Injection molding and additive manufacturing are two very different manufacturing processes. But there seems to be some confusion around whether injection molding can be considered a type of additive manufacturing.
In this post, as a professional plastic injection molding manufacturer, we’ll break down the key differences between these two techniques. And I’ll explain why injection molding is not additive manufacturing.
How Injection Molding Works
First, a quick overview of the injection molding process.
Injection molding has been around since the late 1800s. But it wasn’t until World War II that injection molding really took off as a way to mass produce plastic parts quickly and efficiently.
Here’s a high-level look at how it works:
- Plastic pellets are fed into a large hopper.
- The pellets are heated up until they become a viscous liquid.
- The liquid plastic gets injected under high pressure into a steel mold.
- The plastic cools and solidifies into the shape of the mold.
- The mold opens up and the part gets ejected.
This process allows factories to pump out thousands of identical plastic parts each and every day.
In fact, companies use injection molding to produce everything from Legos to auto parts. It’s one of the most common ways that plastic stuff gets mass produced.
And it’s been crucial for large scale manufacturing over the past 75+ years.
What Is Additive Manufacturing?
On the other hand additive manufacturing (aka 3D printing) is a relative newcomer on the manufacturing scene.
It wasn’t until the early 1980s that additive manufacturing started to become a reality. And the first commercial 3D printer didn’t hit the market until 1987.
So what exactly is additive manufacturing?
Here’s the textbook definition:
“Additive manufacturing refers to processes used to synthesize a three-dimensional object in which successive layers of material are formed under computer control to create the object.”
In plain English:
Additive manufacturing works by creating a 3D object layer-by-layer using some kind of raw material. This material gets laid down one cross-section at a time until the full object has been “printed”.
The most common type of additive manufacturing is fused deposition modeling, better known as FDM. This is what most hobbyist desktop 3D printers rely on today.
But additive manufacturing comes in all shapes and sizes:
As you can see there are LOTS of additive processes. And new techniques seem to pop up every year or two as the technology continues to advance rapidly.
Is Injection Molding Considered Additive Manufacturing?
Injection molding is not considered additive manufacturing. The two processes represent fundamentally different approaches to manufacturing. Injection molding is a subtractive process focused on efficiency and consistency for mass production, whereas additive manufacturing emphasizes customization and complexity, making it suitable for smaller production runs and unique designs.
Why Injection Molding Isn’t Additive Manufacturing
So now that you understand the gist of how injection molding and additive manufacturing work, let’s talk about why they’re totally different processes.
There are a few key reasons that injection molding does not qualify as additive manufacturing:
1. Injection molding isn’t additive
This one seems obvious. But it’s important.
By definition, additive manufacturing refers to adding material layer-by-layer or drop-by-drop. The keyword being “adding”.
As we learned earlier, injection molding works by injecting molten plastic into a mold all at once. The material isn’t added layer-by-layer. It’s injected in one shot using a high pressure injection ram.
So injection molding fails the basic “additive” test that qualifies something as additive manufacturing.
2. No computer-controlled deposition
Another requirement for a process to be considered additive manufacturing is this:
The material must be deposited under computer numeric control.
In other words, a computer needs to precisely control where and how much material gets laid down.
The injection molding process relies on metal molds…not computers…to shape each part.
And the injection of material happens too quickly for a computer to control. We’re talking less than 10 seconds in most cases!
So once again injection molding fails on a technicality.
3. Almost no design flexibility
Another key difference comes down to adaptability and iterations.
One of the huge benefits of additive manufacturing is flexibility. With 3D printing you can tweak a design and print another prototype. Rinse and repeat until you hone in on the optimal design.
But that’s not how injection molding works. Before you can injection mold something, you first need to create (and pay for) an injection mold out of steel or aluminum.
This single mold might cost $10k+. And depending on the complexity it can soar into the $100k+ range.
Either way, once a mold is made you’re locked into whatever design is shaped into that block of metal. Any changes mean starting over from scratch and producing an entirely new mold.
So if design iterations and flexibility are important (like in the prototype stage) injection molding fails big time.
When to Use Injection Molding vs. Additive Manufacturing
At this point I hope I’ve made it crystal clear that injection molding and additive manufacturing are two totally separate animals.
But that begs the question:
If you’re looking to produce plastic parts, when should you choose injection molding instead of 3D printing (or vice versa)?
Like most things in manufacturing, it depends. But here’s a quick cheat sheet:
When injection molding makes more sense:
- Producing 10,000+ identical parts
- Parts have consistent, less complex geometries
- Tight tolerances and precision are needed
- Strength, durability and performance are critical
- The budget allows for expensive injection molds
When additive manufacturing is preferable:
- Prototyping new products
- Customized parts are needed
- Complex geometries and custom designs
- Short production runs (think <1,000 units)
- Speed is critical (no tooling lead time)
- Design changes happen frequently
Obviously this is oversimplified. But you get the point. Each technology has its sweet spot in terms of ideal use cases.
Wrapping Up
Hopefully you now have some clarity around injection molding vs additive manufacturing. And whether injection molding can rightly be considered an “additive” approach.
The TL;DR is no, injection molding does not qualify as additive manufacturing. The process itself fails to meet the official definition that real 3D printing technologies adhere to.
That said, injection molding and additive both have important roles to play when manufacturing plastic components. It just comes down to selecting the best process for your specific needs based on the pros and cons of each.
So as you considers different manufacturing techniques, be sure you fully understand what sets additive and injection molding apart. Even though on the surface they might seem kinda similar.
What about you? Have any other questions around injection molding or additive manufacturing? Let me know in the comments!
