After going through forging, metal structure and its mechanical property can be improved. Original big crystal and prismatic crystal grain become thin and evenly small, then re-organized to make a-liquation, looseness, air bubble and inserted slag be pressed and its structure become close and tight which improve plasticity and mechanical property of metal. But mechanical property of casting piece is worse than other forging piece of the same material. Besides, forging can make sure the continuousness of metal fiber structure and keep the fiber structure and outer shape the same, metal streamline complete and guarantee long life time and good mechanical property. Technique of using precise mould forging. cold press, warm press is incomparable in making forging piece.