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There are cases where we are asked to CNC machine parts, products, or prototypes that are difficult to machine, too complicated geometrically, will not produce high precision, or simply cannot be machined. what do we do? For these scenarios, 3D printing of parts can be a great solution. So why not replace CNC machining with 3D printing every time? Well, there are advantages and disadvantages, pros and cons for each machine and process. So which one is better for our needs? Under what circumstances do we prefer one over the other? And is there another solution that can combine these two to create a combined part?
The basic difference between the two processes is that with CNC machining we are reducing the material when we start with a foam block, for example by carving; whereas with 3D printing we are layering and adding material until we receive the final product, so it is called additive manufacturing.
The 3D printer uses the same materials that make up the part you are creating, for example ABS PLA and nylon, but cannot switch between materials, whereas in CNC machining we can use multiple types of materials, often adding additional materials at the end. However, machining can be tricky – sometimes we need to use a dust collector while operating a CNC router machine to catch all the excess produced in the drilling, carving and milling process, while producing less waste material in printing. and the whole process is less noisy.
CNC machining can be more precise providing more precision because the machines have a higher tolerance for heat. It can also result in a much smoother polished surface finish given the materials being machined. 3D printers can actually distort, bend, and warp if too much heat is used on the layered material, so if exceptional smoothness is required, 3D printing will fall short.
3D printing is generally an easier and more convenient process and is not as labor intensive as CNC machining as with machining we need to program, write a G-code, set up different tools and speeds, decide on the cutting path and clean up afterwards. . However, part size plays a role, as larger parts take longer to print by adding layer by layer. In general, 3D printing can help in some high geometric complexity prototyping cases where the router tool cannot reach the interior of the shape.
3D printers can only use the area of the printer bed itself to make parts. So if large-scale parts are needed, they may not fit there. It is also not recommended for mass production as the materials are much more expensive and time consuming to manufacture. Therefore, 3D printing is more suitable and cost-effective for low-volume production.
CNC machining can rarely be run unattended and requires a skilled operator, while with 3D printing we can easily run the process unattended and requires minimal training for its operator. However, CNC machining is an older practice (started in the 1940s) and still has a stronger position in the manufacturing industry today. 3D printing is relatively new and continues to evolve to become more useful and adaptable, and may not yet be a complete replacement for machining.
In summary, the most appropriate technique to use will be determined by the material, the geometric complexity, the volume of manufacture and our budget. As a general guide, we would switch to 3D printing primarily if turnaround time is critical, if the part is too complex to machine, to prototype in small volumes, and if we need to use certain materials that cannot be easily machined.
Having named most of the pros and cons of each technique, there seems to be a good solution that actually combines the two to create one part. We often machine parts of the desired product using a CNC router, while making other smaller but more complex parts on the 3D printer, then glue all the parts together to form a unit. Another option is to coat all the glued together parts with a hard coat such as polyurea, polystyrene or epoxy, then smooth and paint them. That way we save time by using the CNC machining process and we can also make more complex parts by combining the best of both worlds to create a hybrid.