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Introduction to the improvement method of die casting mold design
Published:19/11/2018

Since China's die-casting industry started late and the starting point is low, die-casting production is basically in full manual operation. After years of development, with the gradual disappearance of China's demographic dividend, labor shortage has become a major problem restricting economic development, coupled with die-casting labor. Unfavorable factors such as high intensity, high temperature, high noise and high pollution, how to solve people's problems has become a top priority for all enterprises. At present, the profit of die-casting products has entered the era of low profit. In order to survive and develop, enterprises must work hard to improve product quality, reduce production costs, and guarantee the supply of OEMs. With the demands of these different levels, the automation of die-casting production has become a top priority for all die-casting companies. Along with the process of die-casting automation, it is followed how the die-casting mold can adapt to the problem of automatic production of die-casting. Whether the original die-casting mold can adapt to the production of die-casting automation has become a major factor affecting the smooth progress of die-casting automation. In order to adapt to the automation of die-casting production, die-casting molds need to be improved in the following aspects.

1. Adaptability of die casting mold

Preventing mold failures in production is a long-term and difficult task. Those seemingly small problems will bring unexpected risks in the automated production process, resulting in batch waste of products, which will bring unnecessary economic losses to the enterprise. Therefore, it must be paid enough attention from the design stage.

(1) The automation of hydraulic cylinder replacing the inclined guide column die-casting production includes the automation of the release agent spraying. At present, the commonly used sprayers are mostly two-axis servo system sprayers and old-fashioned copper nozzle sprayers (of course, there are also a few robot sprays. The nozzles of the two spraying systems are basically vertically entered by the top of the mold after the mold is divided. According to the instruction of the control system, the nozzle is moved up and down at a certain speed, and the moving mold and the fixed mold surface of the mold are taken off for a certain period of time. Mold spray and blow action. Since the nozzle should enter from the top surface of the mold, the original inclined core of the inclined guide column must be changed to the hydraulic cylinder core pulling device (see Figure 1), otherwise it will affect the action of the spray nozzle and even damage the sprayer. .

Since the automatic spray is sprayed according to a preset procedure, the spraying process is far less flexible than manual spraying, and it is often impossible to achieve "special care" for parts requiring a moderate amount of multiple sprays, especially for large sliders. In this case, the back of the slider is still blocked by itself after the mold is opened, and effective spraying cannot be achieved (see Fig. 2). Therefore, it is necessary to appropriately increase the mold "inside spraying" system at the slider portion of the mold to realize the back of the slider. Supplemental spray.

2) Cooling system mold temperature is a very important parameter in the die casting process parameters, it will affect the casting appearance quality, filling time, filling speed, pressure transmission and other factors. It can be said that the correct and constant mold temperature is reliable. The basic premise for producing high quality castings, increasing productivity, reducing scrap rates and extending mold life. The increase in production tempo caused by automated production will inevitably lead to an increase in mold temperature, and the automatic spraying time will be shorter than that of manual spraying, which will increase the temperature of the mold. Therefore, the design requirements for the die-casting mold cooling system in the automated production will be more stringent. The arrangement of the cooling water channel and the point cooling must be scientific and reasonable. In the past, the simple straight-through cooling water channel or the cooling water channel cannot be used. Adapt to the die casting production under the new situation. The mold temperature must be in a reasonable, uniform and controllable range to ensure the stability and reliability of the casting quality.

In the design of the cooling system, a detailed understanding and estimation of the process parameters of the die-casting production must be made. In the entire casting process, the molten metal injected into the mold becomes the sole source of heat, and it must be considered whether the die-casting mold can play a role. The function of the heat sink has a detailed calculation of the heat released by the molten metal and the heat that can be carried away by the mold cooling system. When the heat is lost through the die-casting mold and the heat taken away by the cooling fluid, the metal is continuously poured. When the heat added by the liquid tends to be uniform, the die-casting mold reaches a heat balance. After obtaining these ideal conditions, the temperature of the die-casting mold must be maintained in order to achieve normal and stable production conditions.

In order to optimize the design of the cooling system, the die casting CAE software can be used for simulation calculation, and then the design of the original cooling system is optimized and improved to ensure the balance and consistency of the mold temperature.

(3) The reliability of the mold core is mainly manifested in two aspects: one is bending fracture, and the other is that the core is retreating. For the bending fracture of the core, we can take measures: 1 strictly control the aspect ratio of the small core, and reduce the possibility of core bending. 2 The mold sump prevents direct impact on the small core of the mold. 3 Minimize the chamfering of the core hole and avoid using the step core to eliminate the local stress concentration of the core, as shown in Figure 3. 4 Using high-quality steel and suitable heat treatment process to improve the quality of small core production. 5 Surface treatment of small cores to reduce the holding force of the core.

The retraction of the core during use mainly occurs on the type of quick-replacement core; in general, the tail of the quick-change core has a hexagonal taper end set screw, and the screw loosens during use. Or the screw cannot be tightened after the core is replaced, resulting in the retreat of the core during die casting production. The common solution is to increase the hexagonal taper end set screws to two. At the same time, the inspection and acceptance work after the mold repair is strengthened, which basically ensures that the core does not retreat.

(4) Stabilization of the ejector system The design of the ejector system involves more calculations. In most cases, the mold factory will empirically set the number and diameter of the ejector pins and the thickness of the ejector plates. For the stability of the ejector rod and the deformation of the ejector plate, there is almost no check. In the process of use, the mold damage caused by the bending and breaking of the ejector rod often occurs, and the depth of the ejector surface of the casting caused by the deformation of the ejector plate exceeds The scrapping of castings caused by the machining allowance. Therefore, in order to adapt to the automated production of die casting, it is necessary to carry out necessary accounting for the stability of the ejector rod and the area to be pushed, so as to prevent it from happening.

The stability of the ejector system also includes the setting of the ejector return block. Currently, most of the return limit blocks use a circular limit, as shown in Figure 4. The contact area between the limit block and the ejector plate is small. After long-term use, the limit block is deformed, resulting in unreliable limit of the ejector plate. The ejector mark is higher than the surface of the casting, which sometimes affects the subsequent machining positioning. The reliability of the casting will cause the casting to be scrapped.

The ejector shall be set as far as possible to prevent some parts of the casting from sticking to the mold. If necessary, an auxiliary device for automatically filling the ejector rod should be provided to avoid frequent jamming of the ejector pin and ensure that the casting is smoothly ejected.

2. Mold protection measures

Die casting fully automated production has the following risks:

(1) When the molded product is defective, it cannot be detected in time.

(2) The product or slag package is fixed, or if it is not completely dropped, it will cause the loss of the mold.

(3) What is more serious is that if the product or slag bag is not dropped, the next time the mold is produced, the mold will not be completely closed, which will lead to the safety accident of the mold fly.

Therefore, while ensuring the stability of the mold, it is necessary to adopt some necessary mold protection measures. All the die-casting molds with detectors are not necessary. There is a commercial multi-functional mold monitoring and protection system on the market. The monitoring and protection system is installed on the die casting machine. Before the die casting, the surface of the mold is tested for residual foreign matter or the slider is misaligned. When the abnormality occurs, the mold is automatically prevented from closing and alarming.

After die-casting, it is tested whether the product sticks to the mold, whether it conforms to the expected shape, and quickly determines whether the product is qualified. It effectively solves the problem of mold ejection and the condition of the mold cavity under the automatic working condition with high temperature. . When the abnormality state is found, the mold monitoring system can stop the alarm in time to avoid the secondary loss caused by re-closing after the quality problem occurs.

3. Conclusion

Although these necessary measures have been taken in the design and use of the mold, these measures are not once and for all, especially in the process of using the mold, and the die-casting enterprises must also do the maintenance work of the daily die-casting molds. The life-cycle recording of the use and maintenance of the die-casting mold; summarizing and analyzing the failure law of the die-casting mold during use, and according to these usage rules, regularly replace those vulnerable small cores, ejector pins and other accessories to prevent the preventive maintenance of the die-casting mold Work, lay a good foundation for the automatic production of die casting.

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