Rapid prototyping refers to producing physical models in a short period of time. Some prototypes are used for quick concept visualization while some prototypes are made for specific performance requirements and testing. Prototypes that are made with CNC machining have better strength and high dimensional accuracy. Below are some reasons why CNC machining could be a better option than 3D printing for producing rapid prototypes.
Although initial CNC part programming is required to generate the tool path before setting up the machine, CNC machines can produce parts at a faster rate than 3D printers. So unless the geometry is too complicated, it is a good choice to use CNC machining to produce prototypes.
3D Printing has a dimensional accuracy in the typical range of +/- 0.3 mm whereas CNC machines can deliver much higher dimensionally accurate parts in the typical range of +/- 0.025 mm. So CNC machining can be a great way to produce dimensionally accurate parts with minimum process variation.
3. Choice of Materials
3D Printing is restricted to polymers and plastics but CNC machining is possible for any sort of stock material depending on the availability like ceramics, metals, alloys and many more. The dimensions of the stock is set while preparing the tool cutting path but once the tool path is created, it can be used for various materials if the cutting tools of suitable hardness are loaded on the machine tool head.
With automatic tool change, a CNC machine can change the cutting tools as per the tools that are loaded in the tool magazine. This reduces the time required to change the tools and thus offering a variety of parts to be produced in less time.
CNC machined parts can be made on-demand even if it is one or 5 or a hundred parts. This suits best for new product development and initial launch into market to analyze the demand. Based on demand the same digital manufacturing setup can be used as many number of times as possible on the machine.
CNC machining offers reliability and quality of manufacturing over a large number of parts produced that are functional, high strength and finished components. Surface finish of CNC machined parts is in the range of Ra 3.2 micrometers which is very good compared to the surface finish of Ra 15 micrometers obtained from SLS 3D printed parts.
Dedicated pressure die molds and injection mold dies are needed if the part quantity is more than 10,000. But if the part quantity is lower under a few hundred to a few thousand parts, there is no need for pressure dies for die casting or molds for injection molding and the components can directly be manufactured out of CNC machining by preparing the tool path program. This makes it more economical for small batch production.