3D printing is an additive manufacturing. Its principle is to cut the model into N layers/N multi-points, and then stack them layer by layer/bit by bit in order, just like building blocks. Therefore, 3D printing can effectively produce complex structural parts, such as hollow parts, but CNC is difficult to achieve the processing of hollow parts. CNC machining is a material-reduced manufacturing. Through various tools running at high speed, the required parts are cut according to the programmed tool path.
Therefore, CNC machining can only process rounded corners with a certain degree of arc, but cannot directly process internal right angles. It must be achieved by processes such as wire cutting/sparking.
CNC machining at right angles is no problem. Therefore, parts with inner right angles can be considered for 3D printing and processing.
There is also a curved surface. It is also recommended to choose 3D printing if the surface area of the part is relatively large. CNC machining of the curved surface is time-consuming, and if the experience of programming and operator is not enough, it is easy to notice obvious lines on the parts.