The relentless drive towards electrification in the automotive industry places immense importance on the reliability and durability of electronic control units (ECUs) and power electronics. These components, the neural center of every battery EV car, require robust protection from environmental hazards, mechanical shock, and vibrational stresses encountered during vehicle operation. Injection-molded protective covers are pivotal in fulfilling this role, offering a blend of structural integrity, lightweight design, and design flexibility essential for modern battery EV car architectures. This article details the comprehensive development process for a large, complex electronic protective cover, focusing on a design philosophy guided by the critical analysis and control of fiber orientation within glass-fiber reinforced thermoplastics.
The component in question is a structural housing designed to shield sensitive electronics in a battery EV car. Its primary function is to provide a secure, enclosed environment, safeguarding against physical impacts, dust, moisture, and thermal fluctuations. As a non-aesthetic, internal part, its design prioritizes functionality, leading to a highly complex geometry. The cover features numerous reinforcing ribs, mounting bosses with screw holes, and several large through-holes for connectors and ventilation. A prominent trapezoidal opening and elongated reinforcing ribs, some exceeding 200 mm in length, characterize its challenging form. This complexity directly translates into significant challenges for mold design, including deep cavities, intricate core mechanisms, and a heightened risk of warpage due to non-uniform material behavior. The selection of material is therefore paramount.
For this application in a battery EV car, a 20% glass fiber reinforced polypropylene (20% GF/PP) composite with a UL94 V-1 flame-retardant rating was chosen. This material offers an excellent balance of mechanical properties, weight savings, and cost-effectiveness crucial for battery EV car components. The incorporation of glass fibers significantly enhances tensile strength, flexural modulus, and dimensional stability compared to unfilled PP. However, this enhancement introduces a critical processing variable: fiber orientation. During injection molding, shear forces within the melt cause the glass fibers to align preferentially along the flow direction. This induced anisotropy profoundly affects the final part’s mechanical performance, shrinkage behavior, and susceptibility to warpage and surface defects like “fiber read-through.” A core objective in this project was to harness simulation tools to predict and optimize this orientation to meet the stringent stiffness and reliability requirements of a battery EV car component.
Part Analysis and CAE-Driven Gating Optimization
The initial phase involved a detailed structural and manufacturability analysis. The part’s maximum dimensions are approximately 441.8 mm x 351.3 mm x 262.1 mm, with a mass of 1.93 kg, classifying it as a large, complex structural component. The presence of deep ribs and bosses creates areas of high shear and potential sink marks. The primary challenge was to ensure complete fill, minimize residual stress, and most importantly, control the orientation of glass fibers to achieve predictable and uniform mechanical properties, especially in critical load-bearing sections like the long ribs and mounting points.
Moldflow simulation software was employed to transition from an experience-based to a data-driven design approach. The first step was gate optimization. The software’s automatic gate location analysis suggested an ideal point (G0) within the central trapezoidal opening—a location impractical for tooling. Therefore, three alternative gating strategies were devised and simulated:
- Scheme 1: A single side gate (G1) near the suggested location.
- Scheme 2: A single direct gate (G2) on the top surface.
- Scheme 3: A dual-gate system utilizing both G1 and G2 simultaneously.
The processing parameters for simulation were set to a melt temperature of 230°C, a mold temperature of 50°C, a holding time of 20 s, and a cooling time of 25 s. The comparative results are summarized in the table below.
| Parameter | Scheme 1 | Scheme 2 | Scheme 3 (Selected) |
|---|---|---|---|
| Filling Time (s) | 2.998 | 3.317 | 2.800 |
| V/P Switch Pressure (MPa) | 22.83 | 27.66 | 20.26 |
| Holding Pressure (MPa) | 18 | 22 | 16 |
| Clamping Force (t) | 220 | 260 | 200 |
| Sink Mark Estimate (mm) | 0.3427 | 0.3300 | 0.3444 |
| Total Warpage (mm) | 2.040 | 2.001 | 1.719 |
| Fiber Orientation Tensor (Max) | 0.9899 | 0.9994 | 0.9987 |
| Avg. Tensile Modulus (1st Principal Dir.) (MPa) | 5,171.38 | 5,130.97 | 5,191.4 |
| Avg. Tensile Modulus (2nd Principal Dir.) (MPa) | 2,865.11 | 2,870.06 | 2,874.35 |
While all three schemes were feasible, Scheme 3 demonstrated clear advantages for a high-reliability battery EV car part. It achieved the shortest fill time, lowest injection and holding pressures, and the smallest clamping force, promoting a more stable and energy-efficient process. Crucially, it resulted in the least warpage (1.719 mm). The analysis of fiber orientation was decisive. The fiber orientation tensor, a value between 0 and 1 indicating alignment with the flow direction, was high for all schemes. However, examining the surface layer orientation cloud plots revealed critical differences:
- Scheme 1: The weld line was located directly on a critical mounting boss. The fiber orientation around this weld was chaotic and not aligned with the expected load direction during assembly, creating a potential weak point.
- Scheme 2: Fibers in crucial lower support areas were oriented perpendicular to the primary impact direction, potentially compromising local strength.
- Scheme 3: The weld line was shifted away from high-stress mounting points to a less critical area near a corner of the trapezoidal opening. Furthermore, the fiber orientation near the G1 gate showed a favorable radial pattern aligned with the flow, and the overall distribution of orientation values (0.74–0.98) was the most uniform. This translated into superior predicted mechanical properties, as evidenced by the highest average tensile moduli in both principal directions.
Consequently, Scheme 3 was selected. The final feed system incorporates a hot-runner with two valve gates. Gate G1 feeds into a cold-runner extension forming a fan gate, while G2 is a direct pinpoint valve gate. This configuration optimally balances flow, minimizes orientation-induced anisotropy, and ensures the structural performance required for a battery EV car enclosure.
Advanced Mold Design for Complex Demolding
The part’s geometry necessitated a highly sophisticated mold structure with actions on both the stationary (A) and moving (B) plates. A single-cavity layout was adopted due to the part’s size and complexity.
Stationary (A) Plate Mechanisms
1. Core-Pulling Mechanism: Two holes on the upper left side of the part required a side-action from the A-plate. A hydraulic cylinder, mounted externally, drives a wedge which engages with a T-slot in a sliding block assembly. This provides a reliable and compact solution for a limited-stroke action, with position sensors ensuring precise control integrated into the battery EV car part production cycle.
2. Ejection System: Given the extensive ribbing and bosses on the A-side cavity, a positive ejection system was mandatory to prevent the part from sticking. A novel delayed ejection system was designed. It combines the constant force of springs with a positive mechanical pull from tie rods during the initial, high-friction phase of mold opening. A specially designed delayed opening mechanism ensures disengagement. The mechanism consists of a pivoting latch plate and a fixed pin on the A-plate. Upon opening, the pin’s斜面 (inclined plane) gradually retracts the latch over a set distance (e.g., 7 mm), at which point it releases the tie rod. From there, only the springs drive the ejection plate forward. During mold closing, the B-plate contacts return pins and the tie rods, positively resetting the entire system. This dual-phase approach guarantees reliable ejection for the deep-cavity A-side.
Moving (B) Plate Mechanisms
1. Complex Core-Pulling: The large trapezoidal opening at the front of the part presented a major challenge. The core responsible for this feature has a significant surface area in contact with the plastic, resulting in a substantial demolding force. The required force was calculated to validate the mechanism design. The demolding force \( F \) can be estimated by:
$$ F = \frac{8E \varepsilon t l}{1 – \mu} \times \frac{f – \tan \alpha}{1 + f \times \sin \alpha \times \cos \alpha} $$
Where:
\( E = 3000 \, \text{MPa} \) (Elastic Modulus),
\( \varepsilon = 0.012 \) (Shrinkage),
\( t = 3.8 \, \text{mm} \) (Wall thickness),
\( l = 130 \, \text{mm} \) (Engagement length),
\( \mu = 0.43 \) (Poisson’s ratio),
\( f = 0.3 \) (Friction coefficient),
\( \alpha = 5^\circ \) (Draft angle).
This calculation yielded \( F \approx 52 \, \text{kN} \), indicating that a standard angled-lift (spring-loaded) or even a hydraulic cylinder alone might be insufficient or lead to excessive wear on guide components.
An innovative compound-driven mechanism was engineered. It utilizes a powerful hydraulic cylinder as the primary actuator, supplemented by two angled leader pins from the A-plate and a compression spring. During the initial opening, all three elements (hydraulic cylinder, leader pins, spring) work in unison to initiate movement and overcome the high static friction. Subsequently, the cylinder and leader pins complete the long stroke. This design distributes loads, ensures smooth, jerk-free motion, and provides redundancy, which is critical for the reliable mass production of battery EV car components. Position sensing on the hydraulic cylinder enables precise sequencing.
2. Ejection System: To ensure balanced ejection from the B-side and prevent distortion of the long, thin ribs, a combination of standard ejector pins and large ejector blocks was implemented. The blocks provide support over a larger area, reducing contact pressure. A dedicated cooling channel was routed through the ejector plate, push rods, and into the large ejector blocks to maintain thermal equilibrium between the block and the core, preventing differential expansion that could cause binding or scoring.
Mold Operation Sequence and Control
The interplay of multiple actions required a meticulously planned sequence, integrated with the injection molding machine’s (IMM) programmable logic controller (PLC):
- Mold Closing: All core-pulling mechanisms must be confirmed in their forward (molding) position via sensor signals before the IMM allows high-pressure clamp.
- Injection, Holding, Cooling.
- Mold Opening Sequence:
- Phase 1: The mold opens slowly. The A-plate ejection system is held back by the delayed latch mechanism for the first 7 mm, allowing the part to break free from the A-side cavity.
- Phase 2: After 7 mm, the latch releases. The mold continues opening. Simultaneously, the B-side hydraulic cylinder for the large core and the A-side hydraulic cylinder for the small core are activated, synchronized with the leader pins.
- Phase 3: Once all core-pull actions are complete and confirmed by sensors, the B-plate ejection system advances to demold the part.
- Part Removal, Mold Closing: Ejection retracts, then core-pulling mechanisms return, with the IMM only proceeding to close once all moving components are confirmed home.
This sensor-integrated, sequenced control is essential for protecting the expensive mold and ensuring consistent quality for every battery EV car protective cover produced.
Experimental Validation and Production
Following mold construction, initial trials produced parts that were subjected to rigorous stiffness testing, a key performance indicator for a structural battery EV car component. The test simulated operational loads by applying forces in specific zones (Zone I and Zone II as defined in the analysis). A 300 N load was applied in the -Z direction on Zone I, the +Z direction on Zone I (via a 30.6 kg mass), and at a 45° angle in the XZ plane on Zone II. Displacement was measured using dial indicators. The test was repeated ten times, and the average maximum displacements were recorded and compared against design allowable limits.
| Loading Zone | Direction | Allowable Max. Displacement (mm) | Average Measured Max. Displacement (mm) | Result |
|---|---|---|---|---|
| I | -Z | 0.30 | 0.14 | Pass |
| I | +Z | 2.50 | 2.05 | Pass |
| II | XZ Plane @ 45° | 2.00 | 1.23 | Pass |
The experimental data confirmed that the molded parts, produced with the optimized gating and mold design, comfortably met all stiffness specifications. The measured values had a clear safety margin relative to the allowable limits, validating the fiber-orientation-guided design approach. The mold has since been deployed for mass production, with feedback confirming stable operation and consistent part quality suitable for integration into battery EV car systems.
Conclusion and Future Perspectives
This project successfully demonstrated the development of a complex electronic protective cover for a battery EV car, where controlling glass fiber orientation was central to achieving target mechanical performance. By leveraging CAE simulation to optimize gate location and process parameters, a molding setup was achieved that promoted favorable fiber alignment, minimized warpage, and ensured structural integrity. The innovative mold design, featuring a compound-driven hydraulic/mechanical core pull, a delayed A-side ejection system, and sensor-controlled sequencing, reliably handles the part’s complexity.
Future work will focus on deepening the simulation fidelity through multi-physics, multi-scale modeling. This involves coupling micromechancial models of fiber orientation and distribution with macroscopic structural finite element analysis to more accurately predict the anisotropic mechanical behavior under real-world battery EV car loading conditions. Furthermore, integrating in-mold sensors (for pressure, temperature) with a digital twin of the process could enable predictive quality control and adaptive process optimization, pushing towards zero-defect manufacturing for critical battery EV car components. The methodologies established here—prioritizing material anisotropy in design—provide a robust framework for engineering high-performance, fiber-reinforced plastic parts in the evolving automotive landscape.