CNC Machining vs 3D Printing

The advances in technology have transitioned the original manual machining mill from the 1800s to a computer-driven automated process in the 1960s to a complex electronic operation of today that can complete a production run on its own. This new level of computer technology with G-code navigation has also created the ability to build parts with 3D printing. Whether removing material or building up material to create a part, there are unique applications that are best suited to CNC machining versus 3D printing. We will examine some key points of difference and commonality to help guide your production choice.

CNC Machining

CNC machining uses computer design and software to produce a part with a subtractive process from a solid block of material. There are a variety of tools and feeding methods available, including multi-axis rotations, that limit CNC machining only to your imagination. One of the most common CNC machines is the mill. A milling overview is one of the best ways to understand CNC machining.

CNC Machining

3D Printing

This new technology has only been around for a few decades. As much as CNC machining is changing, 3D printing is advancing tenfold. Responding to a similar computer design with specific G-code instructions, a part is developed layer by layer in a building process. Think of your home printer as it produces a photograph feeding the print head back and forth, but add an additional axis to create height as well.

Differences and Similarities

There is a vastly different market for each production option due to their production variables. They both create 3D products from 3D CAD designs. While the CNC process takes material away, like sculpting, to produce a part, 3D printing adds materials, more like molding. This is not the only difference between these two manufacturing approaches. Where a CNC machine may fabricate parts to build a space shuttle, a compact 3D printer may be onboard to fabricate needed parts for repairs.

Materials – CNC machining is best known for the production of metal alloys, like aluminum, brass, copper, steel, and titanium, due to its robust machine design. CNC machines can also fabricate from wood, foam, fiberglass, and plastics such as polypropylene. 3D printing is expanding its selection of materials and has grown from plastics and polymers to include metals, ceramics, glass, and even foods, like chocolate.

3D printers can’t adapt to new material input, where a CNC easily adapts. Metals with high melting points also cannot be used on 3D printers because of the nature of how materials are heat activated to form the finished product.

Speed – Each 3D print design produces a custom run and can only print at one speed. This creates a great application for prototypes, but not large production runs. CNC machining can produce thousands of pieces an hour once the machine is programmed and bar stock is set to feed. CNC machines also can run at faster speeds with less accuracy, as dictated by the individual production run.

Size – CNC machines can literally fill a room. They are equipped to handle large production pieces for industries like aircraft and automotive production, but can also fabricate a delicate pin for a circuit board. A 3D printer, although far advanced from a home or office printer, has a capacity for parts only as large as the print bed. This can include smaller parts for the automotive industry, furniture parts, toys, jewelry, as well as medical prosthetics and dentures.

Quality – Tolerances and quality differ greatly between these applications. CNC machines can provide accuracy measured in micrometers and, due to their high heat tolerance, can provide beautiful smooth finishes and thin walls for parts made from a variety of materials. Their repeatability is also highly accurate. 3D printing, although advancing, can still show lines between layers, and even warp during production. Parts with complex geometries may be better suited to 3D printing because of the additive approach. Material selection and manufacturing approaches for both CNC and 3D greatly affect quality.

Customization – The easy ability to start a new project on a 3D printer makes it the right choice for custom pieces, such as art, or medical devices. Making a prototype, or single piece on a CNC machine requires a greater setup time, cleaning between jobs, and the cost of equipment sitting idle during the changeover must be considered.

Budget – This now draws our attention to cost. It is evident that large production runs are most cost-effective on a CNC machine. They are most often the economical choice for metal fabrication as well. 3D printing has the same cost regardless of the complexity of the design. This can prove to be more economical than CNC machining when a higher degree of precision is needed.

Environmental Concerns – The act of subtractive manufacturing in CNC production creates waste. There is a market for swarf, and smarter programming and equipment is producing less. With the additive process of 3D printing, there is no waste material. Another environmental concern is the noise created through vibration. CNC machining operations also have a greater carbon footprint than 3D printing.

Benefits of CNC Machining over 3D Printing

With the relative infancy of 3D printing, there is room for growth. Presently it doesn’t offer the variety of options in material strength, speed, quality, or consistency available with CNC machining. This all boils down to cost, and in any business, the cost is always the bottom line. In the comparison of CNC machining versus 3D printing, CNC machining is the clear winner in our assessment.

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