3D Printing vs Injection Molding

You have many options for producing parts, but which manufacturing method is best for you?

Two popular methods that offer unique advantages are 3D printing and injection molding. Understanding the differences between these processes is crucial for making informed decisions. This article compares 3D printing and injection molding across critical factors such as lead times, cost, strength, and material options.

By exploring these aspects, engineers can better evaluate which method suits their project requirements. 

How 3D Printing and Injection Molding Work

3D printing, or additive manufacturing, typically builds three-dimensional objects layer by layer.

There are many different 3D printing technologies, but they all usually involve designing a digital model, slicing it into layers, selecting the appropriate material, and using a 3D printer to deposit and solidify the material layer by layer. Post-processing steps such as removing support structures or surface finishing may be required.

This is a part made with stereolithography 3D printing. Note the support structures that need to be removed in post-processing.

Injection molding is a mass-production process that creates large quantities of identical parts. It involves designing and building a mold, preparing the material, injecting the molten material under high pressure, cooling and solidifying the part within the mold, and ejecting the finished part. Post-processing steps such as trimming or surface treatments may follow.

An injection molding machine in action.

The processes are widely different, as are the advantages and disadvantages of both technologies. Here’s how they stack up against each other.

Design Freedom

3D Printing: 3D printing produces highly intricate and complex geometries, allowing engineers to explore innovative designs that would be challenging with other manufacturing methods. Creating geometrically complex parts with internal features or undercuts provides a significant advantage, as parts can be printed in one rather than assembled separately.

Some of the complex parts are made possible by 3D printing.

Injection Molding: Injection molding requires the creation of molds, which restricts design modifications once the mold is produced. This limitation is particularly relevant for complex geometries, undercuts, or frequent design changes. Any design changes may require additional tooling or mold modifications, leading to increased costs and delays.

Initial Lead Times

3D Printing: Engineers can quickly produce parts for concept validation or end-use. This iterative design process enables engineers to validate and refine their designs before committing to small to medium-scale production, speeding up production and minimizing the risk of costly design flaws.

Injection Molding: The production of molds for injection molding can be expensive and time-consuming, impacting project timelines for initial production. However, this technology can be faster when dealing with large-scale production.

Cost Comparison

3D Printing: This technology eliminates the need for expensive molds required in injection molding, making it cost-effective for low-volume production runs and customized parts. It eliminates the upfront tooling costs and allows on-demand production, reducing inventory requirements and minimizing waste.

Injection Molding: The cost of creating molds for injection molding can be high, especially for intricate designs or multiple cavities. This cost includes mold design, engineering, and precision machining. However, once the mold is created, it can be used for high-volume production, reducing the cost per part due to economies of scale.

Strength

3D Printing: 3D printing offers good strength properties but may not match the strength of injection molded parts, especially when subjected to high-stress or load-bearing applications. The anisotropic properties of 3D printed parts can influence their overall strength and mechanical properties, resulting from layer-by-layer construction.

Injection Molding: Injection molded parts benefit from higher material density and uniformity, resulting in superior strength and structural integrity. The high pressure and temperature in injection molding ensure consistent material distribution, eliminating weak points or variations.

Materials

3D Printing: While 3D printing offers a growing variety of materials, including plastics, metals, and composites, the selection is more limited than injection molding. However, advancements in material development for 3D printing are continuously expanding the range of options and properties available.

Injection Molding: This method provides access to various materials, including engineering-grade plastics. These materials offer specific properties such as high strength, heat resistance, chemical inertness, or electrical conductivity. Additionally, specialized materials like elastomers and thermosetting plastics are readily available for specific applications.

Finishing

3D Printing: Depending on the desired finish and quality, post-processing steps such as sanding, painting, or assembly may add to the overall cost. The level of post-processing required depends on the part’s intended use and aesthetic requirements.

The smooth surface of an injection molded part.

Injection Molding: Depending on the part’s requirements, additional finishing operations like trimming, painting, or assembly may contribute to the overall cost. However, injection molded parts often require minimal post-processing compared to 3D-printed parts. That’s because of the smooth surface and the fact that parts can be molded in different colors, eliminating the need to be colored afterward.

Getting Started

3D printing and injection molding have their strengths and limitations. 3D printing excels in design complexity, rapid prototyping, and cost efficiency for low-volume production. Injection molding offers high production efficiency, superior strength, and a wide range of material options for large-scale manufacturing.

Regardless of what technology you need for your project, MakerVerse is here to help. Please choose from the full range of manufacturing technologies and materials or work closely with one of our experts to help you choose the best process.