Injection molding is one of the popular methods for producing plastic parts. From toys and phone cases to automotive parts, countless everyday products are made using this method. Special equipment such as a “mold” is used to manufacture all those items. However, there are several types of injection molds; each differs in design, size, and shape.
For example, some molds are simple and used for basic products. However, some molds can create intricate and complex parts. Hence, understanding those types is crucial for anyone involved in product design. Are you one who struggles to differentiate mold types? Worry not! This article will make things easy by exploring some common mold types. So, let’s get started!
What is an Injection Mold?
An injection mold is a special tool used in the injection molding process. It has two halves that come together to form a hollow cavity inside. This hollow space is shaped like the final product. The hot and molten material is injected into the mold. On cooling, the material becomes solid and takes the shape of mold.
Once the final product is ready, the mold opens, and it comes out. This mold prepares for the next cycle, which continues until the desired quantity is reached. As molds have to handle high pressure and heat, they are made strong. Common materials used for molds include steel, aluminum, and high-carbon steel.
The injection molds are also made precisely using special techniques such as CNC. This is because the precision of the mold decides the precision of the product. If the mold is precise, the final product has the correct size, shape, and smooth surface. Lastly, these molds are not confined to producing plastic parts but can also handle a variety of injection molding materials.
Main components of an Injection Mold
The injection mold contains two halves. However, these halves have several parts that contribute to the precise production of items. Let’s take a brief look at those parts.
- Mold Base: It is the outer part that holds all other parts. It acts as a frame and supports and aligns the mold body.
- Cavity(A-side): It is the hollow space in which molten material is injected. This part is responsible for making the outer shape of the product.
- Core(B-side): It is the raised part that shapes the inner surface of the product. It is usually located on the back half of the mold.
- Runner and Gate System: Runners are the channels that guide molten material. Chanel helps it run from the injection point to the cavity. However, the gates are small openings. They control flow into each part of the cavity.
- Ejector System: The ejector system includes pins. These pins push the molded part out after it cools.
Types of Injection Mold
As I said above, injection mold comes in various types. All those types differ in several aspects, and understanding them is crucial for precise results. Let’s dive in and explore some common types of injection molds with their specifications.
1- Two-Plate Mold
It is the most common and basic type of injection mold. It is called two plates because it contains two parts: The core side and the cavity side. The core side is moving half while the cavity side is fixed. These two halves come together to make a hollow cavity inside. It also contains special channels called sprue, which leads to the runners.
When you inject the molten material, it follows this path and reaches the cavity. On cooling, the exact mold-shaped product is obtained. However, two-plated molds don’t have a complex structure. Therefore, it is ideal for basic and simple design products like buttons and caps.
2- Three-Plate Mold
A three-plate mold is an advanced injection mold compared to a two-plate mold. As the name suggests, it contains three parts instead of two. Those include a cavity plate, core plate, and runner plate. This extra part makes it flexible for complex parts and offers cleaner finishes.
HOW? Actually, in the two plate molds, the plastic part and runner come together. But in three-plated molds, the mold opens in two places. Once, it releases the leftover runner and again releases the final part. This way, the final product will have a cleaner and smoother finish.
Quick Highlight: The runner is the small channel inside the injection mold. It guides the molten material from the machine to the mold cavity. However, after cooling the material, the runner becomes a solid plastic. So, it must be removed or recycled for better product efficiency.
3- Hot Runner Mold
It is a special type of injection mold where material stays hot and melts inside the system all the time. This system uses metal hot channels instead of regular cold runners. These hot channels directly guide the molten material into the cavity. During this transfer process, materials do not cool to create waste runners.
This reduces material waste and makes injection molding cost-effective. Moreover, these molds come in two basic types. The first is an open hot runner mold in which material flows freely into the part. The second one is a valve-gate hot runner mold. This type uses a special pin to control the flow of material.
4- Family Mold
Family mold is another mold type that can produce two or more different parts in one cycle. Those parts are usually related or used in the same products. That’s why it is known as family mold. But how does it work? Family mold has multiple cavities. Each of those cavities has a different shape.
Different-shaped products are created simultaneously when you pour molten material into the cavities. However, I recommend using the same material for each cavity. Different materials can cause intermixing and product malfunction. Further, due to the simultaneous production of various parts, this mold saves both time and money.
5- Stack Mold
A stack mold is a type of injection mold with multiple cavity layers. All those cavities stack on each other like a sandwich, which is why it is named so. However, the shape of those cavities can be the same or different. There is only one injection unit, which means molten material is injected through one point.
It follows the channel’s path and reaches different layers of the cavity. This feature makes it possible to create several products at the same time. This way, you can double the output without investing in additional machines. That’s why stack mold also proves time-saving and cost-effective.
6- Insert Mold
An Insert mold is a specialized mold type that offers versatility. HOW? The pre-made part is first placed into the mold in the insert molding process. That part is known as the insert mold. It can be made of other materials than plastic. So now, when you inject molten plastic into the mold, it sticks to the insert.
As a result, you will get two materials in one product. These molds are the best way to make two products from two different materials. Moreover, these molds also feature threads. So you can also create durable parts with extra features. This saves time and money in the long run.
7- Unscrewing Mold
Unscrewed molds are specially designed to create parts with thread, such as bottle caps and lids. These parts have grooves that let them screw onto something else to create a sealing. Those groves are made by unscrewing molds. HOW? These molds contain thread cavities that shape like groves. When you inject material into these cavities, they adopt the same thread shape.
However, the key in these molds is unscrewing. These molds do not just pull out the part immediately. Instead, they gently unscrew the part and then eject it. This step is crucial to prevent any damage to the product. For this purpose, these molds use hydraulic motors to rotate or unscrew parts of the mold.
8- Two-Shot Mold
A two-shot mold, also known as a 2K mold, makes a part using two different materials or colors. Let me simplify its role in simple terms. These molds have two cavities. First, you inject one material into the molds. Then, the mold rotates itself and aligns with the second cavity. Now, you inject the second material into the mold.
The two-shot mold rotates again, and the second material bonds with the first. On cooling, you get a product of two materials or colours as one unit. However, these molds use special injecting machines. Those machines have two barrels to inject different materials. Overall, these molds offer good quality products and save time and extra labor costs.
9- Gas-Assisted Injection Mold
Gas-assisted injection mold is another special mold type that handles assisted gas. In the molding process, when plastic is injected, some corners remain unfilled inside the mold. This happens due to the extra thickness of the molten material. However, those hollow corners must be filled to ensure the precise size and shape of the final product.
For this purpose, manufacturers insert assisted gas, usually nitrogen, inside the mold. This gas pushes the hot material into the corner of the mold and fills the empty spaces. As a result, the final part is produced with no empty section. For these prices and defect-free shapes, these gas-assisted molds are handy. With their unique design and material, they can easily handle blowing gas and its pressure.
10- Prototype Mold
Prototype molds are temporary or trial molds. They are used to make small numbers of products before full production begins. Thus, they are primarily used to test the products before investing money in expensive and permanent final products. Prototype molds mainly have very simple designs.
They do not include much detailing and are made of steel or aluminum, so they also come at lower prices. Prototype molds detect the error earlier. This saves money and time before investing in large-scale production. Consequently, they have become a popular choice among large-scale industries.
What Factors Determine the Type of Mold to Use?
Choosing the correct type of injection mold is crucial in manufacturing. A wrong mold wastes time and leads to poor product quality and material waste. However, some factors can help you determine the right type of mold. Let’s discuss those factors in this section.
- Part Design: First, you should understand the part’s design. If it is simple, consider a basic two-plate mold. However, for complex features such as threads, go with three-plate molds.
- Material Used: Different materials behave differently when injected or melted. Some are easy to melt, while others require high temperatures. For such materials, hot runner molds work well.
- Production Volume: The number of needed parts also affects the mold type. If you are making sample products, choose prototype molds. However, for mass production, family molds or stack molds are reliable.
- Surface Finish and Part Quality: Some products must look smooth and shiny. In such a case, a mold that allows central gating is ideal. You should go with gas-assisted and three-plated molds.
- Cost and Budget: Each type of mold has different prices. Your selection depends on your budget and product quantity. If your budget is limited and the part is simple, go with hot-runner molds. However, advanced molds like two-shot molds are best for detailing and long-term savings.
Frequently Asked Questions
Can injection molds be reused?
Yes, injection molds can be reused, and it’s one of their most significant advantages. They are specially designed to be used over and over again. Once the mold is ready, you can use it thousands of times to make products.
Why are some injection molds so expensive?
Some injection molds are expensive because they need to be precise and strong. For this purpose, they are made using special techniques such as CNC and 3D printing. These methods require experienced labor and expensive materials. That’s why the overall cost of some complex and long-lasting molds increases.
How long does an injection mold last?
The lifespan of an injection mold depends on its material and design. Some molds are made with robust materials, such as hardened steel. They can last for 500,000 to over 1 million cycles. However, proper maintenance is also crucial to extending their life.
Conclusion
Injection molding plays a vital role in modern manufacturing. It helps create everything from daily-use products to industrial tools. At the heart of this process, the mold tool determines the final product’s precision and shape. In this article, we have seen several types of injection molds.
All those types vary in design and handling. For example, some molds have a simple design and create basic products. However, some are specialized for creating intricate and complex parts. The precision of these molds decides the precision of the final products. So, they are made using special techniques. Lastly, once a mold is ready, you can repeatedly use it.