5 to drive the semi-hollow rivet 6 to move up and down to be close to or far away from the female die 9; low frequency vibrations are accompanied during the up and down movement of the punch 4 and the semi-hollow rivet 6.

Specifically, the punch 4 and the semi-hollow rivet 6 are operative to pierce the upper and lower sheets 7 and 8. It should be noted that the upper plate 7 is a composite plate, and the composite plate includes a resin matrix composed of a thermoplastic resin matrix or a thermosetting resin matrix and a reinforcing phase; the reinforcing phase is one or more of carbon fiber, glass fiber or aramid fiber; the thermoplastic resin base is one or more of polyamide, polyacetyl imine, polyether-ether-ketone and polystyrene, and the thermosetting resin base is epoxy resin or phenolic resin. The lower plate 8 is a light alloy plate which is made of high-strength aluminum alloy, magnesium alloy or titanium alloy. The semi-hollow rivet 6 is accompanied with longitudinal low-frequency vibration when penetrating the upper plate 7, so that the downward pressing force of the punch 4 is reduced, meanwhile, the friction effect reduces the damage to fibers in the upper plate 7, and the mechanical property of the riveting joint is improved. Meanwhile, the lower plate 8 is pierced by the semi-hollow rivet 6 along with longitudinal low-frequency vibration, so that the material of the lower plate 8 is softened, the deformation of the lower plate 8 is promoted, the cracking of the material of the lower plate 8 in the riveting process is effectively prevented, the lower plate 8 is favorably filled in the female die 9, and meanwhile, the pressing force of the punch 4 is reduced.

In addition, the riveting device also comprises a servo valve 1 for controlling the hydraulic cylinder 2 to work, a displacement sensor for measuring the moving distance of the hydraulic cylinder 2 and a pressure gauge for displaying the stress of the force sensor 3.

In another embodiment of the present invention, there is provided a caulking method using the low frequency auxiliary self-piercing caulking apparatus as described above, comprising the steps of:

s1, pairing an upper plate 7 and a lower plate 8 which need to be riveted, and fully contacting the upper plate and the lower plate together;

s2, placing the assembled upper plate 7 and lower plate 8 above the female die 9;

s3, placing the blank holder 5 above the upper plate 5, and simultaneously compacting the surface of the upper plate 7;

s4, placing the half-hollow rivet 6 in the blank holder 5, and enabling the half-hollow rivet 6 to be in contact with the upper surface of the upper plate 7;

s5, the hydraulic cylinder 2 works, the punch 4 is driven to move downwards and vibrate at a low frequency, the moving speed of the punch 4 is 1-10mm/min, the semi-hollow rivet 6 is driven to penetrate into and penetrate through the upper plate 7, and the time for penetrating through the upper plate 7 is 2-10S; the semi-hollow rivet 6 then penetrates into the lower plate 8, deforming the lower plate 8 until the cavity 9 is completely filled; it is also pointed out that the vibration frequency of the low-frequency vibration is 0-50Hz, the vibration amplitude is 0-0.3mm, and the vibration direction is up-down vibration;

s6, after the female die 9 is completely filled, the punch 4 stops moving and stays for a period of time, and preferably, the stay time of the punch 4 is 5-10 seconds;

and S7, the punch 4 moves upwards away from the return stroke of the semi-hollow rivet 6, simultaneously the blank holder 5 and the female die 9 are removed, the punch 4 moves upwards to a designated position, and the riveting process is completed.

It is worth mentioning that the servo press gives out low frequency vibration to be applied to the punch 4, and during the riveting process, the low frequency vibration of the punch 4 is transferred to the semi-hollow rivet 6; when the semi-hollow rivet 6 is in contact with the upper plate 7, under the drive of low-frequency vibration, the semi-hollow rivet 6 is driven by the upper plate 7 to vibrate longitudinally, meanwhile, the upper plate is driven by the semi-hollow rivet 6 to vibrate so as to rub the surface of the lower plate 8, and after the semi-hollow rivet 6 pierces the upper plate 7, the semi-hollow rivet 6 moves downwards to contact with the lower plate 8, so that the semi-hollow rivet 6 is driven by the lower plate 8 to vibrate longitudinally, and meanwhile, the lower plate 8 is driven by the semi-hollow rivet 6 to vibrate so as to rub the surface of the female die 9. The friction effect fully softens the plate material of the penetration part of the semi-hollow rivet 6 in the riveting process, improves the plasticity of the material, reduces the riveting resistance, reduces the internal damage of the plate, promotes the deformation of the alloy plate, expands the top leg and improves the mechanical inner lock, thereby improving the mechanical property of the joint.

In order to better verify the softening effect by low frequency vibration, tests have been carried out on several sheet alloys as follows:

the Ti45Nb titanium alloy (lower plate) is deformed by low-frequency vibration, the low-frequency vibration with different frequencies and amplitudes has softening effect, and the maximum reduction of rheological stress reaches 54.1 percent, as shown in tables 1 and 2.

TABLE 1

Amplitude of vibration	0mm (without vibration)	0.05mm	0.1mm	0.2mm	0.3mm
						Deformation stress	680.72MPa	568.40MPa	478.95MPa	410.54MPa	312.23MPa
Decrease in amplitude	0％	16.5％	29.5％	39.7％	54.1％

TABLE 2

Frequency of vibration	0Hz (without vibration)	10Hz	20Hz	30Hz
					Deformation stress	677.83MPa	481.26MPa	362.56MPa	338.66MPa
Decrease in amplitude	0％	29％	46.3％	49.8％

The 6063 titanium alloy (lower plate) was deformed by low frequency vibration, which was softened by low frequency vibration of different frequencies and amplitudes to a maximum reduction in rheological stress of 50.4%, as shown in tables 3 and 4.

TABLE 3 Table 3

Amplitude of vibration	0mm (without vibration)	0.05mm	0.1mm	0.2mm	0.3mm
						Deformation stress	69.00MPa	55.72MPa	49.84MPa	40.83MPa	34.21MPa
Decrease in amplitude	0％	19.2％	27.7％	40.8％	50.4％

TABLE 4 Table 4

Frequency of vibration	0Hz (without vibration)	10Hz	20Hz	30Hz
					Deformation stress	69.00MPa	49.62MPa	45.5MPa	39.72MPa
Decrease in amplitude	0％	29.0％	34.0％	42.4％

In the step S1, the lower plate is made of a 2a12 aluminum alloy plate, and the upper plate is made of a carbon fiber reinforced epoxy resin matrix composite material; the amplitude of the low-frequency vibration adopted in the step S5 is 0.1mm, the vibration frequency is 20Hz, and the time for penetrating into the upper plate is 5S; in the step S7, the retention time after the punch stops moving is 8S; other steps in this example are consistent with the implementation described above.

The average peak load of the shaping after low frequency is reduced by 23.8% compared with the shaping under the condition of no vibration; meanwhile, the tensile strength of the formed riveted joint is improved by 8.5%, and the failure displacement is improved by 30.85%.

In an alternative embodiment, when the driving punch 4 drives the semi-hollow rivet 6 to pierce and penetrate the upper plate 7, as the internal hardness of the material inside the upper plate is different due to the characteristics of the processing and manufacturing process and the material itself, the pressure applied to the semi-hollow rivet 6 is different in the penetrating process, and when the pressure sensor 3 detects the pressure difference, the penetrating speed of the semi-hollow rivet 6, the frequency and the amplitude of the low-frequency vibration are adjusted in real time according to the pressure value in the process accompanied with the low-frequency vibration, so that the internal material of the upper plate is subjected to the low-frequency vibration parameter matched with the hardness of the upper plate to achieve the expected softening effect, and the upper plate is prevented from being additionally deformed; similarly, the lower plate is made of alloy materials, the hardness of the inner materials of the lower plate is different from top to bottom, the requirements on the low-frequency vibration parameters are higher in the process of deforming the lower plate, the vibration amplitude is further required to be reduced, the vibration frequency is increased, the descending speed of the punch 4 is reduced, the passing speed of the punch 4, the frequency and the vibration amplitude of the low-frequency vibration are adjusted in real time according to the pressure detected by the force sensor 3, so that the lower plate inner materials are subjected to the low-frequency vibration parameters matched with the hardness of the lower plate to achieve the expected softening effect, and the optimal riveting effect is achieved. That is, based on the pressure value detected by the force sensor 3 in real time, the punch 4 adjusts the amplitude, frequency and descending speed of the low-frequency vibration of the punch 4 in real time according to the difference of the hardness from top to bottom of the upper and lower plates, so as to achieve the optimal softening effect and riveting effect of the inside of each plate. The specific adjustment mode can be as follows: when the pressure value detected by the force sensor 3 in real time is larger (when the hardness is larger), the amplitude is reduced, the low-frequency vibration frequency is quickened, and the descending speed of the punch 4 is reduced; when the pressure value detected by the force sensor 3 in real time is smaller (hardness is smaller), the amplitude is increased, the low-frequency vibration frequency is reduced, the descending speed of the punch 4 is increased, and the softening effect and the riveting effect inside the plate are ensured.

The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.

Claims

1. A staking method using a low frequency assist self-piercing staking device comprising: the device comprises a low-frequency vibration generating device, a hydraulic cylinder (2), a blank holder (5) and a female die (9) which are matched with each other; the output end of the hydraulic cylinder is sequentially connected with a force sensor (3) and a punch (4), and the punch (4) enters the blank holder (5) to drive the semi-hollow rivet (6) to move up and down to be close to or far away from the female die (9);

characterized in that low frequency vibrations are accompanied during the up and down movement of the punch (4) and the semi-hollow rivet (6); the riveting device further comprises a servo valve (1) for controlling the hydraulic cylinder (2) to work, a displacement sensor for measuring the moving distance of the hydraulic cylinder (2) and a pressure gauge for displaying the stress of the force sensor (3);

the riveting method comprises the following steps:

s1, assembling an upper plate (7) and a lower plate (8) which need to be riveted, and fully contacting the upper plate and the lower plate;

s2, arranging the upper plate (7) and the lower plate (8) which are assembled to be finished above the female die (9);

s3, placing the blank holder (5) above the upper plate (7) and simultaneously pressing the surface of the upper plate (7);

s4, placing the semi-hollow rivet (6) in the blank holder (5) to enable the semi-hollow rivet (6) to be in contact with the upper surface of the upper plate (7);

s5, the hydraulic cylinder (2) works, the punch (4) is driven to move downwards and vibrate at a low frequency, the semi-hollow rivet (6) is driven to penetrate through the upper plate (7), and then the semi-hollow rivet (6) penetrates into the lower plate (8), so that the lower plate (8) is deformed until the female die (9) is completely filled;

the punch (4) is based on a pressure value detected by the force sensor (3) in real time, and the amplitude, the frequency and the descending speed of low-frequency vibration of the punch (4) are adjusted in real time according to the difference of the hardness of the upper plate and the lower plate from top to bottom; the adjustment mode is as follows: when the pressure value detected by the force sensor (3) in real time is larger, the amplitude is reduced, the low-frequency vibration frequency is accelerated, and the descending speed of the punch (4) is reduced; when the pressure value detected by the force sensor (3) in real time is smaller, increasing the amplitude, reducing the low-frequency vibration frequency and increasing the descending speed of the punch (4);

s6, after the female die (9) is completely filled, stopping the movement of the punch (4) and staying for a period of time;

s7, the punch (4) moves upwards away from the return stroke of the semi-hollow rivet (6), simultaneously the blank holder (5) and the female die (9) are removed, the punch (4) moves upwards to a designated position, and the riveting process is completed.

2. Riveting process according to claim 1, characterized in that in S5 the punch (4) is moved at a speed of 1-10mm/min, the time to penetrate the upper plate (7) being 2-10S.

3. Riveting process according to claim 2, characterized in that in S6 the residence time of the punch (4) is between 5 and 10 seconds.

4. A riveting method according to claim 3, characterized in that the upper plate (7) is a composite plate comprising a resin matrix consisting of a thermoplastic resin matrix or a thermosetting resin matrix and a reinforcing phase; the reinforcing phase is one or more of carbon fiber, glass fiber or aramid fiber; the thermoplastic resin base is one or more of polyamide, polyacetyl imine, polyether-ether-ketone and polystyrene, and the thermosetting resin base is epoxy resin or phenolic resin.

5. A riveting method according to claim 3, characterized in that the lower plate (8) is a light alloy plate, which is a high-strength aluminium alloy, magnesium alloy or titanium alloy.

6. A caulking method according to claim 3, wherein in S5, the vibration frequency of said low-frequency vibration is 0 to 50Hz, the vibration amplitude is 0 to 0.3mm, and the vibration direction is up-down vibration.

7. A riveting method according to claim 3, characterized in that the force sensor (3) and the punch (4) are connected by means of a bolted connection.