The Challenge
An emergency pressure release valve in an electric motor’s battery system was consistently failing at the center due to a structurally weaker section. Despite increasing part thickness and adding multiple ribs, failures persisted. This weakness caused deformation under high gas pressure, leading to the plunger sticking in its housing. If the pressure could not be released, the battery risked catastrophic failure
Background
The valve plate was prone to bulging at the middle when exposed to gas pressure from the battery pack. This deformation created sidewall collapse around the plunger hole, trapping the plunger and preventing pressure release. A more robust solution was required to prevent deformation, ensure reliable venting, and maintain safety under extreme operating conditions.
The Solution
Goken developed a redesigned pressure release valve integrating a metal wire loop using insert molding technology. This design significantly improved the structural rigidity of the valve plate without adding excessive weight. The process involved:
- Integration of a Metal Wire Loop for Structural Reinforcement
- Incorporated a precision-engineered metal wire loop into the plastic molding design to
provide additional tensile and bending strength. - Positioned the wire to reinforce the weakest section of the valve plate, directly countering bulging under high gas pressure.
- Optimized wire thickness and shape to maximize strength without adding unnecessary mass or affecting assembly tolerances.
- Material Upgrade for Enhanced Mechanical Properties
- Transitioned from PP-GF 25 (25% glass fiber-reinforced polypropylene) to PP-GF 35 (35% glass fiber-reinforced polypropylene) to achieve greater stiffness, creep resistance, and dimensional stability.
- Improved thermal resistance to ensure material performance remained consistent under battery operating temperatures and rapid pressure spikes.
- Precision Mold Design with Cavity Cutouts for Wire Placement
- Developed specialized cavity features in the injection mold to accurately locate and secure the wire loop during the molding process.
- Ensured that the molten PP-GF material encapsulated the wire completely, creating a permanent bond and preventing displacement during cooling.
- Applied tooling tolerances tight enough to maintain positional accuracy of the reinforcement wire, ensuring repeatability in production.
- Iterative Design Optimization through CAD and Simulation
- Used FEA (Finite Element Analysis) in CATIA to simulate stress distribution, deformation patterns, and potential failure points under high-pressure load cases.
- Performed multiple design iterations to refine geometry around the plunger hole and mounting points, balancing structural integrity with manufacturability.
- Adjusted reinforcement placement, rib patterns, and wall thicknesses to achieve the best combination of strength and weight.
- Prototype Validation and High-Pressure Testing
- Manufactured prototype parts using production-intent molds and materials.
- Subjected components to simulated battery venting pressure cycles to confirm real-world performance.
- Verified that deformation was eliminated, plunger operation remained smooth, and no structural cracks occurred even under extreme test loads.
The Outcome
The new insert-molded wire loop design successfully eliminated deformation at the valve’s center, preventing plunger sticking and ensuring consistent pressure release. The solution delivered:
- Structural Integrity Restored — Eliminated center deformation of the valve plate, preventing plunger sticking and ensuring reliable pressure relief.
- Strength Without Weight Penalty — Achieved significant stiffness improvement while keeping the part lightweight for efficiency and cost-effectiveness.
- Safety Risk Reduction — Maintained consistent function under extreme gas pressure, mitigating the risk of catastrophic battery failure.
- Extended Component Lifespan — Improved fatigue resistance and reduced failure rates in long-term use.
- Manufacturing Repeatability — Design and mold improvements ensured consistent quality across mass production runs.
This innovative approach not only met the stringent safety requirements for electric vehicle battery systems but also provided a repeatable, cost-effective manufacturing solution that could be applied to other high-pressure plastic components.
