This guide will provide you with a comprehensive introduction to injection mold types and the manufacturing process of producing plastic parts by injecting molten material into the mold. You will learn about the different categories and characteristics of injection molds, as well as the advantages and disadvantages of each type. Additionally, you’ll get some tips on how to choose the right injection mold for your project.
First, let us understand the basic concepts of injection molds. An injection mold is a tool used to make plastic parts, and it consists of two main parts: the mold and the injection molding machine. The mold is a cavity with a specific shape and size, and the injection molding machine is responsible for injecting the molten plastic material into the mold. When the plastic cools and solidifies, the mold is opened, resulting in the desired plastic part.
Next, we will introduce different types of injection molds in detail. According to their structure and use, injection molds can be divided into the following categories: single-cavity molds, multi-cavity molds, hot runner molds and two-color molds. Each type of injection mold has its unique characteristics and applicable scenarios.
The single-cavity mold is the simplest type of injection mold. It has only one cavity and is suitable for producing a single part. This type of mold is usually used to produce smaller parts such as buttons, switches, etc.
Multi-cavity molds have multiple cavities and can produce multiple identical parts at the same time. This mold is suitable for mass production and can improve production efficiency and reduce costs.
Hot runner mold is an advanced injection mold technology that melts the plastic material before it is injected into the mold by setting up a heating device inside the mold. This kind of mold can reduce the waste of plastic materials and improve product quality and production efficiency.
A two-color mold is an injection mold used to produce parts with different colors or materials. It can achieve the mixing of multiple colors in one production process, saving time and cost.
When selecting an injection mold, there are several key factors to consider. First, you need to determine what type of injection mold your project requires. Secondly, you need to consider whether the size and shape of the mold match your product requirements. In addition, you also need to consider the durability and maintainability of the injection mold to ensure that it can operate stably for a long time.
In short, injection molds are an important tool for manufacturing plastic parts. Different types of injection molds have different characteristics and applicable scenarios. By understanding this information and considering project needs and related factors, you can choose the right injection mold for your project, thereby improving production efficiency and product quality.
What is Injection Moulding?
Injection moulding is a manufacturing process for producing plastic parts by injecting molten material into a mould, or mold. The material for the part is fed into a heated barrel, mixed using a helical screw, and injected into a mould cavity, where it cools and hardens to the shape of the cavity. The mould is made of metal, usually either steel or aluminium, and precision-machined to form the features of the desired part. Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars.
Components of Injection Mould
The structure of injection moulds may vary depending on the material properties, types of injection moulds, and the structure of final products. However, the basic structure remains the same. The main components of injection moulds are:
- Guide Pins: These are used to ensure the perfect alignment of mould halves when the mould is closed. They support mould plates to prevent distortions that may damage the mould or cause injection moulding defects.
- Runner: This is a channel that guides the molten material from the sprue bushing to the gate, the entry point to the moulding cavities.
- Gate: This is a small opening that allows the molten material to enter the mould cavity. The size and shape of the gate affect the flow rate, pressure, and cooling rate of the material.
- Sprue: This is a large-diameter channel that connects the nozzle of the injection machine to the runner.
- Locating Ring: This is a circular component that fits over the nozzle of the injection machine and aligns the sprue with the injection machine.
- Mold Cavity: This is a hollow space in the mould that forms the shape of the part. The number and arrangement of cavities determine the production efficiency and quality of injection moulding.
- Ejector Pins: These are metal rods that push the part out of the mould cavity after it cools and solidifies.
- The Shot: This is the amount of material that is injected into one mould cycle.
- Ejector Plate: This is a plate that holds and moves the ejector pins.
- Clamping Plate: This is a plate that holds and clamps the mould to the injection machine.
Types of Injection Mould Based on Feeding System
The feeding system refers to how the molten material is delivered from the injection machine to the mould cavity. There are two main types of feeding systems: cold runner and hot runner.
Cold Runner Mould
A cold runner mould uses a simple channel that is carved into one or both halves of the mould. The channel remains at room temperature and solidifies after each injection cycle. The solidified material, called a runner, must be separated from the part and recycled or discarded. A cold runner mould has some advantages, such as:
- Low cost and easy maintenance
- Suitable for various materials and colours
- Reduced pressure loss and injection time
However, a cold runner mould also has some disadvantages, such as:
- Material waste and contamination
- Reduced production efficiency and quality
- Increased cooling time and cycle time
Hot Runner Mould
A hot runner mould uses a heated channel that is embedded in the mould or attached to it. The channel maintains the molten state of the material and eliminates the need for runners. A hot runner mould has some advantages, such as:
- No material waste and contamination
- Increased production efficiency and quality
- Reduced cooling time and cycle time
However, a hot runner mould also has some disadvantages, such as:
- High cost and complex maintenance
- Limited to thermally stable materials and colours
- Increased power consumption and thermal expansion
Types of Injection Mould Based on Number of Cavities
The number of cavities refers to how many parts can be produced in one mould cycle. There are three main types of injection moulds based on the number of cavities: single cavity, multiple cavity, and family mould.
Single Cavity Mould
A single cavity mould has only one mould cavity that produces one part per cycle. A single cavity mould is suitable for low-volume production or large and complex parts. A single cavity mould has some advantages, such as:
- Low cost and easy maintenance
- High accuracy and quality
- Flexible design and modification
However, a single cavity mould also has some disadvantages, such as:
- Low production efficiency and output
- High unit cost and material consumption
- Long cycle time and lead time
Multiple Cavity Mould
A multiple cavity mould has more than one mould cavity that produces more than one part per cycle. The number of cavities can range from two to hundreds, depending on the size and shape of the part. A multiple cavity mould is suitable for high-volume production or small and simple parts. A multiple cavity mould has some advantages, such as:
- High production efficiency and output
- Low unit cost and material consumption
- Short cycle time and lead time
However, a multiple cavity mould also has some disadvantages, such as:
- High cost and complex maintenance
- Low accuracy and quality
- Difficult design and modification
A family mould has more than one mould cavity that produces different parts per cycle. The parts are usually related in shape, size, or function, such as a cap and a bottle. A family mould is suitable for medium-volume production or parts that need to be assembled together. A family mould has some advantages, such as:
- Reduced tooling cost and inventory
- Simplified production process and logistics
- Improved product consistency and compatibility
However, a family mould also has some disadvantages, such as:
- Compromised quality and performance
- Imbalanced filling and cooling
- Limited design flexibility and modification
Types of Injection Mould Based on Mold Plate
The mold plate refers to how the mold is divided into two or more parts. There are two main types of injection molds based on the mold plate: two-plate mold and three-plate mold.
A two-plate mold is the simplest type of injection mold that consists of two halves: a fixed mold (or core) and a moving mold (or cavity). The runner system is located on the parting line between the two halves. A two-plate mold is suitable for simple parts with one gate or side gate. A two-plate mold has some advantages, such as:
- Low cost and easy maintenance
- Fast opening and closing
- Reduced flash and deformation
However, a two-plate mold also has some disadvantages, such as:
- Limited gate location and size
- Large runner waste and pressure loss
- Difficult venting and ejection
A three-plate mold is a more complex type of injection mold that consists of three parts: a fixed mold (or core), a moving mold (or cavity), and an intermediate plate (or runner plate). The runner system is located on the intermediate plate between the fixed mold and the moving mold. A three-plate mold is suitable for complex parts with multiple gates or pinpoint gates. A three-plate mold has some advantages, such as:
- Flexible gate location and size
- Small runner waste and pressure loss
- Easy venting and ejection
However, a three-plate mold also has some disadvantages, such as:
- High cost and complex maintenance
- Slow opening and closing
- Increased flash and deformation
Types of Injection Mould Based on Special Features
Injection moulding is a widely used manufacturing process that can produce plastic parts with complex shapes and high precision. Injection moulding involves injecting molten plastic into a mould cavity, where it cools and solidifies into the desired shape. The mould cavity is usually made of metal and can have various special features to enhance the quality and functionality of the final product. In this blog post, we will introduce some types of injection mould based on their special features and how to choose the right one for your project.
- Gas-Assisted Injection Mould: This type of injection mould uses pressurized gas, such as nitrogen, to create hollow sections in the plastic part. The gas is injected into the mould cavity after the plastic injection, creating a bubble that pushes the plastic against the mould walls. This reduces the weight and material usage of the part, as well as eliminates sink marks and warping. Gas-assisted injection moulding is suitable for producing parts with thick walls, such as handles, furniture, and automotive components.
- Thin-Wall Injection Mould: This type of injection mould can produce plastic parts with very thin walls, typically less than 1 mm. Thin-wall injection moulding requires high injection speed and pressure, as well as precise temperature and cooling control. The advantages of thin-wall injection moulding are faster cycle time, lower material consumption, and higher strength-to-weight ratio. Thin-wall injection moulding is commonly used for producing packaging products, such as cups, containers, and lids.
- Liquid Silicone Injection Mould: This type of injection mould can produce parts made of liquid silicone rubber (LSR), which is a high-performance elastomer that has excellent thermal, chemical, and electrical resistance. Liquid silicone injection moulding involves injecting LSR into a heated mould cavity, where it cures rapidly into a solid rubber part. The benefits of liquid silicone injection moulding are high accuracy, flexibility, durability, and biocompatibility. Liquid silicone injection moulding is widely used for producing medical devices, such as catheters, valves, and implants.
- Structural Foam Injection Mould: This type of injection mould can produce plastic parts with a cellular structure that reduces the density and weight of the part. Structural foam injection moulding involves injecting a mixture of plastic and a blowing agent into a low-pressure mould cavity, where the blowing agent creates bubbles in the plastic as it cools. The resulting part has a solid skin and a foam core that provides strength and rigidity. Structural foam injection moulding is ideal for producing large and complex parts, such as housings, enclosures, and panels.
- Metal Injection Mould: This type of injection mould can produce metal parts with intricate shapes and fine details. Metal injection moulding involves injecting a mixture of metal powder and a binder into a mould cavity, where it solidifies into a green part. The green part is then debinded and sintered in a furnace to remove the binder and fuse the metal particles together. The final part has high density, strength, hardness, and corrosion resistance. Metal injection moulding is applicable for producing parts with high performance requirements, such as gears, surgical instruments, and firearms.
How to Choose the Right Injection Mould for Your Project?
Choosing the right injection mould for your project depends on several factors, such as:
- The material of the part: Different materials have different properties and behaviours during the injection moulding process. You should choose a material that meets your specifications for strength, durability, appearance, and functionality. You should also consider the compatibility of the material with the mould design and the injection machine.
- The shape and size of the part: The shape and size of the part affect the complexity and cost of the mould design and fabrication. You should choose a shape and size that can be easily produced by the injection moulding process without compromising the quality and performance of the part. You should also consider the dimensional accuracy and tolerance of the part.
- The quantity and quality of the part: The quantity and quality of the part influence the selection of the injection mould type and features. You should choose an injection mould type that can meet your production volume and quality standards in an efficient and economical way. You should also consider the maintenance and lifespan of the injection mould.
- The budget and timeline of the project: The budget and timeline of the project determine how much you can invest in the injection mould development and production. You should choose an injection mould that fits your budget and timeline without compromising your expectations for the final product.
Choosing the right injection mould for your project can be challenging but rewarding. By considering these factors carefully, you can find an optimal solution that meets your needs and goals.