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At Munro & Associates, the teardown process is more than just disassembly—it’s a forensic dive into design logic, cost efficiency, and manufacturing intent. Our latest focus is the Kia EV9 door teardown, which reveals a complex interplay of material choices, design trade-offs, and manufacturing strategies that differ significantly from competitors like the Tesla Cybertruck and Hyundai Ioniq 5.
Here we unpack every major decision Kia made in its EV9 door design—and what it tells us about engineering priorities in the electric SUV space.
Steel vs Aluminum: The Weight-Cost Tradeoff
The EV9 uses a stamped steel door, weighing around 20 kilograms. That’s nearly double the weight of the 11 kg aluminum door found in the Rivian R1T. While heavier, steel is cheaper and easier to manufacture using traditional stamping and hemming methods.
The steel outer skin is hemmed around the inner door structure—unlike the Cybertruck’s stainless steel door, which required laser welding due to its material’s inability to bend 180 degrees. This traditional steel choice simplifies manufacturing but comes at the cost of added vehicle weight—an important consideration for EV range and battery load.
Kia’s decision reflects a clear cost vs. performance strategy. While aluminum saves weight and benefits range, it demands higher tooling and assembly costs. By contrast, steel delivers a sturdier feel and familiar assembly methods. Ironically, OEMs often strive for lightweight doors, only to add steel weights later to achieve that satisfying “clunk” when closing—defeating the very weight-saving efforts made upstream.
Anti-Intrusion Beams: Tube vs Stamped
Crash protection inside the door reveals another cost-conscious choice. The EV9 uses a tubular steel beam—a basic, low-cost anti-intrusion component. In contrast, the Hyundai Ioniq 5 employs a stamped steel beam, which is potentially lighter but more expensive to manufacture due to the tooling involved.
Stamped beams allow better space utilization inside the door cavity but require added investment. Kia’s approach balances acceptable safety performance with minimized part complexity—fitting for a mainstream, large-format electric SUV like the EV9.
Modular Assembly: Front vs Rear Door Differences
One of the more intriguing elements is how the front and rear doors differ internally. The front door uses an integrated door module where handles are molded directly into the injection-molded plastic—streamlining assembly and reducing labor time.
Oddly, the rear door lacks this module and instead features a more traditional blind install method. The window guide is bolted directly through the steel structure—slower and more labor-intensive.
This disparity suggests modular reuse vs. vehicle-specific compromise. The front door system might be a carryover from other Kia platforms, while the rear door—unique to this three-row SUV—was perhaps deprioritized due to lower volume. It’s a classic example of OEMs allocating design investment where it offers the highest ROI.
Integration Wins: A Smarter Window Track Design
In the EV9, Kia cleverly molds the window track rail directly into the door module’s plastic panel. This eliminates the need to bolt or screw additional steel rails as seen in the Tesla Cybertruck. Instead, only cables and minor retainers are added afterward—reducing parts count and installation time.
Tesla’s design, by contrast, attaches the steel track separately, increasing labor and complexity. The rationale appears structural—Cybertruck doors leave more vertical clearance above the module, necessitating extensions. But the critique remains: why not design both door and module in concert? The missed integration opportunity adds cost and inefficiency that Tesla’s vertically integrated structure could have avoided.
Glass Mounting: A Study in Cost and Labor
Glass attachment also varies. While some vehicles like the F150 use simple snap-in plastic clips, the EV9 employs a combination of threaded and clamp-style attachments. This setup is more secure but increases labor time and hardware expense.
Given that the EV9 uses a full-frame door, such robust glass attachment isn’t strictly necessary. Kia might revisit this in future iterations to reduce cost and simplify assembly.
Exterior Trim: Stylish but Pricey
The EV9’s lower door cladding is another standout—though for different reasons. Composed of multiple layers including high-gloss finishes, matte molded color, and painted inserts, this decorative component is expensive to produce and easily damaged.
Munro’s take: it’s an over-engineered aesthetic flourish. The steel door underneath is structurally sufficient, and the added trim brings minimal functional value. Once damaged, these complex cladding assemblies become non-repairable junk—bad for cost and sustainability.
Interior Trim: Taco Bell Interiors and Cost Stacking
Kia’s door panel construction follows an industry-standard formula: thermal-formed vinyl upper, soft-touch inserts, injection-molded lower plastics. It’s what Sandy affectionately calls the “Taco Bell interior”—same ingredients, different combinations.
Yet deeper inspection reveals mixed attachment methods. Some parts are screwed and welded—a sign of staging the panel into a fixture with light pre-attachment before robotic welds finish the job. By contrast, Tesla’s Model Y doors are entirely fixture-welded—faster but requiring more upfront investment in tooling and fixturing.
It’s another classic trade-off: Kia opts for flexibility and simplicity over high capital expenditure.
Material Interfaces: Foam, Vinyl, and Assembly Detail
Foam-backed vinyl is vacuum-formed into complex contours, with tiny vent holes allowing trapped gases to escape during molding. Adhesive primer is applied to the plastic panel substrate—not the foam—enabling clean, durable adhesion.
Still, small areas like sharp corners often show wrinkles or minor tearing, where the material was stretched and heated to lock around a contour. These imperfections are part of the challenge in balancing visual appeal with manufacturability.
Screws vs Welding: Hidden Costs of Fasteners
One of the teardown’s most insightful takeaways? The real cost of a screw isn’t the screw—it’s the labor and time to place it. Staging screws at workstations, grabbing guns, navigating between points, all add up.
In contrast, robotic welding—in a single pass—saves enormous cycle time. Yet the initial fixture cost for welding is high. That’s why Kia blends approaches: screw where flexibility is needed, weld where mass production permits.
Final Thoughts: Simplicity Is the Real Engineering Challenge
The Kia EV9’s door systems show a mix of clever cost-saving design and legacy carryover. Kia opts for steel, molded integration, and hybrid assembly methods—tailoring complexity based on expected volume and return.
As Sandy often notes, complexity is not impressive. Simplicity—real simplicity—takes more work, more thought, and often more collaboration between teams.
The EV9 door teardown offers valuable lessons in cost engineering, design for manufacturing, and the ongoing challenge of balancing performance, manufacturability, and aesthetic ambition.
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