In the context of global carbon neutrality strategies, the new energy vehicle industry has experienced rapid growth. The performance, lifespan, and safety of EV battery packs are highly dependent on operating temperature. Studies indicate that precisely controlling the battery pack temperature within the optimal range of 15–35°C can enhance energy density and cycle life by 20–30%. Liquid cooling thermal management systems (BTMS) have become the mainstream solution due to their excellent heat exchange efficiency and temperature uniformity. The liquid-cooled plate serves as the core heat exchange carrier in this system. Its performance is critical: microscopically, the dimensional accuracy of internal flow channels (with tolerances ≤ ±0.1 mm) directly affects flow resistance and heat transfer uniformity; macroscopically, the sealing integrity (zero leakage) and mechanical reliability (vibration resistance, thermal fatigue resistance) of the overall structure are directly related to the safety of the EV battery pack. However, traditional manufacturing processes face bottlenecks: single stamping forming leads to geometric distortion of flow channels due to material springback, resulting in uneven subsequent welding interface gaps; conventional brazing processes fail to synergize with the residual stress field of stamped parts, easily causing defects such as lack of fusion and cracks. Therefore, developing a hybrid manufacturing technology that collaboratively addresses “forming-joining-reliability” has become an urgent need for both industry and academia.
Current manufacturing technologies for liquid-cooled plates are diverse but face various challenges. In the field of precision stamping, German company Bosch employs high-precision servo stamping production lines, achieving a relatively high level of flow channel dimensional tolerance of ±0.15 mm. However, their process design does not fully consider the strict requirements of subsequent brazing on assembly gaps, lacking targeted pre-deformation compensation strategies. Domestic leading companies like BYD have suppressed springback to some extent through mold surface optimization, but they have not established a quantitative correlation model between stamping process parameters and brazing gap quality, leading to insufficient process stability. In brazing technology, Japanese company Denso uses nitrogen-protected brazing processes, with joint strength reaching 75 MPa. However, due to limitations in protective atmosphere purity, the probability of interface oxidation still exceeds 5%, affecting yield and long-term reliability. Domestic companies such as CATL have conducted optimization studies on Al-Si brazing filler metal composition, but their reliability verification is mostly limited to static pressure tests, failing to simulate the complex and variable thermal-mechanical-vibration comprehensive conditions in actual vehicle operation. In summary, existing research mostly focuses on local optimization of single process steps, lacking a “collaborative design” mindset that treats stamping and brazing as an organic whole. Their reliability verification systems also struggle to fully cover the real service environment of passenger vehicles.
This study aims to break through these bottlenecks. The core research contents include: precision stamping process optimization and collaborative design—quantifying the impact of stamping parameters on springback and brazing gaps through DOE experiments and finite element simulation, and designing pre-deformation compensation schemes; vacuum brazing interface regulation and process synergy—studying the evolution law of brazing parameters on interface microstructure (especially the diffusion layer), establishing mapping relationships between process, structure, and performance, and achieving synergy with stamped blanks; multi-condition reliability evaluation and simulation—using “experiment + simulation” methods to construct thermal-fluid-mechanical multi-physics coupling models and conducting comprehensive reliability verification under superimposed conditions such as thermal cycling, vibration, and pressure. The technical route is illustrated in a flowchart encompassing material selection, stamping parameter DOE optimization, pre-deformation compensation design via FEA, vacuum brazing parameter debugging, multi-physics coupling simulation, and multi-condition reliability testing, leading to process finalization and optimization.
The research object is a liquid-cooled plate component for a ternary lithium EV battery pack. Its design dimensions are 300 mm × 150 mm × 5 mm, with an internal design of 12 parallel flow channels, each 8 mm wide and 3 mm deep. This design is based on computational fluid dynamics (CFD) optimization to balance flow resistance and heat exchange efficiency. According to the national mandatory standard GB/T 38031-2020 “Safety Requirements for Traction Batteries of Electric Vehicles,” the liquid-cooled plate must meet the following performance indicators: manufacturing accuracy—key flow channel dimensional tolerance ≤ ±0.1 mm; mechanical properties—brazed joint tensile strength at room temperature ≥ 70 MPa; environmental reliability—no leakage or functional failure after 1000 thermal cycles in the temperature range of –40°C to 85°C; vibration reliability—heat dissipation efficiency attenuation ≤ 8% after vibration testing in the frequency range of 10–2000 Hz with 20 g acceleration. The substrate material is aluminum alloy 3003 (3A21), which has excellent plasticity (elongation δ ≥ 25%), good corrosion resistance, and moderate thermal conductivity (λ ≈ 201 W/(m·K)), making it very suitable for manufacturing complex flow channels through cold plastic deformation. The brazing filler metal is Al-12Si (grade 4343) alloy, with a eutectic point of about 577°C, significantly lower than the solidus temperature of 3003 aluminum alloy (about 660°C). This large melting range provides the necessary process window for brazing filler metal melting and filling while the substrate remains solid during vacuum brazing.
The core contradiction in integrating precision stamping and vacuum brazing processes lies in the precise control of interface gaps. Springback generated during stamping is the main factor causing uneven gaps. If the springback amount exceeds 0.05 mm, it will cause the brazing assembly gap to exceed the optimal range (0.05–0.20 mm). A gap that is too small (<0.05 mm) hinders capillary filling of the brazing filler metal, leading to lack of fusion; a gap that is too large (>0.20 mm) destroys capillary forces, causing loss of brazing filler metal and formation of porous defects. Additionally, microscopic residual stress introduced by stamping deformation (if not eliminated, can exceed 150 MPa) redistributes and releases during brazing heating, potentially causing workpiece deformation or even inducing microcracks at interfaces where brittle phases form. Therefore, stamping must be treated as a pre-associated process for brazing in integrated design.
To quantify the impact of stamping parameters on forming quality, a blank holder force (A), stamping speed (B), and die clearance (C) were selected as key influencing factors, with three levels each (A: 10, 15, 20 kN; B: 60, 80, 100 mm/s; C: 0.10, 0.12, 0.14 mm). Springback amount (Y1) and flow channel dimensional tolerance (Y2) were used as evaluation indicators, and an L9(3^4) orthogonal experimental design was conducted. The results are summarized in Table 1.
| Experiment No. | Blank Holder Force A (kN) | Stamping Speed B (mm/s) | Die Clearance C (mm) | Springback Y1 (mm) | Dimensional Tolerance Y2 (mm) |
|---|---|---|---|---|---|
| 1 | 10 | 60 | 0.10 | 0.08 | ±0.12 |
| 2 | 10 | 80 | 0.12 | 0.05 | ±0.09 |
| 3 | 10 | 100 | 0.14 | 0.07 | ±0.15 |
| 4 | 15 | 60 | 0.12 | 0.04 | ±0.07 |
| 5 | 15 | 80 | 0.14 | 0.03 | ±0.08 |
| 6 | 15 | 100 | 0.10 | 0.06 | ±0.10 |
| 7 | 20 | 60 | 0.14 | 0.05 | ±0.11 |
| 8 | 20 | 80 | 0.10 | 0.07 | ±0.13 |
| 9 | 20 | 100 | 0.12 | 0.06 | ±0.10 |
Range analysis of the experimental results shows that for springback Y1, the order of influence of factors is: C (die clearance) > A (blank holder force) > B (stamping speed). The optimal parameter combination is A2B2C2, i.e., blank holder force 15 kN, stamping speed 80 mm/s, die clearance 0.12 mm. Under these parameters, the springback amount is only 0.03 mm, and the flow channel dimensional tolerance is controlled within ±0.08 mm, providing a uniform and ideal assembly gap for subsequent brazing. To further eliminate springback effects, a finite element simulation model for stamping forming was established using ABAQUS software, with the material constitutive model employing the Hill48 anisotropic yield criterion. The simulation accurately predicted that under optimal parameters, local depression of about 0.03 mm still exists at the flow channel edges (due to springback). Therefore, pre-deformation compensation was implemented in the mold design stage, i.e., pre-machining a 0.03 mm convexity in the mold area predicted to experience depression. Simulation results after compensation show that the geometric shape of the workpiece flow channels returns to the theoretical design dimensions after springback, with a regular rectangular cross-section, thereby ensuring uniformity of the entire brazing interface gap (stable at 0.10–0.20 mm).
Brazing quality depends on the precise matching of temperature, time, and vacuum degree. Through single-factor experiments and response surface methodology, joint shear strength was used as the response value for optimization. The optimal brazing parameters were finally determined as: vacuum degree 5×10–5 Pa (effectively removing oxide films and preventing re-oxidation), brazing temperature 600°C (ensuring sufficient melting and flow of brazing filler metal while avoiding excessive grain growth or softening of the base material), holding time 15 min (ensuring sufficient filling of brazing filler metal and completion of necessary interface diffusion reactions). Under these parameters, the average shear strength of brazed joints reaches 82 MPa, representing a 15% improvement compared to unoptimized process parameters (about 71 MPa). Using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), the microstructure of the brazed joint interface was observed. Under optimized parameters, the brazed zone exhibits a dense structure without continuous oxide inclusions or large pores. At the interface between the 3003 substrate and Al-Si brazing filler metal, a continuous and uniform intermetallic compound layer forms, identified by EDS point analysis as silicon-rich Al3Si2 phase, with thickness controlled at 5–10 μm. This diffusion layer is key to achieving high-strength metallurgical bonding. Research indicates that if this compound layer is too thin (<3 μm), bonding strength is insufficient; if too thick (>15 μm), its intrinsic brittleness becomes a crack source, leading to reduced joint toughness. When brazing temperature is too high (e.g., 620°C) or time too long (e.g., 20 min), the diffusion layer grows excessively to over 15 μm, accompanied by coarse silicon particles, causing joint strength to drop significantly below 65 MPa.
Based on ANSYS Fluent module, a three-dimensional fluid-thermal coupling model of the liquid-cooled plate was established to simulate fast-charging (high heat generation rate) conditions: coolant flow rate 8 L/min, inlet temperature 25°C. Simulation results show that for the liquid-cooled plate manufactured using the optimized process, the outlet coolant temperature is 32°C, and the maximum temperature difference (ΔTmax) across the entire cooling plate surface in contact with the EV battery pack is ≤ 4°C. Compared to liquid-cooled plates made with traditional manufacturing processes (surface temperature difference often >6°C), temperature uniformity is improved by over 30%, greatly benefiting consistency management of the EV battery pack. Based on ABAQUS, thermal cycling stress simulation was conducted, simulating the temperature change process of the liquid-cooled plate from –40°C to 85°C (heating/cooling rate 5°C/min). Simulation results show that maximum thermal stress occurs at flow channel corners (stress concentration areas), with a value of about 120 MPa. This value is lower than the room temperature yield strength of 3003 aluminum alloy (145 MPa), indicating that within the elastic range, the design avoids plastic deformation or low-cycle fatigue failure caused by thermal stress. The fundamental heat transfer equation governing the cooling performance can be expressed as:
$$ q = h A \Delta T $$
where \( q \) is the heat flux, \( h \) is the heat transfer coefficient, \( A \) is the surface area, and \( \Delta T \) is the temperature difference. For the EV battery pack, maintaining a low \( \Delta T \) is critical for uniform cell performance.
Basic performance test results are as follows. Dimensional accuracy: using a coordinate measuring machine (CMM) to inspect 30 random samples, the key flow channel dimensional tolerance is ±0.09 mm, better than the design target (±0.1 mm). Sealing performance: using a helium mass spectrometer leak detector for high-sensitivity detection, the leakage rate of all samples is below 5×10–9 Pa·m³/s, far better than national standard requirements. Mechanical properties: through shear testing on a universal testing machine, the average strength of 30 joint samples is 80.5 MPa, with a standard deviation of 3.2 MPa and a coefficient of variation (CV) <4%, indicating stable and highly consistent process. For thermal cycling test: after 1000 cycles of –40°C to 85°C, the sample leakage rate slightly increases but remains at an average of 9×10–9 Pa·m³/s. Heat dissipation efficiency decays by about 4.2% due to possible slight oxidation at interfaces, but still far better than the 8% failure threshold. Vibration test: according to ISO 16750-3 standard, sweep frequency vibration testing from 10–2000 Hz (acceleration 20 g) was conducted. After testing, macroscopic inspection and CMM scanning of samples showed no visible deformation or cracks. Leakage rate remained unchanged upon re-testing. Comprehensive condition test: to simulate the most severe usage conditions, superimposed testing of 500 thermal cycles + 50 hours vibration was conducted. After testing, the final leakage rate of samples is 1.2×10–8 Pa·m³/s, and heat dissipation efficiency decay is 5.0%. These results fully demonstrate that the liquid-cooled plates produced using this hybrid manufacturing technology completely meet the long-term service life requirements of 5 years or 150,000 kilometers for passenger EV battery packs.
The study successfully developed and validated a precision stamping-vacuum brazing hybrid manufacturing technology. Through a combination of DOE and FEA methods, optimal stamping parameters were determined (blank holder force 15 kN, stamping speed 80 mm/s, die clearance 0.12 mm) and effective pre-deformation compensation was achieved; by regulating vacuum brazing interface reactions, the optimal process (600°C/15 min/5×10–5 Pa) was obtained, forming a diffusion layer of appropriate thickness (5–10 μm) of Al3Si2, resulting in joint strength above 80 MPa. Through a systematic evaluation method combining multi-physics simulation and multi-condition superimposed testing, it was confirmed that the liquid-cooled plates manufactured using this technology have extremely high dimensional accuracy (±0.09 mm), sealing performance (<1×10–8 Pa·m³/s), and operational reliability (performance decay ≈ 5% after thermal-vibration combined testing). This hybrid technology route achieves synergistic enhancement of stamping and brazing. Compared to traditional step-by-step optimization processes, production efficiency is expected to increase by 30%, and comprehensive manufacturing costs to decrease by 20%, possessing great potential for large-scale industrial application. Future research work can expand in two directions: first, material system innovation, exploring compatibility processes for stamping-brazing of heterogeneous materials such as aluminum-copper or aluminum-composite liquid-cooled plates, with the aim of further improving thermal conductivity efficiency and lightweight levels; second, digital transformation, deeply integrating digital twin technology to construct real-time mapping and prediction models from process parameters to product performance, achieving intelligent monitoring, optimization, and self-decision-making in the manufacturing process of EV battery pack liquid-cooled plates, ultimately moving towards Industry 4.0-level smart manufacturing.
In summary, the hybrid manufacturing approach for EV battery pack liquid-cooled plates addresses critical challenges in thermal management for electric vehicles. The integration of precision stamping and vacuum brazing ensures that the plates meet stringent requirements for accuracy, strength, and durability. The optimized process parameters and pre-deformation compensation techniques minimize springback and ensure uniform brazing gaps, leading to reliable joints. The multi-physics simulations and comprehensive testing validate the plates’ performance under realistic operating conditions, including thermal cycling and vibration. This research contributes to the advancement of EV battery pack technology by providing a scalable, cost-effective, and high-performance manufacturing solution. As the demand for electric vehicles grows, such innovations will play a pivotal role in enhancing battery safety, efficiency, and lifespan, ultimately supporting the transition to sustainable transportation.
The reliability of EV battery pack components is paramount, and the liquid-cooled plate is no exception. The proposed hybrid manufacturing method not only improves product quality but also offers economic benefits through increased efficiency and reduced costs. Future work could explore the use of advanced materials, such as graphene-enhanced composites, to further boost thermal conductivity. Additionally, implementing artificial intelligence for real-time process control could optimize parameters dynamically, reducing waste and improving consistency. The journey towards fully autonomous manufacturing of EV battery pack parts is underway, and this study lays a solid foundation for that evolution. By continuing to innovate in materials, processes, and digital integration, we can ensure that EV battery packs meet the ever-increasing demands of performance and safety, driving the global shift towards cleaner energy solutions.