Single-head double-sided ultrasonic welding method, wire harness assembly, and ultrasonic welding system

Abstract

The present application belongs to the technical field of ultrasonic welding, and discloses a single-head double-sided ultrasonic welding method, a wire harness assembly and an ultrasonic welding system. The single-head double-sided ultrasonic welding method of the present application places the first workpiece at the energy attenuation end during the final welding in the pre-welding stage on the high-energy side close to the upper welding head for early welding, which is equivalent to reserving a welding basis in advance. After the positions of the first workpiece and the second workpiece are exchanged in the final welding stage, the first workpiece has a pre-welding state, and only a small amount of ultrasonic energy is needed to achieve complete welding with the second workpiece. Such a setting avoids the problem of over-welding of the upper layer in the traditional single-head welding caused by the increase of energy for the welding of the first workpiece, that is, the final welding only needs a small amount of energy, and the second workpiece will not be damaged due to excess energy. In addition, the defect of easy virtual welding of the first workpiece due to energy attenuation is also compensated, and finally the first workpiece and the third workpiece welded on the opposite sides of the second workpiece achieve the best welding effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultrasonic welding, in particular to a single-head double-sided ultrasonic welding method, a wire harness assembly and an ultrasonic welding system. BACKGROUND

[0002] Ultrasonic welding is a method of using high-frequency ultrasonic vibration energy to realize the solid-state connection of materials, and its core principle involves converting electrical energy into high-frequency mechanical vibration, generating heat energy through friction at the joint of the workpiece, and locally melting and pressing the material.

[0003] In the electronic, electrical and automotive industries, ultrasonic welding is often used for welding wire harness assemblies, which are made up of multiple layers (two or more) of stacked workpieces (wires or terminals). When the current ultrasonic welding system with a single welding head is used to weld the wire harness assembly on both sides, the ultrasonic energy decays from top to bottom, resulting in excessive energy at the top layer (easy to over-weld) and insufficient energy at the bottom layer (easy to under-weld), making it difficult to achieve ideal welding quality. With the popularity of high-power electronic devices in electric vehicles, higher requirements are placed on the welding quality of wire harnesses.

[0004] In order to ensure welding quality, the ultrasonic welding system with two welding heads must be used to weld the wire harness assembly on both sides, but both welding heads need to be equipped with acoustic components, resulting in increased procurement costs of the equipment and increased complexity of welding control. Therefore, the production cost of wire harness assemblies is high and needs to be improved. SUMMARY

[0005] The purpose of the present application is to provide a single-head double-sided ultrasonic welding method, a wire harness assembly and an ultrasonic welding system to improve the quality of double-sided welding of multiple layers of workpieces while controlling production costs.

[0006] To achieve this purpose, the present application adopts the following technical solutions:

[0007] The single-head double-sided ultrasonic welding method comprises the following steps:

[0008] Preparation: providing a first workpiece, a second workpiece, a third workpiece and an ultrasonic welding system, the first workpiece having a first welding section, the second workpiece having a first welding surface and a second welding surface, the third workpiece having a second welding section, the ultrasonic welding system including a bottom die and an upper welding head, the bottom die being provided with a plurality of limiting teeth on one side relative to the upper welding head, and the side surface of the upper welding head relative to the bottom die being a tooth-shaped surface;

[0009] The limiting teeth and the tooth-shaped surface have consistent tooth depth, tooth top width, tooth bottom width, tooth spacing, tooth shape angle and round corner transition area;

[0010] Pre-welding: the first workpiece and the second workpiece are stacked on the bottom die, and the second welding surface is in abutment with the bottom die, the first welding section is in abutment with the first welding surface, the ultrasonic welding system is started, the upper welding head welds the first welding section to the first welding surface, the tooth-shaped surface of the upper welding head acts on the first welding section, the first welding section is welded to the first welding surface, and the first welding section is formed with a plurality of positioning teeth adapted to the limiting teeth on the side away from the second workpiece;

[0011] Final welding: the stacking order of the first workpiece and the second workpiece is exchanged, the positioning teeth of the first workpiece are positioned in interlocking engagement with the limiting teeth of the bottom die, the second welding section of the third workpiece is placed on the second welding surface of the second workpiece, and the ultrasonic welding system is started.

[0012] Preferably, the first workpiece and the third workpiece are wire harnesses, and the second workpiece is a terminal.

[0013] Preferably, the limiting teeth are provided in the form of long strip-shaped arc teeth.

[0014] A wire harness assembly made by the single-head double-sided ultrasonic welding method described above.

[0015] An ultrasonic welding system comprising a single upper welding head, a bottom die, and a controller, for implementing the single-head double-sided ultrasonic welding method described above.

[0016] Preferably, the bottom die is provided with a plurality of limiting teeth on one side relative to the upper welding head.

[0017] Preferably, the upper welding head has a tooth-shaped surface on the side relative to the bottom die, so that a plurality of positioning teeth are formed on the side of the first welding section away from the second workpiece after the first workpiece and the second workpiece are pre-welded, and the positioning teeth can interlock with the limiting teeth.

[0018] Preferably, the bottom die is a resonant bottom die, which can be excited by the vibration of the upper welding head to generate a resonance in the opposite direction of the vibration of the upper welding head in the final welding step.

[0019] Advantages of the present application:

[0020] The single-head double-sided ultrasonic welding method of the application, in the pre-welding stage, the first workpiece (the lowermost layer of the final welding) at the energy attenuation end during the final welding is welded in advance near the high-energy side of the upper welding head, which is equivalent to reserving a welding foundation for it; after the positions of the first workpiece and the second workpiece are exchanged in the final welding stage, since the first workpiece has the pre-welding state, only a small amount of ultrasonic energy is needed to achieve the complete welding state with the second workpiece. In this way, the problem of "over-welding of the upper layer caused by the increase of energy for the welding of the first workpiece" in the traditional single-head welding is avoided, that is, only a small amount of energy is needed for the final welding, and the second workpiece will not be damaged due to excess energy, and the defect of the first workpiece being prone to virtual welding due to energy attenuation is also compensated, so that the first workpiece and the third workpiece welded on the opposite sides of the second workpiece achieve the best welding effect.

[0021] In addition, the bottom die of the application is provided with a plurality of limiting teeth on one side relative to the upper welding head, that is, the surface of the bottom die where the workpiece is placed is provided with a tooth surface, first, during the welding process, the tooth surface can increase the friction between the bottom die and the workpiece, avoiding the workpiece from slipping under high pressure or being displaced due to vibration, thereby improving the positioning effect; secondly, the protruding part of the tooth surface forms a local high-pressure area with the contact point of the workpiece, which promotes the more concentrated transmission of ultrasonic energy to the welding interface and reduces energy loss; in addition, the tooth groove structure can guide the flow direction of the molten metal, avoiding overflow or virtual welding.

[0022] The wire harness assembly of the application is made by using the single-head double-sided ultrasonic welding method of the application, which can improve the welding effect of the wire harness assembly and make the quality of the wire harness assembly stable and not prone to over-welding, virtual welding and other adverse phenomena.

[0023] The ultrasonic welding system of the application can realize double-sided welding of the wire harness assembly according to the single-head double-sided ultrasonic welding method, thereby ensuring the quality of double-sided welding while controlling the production cost. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a flowchart of the single-head double-sided ultrasonic welding method of the application;

[0025] Figure 2 is a structural schematic diagram of the ultrasonic welding system of the application;

[0026] Figure 3 is a structural schematic diagram of the wire harness assembly of the application;

[0027] Figure 4 is a state schematic diagram of the first workpiece, the second workpiece and the third workpiece before the final welding in the single-head double-sided ultrasonic welding method of the application.

[0028] In the drawings:

[0029] 1, first workpiece; 2, second workpiece; 21, first welding surface; 22, second welding surface; 3, third workpiece; 4, bottom die; 41, limiting tooth; 42, welding working surface; 5, upper welding head. DETAILED DESCRIPTION

[0030] The application will be further described below in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are intended to be merely exemplary of the application and that the application is not limited to such exemplary embodiments. It should also be noted that, for the purpose of clarity, not all of the structures related to the application are shown in the drawings.

[0031] In the description of the application, unless otherwise explicitly specified and limited, the terms "connected", "connected", "fixed" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0032] In the present application, unless otherwise explicitly specified and limited, the "upper" or "lower" of the first feature to the second feature can include the direct contact of the first and second features, or can include the contact of the first and second features through another feature between them. Moreover, the "upper", "upper" and "upper" of the first feature to the second feature includes the vertical direction of the first feature above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The "below", "below" and "below" of the first feature to the second feature includes the vertical direction of the first feature below and obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0033] In the description of the present embodiment, the terms "upper", "lower", "right", and other orientation or position relationships are based on the orientation or position relationship shown in the drawings, and are only for the convenience of description and simplification of operation, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application. In addition, the terms "first" and "second" are only used to distinguish in the description and have no special meaning.

[0034] The following will be described with reference to Figures 1 to 4 The single-head double-sided ultrasonic welding method and wire harness assembly provided by the present application are described.

[0035] In a first aspect, the present embodiment provides a single-head double-sided ultrasonic welding method, which is described with reference to Figures 1 to 4 The single-head double-sided ultrasonic welding method comprises the following steps:

[0036] S1, preparation: provide a first workpiece 1, a second workpiece 2, a third workpiece 3 and an ultrasonic welding system, the first workpiece 1 has a first welding section, the second workpiece 2 has a first welding surface 21 and a second welding surface 22, the third workpiece 3 has a second welding section, the ultrasonic welding system includes a bottom die 4 and an upper welding head 5, the bottom die 4 is provided with a plurality of limiting teeth 41 on one side relative to the upper welding head 5, and the side surface of the upper welding head 5 relative to the bottom die 4 is a tooth-shaped surface;

[0037] The tooth depth, tooth top width, tooth bottom width, tooth spacing, tooth shape angle and round corner transition area of the limiting teeth 41 and the tooth-shaped surface are consistent;

[0038] S2, pre-welding: stack the first workpiece 1 and the second workpiece 2 on the bottom die 4, and the second welding surface 22 of the second workpiece 2 abuts against the bottom die 4, the first welding section of the first workpiece 1 abuts against the first welding surface 21 of the second workpiece 2, start the ultrasonic welding system, the tooth-shaped surface of the upper welding head 5 acts on the first welding section, welds the first welding section to the first welding surface 21, and forms a plurality of positioning teeth on the side of the first welding section away from the second workpiece 2, which are adapted to the limiting teeth 41.

[0039] S3, final welding: exchange the stacking order of the first workpiece 1 and the second workpiece 2, so that the positioning teeth of the first workpiece 1 and the limiting teeth 41 of the bottom die 4 are mutually engaged and positioned, then place the second welding section of the third workpiece 3 on the second welding surface 22 of the second workpiece 2, start the ultrasonic welding system, and the upper welding head 5 welds the second welding section to the second welding surface 22.

[0040] In the pre-welding stage, the first workpiece 1 at the energy attenuation end in the final welding (the lowest layer in the final welding) is welded in advance near the high-energy side of the upper welding head 5, which is equivalent to reserving a welding foundation in advance; after the positions of the first workpiece 1 and the second workpiece 2 are exchanged in the final welding stage, since the first workpiece 1 already has a pre-welding state, only a small amount of ultrasonic energy is needed to achieve complete welding with the second workpiece 2. By such arrangement, the problem of "increasing energy to let the first workpiece 1 weld together, resulting in over-welding of the upper layer" in the traditional single-head welding is avoided, that is, only a small amount of energy is needed in the final welding in this embodiment, and the second workpiece 2 will not be damaged due to excess energy, and the defect that the first workpiece 1 is prone to virtual welding due to energy attenuation is also compensated, so that the first workpiece 1 and the third workpiece 3 welded on the opposite sides of the second workpiece 2 achieve the best welding effect.

[0041] It can be understood that the above welding scheme only uses a single upper welding head 5 to complete double-sided welding, which does not need to be equipped with two sets of acoustic components compared with the traditional double-head system, greatly reducing the equipment procurement cost. In addition, the control logic of the single welding head does not need to coordinate the synchronous vibration and energy distribution of the two welding heads, greatly simplifying the welding control complexity, so as to realize the control of the production cost while ensuring the welding quality.

[0042] It can also be understood that the bottom die 4 is provided with a plurality of limiting teeth 41 on one side relative to the upper welding head 5, that is, the surface of the bottom die 4 placing the workpiece is provided with a tooth surface. First, during the welding process, the tooth surface can increase the friction between the bottom die 4 and the workpiece, avoid the workpiece from slipping under high pressure or displacement due to vibration, and thus improve the positioning effect. Second, the tooth surface protruding part forms a local high pressure area with the contact point of the workpiece, which promotes the more concentrated transmission of ultrasonic energy to the welding interface and reduces energy loss. In addition, the tooth groove structure can guide the flow direction of the molten metal to avoid overflow or false welding.

[0043] More importantly, by setting the side surface of the upper welding head 5 relative to the bottom die 4 to be a tooth surface consistent with the structure of the limiting teeth 41, a positioning tooth that precisely engages with the limiting teeth 41 is formed on the first welding section during the pre-welding stage. This structural consistency ensures that the tooth shape parameters (including tooth depth and tooth top width) of the positioning tooth are completely matched with the limiting teeth 41, and thus the first workpiece 1 is stably positioned through the mutual engagement of the limiting teeth 41 and the positioning tooth during the final welding, preventing the first workpiece 1 and the second workpiece 2 from displacing due to vibration during the final welding, to further improve the quality of the final welding.

[0044] In order to make the above-mentioned single-head ultrasonic welding method more accurately adapt to the actual welding scene of wire harness assemblies in the electronic, electrical and electric vehicle industry, and clearly reflect the specific types and functional positioning of each workpiece in the three-layer stacked welding structure, in this embodiment, the first workpiece 1 and the third workpiece 3 are wire harnesses, and the second workpiece 2 is a terminal. In actual welding, the wire harness is composed of multiple thin wires, which is easy to cause stacking deviation due to looseness, while the terminal is a regular metal structure with stable shape reference. By setting the terminal as the second workpiece 2 in the middle layer, it can directly provide rigid positioning support for the wire harnesses on both sides. On the one hand, it can constrain the stacking range of the wire harnesses, ensuring that the two wire harnesses are accurately aligned with the conductive contact area of the terminal; on the other hand, it can avoid deformation and misplacement of the wire harnesses under welding pressure, thereby avoiding the problem of defective rate caused by positioning deviation in actual production from the structural level.

[0045] From the actual production needs of the industry, high-power equipment requires wire harnesses to have high current-carrying capacity, so large-diameter wire harnesses are often used. However, if large-diameter wire harnesses are directly welded with terminals, on the one hand, in order to ensure the continuity of current-carrying, the terminal needs to reserve a super-large welding area matching the large-diameter wire harness, which increases the cost of terminal material and expands the installation space, which is contrary to the design trend of lightweight and miniaturization of electric vehicles. On the other hand, the total amount of metal conductors of large-diameter wire harnesses is large, which requires high-power ultrasonic energy to achieve full fusion with the terminal. However, the current high-power ultrasonic welding technology is not mature, that is, too high energy can easily cause local overheating and melting of the wire harness (overwelding), or cause false welding due to uneven energy distribution, which seriously affects the reliability of the wire harness assembly.

[0046] Therefore, in the embodiment, the first workpiece 1 and the third workpiece 3 are two small wire diameter wire harnesses formed by splitting a same large wire diameter wire harness, and the terminal (the second workpiece 2) is an intermediate connection carrier. On the one hand, the welding area of the single small wire diameter wire harness and the terminal is extremely small, the conductive contact area size of the terminal can be greatly reduced, the amount of terminal material can be saved, and the installation space requirement of the compact equipment can be met; on the other hand, the ultrasonic welding power required by the small wire diameter wire harness is low, and the small power ultrasonic welding technology is highly mature, has high energy control accuracy, and can accurately avoid overwelding and virtual welding problems.

[0047] Meanwhile, the terminal (the second workpiece 2) is a metal regular structure, has a stable shape reference, and can directly provide rigid positioning support for the small wire diameter wire harnesses on both sides as an intermediate layer. The terminal can constrain the stacking range of the two small wire diameter wire harnesses, ensure the precise alignment of the welding points of the two small wire diameter wire harnesses on the terminal, and ensure the smoothness of the overall current-carrying path; and can avoid the loosening deformation or misplacement of the small wire diameter wire harnesses under the welding pressure, and further avoid the welding failure problem caused by positioning deviation from the structural level.

[0048] Referring to Figure 2 The limiting teeth 41 are arranged in a long strip-shaped arc shape, and in the pre-welding stage, the second workpiece 2 is in abutment with the long strip-shaped arc-shaped teeth on the bottom die 4, so as to reduce the pressure of the bottom die 4 acting on the second welding surface 22, make the surface of the second welding surface 22 more flat while positioning the second workpiece 2, and achieve the effect of protecting the second workpiece 2.

[0049] With such an arrangement, the long arc-shaped teeth are different from the traditional dense point-shaped teeth in that the area of the long arc-shaped teeth in contact with the first workpiece 1 is linear rather than point-shaped, and the linear contact can disperse the pressure in the ultrasonic welding process, avoiding local pressure concentration that causes the surface of the first workpiece 1 to be concave. At the same time, the position of the action of the tooth shape is clearly limited to the side of the first workpiece 1 away from the second workpiece 2, and only the surface of the first workpiece 1 not abutting the second workpiece 2 forms the positioning teeth in the pre-welding stage, and the second workpiece 2 as an intermediate layer is neither in direct contact with the tooth-shaped surface of the upper welding head 5 nor directly acted on by the limiting teeth 41 of the bottom die 4, and will not be subjected to extrusion or embossing action of the tooth shape structure. The height and pitch of the long arc-shaped teeth are designed to match the energy transmission requirements of ultrasonic welding, and only linear occlusion is needed to achieve the positioning function, without the need to form a deep concave structure by pressing to fix the first workpiece 1 and the second workpiece 2, so that no excess pits are formed on the surface of the first workpiece 1, and the planar form of the second workpiece 2 can be ensured to be always intact. The precise positioning of the workpiece from the pre-welding to the final welding stage is achieved by the occlusion of the positioning teeth of the first workpiece 1 and the limiting teeth 41 of the bottom die 4, avoiding the offset of the first workpiece 1 and the second workpiece 2 in the stage welding that affects the welding quality, protecting the planarity of the second workpiece 2 to ensure stable conductive contact with the electronic device, and avoiding problems such as damage to the insulation layer and corrosion of the metal surface layer on the surface of the first workpiece 1 and the second workpiece 2, further reducing the welding defect rate, and without the need for additional surface repair processes, the welding quality and workpiece performance are ensured, and the demand for controlling production costs is met, perfectly adapting to the actual welding needs of wire harness assemblies in the electronic, electrical and electric vehicle industries.

[0050] At the same time, the long arc-shaped teeth can also effectively increase the structural contact area between the workpieces, thereby significantly improving the welding effect, that is, when the tooth-shaped surface of the upper welding head 5 is in contact with the first workpiece 1 in the pre-welding stage, the linear long arc-shaped teeth will form a positioning tooth structure with concave-convex alternation on the surface of the first workpiece 1, which directly increases the surface structure area of the first workpiece 1 compared to planar contact. According to the principle of ultrasonic welding, a larger contact area can make the friction heat generated by ultrasonic vibration more evenly distributed on the interface between the two workpieces, avoiding the problems of local overheating or insufficient heat, and ensuring more complete fusion.

[0051] In a second aspect, the embodiment also provides a wire harness assembly made by the wire harness double-sided ultrasonic welding method described above, which can improve the welding effect of the wire harness assembly and make the quality of the wire harness assembly stable and less likely to have adverse phenomena such as overwelding and virtual welding.

[0052] In another aspect, the present embodiment also provides an ultrasonic welding system including a single upper welding head 5, a bottom die 4, and a controller, which is used to implement the single-head double-sided ultrasonic welding method described above. As such, the use of only a single upper welding head 5 directly reduces the equipment procurement cost, and the maintenance requirement of the single upper welding head 5 is less, and the long-term operation and maintenance cost is also reduced. In addition, the controller only needs to regulate the ultrasonic energy output of the single upper welding head 5, and cooperates with the workpiece position exchange action, without the need to coordinate the synchronous vibration and energy distribution of the two welding heads, greatly simplifying the control process and reducing the parameter debugging and fault troubleshooting difficulty.

[0053] In the present embodiment, the bottom die 4 is provided with a plurality of limiting teeth 41 on one side relative to the upper welding head 5, so as to disperse the contact pressure between the terminal and the bottom die 4 during pre-welding to protect the terminal and increase the friction to stabilize the initial welding positioning of the terminal and the first workpiece 1. And at the final welding, the limiting teeth 41 can be engaged with the wire harness positioning teeth formed by pre-welding to forcibly fix the position of the first workpiece after the exchange of the stacking order to avoid displacement and constrain the loose wire harness.

[0054] Further, the side surface of the upper welding head 5 relative to the bottom die 4 is a toothed surface, so that a plurality of positioning teeth are formed on the side of the first workpiece 1 away from the second workpiece 2 after pre-welding of the first workpiece 1 and the second workpiece 2, and the positioning teeth and the limiting teeth 41 can be engaged with each other, so as to accurately fix the position of the workpiece after the exchange of the stacking order at the final welding, avoid displacement, ensure the fit of the welding interface, reduce the problem of virtual welding / overwelding, constrain the loose wire harness, and further improve the welding quality stability.

[0055] Reference Figure 4 In particular, the bottom die 4 has a welding working surface 42 for carrying the workpiece, wherein in the present embodiment, the bottom die 4 is a resonant bottom die 4, which can be excited by the vibration of the upper welding head 5 to generate a resonance in a direction opposite to the vibration direction of the upper welding head 5 during the final welding step. It should be noted that the material and geometric size of the bottom die 4 determine that its natural resonance frequency matches the preset ultrasonic working frequency of the ultrasonic welding system, and when the bottom die 4 is excited by the upper welding head 5, it can generate resonance along a predetermined direction, which is configured as a direction opposite to the vibration direction of the upper welding head 5, and the welding working surface 42 is arranged at a position of any vibration antinode when the bottom die 4 resonates.

[0056] During the ultrasonic welding process, the bottom die 4 is excited by the upper welding head 5 to resonate at a frequency matching the preset ultrasonic working frequency of the ultrasonic welding system, so that the bottom die 4 resonates in the opposite direction of the vibration direction of the upper welding head 5, that is, the bottom die 4 generates a reverse resonance at the same frequency as the upper welding head 5 during the ultrasonic welding process. Since the welding working surface 42 is located at the vibration antinode position, the relative movement and friction at the welding interface between the bottom die 4 and the workpiece are increased, so as to improve the efficiency and concentration of the welding energy transmission. In addition, the strength of the welding spot and the consistency of the welding quality can be improved, so as to improve the welding quality; in addition, due to the improvement of the energy transmission efficiency, the welding time of each welding can be shortened, so as to improve the welding efficiency.

[0057] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. For those skilled in the art, various obvious changes, readjustments and substitutions can be made without departing from the scope of the present application. It is unnecessary and impossible to enumerate all the embodiments. Any modification, equivalent substitution and improvement made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. Single-head double-sided ultrasonic welding method, characterized in that, It comprises the following steps: Preparation: providing a first workpiece (1), a second workpiece (2), a third workpiece (3) and an ultrasonic welding system, the first workpiece (1) has a first welding section, the second workpiece (2) has a first welding surface (21) and a second welding surface (22), the third workpiece (3) has a second welding section, the ultrasonic welding system comprises a bottom die (4) and an upper welding head (5), a plurality of limiting teeth (41) are arranged on one side of the bottom die (4) relative to the upper welding head (5), and the side surface of the upper welding head (5) relative to the bottom die (4) is a tooth-shaped surface; The tooth depth, tooth top width, tooth bottom width, tooth spacing, tooth shape angle and round corner transition area of the limiting teeth (41) and the tooth-shaped surface are consistent. Pre-welding: the first workpiece (1) and the second workpiece (2) are stacked on the bottom die (4), and the second welding surface (22) abuts against the bottom die (4), the first welding section abuts against the first welding surface (21), the ultrasonic welding system is started, the tooth-shaped surface of the upper welding head (5) acts on the first welding section, the first welding section is welded to the first welding surface (21), and a plurality of positioning teeth adapted to the limiting teeth (41) are formed on the side of the first welding section away from the second workpiece (2). Final welding: the stacking order of the first workpiece (1) and the second workpiece (2) is exchanged, the positioning teeth of the first workpiece (1) and the limiting teeth (41) of the bottom die (4) are mutually engaged and positioned, the second welding section of the third workpiece (3) is placed on the second welding surface (22) of the second workpiece (2), and the ultrasonic welding system is started. The upper welding head (5) welds the second welding section to the second welding surface (22).

2. The single-head double-sided ultrasonic welding method of claim 1, wherein, The first workpiece (1) and the third workpiece (3) are wire harnesses, and the second workpiece (2) is a terminal.

3. The single-head double-sided ultrasonic welding method of claim 1, wherein, The limiting teeth (41) are arranged in the shape of long strip arc teeth.

4. A wiring harness assembly characterized by, The wire harness assembly is made by the single-head double-sided ultrasonic welding method according to any one of claims 1-3.

5. Ultrasonic welding system comprising a single upper horn (5), a lower die (4) and a controller, characterized in that The ultrasonic welding system is used to realize the single-head double-sided ultrasonic welding method according to any one of claims 1-3.

6. The ultrasonic welding system of claim 5, wherein, The bottom die (4) is provided with a plurality of limiting teeth (41) on one side relative to the upper welding head (5).

7. The ultrasonic welding system of claim 6, wherein, The side surface of the upper welding head (5) relative to the bottom die (4) is a tooth-shaped surface, so that a plurality of positioning teeth are formed on the side of the first welding section away from the second workpiece (2) after the first workpiece (1) and the second workpiece (2) are pre-welded, and the positioning teeth and the limiting teeth (41) can be mutually engaged.

8. The ultrasonic welding system of claim 5, wherein, The bottom die (4) is a resonant bottom die (4), and in the final welding step, the resonant bottom die (4) can be excited by the vibration of the upper welding head (5) to generate a resonance opposite to the vibration direction of the upper welding head (5).

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