Differences Between Injection Molding and CNC Machining

Intro

When it comes to manufacturing a product, you might be torn between CNC machining and injection molding. Both of these are manufacturing methods, and they’re both valid options. Depending on your situation, one of these might be favorable over the other.

To better explain the differences between injection molding and CNC machining, we put together this guide. Each section will describe a comparison between the two manufacturing methods. We’ll also describe which option is better in each of the comparisons.

Overall Turnaround Time

If you need a thousand products delivered as soon as possible, you’ll want to use injection molding. Injection molding machines are seriously fast, and they can operate around the clock. It’s common for facilities to run them

 24/7 in dedicated plants. One of these machines can create one product in less than a minute, and it just keeps going.

With CNC machining, there’s a lot of human interfacing. Materials need to be loaded, programs need to be executed, and parts need to be rotated and centered. Even highly autonomous CNC machines will require a machinist to help along the way.

In addition, CNC machines are a lot slower than injection molding machines. The combination of these factors makes it the slower alternative.

The better option: Injection molding.

Materials Used

When it comes to injection molding, you’ll be choosing between different plastics to work with. The process requires a material that can melt, become moldable, then cool and harden into a solid part. Due to these constraints, you won’t be able to use metals, woods, or ceramics in injection molding — you can only use plastics.

CNC machining offers a wider variety of materials to choose from. In general, you can work with all of the same plastics used in injection molding, plus more. If you want to make a metal part, then CNC machining is your only option.

The better option: CNC machining.

Costs Per Unit

One of the biggest differences when it comes to full-scale production is the total cost. Most of the time, the cost per unit will go down as the order size goes up. In other words, as you order more parts, the total cost per part will be lower.

With injection molding, the cost savings are dramatic. This is because the upfront cost of the tooling becomes diluted as you order more parts. What might cost a dollar per unit for the first 100 parts can go down to a dime per part for the subsequent 10,000 parts.

In this comparison, the overall cost per unit is a lot higher for CNC machining as batches get larger. This is due to the time it takes to machine a part in addition to some operational constraints (since machinists are involved). 

You might still get a discount as you order more parts since there’s less programming and startup time. Still, the savings pale in comparison. 

An injection molder can be run nearly autonomously and can run for days on end. As you get quotes for batches upwards of 100 units, you’ll see the real difference between CNC machining and injection molding.

For small batches of less than 10 parts, CNC machining will be less expensive. Remember, the tooling costs for injection molding only pay off as you make hundreds to thousands of parts.

The better option: CNC machining for small batches, injection molding for medium and large batches.

Total Volume of Production Runs

When it comes to production runs, the quantity will decide which of these two options is right for you. CNC machining can’t keep up with injection molding machines, so they’re typically used for smaller batches (less than 100, but ideally less than 50).

With injection molding, you can make millions of the same part annually as long as you replace the tooling as needed. CNC machines can only offer a fraction of that same throughput, largely due to the operating speed of CNC machines as compared to injection molding machines.

So, if you need thousands of the same part, you should stick to injection molding.

The better option: Injection molding.

Ability to Revise, Prototype, and Iterate Designs

The one big downside when it comes to injection molding is that the design is locked in once the tooling is made. After the mold is fabricated and fine-tuned, you can’t make any adjustments to it, which means your product will be unchanged.

With CNC machining, you can adjust the design repeatedly and keep creating new parts.

This means that CNC machining is a better alternative if you’re in the early stages of a design. You can fabricate a few units, test them, take a close look at the design, then change the design and try again. 

Injection molding should only be used on mature designs that aren’t going to change in the near future.

The better option: CNC machining.

Conclusion

Knowing more about these two manufacturing methods will help you save money and time in the future. For your upcoming project, make sure you have the right machine shop in your corner. You can trust our experts at Rapid Axis to deliver high-quality parts that are either injection molded or CNC machined.

Reach out to us today for a free quote and let us explain which method is right for your project.

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