Overmolding Injection Molding in China: Enhancing Engine Front Right Fender Production

In the modern automotive manufacturing industry, there are extremely high requirements for the durability, aesthetics, and cost control of parts. Overmolding injection molding, also known as double-shot injection molding, is an advanced molding technology that effectively improves the comprehensive performance of products by combining different plastic materials. Taking the engine front right fender as an example, this paper delves into the process flow and key points of its overmolding using PP (polypropylene) and TPU (thermoplastic polyurethane), revealing how this technology meets the high standards of the industry, specifically within the context of China’s thriving manufacturing sector.

As an important part of the interior of the car, the engine front right fender not only needs to have good weather resistance and impact resistance, but also needs to ensure assembly accuracy and visual appearance. Using PP as the base material, its lightweight and good toughness characteristics lay the foundation for the structural strength of the product; while the introduction of TPU, through overmolding injection molding, adds an extra protective layer to the edges of the product, enhancing its wear and scratch resistance.

Process Flow Analysis

Stage 1: PP Base Molding
Material Selection: PP is selected as the first injection material due to its soft and slightly elastic properties.
Dimensional Stability Treatment: After the first injection molding, the parts need to be stored naturally for 12 hours. During this time, the PP completes the recrystallization process to ensure dimensional stability, which is the basis for the subsequent successful encapsulation. Stage 2: TPU Encapsulation
Material Properties: TPU’s low viscosity, high fluidity, and excellent penetration make it an ideal encapsulating material.
Process Parameter Setting:
Temperature Control: According to the material properties of TPU, the injection temperature is set between 200°C and 210°C to ensure the good fluidity of the material.
Injection Speed and Pressure: To avoid edge flash, a low injection speed and pressure strategy is adopted. The recommended injection time is 8 to 9 seconds, and no holding pressure is required.
Mold Temperature Management: Keeping the mold temperature low is crucial. Ideally, use a chiller to maintain the mold temperature between 16°C and 17°C, or at least use cooling water around 20°C to enhance the rapid solidification effect of TPU.

Technical Challenges and Solutions

Edge Flash Control: By precisely adjusting the injection pressure and speed, combined with a low-temperature mold, the generation of edge flash is effectively suppressed, ensuring smooth product edges.
Cooling System Optimization: In the absence of a professional chiller, the performance of the cooling tower can be enhanced, and cooling water with a slightly higher temperature can still be used to achieve a good cooling effect and ensure product quality.

Advantages of Overmolding Injection Molding for Engine Front Right Fenders

Enhanced Durability and Wear Resistance: The TPU layer provides a protective barrier against scratches and abrasions, extending the lifespan of the fender.
Improved Aesthetics: The seamless integration of different materials creates a visually appealing and high-quality finish.
Cost-Effectiveness: Compared to traditional painting or other finishing methods, overmolding offers a more efficient and cost-competitive solution.
Reduced Weight: The use of lightweight materials like PP contributes to overall vehicle weight reduction, improving fuel efficiency.

Overmolding Injection Molding in China’s Automotive Industry

China’s automotive industry is experiencing rapid growth and is a major player in the global market. Overmolding injection molding technology is gaining traction in China due to its numerous advantages and its ability to meet the high standards of the industry.

Increased Production Efficiency: Overmolding allows for the integration of multiple components into a single step, streamlining the manufacturing process and reducing production time.
Improved Quality Control: The precise control of process parameters and the use of high-quality materials ensure consistent product quality and minimize the risk of defects.
Meeting Environmental Regulations: Overmolding can help manufacturers comply with increasingly stringent environmental regulations by reducing waste and solvent emissions.

Overmolding injection molding China is a valuable technology for the production of engine front right fenders, offering significant benefits in terms of durability, aesthetics, cost-effectiveness, and weight reduction. As China’s automotive industry continues to grow and evolve, mastering and optimizing this technology will be crucial for manufacturers to remain competitive and meet the high standards of the global market.

Two-Stage Injection Molding: Overmolding PC and TPE with HS Mold

Watch our latest video to see how HS Mold’s two-stage injection molding process can create high-quality parts with a soft touch. Our video provides a step-by-step guide on how to overmold PC and TPE using our advanced technology and equipment. With our expertise in overmolding and commitment to customer satisfaction, you can trust us to deliver high-quality results every time. Don’t miss this opportunity to learn more about how overmolding with HS Mold can benefit your next project!

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Effective Tips for Overmolding Design: Achieve Strong Bonding and High-Quality Results

  • Optimal Wall Thickness: Aim for wall thicknesses ranging from 0.060″ to 0.120″ (1.5 mm-3 mm) to ensure excellent bonding between materials.

  • Corner Radii: Maintain a minimum radius of 0.020″ or 0.5mm in corners to minimize localized stresses and enhance overall durability.

  • TPE Section Design: When incorporating thick TPE sections, consider coring them out to mitigate shrinkage issues, reduce part weight, and improve cycle time.

  • Avoid Deep Blind Pockets or Ribs: Steer clear of designs with deep or un-ventable blind pockets or ribs to prevent potential complications during overmolding.

  • Gradual Wall Thickness Transitions: Ensure smooth and gradual transitions between wall thicknesses to minimize problems such as back fills and gas traps, ensuring smooth flow.

  • Substrate Thickness: The TPE/TPV overmold material should be thinner than the substrate to prevent warping, particularly in long or flat parts.

  • Bonding Compatibility: Select overmold materials that offer mechanical or chemical bonding properties to ensure a strong bond with the substrate.

By following these design tips, you can optimize the overmolding process, enhance bonding strength, and achieve high-quality results for your project.

Picture of overmolding plastic parts
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HS Mold Company: Your Trusted China Mold Maker for Custom Plastic Overmolding

HS Mold Company is a leading China mold maker specializing in custom plastic overmolding. Our advanced plastic injection molding process seamlessly combines two thermoplastic materials to create visually appealing and ergonomic parts like handles or knobs.

We work with a wide range of materials, including soft plastics (urethanes, TPE) and hard plastics (nylon, polycarbonate), offering versatility and customization options. Our overmolding techniques not only enhance aesthetics but also strengthen and protect parts while reducing costs and labor.

As a trusted China mold maker, we prioritize customer satisfaction, leveraging cutting-edge technology and industry expertise. Experience the difference with HS Mold Company’s tailored overmolding solutions. Contact us today to unlock the full potential of your plastic parts.


Unlocking the Benefits of Plastic Overmolding with Customization and Cost Efficiency
  1. Cost Efficiency: Overmolding reduces secondary operations, assembly, and labor costs since multiple components are molded as a single assembly. It eliminates the need for bonding, improving component reliability and saving time and money.

  2. Enhanced Strength: Overmolding strengthens parts, providing better structural integrity. Components can withstand vibrations and shocks, ensuring long-lasting performance.

  3. Secure Alignment: Overmolded components have precise alignment, preventing loosening or misalignment during use. This improves functionality and durability.

  4. Design Flexibility: Custom plastic overmolding allows for creative design possibilities. Manufacturers can combine multiple thermoplastic materials, enabling the production of multi-material components with unique properties.

By leveraging the advantages of plastic overmolding, manufacturers can achieve cost savings, improved strength, secure alignment, and design flexibility in their products.

Applications of Over-Molding Services:

  1. Medical Devices and Instruments: Overmolding is widely used in the production of medical devices and instruments, providing soft grip handles for surgical tools, ergonomic grips for diagnostic equipment, and comfortable handles for medical instruments.

  2. Soft Grip Handles for Various Parts: Overmolding is utilized to create soft grip handles for a variety of products such as hand tools, power tools, kitchen utensils, and sporting equipment. The added grip enhances user comfort, control, and safety.

  3. Knobs for Appliances, Controls, and Assemblies: Overmolding is employed to manufacture knobs used in appliances, controls, and assemblies. These knobs offer improved ergonomics, functionality, and aesthetics.

  4. Encapsulated Electronic Devices and Electrical Components: Overmolding is utilized to encapsulate electronic devices and electrical components, providing protection against moisture, dust, and mechanical stress. This process ensures reliable performance and extends the lifespan of the components.

In these applications, overmolding offers valuable advantages such as improved ergonomics, enhanced functionality, increased durability, and aesthetic enhancements. By utilizing overmolding services, manufacturers can create high-quality products with added value for various industries.

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