Manufacturing method for ultrasonic welded joints

Abstract

To provide a joining method capable of ultrasonic welding over large areas, even for highly rigid materials such as fiber-reinforced resin.SOLUTION: The present invention for solving the above issues is a method for joining multiple members made of fiber-reinforced resin using an ultrasonic welding machine. It involves stacking and restraining member (II) to be joined onto base member (I), and during the process of pressing an ultrasonic horn against the joint while oscillating, it comprises a first oscillation region defined by ultrasonic output (W)P1, oscillation time (seconds) t1, and horn pressure (MPa) p1, followed by a second oscillation region with ultrasonic output (W)P2, oscillation time (seconds) t2, and horn pressure (MPa) p2, and applying the ultrasonic horn under the condition that p1<p2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a joined body by joining a plurality of members made of fiber-reinforced resin by ultrasonic welding. [Background technology]

[0002] Fiber-reinforced resin materials, which use thermosetting or thermoplastic resin as a matrix and combine it with reinforcing fibers such as carbon fiber or glass fiber, are lightweight yet have excellent mechanical properties such as strength and rigidity, as well as heat resistance and corrosion resistance, and have therefore been applied in many fields, including aerospace, automobiles, railway vehicles, ships, civil engineering and construction, and sporting goods.

[0003] However, fiber-reinforced plastic materials are not suitable for manufacturing parts or structures with complex shapes in a single molding process. Therefore, for these applications, it is necessary to fabricate a component made of the fiber-reinforced plastic material and then integrate it with other components of the same or different types. To integrate fiber-reinforced plastic materials with other components of the same or different types, various methods have been proposed for joining fiber-reinforced plastics that use a thermoplastic resin matrix. These include mechanical joining using bolts, nuts, rivets, etc., chemical joining using adhesives, and thermal joining using ultrasonic welding, vibration welding, etc. Among these, ultrasonic welding is widely used in various industrial fields because it does not require a third material and has a short cycle time.

[0004] Ultrasonic welding is a method of welding components by pressing a resonator called a horn against the components, applying high-frequency mechanical vibrations from the resonator, and converting the mechanical vibrations transmitted to the components into frictional heat, melting the components. For example, Patent Document 1 discloses a technology in which ultrasonic welding is performed while applying surface pressure between an adherend and a molded body with randomly oriented reinforcing fibers that uses a thermoplastic resin as a matrix resin. [Prior art documents] [Patent documents]

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described in Patent Document 1, in order to sufficiently weld a fiber reinforced resin material by ultrasonic welding, it is necessary to apply pressure above a certain level. On the other hand, when welding a highly rigid material such as a fiber reinforced resin material over a large area, if pressure is applied at a high level from the start of oscillation, the member will be strongly constrained. Therefore, when ultrasonic waves are applied, the vibration of the member cannot follow the applied ultrasonic vibration, resulting in an oscillation error and inability to weld. Also, although there are avoidance methods such as welding in a small area in multiple times, there is a problem that the number of welding times increases and the cycle time becomes long.

[0007] Therefore, an object of the present invention is to provide a method for manufacturing a joined body that can be ultrasonically welded over a large area even with a highly rigid material such as a fiber reinforced resin material.

Means for Solving the Problems

[0008] The present invention for solving the above problems is a method for joining a plurality of members made of fiber reinforced resin by an ultrasonic welder. In the step of overlapping and restraining the member (II) to be joined to the base member (I) and oscillating while pressing an ultrasonic horn against the joint portion, a first oscillation region consisting of ultrasonic output (W) P1, oscillation time (seconds) t1, and horn pressure (MPa) p1, and then a second oscillation region consisting of ultrasonic output (W) P2, oscillation time (seconds) t2, and horn pressure (MPa) p2 are provided, and it is a joining method in which the ultrasonic horn is pressed under the condition that p1 < p2.

Effects of the Invention

[0009] By the joining method of the present invention, it is possible to ultrasonically weld over a large area even with a highly rigid material such as a fiber reinforced resin material.

Brief Description of the Drawings

[0010] [Figure 1] 1 is a schematic diagram of an ultrasonic welding device according to the present invention. [Figure 2] 1 is a graph of the relationship between horn pressure and time in the ultrasonic welding method of the present invention, showing the presence of a first oscillation region and a second oscillation region. [Figure 3] 10A and 10B are diagrams showing an example of how to increase the horn pressure in the second oscillation region. [Figure 4] FIG. 10 is a diagram showing the change in horn displacement during ultrasonic welding in a preferred embodiment of the present invention. [Figure 5] FIG. 1 is a diagram showing changes in ultrasonic output during ultrasonic welding in a preferred embodiment of the present invention. [Figure 6] 1 is a graph showing the relationship between horn pressure and time in the ultrasonic welding method of the present invention, showing a configuration having a third oscillation region following a second oscillation region. [Figure 7] 1 is a graph showing the relationship between horn pressure and time in the ultrasonic welding method of the present invention, showing an embodiment having a pressure holding step following the second oscillation region. [Figure 8] 1A and 1B are diagrams showing a method of fixing a member (I) and a member (II) with a jig in an embodiment of the present invention, in which (a) is a cross-sectional view seen from the side, and (b) is a bird's-eye view seen from above. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention is a method for joining members (I) and (II) by overlapping and restraining them and then ultrasonic welding. As shown in Figure 1, an ultrasonic horn is pressed against the members (I) and (II) and vibrated, heating the interface between the members (I) and (II) and joining them. The ultrasonic welding device is equipped with an ultrasonic horn placed above the component (II) and a jig that supports the component (I) from below. The jig is generally made of metal, but other materials may be used as long as it is rigid enough to maintain its shape during welding.

[0012] In ultrasonic welding, ultrasonic vibrations output from an ultrasonic vibrator are transmitted to a member (II) via an ultrasonic horn. The excitation frequency of the ultrasonic horn is a unique value corresponding to the ultrasonic horn, and is, for example, 10 kHz or more and 50 kHz or less.

[0013] In the ultrasonic welding in the present invention, a resonator called an ultrasonic horn is pressed against the member (II) to apply a horn pressure, and high-frequency mechanical vibrations are applied from this resonator. The mechanical vibrations transmitted to the interface between the member (I) and the member (II) are converted into frictional heat, melting the vicinity of the interface between the member (I) and the member (II), and welding the member (I) and the member (II). In the present invention, in the process of oscillating while pressing an ultrasonic horn against a joint portion, by increasing the horn pressure midway, ultrasonic welding over a large area is possible even with a highly rigid material such as a fiber-reinforced resin material. Specifically, as shown in FIG. 2, following a first oscillation region where the horn pressure is p1, there is a second oscillation region where the horn pressure is p2, and ultrasonic welding is performed under the condition that p1 < p2. Also, here, let the ultrasonic output (W) and oscillation time (seconds) in the first oscillation region be P1 and t1 respectively, and the ultrasonic output (W) and oscillation time (seconds) in the second oscillation region be P2 and t2 respectively. Here, the "joint portion" refers not only to the vicinity of the interface where the members are melted among the member (I) and the member (II), but also to the entire portion in the thickness direction, including both states before and after welding. Also, the "joint surface" refers to the surface where the member (I) and the member (II) contact during welding among the above "joint portion".

[0014] The horn pressure in the first oscillation region is not particularly limited as long as p1 < p2 is satisfied. However, if the load is too large, the member (I) and the member (II) are strongly constrained, and an oscillation error occurs when attempting welding over a large area. Therefore, the load is preferably 2000 N or less, and more preferably 1000 N or less.

[0015] The horn pressure (p2) in the second oscillation region is preferably 0.3 MPa or higher, more preferably 0.5 MPa or higher, and even more preferably 1.0 MPa or higher. If p2 is small, the resin may not be heated sufficiently, resulting in poor welding due to insufficient flow. On the other hand, if p2 is too high, the resin flow may become too large. Therefore, p2 is preferably 10.0 MPa or lower, more preferably 7.5 MPa or lower, and even more preferably 5.0 MPa or lower. In order to balance the two, p2 is most preferably 0.5 MPa or higher and 5.0 MPa or lower.

[0016] Furthermore, when an additional oscillating region such as a third oscillating region following the second oscillating region is provided, it is preferable that p2 in the final oscillating region is also 0.5 MPa or more and 5.0 MPa or less, for the same reasons as above.

[0017] The horn pressure can be increased in stages as shown in Figure 3(a), or it can be increased linearly as shown in Figure 3(b). However, from the perspective of control, it is easier to increase the horn pressure in stages.

[0018] Members (I) and (II) are fiber-reinforced resins made of reinforcing fibers and resin. These members contain thermoplastic resin at least on the joining surface and can be welded by applying ultrasonic waves. Examples of thermoplastic resins include polyamide, PEEK, PEKK, PPS, polypropylene, polyetherimide, and PC. Examples of fibers used include carbon fiber, glass fiber, aramid fiber, and Kevlar fiber. It is preferable that either the member (I) or the member (II) has an energy director made of a thermoplastic resin. By having an energy director, vibration energy can be concentrated locally, thereby increasing the efficiency of conversion to thermal energy. The height of the energy director is preferably 10 μm or more, more preferably 50 μm or more, and even more preferably 100 μm or more. However, if the height of the energy director exceeds 1000 μm, there is a possibility that the energy director will not completely melt and will remain after welding, so a height of 1000 μm or less is preferable.

[0019] The thickness of the member (I) and the member (II) is preferably 5 mm or less. This is because if the thickness of the member is too large, the rigidity becomes too high, making it difficult to vibrate the member by applying ultrasonic waves, and it becomes difficult to sufficiently weld the member. In particular, a thickness of 0.5 mm or more and 5 mm or less is more preferable.

[0020] It is preferable that after the member (I) or the member (II) starts to melt, it moves to the second oscillation region. In particular, a behavior as shown in FIG. 4, in which it is pushed in with an ultrasonic horn so that the horn displacement becomes larger in the second oscillation region than in the first oscillation region, is preferable. The horn displacement indicates the amount of displacement of the ultrasonic horn in the pressurizing direction during ultrasonic welding. The larger the horn displacement, the more it is pushed in greatly by the ultrasonic horn. Also, from the viewpoint of ultrasonic output, the ultrasonic outputs in the first oscillation region and the second oscillation region are such that P1 < P2, and in the second oscillation region, a behavior of gradually increasing is preferable. The ultrasonic output is the energy consumed per unit time for vibrating the ultrasonic horn at the set amplitude. After welding, it is obtained as a curve as shown in FIG. 5. In the present invention, the average values of the ultrasonic outputs in the respective regions of the first oscillation region and the second oscillation region are defined as P1 and P2, respectively. By doing so, while applying the horn pressure required for welding, it is possible to suppress the oscillation error generated when the vibration of the member cannot follow the applied ultrasonic vibration. When the energy director is provided in the member (I) or the member (II), in the first oscillation region, the vibration energy is locally concentrated, and after starting to melt the energy director with a small ultrasonic output, it moves to the second oscillation region. When the horn pressure is increased, the melted energy director spreads in the in-plane direction, so that welding can be performed while gradually increasing the area of the welded portion. Therefore, it is easy to prevent a sudden increase in ultrasonic output and achieve the above behavior.

[0021] After the resin starts to melt and can shift to the second oscillation region, the transmission time (t1) in the first oscillation region is preferably 0.3 seconds or more. When the transmission time (t1) in the first oscillation region is too short, the resin does not melt, which becomes a factor of oscillation error when shifting to the second oscillation region. Also, from the perspective of sufficiently flowing and welding the resin, the oscillation time (t2) in the second oscillation region is preferably 0.5 seconds or more. On the other hand, the total (t1 + t2) of the oscillation time (t1) in the first oscillation region and the oscillation time (t2) in the second oscillation region is preferably within 5 seconds. This is because when (t1 + t2) is too long, heat is also transmitted to locations other than the joint surface, and there is a risk that the member will deform after ultrasonic welding. Also, from the balance between the total oscillation time and the oscillation time in each oscillation region, the relationship between the transmission time (t1) in the first oscillation region and the oscillation time (t2) in the second oscillation region is preferably t1 < t2.

[0022] As shown in FIG. 6, the present invention can have a third oscillation region satisfying p2 < p3 after the second oscillation region. This third oscillation region is composed of an ultrasonic output (W) P3, an oscillation time (seconds) t3, and a horn pressure (MPa) p3. By gradually increasing the horn pressure, it is possible to suppress the sharp increase in ultrasonic output and oscillation error accompanying the increase in horn pressure after the first oscillation region. Also, as long as p(n - 1) < pn (n is an integer of 2 or more) is satisfied, it is also possible to have an nth oscillation region and an additional oscillation region.

[0023] After the oscillation of the ultrasonic wave ends, as shown in FIG. 7, it is preferable to have a pressure holding step of continuously pressing the ultrasonic horn. By this pressure holding step, the thermoplastic resin melted by the ultrasonic vibration can be cooled and its shape can be fixed. The horn pressure in the pressure holding step is preferably not less than the horn pressure in the final oscillation region. By having such a pressure holding step, the generation of voids in the joint portion can be suppressed. During ultrasonic welding, the members (I) and (II) must be fixed with a jig to prevent them from moving due to the ultrasonic vibrations applied from the ultrasonic horn. However, if they are fixed too tightly in the out-of-plane direction, it becomes difficult for the members (I) or (II) to vibrate. Therefore, it is preferable that the restraining force when fixing with the jig be such that the restraining force in the in-plane direction (N) is greater than the restraining force in the out-of-plane direction (N).

[0024] The area of the ultrasonic horn contact is 5cm 2 It is preferable to use an ultrasonic horn with a smaller contact area. If an ultrasonic horn with a smaller contact area is used, the number of welding operations required to weld a large area increases, resulting in a longer cycle time. There is no particular upper limit to the contact area of the ultrasonic horn, but it is generally 50 cm. 2 The following is the result. [Example]

[0025] The present invention will be explained in more detail below with reference to the following examples. First, the materials used in the present invention are described below, followed by the methods for producing and ultrasonically welding the fiber-reinforced thermoplastic resin (FRTP) members used as member (I) or member (II), and the methods for evaluating the FRTP joints obtained by ultrasonic welding.

[0026] <Materials used in Examples and Comparative Examples> <Reinforced fiber> A continuous carbon fiber with a total of 24,000 single fibers was obtained by spinning, calcining, and surface oxidation of a copolymer mainly composed of polyacrylonitrile. The properties of this continuous carbon fiber are as follows: Single fiber diameter: 7 μm Density: 1.8g / cm 3 Tensile strength: 4600 MPa Tensile modulus: 220GPa <Thermoplastic resin> A thermoplastic resin sheet was produced using "Amilan (registered trademark)" CM1007 (manufactured by Toray Industries, Inc., melting point 225°C) as the PA resin.

[0027] <Thermoplastic prepreg> The continuous reinforcing fiber sheet with carbon fibers aligned in one direction was drawn out, and the basis weight was adjusted to 131 g / m 2 Two thermoplastic resin sheets were stacked on both sides of the reinforcing fiber sheet, heated with an IR heater set at 270 °C to melt the resin, adhered to the entire surface of the reinforcing fiber sheet, and pressed and cooled with a nip roll maintained at a surface temperature of 100 °C to obtain a thermoplastic prepreg as a precursor of the thermoplastic resin layer. The basis weight of the thermoplastic resin was 87 g / m 2 was used.

[0028] <FRTP member 1 (without energy director)> The obtained thermoplastic prepreg was laminated in the form of [0 / 90 / 0 / 90 / 0 / 90 / 0 / 0 / 90 / 0 / 90 / 0 / 90 / 0], put into a closed mold, and then heated with a press machine heated to 240 °C at a pressure of 3 MPa for 20 minutes. Then, it was transferred to a press machine heated to 100 °C together with the mold, and pressed at a pressure of 5 MPa for 10 minutes to obtain a 2-mm-thick FRTP member 1.

[0029] <FRTP member 2 (without energy director)> The obtained thermoplastic prepreg was laminated in the form of [0 / 90] 5S put into a closed mold, and then heated with a press machine heated to 240 °C at a pressure of 3 MPa for 20 minutes. Then, it was transferred to a press machine heated to 100 °C together with the mold, and pressed at a pressure of 5 MPa for 10 minutes to obtain a 3-mm-thick FRTP member 2.

[0030] <FRTP member 3 (with energy director)> The obtained thermoplastic prepreg was laminated in the form of [0 / 90] 5SThe sheets were laminated so that the thickness was 1 / 4 of the original thickness, and a 200 μm thick thermoplastic resin sheet was placed on one side. The sheets were placed in a closed mold with recesses corresponding to the energy directors so that energy directors were formed on the side where the thermoplastic resin sheet was placed, and then heated for 20 minutes at a pressure of 3 MPa in a press heated to 240°C. The mold was then transferred to a press heated to 100°C and pressed for 10 minutes at a pressure of 5 MPa to obtain an FRTP component 3 with a flat portion thickness of 3 mm. Conical energy directors (height 600 μm, pitch 3000 μm) were formed on part of the surface where the thermoplastic resin sheet was placed in the FRTP component 3.

[0031] <Ultrasonic welding> The resulting FRTP components were cut to the specified dimensions using a diamond cutter and then dried in a vacuum oven for 24 hours. Then, an FRTP assembly was obtained by ultrasonic welding using a Harman Ultrasonics Japan HiQ DIALOG 20 / 6200 ultrasonic welding machine at an amplitude of 31.9 μm (single amplitude). Tabs were attached to the resulting FRTP assembly in accordance with ISO 4587:1995 (JIS K6850(1994)), and the assembly was cut to a width of 25 mm to obtain the desired test specimen. Ultrasonic welding machine specifications Load setting range: 30 to 2480N Ultrasonic output of oscillator: 900W~6200W Ultrasonic horn contact area: 37.5cm 2 (1.5cm long x 25cm wide) Maximum amplitude: 39.9μm (half amplitude) Excitation frequency: 20kHz <Evaluation method 1> Single lap shear (SLS) test of joint The obtained test pieces were dried in a vacuum oven for 24 hours, and the bonding strength was evaluated at an environmental temperature of 23°C based on ISO4587:1995 (JIS K6850 (1994)).

[0032] <Evaluation method 2> Check for the presence of voids by cross-sectional observation The cross section of the bonded body was polished and photographed at a magnification of 200x with a laser microscope (Keyence VHX-5000) with the bonded part at the center. Photographs were taken at five points to check for the presence or absence of voids.

[0033] Example 1 FRTP component 1 (100 mm wide, 100 mm long, and 2 mm thick) was overlapped with FRTP component 3 (100 mm wide, 100 mm long, and 3 mm thick) obtained by the method described above, with the energy director facing the joining surface and the overlapping area being 12.5 mm. The components were then secured in place with a jig, as shown in Figure 8. The in-plane and out-of-plane clamping forces were 200 and 100 N, respectively. An ultrasonic horn was then pressed against the overlapping area of the FRTP components secured with the jig, and ultrasonic welding was performed by applying ultrasonic waves while gradually increasing the horn pressure. The ultrasonic application was then stopped and the components were allowed to cool naturally while maintaining the applied pressure. The horn was then moved away from the FRTP components, resulting in an FRTP joint. The ultrasonic welding conditions were as follows: the first oscillation (first oscillation region) was performed with a horn pressure of 0.5 MPa for 0.9 seconds, followed by the second oscillation (second oscillation region) in which the horn pressure was increased to 0.7 MPa and the oscillation time was set to 1.4 seconds. The pressure holding process was performed with a horn pressure of 0.7 MPa for 5.0 seconds. The bonding evaluation by SLS test is shown in Table 1. Cross-sectional observation of the obtained bonded body revealed no voids in the bonded area.

[0034] Example 2 A bonded body was produced in the same manner as in Example 1, except that the horn pressure for ultrasonic welding was changed to 0.3 MPa in the first oscillation stage (first oscillation region), 0.4 MPa in the second oscillation stage (second oscillation region), and 0.4 MPa in the pressure holding step. The bonding evaluation by SLS test is shown in Table 1. Cross-sectional observation of the obtained bonded body revealed no voids in the bonded portion.

[0035] Example 3 A bonded body was produced in the same manner as in Example 1, except that the oscillation time for ultrasonic welding was changed to 1.2 seconds for the first stage oscillation (first oscillation region) and 1.1 seconds for the second stage oscillation (second oscillation region). The bonding evaluation by SLS test is shown in Table 1. Cross-sectional observation of the obtained bonded body revealed no voids in the bonded portion.

[0036] Example 4 A bonded body was produced in the same manner as in Example 1, except that the oscillation time of the ultrasonic welding was changed to 5.0 seconds in the second oscillation stage (second oscillation region). The bonding evaluation by the SLS test is shown in Table 1. When a cross-section of the obtained bonded body was observed, no voids were observed in the bonded portion, but heat was transmitted to areas other than the bonded interface, and deformation occurred near the bonded portion.

[0037] Example 5 A bonded body was produced in the same manner as in Example 1, except that the in-plane fastening force of the jig fixing the FRTP members was set to 500 N. The bond evaluation by SLS test is shown in Table 1. When the cross section of the obtained bonded body was observed, no voids were observed in the bonded portion.

[0038] Example 6 A bonded body was produced in the same manner as in Example 1, except that a third oscillation region was added for 0.4 seconds at a horn pressure of 0.9 MPa following the second oscillation region, and the horn pressure in the pressure holding step was set to 0.9 MPa. The bonding evaluation by SLS test is shown in Table 1. Cross-sectional observation of the obtained bonded body revealed no voids in the bonded portion.

[0039] Example 7 A bonded body was produced in the same manner as in Example 1, except that the horn pressure in the dwelling step was set to 0.3 MPa. The bonding evaluation by the SLS test is shown in Table 1. As a result of observing a cross section of the obtained bonded body, voids were generated in the bonded portion.

[0040] Example 8 A bonded body was produced in the same manner as in Example 1, except that the pressure-holding step was not performed. The bonding evaluation by the SLS test is shown in Table 1. As a result of observing a cross section of the obtained bonded body, voids were found to have occurred in the bonded portion.

[0041] Example 9 A bonded body was produced in the same manner as in Example 1, except that the FRTP member 3, which was 100 mm wide, 100 mm long, and 3 mm thick, was replaced with the FRTP member 2, which was 100 mm wide, 100 mm long, and 3 mm thick. The bond evaluation by SLS test is shown in Table 1. As a result of observing the cross section of the obtained bonded body, no voids were observed in the bonded portion.

[0042] Comparative Example 1 A bonded body was produced under the same ultrasonic welding conditions as in Example 1, except that the first-stage oscillation (first oscillation region) was performed for 1.4 seconds at a horn pressure of 0.7 MPa, followed by a pressure holding step of 5 seconds at 0.7 MPa without performing a second-stage oscillation. As a result, during the first-stage oscillation, the ultrasonic output rose sharply, causing an oscillation error, which caused the horn oscillation to stop midway, and ultrasonic welding was not possible.

[0043] Comparative Example 2 A bonded body was produced in the same manner as in Example 1, except that the horn pressure for ultrasonic welding was changed to 0.3 MPa in the second oscillation stage (second oscillation region) and the horn pressure in the pressure holding step was changed to 0.3 MPa. The bonding evaluation by SLS test is shown in Table 1. Cross-sectional observation of the obtained bonded body revealed that voids had occurred in the bonded portion.

[0044] [Table 1] [Explanation of symbols]

[0045] 1: Material (I) 2: Materials (II) 3: Jig 4: Horn 5: Energy Director 6: Fixed part (out-of-plane direction) 7: Fixed part (in-plane direction)

Claims

1. This is a manufacturing method of a joined body in which a plurality of members made of fiber-reinforced resin are joined using an ultrasonic welding machine, in which a member (II) to be joined is overlapped and restrained on a base member (I), and an ultrasonic horn is pressed against the joint while oscillating, the method having a first oscillation region consisting of an ultrasonic output (W) P1, an oscillation time (seconds) t1, and a horn pressure (MPa) p1, followed by a second oscillation region consisting of an ultrasonic output (W) P2, an oscillation time (seconds) t2, and a horn pressure (MPa) p2, and the ultrasonic horn is pressed under the condition that p1<p2.

2. The joining method according to claim 1, wherein the horn pressure p2 is 0.5 to 5.0 MPa.

3. The bonding method according to claim 1 , wherein the ultrasonic output is P1<P2.

4. 2. The bonding method according to claim 1, wherein the oscillation time condition is t1<t2.

5. 2. The bonding method according to claim 1, wherein the total oscillation time (t1+t2) is 1 to 5 seconds.

6. The bonding method according to claim 1 , wherein the first oscillation region and the second oscillation region are provided in a stepwise manner.

7. The bonding method according to claim 1 , wherein the ultrasonic horn is pressed under a condition in which a horn displacement (mm) by the second oscillation region is larger than a horn displacement (mm) by the first oscillation region.

8. The area of the ultrasonic horn pressing part is 5 to 50 cm ２ The bonding method according to claim 1 ,

9. The joining method according to claim 1 , wherein the in-plane restraining force (N) of the members (II) to be joined is greater than the out-of-plane restraining force (N) of the members (II).

10. The joining method according to claim 1, further comprising a third oscillation region after the second oscillation region, the third oscillation region consisting of an ultrasonic output (W) P3, an oscillation time (seconds) t3, and a horn pressure (MPa) p3, wherein p2<p3 is satisfied.

11. 2. The bonding method according to claim 1, further comprising a pressure holding step of continuing to press the ultrasonic horn against the workpiece after the ultrasonic oscillation is terminated.

12. 2. The joining method according to claim 1, wherein either the member (I) or the member (II) has a plurality of energy directors made of a thermoplastic resin.

13. 13. The bonding method of claim 12, wherein the height of the energy director is 10 μm or more and 1000 μm or less.

14. 13. The bonding method of claim 12, wherein the energy director is melted in the first oscillation region before transitioning to the second oscillation region.

15. The joining method according to claim 1, wherein the thickness of the member (I) and the member (II) is 0.5 mm or more and 5 mm or less.

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