Analyze the whole process of blanking and deformation, don't understand it after reading it

Punching is a process in which a part of a sheet is separated from another part along a certain contour shape by using a die. After punching, the sheet is divided into a holed part and a punched-out part. If the purpose of punching is to obtain an inner hole of a certain shape and size, this punching is called punching. If the purpose of punching is to obtain a part with a certain outline and size, this punching is called blanking. The properties of blanking and punching are exactly the same, but the purpose of punching is different. When determining the size of the working part of the mold, they should be considered separately. In stamping production, the plastic deformation process of metal materials is carried out at room temperature. As the degree of deformation increases, its strength index yield point and tensile strength and hardness increase accordingly. At the same time, its plasticity The index elongation, reduction of area and impact toughness decrease. This phenomenon of metals is work hardening. The components of metal materials, metallographic structure and deformation conditions, deformation temperature, strain rate and degree of deformation have a great influence on work hardening. Due to work hardening, the deformation resistance of metal materials in the plastic forming process is constantly increasing. The deformation resistance is the resistance of the metal to the external force of plastic deformation, that is, the yield point of the metal is different at each moment. When determining various stamping process parameters and analyzing the stress and strain of the deformed part, the change in deformation resistance caused by work hardening must be considered. Work hardening has a large negative impact on many stamping forming processes. For example, work hardening increases the deformation force, restricts the further deformation of the blank and reduces the limit deformation. Sometimes in order to eliminate the work hardening of the previous process to increase the forming limit of this process , Even to increase the annealing process to eliminate the hardening, as the material hardening at the edge of the hole is likely to cause cracking when the flanging deformation is deformed. However, hardening is sometimes beneficial to deformation. For example, in the case of elongation, the hardening of the deformation zone can make the deformation tend to be uniform and increase the limit deformation. Therefore, when dealing with the actual problems of stamping production, determining various process parameters, and analyzing the stress status of the blank deformation zone, it is necessary to study and master the hardening law of materials and the influence on their stamping process. When sheet metal is formed by stamping, the stress state and strain state are different in different parts of the blank. Only the area where the stress state meets the plastic condition will produce plastic deformation, and the other areas will not produce plastic deformation. Therefore, the blank can be divided into deformation zone and non-deformation zone. The deformation zone is the area in the blank that reaches the plastic condition, and the non-deformation zone is the area in the blank that does not reach the plastic condition. According to the stress and deformation of the non-deformed condition, it can be further divided into the deformed area that has experienced plastic conditions, the area to be deformed to be involved in the deformation, and the non-deformed area that does not participate in the deformation during the entire stamping process. When the deformation zone bears the action of force, it is the force transmission zone. The essence of various stamping forming is the process of deformation of the deformation zone of the blank under the action of external force. Determining the stress and deformation characteristics of the deformation zone is the main basis for studying various stamping forming and its deformation laws. To analyze and study the stamping process, it is necessary to reveal the characteristics of stress and strain and the change law of the deformation zone in essence, and then determine the stamping process and forming parameters. The blanking process of sheet metal is usually simply divided into three stages: elastic deformation, plastic deformation and fracture separation. Since the blanking contour line of the blanking part is mostly a closed curve, during the blanking process of the sheet, along the tangent direction of the closed curve, the deformation is restrained by the mutual restraint of the sheet, so it can be approximately regarded as the deformation of the tangent direction of the sheet. Is zero. Because any micro-segment on the curve can be approximately regarded as a micro-arc, and a straight line can be approximately regarded as a circular arc with an infinite radius, so the circular blanking part is used as an example for the analysis and experiment of the blanking mechanism The conclusions obtained from the research can be applied to blanking parts of any shape. When punching, the punch and the die of the die form a pair of sharp cutting edges, the sheet is placed on the die, and the punch is gradually lowered to force the sheet to deform until it separates. This process can be roughly divided into three stages: in the elastic deformation stage, the punch descends to contact the sheet material, and the sheet material begins to be elastically compressed and bent, and slightly squeezed into the cavity of the cavity. Finally, as the punch continues to press in, the internal stress of the material reaches the elastic limit. In the plastic deformation stage, the punch continues to drop and the pressure continues to increase. When the stress reaches the yield limit, the material undergoes stretching and bending plastic deformation, and stress concentration occurs at the edge of the punch and concave mold. This stage continues until the material near the edge of the convex and concave die appears to be microcracked. , In the shear fracture stage, when the punch continues to drop, the stress reaches the shear strength of the sheet material, and the microcracks of the material near the cutting edge of the punch continue to expand into the sheet material. When the punch gap is reasonable, the upper and lower cracks are connected. The material is disconnected and separated. After that, if the punch continues to descend, the separated material will be pushed out of the concave mold. Previous post: The quality of the stamping process determines the quality of the stamping die