CN109848355B - Two-section type mechanical-solid phase composite connection method based on semi-hollow rivet - Google Patents

Abstract

A two-section mechanical-solid phase composite connection method based on a semi-hollow rivet is characterized in that the semi-hollow rivet and a driving head fixedly connected with a die are coaxially arranged, a groove in a rivet cover is meshed with a boss of the driving head, and the driving head is arranged to drive the driving rivet to be riveted into a material to be connected in a high-speed rotation and low-speed feeding mode in a first process stage; and stopping rotating the rivet in the second stage, feeding at a high speed, avoiding excessive accumulation of heat near the rivet, improving the riveting force, outwards expanding the bottom end of the rivet under the action of deformation resistance of a material to be connected to form mechanical interlocking, eliminating gaps of interfaces between the rivet and the workpiece and between the rivet and the workpiece in the joint under the extrusion action of rapid rivet feeding, and forming solid-phase connection of the interfaces through thermal diffusion at high temperature.

Description

Two-section mechanical-solid-phase composite connection method based on semi-hollow rivets

technical field

The invention relates to a technology in the field of material connection, in particular to a two-stage mechanical-solid phase composite connection method based on semi-hollow rivets.

Background technique

The spot connection of light alloy components is mainly riveted and friction stir spot welding. The riveting process adopts a stamping method to plastically deform the rivet and/or the workpiece to be connected to form an interference interlock to realize a mechanical connection. The riveting process is usually carried out at room temperature. In order to obtain the ideal interference interlocking effect, a large punching force needs to be applied, which requires extremely high structural strength and rigidity of the riveting equipment, reliability of the punching drive mechanism and the strength of the rivet itself. And the mold loss is serious. In addition, for light alloys with low ductility at room temperature, such as 7-series aluminum alloys, magnesium alloys, cast aluminum, etc., the large plastic deformation during the riveting process is prone to cracking of the material, which seriously affects the joint performance. The friction stir spot welding process generates heat in the workpieces to be connected through the rotation, insertion and retraction of the tool head, and the workpieces to be connected form a solid-phase connection under the combined action of the pressure generated by the tool head and the stirring motion. For light alloys that can be strengthened by heat treatment, such as 2 series, 6 series, 7 series aluminum alloys, etc., the joint strength loss is serious due to the influence of frictional thermal softening.

SUMMARY OF THE INVENTION

Aiming at the above-mentioned shortcomings of the prior art, the present invention proposes a two-stage mechanical-solid-phase composite connection method based on semi-hollow rivets. The interlocking effect is interfered, and a solid-phase connection is formed between the rivet and the workpiece, and between the workpiece and the workpiece, and a mechanical-solid-phase composite joint is obtained.

The present invention is achieved through the following technical solutions:

In the present invention, the semi-hollow rivet is coaxially arranged with the driving head of the fixing die and the groove on the rivet cover is engaged with the boss of the driving head, so that the driving head drives the rivet to rotate at a high speed and feed at a low speed in the first stage of the process. The material to be connected is riveted into the material to be connected, and the frictional heat is generated by the rotation of the rivet, which increases the temperature of the workpiece to be connected, avoids cracking of the low-ductility material, and reduces the riveting resistance of the rivet so that the rivet reaches the conversion depth in the workpiece to be connected; After the stage, stop rotating the rivet in the second stage, and feed at a higher rate to avoid excessive accumulation of heat near the rivet, increase the riveting force, and make the bottom end of the rivet open outward under the action of the deformation resistance of the material to be connected, A mechanical interlock is formed, and at the same time, under the extrusion action of the rapid feed of the rivet, the interface gaps between the rivet-workpiece and the workpiece-workpiece in the joint are eliminated, and the interface forms a solid-phase connection through thermal diffusion at high temperature.

The second stage completes the solid-phase connection, that is, when the rivet is fed to a predetermined depth, the driving head feeds backwards and returns to the original position.

The solid-phase connection refers to that the interfacial gaps near the rivet are eliminated, and the solid-phase connection of the materials on both sides at at least one of the following interfaces is realized:

①The interface between the metal and the lower workpiece is trapped inside the rivet;

②The interface between the workpiece outside the rivet and the workpiece material;

③ The interface between the metal trapped inside the rivet and the inner wall of the rivet;

④ The interface between the workpiece material outside the rivet and the outer wall of the rivet.

其中：h_i为第i层工件的厚度，n为被连接工件的层数且n≥2，D为转换深度，并且摩擦热对待连接工件充分软化。The completion of the first stage is determined according to the thickness and material properties of the workpieces to be connected, and the specific needs are met at the same time: the rivet has penetrated all workpieces except the lower workpiece, namely:

Among them: h _i is the thickness of the i-th layer workpiece, n is the number of layers of the workpiece to be connected and n ≥ 2, D is the conversion depth, and the friction heat is fully softened.

The workpieces to be connected include at least two layers of workpieces.

The described lower-layer workpiece refers to the workpiece located above the fixed die and in contact with the fixed die.

The sufficient softening is determined by adopting any one of the following operations or a combination thereof:

a) Use infrared thermometer or thermocouple to measure the temperature of the upper surface of the workpiece to be connected at a distance of 3-10mm from the edge of the rivet. When the temperature at this point rises to 20%-50% of the melting point of the workpiece to be connected, it is judged that the material is sufficient soften;

b) Measure the temperature of the center of the upper surface of the fixed mold by means of embedded thermocouples. When the temperature rises to 15%-30% of the melting point of the workpiece to be connected, it is judged that the material is sufficiently softened;

c) Measure the reaction force received by the driving head, record the first peak value F ₁ of the reaction force, when the reaction force drops to 0.3-0.6F ₁ after the first peak value, it is judged that the material is sufficiently softened;

d) Measure the reaction torque received by the driving head, record the first peak value M ₁ of the reaction torque, when the reaction torque drops to 0.3-0.6M ₁ after the first peak value, it is judged that the material is sufficiently softened;

其中：F为驱动头受到的反作用力，M为驱动头受到的反作用扭矩，f为工艺过程第一阶段的铆钉进给速率，ω为工艺过程第一阶段的铆钉旋转速度，Δt为工艺时间，E₀通过材料的厚度和物理特性进行估算：E₀＝C×ρ×H×4πR_rivet ²×ΔT，其中：C为待连接工件比热容，ρ为待连接工件密度，H为被连接工件的总厚度，

n为被连接工件的层数，R_rivet为铆钉体的半径，ΔT为铆钉附近2R_rivet范围内待连接工件的平均温升，ΔT＝0.2～0.5T_m，T_m为待连接工件的熔点；e) Measure the reaction force and reaction torque on the drive head, record the process time, and calculate the total energy input E. When the total energy input E is greater than the preset value E ₀ , it is judged that the material is sufficiently softened.

Among them: F is the reaction force received by the driving head, M is the reaction torque received by the driving head, f is the feed rate of the rivet in the first stage of the process, ω is the rotation speed of the rivet in the first stage of the process, Δt is the process time, E ₀ is estimated by the thickness and physical properties of the material: E ₀ =C×ρ×H×4πR _rivet ² ×ΔT, where: C is the specific heat capacity of the workpiece to be connected, ρ is the density of the workpiece to be connected, and H is the total amount of the workpiece to be connected. thickness,

n is the number of layers of the workpiece to be connected, R _rivet is the radius of the rivet body, ΔT is the average temperature rise of the workpiece to be connected within the range of 2R _rivet near the rivet, ΔT=0.2～0.5T _m , T _m is the melting point of the workpiece to be connected;

f) Set a fixed conversion depth according to test results and experience.

Further, the first stage of the process can be divided into several sub-stages with different feed rates and/or rotational speeds to achieve fine control of heat input, so as to obtain the best mechanical-solid phase composite bonding effect, all sub-stages The sum of the feed depths is the conversion depth D.

The semi-hollow rivet includes: a rivet cover and a rivet body that are integrally connected, wherein: the upper end of the rivet cover is provided with evenly distributed protrusions and/or positioning grooves for transmitting torque.

The rivet body is a hollow structure, the bottom end is provided with a wedge-shaped taper angle, and the inner and outer walls of the rivet can be of smooth structure or provided with structures such as threads and grooves.

The fixing mold includes: a driving head and a mold, wherein: the driving head is matched with the groove on the top of the semi-hollow rivet through the boss and is located above the workpiece to be connected, the mold is located under the workpiece to be connected, and the driving head has a shaft. The ability to move in a straight line as well as in a circumferential rotational motion.

The position of the upper surface of the fixing die facing the rivet is provided with a fixing structure for cooperating with the rivet to control the flow of the material. Plates and through holes, etc.

technical effect

Compared with the prior art, the present invention realizes the solid-phase connection between the rivet and the workpiece, and between the workpiece and the workpiece on the basis of the mechanical connection, thereby improving the overall strength and rigidity of the joint; The workpieces to be connected reduce the riveting force and improve the reliability of the mechanical self-locking; the heat input is controlled by adjusting the heat input of the rivet speed, feed rate and conversion depth in the first stage of the process. Within the range, the softening caused by friction and heating of light alloys is fully reduced, and the joints are strengthened through the fine-grain strengthening effect generated by the friction stir process, the deformation strengthening effect generated by the second-stage rapid feed, and the solid-phase connection, which effectively reduces the heat. The negative effect of softening on the material properties of the joined workpieces, enhancing the static strength and dynamic fatigue life of the joint.

Description of drawings

Fig. 1 is the structural representation of semi-hollow rivet;

Fig. 2 is the technological process diagram of the present invention;

In the figure: a is the coaxial matching diagram of the driving head and the semi-hollow rivet; b is the high-speed rotation and low-speed feeding diagram of the driving head driving the semi-hollow rivet in the first stage of the process; c is the high-speed feeding of the semi-hollow rivet driven by the driving head in the second stage of the process Figure; d is the rivet feeding to the final predetermined depth to form a mechanical-solid phase composite joint; e is the reverse feeding and returning of the driving head;

Fig. 3 is the schematic diagram of the mechanical-solid phase composite joint obtained by the present invention;

In the figure: semi-hollow rivet 1, driving head 2, fixing die 3, plate to be connected 4, mechanical-solid phase composite joint 5, groove 101, rivet cover 102, rivet body 103, upper plate 401, lower plate 402, Metal 403 is trapped inside the rivet.

Detailed ways

Example 1

As shown in FIG. 2, the specific implementation environment of this embodiment includes: a semi-hollow rivet 1, a driving head 2 and a fixing die 3, wherein: the driving head 2 is matched with the groove 101 on the top of the semi-hollow rivet 1 through the boss And together they are located above the workpiece 4 to be connected, and the fixing die 3 is located below the workpiece 4 to be connected.

As shown in FIG. 1 , the semi-hollow rivet 1 used in this embodiment includes a rivet cover 102 and a rivet body 103 that are integrally connected, wherein a groove 101 in the center of the rivet cover 102 and the rivet body 103 are coaxially arranged.

The inner and outer walls of the rivet body 103 are smooth structures, with an inner diameter of 4.3 mm, an outer diameter of 5.3 mm, and a depth of 4 mm.

The bottom end of the rivet body 103 is provided with a wedge-shaped taper angle 104 with an angle of 45°.

The boss of the driving head 2 and the groove 101 in the center of the rivet cover 102 have the same taper to realize the axial feeding movement and the rotational movement of the semi-hollow rivet 1 .

The fixing die 3 is a concave die with a convex in the middle, and the height of the central convex apex is flush with the outer edge of the concave die.

The center of the fixed mold 3 is embedded with a thermocouple, and the temperature of the center of the upper surface of the mold in the process of changing with time is recorded.

The upper layer plate 401 and the lower layer plate 402 of the workpiece 4 to be connected are both aluminum alloy AA7075-T6, and both have a thickness of 2.0 mm.

This embodiment specifically includes the following steps:

1) According to the material melting point of the workpiece 4 to be connected, the target temperature of the center of the upper surface of the fixed die 3 corresponding to the conversion depth D of the first stage is determined to be 100°C;

2) By engaging the groove 101 on the rivet cover 102 with the boss of the driving head 2, the semi-hollow rivet 1 and the driving head 2 are coaxially arranged;

3) The drive head 2 is fed axially at a linear speed of 50mm/s to a position 2mm from the upper surface of the workpiece 4 to be connected under the action of the servo motor;

4) The driving head 2 drives the rivet 1 into the workpiece 4 to be connected at a rotational speed of 4000 r/min and a feed rate of 2.0 mm/s in the first stage of the process, and generates heat through the friction between the rivet body 103 and the workpiece 4 to be connected, Increase the temperature of the workpiece 4 to be connected, soften the material, and reduce the riveting resistance;

5) When the temperature of the center of the upper surface of the fixing die 3 rises to 100°C and the feed depth is greater than the thickness of the upper plate 401 by 2.0mm, the process enters the second stage, and the rivet 1 stops rotating, at a high speed of 20mm/s. Feed, increase the riveting force, so that the bottom end of the rivet body 103 is stretched outward under the action of the deformation resistance of the workpiece 4 to be connected to form a mechanical interlock; The gap between the workpieces 401 and 402 to be joined is eliminated.

6) When the rivet 1 is fed to a predetermined depth of 5.3mm, the drive head feeds backwards and returns to the original position.

As shown in FIG. 3 , in the finally formed mechanical-solid phase composite joint 5, solid phase connections are formed at three interfaces, including: ① the interface between the metal 403 trapped inside the rivet 1 and the lower workpiece 402; ② the rivet body The interface between the rivet body 103 and its inner retained metal 403; ③ the interface between the rivet body 103 and its outer lower workpiece 402.

Compared with the prior art, the maximum riveting force in the process of fixing the 2.0mm thick aluminum alloy 7075-T6 material in this embodiment is 27.6kN, compared with the existing riveting force of 62.5kN using the traditional self-piercing riveting method. , decreased by 55.8%.

The average tensile shear strength of the joint obtained in this example is 470Mpa, which is an increase of 109 MPa compared with the average tensile shear strength of the joint obtained by traditional self-piercing riveting of 225 MPa and the average tensile shear strength of the backfilled friction stir spot welded joint of 357 MPa. % and 31.6%.

Example 2

Compared with Embodiment 1, the thickness of the upper layer plate 401 of the workpieces 4 to be connected in this embodiment is 2.2 mm, the material is aluminum alloy AA6061-T6, the thickness of the lower layer plate 402 is 2.0 mm, and the material is magnesium alloy AZ31B.

Compared with Example 1, the rivet rotation speed in the first stage of the process used in this example is 3600 r/min, the feed rate is 1.0 mm/s, and the feed rate in the second stage is 11 mm/s.

Compared with Embodiment 1, the conversion depth D of the first stage in this embodiment is determined by measuring the temperature of the upper surface of the upper plate 401 at a distance of 4.0 mm from the edge of the rivet by an infrared thermal imager. When the depth is greater than the thickness of the upper board by 2.2mm, the process enters the second stage.

Other parameters in this embodiment are the same as those in Embodiment 1.

Compared with the prior art, the maximum riveting force in the process of fixing the aluminum alloy AA6061-T6 with a thickness of 2.2 mm and the magnesium alloy AZ31B with a thickness of 2.0 mm in the present embodiment is 14.1 kN, which is different from the existing traditional self-piercing riveting method. Compared with the riveting force of 40.0kN, it is reduced by 64.8%.

The average tensile shear strength of the joint obtained in this example is 198Mpa, which is 59.7% higher than the average tensile shear strength of the joint obtained by traditional self-piercing riveting of 124MPa.

Example 3

Compared with Embodiment 1, the upper plate 401 of the workpiece 4 to be connected in this embodiment is an aluminum alloy AA5182-O with a thickness of 1.5 mm, and the lower plate 402 is an aluminum alloy AA5182-O with a thickness of 2.0 mm.

Compared with Example 1, the rivet rotation speed in the first stage of the process used in this example is 3000 r/min, the feed rate is 2.0 mm/s, and the feed rate in the second stage is 10 mm/s.

Compared with Embodiment 1, the conversion depth D in this embodiment is empirically set to 2.0 mm.

Other parameters in this embodiment are the same as those in Embodiment 1.

Compared with the prior art, the maximum riveting force in the fixing process of the aluminum alloy AA5182-O with a thickness of 1.5 mm and the aluminum alloy AA5182-O with a thickness of 2.0 mm in this embodiment is 19.9 kN, which is different from the conventional self-piercing method in the prior art. The riveting force of the riveting method is 50.5% lower than that of 40.2kN.

The average tensile shear strength of the joint obtained in this example is 218Mpa, which is an increase of 26.3% compared with the average tensile shear strength of the joint obtained by traditional self-piercing riveting of 197MPa; the high cycle tensile strength of the joint obtained by this method under a load of 2.3kN- The tensile fatigue life is 1.7 million times, and the low-cycle pull-pull fatigue life under a load of 3.5kN is 150,000 times, compared with the fatigue life of traditional self-piercing riveted joints under the same load, 950,000 times and 44,000 times , an increase of 79% and 241%, respectively.

Compared with the prior art, the advantages of the present invention are: (1) The riveting force required in the process is reduced, the requirements for the structural strength, rigidity and drive system capability of the equipment are reduced, and the punch and die in the process are also reduced. (2) On the basis of mechanical connection, the solid-phase connection of multiple interfaces between the rivet and the workpiece, and between the workpiece and the workpiece is realized, which improves the overall strength and stiffness of the joint; (3) Controls the heat input to the required level Within the range, the material can be properly softened, and the joints are strengthened through the fine-grain strengthening effect generated by the friction stir process, the deformation strengthening effect generated by the second-stage rapid feed, and the solid-phase connection, which effectively reduces the thermal softening effect on the connected joints. Negative influence of workpiece material properties; (4) Mechanical-solid-phase composite connection improves the fatigue life of joints.

The above-mentioned specific implementation can be partially adjusted by those skilled in the art in different ways without departing from the principle and purpose of the present invention. The protection scope of the present invention is subject to the claims and is not limited by the above-mentioned specific implementation. Each implementation within the scope is bound by the present invention.

Claims (7)

1. A two-stage mechanical-solid-phase composite connection method based on a semi-hollow rivet is characterized in that, by coaxially setting the semi-hollow rivet and the driving head of the fixed die and the convexity of the groove and the driving head on the rivet cover. The table is meshed, and the driving head is set to drive the rivet to riveted into the material to be connected in the first stage of the process by means of high-speed rotation and low-speed feed. Frictional heat is generated by the rotation of the rivet, which increases the temperature of the workpiece to be connected and avoids low ductility. Reduce the riveting resistance of the rivet so that the rivet reaches the transition depth in the workpiece to be connected; when the first stage is completed, stop rotating the rivet in the second stage and feed at a higher rate to avoid excessive heat accumulation near the rivet, Increase the riveting force, so that the bottom end of the rivet is stretched outward under the action of the deformation resistance of the material to be connected, forming a mechanical interlock. The interfacial gaps are eliminated, and the interfaces form solid-phase connections through thermal diffusion at high temperatures; The solid-phase connection refers to that the interfacial gaps near the rivet are eliminated, and the solid-phase connection of the materials on both sides at at least one of the following interfaces is realized: ①The interface between the metal and the lower workpiece is trapped inside the rivet; ②The interface between the workpiece outside the rivet and the workpiece material; ③ The interface between the metal trapped inside the rivet and the inner wall of the rivet; ④The interface between the workpiece material outside the rivet and the outer wall of the rivet; The completion of the first stage is determined according to the thickness and material properties of the workpieces to be connected, and the specific needs are met at the same time: the rivet has penetrated all workpieces except the lower workpiece, namely:

Among them: h _i is the thickness of the i-th layer workpiece, n is the number of layers of the workpiece to be connected and n ≥ 2, D is the conversion depth, and the friction heat is fully softened. 2. The method according to claim 1, wherein the sufficient softening is determined by adopting any one of the following operations or a combination thereof: a) Use an infrared thermometer or a thermocouple to measure the temperature of the upper surface of the workpiece to be connected at a distance of 3-10mm from the edge of the rivet. When the temperature at this point rises to 20%-50% of the melting point of the workpiece to be connected, it is determined that the material is sufficiently softened; b) Use the embedded thermocouple to measure the temperature of the center of the upper surface of the fixed mold. When the temperature rises to 15%-30% of the melting point of the workpiece to be connected, it is judged that the material is sufficiently softened; c) Measure the reaction force received by the driving head, record the first peak value F ₁ of the reaction force, when the reaction force drops to 0.3-0.6F ₁ after the first peak value, it is judged that the material is sufficiently softened; d) Measure the reaction torque received by the driving head, record the first peak value M ₁ of the reaction torque, when the reaction torque drops to 0.3-0.6M ₁ after the first peak value, it is judged that the material is sufficiently softened; e) Measure the reaction force and reaction torque on the drive head, record the process time, and calculate the total energy input E. When the total energy input E is greater than the preset value E ₀ , it is judged that the material is sufficiently softened.

Among them: F is the reaction force received by the driving head, M is the reaction torque received by the driving head, f is the feed rate of the rivet in the first stage of the process, ω is the rotation speed of the rivet in the first stage of the process, Δt is the process time, E ₀ is estimated by the thickness and physical properties of the material: E ₀ =C×ρ×H×4πR _rivet ² ×ΔT, where: C is the specific heat capacity of the workpiece to be connected, ρ is the density of the workpiece to be connected, and H is the total amount of the workpiece to be connected. thickness,

n is the number of layers of the workpiece to be connected, R _rivet is the radius of the rivet body, ΔT is the average temperature rise of the workpiece to be connected within the range of 2R _rivet near the rivet, ΔT=0.2～0.5T _m , T _m is the melting point of the workpiece to be connected; f) Set a fixed conversion depth according to test results and experience. 3. The method according to claim 1, wherein the first stage is divided into several sub-stages with different feed rates and/or rotational speeds, so as to realize fine regulation of heat input, so as to obtain optimal The mechanical-solid phase composite connection effect, the sum of the feed depth of all sub-stages is the transformation depth D. 4. The method according to claim 1, wherein the semi-hollow rivet comprises: a rivet cover and a rivet body that are integrally connected, wherein: the upper end of the rivet cover is provided with evenly distributed projections and/or for transmitting torque. or positioning grooves. 5 . The method according to claim 4 , wherein the rivet body is a hollow structure, the bottom end is provided with a wedge-shaped taper angle, and the inner and outer walls of the rivet can be smooth structures or provided with threads and groove structures. 6 . 6. The method according to claim 1, wherein the fixing die comprises: a driving head and a die, wherein: the driving head is matched with the groove on the top of the semi-hollow rivet through the boss and is co-located in the to-be-connected Above the workpiece, the mold is located below the workpiece to be connected, and the drive head has the ability to move in an axial line as well as in a circumferential rotation. 7 . The method according to claim 6 , wherein the upper surface of the fixing die facing the rivet is provided with a fixing structure for cooperating with the rivet to control the flow of the material. 8 .

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