The complexity of forging geometry determines the obvious difference between die forging process and die design. It is necessary to define the type of forging structure for process design. The pre forging step diagram is designed according to the final forging step diagram, and the following problems must be paid attention to during the design.
In order to make the metal fill the groove with pier thickness in the final forging process, the height size of the pre forging shall be 2-5mm larger than the corresponding height size of the final forging; The horizontal dimension shall be reduced appropriately, and the cross sectional area of the pre forging shall be greater than that of the final forging.
If the section of the final forging is round, the corresponding pre forging section is elliptical, and the elliptical section is about 4% - 5% of the corresponding section diameter of the final forging.
The volume of each part of the pre forging shall be strictly controlled, so that the excess metal can flow reasonably during the final forging process, and the metal reflow, folding and other defects shall be avoided. For example, the metal volume of the pre forging step is 1% - 6% larger than that of the final forging step. For forgings requiring punching, when the hole diameter is small, the difference between the inner hole depth of the pre forging and the corresponding inner hole depth of the final forging shall not be greater than 5 mm, otherwise, when the final forging is made, more metal will flow in the inner hole along the radial direction to form folding or auxiliary. When the hole diameter is large, the connecting skin of the final forging groove must also be designed to accommodate excess metal.
The positioning of the pre forging in the final forging groove shall be considered. Therefore, the shape and size of some parts in the pre forging step diagram shall be basically consistent with that of the final forging to avoid dissatisfaction caused by some blank deviations and excessive edges in the other part.
The pre forging groove generally does not have burr groove, but for some forgings with complex shape, it should be considered to set burr groove at some parts of the pre forging groove. The bridge height is 30% - 60% higher than the final forged rough groove, and the bridge width and warehouse height are smaller.
When the metal cannot fill the groove with the pier thickness during the final forging process, the side of the pre forging must be contacted with the die wall at the beginning of the final forging to limit the outward flow of metal, thus forcing the metal to flow to the depth of the groove. In order to avoid folding of the inner wall of the hole, the fillet of the punch boss in the final forging groove should not be too small.
Die forging can be divided into hot forging, warm forging and cold forging. Warm forging and cold forging are the future development direction of die forging and also represent the level of forging technology.
According to materials, die forging can also be divided into ferrous metal die forging, nonferrous metal die forging and powder product forming. As the name implies, it belongs to powder metallurgy materials, such as carbon steel, copper and aluminum. Extrusion belongs to die forging, which can be divided into heavy metal extrusion and light metal extrusion.
Closed die forging and closed pier forging are two advanced processes of die forging. As there is no flash, the utilization rate of materials is very high. The finishing of complex forgings can be completed through one or several processes. Since there is no flash, the stress area of the forging is reduced, and the required load is also reduced. However, care should be taken not to completely limit whitespace. Therefore, the blank volume shall be strictly controlled, the relative position of forgings shall be controlled, and the forgings shall be measured to try to reduce the wear of forgings.