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Steel for Cold Swing Rolling Die and Its Vacuum Heat Treatment
The cold swing milling process is widely used in the metal plastic precision forming of small and medium-sized rotary parts. Such as automobile gear cams, etc., the mechanical characteristic of the cold swing milling process is that the machining hair is damaged locally and continuously. Periodically deformed by force and gradually formed into parts Therefore, the mold is also subjected to local, sequential (directional) and periodic forces during use. Macroscopic analysis shows that besides high strength and high hardness, cold swing rolling die should also have good toughness and high fatigue resistance.
The cold swing grinding process has the characteristics of high production efficiency, high processing accuracy and small tonnage of equipment, but the force state of the mold is complex and harsh, the force of the cold swing grinding mold is asymmetric, and the pressure on the stressed part can reach 2000MPa~2500MPa And it is periodic; it leads to the fatigue damage of the mold: especially the gear cold swing rolling mold; in the tooth root part of the tooth shape: the fatigue crack is very easy to generate and expand, and the service life of the mold is reduced. According to statistics: in the total processing cost of cold swing mill parts at home and abroad, the cost of mold manufacturing accounts for more than one quarter. For example: the general life of the cold swing rolling mold of the car planetary gear is 1000 to 2000 pieces; it can be seen that the cold swing rolling mold has a great influence on the production cost from the material, processing and heat treatment.
In the traditional process, Cr12MoV steel is generally used as the mold material for cold swing rolling. Cr12MoV has outstanding wear resistance; high compressive strength and compressive yield strength, and good hardenability. However, due to the large amount of excess carbides in the material; especially the unevenness of undissolved carbides after quenching in larger section steels is serious. The above-mentioned traditional mold steel has poor toughness, which is easy to cause peeling, cracking and breaking of the surface of the cold swing rolling mold, which
affects the service life of the mold.
In order to solve the problem of poor toughness of Cr12MoV steel, some high wear resistance and high toughness die steels have been developed in my country in the past 20 years. The typical ones are LD and GM steels.
LD steel and GM steel have both high wear resistance and high toughness. Some data show that the wear resistance of LD steel is comparable to that of high-carbon and high-chromium cold work die steel, and the bending strength and impact toughness after quenching and tempering are higher than those of high-speed steel and high-carbon and high-chromium cold work die steel. Due to the excellent comprehensive properties of LD steel, there is a trend to replace Cr12MoV steel to manufacture cold swing rolling molds. Our practice has also proved that the service life of LD steel cold swing grinding mold is 1 to 3 times higher than that of Cr12MoV steel mold, and the service life is 4,000 to 6,000 pieces.
Heat treatment process:
Practice has proved that vacuum heat treatment is the best way for cold swing rolling mold parts. After vacuum heat treatment, the life of the mold can be increased by 100% to 400% compared with conventional heat treatment. Our equipment for vacuum heat treatment is a double-chamber vacuum quenching furnace, and the double-chamber structure allows tempering to be completed in this furnace.
Vacuum Heat Treatment of Cr12MoV Steel Cold Swing Die
The Cr12MoV steel cold swing rolling mold does not have a pre-heat treatment process. This process is placed in the heating process of the final vacuum heat treatment (quenching), and is carried out by slowly heating to the preheating temperature (platform).
Taking the planetary gear cavity mold as an example, the final vacuum heat treatment process of the cold swing grinding mold: slowly heat to 850 ° C, preheat for 100 minutes, continue to heat to 1040 ° C, keep warm for 90 mm and then quench in oil. In the whole process of heating and heat preservation, the vacuum degree is basically kept at 10.00Pa ~ 0.10Pa. After the mold is oiled, the cold room is immediately filled with air, so that the quenching oil surface always maintains a pressure of one atmosphere during the quenching process. At the same time, start the quenching oil agitator: enhance the cooling and heat transfer intensity. The quenching time is not less than 15min, the larger the die section; the longer the quenching time. The quenching hardness of Cr12MoV steel cold swing rolling mold is 6HRC ~ 64HRC.
The procedure of tempering treatment is as follows: after the quenching of the cold swing grinding mold is completed, remove the oil tank to drain the oil, wait until the inside and outside temperature is completely cooled to room temperature, and then put it into the vacuum furnace. For 100Pa ~ 10Pa tempering hardness is 56HRC ~ 57HRC. The formulation of the tempering temperature is to consider the comprehensive requirements of the mold for hardness, fatigue resistance and toughness. The data show that after quenching from 1000℃ and tempering at 200℃, the q value of impact toughness reaches the extreme value, the deflection is close to the maximum value, and the hardness remains around 60HRC.
Auto planetary gear Cr12MoV steel cold swing grinding mold, the service life of vacuum quenching is up to 3000 pieces. The life of conventional heat treatment molds is only about 1,000 pieces, and some molds only process hundreds of pieces, which are scrapped due to cracking at the root of the tooth shape of the mold cavity.
Vacuum Heat Treatment of LD Steel Cold Swing Die
There is no pre-heat treatment process for LD steel cold swing rolling mold. The final vacuum heat treatment process of LD steel planetary gear cold swing rolling mold is: in order to prevent mold deformation, slowly heat to 850C, preheat and hold for 100 minutes, continue to slowly heat to quenching temperature 1100C, hold for 80 minutes, and then quench in oil. During the whole heating and heat preservation process, the vacuum degree is basically kept at 1000Pa~010Pa, and other quenching operations are the same as those of Crl2MoV steel. The quenching hardness of LD steel cold swing rolling mold is 61HRC~63HRC.
The tempering temperature of the LD steel mold is 530C, and it is tempered 3 times for 1 hour. Tempering hardness 60HRC ~ 62HRC. Practice has proved that the service life of LD steel cold swing rolling die is 1 to 3 times longer than that of Crl2MoV steel; it reaches 4000 to 600 pieces.
Through the VOGQ series vacuum oil quenching furnace produced by SIMUWU, the above processes can be continuously completed in the same vacuum furnace. SIMUWU is equipped with a mature team of engineers, complete installation and after-sales service, convenient and efficient production, and is a high-quality choice for heat treatment plants.