Comparing Additive Manufacturing to Injection Molding

Choosing the right manufacturing process is one of the most critical decisions in product development. Both additive manufacturing and injection molding are powerful options, but they have different strengths. Knowing when to use each one can be the difference between a smooth launch and a series of expensive delays.

This isn't an either/or choice. The real question is which process is right for your project at its current stage. Let's look at the practical differences between the two and how to decide which path to take.

Why the Comparison Matters

Additive manufacturing and injection molding offer unique advantages depending on where you are in the development cycle. Early on, you might need speed and flexibility to iterate on a design. Later, you'll need repeatability and cost-efficiency for production.

Making the right choice involves balancing speed, cost, accuracy, and compliance. A clear understanding of each process helps you create a product development plan that gets you to market faster, with a design that's ready for full-scale production.

Additive Manufacturing

Additive manufacturing, especially with Carbon DLS technology, has changed the way engineers approach design and iteration. It builds parts layer by layer directly from a digital file, which offers several key advantages.

Strengths
The biggest strength of additive is speed. You can get functional prototypes in a matter of days, not weeks. This rapid turnaround allows for more design iterations in a shorter amount of time. Additive also offers exceptional design freedom. You can create complex geometries like lattices, internal channels, and organic shapes that would be impossible to produce with injection molding.

Because there's no need to create a mold, the upfront costs are much lower. This makes it ideal for early-stage projects or low-volume production runs. With modern materials like Carbon's production-grade resins, you can create prototypes with mechanical properties that are very similar to thermoplastics, making your tests more meaningful.
Limitations
The primary limitations of additive are in tolerance and consistency. While accuracy has improved significantly, it can't match the tight tolerances of injection molding. A typical additive process might hold tolerances of ±0.005 inches, which is sufficient for many applications but may not be for precision-critical components.

There can also be slight variations from batch to batch, which requires careful process control to manage. For medical devices, this means that while additive is excellent for prototyping and even some production parts, it may not be suitable for components that require extreme precision and repeatability.

Injection Molding

Injection molding is the established standard for high-volume production, particularly in regulated industries like medical devices, where consistency, repeatability, and validated processes are critical.

Strengths
Injection molding's greatest strength is its repeatability. Once a steel tool is made, it can produce millions of identical parts with extremely tight tolerances, often ±0.001 inches or better. This consistency is critical for medical devices and other applications where performance cannot vary.

The process also offers the lowest cost per part at high volumes. While the initial tooling investment is significant, the cost per part drops dramatically as production scales. For medical devices, injection molding has proven validation pathways, which can simplify regulatory submissions.
Limitations
The main considerations for injection molding are the upfront cost and lead time for tooling. A production-quality steel mold can cost tens of thousands of dollars and take weeks or months to build. This makes it a poor fit for early-stage prototyping or low-volume projects.

Any changes to the part design after the tool is made are often expensive and time-consuming. This is why it's so important to finalize the design through prototyping before committing to production tooling.

Cost & Timeline Considerations

Your budget and timeline will heavily influence your choice. Additive manufacturing has a low startup cost and fast turnaround, but a higher cost per part. This makes it ideal for prototyping and short production runs.

Injection molding has a much higher startup cost and a longer lead time, but the per-part cost is significantly lower as volume increases. The break-even point where molding becomes more cost-effective than additive depends on the part's complexity and material, but it's often in the range of thousands of units.

For many projects, a blended approach works best. You can start with additive to iterate and validate the design quickly, then move to bridge tooling to test for manufacturability, and finally scale into production molding with confidence.

Materials Comparison

One of the most common questions we hear is, "Do additive parts perform like molded thermoplastics?" With modern materials, the answer is often yes, with some trade-offs. While additive resins aren't a direct 1:1 replacement for their thermoplastic counterparts, many are engineered to mimic their key properties.

For example, several of Carbon's resins provide performance comparable to common thermoplastics:

ABS: RPU 70 and UMA 90 offer similar stiffness and toughness to ABS, making them great for functional prototypes of enclosures and housings.
Nylon (PA): RPU 130 can be used for applications requiring the toughness of unfilled nylon, while filled grades like EPX 82 offer higher stiffness.
Polycarbonate: RPU 130 and EPX 82 deliver good strength and heat resistance, and IND 405 provides optical clarity similar to PC.

The key is to understand the specific requirements of your application. While an additive material might not match every property of a thermoplastic, it may be more than sufficient for the functional needs of your part, especially during the prototyping and validation phases.

Tolerance & Accuracy Comparison

When it comes to dimensional precision, additive and molding offer very different performance. While Carbon DLS can achieve tolerances of around ±0.003 inches, injection molding can reliably hold ±0.001 inches or even tighter for demanding applications.

For many prototypes and functional parts, the accuracy of additive is perfectly sufficient. It allows you to test form, fit, and function with confidence. However, when a project demands the highest level of precision for critical components, especially in medical devices, injection molding remains the standard.

Aprios' Role in Helping You Decide

Because Aprios offers both Carbon Additive Manufacturing and Injection Molding in-house, we aren’t pushing you toward one solution. Instead, we help you:

Iterate in additive
Validate in bridge tooling
Scale in production molding

Our goal is simple: make sure your product development path is faster, smoother, and smarter.