Common Misconceptions About Using Plastics in Automotive Injection Molding

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Tech Staff

Key Takeaways:
  • Injection molding offers versatility, but not all shapes are feasible. Complex geometries with sharp angles or deep undercuts can cause warping, uneven cooling, or defects in plastic injection molded parts. To ensure success, mold designs need to include features like uniform wall thickness and draft angles, which facilitate even cooling and reduce the risk of defects.
  • While ideal for high-volume production, injection molding can also accommodate low-volume production runs with aluminum tooling, making it flexible for a range of manufacturing needs, including prototypes. This allows manufacturers to achieve high-quality plastic car parts without incurring excessive costs for tooling or setup.
  • Although it’s often assumed that injection molding uses only a few commonly used plastics, the reality is that the process supports a wide range of plastic resins. Options include polypropylene plastic, PE plastics, and advanced materials like PPS. These types of plastics used in automotive applications provide the flexibility to meet various performance needs, from heat resistance to chemical stability.
  • Changing mold parameters can help address minor issues, but major flaws often require design adjustments. Mold design, cooling rates, and the material selection assistant play a significant role in achieving defect-free plastic car parts. Collaborating with experienced manufacturers ensures that each part is optimized from the design stage.
  • While some believe injection molding is environmentally harmful, the process can be highly sustainable. Many plastics used in injection molding are recyclable, and scrap materials such as sprues and runners can be reprocessed. With advancements in biodegradable resins, manufacturers now have access to eco-friendly alternatives that reduce the environmental impact of plastic injection molded parts.

Injection molding can be expensive for small batches due to initial tooling costs, but alternatives like aluminum molds make the process viable for low-volume production. This flexibility allows for creating high-quality molded plastic components even in small quantities, making it suitable for everything from prototypes to custom orders.

 Myth: Any Shape Can Be Molded

It’s a common belief that plastic injection molding can produce any shape imaginable. While the process is highly versatile, certain design constraints must be considered. Complex geometries, sharp angles, and undercuts can pose challenges during molding, leading to potential defects or weaknesses in the final product.

Fact: Injection molds need to meet specific criteria for moldability. Designs must allow for even flow and cooling rates. Shapes with sharp corners, deep undercuts, or variable wall thicknesses can cause uneven flow or cooling, resulting in issues like warping, sink marks, or structural weakness. For this reason, mold designers often incorporate elements such as draft angles, rounded corners, and uniform wall thickness to ensure the part can be successfully molded.

2. Myth: Injection Molding is Only for Mass Production

Another common misconception is that injection molding is only suitable for high-volume production runs. This perception stems from the relatively high initial costs associated with mold tooling.

Fact: While injection molding is cost-effective for mass production, it’s also a viable option for low-volume production, such as prototypes and small batch runs. Low-volume production methods like aluminum tooling allow manufacturers to create high-quality parts without the expense of steel molds. This flexibility makes injection molding an ideal choice for a wide range of production needs, whether it’s thousands or just a handful of parts.

3. Myth: It’s an Expensive Process

The assumption that injection molding is inherently expensive can deter potential users from considering it as a manufacturing option.

Fact: While initial tooling costs can be high, the per-unit cost decreases significantly as production volume increases. For large production runs, injection molding becomes a cost-effective solution due to its high efficiency and low cycle times. Even with the added expense of creating molds, the overall production costs can be lower compared to alternative manufacturing methods such as CNC machining or 3D printing when large quantities are needed.

4. Myth: Limited Material Options Are Available

Many believe that only a few materials can be used in injection molding, limiting its application across industries.

Fact: There is a wide variety of resins available for injection molding, ranging from standard thermoplastics like polypropylene (PP) and polyethylene (PE) to engineering-grade materials such as polycarbonate (PC) and polyetheretherketone (PEEK). Each material has its unique properties—heat resistance, impact strength, chemical resistance, and more—making it possible to select a resin that meets the specific performance requirements of a given application.

5. Myth: Adjusting Mold Parameters Fixes All Defects

It’s often thought that any issues during the molding process can be corrected by simply adjusting machine parameters such as temperature or pressure.

Fact: While minor defects can sometimes be fixed with parameter adjustments, major design flaws typically require a more comprehensive solution. For example, if a part exhibits warping or voids, the root cause might lie in the mold design itself. In such cases, altering the mold design or even creating a new tool may be necessary to achieve the desired part quality. This highlights the importance of collaborating with experienced mold designers and manufacturers during the early stages of product development.

6. Myth: Injection Molding Produces Excessive Waste

Another misconception is that injection molding is wasteful and environmentally harmful.

Fact: Injection molding can be a highly sustainable manufacturing process. While there is some waste generated during production—such as sprues, runners, and defective parts—much of this material can be recycled and reintroduced into the production process. Additionally, advancements in biodegradable and bio-based resins offer more eco-friendly alternatives, further reducing the environmental impact of the molding process.

Additional Considerations for Automotive Injection Molding

Material Selection and Performance

Choosing the right material is crucial in automotive applications, as parts often need to withstand harsh environments. Materials such as polycarbonate offer excellent impact resistance, while nylon provides superior fatigue and chemical resistance.

When selecting a material, it’s essential to consider the operating conditions, such as temperature variations, exposure to chemicals, and the need for electrical insulation.

Tooling and Mold Design

Proper mold design is critical for ensuring the success of the injection molding process. The tooling must account for factors like shrinkage, cooling rates, and part ejection. In the automotive industry, molds are often made from durable materials like P20 steel or H13 steel, which can withstand the high clamping pressures and repeated use typical of large-scale production runs.

Comparing Injection Molding to Other Manufacturing Methods

While injection molding is not ideal for every application, it offers several advantages over other manufacturing methods:

  • CNC Machining: CNC machining is suitable for producing complex parts with tight tolerances, but it’s typically more expensive for high-volume production due to slower cycle times.
  • 3D Printing: 3D printing excels at producing prototypes quickly and cost-effectively but lacks the ability to produce parts with the strength and durability needed for most automotive applications.
  • Liquid Silicone Injection Molding: This process is ideal for creating flexible, durable parts used in automotive applications like seals and gaskets. However, it requires specialized tooling and machine setups.

Final Thoughts

By understanding and addressing these misconceptions, automotive manufacturers can make better-informed decisions about using injection molding for the production of their plastic parts. Factors such as design constraints, material selection, and production volume must all be considered to optimize both cost and performance.

Understanding the realities of the injection molding process helps manufacturers leverage its capabilities effectively. This process is not just about producing parts; it’s about crafting solutions that combine material science, design, and engineering to meet the complex needs of today’s automotive industry.

Ready to optimize your injection molding process? Contact Marlee – Texen today for tailored solutions that enhance product quality, reduce costs, and ensure reliability in every part.

Ready to optimize your injection molding process? Contact Marlee - Texen today!
Ready to optimize your injection molding process? Contact Marlee - Texen today!
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Injection Molding for Automotive Industry