Injection molding and 3D printing have a lot in common. Both processes create objects from raw materials, typically by applying heat or radiation to a material that hardens. In the case of injection molding, this means molten plastic is forced into a steel mold, cooled, and ejected from the machine as a finished part.
With 3D printing, fine dust of plastic is layered onto a platform until the machine is told to stop, at which point the part has been printed.
Of course, there are significant differences between these two processes as well. For example, 3D printing is becoming a mainstream method for cost-effectively creating prototypes and small batches of parts. On the other hand, injection molding is a high-volume process that remains the domain of large plastic injection mold companies.
Injection molding has been around for many decades now, and it’s still going strong, so why would anyone consider 3D printing an alternative manufacturing method? In this article, we will examine some of the strengths and weaknesses of both processes to determine whether or not 3D printing is a viable option.
3D Printing Strengths
The two most significant advantages of using 3D printers are their flexibility and low cost per part. Unlike injection molding, there’s no need to create a steel mold that will last for thousands of parts.
You don’t even have to create a mold for many types of 3D printing. Several processes build objects by laying down successive layers of material, and there’s no need to create an impression in a mold if this is the case.
Because creating molds isn’t necessary with most 3D printing technologies, they can create just about anything without worrying about upfront costs. However, molds are expensive, especially when made using modern CNC milling equipment, so not having one can help save on manufacturing a part.
Another way 3D printing can save on processing costs is by allowing for an almost infinite range of material properties in the same object. Most objects manufactured by injection molding are made out of homogenous plastic.
A few examples like glass-filled nylon aside, it’s generally impossible to start with one material and end up with something entirely different after the injection molding has taken place.
With 3D printing, on the other hand, you can design your object with whatever materials meet your needs for strength, rigidity, thermal expansion, and so on. A single object can have adjustable physical properties across its surface or throughout its bulk if necessary.
Injection Molding Strengths
There are a few critical areas in which the plastic injection mold remains the undisputed champion, and they all come down to pure output capacity. A modern injection molding machine can consistently produce more than 100,000 parts per year.
Considering that the most prolific 3D printers can produce fewer than 50,000 items annually, it’s easy to see which process is better suited for high-volume production.
Another area where injection molding has a considerable advantage over its printing counterparts is accuracy. For the most part, injection molds are created using CNC milling equipment that can achieve tolerances measured in tenths of a millimeter. On the other hand, 3D printing technologies tend to be less accurate due to layer thickness variations.
Part Geometry Differences
One key difference between injection molding and 3D printing comes down to the limitations of each process as it pertains to part geometry. Injection molding is limited by the size and shape of a steel mold, which can be quite large depending on how many cavities are built into it.
In addition, longer runs involving thousands of parts typically require more individual molds, making injection molding a poor choice for even moderately complex parts.
3D printing, on the other hand, is limited only by the size of a 3D printer and its ability to accommodate long or multiple pieces that may be needed to fabricate an object. This makes it much easier for designers to create highly complex objects like medical devices and sporting goods.
Another key difference is that injection molding can produce parts in a wider variety of materials, including high-performance plastics, rubber, and metals. 3D printing, however, is typically limited to organic polymers or organic/inorganic composites.
That said, several new metal 3D printing processes are emerging on the scene that may compete with injection molding in terms of part accuracy and material variety.
How It Compares To Other Technologies
For the most part, injection molding has a lot to offer when building large quantities of parts. On the other hand, 3D printing is excellent for prototyping and short-run production runs. Still, due to its lower output rates and lack of material variety, it cannot match the speed or part quality.
In low-volume production, one area where 3D printing is beginning to show some real promise beyond traditional prototyping. This new technology can allow manufacturers to produce one-of-a-kind products, which has already led to entire lines of personalized footwear for Adidas and Nike.
The ability to create complex geometries is another area where 3D printing can excel, but it’s not yet there. While the technology has improved significantly over the past few decades, most 3D printers are still limited by either time or build plate size when creating objects with highly detailed features.
Cost Comparisons
The cost of injection molding varies widely depending on the market, product type, and production volume. It can be anywhere from $5,000 for a primary run involving less than 1,000 units to more than $1 million for highly complex or customized products.
3D printing is also quite variable in pricing, but costs are typically much lower than injection molding. Assembling the technology, materials, and labor necessary to produce a single product will usually cost between $100-$500 per unit or more.
Conclusion
When it comes down to it, both injection molding and 3D printing have their advantages and disadvantages, depending on the needs of a company. Injection molding is a tried-and-true process that usually achieves higher part quality, faster lead times, and less waste per unit.
3D printing excels in design flexibility, but its low throughput and material limitations make injection molding a better choice for most manufacturers.