Metal stamping and bending processing is a processing method that applies a bending moment to the material to deform it, so that the material is subjected to the bending moment to generate internal bending stress. The stress distribution is bounded by the neutral plane of the plate, the outer side guillotine is tensile stress and the inner side is compressive stress.
When the bending moment is eliminated, the material returns to the state of elastic deformation and equilibrium moment. Compared with the standard shape of stamping parts, it will produce outward pulling force or inward inclination. This phenomenon is called elastic recovery deformation.
In order to distinguish, sometimes the state that is splayed outward is called rebound, and the state that is inclined inward is called overbending. From the perspective of the bending method of stamping parts, there are v-shaped bending and u-shaped bending, but the two are only different in springback, and the essence is the same.
There are stamping materials, plate thickness, punching force, die size and shape.
⑴The radius of curvature of the punch
The amount of springback increases with the increase of the radius of curvature, and decreases with the decrease of the radius of curvature. Although there are slight differences due to the different materials of the stamping parts, it is generally appropriate to choose the thickness of the plate below. At the same time, the small radius of curvature of the curved plate material should be considered.
⑵Die shoulder radius is too small
When the radius of the die shoulder is too large, the stamping part will open outwards and tilt inward when it is too small. Generally choose 2 to 4 times the plate thickness.
The bending is small and the outward opening is large, and the outward opening decreases as the bending increases. Generally, the bending degree of stamping parts should be more than 4 times the thickness of the plate.
⑷The gap between the convex and concave molds
The gap between the male mold and the female mold is greater than the thickness of the plate, and the plate material cannot fit the male mold well. The larger the corner radius of the punch, the greater the springback. On the contrary, if the gap is too small, the springback is almost the same, but it becomes an inward tilt. Generally, the gap should be less than 0.02-0.05mm of plate thickness.
Due to the existence of the above factors, if we comprehensively examine these factors and the nature of rebound. Understand the bending of precision stamping parts and the reasons for springback, and then stop them according to the reasons.
The root cause of springback is the uneven force on the bending part of the material after the bending process is completed. If this part of the uneven stress is converted into a uniform stress, even if the entire section is compressive or tensile, the amount of springback can be reduced. However, some stamping parts have requirements for deformation, such as not suitable for indentation, which requires corresponding solutions in design and process.
For this kind of stamping parts, it is advisable to adopt the shape of a convex mold or a concave mold, which can also play a good role in the stamping parts with a small springback.