Traditional design of mechanical parts is based on the process, such as turning, milling, planning, grinding, welding and casting etc. , and is limited by these processes. With the development of Additive Manufacturing (3D printing) technology, especially progress inaccuracy and reliability of direct manufacturing of metal parts, the functional and freedom design of mechanical components may be provided. 3D printing technology will inevitably bring design change for CAD models, and that will bring revolutionary changes in design. It is possible that ``manufacturing changes design''. This presentation will show the difference between traditional design and direct freedom 3D design, typical of product design based on additive manufacturing, and application examples in non-assemble mechanism, complex parts with inner structure and medical implants and devices by selective laser melting.