Project Background
EV charging ports endure severe environmental stress daily. While a dust cap appears simple, it serves as a highly critical safety barrier. It must survive over a decade of continuous UV exposure and temperature shifts. It must also handle repeated mechanical stress while maintaining a strict waterproof seal.
We recently partnered with a Leading Chinese NEV Pioneer to manufacture these essential panels, bezels, and covers. The final part is an EV charging port dust cover featuring a Monolithic construction with an attached anti-loss tether. We utilized a custom modified FR-TPU to deliver a soft-touch, high-resilience component. This specific tpu material guarantees instant structural recovery. It maintains a Low compression set after thousands of physical deformations.
Our core engineering objective was to eliminate the mechanical failure points common in traditional multi-part assemblies. Through controlled automotive injection molding, we executed a highly stable, integrated one-piece design. We also applied a fine-grain VDI matte texture with subtle speckling to the exterior surface. This specific finish provides a reliable, non-slip grip for the end-user. This integrated manufacturing approach successfully met strict UL fire safety standards while entirely removing secondary assembly steps.
The Challenge
The client required a soft-touch cover that recovers its shape instantly after severe mechanical deformation. However, blending heavy flame retardant (FR) additives into the tpu material fundamentally increases Shore hardness and restricts polymer elasticity. Our primary technical friction was balancing this chemical matrix to maintain a remarkably low compression set.
If the polymer takes a permanent set under repeated pressure, the physical seal degrades. This structural failure would immediately destroy the critical IP67 waterproof rating and expose high-voltage charging components to moisture ingress.
A smooth exterior surface fails entirely in wet automotive environments. The component required a strictly defined, friction-rich VDI texture to provide a secure user grip. Molding this fine-grain matte finish while compounding UV-stabilizing additives—which present as subtle specks—introduced severe process instability.
We had to rigidly control mold temperatures and cavity pressures during our tpu injection molding services. This closed-loop precision was mandatory to completely eliminate surface ghosting, texture wipe, and uneven cooling rates.
The physical geometry created a massive conflict for internal material flow. In this monolithic design, the abrupt transition from the thick main cap to the thin tether acts as a critical stress concentration point. We optimized the injection mold design and making to push the polymer front through the deep internal ribs and bosses simultaneously.
Filling the entire length of the tether without generating weld lines or trapped gas was our final hurdle. This flaw-free internal structure preserves the ultimate tensile strength of the polymer. It ensures the integrated strap will not snap or shear under daily mechanical loads.
Kravzik’s Solution
We engineered a custom polyether-based FR-TPU to solve the resilience-flame retardancy paradox. This specific tpu material formulation guarantees a low compression set. The cap feels soft but snaps back instantly to maintain a tight structural seal. The subtle surface specks are an intentional visual feature. They are the physical result of halogen-free flame retardant particles dispersed within the polymer matrix to achieve strict UL94 V-0 compliance.
We applied a highly controlled VDI matte texture directly to the tool cavity to create the required non-slip grip. Pushing this viscous polymer through the complex internal ribs demanded a multi-point balanced gating strategy. This internal injection system equalizes cavity pressure and completely prevents short shots. During our injection mold design and making process, we held strict machining tolerances of ±0.05mm to guarantee reliable daily operation.
Our integrated manufacturing model allowed us to mold the cap and tether as a single, monolithic unit. This one-piece design completely eliminates the need for vulnerable secondary assembly joints. The integrated tether easily withstands high-frequency bending and dynamic loads. It operates under severe mechanical stress without risking separation or fatigue failure at the base interface.
Production Control
We utilize closed-loop control to stabilize the mass production of the complex internal ribs. By monitoring injection cavity pressure in real-time, we maintain high Cpk values and strict ±0.05mm tolerances across every batch. This data-driven approach ensures the high-viscosity FR-tpu material completely fills the mold without creating short shots or inducing flash at the tether interface.
We validate physical performance through rigorous mechanical and thermal cycling tests. To verify a low compression set, we compress the component for 72 hours; it must fully recover its original geometry within seconds to guarantee the IP67 waterproof seal remains intact. Furthermore, the monolithic tether undergoes 10,000+ opening/closing cycles, where we actively pull and bend the strap at extreme temperatures (-40°C to 120°C) to ensure no tearing occurs at the structural root.
Every production run undergoes mandatory surface friction testing to confirm the VDI matte texture meets precise non-slip parameters. We log all dimensional and material data in strict compliance with IATF 16949 standards. This validation framework provides absolute traceability from the raw material compounding lot to final delivery.
The Outcome & Metrics
The project successfully transitioned from Design for Manufacturing (DFM) to full-scale Start of Production (SOP). By utilizing monolithic integrated molding in our automotive injection molding process, we reduced the client’s secondary assembly complexity. This streamlined approach ensured consistent, repeatable quality across high-volume production batches.
In field deployment, the component maintains a 0% failure rate. The integrated tethers exhibit zero fatigue cracking after thousands of user interactions. Furthermore, the low compression set of the custom tpu material ensures the cap retains its quick structural recovery. This high resilience guarantees a tight, reliable seal against environmental moisture, regardless of the climate. The final metallic-speckled VDI texture directly aligns with the rigorous aesthetic standards of modern electric vehicles.
Technical Specifications Summary
- Material Type: Polyether-based Modified FR-TPU.
- Fire Safety: UL94 V-0 compliant (Halogen-free).
- Ingress Protection: IP67 (Validated after thermal aging).
- Surface Finish: VDI Fine-Grain Matte (Anti-slip / Non-glare).
- Durability: Passed 10,000+ flex cycles without deformation.
Our integrated manufacturing model delivers a distinct “Under One Roof” advantage. By managing both the complex material compounding and the precision injection mold design and making internally, we significantly lowered the client’s Total Cost of Ownership (TCO). This strategy eliminated supply chain fragmentation, ultimately providing a stable, high-performance physical barrier for the next generation of NEVs.
