Is Injection Molding Additive Manufacturing?

In recent years, the manufacturing industry has been transformed by new production technologies that enable greater flexibility, speed, and precision. Among the most widely discussed terms in this evolution are “additive manufacturing” and “injection molding.” While both are used to create plastic parts and products, they are fundamentally different in how they operate, their applications, and the results they deliver.

This raises a common question: Is injection molding considered additive manufacturing?

The short and simple answer is no, injection molding is not additive manufacturing — but to fully understand why, let’s explore what each term means, how they differ, and when you might choose one over the other.

What Is Additive Manufacturing?

Additive manufacturing (AM) is the technical term for what is commonly known as 3D printing. As the name implies, this process builds objects layer by layer from digital models, typically using materials like plastic, resin, or metal.

Key Characteristics of Additive Manufacturing:

• Layer-by-layer construction: Each part is formed by adding material in thin layers.

• Tool-less production: No molds, dies, or tools are required.

• Rapid prototyping: Ideal for fast design iterations and low-volume production.

• Digital-driven: Based on 3D CAD files that can be edited easily.

• Customizable: Allows for highly complex, customized designs without extra cost.

Popular types of additive manufacturing include:

    - Fused Deposition Modeling (FDM)

    - Stereolithography (SLA)

    - Selective Laser Sintering (SLS)

    - Digital Light Processing (DLP)

    - Direct Metal Laser Sintering (DMLS)

What Is Injection Molding?

Injection molding is a traditional manufacturing process that involves injecting molten material (usually plastic) into a pre-shaped mold under high pressure. Once the material cools and solidifies, the part is ejected from the mold.

Key Characteristics of Injection Molding:

• Mold-based process: Requires expensive and precise molds.

• High production volume: Ideal for producing thousands or millions of identical parts.

• Low cost per unit: Once tooling is done, the marginal cost per part is low.

• High precision: Produces parts with excellent surface finish and tight tolerances.

• Material options: Works with a wide variety of thermoplastics.

The Core Difference: Additive vs. Subtractive vs. Formative

To clarify the relationship between injection molding and additive manufacturing, it helps to understand the three main categories of manufacturing processes:

1. Additive Manufacturing

    - Builds parts by adding material. (Example: 3D printing)

2. Subtractive Manufacturing

    - Creates parts by removing material from a larger block. (Example: CNC machining)

3. Formative Manufacturing

    - Shapes material within a mold or die using pressure or heat.(Example: Injection molding, casting, thermoforming.)

Injection molding falls under the “formative manufacturing” category, not additive.

Why Injection Molding Is Not Additive Manufacturing

Let’s break down the key reasons why injection molding is not considered additive manufacturing:

1. Material Handling

    - Injection molding uses molten plastic injected into molds.

    - Additive manufacturing deposits material layer by layer in precise amounts.

2. Tooling Dependency

    - Injection molding requires a custom mold (a physical tool) for each part design.

    - Additive manufacturing requires no tooling; the design is printed directly from a digital file.

3. Production Intent

    - Injection molding is designed for mass production with low per-part cost.

    - Additive manufacturing is ideal for custom, low-volume, or prototyping use.

4. Speed and Flexibility

    - Injection molding has high setup costs and long lead times but fast cycle times for each part.

    - Additive manufacturing has zero setup time and is slower per part, but flexible for design changes.

5. Design Constraints

    - Injection molding imposes rules like draft angles, uniform wall thickness, and complex gating systems.

    - Additive manufacturing allows freeform geometries, internal features, and topology optimization.

When Injection Molding and Additive Manufacturing Work Together

Although they are different, injection molding and additive manufacturing are increasingly used together in modern production workflows.

Examples of Collaboration:

• Rapid Tooling: 3D printing is used to create prototype molds or mold inserts for short-run injection molding.

• Prototype to Production: Companies may use 3D printing for early prototypes, then move to injection molding for full-scale production.

• Bridge Manufacturing: Additive manufacturing fills the gap before injection molds are ready.

This combination enables faster time to market, reduced risk, and more flexible development cycles.

Choosing Between Injection Molding and Additive Manufacturing

Which process is right for your project depends on several factors:

Criteria	Injection Molding	Additive Manufacturing
Volume	Best for high-volume (1,000+ parts)	Best for low-volume or one-off parts
Upfront Cost	High (due to mold tooling)	Low (no tooling required)
Part Cost	Low for large volumes	Higher per unit
Design Changes	Expensive after mold is made	Easy and low-cost
Lead Time	Long (for mold creation)	Short (almost immediate printing)
Complexity	Limited by mold design	Allows complex, organic, internal geometry
Surface Finish	Excellent	Varies (post-processing often required)

Is There “Additive Injection Molding”?

Some newer technologies are blurring the lines between these categories. For example:

• 3D-printed injection molds: Additive manufacturing can now produce short-life molds from resin or metal.

• Hybrid machines: Some machines combine printing and molding or switch between processes.

• Overmolding and insert molding: Sometimes use 3D-printed inserts as part of the final molded product.

However, these are not examples of injection molding becoming additive manufacturing, but rather of integration for better efficiency and innovation.

Conclusion

Injection molding and additive manufacturing are distinct manufacturing technologies with unique advantages and applications. Injection molding is not additive manufacturing, but a formative process that requires molds and is best suited for mass production of plastic parts.

Additive manufacturing, on the other hand, builds parts layer by layer without molds and is ideal for rapid prototyping, customization, and low-volume production.

Understanding the differences between the two helps businesses and designers choose the right process based on factors like volume, budget, design complexity, and speed to market. In many modern workflows, the real power comes not from choosing one over the other, but from combining them intelligently to bring ideas to life — faster and smarter.