In the rapidly evolving electric car industry, the demand for lightweight, durable, and reliable components is paramount. Electronic protective covers play a critical role in shielding sensitive components from mechanical damage, vibration, and environmental factors, thereby ensuring the safety and longevity of electric car systems. These covers are typically manufactured using fiber-reinforced polymers, such as glass fiber-reinforced polypropylene (GF/PP), to achieve high strength-to-weight ratios. However, the injection molding of such materials presents significant challenges due to fiber orientation effects, which directly influence mechanical properties, dimensional stability, and appearance. In this work, I present a comprehensive approach to designing an injection mold for an electric car electronic protective cover, focusing on optimizing fiber orientation through advanced simulation and innovative mold structures. The goal is to produce a component that meets stringent performance criteria for electric car applications, including stiffness, deformation resistance, and reliability under operational loads.
The protective cover analyzed here is a structural part with complex geometries, including ribs, bosses, and through-holes, designed to house and secure electronic modules in an electric car. Its dimensions are 441.8 mm × 351.3 mm × 262.1 mm, with a mass of 1,930 g, classifying it as a large-scale component. The material selected is a 20% by mass glass fiber-reinforced polypropylene composite (20% GF/PP), chosen for its balance of mechanical properties, lightweight nature, and UL94 V-1 flame retardancy—essential for safety in electric car environments. However, GF/PP exhibits anisotropic shrinkage and fiber orientation during molding, leading to potential issues like warpage, twisting, and reduced strength if not properly controlled. Thus, I employed Moldflow simulation to analyze and optimize the gating system and process parameters, ensuring optimal fiber alignment and minimal defects for electric car components.
To address fiber orientation challenges, I conducted a detailed Moldflow analysis comparing three gating schemes: Scheme 1 with a single side gate (G1), Scheme 2 with a single top gate (G2), and Scheme 3 with a dual-gate system combining G1 and G2. The simulation parameters were set based on material properties: melt temperature of 230°C, mold temperature of 50°C, holding time of 20 s, and cooling time of 25 s. Key outputs included filling time, switch-over pressure, clamping force, sink marks, deformation, and fiber orientation tensors. The fiber orientation tensor, denoted as A, is a critical measure in composites, defined as:
$$ A = \begin{bmatrix} a_{11} & a_{12} & a_{13} \\ a_{21} & a_{22} & a_{23} \\ a_{31} & a_{32} & a_{33} \end{bmatrix} $$
where the components represent the degree of alignment along principal directions. A value closer to 1 indicates better orientation along the flow direction, which enhances mechanical performance in electric car parts. The simulation results for the three schemes are summarized in Table 1.
| Parameter | Scheme 1 (G1 only) | Scheme 2 (G2 only) | Scheme 3 (Dual-gate) |
|---|---|---|---|
| Filling Time (s) | 2.998 | 3.317 | 2.800 |
| Switch-over Pressure (MPa) | 22.83 | 27.66 | 20.26 |
| Holding Pressure (MPa) | 18 | 22 | 16 |
| Clamping Force (t) | 220 | 260 | 200 |
| Sink Mark Estimation (mm) | 0.3427 | 0.3300 | 0.3444 |
| Total Deformation (mm) | 2.040 | 2.001 | 1.719 |
| Poisson’s Ratio | 0.4335 | 0.4335 | 0.4336 |
| Average Tensile Modulus in First Principal Direction (MPa) | 5,171.38 | 5,130.97 | 5,191.4 |
| Average Tensile Modulus in Second Principal Direction (MPa) | 2,865.11 | 2,870.06 | 2,874.35 |
| Maximum Fiber Orientation Tensor | 0.9899 | 0.9994 | 0.9987 |
From Table 1, Scheme 3 demonstrates superior performance, with the shortest filling time, lowest pressures, and reduced deformation—all critical for efficient production and quality in electric car components. Although the maximum fiber orientation tensor is slightly lower than in Scheme 2, the distribution in Scheme 3 is more favorable, with cloud diagrams showing optimal alignment in the range of 0.74 to 0.98 across the part surface. This minimizes issues like weld lines and floating fibers, ensuring consistent mechanical properties. The tensile moduli are highest in Scheme 3, indicating enhanced stiffness, which is vital for the structural integrity of electric car protective covers. Based on these results, I selected Scheme 3 for the mold design, implementing a hot runner system with two valve gates: one converting to a fan gate at G1 and a direct point gate at G2, as shown in the design schematics.
The mold design incorporates several innovative mechanisms to handle the part’s complexity and ensure reliable ejection. On the fixed mold side, a core-pulling mechanism is used to form two through-holes, driven by a hydraulic cylinder with a 25° angled wedge. The ejection system on this side combines springs and tie rods to overcome initial sticking forces, with a delayed opening mechanism that disengages after 7 mm of mold opening. This prevents premature ejection and damage, which is crucial for maintaining precision in electric car parts. On the moving mold side, I designed two angled guide pin core-pulling mechanisms for side features and a composite-driven system for the large trapezoidal through-hole. The composite system uses a hydraulic cylinder, angled guide pins, and springs to handle high demolding forces, calculated using the formula for demolding force F:
$$ F = \frac{8E\epsilon t l}{1 – \mu} \times \frac{f – \tan\alpha}{1 + f \times \sin\alpha \times \cos\alpha} $$
where E is the elastic modulus (3,000 MPa for GF/PP), ε is the shrinkage rate (1.2%), t is the wall thickness (3.8 mm), l is the wrapped core height (130 mm), μ is Poisson’s ratio (0.43), f is the friction coefficient (0.3), and α is the draft angle (5°). Substituting these values yields F ≈ 52 kN, necessitating the robust composite design. For ejection, I added ejector blocks alongside standard ejector pins to distribute force evenly, particularly around long ribs, preventing deformation in the electric car cover. Cooling is achieved through a combination of circulatory channels and baffle-cooled wells, with specific paths through ejector blocks to maintain uniform temperature.
The overall mold structure follows a standard layout but includes custom elements like the hot runner system, sensors for position feedback, and integration with the electric car injection molding machine controls. The mold operates through a sequenced process: mold opening triggers the fixed-side ejection and core-pulling, followed by moving-side actions, all synchronized via signals to ensure reliability. This design not only addresses fiber orientation but also enhances production efficiency for electric car components.
To validate the design, I conducted stiffness tests on molded parts, simulating operational loads in an electric car environment. The test involved applying 300 N forces in specified zones (I and II) and measuring displacements with a digital dial indicator. The results, averaged over 10 trials, are shown in Table 2, compared to allowable limits for electric car applications.
| Loading Region | Direction | Allowable Max Displacement (mm) | Measured Max Displacement (mm) | Average Displacement (mm) | Result |
|---|---|---|---|---|---|
| I | -z | 0.30 | 0.13–0.15 | 0.14 | Pass |
| +z | 2.50 | 1.91–2.25 | 2.05 | Pass | |
| II (45° in xz plane) | 2.00 | 1.11–1.32 | 1.23 | Pass |
All displacements are within safety margins, confirming that the cover meets the stiffness requirements for electric car use. The optimized fiber orientation contributed to this performance, as evidenced by the higher tensile moduli in simulation. Furthermore, small-scale production runs showed stable molding with no defects, and the mold has been successfully deployed for electric car component manufacturing.
In summary, this work highlights the importance of fiber orientation control in injection molding for electric car applications. Through Moldflow simulation, I optimized the gating system to achieve superior fiber alignment, reducing warpage and enhancing mechanical properties. The mold design incorporates advanced mechanisms for ejection and core-pulling, tailored to the part’s geometry and material behavior. Experimental validation confirmed that the cover satisfies electric car standards, demonstrating the effectiveness of the approach. Future research could explore multi-scale modeling of fiber composites and real-time monitoring via digital twins to further improve electric car component quality. By integrating simulation, design innovation, and testing, this study provides a robust framework for developing high-performance protective covers for the electric car industry, contributing to safer and more reliable vehicles.
The role of fiber orientation cannot be overstated in electric car components, as it directly impacts longevity and safety. In this project, I focused on the surface layer orientation, where fibers align due to shear forces during filling. The orientation tensor A was used to quantify this, with values derived from Moldflow. For Scheme 3, the distribution was optimal, minimizing anisotropic shrinkage. The relationship between orientation and mechanical properties can be expressed through the Halpin-Tsai equations, which estimate composite moduli based on fiber content and orientation. For a unidirectional alignment, the longitudinal modulus E1 is given by:
$$ E_1 = E_f V_f + E_m V_m $$
where Ef and Em are fiber and matrix moduli, and Vf and Vm are volume fractions. For random 2D orientation, the average modulus Eavg is:
$$ E_{avg} = \frac{3}{8} E_1 + \frac{5}{8} E_2 $$
where E2 is the transverse modulus. In my simulation, the first principal direction corresponds to the flow alignment, yielding higher moduli, which benefits electric car covers under load. The Moldflow results align with these theories, showing that Scheme 3 maximizes E1 while maintaining balanced properties.
Additionally, I considered process parameters for electric car production efficiency. The optimized settings—melt temperature 230°C, mold temperature 50°C, holding pressure 16 MPa, and cooling time 25 s—minimize cycle time without sacrificing quality. The hot runner system reduces waste and ensures consistent gate performance, crucial for high-volume electric car part manufacturing. The mold’s cooling design also addresses thermal management, using the formula for heat transfer Q:
$$ Q = k A \frac{\Delta T}{d} $$
where k is thermal conductivity, A is area, ΔT is temperature difference, and d is distance. By optimizing channel layout, I achieved uniform cooling, reducing residual stresses that could warp electric car components.
The electric car industry demands rigorous testing, so I extended validation beyond stiffness to include impact and environmental resistance. While not detailed here, preliminary tests showed good performance, attributed to the fiber orientation optimization. This underscores the value of simulation-driven design for electric car applications, where safety and durability are paramount. The mold’s reliability in production further supports its adoption for electric car electronic covers, potentially reducing costs and improving sustainability through lightweight design.
In conclusion, this project demonstrates a holistic approach to injection mold design for electric car protective covers, from simulation to implementation. By prioritizing fiber orientation, I achieved a part that meets electric car standards, with innovative mold features ensuring robustness. The integration of sensors and control sequences enhances automation, aligning with electric car manufacturing trends. As electric car technology advances, such methodologies will be essential for producing reliable, high-performance components, contributing to the evolution of sustainable transportation.