CNC Machining vs 3D Printing for Metal Prototypes

metal prototypes

It is tempting to see CNC machining as a manufacturing process, and 3D printing as prototyping. CNC can create high-precision parts out of industrial-quality metals while additive manufacturing (AM) is cost-effective and optimized for one-off, on-the-spot parts.

The reality is much more complex than that. Metal 3D printing can be a great tool for prototyping, but CNC machining can also be useful if you have the right approach. It can be hard to decide between the two.

There are many factors to consider when comparing CNC machining and AM for prototypes. In this article, we will discuss their difference and benefits.

CNC vs AM: Premium vs economy?

CNC machining can seem more expensive than 3D printing at first glance. While 3D printers are more common in smaller offices than CNC machines, they are used for very serious projects. Desktop 3D printers are affordable at a cost of a few hundred dollars, while CNC machines can be expensive.

The distinction with metal prototypes is not so obvious. Metal additive manufacturing systems cannot be found in the consumer price range so metal 3D printers are similar in price to CNC machines.

Want.Net is a network of manufacturing companies that allows you to order prototypes or production parts. The only thing that matters is the price of the parts. The machine shop’s investment and maintenance is not something you need to be concerned about.

Is there really a significant price difference between 3D printed and machined metal prototypes? The short answer is no. CNC machining has become more efficient than ever. Engineers can now create large quantities of machined parts in a short time. Metal AM is still the most expensive type of 3D printing.

When deciding between 3D printed and CNC machined prototypes, budget should not be the only consideration.

Benefits of CNC Machining for Metal Prototypes

custom cnc parts

CNC machining can be used to manufacture all types of metal parts in a variety of industries. CNC machining is also used extensively for prototyping and production. Machine shops all over the globe frequently take orders for prototypes in final-stage, visual and mechanical stages.

CNC machining has many advantages, including strong parts, scalability, and tight tolerances. This makes it a better process than additive in many cases.

Mechanical properties

CNC machining and AM are fundamentally different methods of manipulating metal. Processes like Selective Laser Melting are used to build layers from melted powder. CNC cuts material from an extruded piece of metal called a “blank”.

AM can be used for prototypes that are quite strong, but CNC has significant mechanical advantages. The extruded blank metal is consistent in physical appearance and does not require adhesion between layers. This solid block can be used to create strong and rugged prototypes with very little deformities.

Scalability

It can be cheaper and faster to use AM machining for metal prototypes in very small quantities. 3D printing is fast, despite its slow pace of printing.

CNC is cheaper and more efficient than any other option if you need more than a few units.

This has many implications. CNC machining can be more cost-effective than 3D printing for a single prototype. CNC machining is much more efficient and quicker if the project has to be scaled up or you need to make more units.

A machined prototype can be a shortcut to mass production, but a 3D printed prototype cannot.

Tolerable tolerances

CNC machining is generally more precise than 3D printing. This means that metal prototypes can now be machined to much tighter tolerances with a CNC machine.

While CNC tolerances can go down to +-0.025mm, high-end metal 3D printing machines can only go up to +- 0.200mm.

A CNC machine can also make metal parts very repeatable. This is especially important in production but also useful when making multiple prototypes for testing mechanically.

Benefits of AM for metal prototypes

metal prototype by 3d printing

CNC machining is a great tool for prototyping. It produces superior metal parts and can be scaled up or bridged.

However, additive manufacturing offers several key advantages.

One-offs: Speed and cost

AM is the best solution for prototypes that need to be produced in a very short timeframe. Because setup times are very short, parts can be 3D printed quickly and shipped within days.

Geometries internal

3D printing technology can create complex shapes with unique geometries even from the inside.

These internal geometries cannot be recreated with a CNC machine because the cutting tool of a CNC machine cannot reach the inside of a part without reaching the outside. 3D printing builds a part in layers across the cross-sections, so there are no geometrical limitations.

How to Make The Decision

CNC machining is preferred for creating metal prototypes. This is because it creates precise, repeatable parts with excellent mechanical properties. The best process for you depends on your specific needs and situation.

There are situations where CNC might be more preferable than AM.

  • For prototypes made of metal that are particularly strong
  • If tight tolerances are necessary
  • If you need multiple copies of the prototype
  • If there’s a possibility of scaling the project in future
  • If the prototype needs radii or rounded edges

There are situations where AM might be more preferable than CNC.

  • If only one or a few prototypes are required and the criteria in the above list don’t apply
  • If the prototype has a complicated internal geometry
  • If there is a tight deadline
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