Explore 3D printing vs. injection molding: how they work, how they fit into the manufacturing process, their merits, and their nuances.

3D printing and injection molding are two manufacturing methods that are taking the industrial world by storm, especially when it comes to the mass production of plastic parts. Both are now essential tools for designers and are powerful product development approaches for teams and individuals alike. However, it’s worth noting that these processes differ in key ways despite sharing some similarities. This article will explore 3d printing vs. injection molding and how each method uniquely excels at crafting complex, plastic parts.

The Emergence of 3D Printing and Injection Molding

While both 3D printing and injection molding have rich histories, the latter has been around much longer. The world’s pioneering injection-molding methods were invented in 1872, birthing a new plastic industry for everyday items and accessories that needed high-volume production. While John and Isaiah Hyatt laid the groundwork, injection molding didn’t begin resembling its current form until the 1930s.

This decade gave rise to new thermoplastics like PVC (and others), which firmly jumpstarted the plastics-manufacturing revolution. Injection molding would take another leap forward after World War II, thanks to James Watson Hendry’s screw-extrusion and gas-aided innovations. Plastics rapidly gained acclaim for their strength and relative weightlessness.

Comparatively, 3D printing is a modern design revelation. The stereolithographic printing method, invented by Charles Hull in the mid-1980s, relied on electronic guidance, and it still does in different forms today. While early equipment was rather expensive, 3D printing is now better-renowned for its higher accessibility. Numerous users have since adopted systems with varying complexity.

How does 3D printing work?

A form of additive manufacturing, 3D printing technology works in a few different ways. This article briefly mentioned stereolithography, where CAD and CAM files essentially ‘instruct’ a UV printer to sculpt objects from sensitive photopolymers. Emitted UV rays precisely cure portions of the polymer, progressively creating a final product. Offshoot methods leverage digital projectors. This polymer-hardening process happens layer-by-layer via light exposure, and the excess liquids simply drain away.

Other additive manufacturing processes use powders derived from various materials in novel ways. The first, called multi-jet modeling (MJM), combines colored binding adhesive with successive powder layers, eventually forming intricate designs. On the other hand, electron-beam melting (EBM) melts similar powders in layers. Both techniques may create products with smooth surfaces.

However, excess supportive adhesives used in MJM may need to be removed before a product is considered finished. A cousin of these is selective laser sintering (SLS), during which strong lasers fuse material particles. 

Finally, Fused Filament Fabrication (FFF) involves melting a filament material — commonly ABS or other thermoplastics. The printer selectively deposits this melted material through a heated nozzle. Gradual layering ensures high-quality construction.

Though plastics are easiest to melt and manipulate, you can also 3D print many other materials. Metals, polymers, glass, ceramics, plasters, and even foods are fair game. This flexibility lends itself to industrial applications as well as fun experiments or project iterations.

How Does Injection Molding Work?

The injection molding process doesn’t stray far from its namesake. Melted polymers, thermoplastics, metal powders, and rubbers travel from a heated barrel (and screw) into a metal molding cast. The pressurized liquid then takes the shape of the mold. Friction may also play a role in prepping the material in question. While injection molding can begin with solids, it’s often quicker and easier to melt down granules.

Molds can also impart textures upon the liquids that fill them. Manufacturers add unique treatments to the molds themselves, enhancing smoothness or coarseness. After hardening and cooling, the product is removed, inspected, and subjected to final finishing processes, which could include polishing, sanding, grinding, or cutting. While injection molding is highly accurate, it’s often tricky to perfectly recreate certain shapes, angles, or radii.

3D Printing vs. Injection Molding: How do These Methods Compare to One Another?

Overall, 3D printing enjoys a wide variety of uses. There are multiple methodologies, types of equipment, and associated software applications that streamline the manufacturing process. 3D printing has also become increasingly popular amongst the hobbyist crowd.

Newer 3D printers are cheaper than ever; accordingly, it’s not uncommon to see tabletop printers producing smaller objects while consuming minimal space. These are ideal for desks, residences, or small workshops. This is a relative assessment — while many personal printers might not be cheap, they’re more economical than molding setups. 

Tooling is fairly diverse. Despite this, 3D printing seems to excel with smaller products. Past a certain point (and complexity), 3D printing is no longer cost-effective. Intricate production is possible with sintering, modeling, and melting. However, these parts are less likely to be mission-critical within tightly controlled systems.

3D printing is ideal for small-batch, or low-volume, manufacturing, whereas other methods’ input costs would never allow manufacturers to break even. The turnaround time for product creation is short, and 3D printers cost much less than injection molding machines. Because of this, designers often turn to print for prototyping. It’s easier to churn out new physical product models, primarily when iterative changes are managed within CAD/CAM programs like Autodesk Fusion 360.

Injection Molding

Full-fledged injection molds are most often found in a manufacturing setting because the machines and components are larger. They must also reach extreme temperatures, raising both viability and safety concerns within a home environment. They are also costly — machinery purchases can set manufacturers back tens of thousands of dollars for a single component, like a junction housing.

Even with higher costs, this method certainly has its benefits. Injection molding shines when producing components with the utmost level of accuracy. Final production — not prototyping — is a suitable match for molding. Additionally, injection molding is perfect for making parts of all sizes and intricacy.

Because it’s easy to melt materials down (under the right conditions), this approach can leverage a wide variety of materials, but plastic injection molding is most common. Accordingly, high-volume production is easier with injection molding because molds are duplicatable. They also produce consistent results, time after time, even with large volumes. Scaling production helps reduce per-unit prices while helping companies break even on upfront costs.

Ironically, however, the turnaround time for injection parts is much longer. This makes prototyping suboptimal and can harm the process’s value proposition when creating smaller product batches.

The Importance of 3D Printing and Injection Molding

The question isn’t so much, “Which method is better?” but more so, “Which method is right for us?” 3D printing and injection molding have their own merits. They’re both ideal solutions for today’s manufacturing challenges, supplementing production when traditional machinery can’t cut it alone. Producers can even leverage these technologies in tandem.

Each manufacturing method is poised for massive growth in the next decade. As adoption spikes, the world will see just how successfully each production method blossoms.

With Autodesk’s integrated CAD/CAM/CAE software, Fusion 360, projects involving 3D printing and injection molding are easily tracked and managed, streamlining the overall design process.