Injection molding is one of the most widely used manufacturing processes for producing high-quality plastic parts at scale. From simple household items to complex automotive and medical components, different injection molding types are used depending on material, part geometry, production volume, and performance requirements.
In this guide, we’ll explore the different types of injection molding, including mold designs, machine types, plastics used, gate systems, and advanced variations used in modern manufacturing.
What is Injection Moulding?
Injection moulding is a manufacturing process where molten plastic is injected into a mold cavity under high pressure, cooled, and then ejected as a finished part. The process supports a wide range of injection molded plastic types, complex geometries, and tight tolerances.
Different Types of Injection Molding Processes
Conventional Plastic Injection Molding
This is the most common type of injection molding used for mass production.
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Uses thermoplastic granules
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Ideal for high-volume parts
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Compatible with many injection molding plastic types
Common applications include packaging, consumer products, automotive interiors, and electronic housings.
Two-Shot (Multi-Shot) Injection Molding
Two-shot molding injects two different plastics or colors into a single mold cycle.
Benefits:
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Strong bonding between materials
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No secondary assembly
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Enhanced aesthetics and functionality
Often used for soft-touch grips, seals, and multi-material components.
Insert Injection Molding
In this method, metal or pre-made components are placed into the mold before plastic injection.
Used for:
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Electrical connectors
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Threaded inserts
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Reinforced plastic parts
This injection mold type improves strength and reduces assembly steps.
Over Molding
Over molding is similar to insert molding but typically involves molding a softer plastic over a rigid substrate.
Common in:
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Medical devices
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Tool handles
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Consumer electronics
Gas-Assisted Injection Molding
This advanced process injects gas (usually nitrogen) to create hollow sections.
Advantages:
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Reduced material usage
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Lighter parts
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Less warping and sink marks
Perfect for rapid prototype lightweight material needs and large plastic parts.
Types of Injection Molding Machines
Hydraulic Injection Molding Machines
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High clamping force
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Ideal for large molds
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Higher energy consumption
Electric Injection Molding Machines
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High precision
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Energy efficient
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Clean operation (medical & electronics)
Hybrid Injection Molding Machines
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Combines electric precision with hydraulic power
Two different types of injection molding machines are hydraulic and electric, with hybrids bridging the gap.
Toggle Type Injection Molding Machine
Uses a toggle mechanism for clamping.
Benefits:
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Faster cycle times
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Energy efficient
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Common in high-speed production
Types of Molds in Injection Molding
Single-Cavity Molds
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One part per cycle
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Ideal for low-volume production
Multi-Cavity Molds
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Multiple identical parts
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High productivity
Family Molds
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Produces different parts in one cycle
These are the most common injection molding mold types used in production environments.
Injection Mold Gate Types
Gates control how molten plastic enters the mold cavity. Choosing the right injection mold gate type affects part quality and appearance.
Common Types of Injection Molding Gates:
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Edge gate
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Pin gate
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Submarine (tunnel) gate
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Hot tip gate
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Valve gate
These are also known as plastic injection molding gate types and are selected based on part design and material flow.
Runner Types in Injection Molding
Cold Runner System
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Lower tooling cost
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More material waste
Hot Runner System
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Reduced waste
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Better surface finish
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Higher initial cost
Both runner types play a key role in overall efficiency.
Injection Molding Screw Types
The screw melts and mixes plastic before injection.
Common Injection Molding Screw Types:
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General-purpose screw
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Barrier screw
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Mixing screw
Screw selection depends on injection molding resin types and material viscosity.
Types of Plastics Used in Injection Molding
Common Injection Mold Plastic Types:
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Polypropylene (PP)
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Polyethylene (PE)
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Nylon (PA)
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Polycarbonate (PC)
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POM (Acetal)
These are the most common types of plastics used in injection molding due to their strength, flow properties, and cost efficiency.
Virgin vs Recycled Plastic Granules
Different types of injection molding grade virgin plastic granules offer:
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Better mechanical properties
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Consistent quality
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Medical and food-grade compliance
Recycled plastics are used for cost-sensitive or non-critical applications.
Injection Molding Nozzle Tip Types
Nozzle tips control melt flow and pressure.
Common injection molding nozzle tip types include:
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Open nozzle
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Shut-off nozzle
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Filter nozzle
Correct nozzle selection improves part quality and reduces defects.
Types of Undercut in Injection Molding
Undercuts prevent straight ejection from the mold.
Common Undercut Types
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Internal undercuts
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External undercuts
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Side undercuts
Solutions include side actions, lifters, or collapsible cores.
Applications of Different Injection Molding Types
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Automotive components
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Medical devices
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Consumer electronics
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Industrial parts
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Packaging products
Each application uses a specific injection molding type, machine, mold, and plastic material.
FAQs
What are the main injection molding types?
The main injection molding types include conventional plastic injection molding, two-shot injection molding, insert molding, over molding, and gas-assisted injection molding. Each type is used based on part complexity, material requirements, production volume, and end-use application.
How do different injection molding types affect product quality?
Different injection molding types directly impact surface finish, strength, weight, and dimensional accuracy. For example, gas-assisted injection molding produces lightweight parts with less warping, while two-shot molding improves aesthetics and material bonding.
Which injection molding types are best for high-volume production?
Conventional plastic injection molding and multi-cavity mold-based injection molding types are best suited for high-volume production. These methods offer fast cycle times, consistent quality, and lower per-unit cost once tooling is established.
Understanding the various injection molding types is essential for selecting the right manufacturing approach. From machine types and mold designs to plastics, gates, runners, and screws, each element plays a critical role in product quality, cost, and efficiency. By choosing the correct injection molding process and materials, manufacturers can achieve consistent, scalable, and high-performance plastic parts.
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