In the forming process, the bending die mainly goes through the control analysis of bending process and the solution of springback and deviation caused by bending. The following two aspects are introduced to you: First, the bending process analysis of the elbow is carried out. In the process of bending, it is the most widely used method to use bending die to bend metal plates. The bending deformation process generally goes through three stages: elastic bending deformation, elastic-plastic bending deformation and plastic bending deformation. Now take the common bending of V-shaped parts as an example. At the beginning of bending, the convex and concave dies of the die contact with the sheet metal respectively, so that the sheet metal is bent. In the initial stage of bending, the radius r0 of bending fillet is very large and the bending moment is very small, which only causes elastic bending deformation of the material. With the increase of the depth of the punch into the female die, the radius R of the bending fillet gradually decreases, that is, R3; At 200, the material in the bending zone begins to enter the stage of elastic-plastic bending, and the inner and outer surfaces of the material thickness in the blank deformation zone (the part where the bending radius changes) first begin to undergo plastic deformation, and then the plastic deformation moves towards the inward expansion direction of the blank. The punch continues to descend, and the deformation gradually transits from elastic-plastic bending to plastic deformation. Finally, the V-shaped inclined plane of the punch bends reversely after contact, and then gradually leans against the inclined plane of the female die until the sheet completely leans against the male and female dies. If at the end of bending, the punch does not press down after connecting with the plate and the die, it is called free bending. If the punch is pressed down again and a certain pressure is applied to the sheet metal, it is called correcting bending. Between corrected bending and free bending, the position of the bottom dead center of the punch is different. The corrected bending makes the bending part upset rigidly at the bottom dead center, which reduces the rebound of the workpiece. Secondly, in the analysis of springback and deflection of bending die, the main technological problems in the bending process are springback and deflection. Let's start with "rebound". You can read the article "The Concept of Bend Springback and the Points for Attention in Operation" first. (1) The phenomenon that the radius of curvature and the bending angle of the bending part of the bending part change after the bending force is removed is called springback when the punch and the die are separated and the workpiece is not affected by external force. Measures to reduce springback: 1) Improve the design of parts, and design stiffeners or forming wings in the deformation zone to increase the rigidity of bent parts and the deformation degree of forming wings; 2) Choosing materials with large elastic modulus, small yield limit and stable mechanical properties can also reduce the springback of bending parts. 3) Use corrected bending instead of free bending to increase bending force. 4) heating and bending. 5)V-bend can subtract the rebound angle from the punch; U-shaped bending can make the punch wall have an inclined angle equal to the rebound angle, or make the top surface of the punch head be cambered to compensate the rebound on both sides. 6) The punch can be made into the shape shown in the figure, so that the contact area between the punch and the workpiece is reduced, the pressure is concentrated in the bending deformation zone, and the deformation degree of the deformation zone is increased. 7) For bending parts made of common materials, the pressing force can be increased or the gap between male and female dies can be reduced to reduce the springback. (2) Deviation during bending Due to the friction between the blank and the die, when the friction is unbalanced, the blank will deviate and the size of the bending part will not meet the requirements. This phenomenon is called deviation. There are many reasons for the deviation: the blank shape is asymmetric, the contact surfaces between the two sides and the concave die are not equal, and the number of bends on both sides is different; Unequal fillet radius, unequal clearance and different lubrication conditions on both sides of the die will lead to deviation in bending. Main measures to prevent deviation: 1) Try to use symmetrical concave die with equal rounded edges and even gap. 2) adopt the mold structure of the elastic ejection device, and 3) adopt the mold structure of the positioning pin, so that the blank cannot be moved.