In the rapidly evolving automotive industry, the shift toward electrification has placed immense emphasis on the safety and reliability of electric vehicle (EV) battery packs. As a critical component, the EV battery pack must be meticulously sealed to prevent ingress of contaminants, moisture, or gases that could lead to thermal runaway, corrosion, or system failure. Sealing rings, typically made from materials like silicone rubber (VMQ), are widely used in EV battery pack designs due to their elasticity, temperature resistance, and chemical inertness. However, despite their simplicity, sealing rings can pose significant challenges during manufacturing, such as detachment issues that compromise seal integrity. This article, from a first-person perspective, explores the sealing principles, common structures, and an in-depth investigation into sealing ring detachment in EV battery packs, focusing on root cause analysis, solutions involving process and design adjustments, and lessons learned for future development.
The sealing mechanism in an EV battery pack relies on the compression of a sealing ring between two mating surfaces, typically the upper cover and the lower tray or立柱. When the EV battery pack is assembled, the sealing ring is installed in a groove on one side and compressed by the opposing surface during bolting, causing elastic deformation that fills micro-gaps and creates a barrier. The sealing effectiveness depends on factors like material properties, groove design, compression ratio, and installation forces. Silicone rubber is often preferred for EV battery pack applications because of its operational temperature range from -50°C to 175°C, excellent insulation, and resistance to degradation. The design of sealing rings and grooves must adhere to standards such as ISO 3601 or GB 3452, but custom designs are also common to meet specific EV battery pack requirements.
To understand the sealing performance in an EV battery pack, we can model the compressive stress using a simplified linear elastic equation: $$ \sigma = E \cdot \epsilon $$ where $\sigma$ is the stress, $E$ is the Young’s modulus of the sealing material, and $\epsilon$ is the strain due to compression. For rubber materials, a more accurate representation involves hyperelastic models, but for initial design, the compression ratio $CR$ is key: $$ CR = \frac{t_0 – t_c}{t_0} \times 100\% $$ where $t_0$ is the original cross-sectional diameter of the sealing ring, and $t_c$ is the compressed height. In EV battery pack designs, a compression ratio of 15-30% is typically targeted to ensure adequate sealing without over-stressing the material. Additionally, the fill ratio $FR$ of the groove must be considered: $$ FR = \frac{A_r}{A_g} \times 100\% $$ where $A_r$ is the cross-sectional area of the sealing ring, and $A_g$ is the cross-sectional area of the groove. A fill ratio below 90% is recommended to prevent extrusion, while maintaining sufficient contact pressure in the EV battery pack.
Common sealing structures in EV battery packs include U-grooves, dovetail grooves, and integrated sealing on fasteners. Each has advantages and drawbacks. For instance, dovetail grooves, as used in some EV battery pack designs, offer ease of machining and installation, but provide only unilateral constraint, which can lead to detachment risks if not properly designed. The contact force or “gripping force” that keeps the sealing ring in place can be approximated by: $$ F_g = \mu \cdot N $$ where $\mu$ is the coefficient of friction between the sealing ring and groove, and $N$ is the normal force due to interference fit. In dovetail grooves, this force is critical for stability during handling and assembly of the EV battery pack.
| Performance Indicator | Requirement | Unit |
|---|---|---|
| Hardness | ≥70 ±5 | Shore A |
| Tensile Strength | ≥5 | MPa |
| Elongation at Break | ≥150 | % |
| Compression Ratio | 15-30 | % |
| Maximum Fill Ratio | ≤90 | % |
| Sealing Pressure | ≥1 | MPa |
In a specific EV battery pack project, a dovetail groove design was employed, where the sealing ring is installed in a machined groove on立柱 welded to the tray. During production, detachment of sealing rings was observed after the upper cover was assembled, with a random occurrence rate of approximately 1.9% across 215 units. This issue posed a significant risk to the EV battery pack密封 integrity, as detached rings could create leakage paths, leading to potential safety hazards like thermal runaway or corrosion. From a first-person viewpoint, we initiated a thorough investigation to identify root causes and implement corrective actions, ensuring the EV battery pack met quality standards without costly rework.
The analysis focused on three main aspects: material quality, production processes, and product design. For material quality, we verified that all components—sealing rings,立柱, and upper covers—conformed to dimensional and surface specifications. Sampling measurements confirmed that sealing ring inner diameters and cross-sectional diameters were within tolerance, and visual inspections ruled out defects or contamination. This eliminated material quality as a primary cause for the EV battery pack issue.
| Potential Cause | Inspection Content | Verification Method | Result |
|---|---|---|---|
| Sealing Ring Dimension Out-of-Spec | Inner Diameter, Cross-sectional Diameter | On-site Sampling Measurement | Pass |
| 立柱 Dimension Out-of-Spec | Groove Diameter, Depth, Surface Profile | Dimensional Check with Gauges | Pass |
| Upper Cover Dimension Out-of-Spec | Surface Profile, Positional Tolerance | Fixture-based Inspection | Pass |
| Surface Defects or Contamination | Visual Quality of All Parts | Visual Inspection | Pass |
Next, we examined production processes, particularly the sealing ring installation and cover assembly steps. Operators were trained according to work instructions, and现场 observations confirmed proper installation without pre-assembly detachment. However, during cover placement—where a robot placed the upper cover onto the tray—we identified potential airflow disturbances that could displace the lightweight sealing rings in the EV battery pack. The robot moved at 500 mm/s and released the cover from a height of 5.5 mm above the tray, creating internal air pressure changes. We measured wind speed around the sealing rings using anemometers and derived a relationship: $$ v \propto \frac{h}{t} $$ where $v$ is the wind speed, $h$ is the drop height, and $t$ is the time of descent. By adjusting parameters, we reduced the robot speed to 125 mm/s and the drop height to 2.5 mm, which minimized wind speeds and stabilized the EV battery pack environment. Additionally, we modified the installation sequence of a vent valve to allow air escape during cover placement, further reducing pressure differentials. Process trials with 100 assembly cycles showed no complete detachments, only minor displacements that were corrected during bolting.
| Parameter | Original Value | Adjusted Value | Effect on Wind Speed | Detachment Rate |
|---|---|---|---|---|
| Robot Speed | 500 mm/s | 125 mm/s | Decreased by ~60% | Reduced to 0% |
| Drop Height | 5.5 mm | 2.5 mm | Decreased by ~55% | Reduced to 0% |
| Vent Valve Installation Timing | Before Cover Placement | After Cover Placement | Reduced Internal Pressure | Eliminated Displacements |
From a design perspective, while the original sealing structure met sealing performance requirements for the EV battery pack—with a maximum gap of 1.2 mm under worst-case tolerances, less than the sealing ring’s minimum cross-sectional diameter of 1.7 mm—the unilateral constraint of the dovetail groove offered limited gripping force. Using finite element analysis (FEA), we calculated the gripping force $F_g$ at the contact points: $$ F_g = \int_A \sigma_n \cdot \mu \, dA $$ where $\sigma_n$ is the normal stress from interference. For the original design, $F_g$ was approximately 0.3 N, which was insufficient to resist disturbances during assembly of the EV battery pack. To enhance stability, we redesigned the sealing ring by increasing the cross-sectional diameter from 1.78 mm to 2.4 mm and reducing the inner diameter from 26.7 mm to 25 mm, with a corresponding groove depth adjustment. This increased the interference fit, boosting the gripping force to 2.7 N, as per revised FEA: $$ F_g_{\text{new}} = k \cdot \delta $$ where $k$ is the stiffness derived from material properties and geometry, and $\delta$ is the interference amount. The new design maintained密封 performance with a compression ratio within 15-30% and passed气密 tests for the EV battery pack. Prototype testing confirmed no detachments over 100 assembly cycles.
The combination of process adjustments and design optimization resolved the sealing ring detachment issue in the EV battery pack. Post-implementation, we monitored 1,386 units with zero detachment occurrences, eliminating the need for rework and ensuring smooth production flow. From a cost perspective, this saved approximately 2.3 million USD across the vehicle platform, based on reduced rework labor, material waste, and potential recall avoidance. The EV battery pack now reliably meets密封 standards, enhancing overall vehicle safety and durability.
| Factor | Before Solution | After Solution | Savings |
|---|---|---|---|
| Detachment Rate | 1.9% | 0% | Eliminated rework for 1,386+ units |
| Rework Time per EV Battery Pack | 2 hours | 0 hours | Saved ~2,772 labor hours |
| Material Cost per Rework | $50 | $0 | Saved ~$69,300 in parts |
| Potential Recall Costs | High risk | Negligible risk | Avoided up to $2.2 million in liabilities |
| Total Estimated Savings | – | – | ~$2.3 million |
In conclusion, sealing ring detachment in EV battery packs is a multifaceted issue that requires systematic analysis of materials, processes, and design. Through this first-hand experience, we demonstrated that工艺 parameter tuning—such as reducing robot speeds and drop heights—can mitigate environmental disturbances, while design enhancements like increasing sealing ring dimensions can improve gripping forces without compromising密封 integrity. For future EV battery pack developments, we recommend early consideration of sealing ring stability in unilateral constraint designs, incorporating FEA for gripping force evaluation, and validating process parameters during pilot production. Additionally, regular monitoring of production metrics can preempt similar issues. By sharing these insights, we aim to contribute to the robust and safe design of EV battery packs, supporting the automotive industry’s transition to electrification.
To further generalize, the sealing performance of an EV battery pack can be modeled using the contact pressure distribution $P(x)$ along the sealing interface: $$ P(x) = P_0 \cdot e^{-\alpha x} $$ where $P_0$ is the initial pressure from compression, and $\alpha$ is a decay constant dependent on material viscoelasticity. This emphasizes the need for consistent compression across the EV battery pack seal. Moreover, statistical quality control methods, such as process capability indices $C_p$ and $C_{pk}$, can be applied to monitor sealing ring installation in EV battery pack assembly: $$ C_p = \frac{USL – LSL}{6\sigma} $$ where $USL$ and $LSL$ are specification limits for sealing ring position, and $\sigma$ is process standard deviation. Maintaining $C_{pk} > 1.33$ ensures robust production for EV battery packs.
In summary, the EV battery pack sealing system is critical for safety, and proactive management of design and process factors can prevent detachment failures. This experience underscores the importance of interdisciplinary collaboration in solving EV battery pack challenges, paving the way for more reliable electric vehicles.