1. The oblique cutting
Slant refers to the deviation of the end face of the blank relative to the longitudinal axis in the process of loading and unloading on the sawing or punching machine.Severe slant, which may fold during forging.
2. The end of the blank is bent with burr
In the cutting machine or punching machine feeding and unloading, because the clearance between the scissors or cutting die edge is too large or because the edge is not sharp, so that the blank has been bent before being cut, as a result, some of the metal is squeezed into the clearance of the blade or die, forming a drooping burr at the end.
The blank with burr is prone to local overheating and over-burning when heated, folding and cracking when forging.
3. Blank end face is concave
When cutting machine fluctuation makings, because the clearance between scissors piece is too small, the crack on metal section, below does not coincide, produce 2 times shear, the result part end part metal is pulled off, end face becomes concave shape.Such billets are easy to fold and crack when forged.
4. End crack
In cold shear large section alloy steel and high carbon steel bar, the end crack is often found 3 ~ 4h after shear.The main reason is that the unit pressure of the blade is too high, so that the blank with circular section is compressed into an oval shape. At this time, great internal stress is generated in the material.The compressed end surface to restore the original shape, in the action of internal stress is often in the cutting after a few hours of crack.When the hardness of materials is too high, the hardness is uneven and the segregation of materials is serious, shear cracks are easy to occur.
When forging a blank with a crack at the end, the crack will expand further.
5. Gas cutting cracks
The gas cutting crack is usually located at the end of the billet. It is caused by the formation stress and thermal stress generated by the raw material without preheating before gas cutting.
When forging a blank with a gas cut crack, the crack will expand further.Therefore, it should be cleaned in advance before forging.
6. Convex core cracking
When the lathe is blanking, the center part of the end face of the bar often has a convex core.In the forging process, due to the small section of the convex core and the rapid cooling, its plasticity is relatively low.Therefore, at the junction of the sudden change of section, the stress is concentrated, and the plasticity of the two parts is quite different. Therefore, under the action of hammer force, the surrounding of the convex core is easy to cause cracking.