Manufacturing Transitions: Moving Between CNC Machining and 3D Printing - MJ Engineering

–  Bailey Hudson

Neither CNC machining nor 3D printing is a new technology. Computer Numerical Control (CNC) has been around since the 1950s, while 3D printing was invented in the mid-1980s. But both technologies are in increasing use today. CNC has become one of the dominant machining methods, with CNC lathes, mills, and routers fast becoming the standard.

As for 3D printing, technology has taken off in recent decades years. With its ability to produce almost any shape, many manufacturers have started to ask about the exact relationship between CNC machining and 3D printing. How do the two technologies work? Can they be used together? Will it ever be possible, or practical, to abandon CNC altogether for 3D printing?

In this article, we’ll look at some of those questions, and suggest some ways that a manufacturer could use both methods in conjunction.

Similar goals, different methods

Both CNC and 3D printing are machining manufacturing techniques, but they take a radically different approach. CNC is a subtractive process whereas 3D printing is an additive process. With CNC, Tto make a cylinder, for example, you might begin with a vaguely rectangular shape, then use a lathe to machine away excess material until the workpiece was cylindrical. The resulting piece will be smaller than the one you began with; you’ve removed material to make the part.

3D printing is the exact opposite. With 3D printing, you begin with no shape at all – simply the printer itself and a metal powder as raw material. The powder is used to slowly build apart from the ground up, adding material layer by layer.

Additive machining manufacturing provides a whole new approach for manufacturers. 3D printing can produce almost any shape, including geometries that might be difficult to achieve through subtractive machining. The potential applications for 3D printing are nearly limitless, with special potential for prototyping and R&D.

Pros and cons

So why not simply abandon CNC subtractive machining-manufacturing and move everything over to 3D printing? Why not stop cutting metal parts (subtractive machining-manufacturing) and only build them instead (additive machining manufacturing)?

Unfortunately, 3D printing does have some drawbacks. First and foremost, the process is quite slow – far slower than the various subtractive machining processes. Large-scale, industrial-sized projects would require a much longer time to build than to cut, particularly if there is a large number of parts to produce. Thus, one of the first questions many manufacturers use to determine the correct method to use is simply to ask, “how many parts do I need?” If the answer is a large number, CNC is likely to be much faster and more efficient. 3D printing also produces parts with much larger tolerances than CNC machining, meaning the parts can be a bit rougher and still in need of finishing. 

Two are stronger than one

The greatest potential for both methods comes when they are used in conjunction with each other. For individual parts, 3D printing provides a way to produce one-off or small runs of parts with geometries that would be difficult to cut on a CNC machine. After the 3D printing is complete, the same part could then be subtractively machined via CNC to finish surfaces, insert threaded holes, or any number of other machining steps.

The two methods can also be used in the overall workflow. 3D printings excel at producing prototypes and models, parts that are often one-off productions or require small numbers, and where the time pressure is not great. Once a part has been prototyped and the design refined, a CNC program can be made that allows operators to produce the part in far greater quantities on a CNC lathe or mill.

Used in this way, the manufacturing process starts with additive machining manufacturing and then moves to subtractive machining-manufacturing, to produce even a difficult or completely new part with tight tolerances.

Back and forth

Using CNC machining and 3D printing isn’t a matter of transitioning entirely from one to another, but of using both technologies at once. In the real world, that means being flexible and deciding on a case-by-case basis which method is best for a given part.