Forging is a complex and fine process, which covers the processing of various materials and the control of various process parameters. The aim is to obtain the desired forgings by heating and applying pressure to the metal blank to change its shape and physical properties. The quality of
forgings is affected by many factors, including material selection, process parameters, mold design and so on. Among these factors, forgings folding is a common quality problem, usually manifested as folds or depressions on the surface or inside the forgings. This folding phenomenon not only affects the appearance of the forgings, but also may affect their mechanical properties and service life. In order to improve the quality of forgings, it is necessary to deeply understand the various causes of folding and take effective countermeasures to solve them.
In the process design of
die forging, the unreasonable selection of blank is an important factor that leads to the folding of forging. Specific issues include:
Backflow or convection phenomenon of blank in the mold cavity can cause folding on the forging surface. The occurrence of this phenomenon is related to the design of the cavity. When the size ratio of the cavity (that is, the ratio of the depth of the cavity to the width of the cavity) is increased, the incidence of folding is usually reduced because the deeper cavity can better direct the blank flow. When the size ratio of the cavity is reduced, the blank flow is not uniform, which easily leads to folding phenomenon.
The ratio between punch diameter and blank diameter directly affects the folding phenomenon. As the ratio of the punch diameter to the blank diameter increases, the blank will be filled more evenly in the cavity, thus reducing the probability of folding. Conversely, a decrease in the ratio increases the probability of folding.
The radius of the punch edge also has a significant impact on the folding phenomenon. A larger edge fillet radius helps reduce the folding of forgings, especially when dealing with billets with a large aspect to diameter ratio (that is, a ratio of height to diameter). For punches with a small ratio of height to diameter, the effect of rounded radius is relatively small, but it still helps to reduce the incidence of folding.
Under normal circumstances, the use of the mold temperature is maintained at about 25℃. In the production process, between the fire of the forging, the repair and treatment temperature of the mold is room temperature. When the die is assembled and disassembled between different fire times, the striking center of the die may not fully coincide, resulting in the boss part of the forging part cannot fully enter the die cavity. This impact deviation causes one side of the forging to fold.
The frequent assembly and disposal of the mold will affect the accuracy of the mold, resulting in the offset of the center of the impact. In order to reduce the folding phenomenon, it is recommended to reduce the number of mold assembly and disassembly during the forging process, and carefully check the alignment of the mold before each use to ensure that the center of the mold is accurate.
In the multi-fire die forging, the forging may be deformed due to the impact, fall, cutting and other factors during the operation. This deformation makes the forging in the subsequent fire forging process, can not fully adapt to the shape of the mold, especially in the hammer center alignment is not correct, the formed convex may not be fully inserted into the mold cavity, resulting in the folding phenomenon.
The folding phenomenon caused by deformation usually worsens with the increase of treatment measures. Therefore, in order to reduce the occurrence of folding phenomenon, the fire should be reduced as much as possible, and the molding should be completed in a die forging by improving the process design and operating process. This can not only reduce the probability of folding, but also improve production efficiency and product quality.
The folding phenomenon of forging is closely related to many factors, including blank selection, die assembly and disassembly process and forging deformation. By optimizing blank selection, reducing mold assembly and disassembly times and improving process design, the incidence of folding phenomenon can be effectively reduced. It is the key to improve the quality and production efficiency of forgings to develop reasonable production process, maintain the accuracy of die and ensure that the shape and size of forgings meet the requirements.
