Plastic processing is traditionally divided into two main categories. One is the production of raw materials (such as tube, plate, type, rod) based processing is called primary plastic processing. The other is the production of parts and their blanks (including forgings, stamping parts, etc.) mainly known as the secondary plastic processing. Because in most cases, secondary processing is to use the raw materials provided by the primary processing for re-processing, but large forgings often use ingot as raw material to directly forge into forgings, and powder forging uses powder as raw material.
According to the different raw materials used, the secondary plastic processing can be divided into Bulk forming and Sheet forming. The former uses bar and block material as raw materials and the force is in the three-way stress state, while the latter uses sheet material as raw material and the deformation process is usually analyzed according to the plane stress state.
It can be seen from the above analysis that forging belongs to secondary plastic processing and the deformation mode is volumetric forming.
As can be seen from Figure 1, the fundamental purpose of any forging process is to obtain forgings with qualified shape, size and internal organizational properties that meet the requirements of the drawing. There are two basic conditions for forming, one is that the material can withstand the required amount of deformation without destruction in the process of deformation, and the other is the force conditions, that is, the equipment through the mold to the workpiece to apply enough large and special distribution of force. It is an important task for forging workers to create conditions, optimize the technological process and produce the combined forgings.
The choice of forging process is flexible and varied, just for the forming process, the same die forging can be completed by different equipment or different methods. For example, if the connecting rod is formed on the forging hammer, the blank is drawn, rolled, pre-forged and final forged in the same pair of die. If a mechanical press is used for die forging, roll forging is required in advance. If it is produced by the forming roll forging method, the qualified parts can be obtained by adding a shaping procedure after the precision roll forging.
Another example is the multi-station cold forging of ladder shaft (see Figure 2). For the same forging, there may be different process routes and different blanks, and accordingly the intermediate processes are different. Some of them include forward extrusion (F in figure), and some use upsetting (U in figure)0, which requires different deformation forces. The mold life difference is also larger.
When equipment conditions (such as tonnage, etc.) are fixed, there are not so many options available. When raw material properties and specifications are fixed, not all of the options in the figure can be applied.
Under the premise of ensuring the appearance and internal quality and productivity of the product, the basic starting point of choosing the forming process scheme should be considered as good economic efficiency, specifically:
1. Save raw materials. Near free forming, or Near net shape forming (i.e. less cutting without forming), is used where possible.
2. Reduce energy consumption. We can not only look at the energy consumption of a certain process, but also look at the total energy consumption. At first it seems that the energy consumption of cold forging will be reduced because the heating process is omitted, but the energy consumption of softening treatment before cold forging and annealing between processes should also be considered. The use of non - tempered steel and residual heat deformation and heat treatment are energy saving processes.
3, reduce the deformation force. Try to use labor-saving forming method, which can not only reduce the equipment tonnage, reduce the initial investment. It can also improve the life of the mold. This is why rotary forming has been widely used in recent years.
4. Good process stability. A good process should be shown in the realization of long-term continuous production, without deliberately pursuing some single index high (such as fewer passes, large deformation per pass), but lead to low yield or often broken mold.
This is forgings of tongxin forging company: