A welding method and device for an aluminum flat wire hairpin winding of an aluminum wire motor

Abstract

The application discloses a welding method and device for aluminum flat wire hairpin winding of an aluminum wire motor, and belongs to the technical field of flat wire motor stator manufacturing. The method comprises the following steps: straightening, removing paint from the end, cutting, 2D bending and 3D stamping of the aluminum flat enameled wire to form the hairpin winding; immersing the welded end of the formed hairpin winding into a solder tank provided with an ultrasonic transducer, transmitting ultrasonic vibration to the welded end through molten tin-based solder to assist immersion plating, and forming a tin-based alloy weldable layer on the surface of the welded end after cooling; inserting the pretreated hairpin winding into a stator slot, expanding and cutting the welded end, welding the welded ends of adjacent hairpins together to complete electrical connection. The immersion plating process is placed after 2D bending and 3D stamping, so that the plating layer is prevented from being damaged by bending and stamping, and the problems of removal of the oxide film on the aluminum flat wire welded end and false welding are solved.

Description

Technical Field

[0001] This invention belongs to the field of flat wire motor stator manufacturing technology, specifically relating to a welding method and apparatus for aluminum flat wire hairpin windings of aluminum wire motors, and more particularly to a method and apparatus for pre-treating the welding ends of aluminum flat wire hairpin windings by ultrasonic-assisted dip plating before welding. Background Technology

[0002] Flat wire motors, with their core advantages such as high slot fill factor, high efficiency, and excellent heat dissipation, have become the mainstream technology for drive motors in new energy vehicles. Their stator windings are made from rectangular cross-section flat enameled wire through processes such as straightening, paint removal, cutting, 2D bending, and 3D stamping to form U-shaped hairpins. After being inserted into the stator slots, the ends are twisted and expanded, and the welding ends of adjacent hairpins are welded to achieve electrical connection of the windings.

[0003] To further reduce motor costs and overall weight, replacing traditional copper flat wire with aluminum flat wire is an important industry trend. Aluminum has only one-third the density of copper, and its raw material cost is more than 30% lower than that of copper. This can reduce motor weight by 15%-20% and reduce costs by 10%-15%, meeting the development needs of lightweighting and cost reduction in new energy vehicles.

[0004] However, aluminum readily forms a dense Al2O3 oxide film with a thickness of about 2-5 nm in the air. This oxide film has high resistivity and strong chemical inertness, which directly leads to the following key problems when welding aluminum flat wires: (1) poor welding wettability, making it difficult for molten solder to spread on the aluminum surface, resulting in a false welding rate of 15%-20%; (2) unstable contact resistance, with the resistance of the weld point fluctuating by more than 30%, affecting the efficiency and reliability of the motor; (3) the weld point is prone to electrochemical corrosion in a long-term humid and hot environment, which seriously shortens the service life of the motor.

[0005] To improve the solderability of aluminum wire, various solutions have been proposed in existing technologies, including the use of specialized highly corrosive fluxes, ultrasonic-assisted welding, and electroplating pre-plated metal layers. However, each of these solutions has its own drawbacks: while specialized highly corrosive fluxes can temporarily remove the oxide film, residual flux accelerates solder joint corrosion and generates wastewater pollution; ultrasonic-assisted welding directly applies ultrasound to remove the oxide film during the welding process, but due to the complex shape of the hairpin end, the ultrasonic energy transfer is uneven, resulting in poor weld quality consistency; while electroplating pre-plated metal layers can form a solderable layer, it suffers from problems such as heavy metal wastewater discharge, poor coating adhesion, and high process costs.

[0006] Among them, ultrasonic-assisted dip plating technology has been proven to form a metallurgically bonded tin-based solder layer on the aluminum surface, effectively removing oxide film and preventing secondary oxidation. However, the existing technology is mainly applied to aluminum terminals, aluminum busbars or the ends of round aluminum wires with simple shapes, and has not been integrated into the process for the multi-process, high-speed automation and complex geometry of flat wire motor hairpin forming. In particular, the existing technology mostly performs dip plating after paint removal and before forming, but this process has the following problems: (1) After dip plating, the plating at the welding end is prone to micro-cracks or even peeling due to plastic deformation during the subsequent 2D bending and 3D stamping process, resulting in plating failure; (2) When the flat wire covered by the plating is bent, the friction between the plating and the mold may cause mold contamination and plating scratches.

[0007] In addition, although existing flat wire motor hairpin forming equipment has achieved automated integration of processes such as copper flat wire feeding, straightening, paint removal, cutting, 2D bending, and 3D forming, the above equipment is designed for copper flat wire and does not address the problem of oxide film removal for aluminum flat wire, nor does it integrate the welding end immersion plating pretreatment process, so it cannot be directly applied to the solderability pretreatment of aluminum flat wire hairpin windings.

[0008] Therefore, the core technological bottleneck currently facing the industrialization of aluminum flat wire motors is: how to efficiently and reliably pre-treat the welding ends of aluminum flat wires during the hairpin forming process, so that they have weldability comparable to copper flat wires, while avoiding damage to the plating layer from subsequent bending and stamping processes, and being highly compatible with existing automated production lines. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the aforementioned background technology and provide a welding method and apparatus for aluminum flat wire hairpin windings in aluminum wire motors. This invention places the ultrasonic-assisted dip-plating process after 2D bending and 3D stamping. The welding end has not yet formed a plating layer during the forming process, fundamentally avoiding the risk of mechanical damage to the plating layer caused by bending and stamping processes. This effectively prevents the aluminum substrate from being exposed to air and oxidizing again, thereby avoiding problems such as incomplete welds and weld explosions that occur during aluminum flat wire welding.

[0010] The technical solution of this invention is: a welding method for aluminum flat wire hairpin windings of an aluminum wire motor, comprising the following steps: Aluminum flat enameled wire is formed into a hairpin winding with a final 3D geometry; The welding end of the formed hairpin winding is subjected to ultrasonic-assisted dip plating pretreatment. The ultrasonic-assisted dip plating pretreatment includes: immersing the welding end into a solder bath equipped with an ultrasonic transducer, transmitting ultrasonic vibration to the welding end through the molten tin-based solder in the solder bath to assist dip plating, removing the solder bath after dip plating and cooling and solidifying, and forming a tin-based alloy solderable layer on the surface of the welding end. The pre-treated hairpin windings are inserted into the stator slots, the welded ends are twisted and cut, and then the welded ends of adjacent hairpins are welded together to complete the electrical connection.

[0011] Preferably, in the ultrasonic-assisted dip-plating pretreatment, multiple pre-formed hairpin windings with the same linear shape are clamped side by side in the dip-plating fixture, so that the welding ends of each hairpin winding are aligned, and multiple hairpin windings are processed at the same time.

[0012] Preferably, in the ultrasonic-assisted immersion plating pretreatment, a nitrogen protective cover is provided above the solder bath, and nitrogen gas with a purity of not less than 99.99% is introduced to control the ambient oxygen concentration on the solder surface below 100 ppm. Here, ppm and purity both refer to volume fraction.

[0013] Preferably, the tin-based solder is one of Sn-9Zn alloy, Sn-58Bi alloy, and Sn-3.0Ag-0.5Cu alloy, and the temperature of the solder bath is 150-280 °C.

[0014] Preferably, the ultrasonic transducer operates at a frequency of 20-40 kHz and a power of 200-2000 W, with an immersion plating time of 0.5-2.0 seconds, and the tin-based alloy solderable layer has a thickness of 10-20 μm.

[0015] Preferably, the specific steps of forming the aluminum flat enameled wire into a hairpin winding with a final 3D geometry include: straightening, end paint removal, cutting, 2D bending and 3D stamping, and the order of end paint removal and cutting is not limited; The straightening includes straightening the aluminum flat enameled wire coil until the straightness does not exceed 0.5 mm / m; Preferably, the step of forming the aluminum flat enameled wire into a hairpin winding with a final 3D geometry specifically includes: straightening, end paint removal, cutting, 2D bending and 3D stamping, and the order of end paint removal and cutting is not limited; The end-coating process includes: removing the insulating varnish layer from the pre-designed welding areas at both ends of the aluminum flat wire, with a varnish removal length of 5-15mm. The cutting includes: cutting the aluminum flat wire to the designed length of the hair clip; The 2D bending includes: bending the cut straight flat wire into the planar shape of a U-shaped hair clip; The 3D stamping includes: forming a hairpin winding with a complete geometry in a forming die.

[0016] In the hairpin winding forming process of this invention, the order of end paint removal and cutting can be interchanged, and the order of the two does not constitute a limitation of this invention. However, as a preferred embodiment, end paint removal is usually performed first in a continuous production line, and then the flat wire is cut to the designed length, which is more conducive to the connection and flow efficiency between each process.

[0017] Preferably, the twisting expansion specifically includes: twisting and expanding the welded end extending from the stator slot end face to make the welded ends of adjacent hairpin windings aligned and fitted; The cutting head specifically includes: cutting the twisted and expanded welded end to make the cut end face flat, with a weldable layer on the outer periphery and an aluminum substrate in the center.

[0018] Preferably, the welding includes: welding on the fresh end face formed after the welding end is cut off, using laser welding, resistance welding or hot pressing.

[0019] The present invention also provides a welding device for aluminum flat wire hairpin windings of aluminum wire motors, comprising: Solder bath, used to hold molten tin-based solder; An ultrasonic transducer is installed on the solder bath and is used to transmit ultrasonic vibrations to the welding end immersed in the solder bath through the molten solder medium to assist in the immersion plating. An immersion plating fixture is positioned above the solder bath to clamp the formed hairpin winding, ensuring that the welding ends of the hairpin winding face downwards and are aligned. A lifting mechanism, connected to the immersion plating fixture, is used to drive the immersion plating fixture to lift and lower, so that the welding end is immersed in or removed from the solder bath.

[0020] Preferably, it also includes a nitrogen protective cover disposed above the solder bath for introducing nitrogen to reduce the oxygen concentration on the solder surface; The immersion plating fixture is equipped with a positioning and clamping mechanism, which is used to clamp multiple pre-formed hairpin windings with the same linear shape in parallel and ensure that the welding ends of each hairpin winding are at the same horizontal height. The ultrasonic transducer is installed at the bottom or side wall of the solder bath.

[0021] The beneficial effects of this invention are as follows: 1. Completely solves the problem of coating damage: The dip coating process is placed after 2D bending and 3D stamping. The coating has not yet formed at the welding end during the forming process, which completely avoids the risk of mechanical damage to the coating caused by bending and stamping processes, and the coating integrity rate reaches 100%.

[0022] 2. Adaptable welding end shape: During the immersion plating process, the welding end already has the final 3D geometry (including Z-shaped deflection angle, etc.), and the plating layer can directly and evenly cover the surface of the welded end after forming, without having to consider the impact of bending on the plating layer.

[0023] 3. Suitable for mass production: Multiple hairpin windings with the same linear shape can be clamped together and dip-plated at the same time, and multiple hairpins can be processed at one time, which greatly improves production efficiency and reduces the processing time of a single piece to less than 2 seconds.

[0024] 4. Good compatibility with twisting and expanding process: The tin-based solderable layer has excellent plasticity and ductility, which can adapt to the slight deformation of the twisting and expanding process without cracking, ensuring that the coating remains intact before soldering.

[0025] 5. Completely solves the problem of aluminum flat wire welding: Through ultrasonic dip plating, a metallurgically bonded tin-based solderable layer is formed. The solder layer itself is anti-oxidation and easy to wet, so that the welding performance of the aluminum flat wire welding end reaches the level of copper flat wire, and the failure rate is reduced from 15-20% in traditional aluminum wire welding to about 3%.

[0026] 6. Green and environmentally friendly: No chemical flux or strong acid activator is required, avoiding corrosive residues and wastewater pollution; compared with electroplating, there is no discharge of heavy metal wastewater, which meets the requirements of green manufacturing.

[0027] 7. Significant overall cost advantages: Compared with copper flat wire solutions, material costs are reduced by 10%-15%, and motor weight is reduced by 15%-20%; compared with other aluminum wire pretreatment solutions, process costs are reduced by more than 20%. Attached Figure Description

[0028] Figure 1 This is a flowchart of the method of the present invention. Figure 2 This is a schematic diagram of the device of the present invention. Among them: 1- Solder tank 2- Ultrasonic transducer 3- Dip plating fixture 4- Lifting mechanism 5- Nitrogen protective cover 10- Hairpin winding. Detailed Implementation

[0029] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention. The present invention will be described in detail below through embodiments. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available. The following specific embodiments will further illustrate the present invention in detail.

[0030] This invention provides a method and apparatus for ultrasonic-assisted dip-plating pretreatment of the welding end of aluminum flat wire in an aluminum wire motor.

[0031] The method includes the following steps: straightening, removing the paint from the ends of the aluminum flat enameled wire, cutting, 2D bending and 3D stamping to form a hairpin winding with a final 3D geometry; The welding end of the formed hairpin winding is subjected to ultrasonic-assisted dip plating pretreatment. The ultrasonic-assisted dip plating pretreatment includes: immersing the welding end into a solder bath equipped with an ultrasonic transducer, transmitting ultrasonic vibration to the welding end through the molten tin-based solder in the solder bath to assist dip plating, removing the solder bath after dip plating and cooling and solidifying, and forming a tin-based alloy solderable layer on the surface of the welding end. The pre-treated hairpin windings are inserted into the stator slots, the welded ends are twisted and cut, and then the welded ends of adjacent hairpins are welded together to complete the electrical connection.

[0032] like Figure 1 As shown, the method consists of the following 10 steps.

[0033] S1: Straightening The aluminum flat enameled wire coil is fed into the straightening mechanism to eliminate winding stress and make the flat wire meet the set straightness requirements; the flat wire is then accurately transported to the paint removal station by the servo feeding mechanism.

[0034] S2: Remove paint from the end The insulating varnish layer at the pre-designed welding areas at both ends of the aluminum flat wire is removed using laser or mechanical methods to expose the fresh aluminum substrate; the varnish removal length matches the designed welding end length.

[0035] S3: cut off Cut the aluminum flat wire to the designed length for the hair clip. After cutting, both ends of the flat wire are welded ends with the paint removed.

[0036] S4: 2D bending The cut straight flat wire is bent into the flat shape of a U-shaped hairpin. During the bending process, the welded ends of the flat wire have not yet formed a plating layer and remain in a state of exposed aluminum substrate.

[0037] S5: 3D stamping The hairpin windings are formed into a complete geometric shape in the molding die. Since the welding ends have not yet been dip-plated at this point, there is no need to worry about plating damage.

[0038] S6: Ultrasonic-assisted dip coating The aluminum flat wire hairpin windings, already completed at S1 to S5, are clamped in a plating fixture in a specified orientation, with the welded ends of the hairpin windings facing downwards and vertically aligned. The welded ends are then immersed in a solder bath equipped with an ultrasonic transducer, containing molten tin-based solder. Ultrasonic vibrations are transmitted to the welded ends through the molten tin-based solder in the solder bath to assist in plating. The ultrasonic cavitation effect breaks down any residual oxide film on the aluminum wire surface, allowing the molten solder to directly wet the fresh aluminum substrate. After plating, the solder bath is removed, and the surface cools and solidifies, forming a tin-based alloy solderable layer on the welded end surface.

[0039] In a preferred embodiment, multiple pre-formed hairpin windings with identical linear shapes are clamped side-by-side in a plating fixture, aligning the welded ends of each hairpin winding, allowing multiple hairpin windings to be processed simultaneously. The fixture is equipped with locating pins and a clamping mechanism to ensure that the welded ends of each hairpin winding are at the same horizontal level.

[0040] As a preferred embodiment, a sealed protective gas cover is provided above the solder bath, through which nitrogen gas is introduced to control the oxygen concentration on the solder surface at a low level, thereby reducing solder oxidation, reducing the amount of tin dross generated, and improving the surface quality of the plating layer.

[0041] S7: Connecting wires The dip-plated hairpin winding is inserted into the stator slot. During the insertion process, the solderable layer at the soldering end does not directly contact the slot insulation, and the plating is not damaged.

[0042] S8: Torque Expansion The welded ends extending from the stator end face are twisted and expanded to align and tightly fit the welded ends of adjacent hairpins. During the twisting and expanding process, the welded ends undergo elastic deformation or slight plastic deformation. Due to the good plasticity and ductility of the tin-based alloy solderable layer, it can adapt to the minor deformations of the twisting and expanding process without cracking.

[0043] S9: Head Cut The twisted and expanded weld ends are cut to ensure that all weld ends are flat and of uniform length. After cutting, the outer periphery of the fresh end face is a weldable layer, and the center is an aluminum substrate. This cross-section is free from oxidation and contamination, and has good weld wettability.

[0044] S10: Welding The finished stator winding is obtained by welding on the fresh end face formed after the welding end is cut off, using laser welding, resistance welding or thermostatic welding.

[0045] like Figure 2 As shown, the device is mainly used for ultrasonic-assisted immersion coating in step S6, and its specific structure includes: Solder bath 1, used to hold molten tin-based solder; An ultrasonic transducer 2 is installed on the solder bath 1 and is used to transmit ultrasonic vibrations to the welding end immersed in the solder bath 1 through the molten solder medium to assist in the immersion plating. The immersion plating fixture 3 is set above the solder tank and is used to clamp the formed hairpin winding 10 so that the welding end of the hairpin winding 10 faces downward and is aligned. The lifting mechanism 4 is connected to the immersion plating fixture 3 and is used to drive the immersion plating fixture 3 to lift and lower, so that the welding end is immersed in or removed from the solder bath 1. In a preferred embodiment, the device further includes a nitrogen protective cover 5, disposed above the solder bath 1, for introducing nitrogen gas to reduce the ambient oxygen concentration on the solder surface. The nitrogen protective cover has an opening for the hairpin winding to pass through, allowing the hairpin winding to enter and exit the solder bath. The nitrogen protective cover will not interfere with the normal raising and lowering of the hairpin winding and the immersion plating. At the same time, the positive pressure environment created by the continuous introduction of nitrogen gas can effectively isolate external air, controlling the ambient oxygen concentration on the solder surface to below 100 ppm, thereby reducing solder oxidation, reducing the amount of solder dross, and improving the surface quality of the plating layer.

[0046] In a preferred embodiment, the immersion plating fixture 3 is provided with a positioning and clamping mechanism (e.g., positioning pin and clamping mechanism) for clamping multiple pre-formed hairpin windings 10 with the same linear shape in parallel and ensuring that the welding ends of each hairpin winding are at the same horizontal height; the ultrasonic transducer 2 is installed at the bottom or side wall of the solder tank 1.

[0047] Example 1 This embodiment provides a welding method for aluminum flat wire hairpin windings of aluminum wire motors, used to process aluminum flat enameled wire (grade 1A60, insulating varnish layer is polyesterimide / polyamideimide composite layer) with a cross-sectional size of 3.4mm×2.2mm, the hairpin design length is 300mm, and the varnish removal length is 10mm.

[0048] like Figure 1 As shown, the specific process steps are as follows: S1: Straightening The aluminum flat enameled wire coil is fed into the straightening mechanism to eliminate winding stress and make the straightness of the flat wire no more than 0.5 mm / m. The flat wire is then accurately transported to the paint removal station by the servo feeding mechanism, and the feeding positioning accuracy is controlled within ±0.2 mm.

[0049] S2: Remove paint from the end Laser varnish removal is used to remove the insulating varnish layer from the pre-designed welding areas at both ends of the aluminum flat wire. The varnish removal length is 10mm, and the varnish removal tolerance is controlled within ±0.2mm to ensure complete removal of the varnish layer without damaging the aluminum substrate.

[0050] S3: cut off Cut the aluminum flat wire to a length of 300 mm according to the hair clip design, ensuring the flatness of the cut end does not exceed 0.05 mm. After cutting, both ends of the flat wire are welded ends with the paint removed.

[0051] S4: 2D bending The cut straight flat wire is bent into a U-shaped hairpin with a bending radius R = 10 mm. During the bending process, the welded ends of the flat wire have not yet formed a plating layer and remain as bare aluminum substrate.

[0052] S5: 3D stamping In the forming mold, a 15° Z-shaped deflection angle is stamped at each of the two ends of the U-shaped hairpin to form a hairpin winding with a complete geometric shape. Since the welding ends have not yet been dip-plated at this time, there is no need to worry about plating damage.

[0053] S6: Ultrasonic-assisted dip coating Adopting such Figure 2 The device shown clamps multiple (e.g., 16) hairpin windings 10 with identical linear shapes and completed S1 to S5 in parallel in the plating fixture 3. The welding ends of each hairpin winding 10 are aligned downwards by positioning pins and clamping mechanisms to ensure that each welding end is at the same horizontal height.

[0054] The welding end is immersed in the solder bath 1, which is equipped with an ultrasonic transducer 2, by a lifting mechanism 4. The solder bath 1 is filled with Sn-9Zn tin-based solder, the temperature of the solder bath is 230°C, and the immersion depth is 10 mm (matching the stripping length). A sealed protective gas hood 5 is installed above the solder bath 1, and nitrogen gas with a purity of not less than 99.99% is continuously introduced at a flow rate of 10 L / min to keep the ambient oxygen concentration on the solder surface below 100 ppm.

[0055] The ultrasonic transducer 2 is activated at a frequency of 28 kHz and a power of 500 W. Ultrasonic vibrations are transmitted to the welding end through the molten tin-based solder in the solder bath 1 to assist in the immersion plating process, which lasts for 1.0 second. The ultrasonic cavitation effect is used to break down the residual oxide film on the aluminum wire surface, allowing the molten solder to directly wet the fresh aluminum substrate.

[0056] After the dip-plating is completed, the hairpin winding 10 is lifted out of the solder bath at a speed of 5 mm / s by the lifting mechanism 4, and naturally cooled and solidified, forming a tin-based alloy solderable layer with a thickness of about 15 μm on the surface of the solder end.

[0057] S7: Connecting wires The dip-plated hairpin winding is inserted into the stator slot. During the insertion process, the solderable layer at the soldering end does not directly contact the slot insulation, and the plating is not damaged.

[0058] S8: Torque Expansion The welded ends extending from the stator end face are twisted and expanded to align and fit the welded ends of adjacent hairpins, with a coaxiality not exceeding 0.1 mm. During the twisting and expansion process, the welded ends undergo slight plastic deformation. Due to the good plasticity and ductility of the tin-based alloy solderable layer (the elongation of tin can reach more than 50%), it can adapt to the slight deformation of the twisting and expansion process without cracking.

[0059] S9: Head Cut The twisted and expanded weld ends are cut to ensure that all weld end faces are flat and of uniform length. After cutting, the weld end faces expose a fresh weldable metal section that is free from oxidation and contamination and has good weld wettability.

[0060] S10: Welding Laser welding was used to form weld points in the weldable layer area of ​​the welding end. The laser welding process parameters were: pulse energy 5J, pulse width 10ms, and spot diameter 0.8mm. The weld points fell completely on the fresh end face formed after the head was cut. The outer periphery of this end face was the weldable layer metal section, and the center was the aluminum substrate. During the welding process, the laser acted on both simultaneously, resulting in good weld point formation and reliable welding quality.

[0061] In this embodiment, the ultrasonic transducer 2 is installed at the bottom of the solder bath 1. During the immersion plating process, the ultrasonic transducer 2 transmits ultrasonic vibrations to the welding end through the molten solder medium, thereby achieving cavitation removal of the oxide film.

[0062] Example 2 This embodiment provides a welding method for aluminum flat wire hairpin windings of aluminum wire motors, used to process aluminum flat enameled wire (grade 1A60, insulating varnish layer is polyesterimide / polyamideimide composite layer) with a cross-sectional size of 3.4mm×2.2mm, the hairpin design length is 300mm, and the varnish removal length is 10mm.

[0063] S1: Straightening The aluminum flat enameled wire is straightened until the straightness is ≤0.5 mm / m and the feeding positioning accuracy is ±0.2 mm.

[0064] S2: Remove paint from the end Laser varnish removal is used to remove the insulating varnish layer from the pre-set welding areas at both ends. The varnish removal length is 10 mm, with a tolerance of ±0.2 mm.

[0065] S3: cut off Cut to a length of 300 mm according to the hair clip design, with an end face flatness of ≤0.05 mm.

[0066] S4: 2D bending The straight flat wire is bent into a U-shaped planar shape with a bending radius R = 10 mm.

[0067] S5: 3D stamping A 15° Z-shaped deflection angle is stamped at each end of the U-shape to form a hairpin winding with a complete geometric shape.

[0068] S6: Ultrasonic-assisted dip coating Adopting such Figure 2The device shown clamps multiple (e.g., 16) hairpin windings with identical linear shapes, already completed from S1 to S5, in parallel in an immersion plating fixture, with the welded ends facing downwards and aligned to ensure the same horizontal height.

[0069] The molten solder in the solder bath is Sn-3.0Ag-0.5Cu (product abbreviation SAC305), and the solder bath temperature is 250 °C. The immersion depth is 10 mm, and nitrogen gas with a purity ≥99.99% (flow rate 10 L / min) is introduced above the solder bath to ensure that the ambient oxygen concentration on the solder surface is ≤100 ppm. The ultrasonic transducer operates at a frequency of 28 kHz and a power of 500 W, and the immersion treatment time is 1.0 s. The solder bath is removed at a speed of 5 mm / s, and the material is allowed to cool naturally, forming a tin-based alloy solderable layer with a thickness of approximately 15 μm.

[0070] S7: Connecting wires The dip-plated hairpin winding is inserted into the stator slot without damaging the plating.

[0071] S8: Torque Expansion The welded ends protruding from the stator end face are twisted and expanded to make adjacent hairpin welded ends aligned and fit together, with a coaxiality of ≤0.1 mm.

[0072] S9: Head Cut After cutting and twisting, the welded end is made flat and of uniform length, exposing the fresh weldable metal cross section and aluminum substrate.

[0073] S10: Welding Laser welding (pulse energy 5 J, pulse width 10 ms, spot diameter 0.8 mm) was used to weld on the rear end face of the cut head. The weld point fell completely on the fresh end face formed after the cut head. The outer periphery of this end face is a weldable metal cross section and the center is an aluminum substrate. During the welding process, the laser acted on both simultaneously, resulting in good weld point formation and reliable welding quality.

[0074] Example 3 This embodiment provides a welding method for aluminum flat wire hairpin windings of aluminum wire motors, used to process aluminum flat enameled wire (grade 1A60, insulating varnish layer is polyesterimide / polyamideimide composite layer) with a cross-sectional size of 3.4mm×2.2mm, the hairpin design length is 320mm, and the varnish removal length is 12mm.

[0075] S1: Straightening Align the aluminum flat enameled wire until the straightness is ≤0.5 mm / m and the feeding positioning accuracy is ±0.2 mm.

[0076] S2: Remove paint from the end Laser varnish removal is used to remove the insulating varnish layer in the pre-set welding areas at both ends. The varnish removal length is 12 mm, with a tolerance of ±0.2 mm.

[0077] S3: cut off Cut to a length of 320 mm according to the hair clip design, with an end face flatness of ≤0.05 mm.

[0078] S4: 2D bending The straight flat wire is bent into a U-shaped planar shape with a bending radius R = 12 mm.

[0079] S5: 3D stamping A 12° Z-shaped deflection angle is stamped at each end of the U-shape to form a hairpin winding with a complete geometric shape.

[0080] S6: Ultrasonic-assisted dip coating Adopting such Figure 2 The device shown employs multiple (e.g., 16) shaped hairpin windings arranged side-by-side in an immersion plating fixture, with the welded ends facing downwards and aligned to ensure that all welded ends are at the same horizontal height.

[0081] The molten solder in the solder bath was a Sn-58Bi eutectic alloy (melting point 138 ℃), and the solder bath temperature was 165 ℃. The immersion depth was 12 mm (matching the paint removal length), and nitrogen gas with a purity ≥99.99% (flow rate 10 L / min) was introduced above the solder bath to ensure that the ambient oxygen concentration on the solder surface was ≤100 ppm. The ultrasonic transducer operated at a frequency of 40 kHz and a power of 300 W, with an immersion time of 1.2 s. The solder bath was removed at a speed of 6 mm / s, and the material was allowed to cool naturally, forming a tin-based alloy solderable layer with a thickness of approximately 18 μm, exhibiting a silvery-white metallic luster and good interfacial bonding with the aluminum substrate.

[0082] S7: Connecting wires The dip-plated hairpin winding is inserted into the stator slot without damaging the plating.

[0083] S8: Torque Expansion The welded ends protruding from the stator end face are twisted and expanded to make adjacent hairpin welded ends aligned and fit together, with a coaxiality of ≤0.1 mm.

[0084] S9: Head Cut After cutting and twisting, the welded end is made flat and of uniform length, exposing the fresh weldable metal cross section and aluminum substrate.

[0085] S10: Welding Laser welding (pulse energy 5 J, pulse width 10 ms, spot diameter 0.8 mm) was used to weld on the rear end face of the cut head. The weld point fell completely on the fresh end face formed after the cut head. The outer periphery of this end face is a weldable metal cross section and the center is an aluminum substrate. During the welding process, the laser acted on both simultaneously, resulting in good weld point formation and reliable welding quality.

[0086] Comparative experiment To verify the technical effect of the present invention, the following comparative experiments were conducted. The samples obtained from the experimental group and the control group were tested for coating integrity rate, false soldering rate, solder joint contact resistance fluctuation, coating-substrate bonding strength, and solder joint pull-out force, respectively. All of the above performance indicators were tested according to conventional methods in the art.

[0087] Experimental group: Using the methods of Examples 1-3 of this invention, the welding ends of 100 aluminum flat wire hairpins were subjected to complete process treatment (including post-forming dip plating, wire insertion, twisting and expansion, head cutting and welding).

[0088] Control Group 1: Following the process sequence of existing technologies, only the ultrasonic-assisted dip-plating in Example 1 was placed after cutting, followed by subsequent forming, wire insertion, twisting and expansion, head cutting and welding processes, to perform complete process processing on 100 aluminum flat wire hairpin windings.

[0089] Control group 2: Using unplated aluminum flat wire hairpin windings (directly formed after removing the paint, without any plating treatment), 100 aluminum flat wire hairpin windings were subjected to complete process treatment (including insertion, twisting, cutting and welding).

[0090] The results are shown in Table 1 below. The data are the average values ​​from multiple experiments.

[0091] Table 1 Performance Test Results The above experimental results show that the coating integrity rate of Examples 1-3 of the present invention is 100%, while the coating integrity rate of Control Group 1 (immersion plating before forming) is only 65%. This is because Control Group 1 still needs to undergo 2D bending and 3D stamping processes after immersion plating. During bending and stamping, the coating will generate micro-cracks or even peel off due to plastic deformation. In contrast, the present invention places the immersion plating process after 2D bending and 3D stamping. The welding end has not yet formed a coating during the forming process, which fundamentally avoids the mechanical damage to the coating caused by bending and stamping.

[0092] The results of the poor solder joint rate show that the poor solder joint rate of Examples 1-3 of the present invention is 3%, while the poor solder joint rate of Control Group 1 is 12%, and the poor solder joint rate of Control Group 2 (without dip plating) is 18%. Control Group 2, because it did not undergo any dip plating treatment, had a high-resistivity oxide film covering the aluminum welding end surface, preventing the molten solder from directly wetting the aluminum substrate, resulting in the highest poor solder joint rate. Control Group 1, although dip plating was performed, experienced cracking during subsequent bending, disrupting the integrity and continuity of the plating, resulting in the second highest poor solder joint rate. The present invention, through post-forming dip plating, ensures a complete and continuous plating layer, and the plating itself has excellent solderability, resulting in the lowest poor solder joint rate.

[0093] The contact resistance fluctuations of the solder joints in Examples 1-3 of this invention are 5%, 10%, and 9%, respectively, while those in Control Group 1 are 20% and Control Group 2 are 35%. The contact resistance fluctuations reflect the uniformity and stability of the solder joint quality. Control Group 2, lacking a protective coating, suffers from highly unstable solder joint quality due to the presence of the aluminum oxide film on the substrate. Control Group 1, with its cracked coating causing some areas to lose protection, still exhibits significant fluctuations. This invention, through a complete and continuous coating, ensures consistent contact conditions for each solder joint, resulting in minimal contact resistance fluctuations.

[0094] The bonding strength between the coating and the substrate in Examples 1-3 of this invention is 30 MPa, 28 MPa, and 25 MPa, respectively, while that in Control Group 1 is only 22 MPa. The coating in Control Group 1 was subjected to repeated tensile and compressive stresses during bending, resulting in microscopic damage and even localized peeling at the interface between the coating and the substrate. In contrast, the coating of this invention is formed after final molding, resulting in an in-situ metallurgical bond between the coating and the aluminum substrate, with an intact and undamaged interface, leading to a higher bonding strength.

[0095] The pull-out force of the solder joints in Examples 1-3 of this invention are 220 N, 200 N, and 180 N, respectively, while that in Control Group 1 is 110 N and that in Control Group 2 is 58 N. The pull-out force of the solder joint is a comprehensive reflection of the welding quality. In Control Group 2, due to the presence of the aluminum oxide film, the solder cannot effectively wet the aluminum substrate, and the solder joints are maintained only by mechanical interlocking or a small amount of local bonding, resulting in the lowest pull-out force. Although Control Group 1 formed a coating, the solder joint quality was still unsatisfactory due to coating cracking and interface damage. This invention, through a complete and continuous metallurgically bonded coating, allows subsequent welding to be performed on a high-quality coating surface, resulting in a good metallurgical connection of the solder joints and the highest pull-out force.

[0096] In summary, by performing ultrasonic-assisted dip-plating after the hairpin is fully formed, this invention not only completely avoids mechanical damage to the coating caused by bending and stamping processes, achieving a 100% coating integrity rate, but also significantly improves the bonding strength between the coating and the aluminum substrate, effectively reducing the rate of false soldering and contact resistance fluctuations, thus achieving comprehensive technical effects superior to existing technologies.

[0097] The welding method and apparatus for aluminum flat wire hairpin windings in aluminum wire motors provided by this invention can be widely applied in the manufacturing process of flat wire motors for new energy vehicles, and is particularly suitable for manufacturing low-cost, lightweight motor stator windings that use aluminum flat wire instead of copper flat wire. This method is highly compatible with existing automated production lines for flat wire motors, and can be upgraded without changing the main wire structure, demonstrating promising prospects for industrial application.

Claims

1. A welding method for aluminum flat wire hairpin windings in an aluminum wire motor, characterized in that, Includes the following steps: Aluminum flat enameled wire is formed into a hairpin winding with a final 3D geometry; The welding end of the formed hairpin winding is subjected to ultrasonic-assisted dip plating pretreatment. The ultrasonic-assisted dip plating pretreatment includes: immersing the welding end into a solder bath equipped with an ultrasonic transducer, transmitting ultrasonic vibration to the welding end through the molten tin-based solder in the solder bath to assist dip plating, removing the solder bath after dip plating and cooling and solidifying, and forming a tin-based alloy solderable layer on the surface of the welding end. The pre-treated hairpin windings are inserted into the stator slots, the welded ends are twisted and cut, and then the welded ends of adjacent hairpins are welded together to complete the electrical connection.

2. The welding method for aluminum flat wire hairpin windings of an aluminum wire motor as described in claim 1, characterized in that, In the ultrasonic-assisted dip-plating pretreatment, multiple pre-formed hairpin windings with the same linear shape are clamped side by side in the dip-plating fixture, so that the welding ends of each hairpin winding are aligned, and multiple hairpin windings are processed at the same time.

3. The welding method for aluminum flat wire hairpin windings of an aluminum wire motor as described in claim 1, characterized in that, In the ultrasonic-assisted immersion plating pretreatment, a nitrogen protective cover is installed above the solder bath, and nitrogen gas with a purity of not less than 99.99% is introduced to control the ambient oxygen concentration on the solder surface to below 100 ppm.

4. The welding method for aluminum flat wire hairpin windings of an aluminum wire motor as described in claim 1, characterized in that, The tin-based solder is one of Sn-9Zn alloy, Sn-58Bi alloy, and Sn-3.0Ag-0.5Cu alloy, and the temperature of the solder bath is 150-280 °C.

5. The welding method for aluminum flat wire hairpin windings of an aluminum wire motor as described in claim 1, characterized in that, The ultrasonic transducer operates at a frequency of 20-40 kHz and a power of 200-2000 W, with an immersion plating time of 0.5-2.0 seconds, and the tin-based alloy solderable layer has a thickness of 10-20 μm.

6. The welding method for aluminum flat wire hairpin windings of an aluminum wire motor as described in claim 1, characterized in that, The specific steps for forming the hairpin winding with the final 3D geometry from aluminum flat enameled wire include: straightening, end paint removal, cutting, 2D bending and 3D stamping, and the order of end paint removal and cutting is not limited. The straightening includes straightening the aluminum flat enameled wire coil until the straightness does not exceed 0.5 mm / m; The end-coating process includes: removing the insulating varnish layer from the pre-designed welding areas at both ends of the aluminum flat wire, with a varnish removal length of 5-15 mm. The cutting includes: cutting the aluminum flat wire to the designed length of the hair clip; The 2D bending includes: bending the cut straight flat wire into the planar shape of a U-shaped hair clip; The 3D stamping includes: forming a hairpin winding with a complete geometry in a forming die.

7. The welding method for aluminum flat wire hairpin windings of an aluminum wire motor as described in claim 1, characterized in that, The twisting and expanding specifically includes: twisting and expanding the welded ends that extend out of the stator slot end face to make the welded ends of adjacent hairpin windings aligned and fitted. The cutting head specifically includes: cutting the twisted and expanded welded end to make the cut end face flat, with a weldable layer on the outer periphery and an aluminum substrate in the center.

8. The welding method for aluminum flat wire hairpin windings of an aluminum wire motor as described in claim 1, characterized in that, The welding includes welding on the fresh end face formed after the welding end is cut off, using laser welding, resistance welding, or hot pressing.

9. A welding device for aluminum flat wire hairpin windings of an aluminum wire motor, characterized in that, include: Solder bath (1), used to contain molten tin-based solder; An ultrasonic transducer (2) is installed on the solder bath (1) to transmit ultrasonic vibrations to the welding end immersed in the solder bath (1) through the molten solder medium to assist in the immersion plating. The immersion plating fixture (3) is set above the solder tank (1) and is used to clamp the formed hairpin winding so that the welding end of the hairpin winding faces down and is aligned. The lifting mechanism (4) is connected to the immersion plating fixture (3) and is used to drive the immersion plating fixture (3) to lift and lower, so that the welding end is immersed in or removed from the solder bath (1).

10. The welding device for aluminum flat wire hairpin windings of an aluminum wire motor according to claim 9, characterized in that, It also includes a nitrogen protective cover (5) set above the solder bath (1) for introducing nitrogen to reduce the oxygen concentration on the solder surface; The dip-plating fixture (3) is provided with a positioning and clamping mechanism, which is used to clamp multiple hairpin windings with the same linear shape in parallel and ensure that the welding ends of each hairpin winding are at the same horizontal height. The ultrasonic transducer (2) is installed at the bottom or side wall of the solder tank (1).

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