Injection molding includes a range of specialized processes, each designed to solve different manufacturing challenges—from high-volume plastic production to multi-material parts and lightweight structures.
Instead of listing every variation, this guide focuses on the most widely used injection molding types, explaining how they work, where they fit, and how to choose the right one for your project.
Before going into each type, it helps to have a basic idea of how these processes are typically selected in real projects. In most cases, the choice comes down to three key factors:
- Part structure – simple, hollow, thick-wall, or multi-material
- Production volume – prototype, medium batch, or mass production
- Material requirements – plastic, rubber, metal, or combinations
A quick rule of thumb:
- High-volume standard parts → Plastic injection molding
- Lightweight or thick sections → Gas-assisted molding
- Multi-material or soft-touch → Overmolding / two-shot
- Embedded components → Insert molding
Comparison of Injection Molding Types
| Process | Best For | Key Advantage | Limitation |
|---|---|---|---|
| Plastic Injection Molding | General plastic parts | Cost-effective for high volume | High tooling cost |
| Gas-Assisted Molding | Thick or hollow parts | Reduces weight and sink marks | Higher setup complexity |
| Insert Molding | Parts with metal inserts | Eliminates assembly | Requires precise positioning |
| Overmolding | Multi-material parts | Better grip and appearance | Material compatibility limits |
| Two-Shot Molding | Complex multi-material parts | Strong bonding, high efficiency | Expensive tooling |
| Micro Injection Molding | Small precision parts | High accuracy | Limited material range |
Main Types of Injection Molding Processes
Plastic Injection Molding
Plastic injection molding is the most widely used process for producing high volumes of plastic parts. Molten plastic is injected into a mold, cooled, and solidified into the final shape. It works well for a wide range of thermoplastics and is ideal when consistency and cost efficiency matter.
Where it fits:
Automotive parts, housings, consumer products, and industrial components. For most projects, this is the baseline process everything else is compared to.
Plastic Injection Molding Service
Gas-Assisted Injection Molding
Gas-assisted injection molding introduces pressurized gas (usually nitrogen) into the molten plastic to create hollow sections inside the part. This reduces material usage while improving structural strength and minimizing defects like sink marks.
Where it fits:
Thick parts, handles, enclosures, and structural components. Useful when weight reduction and surface quality are both important.
Read the Guide for Gas-Assisted Injection Molding.
Insert Molding
Insert molding involves placing a pre-formed component (usually metal) into the mold, then injecting plastic around it to form a single integrated part. It removes the need for secondary assembly and improves overall strength.
Where it fits:
Threaded parts, connectors, electrical components, and reinforced structures. Best choice when combining metal and plastic into one part.
Overmolding
Overmolding adds a second material over a base substrate to create a multi-material part. This is commonly used to improve grip, sealing, or product appearance.
Where it fits:
Tool handles, medical devices, consumer electronics. Ideal for soft-touch surfaces or improved ergonomics.
Overmolding and Insert Molding Service
Two-Shot Injection Molding
Two-shot molding injects two materials in sequence within a single mold, forming a fully bonded multi-material part in one cycle. Compared to overmolding, it offers stronger bonding and better production efficiency.
Where it fits:
Complex parts requiring multiple materials, colors, or functions. Suitable for high-volume production where consistency matters.
Micro Injection Molding
Micro injection molding is designed for producing extremely small and precise components with tight tolerances. It requires specialized equipment and tooling.
Where it fits:
Medical devices, micro electronics, precision components. Used when accuracy at a very small scale is critical.
How to Choose the Right Injection Molding Process
There is no “best” injection molding type—only the one that fits your part design, material, and production goals.
Especially for complex or multi-material parts, process selection directly affects manufacturability. In many cases, optimizing the process early can:
- Reduce material waste
- Shorten cycle time
- Lower total production cost
As mentioned earlier, most decisions come down to a few key factors. In practice, selecting the right process is less about the process itself, and more about how your part needs to perform in real use.
Start with the part design.
Simple, solid parts are typically suited for standard plastic injection molding. If the design includes thick sections, hollow areas, or requires weight reduction, processes like gas-assisted molding are often a better fit.
Then consider material and functionality.
For multi-material parts, overmolding or two-shot molding is commonly used. If metal components need to be integrated, insert molding helps combine parts into a single, more durable structure.
Finally, look at production volume and cost.
High-volume production can justify more complex tooling to reduce unit cost, while lower volumes usually favor simpler, more flexible processes.
In the end, the right choice is the one that balances design feasibility, material performance, and total production cost—not just the lowest upfront investment.
Need Help Selecting the Right Injection Molding Process?
Choosing the wrong process can lead to unnecessary tooling costs or production issues later. Get support from Zhongde Engineering Team early to avoid redesigns.
- Review your part design
- Recommend the most suitable molding process
- Optimize for cost and manufacturability
