An ultrasonic welding process for composite material layup

Abstract

The present application relates to the technical field of thermoplastic composite material connection, and discloses an ultrasonic welding process method for composite material laying, comprising: establishing the corresponding acoustic characteristic threshold value when the welding point reaches the predetermined melting state through calibration test; in actual welding, ultrasonic wave energy and pressure are applied to the composite material layer, and the acoustic characteristics of the welding area are monitored in real time; when the real-time monitored acoustic characteristics reach the preset threshold value, the application of ultrasonic wave energy is terminated, replacing the fixed welding time. The present application changes the determination condition of welding termination from the fixed time parameter to the real-time acoustic characteristics directly related to the internal physical state of the material, realizes the closed-loop control of the welding process, effectively solves the problems of unstable welding quality and poor consistency caused by the open-loop control mode in the prior art, and significantly improves the reliability of the welding point and the automation level of the process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermoplastic composite material connection, in particular to an ultrasonic welding process method for composite material laying. BACKGROUND

[0002] Carbon fiber reinforced polyether ether ketone (CF / PEEK) is a high-performance thermoplastic composite material. Its repeatable melting welding characteristics make it highly concerned in the manufacturing of complex structures in the field of aerospace and other fields. During the laying manufacturing process, it is often necessary to temporarily splice and fix the single-layer sheet. Local welding by electric soldering iron is a common means to achieve such fixation. However, this direct heating method exposes many problems in practice, the consistency of welding quality is difficult to guarantee, and the interface bonding strength of the welding point often cannot meet the expectation, which restricts the development of automatic laying technology of thermoplastic composite materials.

[0003] The fundamental limitation of the existing welding method lies in its open-loop process characteristics. The temperature control of the electric soldering iron is its inherent defect, and its working temperature fluctuates in a large range. However, the melting window of PEEK resin is very narrow, which makes it difficult to accurately match the temperature of the welding area to the process requirements. If the temperature is too low, the resin cannot flow sufficiently, resulting in a false weld; if the temperature is too high, it will immediately cause thermal degradation of the matrix, making the material brittle. The mode of heat transfer also exacerbates this problem. The soldering iron tip directly contacts, the heat is highly concentrated, and the high thermal conductivity of carbon fiber will quickly conduct this excessive heat to the adjacent area, often causing the center of the welding point to appear intact, but the edge has already been damaged. In addition, manual operation introduces uncontrollable human factors, the pressure applied by the operator is not constant, and the moving speed of the soldering iron tip cannot be kept uniform, which together causes great dispersion of the performance of the welding point.

[0004] The existing electric soldering iron welding method is essentially a process that relies on the experience of the operator, lacks perception of the real physical state of the material, and cannot adjust in real time according to the changes in the material state, which makes the welding process full of uncertainty. SUMMARY

[0005] In view of the shortcomings of the prior art, the present application provides an ultrasonic welding process method for composite material laying, which solves the problem that the direct contact of the iron head causes heat concentration, the rapid thermal conduction of carbon fiber causes peripheral thermal degradation, and part of the welding area is brittle.

[0006] To achieve the above purpose, the present application is implemented by the following technical scheme: an ultrasonic welding process method for composite material laying, comprising the following steps:

[0007] S1: determining a preset acoustic characteristic threshold. This step is completed by performing a welding test on a composite sample. Specifically, in the test, the composite sample is subjected to ultrasonic energy for welding, and the acoustic characteristic during the welding process is monitored synchronously. After the welding is completed, the time point at which the welding spot reaches a predetermined molten state is determined by analyzing the microstructure or mechanical properties of the welding spot under different welding durations. The analysis method here can include observing the porosity and interface bonding state of the welding spot section using a metallographic microscope, or testing the shear strength of the welding spot using a mechanical testing machine. The acoustic characteristic corresponding to the determined time point is identified and recorded as the preset acoustic characteristic threshold.

[0008] S2: providing a carbon fiber reinforced polyether ether ketone composite layup and positioning the composite layup according to the layup design requirements.

[0009] S3: applying ultrasonic energy to the to-be-welded area of the composite layup through an ultrasonic welding head. In a specific embodiment, the working frequency of the ultrasonic welding head is 20 kHz, the amplitude is set to 26.2-27.0 μm, and at the same time of applying the ultrasonic energy, a pressure of 0.4-0.8 MPa is applied to the to-be-welded area.

[0010] S4: monitoring the acoustic characteristic of the to-be-welded area in real time during the entire process of applying ultrasonic energy in step S3.

[0011] S5: continuously comparing the real-time monitored acoustic characteristic with the acoustic characteristic threshold determined in step S1, and when the real-time monitored acoustic characteristic reaches the acoustic characteristic threshold, terminating the application of the ultrasonic energy, which replaces the traditional fixed welding time control.

[0012] In an embodiment, the acoustic characteristic is at least one selected from the group consisting of acoustic attenuation spectrum, acoustic energy accumulation value, and time-domain attenuation curve of reflected acoustic signal.

[0013] wherein the acoustic energy accumulation value can be calculated by the following formula:

[0014] ;

[0015] wherein:

[0016] is the acoustic energy accumulation value from the start of welding to time ;

[0017] is the current time from the start of welding, and at the same time as the upper limit of integration;

[0018] is the acoustic energy accumulation value at the time point Instantaneous ultrasonic power at that time;

[0019] For integration variables An infinitesimal increment of is also called a differential element;

[0020] For 0 to The integral variable over the time interval.

[0021] The time-domain attenuation curve of the reflected sound wave signal can be characterized by an exponential attenuation model:

[0022] ;

[0023] In the formula:

[0024] In time The amplitude of the reflected sound wave signal at that time;

[0025] Initial time The amplitude of the reflected sound wave signal;

[0026] It is the natural constant or Euler's number.

[0027] This is the attenuation coefficient of the sound wave signal, which is related to the viscoelastic state of the material;

[0028] The current time since the start of welding.

[0029] In a preferred embodiment, in step S1, when establishing the correspondence between the acoustic characteristics and the melting state of the solder joint, a temperature measuring device is used to ensure that the temperature of the solder joint is within the range of 330 to 350°C.

[0030] In a preferred embodiment, in step S3, the amplitude of the ultrasonic welding head is set to 26.5±0.3μm, and the pressure applied to the area to be welded is set to 0.6±0.1MPa.

[0031] The method of this invention can be applied to different welding scenarios.

[0032] In one application scenario, when the composite material layup is composed of at least two sheets joined together on the same plane, this method is used for in-layer welding. In this case, the area to be welded is the seam between the sheets. To ensure a connection, at least three weld points are welded at the seam. In a specific operation of this scenario, after the application of ultrasonic energy is terminated at the weld point, the ultrasonic welding head is lifted to allow the weld point to cool naturally in the environment until the resin flowability at the weld point decreases.

[0033] In another application scenario, when at least two layers of the composite material layup are provided, this method is used for interlayer welding to weld the different layers of the composite material layup together. In a specific operation of this scenario, the welding sequence includes: first, welding at least three weld points in the middle region of the composite material layup; then, adding weld points radially from the middle region outwards; and finally, welding the edge regions of the composite material layup.

[0034] To ensure the flatness of the layup, an auxiliary step is included in the process of adding weld points radially from the central area to the surrounding areas: before welding the next weld point, a rolling pin is used to compact the composite material layup from the welded points toward the area to be welded.

[0035] To ensure a uniform distribution of interlayer connection points, in one specific embodiment, when increasing solder joints radially from the central region outwards, the distance between adjacent solder joints is set to 100mm.

[0036] This invention provides an ultrasonic welding process for composite material laying. It has the following beneficial effects:

[0037] 1. This invention terminates welding by real-time monitoring of acoustic wave characteristics and comparing them with a preset threshold, ensuring that the end point of the welding process depends on the actual melting state of the material itself, rather than a fixed time. This method effectively compensates for the effects of local conditions such as material thickness and interface adhesion, avoiding resin degradation due to overheating or insufficient melting due to insufficient energy, thereby ensuring the uniformity of quality and interfacial bonding of each weld point.

[0038] 2. This invention transforms the control of welding quality from the control of indirect process parameters such as time and power to the direct control of acoustic characteristics that are directly related to the melting state of the material. In the calibration test of step S1, by correlating the acoustic characteristic threshold with the ideal melting state achieved within a specific temperature window, precise control of the thermal cycle of each weld point is achieved, ensuring that it reaches the predetermined physical state.

[0039] 3. This invention replaces the fixed welding time with real-time determination of the welding endpoint using acoustic wave characteristic thresholds. This allows for automatic shortening of welding time for well-fitting and energy-efficient welding points, avoiding the time waste caused by setting conservative long delays uniformly to cope with worst-case scenarios in traditional methods. This significantly reduces the average welding time per point and improves the efficiency of the overall tiling process. Attached Figure Description

[0040] Figure 1 This is a flowchart of the method of the present invention;

[0041] Figure 2 This is a schematic diagram of the acoustic wave feature threshold determination method of the present invention;

[0042] Figure 3 This is a schematic diagram of the composite material layup positioning of the present invention;

[0043] Figure 4 A schematic diagram illustrating the energy and pressure applied to the ultrasonic welding head of the present invention;

[0044] Figure 5 This is a logic block diagram of the closed-loop control of the welding process according to the present invention. Detailed Implementation

[0045] The technical solutions in 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] See attached document Figure 1 , Figure 1 This is a schematic flowchart of an ultrasonic welding process for composite material layup according to an embodiment of the present invention. The present invention provides an ultrasonic welding process for composite material layup, which is applied to the layup and fixation of thermoplastic composites such as carbon fiber reinforced polyetheretherketone (CF / PEEK). The method may include the following steps:

[0047] S1: By conducting welding tests on composite material samples, monitoring the acoustic characteristics during the welding process, and analyzing the microstructure or mechanical properties of the weld joint to determine the time point at which the weld joint reaches the predetermined melting state, the acoustic characteristics corresponding to this time point are determined as the preset acoustic characteristic threshold.

[0048] S2: Provide a carbon fiber reinforced polyetheretherketone composite material layup and position the composite material layup;

[0049] S3: Apply ultrasonic energy to the area to be welded of the composite material layup using an ultrasonic welding head with a working frequency of 20kHz. The amplitude of the ultrasonic welding head is 26.2 to 27.0 μm. At the same time as applying the ultrasonic energy, apply a pressure of 0.4 to 0.8 MPa to the area to be welded.

[0050] S4: While applying the ultrasonic energy, monitor the acoustic characteristics of the area to be welded in real time;

[0051] S5: When the real-time monitored acoustic wave characteristics reach the determined acoustic wave characteristic threshold, the application of ultrasonic energy is terminated to replace the fixed welding time.

[0052] This method is also applicable to other thermoplastic composites with obvious melting windows, such as carbon fiber reinforced polyether ketone ketone (CF / PEKK), carbon fiber reinforced polyimide (CF / PI), or glass fiber reinforced polypropylene (GF / PP). For different materials, it is only necessary to determine their corresponding acoustic characteristic thresholds according to the calibration test method described in step S1.

[0053] The real-time monitoring, comparison, and control commands issued in steps S3 to S5 are all automatically executed by the central control unit (e.g., a programmable logic controller (PLC) or an industrial computer (IPC)) according to a preset program. The criteria for determining the termination of welding are changed from fixed time or energy input to real-time acoustic characteristics that are directly related to the internal physical state of the material. During ultrasonic welding, as the polymer matrix melts and flows, the viscoelasticity of the material changes significantly, which in turn causes changes in the attenuation characteristics and energy absorption rate of ultrasonic waves propagating within it. By conducting calibration tests before welding, a correspondence between acoustic characteristics and the weld reaching a predetermined melting state is established, thereby determining one or more acoustic characteristic thresholds.

[0054] During actual welding, the system monitors the acoustic characteristics in real time. When the characteristics reach a preset threshold, it indicates that the weld joint has reached the required melting state, and the system then terminates the welding.

[0055] In one specific embodiment, the acoustic feature may be selected from at least one of the group consisting of acoustic attenuation spectrum, acoustic energy accumulation value, and time-domain attenuation curve of reflected acoustic signal.

[0056] The cumulative acoustic energy is an indicator for evaluating the energy input in the welding process. It is calculated by integrating a function of ultrasonic power over time, as shown in the following formula:

[0057] ;

[0058] In the formula:

[0059] From the start of welding to the time The cumulative value of sound wave energy at that time;

[0060] This is the current time from the start of welding, and also serves as the upper limit for integration;

[0061] For at a certain point in time Instantaneous ultrasonic power at that time;

[0062] It is an integral infinitesimal element;

[0063] It is the integral variable.

[0064] The time-domain attenuation curve of the reflected sound wave signal can be characterized by an exponential attenuation model:

[0065] ;

[0066] In the formula:

[0067] In time The amplitude of the reflected sound wave signal at that time;

[0068] Initial time The amplitude of the reflected sound wave signal;

[0069] is the base of the natural logarithm;

[0070] This is the attenuation coefficient of the sound wave signal, which is related to the viscoelastic state of the material;

[0071] The current time since the start of welding.

[0072] Through the calibration test in step S1, a deterministic correspondence between acoustic wave characteristics and the physical state of the weld joint (i.e., the molten state) is established in advance, and the acoustic wave characteristics that characterize the ideal molten state are defined as the threshold. In the subsequent actual welding operation, the system no longer relies on fixed time parameters, but compares the acoustic wave characteristics, which directly reflect the changes inside the material, with the established threshold in real time, thereby achieving closed-loop control of the welding endpoint. When the material reaches the predetermined molten state, the welding process is immediately terminated.

[0073] See attached document Figure 2 , Figure 2This is a flowchart illustrating a method for determining an acoustic characteristic threshold according to an embodiment of the present invention. To determine a preset acoustic characteristic threshold for welding control, a calibration test needs to be performed beforehand. The method may include:

[0074] First, prepare the test system and materials. The test system includes: an ultrasonic welding device equipped with an ultrasonic generator, transducer, and welding head with a working frequency of 20kHz; a pressure application device to apply a set pressure to the welding head; an acoustic signal acquisition system, such as consisting of an acoustic emission sensor, a data acquisition card, and a computer, to record the acoustic signals during the welding process; and temperature monitoring equipment, such as an infrared thermal imager or thermocouple. Prepare composite material samples with the same specifications as those used in actual production, such as carbon fiber reinforced polyetheretherketone prepreg sheets with a size of 100mm×25mm. Before the test, clean the surface of the sample to be welded with solvents such as anhydrous ethanol.

[0075] Secondly, a series of welding tests were conducted to prepare weld point samples. Two prepreg sheets were stacked in a single overlap manner. During the test, parameters such as amplitude and pressure were fixed. For example, the pressure was set to 0.6 MPa and the amplitude was set to 26.5 μm. Welding time was used as the only variable to create multiple weld points. For example, the welding time was set to a series of time points such as 0.5s, 0.7s, 0.9s, 1.1s, and 1.3s. During each welding process, the acoustic signal acquisition system synchronously recorded complete acoustic characteristic data, and the temperature monitoring equipment recorded the temperature change curve of the weld point area.

[0076] Then, the performance of the welded specimens is analyzed to determine the time point when the predetermined melting state is reached. The analysis includes mechanical property testing and microstructure analysis. Single lap shear tests are performed on each specimen using a universal testing machine to obtain the maximum shear load at different welding times and plot the relationship curves. At the same time, the weld joint is cut along the cross section, inlaid and polished, and the fusion, porosity and fiber distribution of the weld interface are observed using a metallographic microscope. Based on the above analysis results, the time point when the predetermined melting state is reached is determined. This time point corresponds to the weld joint with a dense and non-porous microstructure and a shear strength that reaches a predetermined value (e.g., 90% of the strength of the matrix material).

[0077] Finally, based on the determined time points, the acoustic characteristic threshold is extracted and set. The corresponding acoustic characteristic values ​​are extracted from the acoustic characteristic data records corresponding to the time points when the predetermined melting state is reached. For example, the cumulative acoustic energy value or the time-domain attenuation coefficient α of the reflected acoustic signal at this time is extracted. This characteristic value is determined as the preset acoustic characteristic threshold and stored in the central control unit. During the above calibration test, the temperature monitoring equipment confirms that the peak temperature of the welding area of ​​the weld point that has reached the predetermined melting state is in the range of 330 to 350°C. This step ensures that the established acoustic characteristic threshold corresponds to the optimal melting temperature window of the material.

[0078] See attached document Figure 3 , Figure 3 This is a schematic diagram of composite material layup positioning according to an embodiment of the present invention. After the acoustic characteristic threshold is calibrated, the actual layup and welding process begins.

[0079] A composite material layup for application is provided. In this embodiment, the composite material layup is a carbon fiber reinforced polyether ether ketone (CF / PEEK) composite material, which is provided in the form of a prepreg, which may be a unidirectional prepreg tape or a woven fabric.

[0080] The composite material layup is placed in a predetermined position, which is either the surface of a molding die or the surface of a lower composite material layup that has already been laid.

[0081] The positioning operation of the layup is carried out according to the pre-set process requirements. To ensure the accuracy of the positioning, the layup is carried out according to the outline projected by the laser projection system on the mold or the surface of the lower layup, or with the help of physical positioning fixtures.

[0082] When splicing materials in the same plane, place the materials to be spliced ​​close to the positioned materials to ensure that the gap at the joint meets the process specifications. When performing interlayer layup, completely cover the lower layer with the new composite material layup and align it with the reference edge or positioning mark. After positioning, apply slight pressure to make the layup initially adhere to the lower surface to prevent it from shifting before subsequent welding operations.

[0083] See attached document Figure 4 , Figure 4 This is a schematic diagram of the application of energy and pressure by the ultrasonic welding head according to an embodiment of the present invention.

[0084] The ultrasonic welding head is precisely positioned to the pre-defined welding area on the composite material layup by an actuator. Then, the ultrasonic welding head is driven to press down vertically by a pressure application device (e.g., a servo cylinder) so that its working end face establishes stable contact with the upper surface of the composite material layup and applies a pre-defined welding pressure to the welding area. The welding pressure is used to ensure a tight fit between the layups and between the welding head and the layup surface, providing physical conditions for the effective transmission of ultrasonic energy and helping to compact the molten resin during the welding process.

[0085] Under the control of the central control unit, the welding pressure is set within the range of 0.4 to 0.8 MPa. The selection of this pressure range balances energy transmission efficiency and avoidance of damage to the composite material: too low a pressure will lead to insufficient energy coupling, while too high a pressure may cause excessive crushing of the fibers or undesirable material deformation. In a preferred embodiment, the welding pressure is set to 0.6 ± 0.1 MPa. To ensure that the initial conditions for each welding are consistent, after the pressure reaches the set value, the system will perform a short pressure holding delay (e.g., 0.1 seconds) until the pressure stabilizes before proceeding to the next step.

[0086] With the pressure applied stably, the central control unit sends a trigger signal to the ultrasonic generator. The ultrasonic generator converts the power frequency AC power into high frequency electrical energy and sends it to the transducer. The transducer uses the piezoelectric effect to convert the high frequency electrical energy into longitudinal mechanical vibration of the same frequency. This mechanical vibration is then transmitted to the ultrasonic welding head after the amplitude is adjusted by the booster.

[0087] The ultrasonic welding head applies amplified mechanical vibration energy to the area to be welded. The parameters of the ultrasonic energy are preset: the working frequency is fixed at 20kHz, and the amplitude at the end of the welding head is set to a range of 26.2 to 27.0μm. In a preferred embodiment, the amplitude is set to 26.5±0.3μm. The selection of this amplitude matches the viscoelastic properties of the CF / PEEK material to ensure a sufficient energy input rate. The high-frequency vibration generates concentrated heat at the interface of the composite material through two mechanisms: interfacial friction and the viscoelastic hysteresis of the matrix material. This causes the resin matrix at the interface to heat up rapidly in a very short time (usually within seconds) and reach its melting temperature, forming a molten weld nugget.

[0088] Compared with existing technologies, this method improves the consistency of welding quality by using closed-loop control to determine the welding endpoint and incorporate acoustic characteristics that directly characterize the internal molten state of the material. Because the control system directly responds to the actual physical state of the material, it eliminates the impact of batch-to-batch material differences, environmental temperature and humidity fluctuations, or minor changes in equipment status on the welding results. It also optimizes the process window, avoiding incomplete welds due to insufficient welding time or thermal degradation due to excessive welding time, ensuring that each weld point is in its optimal molten state. Furthermore, it improves production efficiency and automation levels. This closed-loop control method requires no manual intervention and enables precise and repeatable automated control of the welding process.

[0089] See attached document Figure 5 , Figure 5 This is a logic block diagram of closed-loop control of the welding process according to an embodiment of the present invention.

[0090] From the moment the ultrasonic energy is applied in step S3, the acoustic signal acquisition system begins to operate. This system continuously acquires acoustic characteristic data reflecting the state of the welding area at a preset high sampling frequency (e.g., every 1 millisecond). In one embodiment, the central control unit receives instantaneous power values ​​from the internal measurement circuitry of the ultrasonic generator in real time. The cumulative sound wave energy at the current moment is calculated by performing real-time numerical integration based on this value. .

[0091] In each sampling cycle, the central control unit compares the real-time calculated acoustic wave characteristic value with the acoustic wave characteristic threshold calibrated and pre-stored in step S1. This comparison is a continuous logical judgment process that runs through the entire ultrasonic energy application stage.

[0092] When the real-time monitored acoustic characteristic value reaches or exceeds the preset acoustic characteristic threshold for the first time, the logical judgment condition is met. At this time, the central control unit determines that the welding area has reached the predetermined melting state and immediately generates and sends a termination command.

[0093] The termination command is an electrical signal sent to the control port of the ultrasonic generator. Upon receiving the command, the ultrasonic generator immediately stops its high-frequency electrical energy output. As a result, the mechanical vibration of the transducer and the ultrasonic welding head ceases, and the process of applying ultrasonic energy to the area to be welded is precisely terminated.

[0094] After the ultrasonic energy is stopped, the ultrasonic welding head does not lift up immediately, but continues to maintain the preset welding pressure in the area to be welded, and enters the pressure holding and cooling stage. The duration of this stage is preset (e.g., 0.5 seconds) to ensure that the molten resin cools and solidifies under pressure, thereby forming a dense weld joint. After the pressure holding and cooling stage ends, the welding head is lifted up, and the welding process of one weld point is completed. Example 1:

[0095] This embodiment provides a specific application of the method of the present invention in the scenario of splicing and fixing within a composite material layer. The purpose of this application is to splice two or more carbon fiber reinforced polyether ether ketone (CF / PEEK) prepreg sheets in the same plane to form a larger single-layer layup, and to maintain the precise relative position of each sheet before subsequent overall curing.

[0096] First, as described in step S2, the two CF / PEEK prepreg sheets are positioned on the surface of the molding die, and the edges of the sheets to be spliced ​​are aligned so that they fit tightly together to form a seam.

[0097] Then, the working end of the ultrasonic welding head is attached to the joint, allowing the welding head to act on both pieces of material simultaneously. Subsequently, the closed-loop control welding process described in steps S3 to S5 is executed. In this process, the application of ultrasonic energy and pressure, the real-time monitoring of acoustic characteristics, and the termination of welding based on a preset acoustic characteristic threshold are all performed as described above. This process forms a localized molten weld point at the joint.

[0098] To ensure the initial connection stability after splicing, the above welding operation is performed multiple times along the length of each seam at predetermined intervals to form at least 3 independent welding points.

[0099] At each welding point, as described in step S5, after the ultrasonic energy terminates, the welding head continues to maintain pressure to complete pressure holding and cooling. Subsequently, the welding head is lifted, and the welding point cools naturally in the environment, causing the molten resin matrix to solidify, thereby completing the physical connection between the two sheets. Multiple welding points formed in this way reliably fix the spliced ​​sheets together as a single unit. Example 2:

[0100] This embodiment provides a specific application of the method of the present invention in the context of interlayer fixing of composite materials. The purpose of this application is to reliably fix a new carbon fiber reinforced polyether ether ketone (CF / PEEK) layup on top of an already laid lower layup to construct a multilayer composite material structure. This operation is crucial for preventing relative slippage of the layup in subsequent processing and for removing trapped air between the layers.

[0101] First, as described in step S2, a new CF / PEEK layup is placed over the lower layup and precisely positioned.

[0102] To ensure a tight fit between the layers and effectively remove air, the welding operation follows a preset welding sequence. First, the first welding operation is performed in the geometric center area of ​​the new layer to form the first fixed point. This operation follows the closed-loop control welding process described in steps S3 to S5 to ensure welding quality.

[0103] Using the first center fixing point as a reference, subsequent welding points expand radially outwards, following the order of first the center, then the perimeter, and finally the edges. During radial welding, auxiliary operations can be used to improve interlayer adhesion. Specifically, before welding the next point, use a rolling pin to roll the ply surface from the completed welding point toward the point to be welded. This operation helps to drive any residual air between the two ply layers toward the edges.

[0104] The spacing between adjacent welding points is set to a predetermined value, such as 100mm. This spacing balances the fixing effect and process efficiency. By repeatedly performing the above welding and auxiliary rolling operations, the entire new layup is firmly fixed to the lower layup according to the process requirements.

Claims

1. An ultrasonic welding process method for composite layup, characterized by, The method comprises the following steps: S1: monitoring acoustic characteristics during welding by performing a welding test on a composite sample, and determining a time point at which a weld reaches a predetermined molten state by analyzing the microstructure or mechanical properties of the weld, and determining the acoustic characteristics corresponding to the time point as a preset acoustic characteristic threshold value; S2: providing a carbon fiber reinforced polyether ether ketone composite layer, and positioning the composite layer; S3: applying ultrasonic energy to the to-be-welded area of the composite layer by an ultrasonic welding head with a working frequency of 20 kHz, the amplitude of the ultrasonic welding head being 26.2-27.0 μm, and at the same time, applying a pressure of 0.4-0.8 MPa to the to-be-welded area; S4: monitoring the acoustic characteristics of the to-be-welded area in real time while the ultrasonic energy is being applied; S5: when the acoustic characteristics monitored in real time reach the determined acoustic characteristic threshold value, the application of the ultrasonic energy is terminated, instead of a fixed welding time; The acoustic characteristics are selected from at least one of the group consisting of acoustic attenuation spectrum, acoustic energy accumulation value, and time domain attenuation curve of reflected acoustic signal.

2. A process for ultrasonic welding of a composite material lay-up according to claim 1, wherein, In step S1, when establishing the correspondence between the acoustic characteristics and the molten state of the weld, the temperature of the weld is ensured to be in the range of 330-350 °C.

3. A method of ultrasonic welding process for composite lay-up as claimed in claim 1 wherein, In step S3, the amplitude of the ultrasonic welding head is 26.5±0.3 μm, and the pressure applied to the to-be-welded area is 0.6±0.1 MPa.

4. The ultrasonic welding process for composite layup of claim 1, wherein, When the composite layer is spliced by at least two pieces of material located in the same plane, the to-be-welded area is the joint between the pieces of material, and at least 3 welds are welded at the joint.

5. A process for ultrasonic welding of a composite material lay-up according to claim 4, wherein, After the ultrasonic energy is terminated at the weld, the ultrasonic welding head is lifted to allow the weld to cool naturally until the fluidity of the resin at the weld decreases.

6. The ultrasonic welding process for composite layup of claim 1, wherein, When at least two layers of the composite layer are provided, the composite layers of different layers are welded together.

7. A method of ultrasonic welding process for composite lay-up as claimed in claim 6 wherein, The sequence of welding the composite layers of different layers together comprises: First, at least 3 welds are welded in the middle region of the composite layer; Then, the welds are increased radially from the middle region of the composite to the periphery; Finally, the edge region of the composite layer is welded.

8. A method of ultrasonic welding process for composite lay-up as claimed in claim 7 wherein, During the process of increasing the welds radially from the middle region to the periphery, the composite layer is rolled using a rolling plate from the welded area to the to-be-welded area before welding the next weld.

9. A method of ultrasonic welding process for composite lay-up as claimed in claim 7 wherein, When the welds are increased radially from the middle region to the periphery, the spacing between adjacent welds is 100 mm.

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