Forging special-shaped parts in the production of forging to prepare metal raw materials, if the raw materials are improper, the defects and their impact on the forging. The defects caused by improper material preparation in forging factory are as follows.
1. Cutting Angle:
The slant is that the slant of the blank end face relative to the longitudinal axis exceeds the specified allowable value because the bar material is not pressed tightly when the forging factory is loading and unloading the sawing machine or punch. Severe cut inclination may form folding during forging.
2. The billet end is bent with burr:
During the loading and unloading of the cutting machine or punch, the blank of the forging has been bent before being cut because the gap between the blade or cutting die is too large or because the edge is not sharp. As a result, part of the metal is squeezed into the gap of the blade or die, forming the drooping burr at the end.
3. Billet end face depression:
When loading and unloading on the cutting machine, because the gap between the scissors is too small, the upper and lower cracks of the metal section do not coincide, resulting in secondary shear. As a result, part of the end metal is pulled out and the end face becomes concave. Such billets are prone to folding and cracking when forged.
4. End crack:
In cold shear of large section alloy steel and high carbon steel bar, cracks are often found in the end 3 ~ 4h after shear. The main reason is that the unit pressure of the blade is too large, so that the blank of the circular section is flattened into an ellipse, and a great deal of internal stress is generated in the material. While the flattened end face tries to restore the original shape, under the action of internal stress, cracks often appear within a few hours after cutting. The shear crack is easy to occur when the material hardness is too high, the hardness is uneven and the material segregation is serious. The billet with an end crack will expand further during forging.
5. Gas cutting cracks:
The gas cutting crack is usually located at the billet end, which is caused by the tissue stress and thermal stress during gas cutting because the raw material is not preheated before gas cutting. The billet with gas cut cracks will further expand during forging.
6, convex core cracking:
A convex core is often left in the center of the bar end face when the lathe is blanking. In the forging process, due to the small section of the convex core and the rapid cooling, its plasticity is low, but the billet matrix part has a large section, slow cooling, and high plasticity. Therefore, the intersection of the sudden change in the section becomes the part of the stress concentration, and the plastic difference between the two parts is large, so under the action of the hammer force, the crack around the convex core is easy to cause.