1.Material authenticity of CNC machining: In CNC machining, any material specified by the customer, such as aluminum, steel, alloy steel, plastic, etc., can be used to achieve material diversity. CNC machining starts with a piece of solid raw material, and removes material through cutting, milling or other mechanical processing methods to finally form the desired part. This method maintains the original characteristics of the material, because the processing process only removes excess material without changing the properties of the remaining material. Customers can choose materials with specific grades (i.e. specific models and specifications) with known mechanical properties and chemical composition, which keep the material natural, real, 100% of the raw material characteristics from before to after processing. Unlike CNC prototype machining, 3D printing and prototyping can only use specific materials, such as plastic filaments, powders (metal or plastic) or photosensitive resins, which must be able to melt or solidify to form each layer. Especially those grades of materials that are not specially designed for 3D printing, which means that 3D printing cannot use those materials with specific mechanical properties and chemical composition.
2. Low cost: For certain types of parts, CNC machining is a high-speed manufacturing process. A CNC machine equipped with a powerful spindle and good machine tooling can remove raw material quickly. If the part geometry is simple (for example, a solid base plate that requires holes, threads, steps, or slots), very little raw material is removed. In this case, the unit price of CNC machining will be much lower than 3D printing, because it takes many hours to print such a part.
3. High precision: CNC machines can process parts very accurately according to the design drawings, and the error range is usually within a few microns. On a good CNC milling machine or CNC lathe machine, the machine tolerance can reach ±0.005 mm. If we can remove 0.005 mm in the final cutting of the workpiece, it means that we can easily get parts with a tolerance within ±0.01 mm. In contrast, the 3D printing process prints parts layer by layer, with a minimum layer height of 0.05 mm, which means that the tolerance of the part cannot be less than 0.05 mm.
4. Better surface quality: CNC machining can provide a better surface finish, sometimes even eliminating the polishing step. When the CNC milling machine reaches 15,000 rpm and the lathe reaches 6,000 rpm, the surface roughness of CNC machined parts is less than Ra 0.8, which is good for surfaces that can be bead blasted, painted or anodized without manual grinding. Meanwhile, parts manufactured by selective laser sintering (SLS), selective laser melting (SLM) or direct metal laser sintering (DMLS) processes have a surface roughness much greater than Ra 3.2.
5.More flexible part size: Large CNC machining centers can have a 6m x 3m or larger table, which means that very large parts can be milled. As far as we know, the largest lathe can reach a diameter of 5 meters. At the other end, with a precise 5 axis CNC milling machine and a cutting tool with a diameter of 0.05mm, we can mill tiny geometries from a small piece of material of 1mm x 1mm x 1mm.
6. Complexity: CNC machines can process complex geometric prototypes and parts, including those that are difficult to achieve with traditional manual processing, and can process complex contours and 3D shapes, such as non-linear curves, free-form surfaces, etc. They can easily process complex internal features, such as oblique holes, irregularly shaped holes, and internal threads. Modern CNC machines can perform 5 axis or even more-axis processing, making it possible to process complex 3D shapes.