Thermoplastic composite ultrasonic welding interface crystallinity control device and method

Abstract

The present application relates to the technical field of ultrasonic welding, and particularly relates to a thermoplastic composite ultrasonic welding interface crystallinity regulation device and method, which is used for ultrasonic welding of a first workpiece and a second workpiece arranged in a stack and forming a welding interface, and comprises a welding mechanism, a preheating mechanism, a regulation mechanism and a control mechanism; the welding mechanism comprises an ultrasonic welding head; the preheating mechanism is used for preheating the first workpiece and the second workpiece before welding; the regulation mechanism is used for heat preservation or pressure and heat preservation of a region where the welding interface is located after welding; and the control mechanism controls heating states of the preheating mechanism and the regulation mechanism according to temperature data of ultrasonic welding, so that the problem of difficulty in controlling a post-welding cooling process of the welding interface and instability of crystallinity is solved, the welding interface is in a preheating state before welding and in a regulation state after welding, and the consistency of interface crystallinity regulation is improved, and the strength and stability of a welded joint are improved.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic welding technology, and in particular to a device and method for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites. Background Technology

[0002] Thermoplastic composites are characterized by being remeltable, weldable, and suitable for lightweight structural applications. They are widely used in aerospace, rail transportation, automotive structural components, and composite material assembly. Ultrasonic welding, as a process suitable for joining thermoplastic composites, typically involves applying pressure and high-frequency vibration to two stacked workpieces using an ultrasonic welding head, causing the interface resin between the two workpieces to melt and form a welding interface.

[0003] In actual welding operations, the workpiece to be welded usually needs to reach a relatively stable initial temperature state before welding, and the area where the welding interface is located also needs to maintain an appropriate temperature environment after welding. For different scenarios such as spot welding, straight continuous welding and curved continuous welding, the workpiece size, welding path and heated area are different, and the requirements for the coordination of preheating before welding, contact during welding and heat preservation or pressure preservation after welding are also different. In addition, after ultrasonic vibration, the welding interface cools down naturally during the pressure preservation process without controlling the cooling rate. During this process, the temperature of the interface resin drops rapidly, resulting in low and uncontrollable crystallinity of the resin at the welding interface, which affects the strength and stability of the weld joint. Summary of the Invention

[0004] The main objective of this invention is to provide a device and method for regulating the crystallinity of the ultrasonic welding interface of thermoplastic composites, aiming to solve the problem that the existing technology has difficulty in controlling the cooling rate, resulting in low and uncontrollable crystallinity of the resin at the welding interface, which affects the strength and stability of the welded joint.

[0005] To achieve the above objectives, the present invention provides a device for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites. The device is used for ultrasonic welding of a first workpiece and a second workpiece stacked together to form a welding interface. The device includes: Welding mechanism, the welding mechanism including ultrasonic welding head; A preheating mechanism is used to preheat the first workpiece and the second workpiece before ultrasonic welding; The control mechanism is used to keep the area where the welding interface is located warm after the ultrasonic welding is completed, or to keep the area where the welding interface is located under pressure and heat, so as to control the cooling process of the welding interface. The control mechanism is used to control the heating state of the preheating mechanism and the regulating mechanism according to the temperature data of ultrasonic welding, so that the welding interface is in a preheated state before ultrasonic welding and in a regulating state after ultrasonic welding, so as to regulate the crystallinity of the corresponding welding interface between the first workpiece and the second workpiece.

[0006] Optionally, when the device is used for ultrasonic spot welding, an energy-conducting rib is provided between the first workpiece and the second workpiece, the preheating mechanism includes a first temperature chamber, a sliding door is provided on the upper surface of the first temperature chamber, and a heating tube is provided inside the first temperature chamber; the control mechanism includes a patch thermocouple and an insertion thermocouple disposed in the first temperature chamber, and the patch thermocouple abuts against the first workpiece.

[0007] Optionally, when the device is used for ultrasonic continuous welding, the device further includes a gantry frame and a pressure holding mechanism, the pressure holding mechanism being disposed on the gantry frame, and the preheating mechanism including a second temperature chamber, the second temperature chamber being provided with a sliding door, a welding window and a pressure holding window.

[0008] Optionally, the preheating mechanism further includes a heating table and a preheating blanket, wherein the first workpiece and the second workpiece are placed together on the heating table, and the preheating blanket is attached to the upper surface of the first workpiece; the device further includes a heating and pressure holding module, wherein a heating tube is provided on the side of the heating and pressure holding module near the first workpiece, and the heating and pressure holding module is mounted on the gantry via a servo motor.

[0009] Optionally, the device is used to perform continuous ultrasonic welding on a workpiece on a curved surface and a workpiece below the curved surface that are stacked together. The welding mechanism further includes a robotic arm, the ultrasonic welding head includes a circular arc welding head, and the circular arc welding head is disposed on the robotic arm, and the robotic arm is also provided with a conformal pressure holding module; The preheating mechanism includes a curved platform, a preheating blanket, and a heating blanket. The workpiece on the curved surface and the workpiece below the curved surface are stacked sequentially on the curved platform from top to bottom. The preheating blanket and the heating blanket both cover the upper end surface of the workpiece on the curved surface. One end of the preheating blanket is provided with a traction hook and is connected to the robot arm through the traction hook.

[0010] Optionally, before ultrasonic welding, the control mechanism controls the first temperature chamber to preheat the first workpiece and the second workpiece based on the temperature data obtained by the patch thermocouple and the inserted thermocouple. The preheating temperature is 120°C, and the temperature is maintained for 15 minutes after the first temperature chamber reaches a constant temperature. After ultrasonic welding is completed, the sliding door is controlled to be in the closed position, and the heating tube is controlled to maintain the heat preservation state in the first temperature chamber according to the temperature data, so that the welding interface is in the controlled state in the first temperature chamber, wherein the heat preservation state is 140°C for 10 minutes.

[0011] Optionally, the preheating blanket is connected to a traction mechanism, which is used to move the preheating blanket as the ultrasonic welding head moves along the welding path, so as to expose the area to be welded.

[0012] Optionally, the heating and pressure holding module is used to press against the welded area after ultrasonic welding is completed in the area to be welded, so as to maintain pressure and temperature in the welded area, and the temperature is maintained at 120°C for 20 minutes.

[0013] Optionally, the heating blanket is used to cover the welded area after the arc welding head has completed the ultrasonic welding of the area to be welded; The conformal pressure holding module is used to abut against the welded area after the arc welding head moves along the welding path, and to hold pressure on the welded area according to the curved shape of the workpiece on the curved surface. The robotic arm is used to move the arc welding head and the conformal pressure holding module along the curved welding path, and to pull the preheating blanket through the traction hook so that the curved area to be welded is exposed, while the welded area is covered and kept warm by the heating blanket at a temperature of 150°C for 20 minutes.

[0014] To achieve the above objectives, the present invention also provides a method for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites, the method comprising: Obtain the base material of the first workpiece and the second workpiece, and determine the corresponding preheating temperature and post-weld conditioning temperature based on the base material; The first workpiece and the second workpiece are stacked together to form a welding area between the first workpiece and the second workpiece; Before ultrasonic welding, the first workpiece and the second workpiece are preheated, and the temperature data of ultrasonic welding is obtained. The heating state of the preheating process is controlled according to the temperature data so that the area to be welded reaches the preheated state. Pressure and ultrasonic vibration are applied to the area to be welded by an ultrasonic welding head, causing the interface resin between the first workpiece and the second workpiece to melt and form a welding interface. After ultrasonic welding is completed, the area where the welding interface is located is kept warm, or the area where the welding interface is located is kept under pressure and kept warm. The heating state of the post-weld conditioning process is controlled according to the temperature data so that the welding interface is in a regulated state according to the post-weld conditioning temperature.

[0015] The beneficial effects that this invention can achieve are as follows: This invention solves the problem in existing ultrasonic welding of thermoplastic composites where the welding interface easily cools down naturally after welding, the cooling process lacks effective control, and the crystallinity of the interface is difficult to stabilize, thus affecting the strength and stability of the welded joint. This is achieved by setting up a welding mechanism including an ultrasonic welding head, a preheating mechanism for preheating before welding, a control mechanism for post-weld heat preservation or pressure preservation, and a control mechanism that can control the heating state of the preheating mechanism and the control mechanism according to ultrasonic welding temperature data. Through the aforementioned structural combination, the temperature change of the welding interface no longer depends solely on natural heat dissipation after welding. Instead, a continuous temperature management process is formed before, during, and after welding, allowing the interface resin to obtain more stable cooling conditions after melting and forming. This is beneficial for improving the controllability of the interface resin crystallization process and enhancing the performance consistency of welded joints from different batches. At the same time, the control mechanism can select heat preservation or pressure preservation methods according to actual welding needs, ensuring that the welding interface maintains the necessary thermal environment and interface adhesion state during the cooling stage. This reduces the adverse effects of post-weld cooling fluctuations on the interface forming quality and improves the reliability of ultrasonic welding joints of thermoplastic composites. Attached Figure Description

[0016] Figure 1 The ultrasonic spot welding control device equipped with a first temperature chamber is shown in Embodiment 1 of the present invention; Figure 2 The ultrasonic continuous welding control device equipped with a second temperature chamber is shown in Embodiment 2 of the present invention; Figure 3 The ultrasonic continuous welding control device equipped with a heating table and a preheating blanket is shown in Embodiment 3 of the present invention. Figure 4 The ultrasonic continuous welding control device equipped with a hot table, a preheating blanket, and a heating blanket is shown in Embodiment 4 of the present invention. Figure 5 This is a flowchart illustrating the control method in Embodiment 5 of the present invention.

[0017] Figure label: 1-Ultrasonic welding head, 2-First temperature chamber, 3-Sliding door, 4-Heating tube, 5-First workpiece, 6-Second workpiece, 7-Energy-conducting rib, 8-Patch thermocouple, 9-Inserted thermocouple, 10-Control mechanism, 11-Gantry frame, 12-Pressure holding mechanism, 13-Second temperature chamber, 14-Sliding door, 15-Welding window, 16-Pressure holding window, 17-Heating table, 18-Preheating blanket, 19-Servo motor, 20-Heating and pressure holding module, 21-Robot arm, 22-Circular arc welding head, 23-Conformal pressure holding module, 24-Workpiece on curved surface, 25-Workpiece with curved surface, 26-Curved table, 27-Traction hook, 28-Heating blanket.

[0018] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0021] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0022] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0023] Example 1: As attached Figure 1 As shown, this embodiment provides a device for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites. The device is used to perform ultrasonic welding on a first workpiece 5 and a second workpiece 6 stacked together to form a welding interface. The device includes: The welding mechanism includes an ultrasonic welding head 1; A preheating mechanism is used to preheat the first workpiece 5 and the second workpiece 6 before ultrasonic welding. The control mechanism is used to keep the area where the welding interface is located warm after the ultrasonic welding is completed, or to keep the area where the welding interface is located under pressure and heat, so as to control the cooling process of the welding interface. The control mechanism 10 is used to control the heating state of the preheating mechanism and the regulating mechanism according to the temperature data of ultrasonic welding, so that the welding interface is in a preheating state before ultrasonic welding and in a regulating state after ultrasonic welding, so as to regulate the crystallinity of the corresponding welding interface between the first workpiece 5 and the second workpiece 6.

[0024] It should be noted that this embodiment provides a thermoplastic composite ultrasonic welding interface crystallinity control device, which is used to perform ultrasonic welding on a first workpiece 5 and a second workpiece 6 stacked together, so that the area to be welded between the first workpiece 5 and the second workpiece 6 forms a welding interface under the action of ultrasonic waves. The first workpiece 5 and the second workpiece 6 can be composite material workpieces with thermoplastic resin as the matrix. Before welding, the two are stacked according to a predetermined overlap position so that the area to be welded corresponds to the welding mechanism.

[0025] It should also be noted that the welding mechanism includes an ultrasonic welding head 1, which can move towards the welding area of ​​the first workpiece 5 and the second workpiece 6, and apply pressure and ultrasonic vibration to the welding area during the welding process, causing the interface resin between the first workpiece 5 and the second workpiece 6 to melt and form a welding interface. A preheating mechanism is located near the bearing position of the first workpiece 5 and the second workpiece 6, and is used to preheat the first workpiece 5 and the second workpiece 6 before ultrasonic welding, ensuring that the welding area is preheated before the ultrasonic vibration begins, thus reducing the impact of workpiece temperature fluctuations on the interface formation process before welding.

[0026] Understandably, the control mechanism is set up corresponding to the area where the welding interface is located, and is used to continue to keep the area where the welding interface is located at a constant temperature after ultrasonic welding is completed, or to keep the area at a constant pressure while keeping it at a constant temperature. In other words, after the ultrasonic welding head 1 completes the welding action, the welding interface does not immediately leave the controlled temperature environment, but is maintained at a certain post-weld thermal environment by the control mechanism, so that the cooling process of the welding interface is in a controllable state, thereby providing relatively stable temperature conditions for the crystallization process of the interface resin.

[0027] It is also understood that the control mechanism 10 is connected to the preheating mechanism and the regulating mechanism respectively, and controls the heating state of the preheating mechanism and the regulating mechanism according to the temperature data during the ultrasonic welding process. Before welding, the control mechanism 10 adjusts the heating state of the preheating mechanism to make the welding interface reach the preheating state; after welding, the control mechanism 10 adjusts the heating state of the regulating mechanism to make the welding interface in the post-weld regulating state.

[0028] Based on the above structure, this embodiment integrates preheating before welding, ultrasonic welding, and post-weld heat preservation or pressure preservation into a continuous process, avoiding the direct and rapid cooling of the welding interface after ultrasonic welding, thereby achieving the control of the crystallinity of the corresponding welding interface between the first workpiece 5 and the second workpiece 6.

[0029] In some specific embodiments, when the device is used for ultrasonic spot welding, an energy-conducting rib 7 is provided between the first workpiece 5 and the second workpiece 6. The preheating mechanism includes a first temperature chamber 2, a sliding door 3 is provided on the upper end face of the first temperature chamber 2, and a heating tube 4 is provided inside the first temperature chamber 2. The control mechanism includes a patch thermocouple 8 and an insert thermocouple 9 disposed in the first temperature chamber 2, and the patch thermocouple 8 abuts against the first workpiece 5.

[0030] In this embodiment, before ultrasonic welding, the control mechanism 10 controls the first temperature chamber 2 to preheat the first workpiece 5 and the second workpiece 6 based on the temperature data obtained by the patch thermocouple 8 and the inserted thermocouple 9. The preheating temperature is 120°C, and the first temperature chamber 2 is kept at a constant temperature for 15 minutes after reaching a constant temperature. After ultrasonic welding is completed, the sliding door 3 is controlled to be in the closed position, and the heating tube 4 is controlled to maintain the heat preservation state in the first temperature chamber 2 according to the temperature data, so that the welding interface is in the controlled state in the first temperature chamber 2, wherein the heat preservation state is maintained at 140°C for 10 minutes.

[0031] In some more specific embodiments, this embodiment adopts a first temperature chamber 2 structure with a sliding door 3, the overall structure of which is shown in the attached figure. Figure 1 As shown, the first temperature chamber 2 is used to preheat the workpiece and keep it warm after welding. The chamber is equipped with a temperature control system, and the working temperature range is 30℃-300℃. The sliding door 3 is closed before welding to ensure temperature stability and is opened during welding to facilitate the insertion of the ultrasonic welding head 1. The ultrasonic welding head 1 is provided with high-frequency vibration by an ultrasonic generator. In this embodiment, the first workpiece 5 and the second workpiece 6 are thermoplastic carbon fiber composite workpieces. Energy-conducting ribs 7 are placed between the workpieces to ensure that the energy generated by ultrasonic vibration is concentrated at the connection interface. The size of the workpiece is 150mm×25.4mm×2mm.

[0032] In addition, the temperature control of the first temperature chamber 2 and the workpiece to be welded is based on the temperature values ​​measured by the patch thermocouple 8 and the inserted thermocouple 9 fixed on the surface of the first workpiece 5, as well as the control mechanism 10.

[0033] Its specific implementation steps include: Workpiece preheating: The temperature of the temperature chamber is set to 120℃. The CF / PPS composite material workpiece and the energy conduction rib 7 are stacked and clamped in the first temperature chamber 2. After the first temperature chamber 2 reaches a constant temperature, it is kept for 15 minutes to ensure that the workpiece is heated evenly.

[0034] Ultrasonic welding: Open the sliding door 3, the ultrasonic welding head 1 descends to the surface of the workpiece and applies a welding pressure of 1200N. The ultrasonic welding amplitude is 70µm, the frequency is 20kHz, the welding time is 1s, and the holding pressure time is 3s.

[0035] Controlled cooling: After welding is completed, the welding head is lifted, the sliding door 3 is closed, the temperature of the chamber is maintained at 140℃ for 10 minutes, then the heating of the first chamber 2 is stopped and the sliding door 3 is opened to allow the welded joint to cool naturally to room temperature.

[0036] The final welded joint shear strength reached 35 MPa, and the resin crystallinity at the weld interface was 30.6%.

[0037] Comparative Example 1: All the above implementation conditions are the same, but the temperature of the welding process is not controlled, that is, the first temperature chamber 2 is not used. After the welding process is completed, the joint cools naturally. The shear strength of the welded joint is 29.8 MPa and the crystallinity of the resin at the welding interface is 22.8%.

[0038] Example 2: As attached Figure 2 As shown, in this embodiment, when the device is used for ultrasonic continuous welding, the device further includes a gantry frame 11 and a pressure holding mechanism 12. The pressure holding mechanism 12 is disposed on the gantry frame 11. The preheating mechanism includes a second temperature chamber 13, on which a sliding door 14, a welding window 15 and a pressure holding window 16 are disposed.

[0039] In some specific embodiments, the second temperature chamber 13 is 800mm long, and the internal temperature can be controlled between 30℃ and 300℃. It has a sliding door 14, a welding window 15 at the door, through which the welding head enters to weld the workpiece, and a pressure holding window 16 through which the pressure holding mechanism 12 enters to maintain pressure on the welded part. During the welding process, the welding head, the pressure holding mechanism 12, the welding window 15 and the pressure holding window 16 move synchronously along the welding direction.

[0040] It is understood that in this embodiment, the second temperature chamber 13 is used to accommodate the first workpiece 5 and the second workpiece 6 to be continuously welded along the length direction, and to preheat the workpiece as a whole before welding, so that the area to be welded is in a relatively stable temperature environment before the start of ultrasonic welding. The sliding door 14 is set on the second temperature chamber 13, and the welding window 15 and the pressure holding window 16 are arranged with the sliding door 14, so that the ultrasonic welding head 1 and the pressure holding mechanism 12 can respectively extend into the second temperature chamber 13 from the corresponding window to perform operations.

[0041] During continuous welding, the ultrasonic welding head 1 enters the second temperature chamber 13 through the welding window 15, applying pressure and ultrasonic vibration to the area to be welded between the first workpiece 5 and the second workpiece 6, so that a welding interface is formed in this area; the pressure holding mechanism 12 enters the second temperature chamber 13 through the pressure holding window 16, and holds pressure on the welded area behind the ultrasonic welding head 1. During the welding process, the gantry 11 drives the ultrasonic welding head 1 and the pressure holding mechanism 12 to move synchronously along the welding direction, and at the same time the welding window 15 and the pressure holding window 16 move synchronously, so that both the area to be welded and the welded area can be in the controlled temperature environment formed by the second temperature chamber 13.

[0042] With the above structure, the second temperature chamber 13 is not only used for preheating before welding, but also for continuous heat preservation of the area where the welding interface is located during continuous welding. The pressure holding mechanism 12 acts on the welded area in time after welding, so that the welding interface cools slowly under pressure, thereby avoiding rapid temperature loss of the welding area after ultrasonic welding, which is beneficial to improving the stability of the resin crystallinity of the welding interface.

[0043] The specific implementation steps include: Workpiece preheating: Set the temperature of the second temperature chamber 13 to 120℃, and preheat the workpiece in the second temperature chamber 13 for 20 minutes.

[0044] Ultrasonic welding: The welding head is inserted through the welding window 15 and continuous welding is performed in a 600mm direction. The ultrasonic welding frequency is 20kHz, the amplitude is 40µm, the welding pressure is 1500N, and the welding speed is 40mm / s.

[0045] The pressure holding mechanism 12 extends into the pressure holding window 16 to apply a pressure of 1000N to the welding area and moves synchronously with the welding head.

[0046] Controlled cooling: After welding is completed, the welding head and pressure holding mechanism 12 are raised, the welding window 15 and pressure holding window 16 are closed, the temperature of the chamber is maintained at 120℃ for 20 minutes, then the heating of the chamber is stopped and the chamber door is opened to allow the welded joint to cool naturally to room temperature. Finally, the shear strength of the welded joint reaches 33.8MPa and the crystallinity of the resin at the welding interface is 30.2%.

[0047] In this embodiment, the workpiece in the above implementation steps is a thermoplastic composite material with dimensions of 600mm×30mm×2mm, and the material is specifically CF / PPS.

[0048] Comparative Example 2: The implementation conditions of the above embodiment 2 are the same, but the temperature control of the welding process is not performed, that is, the second temperature chamber 13 is not used. After the welding process is completed, the joint cools naturally. The shear strength of the obtained welded joint is 27.3 MPa, and the average crystallinity of the resin at the welding interface is 23.9%.

[0049] Example 3: As attached Figure 3 As shown, in this embodiment, the preheating mechanism further includes a heating table 17 and a preheating blanket 18. The first workpiece 5 and the second workpiece 6 are placed together on the heating table 17, and the preheating blanket 18 is attached to the upper surface of the first workpiece 5. The device further includes a heating and pressure holding module 20. The heating and pressure holding module 20 is provided with a heating tube 4 on the side of the heating and pressure holding module 20 near the first workpiece 5. The heating and pressure holding module 20 is mounted on the gantry frame 11 via a servo motor 19.

[0050] In this embodiment, the heating and pressure holding module 20 is used to press against the welded area after ultrasonic welding is completed in the area to be welded, so as to keep the welded area under pressure and heat, and the heat holding state is 120°C for 20 minutes.

[0051] Based on the above structure, in this embodiment, the heating table 17 is used to support the first workpiece 5 and the second workpiece 6 stacked together, and to preheat the area to be welded from the bottom side of the workpiece; the preheating blanket 18 is attached to the upper surface of the first workpiece 5, and is used to cover and insulate from the top side of the workpiece, so that the first workpiece 5 and the second workpiece 6 are in a relatively stable preheated state before ultrasonic welding.

[0052] During ultrasonic welding, the ultrasonic welding head 1 moves along the welding path and welds the exposed area to be welded. After the area to be welded forms a welding interface, the heating and pressure holding module 20 approaches and abuts the welded area under the drive of the servo motor 19. Since the heating and pressure holding module 20 is provided with a heating tube 4 on the side close to the first workpiece 5, it can maintain the heat preservation state while applying pressure to the welded area, so that the welding interface is in a controlled cooling environment after welding.

[0053] By cooperating with the heating table 17, the preheating blanket 18, and the heating and pressure holding module 20, the preheating before welding, the pressure holding after welding, and the heat preservation after welding in the continuous welding process are connected to each other, avoiding the rapid cooling of the welded area after welding is completed, which helps to improve the stability of the crystallinity control of the welding interface.

[0054] Specifically, the heating table 17 is heated to 30-350°C to clamp the upper and lower workpieces and preheat their bottoms; Preheating blanket 18: The temperature can be set between 30℃ and 350℃. It is used to cover the entire workpiece before welding begins and to preheat the workpiece and keep it warm during the welding process. Heating and pressure holding module 20: It is connected to the gantry frame 11 by servo motor 19 and has a built-in heating tube 4. It is used to maintain pressure and control temperature in a timely manner in the area after welding of large workpieces. The maximum pressure of the pressure holding module is 2000N and the temperature can be set between 30℃ and 350℃.

[0055] The workpiece dimensions are 600mm×30mm×2mm, and the material is CF / PEEK.

[0056] In this embodiment, the first workpiece 5 and the second workpiece 6 are both provided with energy-conducting ribs 7, which are preferably PEEK films with a thickness of 200 micrometers.

[0057] The specific implementation steps of this embodiment include: Workpiece preheating: Set the temperature of the heating table 17 to 150℃, overlap and clamp the CF / PEEK workpiece and energy conduction rib 7 onto the heating table 17, and then cover it with a preheating blanket 18 with a temperature set to 150℃. After the workpiece temperature stabilizes, maintain it for 10 minutes.

[0058] Ultrasonic welding: Start the ultrasonic welding device, press down the ultrasonic welding head 1 to contact the workpiece, and move to the right under the traction of the gantry 11 to start continuous ultrasonic welding. The welding frequency is 20kHz, the amplitude is 40µm, and the welding speed is 30mm / s.

[0059] Synchronously, the traction mechanism drags the preheating blanket 18 to the right at the same speed as the welding head, exposing the area to be welded and preparing for welding. Synchronously, after welding is completed, the heating and pressure holding module 20 is pressed down step by step to the area that has just been welded, and the welded area is kept warm and pressure is maintained. The temperature of the heating and pressure holding module 20 is set to 150℃ and the pressure is 1000N.

[0060] Controlled cooling: After welding is completed, the welding head is lifted, and the heating and pressure holding module 20 continues to apply pressure, maintaining the temperature at 150°C for 20 minutes. Then, the heating of the heating stage 17 and the pressure holding module is stopped, and the welded joint is allowed to cool naturally to room temperature. Finally, the shear strength of the welded joint reaches 36.7 MPa, and the crystallinity of the resin at the welding interface is 29.4%.

[0061] Comparative Example 3: The implementation conditions of the above embodiment 3 are the same, but the temperature control of the welding process is not performed, that is, the heating functions of the hot table 17, the preheating blanket 18 and the pressure holding module are not used. After the welding process is completed, the joint cools naturally. The shear strength of the welded joint is 28.5 MPa and the average crystallinity of the resin at the welding interface is 22.3%.

[0062] Example 4: As attached Figure 4 As shown, in this embodiment, the device is used to perform continuous ultrasonic welding on the workpiece 24 on the curved surface and the workpiece below the curved surface that are stacked together. The welding mechanism also includes a robot arm 21, the ultrasonic welding head 1 includes a circular arc welding head 22, and the circular arc welding head 22 is disposed on the robot arm 21, and the robot arm 21 is also provided with a conformal pressure holding module 23; The preheating mechanism includes a curved platform 26, a preheating blanket 18, and a heating blanket 28. The workpiece 24 on the curved surface and the workpiece below the curved surface are stacked sequentially on the curved platform 26 from top to bottom. The preheating blanket 18 and the heating blanket 28 both cover the upper surface of the workpiece 24 on the curved surface. One end of the preheating blanket 18 is provided with a traction hook 27, and is connected to the robot arm 21 through the traction hook 27.

[0063] In this embodiment, the preheating blanket 18 is connected to a traction mechanism, which is used to pull the preheating blanket 18 to move when the ultrasonic welding head 1 moves along the welding path, so as to expose the area to be welded.

[0064] In this embodiment, the heating blanket 28 is used to cover the welded area after the arc welding head 22 has completed the ultrasonic welding of the area to be welded. The conformal pressure holding module 23 is used to abut against the welded area after the arc welding head 22 moves along the welding path, and to hold pressure on the welded area according to the curved shape of the workpiece 24 on the curved surface; The robotic arm 21 is used to drive the arc welding head 22 and the conformal pressure holding module 23 to move along the curved welding path, and to pull the preheating blanket 18 to move through the traction hook 27 so that the curved area to be welded is exposed, while the welded area is covered and kept warm by the heating blanket 28. The temperature of the covering and keeping is 150°C and the covering and keeping is for 20 minutes.

[0065] Based on the above structure, during continuous welding, the robot arm 21 pulls the preheating blanket 18 to move via the traction hook 27, exposing the curved surface to be welded, thus preventing the preheating blanket 18 from blocking the arc welding head 22 from acting on the workpiece surface. After the area is welded, the heating blanket 28 covers the welded area and maintains it at 150°C for 20 minutes, allowing the welded area to cool slowly in a controlled temperature environment. Furthermore, through the cooperation of the arc welding head 22, the conformal pressure holding module 23, the preheating blanket 18, and the heating blanket 28, this embodiment can adapt to the continuous welding requirements of curved components and create a continuous connection between preheating, forming during welding, and post-weld heat preservation and pressure holding at the curved surface welding interface, thereby improving the stability of crystallinity control at the curved surface welding interface.

[0066] In some specific embodiments, the curved surface heating table 17 can be heated to 30℃-350℃ and is used to clamp the upper and lower workpieces to be curved and preheat their bottoms. Preheating Blanket 18: The temperature can be set between 30℃ and 350℃. It is used to cover the entire workpiece before welding to preheat it before welding and to keep it warm during the welding process. Heating Blanket 2828: The temperature can be set between 30℃ and 350℃. It is used to cover the welded area in time after welding begins to keep it warm, and to cover the entire workpiece after welding is completed. Robotic arm 21: used to grasp and control the movement trajectory of the arc welding head 22 and the conformal pressure holding module 23 to realize curved surface ultrasonic welding; at the same time, it pulls the traction hook 27 of the heating blanket 28 to ensure that the heating blanket 28 moves synchronously with the welding head and covers the welded area of ​​the workpiece in time.

[0067] For workpiece 24 on the curved surface and workpiece below the curved surface: the curved surface dimensions are 800mm (arc length) × 30mm × 1.6mm, the radius is 0.5m, and the material is CF / PEEK.

[0068] The specific implementation steps of this embodiment include: Workpiece preheating: Set the temperature of the curved stage 26 to 150℃, clamp the curved CF / PEEK workpiece onto the heating stage 17, and then cover it with a preheating blanket 18 with a temperature set to 150℃. After the workpiece temperature stabilizes, maintain it for 10 minutes.

[0069] Ultrasonic welding: Start the ultrasonic welding device. The ultrasonic welding head 1 and the pressure holding module press down to contact the workpiece under the control of the robot arm 21, and move to the right under the traction of the robot arm 21 to start continuous ultrasonic welding. The pressure holding welding frequency is 20kHz, the amplitude is 40µm, and the welding speed is 20mm / s.

[0070] Synchronously, the traction mechanism drags the preheating blanket 28 to the right at the same speed as the welding head, exposing the area to be welded and preparing it for welding. Simultaneously, under the traction of the robotic arm 21, the heat-insulating heating blanket 28 covers the welding area that has just been welded, until the welding is completed and the entire workpiece is covered.

[0071] Controlled cooling: After welding is completed, the welding head and pressure holding module are lifted, and the welded workpiece is kept warm on the curved stage 26 and heating blanket 28. The temperature is maintained at 150℃ for 20 minutes. Then the heating stage 17 is stopped and the heating blanket 28 is removed, allowing the welded joint to cool naturally to room temperature. Finally, the shear strength of the welded joint reaches 35.3MPa, and the crystallinity of the resin at the welding interface is 29.2%.

[0072] Comparative Example 4: The implementation conditions of the above embodiment 3 are the same, but the temperature control of the welding process is not performed, that is, the heating functions of the curved table 26, the preheating blanket 18 and the heating blanket 28 are not used. After the welding process is completed, the joint cools naturally. The shear strength of the welded joint is 27.5 MPa and the average crystallinity of the resin at the welding interface is 24.5%.

[0073] Example 5: As attached Figure 5 As shown in the figure, this embodiment provides a method for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites, the method comprising: Obtain the base material of the first workpiece 5 and the second workpiece 6, and determine the corresponding preheating temperature and post-weld control temperature based on the base material. The first workpiece 5 and the second workpiece 6 are stacked together to form a welding area between the first workpiece 5 and the second workpiece 6. Before ultrasonic welding, the first workpiece 5 and the second workpiece 6 are preheated, and the temperature data of ultrasonic welding is obtained. The heating state of the preheating process is controlled according to the temperature data so that the area to be welded reaches the preheated state. Pressure and ultrasonic vibration are applied to the area to be welded by ultrasonic welding head 1, so that the interface resin between the first workpiece 5 and the second workpiece 6 melts and forms a welding interface. After ultrasonic welding is completed, the area where the welding interface is located is kept warm, or the area where the welding interface is located is kept under pressure and kept warm. The heating state of the post-weld conditioning process is controlled according to the temperature data so that the welding interface is in a regulated state according to the post-weld conditioning temperature.

[0074] Based on the above steps, the matrix material identification, preheating before welding, ultrasonic welding, and post-weld heat preservation or pressure preservation are formed into a continuous process. This ensures that the welding interface is under control from melting and forming to cooling and solidification. As a result, the rapid cooling of the welding interface after ultrasonic welding is avoided, allowing the interface resin to obtain more stable crystallization conditions. This improves the consistency of crystallinity control of the thermoplastic composite welding interface and enhances the strength and stability of the welded joint.

[0075] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A device for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites, characterized in that, The device is used to perform ultrasonic welding on a first workpiece and a second workpiece stacked together, and to form a welding interface. The device includes: Welding mechanism, the welding mechanism including ultrasonic welding head; A preheating mechanism is used to preheat the first workpiece and the second workpiece before ultrasonic welding; The control mechanism is used to keep the area where the welding interface is located warm after the ultrasonic welding is completed, or to keep the area where the welding interface is located under pressure and heat, so as to control the cooling process of the welding interface. The control mechanism is used to control the heating state of the preheating mechanism and the regulating mechanism according to the temperature data of ultrasonic welding, so that the welding interface is in a preheated state before ultrasonic welding and in a regulating state after ultrasonic welding, so as to regulate the crystallinity of the corresponding welding interface between the first workpiece and the second workpiece.

2. The device for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites as described in claim 1, characterized in that, When the device is used for ultrasonic spot welding, an energy-conducting rib is provided between the first workpiece and the second workpiece. The preheating mechanism includes a first temperature chamber with a sliding door on the upper surface of the first temperature chamber and a heating tube inside the first temperature chamber. The control mechanism includes a patch thermocouple and an insertion thermocouple disposed in the first temperature chamber, and the patch thermocouple abuts against the first workpiece.

3. The device for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites as described in claim 1, characterized in that, When the device is used for ultrasonic continuous welding, the device also includes a gantry frame and a pressure holding mechanism. The pressure holding mechanism is mounted on the gantry frame. The preheating mechanism includes a second temperature chamber, which is equipped with a sliding door, a welding window, and a pressure holding window.

4. The device for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites as described in claim 3, characterized in that, The preheating mechanism further includes a heating table and a preheating blanket. The first workpiece and the second workpiece are placed together on the heating table, and the preheating blanket is attached to the upper surface of the first workpiece. The device further includes a heating and pressure holding module. A heating tube is provided on the side of the heating and pressure holding module near the first workpiece. The heating and pressure holding module is mounted on the gantry frame via a servo motor.

5. The device for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites as described in claim 1, characterized in that, The device is used for continuous ultrasonic welding of workpieces on a curved surface and workpieces below the curved surface that are stacked together. The welding mechanism further includes a robotic arm, the ultrasonic welding head includes a circular arc welding head, and the circular arc welding head is disposed on the robotic arm, and the robotic arm is also provided with a conformal pressure holding module; The preheating mechanism includes a curved platform, a preheating blanket, and a heating blanket. The workpiece on the curved surface and the workpiece below the curved surface are stacked sequentially on the curved platform from top to bottom. The preheating blanket and the heating blanket both cover the upper end surface of the workpiece on the curved surface. One end of the preheating blanket is provided with a traction hook and is connected to the robot arm through the traction hook.

6. The device for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites as described in claim 2, characterized in that, Before ultrasonic welding, the control mechanism controls the first temperature chamber to preheat the first workpiece and the second workpiece based on the temperature data obtained by the patch thermocouple and the inserted thermocouple. The preheating temperature is 120°C, and the temperature is maintained for 15 minutes after the first temperature chamber reaches a constant temperature. After ultrasonic welding is completed, the sliding door is controlled to be in the closed position, and the heating tube is controlled to maintain the heat preservation state in the first temperature chamber according to the temperature data, so that the welding interface is in the controlled state in the first temperature chamber, wherein the heat preservation state is 140°C for 10 minutes.

7. A device for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites as described in claim 4 or 5, characterized in that, The preheating blanket is connected to a traction mechanism, which is used to move the preheating blanket as the ultrasonic welding head moves along the welding path, so as to expose the area to be welded.

8. The device for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites as described in claim 3, characterized in that, The heating and pressure holding module is used to press against the welded area after ultrasonic welding is completed in the area to be welded, so as to maintain pressure and temperature in the welded area, and the temperature is maintained at 120°C for 20 minutes.

9. The device for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites as described in claim 5, characterized in that, The heating blanket is used to cover the welded area after the arc welding head has completed the ultrasonic welding of the area to be welded. The conformal pressure holding module is used to abut against the welded area after the arc welding head moves along the welding path, and to hold pressure on the welded area according to the curved shape of the workpiece on the curved surface. The robotic arm is used to move the arc welding head and the conformal pressure holding module along the curved welding path, and to pull the preheating blanket through the traction hook so that the curved area to be welded is exposed, while the welded area is covered and kept warm by the heating blanket at a temperature of 150°C for 20 minutes.

10. A method for controlling the crystallinity of the ultrasonic welding interface of thermoplastic composites, characterized in that, The method includes: Obtain the base material of the first workpiece and the second workpiece, and determine the corresponding preheating temperature and post-weld conditioning temperature based on the base material; The first workpiece and the second workpiece are stacked together to form a welding area between the first workpiece and the second workpiece; Before ultrasonic welding, the first workpiece and the second workpiece are preheated, and the temperature data of ultrasonic welding is obtained. The heating state of the preheating process is controlled according to the temperature data so that the area to be welded reaches the preheated state. Pressure and ultrasonic vibration are applied to the area to be welded by an ultrasonic welding head, causing the interface resin between the first workpiece and the second workpiece to melt and form a welding interface. After ultrasonic welding is completed, the area where the welding interface is located is kept warm, or the area where the welding interface is located is kept under pressure and kept warm. The heating state of the post-weld conditioning process is controlled according to the temperature data so that the welding interface is in a regulated state according to the post-weld conditioning temperature.

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