Monolithic component FR-TPU Dust Cover Molding for NEV Charging Ports

The Challenge

A charging-port dust cover protects the connector of a new-energy vehicle from dust, water, and casual contact when the vehicle is not charging. The part had to be flame-retardant, flexible, and weather-resistant, and it had to do all of that with no assembled seams that could leak. The cover was molded from a custom polyether-based flame-retardant thermoplastic polyurethane (FR-TPU) rated UL94 V-0, a halogen-free flame class where burning stops within 10 seconds with no flaming drips.

A monolithic part replaced a multi-part gasket assembly. The previous approach used a separate cover plus a bonded gasket, which introduced a seam and an assembly step and a place for water to find a path. Molding the cover in one FR-TPU shot removed the seam and the bond, but it put the entire sealing and flexibility requirement onto a single elastomeric part that had to hold its shape and its seal through years of outdoor weathering. The program tolerance was ±0.05 mm on the sealing and locating features.

Material processing was the technical hurdle. FR-TPU is a moisture-sensitive elastomer that must be dried before molding, and it is processed at a lower melt than engineering plastics with careful temperature control to avoid degradation of the polyether backbone and the flame-retardant package. The durometer and the V-0 rating both had to be verified per batch, because a process drift could soften the part or change its burn behavior without changing its appearance.

The program was a high-volume automotive engagement. The client was a leading Chinese NEV manufacturer at Tier-1 level, the volume was 500,000-plus units per year, and the schedule ran 6 weeks from design-for-manufacture to start of production. The single-shot tool and process had to be correct at SOP, because a sealing or flame-rating defect at half a million units a year is a field campaign, not a rework.

Safety and durability at the charging port are non-negotiable. The cover is the first line of defense against dust and water at a high-voltage charging interface, and a seam or a lost seal is both a functional and a safety concern. At 500,000-plus units per year, the monolithic part had to be right at start of production, because a sealing or flame-rating defect at that volume is a field campaign rather than a rework.

The flame rating had to be held through production, not just at qualification. UL94 V-0 behavior depends on the FR-TPU compound and the process staying within window; a melt-temperature or moisture drift could change the burn behavior without changing appearance. The 6-week DFM-to-SOP window meant the durometer and V-0 controls had to be specified and verified per batch from the first shot.

A monolithic seal removes the weak point but raises the bar. By molding the cover and its seal in one FR-TPU shot, the program eliminated the bonded gasket seam that water exploits, but it put the entire sealing requirement onto a single elastomeric part that had to hold shape and seal through years of outdoor weathering. The ±0.05 mm sealing and locating features had to be held by a compensated mold on a flexible material.

FR-TPU processing is exacting. The custom polyether-based compound is moisture sensitive and must be dried before molding, then processed within a safe melt and mold-temperature window so the polyether backbone and the flame-retardant package are not degraded. A drift changes the durometer or the UL94 V-0 behavior without changing appearance, so the process had to be locked and verified per batch from the first shot of the 500,000-unit run.

The program also had to respect the charging system. The cover located into the NEV charging port where its seal and its snap decided ingress protection and user feel, so the molded dimensions had to hold relative to the port, not just to the cover drawing. A cover perfect in isolation but off at the seat would still leak, so the ±0.05 mm sealing and locating features were managed against the whole charging interface.

The Solution

We replaced the multi-part gasket assembly with a single FR-TPU shot so the cover and its seal were one monolithic part with no bonded seam to leak. The part geometry was designed so the flexible polyether-based TPU both snapped over the port and sealed it, and the ±0.05 mm sealing and locating features were held by a compensated mold.

Material control protected the specification. The custom FR-TPU was dried to the correct moisture before molding and processed within its safe melt and mold-temperature window so the polyether backbone and the flame-retardant additives were not degraded. The durometer and the UL94 V-0 rating were verified per batch, confirming both the flexibility and the flame behavior of the shipped material.

The tool was built for a clean single-shot part. Gate and vent placement prevented burn and short shots in the elastomer, and the mold was cut to the compensated geometry so the sealing land landed on the ±0.05 mm target after shrink. Ejection was tuned to avoid witness marks on the visible and sealing surfaces.

The 6-week DFM-to-SOP window was met with a validated tool and locked process. First-article inspection confirmed the dimensions and the seal, and the flame rating and durometer were released per batch so the part could enter start of production at the 500,000-plus-unit yearly volume.

Inspection verified both the seal and the spec. First-article measurement confirmed the ±0.05 mm sealing and locating features, and the UL94 V-0 rating and durometer were checked per batch so the flame behavior and flexibility shipped as specified. The single-shot tool was verified to produce a clean monolithic part with no seam.

The tool and process were released to SOP for the 500,000-unit load. The FR-TPU was dried and processed within its safe window on a locked setup, and the documented process allowed a repeatable second tool if the program scaled. Lot records supported traceability for the automotive charging application.

We controlled the compound and the seal together. The FR-TPU was dried and processed within its safe window on a locked setup, and the geometry was designed so the flexible TPU both snapped over the port and sealed it, holding the ±0.05 mm features from a compensated mold. The single-shot tool produced a clean monolithic part with no seam to leak.

We verified both the seal and the spec per batch. First-article measurement confirmed the sealing and locating features, and the UL94 V-0 rating and the durometer were checked per batch so flame behavior and flexibility shipped as specified. The tool and process were released to SOP for the 500,000-unit load inside the 6-week DFM-to-SOP window, with lot records for traceability.

We qualified the cover against the charging port. The sealing and locating features were measured so the monolithic FR-TPU part snapped over and sealed the port as designed, and the per-batch V-0 and durometer checks held that relationship across 500,000-plus units per year. The 6-week DFM-to-SOP window delivered a tool and process the NEV Tier-1 could release to production.

The Result

The program delivered monolithic, UL94 V-0 dust covers with no seam leaks, molded from custom polyether-based FR-TPU and held to ±0.05 mm on the sealing and locating features. Replacing the multi-part gasket assembly with a single shot removed the leak path and the assembly step while keeping the flexibility and weather resistance the charging port required.

The leading Chinese NEV Tier-1 customer took the part to start of production inside the 6-week DFM-to-SOP window, and the 500,000-plus-unit yearly volume ran from a validated single-shot process. Flame rating and durometer were verified per batch across the production run.

First-pass yield met the program target across the 500,000-plus-unit yearly volume, and the monolithic UL94 V-0 cover held its seal with no seam leaks, which is what protects the charging port from dust and water ingress. Replacing the multi-part gasket assembly removed a failure path and an assembly step.

The leading Chinese NEV Tier-1 customer took the part to start of production inside the 6-week DFM-to-SOP window, with per-batch flame-rating and durometer verification. The validated single-shot approach gave a baseline for follow-on charging-port components using the same FR-TPU discipline.

The charging-port cover met the ingress and safety requirement at volume. Monolithic, UL94 V-0, and held to ±0.05 mm with no seam leaks, it protected the port from dust and water while keeping the flexibility the application needs, and replacing the multi-part gasket assembly removed a failure path and an assembly step. The 500,000-plus-unit yearly volume ran from a validated single-shot process.

The leading Chinese NEV Tier-1 customer took the part to start of production inside the 6-week window, with per-batch flame-rating and durometer verification and the traceability the automotive charging application requires. The validated FR-TPU approach gave a baseline for follow-on charging-port components and a documented basis for the V-0 and sealing claims the program depends on.

The dust cover performed as a charging-system component. By holding the ±0.05 mm sealing and locating features with a monolithic UL94 V-0 seal relative to the port, it gave the 500,000-plus-unit yearly volume the ingress protection the interface required, and the start-of-production release carried per-batch verification and the traceability the automotive application demands.