What is the principle of die casting of aluminium alloy die casting
1. low-pressure casting means putting dry compressed air, with a certain flow rate, into the sealed container; the role is to maintain a certain temperature on the surface of the aluminium alloy die casting and, under the action of lower gas pressure to make the aluminium alloy liquid rise from the bottom up, through the pouring mouth smoothly into the cavity, maintain the gas pressure, until the aluminium die casting is completely solidified. Then lift the pressure above the aluminium alloy die-casting so the required aluminium die-casting parts can be obtained. The aluminium die-casting parts should be taken out and re-clad for the second pouring, and so on, repeatedly can be poured into a batch of aluminium die-casting parts.
2. die-casting aluminium mould is fixed, and dynamic mould two is the important component. The fixed mould is fixed on the die-casting machine’s fixed mould mounting plate and connected to the pressure chamber of the die-casting machine. The moving die is installed in the die-casting machine’s moving-to-die mounting plate and moves with the moving version of the moving die to close or separate from the fixed die. The die casting of aluminium dies castings is divided into forming parts, mould frame parts, gate system, overflow discharge system, ejector mechanism, guiding parts, etc.
The forming part is the main component that determines the accuracy of the shape and size of the aluminium die casting. The outer surface of the casting is called the cavity, and the inner surface of the casting is called the core; the mould frame part is combined and fixed the die-casting mould according to certain rules and positions so that the die-casting mould can be installed in the die-casting machine frame; the gate system is the part that communicates the die-casting mould cavity and the die-casting machine chamber, i.e. the channel for the metal liquid to enter the cavity; the overflow system is to exclude the gas in the pressure chamber sprue and the cavity, generally including Exhaust channel and overflow groove; Ejector mechanism is the fixed castings to make the die-casting mold parts on the formation of the mechanism off; Guide parts is to guide the mold within the sliding parts of the parts.
3.the design of die-casting aluminium mold should be familiar with the characteristics and technical specifications of the die-casting machine to meet the basic requirements of aluminium alloy die-casting mechanical properties and surface quality. Die-casting aluminium mould has a good use effect; using a good mould structure in line with the process requirements of die-casting production should also choosing suitable mould material to match the appropriate manufacturing quality so that the die-casting mould is easy to operate, safe and reliable. Die-casting die of the dynamic die and fixed die of the combination of the surface is called type surface. Usually mainly distributed in the moulding surface of the moving and fixed die, so the parting surface is mainly made by the specific structure of the casting. The basic form of the parting surface can be divided according to the position of the casting.
4.messy shapes, clear contours, and thin-walled deep cavity metal parts can be made. Because the molten metal in high pressure and high speed adheres to the high mobility and thus can obtain other process methods difficult to process metal parts.
5. aluminium alloy die-casting dimensional accuracy is high, up to IT11-13 grade, sometimes up to IT9 grade, external roughness up to Ra0.8 ~ 3.2um, and interchangeability is good.
6.high material utilization rate. Because of the high precision of die-casting, only after a small amount of mechanical processing can be installed and used can some die-casting be installed directly. Its material utilization rate is about 60%~80%, and the utilization rate of the blank reaches 90%.
7.high production efficiency. Because of high-speed filling, filling time is short, metal industry condensation quickly, and die-casting operation cycle speed. The die-casting method production rate is the highest in all casting processes, which is suitable for large production quantities.
8.Convenient to use inlay parts. Easy to set up the positioning mechanism on the die-casting mould and convenient inlay casting mosaic to meet the local special performance needs of the die-casting.
The casting temperature of aluminium alloy die casting is important, and the gate design is also very important. Because the casting at the inner sprue is easy to overheat and leads to the coarse grain of the casting, or loosening and other casting defects, the casting is generally used to reduce the bright cylindrical riser; this riser manufacturing is simple, smooth exhaust, fit casting and other characteristics.
What are the processes of aluminium alloy die-casting production
Whether with robotic or manual pouring, the following should be noted: Whether with robotic or manual pouring, the following should be noted.
(1)When scooping material, clean molten metal should be taken, molten metal below the oxide film should be drawn in, and the oxide scale and molten metal should not be injected into the injection chamber together.
(2)When pouring material, the scoop should be as close as possible to the injection port of the injection chamber. If it is poured from the high position of the injection port, the molten metal will splash, oxidize and become entrapped in the air and the temperature will also decrease, so avoid it.
(3) Depending on the structure of the casting, the wall thickness and the structure of the alloy grade, the pouring temperature varies slightly. Aluminium alloys are generally 620 to 700°C. When producing thin-walled castings, the upper limit of temperature and the lower limit can be taken for thick-walled castings. The pouring temperature is also related to the mould (die) temperature. When production starts, the mould temperature is always low, and the pouring temperature can be increased slightly; when the mould temperature rises, the pouring temperature can be reduced appropriately. As far as the relationship between the overall pouring temperature and the casting quality is concerned, a high pouring temperature results in a good flow of the alloy and a good surface quality of the casting. On the other hand, high temperatures increase the factor of gas absorption. The castings are prone to pores and shrinkage during filling and accelerate the degree of flushing, adhesion and damage to the mould (die). The low pouring temperatures of some alloys, which remain in the furnace, tend to deviate and lead to hard spots in the castings. However, in general, the pouring temperature is generally low under the principle of not affecting the quality of the casting.
(4) The temperature of the molten metal starts to drip from the time the feed ladle is scooped out. After pouring into the injection chamber, the temperature is even faster. Therefore, maintaining the alloy temperature in the furnace is not representative of the pouring temperature, let alone the filling temperature, especially for pouring. When the volume is small, it loses even more temperature. Therefore, the injection should be carried out immediately after the alloy has been injected into the pouring port of the injection chamber and without waiting; otherwise, the temperature of the molten metal in the injection chamber will drop sharply, and this will affect the filling properties.
(5) The amount of molten metal should be stable, especially when preparing different scoops for different product weights when scooping the material manually. As a general rule, the thickness of the cake should be controlled to 15-25mm. It is not only a question of controlling the final pressure transfer but also the state of the filling fluid of the alloy. They are important process parameters in die-cast production, which affects the quality of the casting. There are certain influences.
Condensation and openings
After filling the cavity with the alloy fluid, it cools quickly and starts to solidify as it fills the cavity. However, the opening (mould) time must wait until the product has some strength and needs to be relatively stretched during movement and finalization. The mould should only be opened if the casting is deformed or damaged. The opening time should therefore vary according to the casting’s size, shape and wall thickness. However, if the casting is left in the mould too long and the temperature drops too much, the solidification and shrinkage of the casting will increase, which will increase the moulding forces, and the casting will have difficulty in pushing out the core, especially for large, thin, low strength castings. The casting will be prone to distortion or damage. Mould opening time is also related to the temperature of the mould (die), which is related to the cooling capacity of the mould (die), especially when too much-molten metal is poured in, the filter cake is too thick, and the condensation time is too short. The thick cake has not yet been set. When the mould is opened (mould), parts of the cake can burst and splash, causing injuries and accidents, so attention must be paid.
Ejecting and picking up
The switch will signal when the mould opening reaches its end. Under normal circumstances, this signal is received by the ejector hydraulic cylinder to push out the casting. When the mould (die) is equipped with a core pull hydraulic cylinder, this signal is received by the hydraulic cylinder of the core pull for the pulling and insertion action. After the pulling and inserting action is completed, the signal is received by the hydraulic cylinder for injection and pushed out. Casting action. The designer arranges the drawing sequence and inserts the core according to the needs of the casting. This procedure should be indicated on the die-casting production process card. In general, these procedures cannot be abnormal in production. However, whether these procedures can be performed properly is related to the operating condition of the limit travel switches on the injector hydraulic cylinder and the core-loaded hydraulic cylinder. If the travel switch is displaced or faulty, the core pull action procedure or stroke will be abnormal. Interruption of work or even damage to the mould accident.
The proper ejection distance of the ejector pin should allow the casting to not only fall naturally from the mould , allowing the operator to use a portable tool to remove the mould die from it. Coming down for the purpose. The period when the mould is re-closed from the mould opening is the only time in mould casting production during which abnormal parts of the mould can be observed, and more timely maintenance can be achieved. It is also a key part of maintaining high production and quality.
Control and function of specific pressures
The “specific pressure” is the pressure per unit area. In each jet, the punch is pushed through the pressure and the molten metal in the jet chamber is filled with cavities through the inner grid until it is compacted and formed. Depending on the filling and pressurization procedure and function, the process is divided into two parts, the injection-specific pressure and the pressurization ratio pressure.
Controlling the accumulator pressure
The accumulator is the energy storage vessel of the die-casting machine. Under normal conditions, the accumulator contains 75- 80 of the nitrogen pressure and about 20-25 of the hydraulic oil pressure. It supplies the high-pressure working fluid to the machine’s hydraulic cylinders, so the accumulator is where the energy is supplied when the machine is working. Still, its energy storage is limited and only provides the required working energy when the ratio of nitrogen pressure to hydraulic oil pressure is within a specified range. Under normal conditions, the pressure drop across the accumulator should not exceed the working pressure of each injection. If it is greater than 10, it is abnormal. The reasons for an abnormality are.
(1) The nitrogen pressure is less than the specified range, and the nitrogen needs to be filled to the specified value.
(2) The hydraulic cylinder supplied by the accumulator is leaking, and the capacity of the high-pressure oil discharged from the accumulator exceeds the specified capacity. The cause of the leak must be checked.
It should be noted that if the nitrogen charge exceeds the specified pressure, the nitrogen in the accumulator will occupy too much volume, and the capacity of the working fluid will not be sufficient for a single injection. The hydraulic oil from the accumulator will be all. When the energy is discharged, the energy in the accumulator is exhausted, and its function is lost.
Considerations in aluminium die casting
Firstly, we are considering the problem of releasing the aluminium alloy die casting.
The second, secondly, is to consider the problem of the wall thickness of aluminium alloy die-casting for all products large; the gap of thickness will be too big to bring influence filling.
Third, in the structure, to try to avoid the emergence of complex structures that lead to mould structure, we have to use multiple cores or spiral cores.
Four, some die-casting appearances, such as oil spray, may have special requirements.
Fifth, the design considers the mould problems; if there are multiple positions of the core extraction bit, try to put both sides; better not to put in the lower core extraction so that over time the aluminium alloy die casting under the core extraction will have problems.
Overview of the advantages of aluminium die casting
Firstly, because of the characteristics of the metal, due to the thermal and electrical conductivity of aluminium alloy, and its easy cutting performance, the production of aluminium alloy die casting products also have these several properties, loved by various industries.
Secondly, aluminium alloy dies casting has good performance to fill, but also because of this, easy to appear in the solidification of the shrinkage phenomenon.
Third, the aluminium alloy die-casting year is strong, with tensile strength and density ratio of about 9:15; density is small, even in the high-temperature working environment, and can also maintain its good performance.
Fourth, it is easy to stick to the mould when producing aluminium alloy die casting, so the quality should be controlled.
Fifthly, aluminium alloy has good corrosion resistance and oxidation resistance. Most aluminium alloys have good corrosion resistance in fresh water, seawater, concentrated nitric acid, nitric acid, gasoline and various organic substances.
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