Through the homogenization treatment of the steel ingot, the degree of segregation in the alloy mold steel is lowered, and the longitudinal and lateral properties after forging are close. For the type of eutectic steel, the fish bone eutectic carbide is crushed by rolling and forging, and the multi-directional forging is performed to make the carbide amount uniform and fine. Process Technology Discussion The main failure types of cold working molds are overload failure and wear failure, accounting for one of the total failures.
The cold and tender mold is mainly broken or abnormally worn, and the cold extrusion die is mainly composed of brittle fracture or wear failure, while the cold stamping die is mainly caused by wear failure. The cold extrusion of high working stress, large wave stress and the failure rate of brittle cracking of cold pier mold are significantly higher than those of cold working die with low working stress. The statistical results show that for the standard part of the product is steel material, the average working stress of the cold extrusion die is about the average working stress of the hardness-cooling die, and the average working stress of the hardness-cooling die is used. Hardness one. Among them, the cold extrusion die stress is the largest, and actually has to bear a random load, and the local stress of the mold should exceed the above stress.
The effect of working hardness on the life of cold work die steel is the result of a comprehensive effect. Therefore, heat treatment is an important part. Looking at the failure factors and percentage of cold-working molds, see the table.
If the interference is not enough, the interference of the pre-stressed part of the mold is too small or the bearing area is too small, which can not offset the expansion stress caused by the cold heading force, and the effect of the pre-stress combination of the mold press-fit is not achieved, resulting in the stress of the hole wall. Large and cracked. Chamfering, rounding is not suitable for adjustment sleeve, the round end of the mandrel die is too small, the chamfering angle of the press fitting angle is not suitable, and there is burr, which affects the fluidity of the metal and the press-fit quality of the mold, resulting in excessive tender forging force. The joint strength of the Bolt head rod is reduced, and the outer circumference of the core and the wall of the mold sleeve are pulled to reduce the service life of the mold.
Table cold work die failure factor failure factor heat treatment raw material forging use mechanical design percentage of the name of the cold work chess design details cold work die long-term bearing a large unit pressure and alternating impact load, material toughness is easy to cause fracture failure, Such as the rupture of the head, cracking, and even bursting. When there is stress concentration in the mold structure and the transition zone of the hexagonal cold and tender punch tail, the stress concentration factor å…€ coldly squeezes the step of the punch, even the machining tool marks, rough grinding marks, etc. can become weak links, resulting in failure fracture.
To this end, in addition to standardizing the normal design, cold work dies must also consider the following aspects. Avoid stress concentration, the wall thickness of the mold part is not uniform, the dimensional transition is too different, the corner radius of the dimensional transition is too small, the root of the undercut is sharp, the position of the exhaust groove is improper, etc., which may lead to heat treatment or early use. The stress is concentrated, causing fatigue cracking of the mold.
Materials and heat treatment, pre-heat treatment In order to connect the cold and hot processing steps and prepare the structure for the final heat treatment, it is usually necessary to arrange the mold preheating. The pre-heat treatment currently used is not just a conventional annealing or normalizing.
For example, some alloy die steels used spheroidizing annealing or isothermal spheroidizing annealing, and now they are replaced by quenching and tempering treatment or ultra-fine processing. Some of them are combined with forging process to carry out after-heating quenching and then tempering or spheroidizing annealing. It is necessary to further improve the life of the cold-working mold and give full play to the potential of the material.
The final heat treatment should be based on the conditions of use of the cold work die, select the appropriate technical requirements, and then choose the appropriate final heat treatment system, including preheating, heating temperature, tempering temperature and so on. The table is a heat treatment process and application of some cold work die steel.
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