Injection Molding Process – A Complete Guide

One of the world’s most commonly used manufacturing processes is injection molding. It is a manufacturing process that involves injecting molten material, typically plastic, metal, or ceramic, into a mold. Once the material has cooled and solidified, it is removed from the mold and can be used as, or further processed.

An emerging world of customization and personalization has seen a corresponding increase in the popularity of injection molding. This is because it can create products with precise dimensions and designs. In addition, injection molding process can be used to mass-produce products quickly and efficiently. This blog post will explore the basics of injection molding, its applications, and its benefits. So let’s begin!

The injection molding process

When we hear the term “injection molding,” most of us think of the plastic parts we use daily. But injection molding can create parts from various materials, including metals, ceramics, and glass. Injection molding process is not limited to only one sector; it is widely used in the medical, automotive, aerospace, and consumer goods industries.

Figure 1: Plastic injection moulding process

The process begins at a molten state, as the material is injected into a mold cavity. The cavity is usually cooled so that the material can solidify quickly. Once solidified, the part is ejected from the mold and can be used as-is or further processed.

The basic plastic injection molding process cycle | Step by step

Figure 2: Scientific diagram of injection molding process

With knowledge of the basic plastic injection molding process, you can make informed decisions when working with a plastic injection molder. The process cycle for a plastic part can vary based on material choice and complexity of the part, but it generally falls into these five main stages:

• Clamping

Prior to injection, the mould must be closed and clamped. The two metal halves of the mould are closed with significantly greater pressure than is required to keep them shut during the injection and cooling cycles. This compression is necessary because the plastic flow front can exert tremendous force on the mold’s walls as it advances. Each half of the mould is attached to the platens of the injection machine, one fixed and one moving. The moving platen is attached to a hydraulic or electric motor which provides the clamping force.

• Injection

Once the mould is closed and clamped, the screw of the injection machine begins to rotate, and plastic feedstock is fed into the barrel. The screw forces the plastic through the nozzle into the mould cavity, where it begins to fill the cavity. The raw material must be fed in the form of pellets or granules. The screw feeds the material in a metered fashion and also melts it. The molten plastic is then propelled under high pressure into the mould cavity.

• Cooling

After the cavity is filled, the mould must be cooled so the part can solidify. The cooling time will vary depending on the material used and the part’s size. Once the part has solidified, it can be ejected from the mould. The temperature of the mould is controlled by circulating water through channels in the mould.

• Ejection

Once the part has solidified, it must be ejected from the mould. The ejection process varies depending on the type of mould being used. The sprue and runners are ejected with the part for a cold runner mold. The runners are melted and ejected separately from the part for a hot runner mold.

• Post-Processing

Once the part is ejected from the mould, it can be further processed if necessary. This may include trimming, painting, or other operations. The manufacturing process is now complete, and the part is ready for use.

Types of equipment used in injection molding

Equipment and components are essential in any manufacturing process. The types of equipment used in plastic injection molding are designed to meet the specific needs of this process. Each type of equipment has unique features and benefits that make it ideal for injection molding.

Figure 3: Plastic injection molding machine parts

• Injection Unit

The injection unit is the part of the machine that melts the plastic and injects it into the mold. It consists of a barrel, screw, heater, and nozzle. The barrel holds the plastic material that will be melted and injected into the mold. The screw is used to advance the plastic material through the barrel and melt it. This unit is responsible for melting and injecting the plastic into the mold. The hopper is also a part of this unit, where the plastic material is fed into the barrel. The heater helps to melt the plastic material. The nozzle is used to inject the molten plastic into the mold. The screw controls the flow of the plastic.

• Clamping Unit

The clamping unit is responsible for holding the mold during the injection process. It consists of a platen, toggle, and clamp. The platen is the platform on which the mold is mounted. The toggle is used to apply pressure to the mold during the injection. The clamp is used to hold the mold in place during the injection. The hydraulically powered motor is used to provide the power for the clamping unit. The operator controls the working of this unit. The operator will start the injection process when the mold is placed in the clamping unit. The clamp will hold the mold in place while the plastic is injected into it.

• Ejector Unit

For the final step, the ejector unit removes the mold from the machine. It consists of an ejector pin and an ejector plate. The ejector pin is used to push the mold out of the machine. The ejector plate supports the mold as it is being ejected from the machine. After the plastic has cooled and solidified, the mold will be ejected from the machine. The composite molding process is now complete.

These are the three central units that are used in injection molding. Each unit has its unique purpose and function. Injection molding is a complex process that requires the use of specialized equipment. The type of equipment used will depend on the specific needs of the injection molding process. To ensure that the process is carried out correctly, it is essential to use the correct equipment.

Tools required for plastic injection moulding

The plastic injection molding process uses molds, typically made of steel or aluminum, as the custom tooling. The mold is connected to the plastic injection molding machine, which melts the plastic and injects it into the mold. Once the plastic has cooled and solidified, the part is ejected from the mold.

The cycle time, or time it takes to inject the molten plastic, cools the plastic, and eject the part, can vary based on many factors but is typically between 7-120 seconds.

• Dies

The term “die” is often used interchangeably with “mold.” However, molds and dies are two different types of tooling used in the injection molding process. Molds are generally used for lower volume applications, while dies are typically used for higher volume applications.

• Moulds

Moulds are typically made from steel or aluminum and can be either single or multiple cavities. Single cavity molds produce one part per cycle, while multiple cavity molds can produce multiple parts per cycle. Molds can be designed to produce parts with features such as threads, undercuts, and snap fits in injection moulding production.

• Mold Channels

Mold channels are the passages in the mold through which the molten plastic flows to fill the cavities. The design of the mold channels is an essential factor in determining the overall efficiency of the injection molding process.

• Cavity

The cavity is the negative space in the mold that defines the shape of the part. Cavities can be either single cavities or multiple cavities. Single cavity cavities produce one part per cycle, while multiple cavity Cavities can produce multiple parts per cycle.

• Runner

The runner is the channel through which the molten plastic flows from the injection molding machine to the micro cavity. The runner system is an essential factor in determining the overall efficiency of the injection molding process. For vertical injection molding applications, the runner system is typically designed so that the molten plastic flows downward through the channels.

Materials used in injection molding process

There are a wide variety of plastics that can be used in the simple injection molding process. The most common materials are:

• ABS (acrylonitrile butadiene styrene)
• PVC (polyvinyl chloride)
• PE (polyethylene)
• PP (polypropylene)
• PA (polyamide or nylon)
• PC (polycarbonate)

Figure 4: Material used in plastic injection moulding

These plastics are all thermoplastics. This means they can be turned into powder, melted, and reformed multiple times without changing the material’s chemical structure. This is in contrast to thermosetting plastics, which can only be molded once before they harden and cannot be melted again.

The specific material polymer you choose for your project will be determined by the properties you need the final product. It is essential to consult with an expert in the field to ensure that you are using the suitable material for your needs. Go4mould is the expert in the field and can advise you on the best material for your project.

Go4mould | A trusted name in plastic injection molding

Go4mould is a trusted name in plastic injection molding in China. We have been in this business for over 20 years. We provide our clients with high-quality plastic products with a precise and scientific sheet mold design. All our products are made with the highest quality materials and strictest quality control. We have highly skilled and experienced engineers who can design and manufacture any plastic product.

We also provide customization quotes for multi-color or two-color moulding, shoe box mould, fruit container mould, and any other product you can think of. We gain insights from your design requirements and injection molding process to deliver a highly customized end product. Our sales and customer service representatives are always available to answer any questions you may have.

In addition, we also offer a wide range of services such as product development, mold making, prototyping, assembly, and packaging. We are dedicated to providing our clients with the best possible experience and service. Contact us today to learn more about our services and how we can help you with your next project.