In the manufacturing field, normally a product is expected to be beautiful, not so heavy,small size, easy to move and more important, as much cheap as possible. But how about producinga mechanical product, a shaft or a gear in a gearbox for example? It is clear that the requirement forthe product will not be like that. In fact, our mechanical product must be high in precision and canwork effectively in harsh environment. Which decides this expectation? The answer is so many,namely the material, the geometry (or technical design), the working regime, the way the part hasbeen fabricated….If from a available design, but the part is produced by different process, thenfinal quality will be very different like, surface roughness, the precision level….So, it is reallyimportant to design a good manufacturing process just to ensure that our mechanical product willwork correctly, effectively and long life time.