I have recently collaborated with a mechanical designer on a proposal to turn an older model robot arm into a plasma cutting system. This experience has left me pondering exactly this same question. Would this plasma cutting system be robotic because it's based on a six-axis robot arm, or CNC because it accepts a fixed tool path written in G-code?
Advances in the various CNC machine tool technologies are allowing the newer CNC systems to perform tasks that have traditionally been thought of as robotic. So as the traditional boundary between CNC and robotics disappears, and these two words become a distinction without a difference, we can either learn to live with that ambiguity, or attempt to bring the boundary between robotics and CNC back into focus by redefining what we mean by robotic
What that redefinition might be, I’m not ready to propose. But for my own personal usage, I’m finding that my notion of CNC is broadening to include any system that works via computer/ numerical control and then to reserve the term robotic for those systems that require an additional layer of independent decision making beyond that of simply running a hard-coded tool path.
For example, a CNC welding system would expect the work piece to be clamped in a known fixed position. While a robotic welding system would be one that, based on work piece and welding-head position information, could adjust its operation to a range of varying working situations.
Here is an example from YouTube of what I would call a robotic welding system,
In other words, I’m beginning to see CNC and robotic systems, not as two separate things, but rather I see robots as a subgroup within the category of CNC, i.e. robot = (CNC + AI).