What is plastic injection molding and how does it work?

Injection molding is a complex manufacturing process. Using a specialized hydraulic or electric machine, the process melts, injects and sets plastic into the shape of a metal mold that’s fitted into the machine.

Plastic injection molding is the most widely used components manufacturing process for a variety of reasons, including:

• Flexibility: manufacturers can choose the plastic injection mold design and type of thermoplastic that’s used for each component. This means the injection molding process can produce a variety of components, including parts that are complex and highly detailed.
• Efficiency: once the process has been set up and tested, injection molding machines can meet high volume production. Using electric injection molding machines also makes the process relatively energy efficient.
• Consistency: if the process parameters are tightly controlled, the injection molding process can produce thousands of plastic parts quickly at a consistent quality.
• Cost-effectiveness: once the mold (which is the most expensive element) has been built, the cost of production per component is relatively low, particularly if created in high volumes for mass production.
• Quality: whether manufacturers are looking for strong, tensile or highly detailed components, the injection molding process is able to produce them at a high quality repeatedly.

This cost-effectiveness, efficient production time and component quality are just some of the reasons why many industries choose to use injection molded parts for their products.

As well as the fact that plastic injection molding process can be optimized to have a lower carbon impact. Find out more in our guide, Design for Sustainability: Optimizing Plastic Injection Molding Processes.

The injection molding cycle includes many parameters which need to be tightly controlled to ensure the overall quality of the plastic components produced. Understanding the process and parameters in some depth will help manufacturers to identify plastic components producers who can provide the quality and consistency they need.

• Product Design: The process begins with a detailed product design or concept. Design considerations include functionality, aesthetics, material selection, and manufacturability.
• Mold Design: A mold, also known as a tool or die, is created based on the product design. The mold consists of two halves – the cavity and the core – that create the shape of the final product.
• Material Selection: Choose the appropriate plastic material based on the product’s requirements, considering factors like mechanical properties, chemical resistance, and temperature stability.
• Mold Fabrication: Skilled toolmakers manufacture the mold using precision machining techniques. The mold’s complexity and size influence the time and cost of fabrication.

Step 2

Injection Molding Process

• Clamping: The mold is mounted onto the injection molding machine. The two halves are securely closed using hydraulic or mechanical force to ensure proper alignment.
• Injection: Plastic pellets, known as resin, are fed into the injection molding machine’s hopper. The pellets are heated and melted within the barrel to a consistent molten state.
• Injection Pressure and Speed: The molten plastic is injected into the mold’s cavity under high pressure. The injection speed and pressure are controlled to fill the mold and prevent defects like voids or sink marks.
• Cooling: After the mold is filled, the plastic inside begins to cool and solidify. Cooling time is carefully controlled to achieve the desired part quality.
• Holding Pressure: Some molds include holding pressure to compensate for material shrinkage during cooling. This ensures the part retains its shape and dimensions.

Step 3

Mold Opening and Ejection

• Cooling Completion: Once the plastic has sufficiently cooled and solidified, the mold opens, revealing the solidified part inside.
• Ejection: The mold ejector pins push the part out of the mold cavity. Ejection must be gentle to avoid damaging the part’s surface.

Step 4

Post-Processing

• Trimming and Deflashing: Excess material, called flash, is removed from the part. Trimming may involve manual or automated processes to achieve the final shape.
• Secondary Operations: Depending on the product’s requirements, additional processes like drilling, machining, or assembling may be performed.

Step 5

Quality Control and Inspection

• Visual Inspection: Each part is visually inspected for defects, such as surface imperfections, color inconsistencies, or distortion.
• Dimensional Checks: Parts are measured and compared to the specifications outlined in the design. Advanced measurement equipment ensures accuracy.

Step 6

Packaging and Shipping

• Packaging: Finished parts are carefully packaged to prevent damage during transportation.
• Shipping: The parts are shipped to the customer or assembly facility for integration into larger products or distribution to end-users.

Injection molding at HWPLASTICPARTS

At HWPLASTICPARTS, injection molding is a key production process. As part of our strategy, we are optimizing our plastic injection molding processes, including replacing old hydraulic machines with electric machinery.

We continue to invest in material innovation and have a new Centre Of Excellence at our CHN headquarters, which will help us to test and develop new materials that will in turn enable us to offer even more sustainable product ranges globally for our customers.

Our team of experts are on hand to help you create consistent, high quality parts for your next project. With over 45,000 molds to choose from and custom solutions available, we can deliver the parts you need. As well as plastic parts, we also have a range of metal components manufactured using hot chamber die casting.

Free CADs are available for most solutions, which you can download. You can also request free samples (some exclusions apply) to make sure you’ve chosen the right product for what you need.  Same day dispatch for sample requests received by 4pm.

If you’re not quite sure which solution will work best for your application, our experts are always happy to advise you.

Request your samples or download free CADs now.

Questions?

Email us at kama@hwplasticparts.com or speak to one of our experts for further information on the ideal solution for your application 15069372818