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Causes and elimination methods of cracks in die forgings


Most of the defects of die forgings are caused by unreasonable die design, slightly poor die forging equipment and improper operation.

The common causes of defects and their elimination methods are as follows:

1. Misplacement. The displacement of the forging from the half to the lower half of the parting surface is called misalignment. The causes and troubleshooting methods of misshift are as follows:

(1) The gap between the hammer head and the guide rail is too large. The equipment should be adjusted immediately after discovery.

(2) The forging die is installed incorrectly or the forging die is loose during the forging process, or the die seat is loose. The forging die should be adjusted immediately after discovery, and the die and die seat should be tightened.

(3) Locks or guide posts without balance or misalignment force, or the gap between the locks and guide posts is too large. The design should be improved to increase the balance lock or guide post, or repair the gap between the lock and guide post.

2. Partially dissatisfied. The phenomenon that the metal does not completely fill the die cavity, resulting in lack of meat in the corners and ribs of the forging, and the unclear outline of the forging is called partial dissatisfaction.

The reasons for the dissatisfaction of die forgings and the troubleshooting methods are as follows:

(1) Insufficient heating. The heating temperature of the blank is low or uneven, resulting in reduced metal plasticity, poor fluidity and insufficient filling of the mold cavity. Therefore, it should be heated strictly according to the heating temperature specified by the process, and the blank should be heated evenly before forging.

(2) The design of blank or pre-forging die cavity is unreasonable. The design should be improved and the forging die should be repaired before production.

(3) The equipment tonnage is too small. You can choose equipment with larger tonnage or add a pre-forging.

(4) The blank is too large or too small. The cutting size should be strictly controlled.

(5) Improper lubrication. Excessive lubricant or local accumulation will generate high-pressure gas in the die cavity, preventing the metal from filling the die cavity, so the lubricant should be appropriate and uniform. Particular attention should be paid to excessive humidity and accumulation when using wet sawdust.

(6) Improper operation. During operation, squeezing, improper bending or partial discharge will cause local dissatisfaction. The operation method should be improved immediately after discovery.

3. Fold. During die forging, due to metal convection or backflow, defects that look like cracks in the corresponding parts of the forging are called folds.

The causes and elimination methods of die forging folding are as follows:

(1) The design is unreasonable. The pre-forging die cavity is not compatible with the final forging die cavity (especially the pre-forging die cavity with I-shaped section), or the fillet radius is too small may cause folding. After discovery, the design can be improved or the fillet of the corresponding part of the large die cavity can be repaired.

(2) Improper operation. Due to improper operations during billet making, if the material is not placed straight or stretched, or hammered too heavily during rolling, folding may occur in the subsequent forging. After the occurrence, the blank should be folded, the steps should be polished and cleaned, and then the final forging should be carried out, and the operation method should be improved.

4. Undervoltage. The height dimension of the forging exceeds the positive tolerance requirement of the drawing, which is usually called underpressure.

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