Designing plastic parts for manufacturing? The process you design for depends on many factors including part geometry, function, quantity, material, and your place in the development cycle.
We’ll look at some of these common considerations when comparing 3D printing and injection molding and the benefits of the two processes. We’ll also talk about how you can efficiently leverage both manufacturing methods. So, which one is better? It depends.
When Should I Use 3D Printing or Injection Molding?
|
FEATURES/BENEFITS |
3D Printing |
Injection Molding |
|---|---|---|
| Design Versatility | Complex design or geometry | |
| Complex Geometries | X | |
| Assembly Reduction | X | |
| Scalability < 1,000 parts | X | |
| Speed | X | X |
| Customization | X | X |
| Piece-part Price | X | |
| Material Choices | X | |
| Scalability > 1,000 parts | X |
The Benefits of 3D Printing
Versatile and Fast. 3D printing is best suited for precise, repeatable prototyping and low-volume end-use part production to reliably deliver parts fast. The technology’s original use was for rapid prototyping, and it remains a valuable prototyping tool. But advances in new processes and in AM materials have made the versatile technology a viable manufacturing choice for end-use production parts.
Designing for Complex Geometries. For parts with relatively simple geometries, injection molding—and, for that matter, CNC machining—will likely be more cost-effective manufacturing options than 3D printing. However, for more complex or organic geometries, 3D printing is often used. Designs with frequent iterations are also well-suited for AM, which is also why the technology continues to be popular for prototyping. Extremely small plastic parts can also be built in micro-resolutions—a prime benefit for medical component and device design. In fact, additive manufacturing, in many cases, can provide far greater design freedom, though, this freedom can sometimes result in the expense of more production time and greater costs if parts are not well designed for AM. Complexity isn’t necessarily free, as some experts have cautioned.
Combining of Part Assemblies. Related to overcoming complex geometry challenges, however, is an especially key benefit of 3D printing—its ability to consolidate existing part assemblies made from many pieces into a single part. The benefit of a consolidated assembly goes beyond the basic sourcing cost of parts being replaced—the savings could go much deeper to include items such as: elimination of assembly costs like labor, fewer points of failure, and lower operation costs.
When Should I Use 3D Printing or Injection Molding?
|
FEATURES/BENEFITS |
3D Printing |
Injection Molding |
|---|---|---|
| Design Versatility | X | |
| Complex Geometries | X | |
| Assembly Reduction | X | |
| Scalability < 1,000 parts | X | |
| Speed | X | X |
| Customization | X | X |
| Piece-part Price | X | |
| Material Choices | X | |
| Scalability > 1,000 parts | X |
Materials Allow Lightweight Yet Durable Parts. 3D-printed parts offer the benefit of being lightweight yet retain their durability, a major reason why aerospace and automotive companies use AM. Speaking of durability, the advances in additive materials have been significant. Though we’re talking in this post about plastic, it bears noting that additive metals—especially printed aluminum (ALSi10Mg)—have emerged as particularly popular for end-use parts. Our materials comparison guide and 3D printing materials selection guide can offer you some key insights on AM material properties.
Custom Made for Custom Made. The customizable nature of 3D printing is yet another benefit. AM is perfect for low-volume, end-use parts such as wearables, patient-specific medical needs (think dental components and hearing aids), and even low-scale high-performance aerospace parts. The customizable nature of AM allows for reconstruction of low-volume parts that may have been previously cast or molded, but their tooling is no longer running production.
The Benefits of Injection Molding
Hundreds of Material Choices. As we mentioned, you have hundreds of thermoplastic resins as well as elastomeric and liquid silicone rubber options to choose from for production-grade parts. By comparison, we offer around 30 different material options in 3D printing. You can consult our material comparison guide (with data sheets) to focus in on a material, or set of materials, that work best. In addition, check out our alternative materials guide for options to choose from during supply shortages. It even highlights some 3D printing options available when thermoplastics intended for molding are unavailable.
This type of variety is important, especially when determining your part’s application and function. This variety will help you better match the material to the part’s function.
Larger Volumes. Plastic injection molding is best suited for end-use production parts for runs of 1,000-plus parts of most sizes and complexity. Molding provides a range of lifetime part volumes.
Scalability of Products. If you’re designing a part that you’ll need to scale into the thousands, tens of thousands, or even millions, 3D printing isn’t a viable option. There are certain technologies within 3D printing, like Multi Jet Fusion for example, that can be economical choices for scaling when runs of less than around 1,000 parts are desired. Injection molding at Protolabs lets you prototype designs quickly and in the right material, before moving to production. Then, when you’re ready to ramp up production volumes, your design will be optimized for moldability—and scalable into million-plus part quantities.
Also Fast. While some traditional manufacturers may require longer turnaround times for molded parts—several weeks or months in some cases—we’re able to deliver a quicker turnaround for both prototypes and final production parts. Depending on the project and the size of the production run, we can generally mill your mold and ship plastic parts in less than 15 days.
Comparing Cost Between 3D Printing and CNC Machining
Lower Piece-part Price. Cost efficiency is a prime benefit of injection molding. As production volumes scale up into the thousands, injection molding will be a more cost-effective manufacturing choice than 3D printing all things being equal. Granted there will be an initial investment into tooling which can be in the tens of thousands of dollars, the savings in piece-part price will more than make up for that cost.
The primary factors that influence 3D printing cost are the amount of material used and post-processing required.
Moving from 3D Printing to Injection Molding
In many cases, these manufacturing methods play well together in the life cycle of a product, starting with the superior design-mitigation capabilities of 3D-printed prototypes and then shifting to injection molding for increased part quantities. In fact, as one of our Tech Tips on navigating from AM to injection molding points out, for millions of part designs over the years, this has been the preferred combination. The Tech Tips article dives deeper into making the move from AM to molding, covering: Defining a part before designing a part, using multiple prototypes and “cross-quoting” manufacturing processes within our digital quoting platform, maneuvering through molding, choosing materials, and considering costs and timelines.
Examples of companies using both processes abound. An aerospace and defense industry case in point is Lockheed Martin’s quadcopter drone. Miguel Perez, a Lockheed Martin engineer, worked with our online digital quoting platform, which eventually led him to shift from prototyping with 3D printing to low-volume end-use production with injection molding. A medical industry example is The Aura Project, a group of medical-device designers who created the Aura Ventilator during the pandemic last year. The designers first used our 3D printing (and sheet metal fabrication) services for quick-turn prototypes before moving to production with injection molding.
Ultimately, the manufacturing method you choose for your part should be well-suited to your part’s application and function. And, of course, molding and AM are not the only two manufacturing methods in your toolbox. You may want to add CNC machining, which can also be used in combination with 3D printing. Or sheet metal fabrication. Or another process.
For questions on 3D printing, injection molding, or any of our other manufacturing services, or our supplier distribution network, please contact an applications engineer at [email protected] or 877-479-3680. Have a design ready? Upload it now for an instant quote.
