An automatic welding device for protecting the heater wire of a protector and a welding method thereof

Abstract

The application discloses an automatic welding device for a protector heating wire and a welding method thereof, and belongs to the technical field of heating wire welding. The automatic welding device comprises the following steps: overlapping and pressing an aluminum-based heating wire and a copper-based terminal, rapidly heating a to-be-welded interface under a protective atmosphere, utilizing the difference between the thermal expansion coefficients of the surface layer of the aluminum-based heating wire and the oxide film thereof to make the aluminum oxide film form a thermal crack; applying a periodic alternating pressure to the to-be-welded interface at the final temperature to make the aluminum oxide film forming the thermal crack broken and dispersed along with the plastic deformation of the surface layer of the aluminum-based heating wire; rapidly heating the to-be-welded interface of the overlapped and pressed aluminum-based heating wire and the copper-based terminal under the protective atmosphere, and applying a periodic alternating pressure after the aluminum oxide film forms the thermal crack, so that the aluminum oxide film is changed from an intact continuous barrier layer into a state of being cracked, fragmented and dispersed in the aluminum-based surface layer; and the aluminum-oxygen bond structure in the aluminum oxide film is stable.

Description

Technical Field

[0001] This invention relates to the field of heating wire welding technology, and in particular to an automated welding device and welding method for a protector heating wire. Background Technology

[0002] Protectors are typically used in electrical equipment, electric heating appliances, or temperature control protection scenarios. Their operation often relies on the heating wire generating heat after being energized, and the temperature detection, disconnection, or protection action is achieved through a thermal response structure. Therefore, the connection quality between the heating wire and the conductive terminal directly affects the conductive stability, thermal response consistency, and long-term service reliability of the protector. If there are problems such as poor soldering, high contact resistance, or insufficient interface strength at the connection interface between the heating wire and the terminal, local overheating, uneven heat transfer, and fatigue cracking at the connection may easily occur during the power-on and power-off cycle, thereby affecting the protector's operating accuracy and service life.

[0003] In the existing protection device manufacturing process, the connection between the heating wire and the conductive terminal can usually be achieved by brazing, resistance welding, laser welding, ultrasonic welding or solid-state diffusion bonding. Among them, solid-state diffusion bonding mainly involves plastic deformation and atomic diffusion on the surface of the metal to be joined under certain temperature and pressure conditions, thereby forming a metallurgical bond at a temperature lower than the melting point of the base material. This type of process can reduce the spatter, melt loss and coarsening problems caused by fusion welding, and is theoretically suitable for connecting heating wires and terminals with small size and heat-affected zones, and can also be used to improve the stability of the connection interface.

[0004] However, for the connection between aluminum-based heating wires and copper-based terminals, in the traditional solid-phase diffusion connection process, on the one hand, a dense and stable alumina film easily forms on the surface of the aluminum-based heating wire. This alumina film has a high melting point and strong chemical stability, and is difficult to be effectively broken down under the conventional diffusion connection temperature and pressure conditions, which will hinder the direct contact and atomic diffusion between the aluminum substrate and the copper-based terminal. On the other hand, if the temperature is increased or the holding time is extended in order to improve the diffusion connection effect, a continuous brittle intermetallic compound layer is easily generated at the aluminum-copper interface, causing the joint to become embrittled, cracked or have increased resistance under thermal cycling and mechanical stress. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides an automated welding device and welding method for the heating wire of a protector.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: an automated welding method for the heating wire of a protector, comprising the following steps:

[0007] S1. The aluminum-based heating wire is overlapped and pressed with the copper-based terminal, and the interface to be welded is rapidly heated under a protective atmosphere. The difference in thermal expansion coefficient between the surface of the aluminum-based heating wire and its oxide film is used to cause thermal cracks in the aluminum oxide film. The heating rate is 200-350℃ / s, and the final temperature is 380-430℃.

[0008] S2. At the final temperature, apply periodic alternating pressure to the interface to be welded, so that the alumina film with hot cracks breaks and disperses with the plastic deformation of the surface layer of the aluminum-based heating wire, wherein the peak pressure is 15-30 MPa, the frequency is 1-5 Hz, and the number of cycles is 8-15.

[0009] S3. Apply a DC pulse current to the interface to be welded in a pressed state to form discrete initial metallurgical bonding points in the local contact area between the aluminum-based heating wire and the copper-based terminal, wherein the peak current is 200-400A.

[0010] S4. Continue to press the interface to be welded and apply a high-frequency alternating pulse current to make the discrete initial metallurgical joints undergo low-temperature diffusion connection, wherein the frequency is 1 to 10 kHz, the peak current is 150 to 300 A, and the interface temperature is 400 to 450 °C.

[0011] S5. After stopping the application of high-frequency alternating pulse current, maintain the pressure state of the interface to be welded and cool it to solidify the diffusion connection interface and obtain the welded joint of the protector heating wire.

[0012] In a preferred embodiment of the present invention, in step S1, the pre-pressure when the aluminum-based heating wire and the copper-based terminal are overlapped and pressed together is 1 to 3 N; the protective atmosphere is nitrogen or argon, and the oxygen content is not higher than 1000 ppm.

[0013] In a preferred embodiment of the present invention, in step S1, before rapidly heating the interface to be soldered, a protective atmosphere is first introduced for 1 to 5 seconds, and the protective atmosphere covers the overlapping area between the aluminum-based heating wire and the copper-based terminal.

[0014] In a preferred embodiment of the present invention, in step S2, the periodic alternating pressure includes a peak pressing stage and an unloading and springback stage, and after each unloading and springback stage, the interface to be welded is kept in contact so that the broken alumina film fragments are pressed into the surface of the aluminum-based heating wire.

[0015] In a preferred embodiment of the present invention, in step S2, the valley pressure of the periodic alternating pressure is 0.5 to 2 MPa, and the holding time of a single peak pressure is 0.05 to 0.2 s.

[0016] In a preferred embodiment of the present invention, in step S3, the pulse width of the DC pulse current is 0.5 to 1.5 ms, and the DC pulse current is applied during the last peak pressing stage of the periodic alternating pressure.

[0017] In a preferred embodiment of the present invention, in step S4, the single pulse width of the high-frequency alternating pulse current is 50-200 μs, the duration is 0.5-1 s, and the high-frequency alternating pulse current causes the temperature of the interface to be soldered to fluctuate periodically within the range of 400-450°C.

[0018] In a preferred embodiment of the present invention, in step S5, after the application of the high-frequency alternating pulse current is stopped, the pressing pressure of the interface to be welded is maintained at 10-25 MPa, and the welded joint is cooled to below 120°C at a cooling rate of 50-80°C / s before the pressing state is released.

[0019] In a second aspect, the present invention provides an automated welding apparatus for a protector heating wire, comprising:

[0020] frame;

[0021] A welding platform is mounted on the frame;

[0022] A pressure actuation assembly is mounted on the frame and positioned above the welding platform;

[0023] A welding head assembly is disposed at the lower end of the pressure actuation assembly;

[0024] The welding platform is used to carry the workpiece and provide the lower electrode and cooling. The pressure actuation component is used to provide pre-pressure, periodic alternating pressure, holding pressure and real-time pressure detection. The welding head assembly is used to clamp the workpiece, apply pulsed current and provide a protective atmosphere to the welding area.

[0025] In a preferred embodiment of the present invention, the pressure actuation component includes an actuation component, a pressure holding module, and a pressure control sensor; the welding head assembly includes a welding head and an atmosphere nozzle.

[0026] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0027] (1) By rapidly heating the interface between the aluminum-based heating wire and the copper-based terminal after overlapping and pressing under a protective atmosphere, and applying periodic alternating pressure after the alumina film forms hot cracks, the alumina film is transformed from a complete and continuous barrier layer into a cracked, fragmented state that is dispersed on the surface of the aluminum substrate. The aluminum-oxygen bond structure in the alumina film is stable and difficult to be directly destroyed under conventional solid-phase diffusion conditions. Rapid heating causes a thermal deformation difference between the aluminum substrate and the alumina film, and the alternating pressure further causes micro-plastic flow on the surface of the aluminum substrate, thereby promoting the rupture, shearing and embedding of the alumina film. This can expose more fresh aluminum substrate surfaces and reduce the obstruction of the alumina film to the direct contact between aluminum atoms and copper atoms. Compared with the traditional static pressure diffusion connection, which mainly relies on continuous heating and unidirectional pressing, it can complete the interface film breaking and surface renewal under lower heat input conditions, and improve the actual contact area and solderability between the aluminum-based heating wire and the copper-based terminal.

[0028] (2) By applying a DC pulse current to the bonding interface after the film is broken, discrete initial metallurgical bonding points are first formed in the local contact area between the aluminum-based heating wire and the copper-based terminal. Then, a high-frequency alternating pulse current is applied under the subsequent pressure holding state to make low-temperature diffusion connection occur between the discrete initial metallurgical bonding points. The DC pulse current preferentially acts on the micro-region that has formed metal contact, so that the aluminum and copper atoms in the micro-region obtain high migration activity and form the initial bonding core. The high-frequency alternating pulse current further improves the migration activity of interface atoms, so that the bonding points gradually expand and connect at a lower temperature. This can reduce the dependence on high temperature and long-term diffusion and form a stable metallurgical connection in a shorter process path. Compared with the traditional solid-phase diffusion connection, which makes up for the lack of diffusion by raising the temperature or extending the holding time, the pulse energy input promotes the migration of interface atoms and improves the connection strength and conductivity stability of the welded joint.

[0029] (3) By continuously connecting rapid thermal cracking, alternating pressure film breaking, DC pulse point establishment, high-frequency alternating pulse diffusion, and pressure holding cooling, the connection process between aluminum-based heating wire and copper-based terminal avoids the formation of a continuous brittle intermetallic compound layer, and the diffusion connection interface is shaped under controlled pressure. Discretized initial metallurgical bonding points allow the aluminum-copper reaction to occur first in the dispersed micro-region. The interface temperature fluctuation caused by high-frequency alternating pulses limits the continuous growth of intermetallic compounds along the interface. Pressure holding cooling maintains the adhesion state of the already formed diffusion area and reduces interface separation caused by cooling contraction. Thus, while achieving metallurgical bonding, the risk of interface embrittlement, microcracks, and contact resistance fluctuations can be reduced. Compared with the problem of continuous brittle reaction layer easily generated by high temperature and long-term action in traditional diffusion connection, it can take into account the alumina film breaking, low-temperature diffusion, and interface shaping, and improve the reliability and service life of the heating wire welding joint of the protector under the conditions of on-off electrothermal cycle. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a perspective structural diagram of a preferred embodiment of the present invention;

[0032] Figure 2 This is a three-dimensional structural diagram of the welding head according to a preferred embodiment of the present invention;

[0033] Figure 3 This is a flowchart of a preferred embodiment of the present invention;

[0034] In the diagram: 1. Frame; 2. Welding platform; 3. Actuation components; 4. Pressure control sensor; 5. Pressure holding module; 6. Welding head; 7. Atmosphere nozzle. Detailed Implementation

[0035] 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 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.

[0036] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0037] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the scope of protection of this application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0038] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

[0039] Application Overview:

[0040] Lower temperatures and shorter times are beneficial for reducing the formation of a continuous brittle intermetallic compound layer at the aluminum-copper interface, but they are insufficient to break the alumina film on the surface of the aluminum-based heating wire, nor are they sufficient to provide a driving force for diffusion. Higher temperatures or longer times can enhance the degree of diffusion bonding, but they will promote the continuous reaction of aluminum and copper atoms and form a continuous brittle phase layer, resulting in a decrease in joint strength, a reduction in toughness, and a deterioration in thermal cycling reliability. It can be seen that the key obstacle faced by the traditional solid-phase diffusion bonding process in the welding of aluminum-based heating wires is not simply insufficient bonding strength, but a comprehensive process contradiction caused by the mutual constraints between alumina film obstruction, insufficient low-temperature diffusion, and continuous growth of brittle phases.

[0041] The applicant discovered that by controlling the alumina film removal, initial bonding point formation, and low-temperature diffusion bonding as continuous but distinct processes, the traditional process relying on a single high-temperature, long-term diffusion path can be avoided. Although the alumina film on the surface of the aluminum-based heating wire is difficult to remove by ordinary heating, there is a difference in thermal deformation between it and the aluminum substrate. Under rapid heating conditions, thermal stress can be generated and cracks can be formed. After the alumina film cracks, applying periodic alternating pressure can further break and disperse the alumina film by utilizing the local plastic deformation of the surface of the aluminum-based heating wire, thereby exposing a fresh aluminum substrate surface that can participate in bonding. At the same time, after the alumina film is broken, discrete initial metallurgical bonding points are formed first, and then diffusion between the bonding points is promoted by subsequent pulse energy input, which helps to avoid the formation of a large-area continuous reaction layer at the interface in the initial stage.

[0042] The applicant proposes a method to rapidly heat the interface to be welded under a protective atmosphere after overlapping and pressing an aluminum-based heating wire with a copper-based terminal, causing thermal cracks to form in the alumina film. Subsequently, periodic alternating pressure is applied at a set temperature to break up the cracked alumina film and disperse it to the surface of the aluminum-based heating wire. A DC pulsed current is then applied to form discrete initial metallurgical bonding points. Afterward, a high-frequency alternating pulsed current is applied under pressure holding to induce diffusion bonding at a lower temperature, and the pulse action suppresses the formation of a continuous brittle intermetallic compound layer. Finally, pressure holding and cooling are performed to solidify the diffusion bonding interface. This method enables a reliable connection between the aluminum-based heating wire and the copper-based terminal without relying on high-temperature, long-term diffusion, while simultaneously addressing alumina film breakage, low-temperature diffusion, and brittle phase suppression, thereby improving the electrical conductivity, connection strength, and thermal cycling reliability of the welded joint.

[0043] Example 1:

[0044] like Figure 3 As shown, an automated welding method for a protector heating wire includes the following steps:

[0045] S1. The aluminum-based heating wire is overlapped and pressed with the copper-based terminal, and the interface to be welded is rapidly heated under a protective atmosphere. The difference in thermal expansion coefficient between the surface of the aluminum-based heating wire and its oxide film is used to cause thermal cracks in the aluminum oxide film. The heating rate is 200-350℃ / s, and the final temperature is 380-430℃.

[0046] S2. At the final temperature, apply periodic alternating pressure to the interface to be welded, so that the alumina film with hot cracks breaks and disperses with the plastic deformation of the surface layer of the aluminum-based heating wire, wherein the peak pressure is 15-30 MPa, the frequency is 1-5 Hz, and the number of cycles is 8-15.

[0047] S3. Apply a DC pulse current to the interface to be welded in a pressed state to form discrete initial metallurgical bonding points in the local contact area between the aluminum-based heating wire and the copper-based terminal, wherein the peak current is 200-400A.

[0048] S4. Continue to press the interface to be welded and apply a high-frequency alternating pulse current to make the discrete initial metallurgical joints undergo low-temperature diffusion connection, wherein the frequency is 1 to 10 kHz, the peak current is 150 to 300 A, and the interface temperature is 400 to 450 °C.

[0049] S5. After stopping the application of high-frequency alternating pulse current, maintain the pressure state of the interface to be welded and cool it to solidify the diffusion connection interface and obtain the welded joint of the protector heating wire.

[0050] The core innovation of this invention lies in the following: First, by utilizing the difference in thermal expansion between aluminum and alumina film, the alumina film barrier is completely broken through through thermal shock and mechanical crushing. Then, abandoning the traditional isothermal diffusion logic, discrete initial solder joints are first established under low temperature window. Then, a high-frequency alternating current is cleverly introduced to force atomic migration using the electromigration effect to compensate for insufficient low-temperature diffusion power. At the same time, the temperature oscillation caused by the current dynamically interferes with the interface reaction, causing the brittle phase to repeatedly undergo recovery and fragmentation, thereby blocking its continuous layering. Finally, the long-standing technical contradictions of difficult removal of alumina film, easy formation of brittle phase and insufficient low-temperature diffusion are simultaneously overcome in a very short time.

[0051] Each step will be explained in detail below.

[0052] In step S1, the aluminum-based heating wire and the copper-based terminal are overlapped, and a pre-pressure is applied to make the two fit tightly together; wherein, the pre-pressure is 1 to 3 N.

[0053] The interface to be welded is then rapidly heated under a protective atmosphere, which is either nitrogen or argon, and the oxygen content is not higher than 1000 ppm.

[0054] Before rapid heating, a protective atmosphere is introduced for 1 to 5 seconds to fully cover the overlapping area between the aluminum-based heating wire and the copper-based terminal, thereby venting oxygen near the interface and preventing accelerated oxidation of the aluminum-based surface during heating.

[0055] Rapid heating employs high-frequency induction heating, utilizing the difference in thermal expansion coefficients between the aluminum-based heating wire substrate and its surface alumina film to generate thermal stress at the interface, causing thermal cracks to form in the dense alumina film and exposing part of the fresh aluminum-based surface; the heating rate is 200–350℃ / s, and the final temperature is 380–430℃.

[0056] The high heating rate ensures that thermal stress accumulates rapidly within the alumina film and exceeds its fracture strength, while the final temperature is controlled below the melting point of the aluminum-based heating wire to prevent the substrate from melting.

[0057] In step S2, after reaching the final temperature, periodic alternating pressure is applied to the interface to be welded. The micro-plastic deformation of the surface layer of the aluminum-based heating wire further breaks the aluminum oxide film that has formed hot cracks into fragments, which are dispersed and embedded into the aluminum matrix with the plastic flow of the surface material, thereby eliminating the continuous obstruction of atomic diffusion by the aluminum oxide film.

[0058] The peak pressure of the periodic alternating pressure is 15–30 MPa, the valley pressure is 0.5–2 MPa, the frequency is 1–5 Hz, the number of cycles is 8–15, and the holding time of the single peak pressure is 0.05–0.2 s.

[0059] The cyclic alternating pressure includes a peak pressing stage and an unloading and springback stage. After each unloading and springback stage, the interface to be welded is kept in contact to ensure that the alumina film fragments are continuously pressed into the surface of the aluminum-based heating wire, rather than springing back to the interface.

[0060] In step S3, after the periodic alternating pressure sequence ends, the bonding pressure of the interface to be welded is maintained at the peak pressure level of S2. A DC pulse current is applied so that the current preferentially passes through the local metal contact micro-region where the alumina film has been broken. The Joule heating effect of the current causes the temperature of the micro-region to rise instantaneously, and aluminum and copper atoms acquire migration activity to form discrete initial metallurgical bonding points.

[0061] The peak current of the DC pulse current is 200–400A, the pulse width is 0.5–1.5ms, the number of pulses is 3–8, and the pulse interval is 50–100ms.

[0062] Multiple pulses can sequentially form junctions in different micro-regions, avoiding interface overheating caused by a single large energy input.

[0063] In step S4, after the DC pulse is applied, the bonding pressure of the interface to be welded is switched from the peak pressure of S2 to 10-25 MPa and maintained. A high-frequency alternating pulse current is applied to conduct the heat accumulated at the discrete initial metallurgical bonding point to the surrounding area, enhance the migration activity of interface atoms, promote low-temperature diffusion connection between bonding points, and gradually expand and connect to form a continuous metallurgical bonding region.

[0064] The high-frequency alternating pulse current has a frequency of 1–10 kHz, a peak current of 150–300 A, a single pulse width of 50–200 μs, and a duration of 0.5–1 s.

[0065] The high-frequency alternating pulse current causes the temperature of the interface to be welded to fluctuate periodically within the range of 400 to 450°C. The temperature fluctuation restricts the continuous growth of aluminum-copper intermetallic compounds along the interface, thus avoiding the formation of a continuous brittle phase layer.

[0066] After stopping the application of high-frequency alternating pulse current in step S5, the pressing pressure of the interface to be welded is maintained at 10-25 MPa for cooling. This allows the formed diffusion connection interface to solidify under controlled pressure, preventing interface separation or microcracks caused by cooling shrinkage, and finally obtaining the welded joint of the protector heating wire.

[0067] The cooling rate is 50-80℃ / s, and the pressing state is released after the welded joint is cooled to below 120℃.

[0068] A faster cooling rate further suppresses the continuous precipitation and growth of intermetallic compounds during the cooling process.

[0069] Experimental Example 1:

[0070] S1. Align the aluminum wire and copper terminal at the welding position, and apply a 2N pre-pressure to the welding head to ensure contact conductivity. Under a nitrogen protective atmosphere, rapidly heat the interface to be welded to 405℃ at a heating rate of 275℃ / s. Utilize the difference in thermal expansion coefficients between the aluminum substrate and the alumina film to induce dense microcracks in the alumina film.

[0071] S2. Maintain the interface temperature at 405℃, switch the welding head pressure to pulse mode, with a peak pressure of 22.5MPa, a valley pressure of 1.25MPa, a pulse frequency of 3Hz, and repeat 11 times. Utilize periodic alternating stress to crush and break the cracked alumina film and force it into the aluminum matrix, thus exposing the pure aluminum surface to be welded.

[0072] S3. Maintain a pressure of 22.5 MPa at the peak pressure of the last pressure pulse, and apply a single DC pulse current with a peak current of 300 A and a pulse width of 1.0 ms. Utilize this instantaneous high energy to form discretely distributed initial metallurgical bonding points on the clean aluminum-copper interface, establishing stable conductive and heat transfer channels;

[0073] S4. Maintaining the welding pressure at 22.5 MPa, switch the welding power source to a high-frequency alternating pulse current sequence output with a frequency of 5.5 kHz, a single pulse width of 125 μs, and a peak current of 225 A. By adjusting the duty cycle, control the interface temperature within the 425℃ range and induce high-frequency oscillation for 0.75 s. During this process, the electromigration effect of the alternating current is used to accelerate atomic diffusion, and temperature oscillation is used to achieve dynamic recovery of the initial brittle phase and prevent its continuous layering.

[0074] S5. After stopping heating, continue to maintain the welding pressure at 22.5MPa and cool the weld at a controlled cooling rate of 65℃ / s until the joint temperature drops below 120℃. Then release the pressure and remove the workpiece.

[0075] Experimental Example 2:

[0076] This experimental example is basically the same as Experiment 1, except that the heating rate is taken as the minimum value of the interval. Specifically, S1 is: the interface to be welded is rapidly heated to 405℃ at a heating rate of 200℃ / s.

[0077] Experimental Example 3:

[0078] This experimental example is basically the same as Experiment 1, except that the heating rate is taken as the maximum value of the range. Specifically, S1 is: the interface to be welded is rapidly heated to 405℃ at a heating rate of 350℃ / s.

[0079] Experiment Example 4:

[0080] This experimental example is basically the same as Experiment 1, except that the peak pulse pressure is taken as the minimum value of the interval. Specifically, S2 is: peak pressure 15MPa, valley pressure 1.25MPa, pulse frequency 3Hz, and 11 cycles.

[0081] Experimental Example 5:

[0082] This experimental example is basically the same as Experiment 1, except that the peak pulse pressure is taken as the maximum value of the interval. Specifically, S2 is: peak pressure 30MPa, valley pressure 1.25MPa, pulse frequency 3Hz, and 11 cycles.

[0083] Experimental Example 6:

[0084] This experimental example is basically the same as Experiment 1, except that the frequency of the high-frequency alternating pulse is taken as the minimum value of the interval. Specifically, S4 has the following characteristics: frequency 1kHz, single pulse width 125μs, peak current 225A, interface temperature 425℃, and duration 0.75s.

[0085] Experiment Example 7:

[0086] This experimental example is basically the same as Experiment 1, except that the frequency of the high-frequency alternating pulse is taken as the maximum value of the interval. Specifically, S4 is: frequency 10kHz, single pulse width 125μs, peak current 225A, interface temperature 425℃, duration 0.75s.

[0087] Experimental Example 8:

[0088] This experimental example is basically the same as Experiment 1, except that the pulse pressure and pulse frequency are taken as the minimum value of the interval. Specifically, S2 is: peak pressure 22.5MPa, valley pressure 1.25MPa, pulse frequency 1Hz, and 11 cycles.

[0089] Experiment Example 9:

[0090] This experimental example is basically the same as Experiment 1, except that the pulse pressure and pulse frequency are taken as the maximum value of the interval. Specifically, S2 is: peak pressure 22.5MPa, valley pressure 1.25MPa, pulse frequency 5Hz, and 11 cycles.

[0091] Experimental Example 10:

[0092] This experimental example is basically the same as Experiment 1, except that: the peak current of the single-pulse pre-connection is taken as the minimum value of the interval, and S3 is: a single DC pulse current is applied, with a peak current of 200A and a pulse width of 1.0ms.

[0093] Experimental Example 11:

[0094] This experimental example is basically the same as Experiment 1, except that: the peak current of the single-pulse pre-connection is taken as the maximum value of the interval, and S3 is: a single DC pulse current is applied, with a peak current of 400A and a pulse width of 1.0ms.

[0095] Comparative Example 1:

[0096] This comparative example is basically the same as Experimental Example 1, except that it uses a traditional solid-state diffusion bonding process, excluding thermal shock, pulsed pressure film rolling, single-pulse pre-bonding, high-frequency alternating pulses, and controlled cooling. The specific steps are as follows:

[0097] S1. Align the aluminum wire and copper terminal at the welding position, and apply a 2N pre-pressure to the welding head to ensure contact conductivity. Under a nitrogen protective atmosphere, heat the interface to be welded to 405℃ at a heating rate of 10℃ / s and hold at that temperature to prevent thermal shock from cracking the aluminum oxide film.

[0098] S2. Maintain the interface temperature at 405℃, keep the welding head pressure at a constant value of 22.5MPa, and continue to work for 11 cycles without pulsed alternating stress. Use constant pressure to roll the alumina film.

[0099] S3. Maintain the welding pressure at 22.5MPa and output a constant DC current of 225A for 0.75s to keep the interface temperature at 405℃ and achieve the connection by relying on simple thermal diffusion.

[0100] S4. After stopping heating, continue to maintain the welding pressure at 22.5MPa and allow it to cool naturally at a rate of 10℃ / s until the joint temperature drops below 120℃. Then release the pressure and remove the workpiece.

[0101] Comparative Example 2:

[0102] This comparative example is basically the same as Experimental Example 1, except that thermal shock is omitted and replaced with slow heating. Specifically, S1 is: the interface to be soldered is slowly heated to 405℃ at a heating rate of 10℃ / s; subsequent S2 to S5 are the same as Experimental Example 1.

[0103] Comparative Example 3:

[0104] This comparative example is basically the same as Experimental Example 1, except that the pulse pressure is omitted and replaced with constant pressure. Specifically, S2 is: maintain the interface temperature at 405℃, keep the welding head pressure at a constant value of 22.5MPa, and do not perform pulse cycling; the rest of the steps are the same as Experimental Example 1.

[0105] Comparative Example 4:

[0106] This comparative example is basically the same as Experimental Example 1, except that: the single pulse pre-connection is omitted, and no single DC pulse is applied in S3, directly entering S4; S4 is the same as S4 in Experimental Example 1; the remaining steps are the same as in Experimental Example 1.

[0107] Comparative Example 5:

[0108] This comparative example is basically the same as Experimental Example 1, except that the high-frequency alternating pulse is replaced with a constant DC pulse. Specifically, S4 is: keep the welding pressure at 22.5MPa constant, output a constant DC current of 225A for 0.75s, and control the interface temperature at 425℃ and keep it constant; the rest of the steps are the same as Experimental Example 1.

[0109] Comparative Example 6:

[0110] This comparative example is basically the same as Experimental Example 1, except that the temperature oscillation is omitted and replaced with constant temperature heating. Specifically, S4 is: keep the welding pressure of 22.5MPa constant, output low-frequency smooth DC, and use closed-loop control to accurately maintain the interface temperature at 425℃ for 0.75s; the rest of the steps are the same as Experimental Example 1.

[0111] Comparative Example 7:

[0112] This comparative example is basically the same as Experimental Example 1, except that the heating rate is lower than the minimum value in the range. Specifically, S1 is to rapidly heat the interface to be welded to 405℃ at a heating rate of 150℃ / s; the rest of the steps are the same as Experimental Example 1.

[0113] Comparative Example 8:

[0114] This comparative example is basically the same as Experimental Example 1, except that the heating rate is higher than the maximum value in the range. Specifically, S1 is to rapidly heat the interface to be welded to 405℃ at a heating rate of 400℃ / s; the remaining steps are the same as in Experimental Example 1.

[0115] Comparative Example 9:

[0116] This comparative example is basically the same as Experimental Example 1, except that the peak pulse pressure is lower than the minimum value of the interval. Specifically, S2 is: peak pressure 10MPa, valley pressure 1.25MPa, pulse frequency 3Hz, and 11 cycles; the rest of the steps are the same as Experimental Example 1.

[0117] Comparative Example 10:

[0118] This comparative example is basically the same as Experimental Example 1, except that the peak pulse pressure is higher than the maximum value in the range. Specifically, S2 is: peak pressure 35MPa, valley pressure 1.25MPa, pulse frequency 3Hz, and 11 cycles; the remaining steps are the same as Experimental Example 1.

[0119] Comparative Example 11:

[0120] This comparative example is basically the same as Experimental Example 1, except that the frequency of the high-frequency alternating pulse is lower than the minimum value of the interval. Specifically, S4 is: frequency 0.5kHz, single pulse width 125μs, peak current 225A, interface temperature 425℃, duration 0.75s; the rest of the steps are the same as Experimental Example 1.

[0121] Comparative Example 12:

[0122] This comparative example is basically the same as Experimental Example 1, except that the frequency of the high-frequency alternating pulse is higher than the maximum value in the range. Specifically, S4 is: frequency 12kHz, single pulse width 125μs, peak current 225A, interface temperature 425℃, duration 0.75s; the rest of the steps are the same as Experimental Example 1.

[0123] Comparative Example 13:

[0124] This comparative example is basically the same as Experimental Example 1, except that the pulse pressure and pulse frequency are lower than the minimum value of the interval. Specifically, S2 is: peak pressure 22.5MPa, valley pressure 1.25MPa, pulse frequency 0.5Hz, and 11 cycles; the rest of the steps are the same as Experimental Example 1.

[0125] Comparative Example 14:

[0126] This comparative example is basically the same as Experimental Example 1, except that the pulse pressure and pulse frequency are higher than the maximum value in the range. Specifically, S2 is: peak pressure 22.5MPa, valley pressure 1.25MPa, pulse frequency 6Hz, and 11 cycles; the remaining steps are the same as Experimental Example 1.

[0127] Comparative Example 15:

[0128] This comparative example is basically the same as Experimental Example 1, except that the peak current of the single-pulse pre-connection is lower than the minimum value of the interval, and S3 is specifically: apply a single DC pulse current with a peak current of 150A and a pulse width of 1.0ms; the rest of the steps are the same as Experimental Example 1.

[0129] Comparative Example 16:

[0130] This comparative example is basically the same as Experimental Example 1, except that the peak current of the single-pulse pre-connection is higher than the maximum value in the interval. Specifically, S3 is to apply a single DC pulse current with a peak current of 450A and a pulse width of 1.0ms; the rest of the steps are the same as Experimental Example 1.

[0131] Performance testing: The heating wires of the protectors obtained in Experimental Examples 1-11 and Comparative Examples 1-16 were subjected to performance tests in sequence, including alumina film breakage rate, initial junction coverage rate, interface bonding rate, intermetallic compound parameters, and joint electrical performance. The results are shown in Table 1.

[0132] Alumina film removal rate: The welded joint was cut axially, and cross-sectional transmission electron microscopy (TEM) samples were prepared using focused ion beam (FIB) with a sample thickness controlled below 100 nm. The aluminum-side surface region at the interface between the aluminum-based heating wire and the copper-based terminal was observed under a TEM at 20,000x magnification. Ten fields of view were randomly selected, each with an area of ​​not less than 2 μm × 2 μm. The oxygen element distribution on the aluminum-side surface was scanned using energy dispersive spectroscopy (EDS), and the proportion of the area of ​​the residual alumina film to the total observed area of ​​the aluminum-side surface was recorded as _____. Meanwhile, a control sample that did not undergo steps S1 and S2 but had the same temperature history was used as a benchmark, and its alumina film area ratio was recorded as follows: Alumina film breakage rate Calculate using the following formula:

[0133] ;

[0134] The unit is a percentage. The higher the value, the more significant the effect of thermal shock and cyclic alternating pressure on the breakage and dispersion of the alumina film.

[0135] Initial bonding coverage: After applying the DC pulse current in step S3, but before entering the high-frequency alternating pulse stage in step S4, the joint to be welded is immediately removed from the welding device and rapidly quenched to preserve the interface microstructure. Metallographic sample preparation is used, cutting along the direction perpendicular to the welding interface. After grinding and polishing, it is etched with a 5 vol% oxalic acid solution for 10 seconds. The interface region is observed under a scanning electron microscope at 5000x magnification, with 20 randomly selected fields of view, each with an area of ​​20 μm × 20 μm. The proportion of the metal contact micro-region showing obvious atomic diffusion within the field of view is statistically analyzed. This micro-region is defined as the area between aluminum and copper without an aluminum oxide film barrier and with a continuous lattice transition. This proportion is denoted as [missing information]. Initial junction coverage Calculate using the following formula:

[0136] ;

[0137] The unit is a percentage. This value reflects the density of discrete junctions formed by the DC pulse current on the interface after the membrane is broken. The higher the value, the richer the starting nuclei for subsequent diffusion connections.

[0138] Interface bonding rate: Metallographic specimens were prepared from the welded joint (completed in step S5) along a direction perpendicular to the weld interface. A complete backscattered electron image of the interface was captured under a scanning electron microscope at 1000x magnification, with the image length covering the entire width of the weld interface. Image analysis software was used to segment the interface. Regions where complete atomic diffusion occurred between aluminum and copper without continuous pores were marked as bonding regions, while regions with residual alumina film, undiffused contact, or micropores were marked as unbonded regions. The length of the bonding regions was statistically analyzed. Total length of the interface Interface integration rate Calculate using the following formula:

[0139] ;

[0140] The unit is a percentage. This value comprehensively represents the effect of the high-frequency alternating pulse current in step S4 on promoting the expansion and connection of discrete joints. The higher the value, the greater the proportion of continuous metallurgical bonding formed in the joint.

[0141] Intermetallic compound parameters: Regions with good interfacial bonding were selected from the metallographic samples. At least 10 high-resolution backscattered electron images were acquired using a scanning electron microscope at 5000x magnification, with each image covering an interface length of approximately 30 μm. The thickness of the intermetallic compound layer at the aluminum-copper interface in each image was measured using image analysis software. Twenty measurement points were taken at equal intervals on each image, and the thickness values ​​at each point were recorded. Calculate the arithmetic mean of all measurement points as the average thickness of the intermetallic compound layer. The unit is μm; at the same time, the number of measuring points with a thickness exceeding 1.5 times the average thickness is counted. Calculate the continuity factor using the following formula. ,in Total number of measurement points; intermetallic compound parameters Calculate using the following formula:

[0142] ;

[0143] The unit is μm. The smaller the parameter and the closer the continuity factor is to 0, the more ideal the effect of high-frequency alternating pulse current in suppressing the continuous layering of intermetallic compounds, and the more dispersed the brittle phase distribution at the interface.

[0144] Electrical and mechanical properties of the joints: Five welded joint samples were randomly selected from the same welding batch. Tensile tests were performed on the joints using a universal testing machine. A tensile force of 2 mm / min was applied along the normal direction of the weld interface, and the maximum tensile force at which the joint fractured was recorded. The unit is N. Calculate the average value of 5 samples. Five additional samples were taken and their contact resistance was tested using a micro-ohmmeter. The voltage drop at a distance of 5 mm from each side of the weld interface was measured using the four-terminal method. A constant DC test current of 1 A was applied, and the contact resistance values ​​were recorded. Calculate the average value of 5 samples, in mΩ units. Simultaneously, the welded joint was placed in a high and low temperature cycling test chamber, heated from -40℃ to 125℃ and held for 30 minutes, then cooled to -40℃ and held for 30 minutes, with a heating and cooling rate of 10℃ / min. After 300 cycles, the tensile strength and contact resistance were tested again, and recorded as follows: and The tensile strength retention rate is calculated using the following formula.

[0145] ;

[0146] The rate of change of contact resistance is:

[0147] ;

[0148] The units are percentages. The above indicators directly reflect the mechanical strength, electrical reliability, and stability of the welded joint under thermal cycling conditions. The higher the value or the smaller the change, the better the low-temperature diffusion bonding and brittle phase suppression effect of the present invention.

[0149] Table 1: Performance test results of the protector heating wire in Experimental Examples 1-11 and Comparative Examples 1-16

[0150] Group Alumina film removal rate (%) Initial junction coverage (%) Interface integration rate (%) Average thickness (μm) of intermetallic compound layer Tensile strength retention rate (%) Contact resistance change rate (%) Experimental Example 1 96.8 72.4 95.6 0.62 94.6 3.2 Experiment Example 2 92.6 66.1 90.8 0.58 91.5 5.1 Experimental Example 3 95.1 69.5 93.2 0.79 90.8 5.8 Experiment Example 4 90.9 63.8 88.6 0.61 88.9 7.4 Experimental Example 5 97.2 70.6 94.1 0.91 89.7 6.6 Experimental Example 6 93.8 68.4 91.7 0.86 88.1 8.3 Experimental Example 7 95.9 71.2 94.5 0.74 92.4 4.7 Experimental Example 8 91.7 65.3 89.4 0.65 89.2 7.0 Experimental Example 9 95.4 70.1 93.8 0.73 91.6 5.2 Experimental Example 10 94.2 58.7 88.9 0.57 87.6 8.8 Experimental Example 11 96.1 76.5 94.8 1.06 88.4 7.5 Comparative Example 1 48.5 24.8 52.6 4.85 61.2 38.5 Comparative Example 2 56.7 31.2 60.4 0.74 70.5 24.6 Comparative Example 3 62.4 38.6 65.1 0.81 73.6 21.8 Comparative Example 4 91.5 18.9 67.8 0.69 76.4 18.2 Comparative Example 5 93.6 61.5 82.3 3.24 72.8 22.4 Comparative Example 6 94.1 63.2 84.6 2.86 75.1 19.7 Comparative Example 7 78.4 49.7 75.8 0.68 81.3 14.6 Comparative Example 8 97.9 71.8 90.5 1.38 82.5 13.2 Comparative Example 9 70.2 43.1 71.4 0.64 78.4 17.5 Comparative Example 10 98.4 72.6 91.2 1.52 80.1 15.8 Comparative Example 11 92.1 64.4 86.5 1.95 78.2 17.9 Comparative Example 12 96.5 70.8 90.9 1.64 81.7 14.1 Comparative Example 13 76.8 52.6 78.3 0.66 80.8 15.3 Comparative Example 14 88.9 59.4 83.7 0.88 79.6 16.4 Comparative Example 15 93.8 34.6 74.2 0.59 77.3 18.6 Comparative Example 16 95.7 79.8 89.1 1.72 78.9 16.9

[0151] A comparison between Experimental Example 1 and Comparative Example 1 reveals that: Comparative Example 1 employs a traditional solid-state diffusion bonding process, without using the combined process of rapid thermal cracking of the alumina film, periodic alternating pressure film breaking, DC pulse pre-connection, and high-frequency alternating pulse low-temperature diffusion. This results in lower alumina film breakage rate, initial bonding point coverage, and interface bonding rate compared to Experimental Example 1. The alumina film on the surface of the aluminum-based heating wire is composed of stable aluminum-oxygen bonds, making it difficult to form sufficient cracks under slow heating and constant pressure conditions. The alumina film still acts as a continuous film layer, preventing direct contact between aluminum and copper atoms. Simultaneously, traditional solid-state diffusion bonding relies on continuous thermal action to promote atomic migration, leading to continuous reactions between aluminum and copper atoms at the interface, which easily forms a thicker intermetallic compound layer. Consequently, the average thickness of the intermetallic compound layer in Comparative Example 1 increases, the tensile strength retention rate decreases, and the contact resistance change rate increases.

[0152] A comparison between Experimental Example 1 and Comparative Example 2 reveals that: Experimental Example 1, through appropriate rapid heating, establishes a thermal deformation difference between the surface of the aluminum-based heating wire and the alumina film, causing the alumina film to form a cracked structure, which is beneficial for subsequent periodic alternating pressure to break and disperse the alumina film; Comparative Example 2, using slow heating, results in insufficient instantaneous thermal stress between the aluminum substrate and the alumina film, reducing the number of internal cracks in the alumina film, and preserving a large area of ​​the continuous film layer composed of aluminum-oxygen bonds; because the alumina film is not fully cracked, subsequent pressure is insufficient to cause large-area breakage of the alumina film, reducing the contact channels between aluminum and copper atoms, decreasing the initial bonding point coverage and interfacial bonding rate, and making the joint more prone to increased contact resistance after thermal cycling.

[0153] A comparison between Experimental Example 1 and Comparative Example 3 reveals that in Experimental Example 1, after thermal cracks formed in the alumina film, periodic alternating pressure was applied. During repeated loading and unloading, the surface of the aluminum-based heating wire underwent microplastic flow, and the cracked alumina film was sheared into fragments and pressed into the aluminum matrix, resulting in numerous direct aluminum-copper contact micro-regions at the interface. In Comparative Example 3, constant pressure was used. Although constant pressure could maintain the adhesion of the overlapping area, it lacked the shearing and redistribution effects brought about by alternating loads. The cracked alumina film was still prone to remain at the interface in sheet form. The residual alumina film blocked the diffusion paths of aluminum and copper atoms, reducing the interfacial bonding rate. During thermal cycling, the unbonded areas were prone to micro-gaps and stress concentration, leading to a decrease in tensile strength retention and an increase in the contact resistance change rate.

[0154] A comparison of Experimental Example 1 and Comparative Example 4 reveals that in Experimental Example 1, applying a DC pulse current after film rupture preferentially generates energy input in the micro-regions where metal contacts have already formed. Aluminum and copper atoms undergo short-range migration in local areas, forming discrete initial metallurgical bonding points. In Comparative Example 4, the DC pulse pre-connection process is omitted. Although the alumina film rupture rate is close to that of Experimental Example 1, the interface lacks stable initial bonding nuclei. If the exposed aluminum and copper atoms after film rupture do not receive instantaneous electrothermal activation, local atomic migration is insufficient. The subsequent high-frequency alternating pulse current lacks a uniform conductivity and heat transfer starting point, resulting in discontinuous interface diffusion connections. Consequently, the initial bonding point coverage rate of Comparative Example 4 is significantly reduced, and the interface bonding rate and thermal cycling stability are lower than those of Experimental Example 1.

[0155] A comparison between Experimental Example 1 and Comparative Example 5 reveals that: Experimental Example 1 uses high-frequency alternating pulsed current to promote low-temperature diffusion connections between discrete initial metallurgical bonding points. The electromigration effect caused by the alternating current can compensate for the insufficient thermal diffusion of aluminum and copper atoms under low-temperature conditions, and the interface temperature fluctuation can limit the continuous growth of intermetallic compounds. In Comparative Example 5, the high-frequency alternating pulse is replaced with constant DC, and there is a lack of periodic current direction changes and temperature fluctuations at the interface. Under continuous heating, aluminum and copper atoms react continuously along the interface, and the already formed intermetallic compound nuclei continuously absorb surrounding atoms and connect to form layers. As a result, the average thickness of the intermetallic compound layer in Comparative Example 5 increases, the tensile strength retention rate decreases, and the contact resistance change rate increases.

[0156] A comparison between Experimental Example 1 and Comparative Example 6 reveals that: In Experimental Example 1, the high-frequency alternating pulsed current causes the temperature of the interface to be welded to fluctuate within the target range. This temperature fluctuation restricts the nucleation, growth, and bonding processes of intermetallic compounds at the interface, which is beneficial for obtaining a dispersed reaction phase distribution. In Comparative Example 6, constant-temperature heating is used, keeping the interface temperature stable. Aluminum and copper atoms continuously migrate towards the reaction layer, and the intermetallic compound grains easily connect and thicken along the interface. Under constant-temperature conditions, the concentration gradient on both sides of the reaction layer persists, and aluminum and copper atoms continuously replenish the growth front of the intermetallic compounds, increasing the brittle phase layer at the interface. As a result, although Comparative Example 6 has a certain interface bonding rate, the average thickness of the intermetallic compound layer is higher than that of Experimental Example 1, and the electrical and mechanical retention properties decrease after thermal cycling.

[0157] A comparison of Experiments 1 / 2-3 with Comparative Examples 7-8 reveals that: the heating rates in Experiments 1, 2, and 3 are within a suitable range, enabling the formation of a thermal deformation difference between the aluminum-based heating wire surface and the alumina film, causing cracks in the alumina film, while avoiding excessive local heat input concentration at the interface; the heating rate in Comparative Example 7 is below the suitable range, resulting in insufficient thermal stress accumulation, inadequate crack formation in the alumina film, and difficulty in obtaining sufficient basis for subsequent periodic alternating pressure to break the film, leading to a decrease in the alumina film breakage rate, initial bonding point coverage, and interfacial bonding rate; the heating rate in Comparative Example 8 is above the suitable range, although the alumina film breakage rate is improved, the local temperature rise at the interface is uneven, the reactivity of aluminum and copper atoms is too strong, and the average thickness of the intermetallic compound layer increases. Therefore, a heating rate that is too low will retain the alumina film barrier, while a heating rate that is too high will accelerate the growth of the aluminum-copper reaction layer, both of which will reduce the overall stability after thermal cycling.

[0158] A comparison of Experiments 1 / 4-5 with Comparative Examples 9-10 reveals that: the peak values ​​of the periodic alternating pressure in Experiments 1, 4, and 5 are within a suitable range, enabling moderate micro-plastic deformation of the surface layer of the aluminum-based heating wire. The cracked alumina film is crushed and dispersed into the aluminum matrix, increasing the direct contact area between aluminum and copper atoms. In Comparative Example 9, the peak pressure is below the suitable range, and the pressure is insufficient to fully shear and break the alumina film. The remaining alumina film still isolates the diffusion of aluminum and copper atoms, leading to a decrease in the alumina film breakage rate and interfacial bonding rate. In Comparative Example 10, the peak pressure is above the suitable range. Although the alumina film can be fully broken, the surface layer of the aluminum-based heating wire undergoes excessive plastic deformation, resulting in enhanced reaction in local contact areas and an increase in the average thickness of the intermetallic compound layer. Therefore, excessively low peak pressure will cause insufficient film breakage, while excessively high peak pressure will cause interfacial deformation and uneven reaction, both of which are detrimental to the performance maintenance of the joint after thermal cycling.

[0159] A comparison of Experimental Examples 1 / 6-7 with Comparative Examples 11-12 reveals that: the high-frequency alternating pulse frequencies in Experimental Examples 1, 6, and 7 achieve a balance between atomic migration and heat input control, allowing the discrete initial metallurgical bonding points to gradually expand and connect, while simultaneously limiting the formation of a continuous brittle intermetallic compound layer; the high-frequency alternating pulse frequency in Comparative Example 11 is below the suitable range, resulting in fewer pulses per unit time, weakening the promoting effect of electromigration on aluminum and copper atoms, insufficient diffusion connectivity between discrete bonding points, and a decrease in interfacial bonding rate; the high-frequency alternating pulse frequency in Comparative Example 12 is above the suitable range, resulting in shorter pulse intervals, insufficient interfacial heat release, and local heat accumulation that promotes the thickening of the aluminum-copper reaction layer; thus, excessively low frequencies lead to insufficient low-temperature diffusion driving force, while excessively high frequencies weaken the brittle phase suppression effect, both of which reduce the thermal cycling stability of the joint.

[0160] A comparison of Experimental Examples 1 / 8-9 with Comparative Examples 13-14 reveals that: the periodic alternating pressure frequency in Experimental Examples 1, 8, and 9 allows the alumina film to be continuously subjected to shearing during loading and unloading, while maintaining a stable contact state at the interface to be welded; the pressure frequency in Comparative Example 13 is below the appropriate range, resulting in insufficient dynamic shearing cycles, preventing the cracked alumina film from fully dispersing into the aluminum matrix, and reducing the diffusion channels for aluminum and copper atoms due to alumina film residue; the pressure frequency in Comparative Example 14 is above the appropriate range, and the surface of the aluminum-based heating wire does not undergo sufficient plastic flow and stress release after a single loading before entering the next loading cycle, making it easy for alumina film fragments to accumulate at local interfaces, thus reducing the surface renewal effect; consequently, the interface bonding rate in Comparative Examples 13 and 14 is lower than that in Experimental Example 1, while the contact resistance change rate is higher than that in Experimental Example 1.

[0161] A comparison of Experimental Examples 1 / 10-11 with Comparative Examples 15-16 reveals that: the DC pulse peak current in Experimental Examples 1, 10, and 11 can form discrete initial metallurgical bonding points in the metal contact micro-regions after the film is broken, providing a basis for electrical conductivity and heat transfer for high-frequency alternating pulse diffusion connection; the DC pulse peak current in Comparative Example 15 is below the appropriate range, resulting in insufficient instantaneous energy obtained by the local metal contact micro-regions, low migration activity of aluminum and copper atoms, reduced coverage of initial bonding points, and difficulty in achieving sufficient subsequent diffusion connection; the DC pulse peak current in Comparative Example 16 is above the appropriate range, resulting in higher coverage of initial bonding points, but excessive local instantaneous heat input, rapid aluminum-copper reaction, and increased average thickness of the intermetallic compound layer; thus, a DC pulse peak current that is too low will cause insufficient pre-connection, while a DC pulse peak current that is too high will induce local over-reaction, both of which will reduce the mechanical retention performance and resistance stability of the welded joint after thermal cycling.

[0162] Example 2:

[0163] like Figure 1 and Figure 2 As shown, an automated welding device for a protector heating wire includes: a frame 1, a welding platform 2, a pressure actuation component, and a welding head assembly.

[0164] It is understood that the welding platform 2 is set in the working area of ​​the frame 1, the pressure actuation component is set on the frame 1 and located above the welding platform 2, and the welding head component is set at the lower end of the pressure actuation component and is vertically opposite to the welding platform 2.

[0165] Specifically, the frame 1 serves as the mounting base for the welding platform 2, the pressure actuation component, and the welding head component. The welding platform 2 is fixed on the worktable of the frame 1, and the upper surface of the welding platform 2 forms the workpiece bearing surface, which bears the overlapping area of ​​the aluminum-based heating wire and the copper-based terminal.

[0166] Furthermore, the welding platform 2 is electrically connected to the lower output terminal of the welding power source, so that the welding platform 2 forms the lower electrode; an insulating connection is provided between the welding platform 2 and the frame 1 to reduce the conduction of welding current to the frame 1.

[0167] Specifically, a cooling channel is provided inside the welding platform 2, which extends along the length or width of the welding platform 2 and is connected to an external cooling medium pipeline. During the welding process, the welding platform 2 supports the aluminum-based heating wire and the copper-based terminal on the one hand, and participates in the welding current circuit through the lower electrode on the other hand. After the welding is completed, the cooling medium flows in the cooling channel, which allows the welding platform 2 to carry away heat from the lower side of the weld joint, and cooperates with the welding head assembly to maintain pressure and cool the weld joint.

[0168] Specifically, the pressure actuation assembly includes an actuation component 3, a pressure control sensor 4, and a pressure holding module 5; wherein the actuation component 3 is a servo electric cylinder, the actuation component 3 is mounted on the frame 1, the output end of the actuation component 3 is positioned facing the welding platform 2, and the output end of the actuation component 3 can move in a direction close to or away from the welding platform 2.

[0169] Furthermore, the pressure control sensor 4 is connected between the output end of the actuator 3 and the pressure holding module 5. The force direction of the pressure control sensor 4 is consistent with the output direction of the actuator 3. The pressure holding module 5 is located below the pressure control sensor 4, and the lower end of the pressure holding module 5 is connected to the welding head assembly.

[0170] Understandably, when the actuator 3 outputs linear displacement, the pressure control sensor 4, the pressure holding module 5, and the welding head assembly move synchronously toward the welding platform 2 along with the actuator 3. After the welding head assembly contacts the overlapping area of ​​the aluminum-based heating wire and the copper-based terminal, the continued output displacement of the actuator 3 is converted into the pressing pressure of the interface to be welded. The pressure control sensor 4 detects this pressing pressure and feeds back the pressure signal to the pressure control system, so that the output displacement or output force of the actuator 3 is adjusted according to the set pressure.

[0171] Specifically, the pressure holding module 5 is used to maintain continuous contact between the welding head assembly and the interface to be welded when the actuator 3 switches pressures; when the actuator 3 outputs periodic displacement or periodic pressure, the pressure holding module 5 undergoes slight compression and rebound as the output of the actuator 3 changes, and the welding head assembly forms a peak compression stage and an unloading and rebound stage at the interface to be welded; during the unloading and rebound stage, the pressure holding module 5 releases the stored compression, so that the welding head assembly still maintains the contact pressure at the interface to be welded, and avoids the aluminum-based heating wire and the copper-based terminal from losing contact during the alternating pressure process.

[0172] Furthermore, the welding head assembly includes a welding head 6 and an atmosphere nozzle 7; the welding head 6 is connected to the lower end of the pressure holding module 5, and the welding head 6 is vertically opposite to the welding platform 2. The lower end of the welding head 6 forms a pressing end that contacts the aluminum-based heating wire or the copper-based terminal; the welding head 6 is electrically connected to the upper output end of the welding power supply, and the welding head 6, the interface to be welded between the aluminum-based heating wire and the copper-based terminal, and the welding platform 2 together form a welding current loop.

[0173] Specifically, the atmosphere nozzle 7 is positioned circumferentially on the welding head 6, with the outlet of the atmosphere nozzle 7 facing the welding area between the welding head 6 and the welding platform 2. The atmosphere nozzle 7 is connected to the protective atmosphere supply pipeline, and the protective atmosphere flows through the atmosphere nozzle 7 to the overlapping area of ​​the aluminum-based heating wire and the copper-based terminal, thereby creating a local protective atmosphere environment in the welding area and reducing the continued oxidation of the aluminum-based heating wire during rapid heating and pulse welding.

[0174] When this invention is used, the welding platform 2 carries the copper-based terminal, the welding head 6 presses the aluminum-based heating wire onto the copper-based terminal under the drive of the execution component 3, and the atmosphere nozzle 7 introduces a protective atmosphere into the welding area.

[0175] Subsequently, the welding head 6 and the welding platform 2 cooperate to form a welding current loop. The execution component 3 outputs pre-pressure, periodic alternating pressure and holding pressure in sequence. The welding power supply outputs DC pulse current and high-frequency alternating pulse current in sequence, so that the interface to be welded completes the alumina film breakage, the initial metallurgical bonding point formation and low-temperature diffusion connection.

[0176] After the high-frequency alternating pulse current stops, the pressure holding module 5 maintains the pressure state of the welding head assembly, and the welding platform 2 removes the heat of the welding joint through the cooling channel, so that the diffusion connection interface cools and solidifies under pressure.

[0177] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. An automated welding method for a protector heating wire, characterized in that, Includes the following steps: S1. The aluminum-based heating wire is overlapped and pressed with the copper-based terminal, and the interface to be welded is rapidly heated under a protective atmosphere. The difference in thermal expansion coefficient between the surface of the aluminum-based heating wire and its oxide film is used to cause thermal cracks in the aluminum oxide film. The heating rate is 200-350℃ / s, and the final temperature is 380-430℃. S2. At the final temperature, apply periodic alternating pressure to the interface to be welded, so that the alumina film with hot cracks breaks and disperses with the plastic deformation of the surface layer of the aluminum-based heating wire, wherein the peak pressure is 15-30 MPa, the frequency is 1-5 Hz, and the number of cycles is 8-15. S3. Apply a DC pulse current to the interface to be welded in a pressed state to form discrete initial metallurgical bonding points in the local contact area between the aluminum-based heating wire and the copper-based terminal, wherein the peak current is 200-400A. S4. Continue to press the interface to be welded and apply a high-frequency alternating pulse current to make the discrete initial metallurgical joints undergo low-temperature diffusion connection, wherein the frequency is 1 to 10 kHz, the peak current is 150 to 300 A, and the interface temperature is 400 to 450 °C. S5. After stopping the application of high-frequency alternating pulse current, maintain the pressure state of the interface to be welded and cool it to solidify the diffusion connection interface and obtain the welded joint of the protector heating wire.

2. The automated welding method for a protector heating wire according to claim 1, characterized in that: In step S1, the pre-pressure when the aluminum-based heating wire and the copper-based terminal are overlapped and pressed together is 1 to 3 N; the protective atmosphere is nitrogen or argon, and the oxygen content is not higher than 1000 ppm.

3. The automated welding method for a protector heating wire according to claim 1, characterized in that: In step S1, before rapidly heating the interface to be soldered, a protective atmosphere is introduced for 1 to 5 seconds, and the protective atmosphere covers the overlapping area between the aluminum-based heating wire and the copper-based terminal.

4. An automated welding method for a protector heating wire according to claim 1, characterized in that: In step S2, the periodic alternating pressure includes a peak pressing stage and an unloading and springback stage, and the interface to be welded is kept in contact after each unloading and springback stage so that the broken alumina film fragments are pressed into the surface of the aluminum-based heating wire.

5. An automated welding method for a protector heating wire according to claim 1, characterized in that: In step S2, the valley pressure of the periodic alternating pressure is 0.5 to 2 MPa, and the holding time of a single peak pressure is 0.05 to 0.2 s.

6. An automated welding method for a protector heating wire according to claim 1, characterized in that: In step S3, the pulse width of the DC pulse current is 0.5 to 1.5 ms, and the DC pulse current is applied during the last peak pressing stage of the periodic alternating pressure.

7. An automated welding method for a protector heating wire according to claim 1, characterized in that: In step S4, the single pulse width of the high-frequency alternating pulse current is 50-200 μs, the duration is 0.5-1 s, and the high-frequency alternating pulse current causes the temperature of the interface to be welded to fluctuate periodically within the range of 400-450℃.

8. An automated welding method for a protector heating wire according to claim 1, characterized in that: In step S5, after stopping the application of the high-frequency alternating pulse current, the pressing pressure of the interface to be welded is maintained at 10-25 MPa, and the welded joint is cooled to below 120°C at a cooling rate of 50-80°C / s before the pressing state is released.

9. An automated welding device for a protector heating wire, characterized in that, include: Rack (1); Welding platform (2) is mounted on the frame (1); The pressure actuation assembly is mounted on the frame (1) and located above the welding platform (2); A welding head assembly is disposed at the lower end of the pressure actuation assembly; The welding platform (2) is used to carry the workpiece and provide the lower electrode and cooling. The pressure actuation component is used to provide pre-pressure, periodic alternating pressure, holding pressure and real-time pressure detection. The welding head component is used to clamp the workpiece, apply pulse current and provide a protective atmosphere to the welding area.

10. An automated welding device for a protector heating wire according to claim 9, characterized in that: The pressure actuation assembly includes an actuation component (3), a pressure holding module (5), and a pressure control sensor (4); the welding head assembly includes a welding head (6) and an atmosphere nozzle (7).

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