With the wide application of bending parts in machinery, steel structure, vehicle engineering and other fields, in order to meet its product quality and production needs, its quality standards are gradually improved. Numerical control bending machine in the cold state can be equipped with a universal mold (or special mold) bending metal sheet into a variety of required geometric section shape of the workpiece, but the improper bending process will cause a series of problems, such as bending cracking.

(1) burr or small cracks caused by cracking: the material after shearing or blanking, in the edge often appear burr or small cracks, bending easy to form stress concentration and be cracked, through figure 1 shows the workpiece when cracking shear surface (with burr surface) outwards, cracking position occurs in the workpiece shear zone and kneading zone.

In this regard, the technological measures taken are as follows: (1) After cutting or blanking the workpiece, when bending to ensure that the shear face, that is, in the state of compression, as shown in Figure 2, the forming effect is good. (2) Deburring the workpiece before bending, and use manual grinding wheel machine to repair the broken part after bending.

(2) cracking caused by shear residual internal stress. The situation is similar to Figure 1, but cracking still occurs even when turning over and removing burrs. The bending Angle and bending radius also meet the standard, and the cracking location is shown in Figure 3:

This situation may be the material shear process left too much residual stress and work hardening change the plastic of the material, resulting in bending cracking of the material, in most cases only from the shear part of the cracking.

The technological measures to be taken are: 

(1) change the processing technology, bending and cutting first.

（2） Change parts design drawings and processing technology, slow drilling in the cracking position to prevent the formation of internal stress or release internal stress, or increase the bending radius. . Change the parts design drawings, the crack position drilling, prevent the formation of internal stress or release of internal stress

 (3) in cracking stress relief measures, such as flame roasting the location, in 150-200 ℃, temperature control heating oven width and time according to the material thickness and the crack depth on the specific situation, avoid by all means the steel overbaking changed the materials organization performance.

There are many causes of bending cracking, such as material inclusion, segregation, grade selection error, or bending tool design, lubrication process, bending radius, bending Angle design is not reasonable, today just say these two points, I hope to help you in the process of processing and trade.

The problem about steel is ever-changing, from the basic to understand steel often a lot of problems will be solved, of course, it is not only the material to understand, processing, warehousing, logistics and other knowledge on the whole chain to understand, in a word, "endless learning, only know steel know steel, can be more competitive".