Plastic Mold: What is it, How it works, and Who is it For?

Plastic Mold- What is it, How it works, and Who is it For

Have you ever wondered what a plastic mold is and how it works?

Chances are, you’ve encountered one without realizing it—plastic molds shape products in anything from the food industry to consumer goods.

But what exactly is a plastic mold? How does it work?

And who should use one when manufacturing products? In this blog post, we’ll break down all of these questions and show why using a plastic mold might be the best choice for your upcoming production needs.

What Is Plastic Mold?

A plastic mold is a device or tooling system used for making molds from plastics. You will see many people call it plastic injection molding.

You can create various forms from plastics by using plastic molds and create parts according to your manufacturing requirement.

The process involves a heating process to melt the plastic and then you can place the plastic into a mold to create different shapes. You can eject the product or parts when the shape is formed.

It’s a great way to mass produce identical high-quality products quickly and can be used for a variety of different materials, including polystyrene, PVC, acrylic, and more.

Plastic molding is traditionally done using injection or compression machines, depending on what suits your product’s design best.

How does the Plastic Molding System Work?

How does the Plastic Molding System Work

Plastic injection molding (PIM) is a manufacturing process that helps create plastic parts and products by forcing molten plastic through a nozzle into the desired shape.

The basic part of this system is to inject molten plastic into the mold cavity. You have to maintain high pressure while doing that. And when the part is formed you can take the part out.

The PIM system uses a series of pistons and moveable parts called molds to create the desired part.

  • First, the customer provides a design for the part they want to make. This design is then transferred onto a specially designed three-dimensional printer, which creates a digital model of the part. From here, the model is used to create the molds.
  • There are various types of molds.  These include standard molds, such as cylinder molds and cup molds; compound molds, which are made up of several different types of molds; and specialties, such as sandblast molds and vacuum bagging machines.
  • Once all the necessary molds are created, they are cleaned and inspected for defects or imperfections.
  • Next, they are loaded with molten plastic and heated until it reaches their melting point.
  • Then, using a precision piston mechanism controlled by an electronic controller, the plastic is forced through the nozzle at high pressure and temperature. This process creates highly detailed parts that can be easily removed.

The Structure Of An Injection Mold

Injection molding involves injecting the material into a machine that creates the desired object. The mold itself is a metal or plastic frame that’s divided into several sections. These sections are called cavities and are designed to hold the liquid or molten material. They are

  • The mold base
  • The core
  • The mold cavity
  • The gates
  • Sprue and runners
  • The cooling system,
  • The ejector pins

When the machine is started, the electric motor’s heat starts the molten material to flow through these cavities. This flow creates pressure that pushes the material out of the nozzle on top of the mold and into whatever shape you’ve chosen for your object.

Depending on how complex your object is, there may be several molds necessary to create it. For example, if you’re making a toy car, you’ll need at least one toy car mold, one bumper mold, and one wheel mold.

After your object has been created using this process, it will usually require some additional steps before it can be sold to consumers. For example, toys often need to be painted or decorated prior to being sold.

Classification of Injection Mold

Classification of Injection Mold

You can use either two or three plates to make a plastic injection mold. Two-plate molding is the most common type of molding. To make the final product, two plates are pressed together.

Sometimes seen, three-plate molding is made by connecting three plates together to make the final shape. Molds come in many different sizes and shapes, and each one has its own pros and cons.

Two Plates Mold

One advantage of using a two-plate mold is that it’s very cost-effective. It’s also simple to use – simply put the parts you want to cast into the mold, press them together, and wait for the finished product to come out.

However, two plates molds can’t handle complex products very well – they’re best suited for small pieces that don’t require a lot of detail or intricate shapes.

Three Plates Mold

As we stated earlier three plate molds are much more complex than two-plate molds. But at the same time, these molds are more accurate and versatile.

Additionally, three plates molds allow for more complex designs – you can create intricate patterns or designs on top of your product as it comes out of the mold.

However, three plates molds are more expensive than two plates molds, and they require a bit more expertise to use correctly.


The most significant is three plates mold comes with an additional runner plate.

Two plates molding is the most common and uses two plates held together by springs or clips. This type of mold is good for small parts because it’s easy to get the parts out, but it’s not as efficient as a three plates mold because you need more pieces to make a part.

A three plates mold uses three plates that are held together by screws or clamps. This type of mold is better for large parts because it can create more accurate copies, but it’s harder to get the parts out.

The Main Plastic Mold System

The Main Plastic Mold System

In this section, we will discuss the main plastic mold system and things to consider while making a system.

1. Runner

When creating a plastic mold system, the runner is one of the key components that should be designed with care. You can consider the runner as the pathway to deliver molten plastic to the cavity from the injection nozzle.

To ensure the accuracy and precision of the part being created, understanding gate location and size is vital for achieving great results.

If you want to create large volumes of parts quickly and correctly, then careful consideration should be given to designing your system’s sprues, runners, gates, and shapes to optimize flow. By doing so, you can ensure a reliable source of high-quality parts.

Main Runner

The main runner of a plastic mold system is an awesome tool that’s key when connecting the nozzle of an injection molding press to the sprue. It works by making its one-end diameter slightly larger than the nozzle size (0.8 mm).

This helps to streamline production and avoids any issues arising from incorrect positionings, such as clogging or overflowing. Taking time to understand how to install, use and maintain the main runner can help ensure the maximum efficiency of your plastic mold system.


The Sub-Runner of the Main Plastic Mold System is an important part of resin mold building. In a multi-cavity mold, this tiny runner connects the primary runner to each cavity. Thus this runner ensures that the molten resin travels at the same rate to all the mold’s indentations.

This is an essential step to ensure that all mold cavities are produced to the same quality standard, so symmetrical and evenly spread runners should be considered when designing the mold.

Cold Slug

The introduction of the Cold Slug into the main plastic mold system is a crucial aspect of the injection-molding process.

It is a protracted runner that is located at the very end of the primary runner in order to collect the cold resin between two cycles without interfering with the primary runner or the gate.

This Cold slug typically has a diameter of around 8.5-10.5 mm and is 6.5 mm deep. Its purpose is to reduce the buildup of any stress within an injection molded item should cold resin be blended directly into the cavity.

That’s why it’s so important for getting the exact injection-molded product you want.

2. Temperature Control

Temperature Control

Controlling the temperature of the plastic mold system is crucial because it impacts the cooling time, which in turn impacts the quality of the final product.

It is important to maintain a consistent and optimal temperature during cooling. Otherwise, your parts could suffer from deformations or warping.

An effective cooling system will have a temperature control unit that can give you precise readings on the amount of heat being produced within the mold and will monitor any changes in ambient temperatures to ensure consistency.

The most common type of cooling system is an air-based system. These work by circulating air around the mold using fans or ductwork.

The surrounding environment cools the air, reducing the Mold’s surface temperature. This method is generally effective but can be expensive and require regular maintenance.

Water-based cooling systems use a water reservoir to reduce Mold’s surface temperature. The water is circulated through pipes or tubes around the mold, which causes it to evaporate and Condense on the Mold’s surface, creating a cold liquid film.

This system is less expensive than air-based systems but can be less effective because water droplets may not reach all parts of the Mold. Additionally, this system requires regular maintenance to keep the Liquid Film from becoming frozen over time.

A hybrid cooling system combines features from both air-based and water-based systems. This type uses an air conditioning unit to cool the room while circulating water through pipes or tubes around the Mold to create a Liquid Film.

This approach is more effective than either one alone but still requires regular maintenance to keep freezing caused by condensation from happening.

Temperature control is key for successful plastic injection molds and should not be overlooked when considering production.

3. Venting

Venting is a very important part of the plastic mold system. The vents create an air passageway to help prevent air bubbles from getting stuck in the finished product – something no one wants.

This process is often overlooked, but providing a uniform graining and groove depth on the mold cavity walls is essential for proper and professional-looking product results.

This can be achieved with a manual or automatic method such as electrical spark erosion or laser cutting, ensuring that there are no trapped air pockets left behind.

Plastic Mold Venting Slots Size

plasticdepth of slotplasticdepth of slot
PA(GF)            0. 03 〜0. 04 mmPOM0. 02 mm
PC(GF)0.05〜0. 07 mmASA0. 03 mm
PA0. 02 mmSAN0. 03 mm
PC0. 04 mmABS0. 03 mm
PBT0. 02 mmPS0. 02 mm
PBT(GF)0. 03〜0. 04 mmPP0. 02 mm
PMMA0. 04 mmPE0. 02 mm
PBT0. 02 mmPMMA0. 04 mm

4. Ejection

Ejection is one of the most important aspects of a successful injection molding process. Without it, parts may not come out correctly or at all. You will see different types of ejection pins, stripper rings, stripper plates, and sleeves. 

Ejector pins are small metal pieces that fit inside the cavities of the part during the injection. They help hold the part together while it’s being molded and help it break free from the mold when it’s finished.

Sleeves are similar to ejector pins but are made of plastic instead of metal. They’re sealed with a thin plastic strip called a “striker” after being put into the part’s outer channels.

Stripper rings are made entirely of plastic and fit around the part’s top and bottom surfaces. When you hit them with a tool called a “striker,” they break open and release the part from the mold.

Finally, Stripper plates are simply large plates that sit on top of other parts in a mold and get hit with a striker when you want to release it apart from it.

In order to achieve reliable ejection, it is necessary to ensure that none of the four components—ejector pins, sleeves, stripper rings, and stripper plates—are impeded in any way.

However, depending on your project requirements, you might choose one over another. For example, if you need very precise ejection rates or if your parts must be able to move easily in and out.

Plastic Molding: Understanding The Types

Plastic Molding- Understanding The Types

Now we hope you know about the process of plastic injection mold. But what about the different types? Understanding the different types will help you to find the best method for your project.

Blow Molding

Plastics may be molded into various shapes using different techniques, and one of those is called “blow molding,” which is used to create hollow things from molten thermoplastic.

This process begins by heating the chosen plastic until it reaches a molten state, then the molten plastic material is forced into a mold cavity that is in the shape of the desired object.

Blow molding forms items with thin walls and complex shapes while still remaining strong and lightweight, making this method extremely useful for creating many everyday items such as pet food containers, car parts, medical equipment, bottles, and piping.

Once the plastic material has been loaded into the mold cavity, pressurized air is utilized to shape and form the product within the confines of the mold. Afterward, the molded product undergoes chilling to solidify its shape before being removed from the mold.

There are three main types of blow molding: barrel, cage, and plunger. In barrel blow molding, the heated air is forced into a long, narrow nozzle called a barrel.

This forms the part in one continuous flow. Cage blow molding uses two nozzles side by side to form the part. Plunger blow molding uses one nozzle surrounded by a depression in which the object to be molded is placed.

As the depression fills with air, it forces the plastic around it into place.

The main advantage of blow molding over other methods is its versatility. It can be used for simple parts with few details or for more complex objects where multiple parts are needed.

Compression Molding

Many goods are made using compression molding. This method compresses pre-heated thermoplastic or thermoset material in a mold.

This forces the material inside the cavity of the heat and applies pressure to the form, which shapes it into the desired size and shape of the product.

As with other types of plastic molding methods, compression molding can provide a high degree of accuracy when it comes to producing parts with complex shapes and sizes, making it an ideal choice for applications where precision matters.

Compression molding is its versatility. Therefore, you can use this method for many purposes such as manufacturing plastic parts.

Extrusion Molding

Extrusion molding is a manufacturing process used to produce plastic products. It is one of the most common types of plastic molding.

The process of extrusion molding consists of forcing molten plastic through a nozzle and into a mold in order to shape the final product. The die is attached to a machine that moves the die and the molten plastic around together. This technique is used to produce products that are often simple in shape, like toys or pens.

Extrusion molding is versatile because it can be used to make many different types of products. Some common products that are produced with extrusion molding include bottles, food containers, medical devices, and eyeglasses.

Each type of product has its own set of benefits and drawbacks, which will be discussed in more detail below.

One of the main advantages of extrusion molding is that it is relatively quick and easy to set up. This makes it ideal for quickly producing large quantities of products, which is often necessary for companies that need to meet tight deadlines.

Additionally, extrusion Molding produces products with high-quality standards due to its precision and uniformity. This means that even small defects can lead to irregularities in the final product, which can be challenging to fix.

Injection Molding

Injection Molding is the most common and popular type, but other options include Sublimation and Vacuum Casting. Understanding the differences between these three methods can help you decide which one is best for your project.

Injection For plastics, molding is the most typical technique. Machines are used to inject hot, molten plastic into a mold, where it cools and hardens around the thing being created.

The advantages of injection molding are that it’s fast and easy to set up, making it ideal for mass production. However, injection molding also has some disadvantages: while it’s resistant to damage, it’s not very durable, so parts can break easily.

How to Choose Plastic Mold Steel

Mold life> 1 million0.5-1 million0.2-0.5 million<0.2 million
insert steelAIASA420/S136SKD61/TDAC(DH2F)NAK80/718HP20/PX5 738
insert hardness(60±2)HRC(52±2)HRC(38±2)HRC       (30±2)HRC
base steel           S55CS55CS55C     S55C
base hardness(18±2)HRC(18±2)HRC(18±2)HRC(18±2)HRC

Mold Development Process

Mold Development Process

The mold development process for plastic mold starts with the choice of the right substrate. The type of plastic and the desired end product must be taken into account when choosing the substrate.

For example, a polymer that is brittle may not be suitable for injection molding because it will break during manufacturing. There are a variety of other factors to consider, such as how easy the material is to work with and how reproducible the final product will be.

Manufacturers must first choose the substrate they will be working with before settling on the mold they will employ. There are a variety of different types of molds available, each with its own advantages and disadvantages.

Some molds are easier to use than others, but all have their own set of specifications that must be met in order for them to function properly. Once these requirements have been established, manufacturers can start designing their molds using CAD software or 3D printers.

Next, manufacturers must create a prototype mold using this design information. The purpose of this test mold is to determine whether or not mass production utilizing this mold type is possible.

The prototype model is designed to help choose the correct size and shape for the final product and is also used to test out different production methods.

Once the model has been finalized, you can create mold by using an injection molding process or other molding processes that you prefer. This mold typically takes the shape of the finished product and can be used multiple times to create identical copies.

Once the mold has been created, liquid plastic is poured into it and heated until it reaches its melted state. The temperature at which this happens is known as Pour Point Temperature (PPT).

It is important to keep this temperature consistent throughout the entire process to avoid damage to both the mold and the plastic. Once PPT has been reached, the molten plastic flows into and fills every nook and cranny in the mold, forming a perfect replica of whatever was originally modeled.

Mass production typically involves several stages that are necessary in order to produce high-quality products. These stages include pre-production, production, quality control, and packaging/shipping.

It is important to pay close attention to detail throughout all of these stages to ensure that each product reaches its intended specification. If there are any problems with any of the products produced during mass production, they can often be difficult to rectify.

Overall, understanding the mold development process for plastic molding is essential in order to produce high-quality products that meet customer expectations.

Building Blocks of a Plastic Mould

The components of a mold are many and varied. In this section, we will talk about those elements for people who are interested in the plastic molds making process.

Here are they:

1. Recognizing the location of the cavities and their respective centers. Molds made from plastic might have as many as 144 individual cavities.

2. A passageway connecting the machine’s nozzle and the mold’s cavity through which polymers are injected at high temperatures. You have two options here:

  • Hot Runners
  • Cold Runners (2 or 3 plates)

3. The cooling system aids in the deformation of the mold and the ejection of the finished item.

4. Ventilation system.

5. Mole Ejection mechanism. You have many options here:

  • Automatic removal.
  • Hand removal
  • Air-ejection
  • Pins or Sleeves
  • Force ejection
  • Stripper
  • Attaching the mold to

6. Adding the mold to the machine:

  • Easy mold changing.
  • One machine molds.
  • Molds on multiple machines.

7. Cavity and core alignment: You have the following options here:

  • No alignment
  • 2,3,4 brass pins and bushings.
  • Using Leader bushing and pins
  • Taper locker

8. For the support and stability mentioned above, you would need several mold plates.

Although these features will increase the price of the mold (sometimes significantly), they can improve the mold’s efficiency and hence lower the overall cost of production.

Plastic Mold Gates

Plastic Mold Gates

A plastic mold gate is an important part of a plastic mold. It is a short flow path between the runner and the cavity, which is the entrance of the resin into the cavity. The gate prevents resin from flowing back into the runner, which can cause problems with the quality of your product.

There are many types of gates available, each with its advantages and disadvantages. Some gates are very simple, while others are more complex. The choice of which gate to use depends on various factors, including your mold design and manufacturing process.

Direct Gate

This type of gate relies on friction between the part and the gate to keep it in place. Because low-pressure loss is critical in plastic molding, direct gates are often very efficient.

Direct Gate has some clear advantages. Low-pressure loss and processing are simple.

Regarding applications, Direct Gate is best suited for large and deep barrel-shaped parts or parts that are not allowed to have gate marks on the surface.

But it isn’t without its flaws. First of all, there is a lot of stress near the gate, and the stress on the product is uneven and easy to bend. And there’s more work involved in manually removing the gate. At the end of the process, the final surface will be marred by apparent gate markings.

Side Gate

A side gate is another type of gate you will see in many applications.  It is simple in shape and easy to machine, but it can be challenging to remove the gate automatically.

Additionally, the plastic part left behind on the product can have “gate marks” that show up on the finished product.

This type of gate is best suited for parts that don’t require a long barrel profile or that don’t require frequent separation between the product and the mold.

Pinpoint Gate

For plastic injection molding, there is now Pinpoint Gate to consider. It can be placed on virtually any flat surface and automatically detach the gate from the component.

Glue areas are minimally sized thanks to the small gate markings, making it simple to inject mold components without warping. When pieces are placed near a gate, there is less stress and consequently little chance of distortion.

Nonetheless, this gate structure requires a high injection pressure, therefore it can’t be used with plastics that have low fluidity. As a rule of thumb, a three-plate mold structure is required for optimal performance.

Submarine Gate (Set on Ejector Pins or Ribs)

The submarine gate is popular because of its flexibility and ease of use. The gate can be positioned in several ways, making it more versatile than other gates.

Additionally, the gate can be automatically separated from the plastic part without any post-processing. This means that you don’t have to worry about affecting the appearance of the part.

The downside to this gate is that it can be difficult to remove the cloudy area created by the gate. Furthermore, since the gate is located inside the part, it can lead to fingerprints on the surface.

However, this drawback can be easily overcome by using an appropriate machining process.

Overall, the submarine gate is a reliable option for plastic molds that require an external appearance with no visible gate marks. It should be noted that this type of gate is not suitable for rigid materials such as PC and PMMA due to its high-pressure loss properties.


So, if you were looking for a basic understanding of plastic mold, we hope this article was helpful to you.

Plastic molding is an important process for many industries and can be used to create a wide variety of products. If you are interested in learning more about plastic molding or working with a plastic injection molding company, we encourage you to contact us.

We would be happy to answer any questions you have and provide additional information about our services.

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