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Process Characteristics Of Aluminum Alloy Die Casting (Cold-Chamber Die Casting)

1. According to the principle of fluid mechanics, the theoretical analysis and some calculations of the movement of liquid metal in the pressure chamber of the horizontal cold-chamber die casting machine are based on the analysis that: the slow injection process of the horizontal cold chamber die casting machine punch is accelerated The combination of motion and uniform motion, the result of the combination directly affects the quality of die castings. The amount of air that the liquid metal is involved in the pressure chamber is related to the slow injection acceleration, slow injection speed, initial fullness, and pressure chamber diameter, and there is a critical slow injection speed and optimal acceleration, where the speed and acceleration It can minimize the amount of air involved and minimize the porosity of castings.

2. The filling process of liquid metal during die casting is a process in which many contradictory factors are unified. Among the many factors affecting filling, mainly pressure, speed, temperature and time, etc., time is the result of the coordination and synthesis of related process parameters, and each process factor influences and restricts each other, adjust a certain process Factors, it will inevitably cause the corresponding process factors to change, and may in turn affect the adjusted process factors to cause changes. Therefore, only by correct selection, control and adjustment of these process parameters, so that the various process parameters meet the needs of die casting production, can it be guaranteed that qualified die casting parts can be produced under other good conditions.

3. The basic characteristics of aluminum alloy die casting are filling under high pressure and high speed, and crystallization under high pressure. During the entire rapid injection stage, the molten metal enters the cavity in the form of a jet at a speed of 30 to 60 m/s, and the molten metal does not envelop the gas. It is impossible. In this case, by adjusting the process parameters and the process plan, the key is where and in what form the pores are distributed reasonably. Because the high-pressure jet breaks the gas into dispersed small pores and remains in the casting, the strength cannot be improved by heat treatment, and the elongation of the die casting is low. Therefore, die casting is generally suitable for the production of thin-walled shells and outer covers that do not need to bear large impact loads, and is not suitable for manufacturing important safety components.

4. According to the process characteristics of aluminum alloy die casting, it is difficult to form thin-walled large areas. If the wall thickness is too large or severely uneven, defects and cracks are easy to occur. It is hoped that the wall thickness of the die casting parts will be as uniform as possible. For large aluminum alloy die casting parts, Generally, the wall thickness should not exceed 6mm. Under normal process conditions, the wall thickness of die castings should not exceed 4.5m. The thickness of the die casting

At the wall, in order to avoid shrinkage and other defects, the wall thickness should be reduced and reinforced ribs should be added.

5. Due to the characteristics of the aluminum alloy die casting process, the alloy used requires a small crystallization temperature range, a small thermal cracking tendency and a small shrinkage coefficient.

6. It is a feature of die casting process to be able to cast relatively deep holes well. For some holes with low precision requirements, they can be used directly without machining, thus saving machining man-hours. There is a certain relationship between the diameter and depth of the die cast hole on the part, and the smaller hole can only be die cast to a shallower depth. Generally, the hole diameter is not less than 2mm, and the hole depth is not more than 4~8 times the hole diameter.

The threaded holes on the castings are often die cast to meet the requirements of the core hole, and then processed (mostly tapping) to make the threaded hole.

7. At the junction of the die casting wall and the wall, whether it is a right angle, an acute angle or an obtuse angle, it should be designed to be rounded. In order to facilitate the removal of die castings from the cavity and core of the mold, prevent surface scratches, and extend the life of the mold, the die castings should have a reasonable draft angle. Its size depends on the wall thickness of the casting and the type of alloy. The thicker the wall thickness of the casting, the greater the tightness of the alloy to the core, and the greater the draft angle. The greater the shrinkage of the alloy, the higher the melting point, and the greater the draft angle. In addition, the inner surface of the casting or the inner wall surface of the hole has a larger draft angle than the outer surface. Within the allowable range, a larger draft angle should be used to reduce the required pushing force or core pulling force. Generally, the draft angle is 0.5°-1.5.

8. In die casting process, threads can be directly die cast under certain conditions.

9. Various embossing, netting, text, signs and patterns can be die cast on die casting.

10. Metal or non-metal parts (inserts) can be embedded in the die casting mold first, and then cast together with the die casting parts. This can make full use of the properties of various materials (such as strength, hardness, corrosion resistance, wear resistance, magnetic permeability, conductivity, etc.) to meet the requirements for use under different conditions, and it can also make up for the poor processability of the casting structure. The lack of point, and solve the die casting problem of parts with special technical requirements.

11. Die castings have precise dimensions and good casting surfaces, and generally do not need to be machined. At the same time, due to the existence of internal pores in die casting, mechanical processing should be avoided as much as possible. However, after all, the die cast parts cannot be directly assembled and used in any situation. Therefore, in some cases, some surfaces or the parts are machined. The surface layer of the die casting is dense and uniform, with good mechanical and physical properties. The thickness of this surface layer is about 0.5~0.8mm, so the general machining allowance is preferably 0.3~0.5mm.

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