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Causes of cracks in precision forgings
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- Time of issue:2021-09-02
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(Summary description)(1) Surface cracks are caused by over-burning or overheating of the billet due to excessive forging temperature or excessive hammering speed. The crack is wide, the fracture is uneven, and the structure is coarse and dark gray. In the low magnification structure, the crack end is zigzag,
Causes of cracks in precision forgings
Causes of cracks in precision forgings
Causes of cracks in precision forgings
(Summary description)(1) Surface cracks are caused by over-burning or overheating of the billet due to excessive forging temperature or excessive hammering speed. The crack is wide, the fracture is uneven, and the structure is coarse and dark gray. In the low magnification structure, the crack end is zigzag,
- Categories:Info-Center
- Author:
- Origin:
- Time of issue:2021-09-02
- Views:0
(1) Surface cracks are caused by over-burning or overheating of the billet due to excessive forging temperature or excessive hammering speed. The crack is wide, the fracture is uneven, and the structure is coarse and dark gray. In the low magnification structure, the crack end is zigzag, which has nothing to do with the streamline. The high magnification observed that the cracks extend along the grain boundaries, the recrystallization is complete, and there are no inclusions and other metallurgical defects. When the forging temperature is too low and the hammering is too heavy, the side surface of the billet is 45 degrees from the hammering direction. , 90~ or triangular crack, the fracture is flush with metallic luster. High magnification observation, cracks transgranular and work hardening phenomenon.
(2) One of the internal cracks occurs during free forging. When the round section billet is drawn and rounded, the amount of feed is too large, the amount of reduction is too small, and the transverse flow of the metal is intense, resulting in transverse tensile stress. The closer to the core, the greater the tensile stress, causing internal longitudinal cracks. Another kind of internal crack is the micro-crack caused by excessively coarse intermetallic compounds or inclusions in the alloy during forging, which hinders the regular flow of the metal. Usually, such cracks can only be revealed after the forging is processed. The former method of preventing longitudinal cracks is to round the round billet first and then round it in all directions, and the reduction amount should be greater than 20% each time. The latter crack prevention method is to strictly inspect the forging blanks and control the unqualified blanks to enter the car.
(3) Burr cracks often occur when forging aluminum alloys on a hammer, usually along the parting line (see parting surface) when the burr is removed. This is due to the fact that when the forging temperature is too high or the forging process is struck rapidly and continuously, the excess metal that has filled the die groove is forced out at the burrs, and there is friction between the die surface and the metal on the surface of the forging, and the metal adjacent to the die surface The flow difficulty is at rest. The metal where the flow occurs has a certain depth from the die surface. Therefore, between the flowing and stationary metal, a large amount of heat is generated due to the violent relative motion, which overheats the metal in this range, and when the excess metal squeezes the burr groove, a large shear occurs in this part. Under the action of stress, cracks occur in the overheated parts of the burrs. In addition, there are other reasons such as improper mold design, too small radius of rib root fillet, and overburning during quenching and heating, etc., which can also cause burr cracks. In order to prevent the occurrence of such cracks, it is necessary to appropriately reduce the forging temperature and hammering speed, increase the radius of the fillet, and reduce the shear stress.
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Relevant information
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Non-ferrous metal forging processForging is one of the methods of non-ferrous metal pressure processing and a link in machinery manufacturing. According to the different temperature states of metal materials during forging and working, forging can be divided into hot forging, warm forging and cold forging. - Application fields and specific cases of cold forging technology 09-02
- Causes of cracks in precision forgings 09-02
- Description of materials and processes suitable for cold forging 09-02
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