Springback of hottest bending and its control

Bending springback and its control

[Abstract] this paper analyzes the influencing factors of bending springback, and emphatically introduces the specific measures to control bending springback

just as wrinkling affects the quality of deep drawing parts, springback mainly affects the quality of bending parts, so bending springback and its control have always been the concern of die workers. It can be said that any plastic deformation of plate will inevitably rebound after unloading, but the bending performance is more prominent. The reasons are as follows: first, the stress properties of the inner and outer layers are opposite during bending deformation, and the rebound direction is the same after unloading, so the shape and size of the bending parts change greatly; The second is that the bending process is not closed stamping like the deep drawing, flanging and other processes, but in a non closed state, so there is less mutual traction, which is easy to cause a large rebound; The third is that the deformation area is small and the non deformation area is large in bending processing, and the non deformation area of a large area changes to a small area. 5. This kind of new material will be the preferred material for skull repair. The influence of the mixing blade and the gap area of the bottom and side wall of the mixing material makes it difficult for the deformation area of a small area to reach the pure plastic bending state

the existing theory believes that even if all the internal and external fibers of the material enter the plastic state during processing, the elastic deformation disappears, and the rebound phenomenon will occur

a elastic bending B elastic-plastic bending C pure plastic bending

tangential stress distribution in the hairy deformation zone during bending. Figure La shows that in the initial stage of bending, the relative bending radius r/t is large, and only elastic bending occurs inside the sheet; With the increase of bending force, the small r/t value and the gradual increase of bending deformation, the tangential stress of the surface layer reaches the yield point, and then extends to the center of the sheet, so the interior of the sheet is in the state of elastic-plastic deformation; When the r/t value continues to decrease to a certain extent, the tangential stresses in the inner, outer and center of the sheet exceed the yield point and enter the fully plastic state. Plastic bending is always accompanied by elastic deformation. 2A shows the pure plastic bending stress state, 2b is its unloading stress, and 2C is the residual stress in the section of the bending part in the free state after unloading; 3 is the change of internal tangential stress guided by the policy of rough section in the process of elastic-plastic bending unloading. 3a is the stress during unloading, and 3C is the residual stress in the section of the bending part in the free state after unloading. It can be seen that elastic recovery after plastic bending unloading is inevitable

change of tangential stress of blank section

it can be seen from the above that the springback of dry blank is objective and cannot be changed. Only by taking advantage of the situation, mastering the springback law of material, and calculating the springback value as accurately as possible, can the bending springback of blank be effectively reduced and controlled. This is the main problem to be considered in studying springback, formulating bending process and designing die

1 influencing factors of bending springback

springback includes angle springback and curvature springback, which is the result of the combined effect of springback in bending deformation zone and non deformation zone. There are many factors affecting springback, mainly including: ① mechanical properties of bad materials σ s、Eo σ The higher s, the smaller e value, the greater bending springback; ② Deformation degree r/t. Under the same conditions, the angular springback increases with the increase of r/t value; The curvature springback decreases with the increase of r/t value; ③ Bending center angle α O bending center angle α Large springback angle; ④ Mold clearance Z. The gap between punch and die is large, and the springback is large; ⑤ Bending mode. The springback of free bending is large, the springback of positive bending is small, and the springback of full shape upsetting correction bending is the smallest; ⑥ Workpiece shape and material organization status. The shape is complex, the mutual involvement is many, and the springback is small, but it indicates the utilization prospect of carbon nanotubes in the superconducting field, and the springback is large after cold work hardening; ⑦ Die structure and blank holder force. The blank holder force is large, and the springback of the workpiece after bending is small