Introduction of Plastic Injection Molding Process

If you’re new to the plastic products industry, understanding the production processes behind it is crucial for you. Among various plastic manufacturing processes, plastic injection molding is an efficient and globally widespread manufacturing technique. It can produce plastic products in various shapes and sizes, spanning a wide range from everyday items to industrial components. This article aims to provide an in-depth understanding of the entire plastic injection molding process by showcasing the production of a custom plastic toy, from design concepts to the manufacturing of the final product.


  1. Product Design
  2. Molds Creation
  3. Material Selection & Preparation
  4. Mold Installation & Machine Adjustment
  5. Trial Molding & Injection Process
  6. Inspection and Quality Control

1. Product Design

In the entire process of plastic injection molding, product design is always the first crucial step to consider. Designers use Computer-Aided Design (CAD) software to create a three-dimensional model of the product, taking into account the shape, size, and material selection. At this stage, it is essential to clarify the functionality and requirements of your product, including its main purpose, performance needs, and durability. For example, in the case of children’s toys, the design phase may pay special attention to safety and durability, ensuring that the product not only meets design requirements but also complies with relevant safety standards. The design process also needs to consider potential challenges in the injection molding process, which may require optimizing the product’s structure to enhance manufacturability. Integrating these factors, the design phase is not only about creative conception but also a critical step in ensuring the successful manufacture of the final product.


2. Mold Creation

Once the product design is complete, attention shifts to the crucial step of manufacturing the injection molding molds. The mold plays a vital role in the plastic injection molding process as it directly determines the shape and size of the final product. Typically, molds are made from high-strength metals such as steel or aluminum to ensure durability and stability. High-precision machining techniques, such as CNC machining and electrical discharge machining, are employed in the mold manufacturing process to ensure accuracy and surface smoothness. Each step in the manufacturing process requires strict control to meet design requirements and maintain consistent production quality.

Mold Creation also involves several key aspects:

  1. Design Validation: Before formally manufacturing the mold, design validation is often conducted to ensure that the mold’s geometry and structure align with the product design requirements, helping to avoid issues during the actual injection molding process.
  2. Mold Material Selection: Choosing the right metal material is crucial for mold performance, considering the high temperature and pressure during the injection molding process.
  3. Mold Surface Treatment: Manufacturers typically apply surface treatment to the molds after determining the product structure in the first trial run but before the second trial run. To enhance the appearance of the final product, the molds’ surfaces are often treated with processes such as polishing, sandblasting, or creating specific textures.

The quality and precision of mold creation directly impact the quality of the final product. Therefore, careful design and manufacturing at this stage are crucial for the overall success of the injection molding process.

Detailed information about mold creation for injection molding manufacturing can be found in this blog: How to Custom Injection Molding Parts in China


3. Material Selection & Preparation

Before commencing the injection molding process, selecting the appropriate plastic material for the product is a critical step. Different plastic materials possess various characteristics such as rigidity, wear resistance, tensile strength, and heat resistance. During the design phase, these characteristics must be considered to ensure that the chosen material can meet the functional and performance requirements of the product.

The following injection molding materials are commonly used for plastic ride-on toys:

  • PP (Polypropylene)
  • ABS (Acrylonitrile Butadiene Styrene)
  • PVC (Poly Vinyl Chloride)
  • PS (Polystyrene)
  • PA (Polyamide) – Nylon
  • POM (Polyoxymethylene)
  • PU (Polyurethane Resin)
  • TPR/TPE (Thermoplastic Rubber)

More details about these common materials can be found in this blog: What Plastic Are Toys Made From?

Once the appropriate materials are chosen, manufacturers also need to color the materials based on the desired appearance of the product, a process known as “Plastic Color Compounding”.

Plastic Color Compounding

In the compounding area of the injection molding factory, Color Masterbatches or Pigment Powder are mixed in the right proportions with the selected raw materials according to the product’s design colors.

Color Masterbatches
Pigment Powder

One obvious difference between Color Masterbatches and Pigment Powder lies in their physical form; Color masterbatches are typically in granular form, while pigment powder is in powder form. Pigment powder offers a wide range of color choices and good color dispersion, adhering quickly and uniformly to the surface of the plastic raw material during the mixing process. On the other hand, masterbatch is a pre-mixture prepared with precise formulations, ensuring color consistency and accuracy during the compounding process. Besides, color masterbatches are more environmentally friendly.

When choosing between color masterbatches and pigment powder, considerations should be made based on the specific requirements of the product and the scale of production. Large-scale production is generally more suitable for using masterbatch, while pigments might be a more flexible choice for small-scale production or situations requiring a wide range of color options.


4. Mold Installation & Machine Adjustment

The precise installation of the mold is crucial for producing high-precision and consistent plastic products. The mold installation process requires meticulous attention to detail, ensuring its accurate positioning on the injection molding machine. Before installing the mold, the machine specifications should be checked to ensure it can accommodate the mold’s size and weight. Next, the mold is carefully transported to the area above the target injection molding machine by using an overhead traveling crane. Then, the overhead crane slowly lowers the mold to the position. The worker will inspect the mechanical connections between the mold and the injection molding machine. Once in place, the mold is immediately secured to the machine platen using bolts, clamps, or other fastening mechanisms, ensuring all bolts and fasteners are securely tightened. Additionally, it is essential to ensure the mold’s cooling system is working to effectively control the temperature during the injection molding process.

After completing the mold installation, production workers proceed with the machine adjustment process. The following three tasks are the main focus during the machine adjustment process:

  1. Temperature Adjustment: Gradually raise and stabilize the temperature of the injection molding machine during the adjustment process to ensure uniform melting and flow of the plastic material.
  2. Pressure Adjustment: Adjust the pressure system of the injection molding machine to ensure sufficient pressure is provided during the injection process, allowing the plastic to fill the mold cavities adequately.
  3. Speed Adjustment: Gradually adjust the injection speed of the injection molding machine based on the specific product and mold design to achieve optimal injection molding results.

During the machine adjustment, special attention should be paid to monitoring the operational status of the injection molding machine, ensuring its stable operation, and promptly addressing any issues that may affect production.


5. Trial Molding & Injection Process

After the mold is installed and the machine is properly adjusted, it’s time to proceed with the first trial run. This marks the production of the very first plastic piece coming out through the injection molding machine. Here, I will provide a detailed explanation of how a professional injection molding machine transforms plastic raw materials into finished plastic products:

Injection Molding Process
  1. Add material from the hopper into the injection molding machine.
  2. The material is conveyed forward by the rotating screw while being heated by the heater. It is pushed to the head of the screw, forming a discharge space and completing the plasticization process.
  3. Injection: The molten plastic is injected into the mold.
  4. Filling: The cavity in the mold is filled with molten plastic.
  5. Cooling: The plastic cools and solidifies in the mold.
  6. Ejection: The mold automatically opens, and the molded part is ejected by the built-in ejector pin.

After completing these 6 steps, a plastic component is officially produced. However, this is only the first trial run stage. Any newly customized mold needs to undergo at least 3 trial runs:

1st Trial Run: Confirm the correct structure of the product or component inside the mold. If there are discrepancies, adjustments to the mold may be necessary before another trial run to ensure the correct structure.

2nd Trial Run: After confirming the correct structure, the mold is sent for surface treatment (examples of specific surface treatments are mentioned in the Molds Creation section). The second trial run is conducted to ensure that the plastic component with the surface treatment matches the expectations. If there are discrepancies in the surface treatment process, adjustments to the mold may be necessary before another trial run.

3rd Trial Run: Once the final structure and designed surface treatment of the product or component are confirmed, the product enters the stage of trying colors. In the third trial run, injection molding workers add materials pre-mixed with Color Masterbatches and Pigment Powder into the hopper. The injection steps are repeated to see if the produced color matches the design expectations. If there are color discrepancies, adjustments to the material-masterbatches/pigment mixing ratio may be necessary before another trial run.

Each trial run involves repeating the injection molding process dozens of times, producing dozens of samples, regardless of quality. Therefore, before mass production begins, all custom plastic products need to undergo a lengthy and rigorous trial run process. However, precise control of each step in this process is crucial to ensuring the success of the injection molding process. From design to production, close collaboration is required at every stage to ensure the final plastic products meet the expected quality standards.


6. Inspection and Quality Control

Once your product has successfully passed numerous trial runs and all parameters have been adjusted, your product can enter formal mass production. At this stage, regular quality inspections are essential to ensure that the produced plastic items meet design requirements and are free from defects and issues. As an importer from a foreign country, it’s important to note that different countries have varying safety standards for plastic toys. Therefore, you need to ensure transparent and frequent communication with the injection molding manufacturer you are collaborating with. This is crucial to ensure that your product is manufactured in compliance with safety regulations and meets the standards and requirements of your target market.


ZHXTOYS Injection Molding Factory
Sky View of ZHXTOYS Company

Yiwu Zhihuixing Toys Co., Ltd., (ZHXTOYS) with over 30 years of experience in the field of children’s ride on toys and equipped with 68 professional injection molding machines, is committed to providing customers from all over the world with high-quality and creative riding toys. We have a professional R&D design team with over 20 years of experience, continuously developing and innovating products based on global market feedback. In addition to manufacturing strength, we also have a dedicated sales and service team, dedicated to providing the best support and service to domestic and international customers. To date, our products have reached global markets, and exported to 43 countries, bringing smiles to children.

If you are interested in importing high-quality ride on cars from China or planning to customize plastic injection molding parts, please feel free to contact us by visiting our official website: www.zhxtoys.com, or directly through email: [email protected] to initiate a business inquiry. Also, don’t forget to leave your contact information and any valuable suggestions below the blog! Looking forward to engaging in more discussions with you! Thank you for choosing Zhihuixing Toys Co., Ltd., (ZHXTOYS) and we look forward to establishing a long-term partnership with you!

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