Blog Post

Injection Molding vs. 3D Printing: Ten Considerations

Injection molding vs. 3D printing doesn’t have to be an either/or proposition. Some projects use both processes during a product’s lifecycle. Traditionally, 3D printing has been used for prototyping and injection molding has been used for production. Additive manufacturing has advanced, however, and 3D printed parts aren’t limited to prototypes anymore.

Today, there are 3D printing technologies that can create production-quality components – and in the volumes you may require. These technologies include Projection Micro Stereolithography (PµSL) from Boston Micro Fabrication (BMF), a form of microscale 3D printing that supports the use of plastics, metal-plated plastics, ceramics, hydrogels, and composites resins.

Metal-plated 3D printed plastic parts

3D printing has many advantages, but there’s often a part volume – a crossover point – where injection molding is used. With plastic injection molding, tooling that costs tens or even hundreds of thousands of dollars can be amortized across these high production volumes. Quantity is just one consideration, however, so consider these ten factors when comparing injection molding vs. 3D printing for your project.

  1. Lead Times
  2. Setup Costs
  3. Volumes
  4. Materials
  5. Part Size
  6. Part Tolerances
  7. Part Strength
  8. Design Maturity
  9. Design Complexity
  10. Surface Finish

The following sections explain.

#1 Lead Times

The steel or aluminum molds that are used with injection molding can take weeks or months to machine. The injection molder then sends a customer part samples for functional testing and dimensional measurements. If the initial samples aren’t suitable, the mold maker may have to adjust the tool, which extends project timetables.

3D printing has shorter lead times. Unlike injection molding, there’s isn’t a metal tool that needs to be CNC or EDM machined. Customers still need part samples, but there isn’t a mold to modify if changes are required – and the settings on a 3D printer can be adjusted. Using 3D printing, it’s even possible to produce low-volume injection molds.  For high volumes in a single run, however, injection molding is faster.

#2 Setup Costs

Most injection molding costs are associated with the tool. Steel costs more than aluminum, and both metals cost more than the 3D plastics that are used to build some low-volume molds. Production molds cost more than prototype molds as well. With injection molding, tooling costs also vary with mold size and complexity. 3D printing eliminates these costs and the variability that comes with them.

#3 Volumes

There are four volumes of parts to consider when comparing injection molding vs. 3D printing: initial order quantity, annual order quantity, total quantity, and crossover volume. Standard parts have a crossover volume in the low thousands. Small, high-precision parts have crossover volumes in the tens of thousands, and that’s part of the reason BMF’s microscale 3D printers are used instead of micro injection molding.

Cost of injection molding vs. 3D printing of standard parts
Cost of injection molding vs. 3D printing of small and complex parts

#4 Materials

Injection molding and 3D printing support many of the same materials. Examples include ABS, acetal, acrylic, PEEK, PEI, polycarbonate, polyethylene, and PTFE. The end-use properties of injection molded and 3D printed materials aren’t the same, however, and injection molding supports some materials that 3D printing does not, and vice versa. With BMF’s open material system, designers can print with the materials of their choice (including non-plastics) or with BMF’s own specially formulated polymers.

#5 Part Size

Micro injection molding can produce small parts, but with high tooling costs and practical limitations such as the size of the mold, the capabilities of the machine, and the part’s minimum wall thickness. Most 3D printers can’t produce microscale components, but PµSL technology can print parts that are smaller than a human hair, which is roughly 70 microns across. PµSL doesn’t just rival precision injection molding in terms of size, however. This form of 3D printing can also achieve extremely tight tolerances.

Micro Nut and Bolt with M0.3 Threads

#6 Part Tolerances

For non-critical applications, the tolerance of injection molded parts is usually ± 0.1 mm. For critical components, such as those used in medical applications, ± 0.025 mm is typical. With PµSL technology, manufacturing tolerances are measured in terms of microns instead of millimeters (mm). Given that 1 micron equals 0.001 millimeter, PµSL printing tolerances of ± 10µm ~ ± 25µm are especially tight.

#7 Part Strength

Injection molded parts tend to be stronger than 3D printed components. Mainly, that’s because injection molded parts are made are made of a single layer of material. By contrast, 3D printing produces parts layer by layer. Material selection matters, however, and BMF materials such as RG resin are durable engineering materials that can be used to produce functional end-use parts.

#8 Design Maturity

Injection molding is ideal for manufacturing parts with mature designs in high volumes. Once manufacturing begins, however, design changes are impractical. 3D printing readily supports design changes from prototyping through production. In other words, it’s easier to identify and correct problems without scrapping tools or wasting materials, a key consideration for designs that are still maturing.

#9 Design Complexity

Compared to injection molding, 3D printing supports greater complexity. From holes in the middle of parts to intricate shapes or spoke-like features, there’s greater design freedom with this form of additive manufacturing. With injection molding, the tool limits part design. For example, parts with right angles may break during ejection and ribs are needed for support.

Chip Array Socket with Arrays of 130µm Through Holes

#10 Surface Finish

Finally, comparisons of injection molding vs. 3D printing need to account for surface finish. Generally, 3D printed parts have a rougher surface finish; however, post-build smoothing can be used. Injection molded parts can have a fine finish, but with higher tooling costs. With plastic injection molding, parts are also subject to surface defects such as mold flash.

Comparing Injection Molding vs. 3D Printing

Injection molding is ideal for high-volume production and for projects with longer turnaround times. Although it can be used with parts of various sizes, injection molding offers less design freedom. 3D is better for low-volume production runs, designs with frequent changes, and projects with quick turnaround times.

There are many types of 3D printers, but PµSL technology from Boston Micro Fabrication (BMF) lets designers get prototypes and production-quality parts in small sizes – and without the high costs of micro injection molds. To learn more, contact BMF.