Die casting refers to the use of a die casting machine to inject aluminum, zinc, magnesium, tin and other alloy melt into a mold, and then press-form and solidify in a molten state, and produce a large number of castings with high dimensional accuracy and good internal structure compactness in a short time. To reduce the machining allowance and ensure the inherent quality of the casting. Therefore, the rational use of mold cooling circulating water is particularly important in complex die casting molds.
Effect of circulating cooling water on die-casting mold
The die-casting mold cooling can be divided into external cooling and internal cooling. After the casting is demolded, the surface of the cavity is sprayed and cooled by the nozzle, and the release agent is sprayed; the internal cooling is circulating cooling water inside the mold, which is the main mold. Cooling method . In Dongfeng Honda Engine Co., Ltd.'s first domestic car aluminum cylinder die-casting project, the complex core of the cylinder die-casting mold and the majority of the hole-forming pins are internally cooled with cooling water to control the various parts of the mold. temperature.
The temperature control of the mold is relatively high, which is beneficial to the filling of the aluminum liquid in the mold and is beneficial to the forming of the casting. However, when the mold temperature is close to 300 ° C, the aluminum sticking phenomenon will be obvious, and the surface of the casting is rough or missing. Grind the mold frequently. At the same time, the casting is not fully cooled within a predetermined time to open the mold, the casting is not sufficiently formed due to insufficient cooling and the mold release gap between the molds, and the aluminum sticking phenomenon causes the module and the forming pin to be stressed when the mold is released. Excessively large and cracked and damaged (the sound when opening the mold will also increase significantly). Too low mold temperature control will affect the fluidity of the aluminum liquid and cause cold casting of the casting. We hope that the temperature of each part of the mold should not be too different, otherwise the module will be cracked due to uneven expansion and contraction of the mold, and the tiny crack will expand due to stress concentration and infiltration of aluminum liquid, resulting in partial cracking of the module. It directly affects the service life of the mold. In production practice, we have encountered scale due to poor water quality and caused blockage of some cooling tubes. As a result, the temperature of the moving core on one side of the moving mold is too high (the surface temperature is close to 300 ° C), resulting in a serious adhesion of the cavity surface. Aluminum, the mold is polished almost every shift, and the cracking phenomenon is significantly increased at the corners of the module. The situation has improved significantly through measures to clear the pipeline and improve water quality.
Effect of mold cooling water on casting quality
The temperature of each part of the mold varies depending on the needs. The aluminum liquid with a large wall thickness of the workpiece solidifies slowly, and the mold temperature can be slightly lower. The rib, the boss or the thin wall is used to prevent cold separation, and the liquid flow should be increased. Sex, the mold temperature should be relatively increased. Controlling the temperature of each part of the mold can also change the distribution of shrinkage cavities in the casting . The aluminum cylinder blanks we produce are prone to shrinkage between the water jacket and the bolt holes, causing leakage between the water channel and the bolt holes. If the cooling of the hole-forming pins is strengthened, the aluminum liquid around the bolt holes can be accelerated and the other parts are cooled. Slow, the shrinkage cavity is always formed at the position where the aluminum liquid is finally solidified. The shrinkage hole between the water jacket and the bolt hole is transferred, and the leakage rate of the casting is controlled.
Poor mold cooling causes the mold temperature to be high. In addition to causing the aluminum to affect the surface finish of the workpiece, the workpiece is not sufficiently cooled and formed, and tensile stress is generated during demolding, causing internal cracking. In the production of cylinder blank die casting, we have encountered significant leakage during the pressure test of the blank due to poor cooling of the fixed mold.
In order to reduce the pores in the casting, the mold must have a certain volume of risers and a perfect exhaust passage. The exhaust gap between the static and dynamic modes is too small, the air in the cavity can not be fully discharged during the filling process, which will increase the pores in the casting; if the gap is too large, the aluminum liquid will rush out from the gap to form an excessive flash. . In order to solve the contradiction that the exhaust gas is smooth and the aluminum liquid is not leaked, a water-cooled pipe can be added to the cold iron at the outer exhaust portion of the riser, and when the aluminum liquid passes the cavity gas through the riser from the air passage of the larger gap. When discharged smoothly, the aluminum liquid encounters the cold iron with internal cooling and condenses rapidly without causing excessive burrs. In order to enhance the cooling effect of cold iron, in addition to cooling water cooling, some also use high thermal conductivity alloy materials.
cooling water system
In order to ensure the cleanliness of the current mold cooling water, we use a closed cooling tower circulation system; in order to avoid scale blocking the pipeline, the circuit is equipped with a multi-function high-frequency electronic descaler and a dosing and anti-corrosion device. In order to prevent rust, the metal components in the reservoir are all made of stainless steel, and the suction port is at a certain distance from the bottom of the pool to avoid inhalation of sediment. According to the needs of the cylinder mold, the cooling capacity of the cooling water system is 100RT (RT-Japan cold tons, 1RT=3320kCal/h=3.861kW). The maximum cooling water circulation is 13090L/min, the water supply pressure is 0.3-0.4MPa, and the water supply temperature is 20 -35 ° C, the inlet and outlet water temperature difference is 5 ° C.
During the training of Honda Automobile Co., Ltd., we carefully observed and analyzed the cooling water system of the cylinder die-casting mold. In addition to the closed loop system, they also use a computer control system, and the temperature at each point on the mold can be set by computer. The mold is equipped with a sensor for detecting the temperature of each part, and the temperature is converted into an electric signal and fed back to the computer control system to compare with the set temperature to adjust the flow rate of the cooling water.
The internal cooling water of complex molds directly affects the life and quality of the mold. For complex molds such as die-casting cylinders, there are hundreds of cooling water inlet and outlet branches. The amount of cooling water in the mold should be adjusted accordingly. If valve control is used, not only the layout is difficult, but also quantitative adjustment is not possible. Only by using a computer control system can it be convenient to adjust and stabilize the temperature of each point of the mold.
The structure of the mold, the thickness and complexity of the workpiece, the temperature change, etc., have different requirements for the cooling water flow of the mold, which requires a certain period of time to test and explore to obtain the best data.
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