What are the factors that affect aluminum alloy die-casting ?

People engaged in the die-casting industry know that aluminum alloy die-casting molds are complex equipment that must complete multiple functions simultaneously. Its appearance has a significant impact on the size of aluminum alloy die castings. The fixed or movable core enhances the sensitivity of aluminum alloy die-casting, allowing for the production of complex and precise parts. The geometric shape of the runner mouth affects the filling of the mold. The thermal conditions of aluminum alloy die-casting molds determine the solidification, microstructure, and quality of the parts. In mass production, the thermal conductivity of the mold determines the cycle time. Therefore, it can be said that there are many factors that affect the aluminum alloy die-casting process.

1. Aluminum alloy die-casting is mainly affected by factors such as injection pressure, injection speed, filling time, and mold temperature in production. These elements influence and constrain each other, and adjusting one element will cause corresponding process changes. Therefore, it is important to choose the correct process parameters.

2. The most commonly used in the die-casting industry is aluminum alloy die-casting, which cannot be compared with other alloys during use. Due to the different components in aluminum alloy die-casting, the physical and chemical functions of the alloy exhibited during use are different.

3. The crystallization of aluminum alloy die-casting during manufacturing is also different. It is necessary to choose a reasonable casting method based on the characteristics of its aluminum alloy during application, in order to effectively prevent casting defects.

4. The process of aluminum alloy die-casting is usually understood as filling the mold in application. The most prominent performance in the cooling and crystallization process of equipment is the comprehensive utilization of those functions. These characteristics of aluminum alloys depend on the composition of the alloy, but are also related to casting elements, alloy heating temperature, complexity of the casting mold, gating system, gate shape, etc.

5. The activity of aluminum alloy die casting mainly refers to the filling of the mold in the alloy liquid, and the magnitude of its activity effectively determines whether the alloy can cast complex castings to a certain extent. The activity of eutectic alloys in aluminum alloy die casting is the best.

In fact, there are many factors that affect the aluminum alloy die-casting process, mainly including composition, temperature, and solid particles containing metal oxides, compounds, and other pollutants in the alloy liquid. However, the fundamental internal factors are pouring temperature and pouring pressure. In the theory of aluminum alloy die-casting, when the alloy has been determined, in addition to strengthening the melting process, it is also necessary to improve the casting process, increase the pouring temperature without affecting the quality of the casting, and ensure the activity of the alloy.

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Key equipment for integrated die-casting

Since Tesla launched an innovative trend of integrated die-casting, its application range has extended from the rear bottom plate to the front bottom plate, driving a strong demand for large die-casting machines.

The core of integrated die-casting technology lies in integrating numerous automotive components through one-time die-casting, thus setting strict standards for the raw materials and die-casting technology of vehicle body structural components.

Ultra large die-casting machines are an important development direction of die-casting technology. As the core equipment of integrated die-casting, ultra large die-casting machines have extremely high technical and market value.

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What surface treatments are available for aluminum alloy die casting

 Anodizing: 

The surface corrosion resistance of extruded aluminum alloy profiles is not strong, and surface treatment through anodizing is necessary to increase the corrosion resistance, wear resistance, and aesthetic appearance of the aluminum material.

Electrophoretic painting: 

The surface of electrophoretic painted profiles has a soft luster and can resist the erosion of cement and mortar acid rain.

Powder electrostatic spraying: 

The characteristics of powder electrostatic spraying profiles are excellent corrosion resistance, acid, alkali, and salt spray resistance, which is much better than that of oxidized colored profiles.

Titanium plating and titanium gold plating process: 

The titanium gold plating process on aluminum profiles belongs to the coating technology. It adds pre plating and electroplating process steps on the basis of conventional titanium plating process. The pre plating process is to chemically treat the activated plated parts in an aqueous solution of salt and hydrochloric acid, thereby producing a colorful effect.

Wood grain transfer printing: 

Vacuum wood grain coating technology is used to transfer wood grain onto the surface of a workpiece through thermal transfer printing after electrostatic spraying of metal products. Not easy to fade, realistic wood grain, improving product grade.

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Aluminum alloy die-casting process flow

 1) According to the principles of fluid mechanics, a theoretical analysis and some calculations were conducted on the movement of liquid metal in the pressure chamber of a horizontal cold chamber die casting machine. Based on this analysis, it is believed that the slow injection process of the punch in the horizontal cold chamber die casting machine is a combination of accelerated and uniform motion, and the combined result directly affects the quality of the die casting. The amount of air entrained by liquid metal in the pressure chamber is related to the slow injection acceleration, slow injection velocity, initial filling degree, and pressure chamber diameter, and there exists a critical slow injection velocity and optimal acceleration. At this velocity and acceleration, the amount of air entrained can be minimized, and the porosity of the casting can be minimized.

2) The process of liquid metal filling during die casting production is a process where many conflicting factors are unified. Among the many factors that affect filling, the main ones are pressure, speed, temperature, and time. Time is the result of the coordination and synthesis of process parameters, and various process factors are interdependent and mutually restrictive. When adjusting a certain process factor, it will inevitably cause changes in the corresponding process factor, and may in turn affect the already adjusted process factor, causing it to change. Therefore, only by correctly selecting, controlling, and adjusting these process parameters to meet the needs of die-casting production can qualified die-casting parts be produced under other good conditions.

3) The basic characteristics of aluminum alloy die casting are filling under high pressure and high speed, crystallization under high pressure. During the entire rapid injection stage, the metal liquid enters the mold cavity in the form of a jet at a speed of 30-60m/s, and it is impossible for the metal liquid to not wrap up the gas. In this case, adjusting the process parameters and plan is the key to where and in what form the gas pores are reasonably distributed. Due to the high-pressure jet breaking gas into dispersed small pores and leaving them in the casting, it is not suitable to manufacture important safety components such as shells and outer covers through heat treatment. Improve strength and lower elongation of die castings. Therefore, die casting is generally suitable for producing thin-walled structures that do not require significant impact loads.

4) According to the process characteristics of aluminum alloy die casting, it is difficult to form large-area thin-walled parts. If the wall thickness is too large or severely uneven, defects and cracks are prone to occur. It is hoped that the wall thickness of the die casting will be as uniform as possible. For large aluminum alloy die castings, the wall thickness should generally not exceed 6mm. Under normal process conditions, the wall thickness of die castings should not exceed 4.5mm. To avoid defects such as shrinkage and porosity at the thick wall of the die casting, it is necessary to reduce the thickness of the thin wall and add strengthening ribs.

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

6) The ability to cast deeper and smaller holes is a characteristic of die casting technology. For some holes with low precision requirements, they can be directly used without the need for mechanical processing, thereby saving machining time. The diameter and depth of the holes cast on the parts are related, and smaller holes can only be cast at shallower depths. The general aperture is not less than 2mm, and the hole depth is not greater than 4-8 times the aperture. The threaded holes on castings are often made by first die-casting a core hole that meets the requirements, and then machining (mostly by tapping) to create a threaded hole.

7) At the connection between the walls of die castings, whether it is a right angle, acute angle, or obtuse angle, it should be designed as a rounded corner. In order to facilitate the demolding of die castings from the mold cavity and core, prevent surface scratches, and extend the life of the mold, die castings should have a reasonable demolding 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 clamping force of the alloy on the core, and the greater the demolding angle. The larger the shrinkage rate of the alloy, the higher the melting point, and the greater the demolding angle. In addition, the demolding angle on the inner surface or inner wall of the hole of the casting is larger than that on the outer surface. Within the allowable range, a larger demolding angle should be used to reduce the required ejection force or core pulling force. The general demolding angle is taken as 0.5 °~1.5 °.

8) In terms of die casting technology, threads can be directly cast under certain conditions.

9) Various convex patterns, mesh patterns, characters, logos, and patterns can be cast on the die casting.

10) Metal or non-metallic parts (inserts) can be first embedded in the die casting mold and then cast together with the die casting. This can fully utilize the properties of various materials (such as strength, hardness, corrosion resistance, wear resistance, magnetic conductivity, conductivity, etc.) to meet the requirements for use under different conditions, compensate for the shortcomings caused by poor casting structure and process, 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 require further mechanical processing. Meanwhile, due to the presence of internal pores in die casting, further mechanical processing should be avoided as much as possible. However, the parts produced by die casting cannot be directly assembled and used in any situation, so in some cases, mechanical processing is also required on some surfaces or parts. The surface of die-casting parts is dense and uniform, with good mechanical and physical properties. The thickness of this surface is approximately 0.5-0.8 mm, so the general machining allowance is recommended to be 0.3-0.5 mm.

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What are the characteristics of aluminum alloy die-casting products

 1) Aluminum alloys can be classified according to their performance characteristics and uses

Four types of rust proof aluminum (LF), hard aluminum (LY), ultra hard aluminum (LC), and forged aluminum (LD)

2) Cast aluminum alloys are divided into different types based on the addition of the main alloying elements

Four types of aluminum silicon system (AL Si), aluminum copper system (Al Cu), aluminum magnesium system (Al Mg), and aluminum zinc system (Al Zn)

Commonly used grades include ADC12 (A383) and ADC10 (A380)

3) Advantages of Aluminum Alloy Die Casting

Good product quality: The casting has high dimensional accuracy, good surface smoothness, high strength and hardness. The strength is generally increased by 25-30% compared to sand casting, but the elongation is reduced by about 70%. The size is stable and the interchangeability is good. Die cast aluminum thin-walled complex castings, for example: the current minimum wall thickness of zinc alloy die casting can reach 0.3mm, and aluminum alloy die casting can reach 0.5mm. High production efficiency: The machine has high productivity. For example, the domestically produced J-III3 horizontal cold air die casting aluminum machine can die cast aluminum 600-700 times per eight hours on average, and the small hot chamber die casting aluminum machine can die cast aluminum 3000-7000 times per eight hours on average. Excellent economic effect: Due to the precise size and smooth surface of die cast aluminum parts. Generally, it is used directly without mechanical processing or with a small amount of processing, which not only improves the metal utilization rate but also reduces a large amount of processing equipment and working hours. The cost of castings is cheap, and composite die cast aluminum can be used with other metal or non-metallic materials, saving both assembly time and metal.

4) Disadvantages of aluminum alloy die-casting

Due to the high filling speed and unstable flow state of liquid metal in the mold cavity during die casting, the general die casting aluminum method is used. However, the casting is prone to porosity and cannot undergo heat treatment. Die casting is more difficult for castings with complex concave surfaces. The lifespan of aluminum alloy die casting molds is relatively low, with a lifespan of approximately 80000 strokes. Small batch production is not suitable, mainly due to the high manufacturing cost of die cast aluminum molds and the uneconomical nature of small batch production. Aluminum alloy die-casting is not easy to achieve anodizing, as it is prone to leaving many bubbles or sand holes after die-casting, resulting in poor repair of the appearance and inability to cover the appearance after oxidation.

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The tips of die casting design

 Under the premise of meeting the product function, the die castings are reasonably designed, the die casting mold structure is simplified, the die casting cost is reduced, the die casting defects are reduced and the quality of die casting parts is improved. Since the injection molding process is derived from the casting process, the die casting design guide is very similar to the plastic parts design guide in some aspects. For detailed die casting part design, refer to the book "Design Guide for Manufacturing and Assembly Products" published by the Machinery Industry Press.

Fillet

(including corners) The casting drawing often indicates the requirements of unfilled corners R2 and so on. When making the mold, we must not ignore the role of these unmarked fillets, and never make them clear corners or too small fillets. Casting fillets can make the metal liquid fill smoothly, so that the gas in the cavity is discharged in sequence, and can reduce stress concentration and extend the service life of the mold. (It is also not easy for the casting to crack at this place or various defects due to improper filling). For example, there are more clear corners on the standard oil pan mold. Relatively speaking, the brother oil pan mold is the best at present, and there are more heavy oil pans.

Demolding slope

It is strictly forbidden to have artificial side concave in the demolding direction (often when the casting is stuck in the mold during the mold trial, and when it is handled by incorrect methods, such as drilling, hard chiseling, etc., it causes local concave).

Roughness

The molding parts and pouring system should be carefully polished as required, and should be polished along the demolding direction. Since the entire process of the molten metal entering the pouring system from the pressure chamber and filling the cavity only takes 0.01-0.2 seconds. In order to reduce the resistance of the molten metal flow and minimize the pressure loss, the surface finish of the flow needs to be high. At the same time, the heating and erosion conditions of the pouring system are relatively severe. The worse the finish, the easier it is to damage the mold.

Hardness of the molding part of the mold Aluminum alloy: about HRC46° Copper: about HRC38° During processing, the mold should leave a margin for repair as much as possible, make the upper limit of the size, and avoid welding.

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The advantages and disadvantages of die casting

 Advantages

Advantages of die casting include excellent dimensional accuracy. This generally depends on the casting material, but typical values ​​are 0.1 mm for the first 2.5 cm of the casting and 0.002 mm for each additional cm. Compared to other casting processes, it produces smooth casting surfaces with corner radii of approximately 1-2.5 μm. It can produce castings with wall thicknesses of approximately 0.75 mm compared to sandbox or permanent mold casting. It can directly cast internal structures such as wire sleeves, heating elements, and high-strength bearing surfaces. Other advantages include the ability to reduce or avoid secondary machining, high production speeds, casting tensile strengths of up to 415 MPa, and the ability to cast highly fluid metals.

Disadvantages

The biggest disadvantage of die casting is its high cost. The casting equipment, as well as the molds and mold-related components, are relatively expensive compared to other casting methods. Therefore, it is economical to produce die castings in large quantities. Other disadvantages include that the process is only suitable for metals with high fluidity and that the casting mass must be between 30 g and 10 kg [5]. In conventional die casting, the final batch of castings will always contain porosity. Therefore, no heat treatment or welding can be performed because the gas in the gap will expand under the action of heat, causing internal micro-defects and surface peeling.

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