With the wide application of bending parts in machinery, steel structure, vehicle engineering, and other fields, in order to meet their product quality and production needs, their quality standards are gradually improved. CNC bending machines can use universal molds (or special molds) equipped to bend steel plates into various required geometric cross-sectional shapes in a cold state, but inappropriate bending processes will cause a series of problems, such as bending cracking. Cracking is caused by the bending process and its solutions.
(1) Burrs or fine cracks cause cracking: After shearing or punching, burrs or fine cracks often appear on the edges of the material, which are prone to stress concentration and fracture when bent. When the workpiece is fractured, the shear surface (burred surface) faces outward, and the cracking position occurs in the shearing zone and kneading zone of the workpiece.
The process measures taken for this are:
① For the workpiece after shearing or punching, ensure that the shear surface faces inward during bending, that is, it is under pressure, and the forming effect is better.
② Deburr the workpiece before bending, and use a manual grinder to grind the cracked part after bending.
(2) Cracks caused by shear residual internal stress. However, even if the workpiece is turned over and the burrs are removed, cracks will still occur, and the bending angle and bending radius are also in line with the standards.
This situation may be caused by too much residual stress left in the material shearing process and the work hardening changes the plasticity of the material, resulting in the material bending and cracking. In most cases, the cracking only occurs at the shearing position.
The process measures taken for this are:
① Change the processing technology, bend first, and then shear.
② Change the part design drawings and processing technology, slowly drill holes at the cracking position to prevent the formation of internal stress release internal stress, or increase the bending radius. Change the design drawings of parts, drill holes at the cracking position to prevent the formation of internal stress or release internal stress
③Take stress relief measures at the cracking position, such as baking the position with flames, and control the temperature at about 150-200℃. The heating and baking width and time are determined according to the thickness of the material and the depth of the cracking. Do not over-bake the steel to change the material structure and properties.
There are many causes of bending cracking, such as serious inclusions and segregation of the material, wrong grade selection, or unreasonable design of bending molds, lubrication process, bending radius, and bending angle. Today, I will only talk about these two points, hoping to help everyone in the processing and trade process.
The problems with steel are ever-changing. Understanding steel from the basics often solves many problems. Of course, it is not just about materials, but also about the knowledge of the entire chain such as processing, warehousing, and logistics.
Post time: Apr-10-2025