Vacuum Die-Casting Technology: Cutting-Edge Technology to Improve the Quality of Die-Casting Parts

Vacuum die-casting technology is one of the most advanced processes in the die-casting industry, effectively addressing defects like pores and shrinkage holes found in traditional die-casting. In conventional methods, residual air in the material tube and mold cavity is difficult to expel, leading to internal gas entrapment that affects product quality. The core of vacuum die-casting is to create a vacuum environment before filling the mold, resulting in more stable casting quality and a smoother surface.

Working Principle of Vacuum Die Casting

The basic principle of vacuum die casting is to maintain the mold cavity in a vacuum state through a vacuum pump and a wave exhaust valve until the molten metal completely fills the mold cavity. During this process, the air in the mold is quickly extracted to prevent gas from being entrained when the melt is filled, thereby eliminating internal defects. In a vacuum environment, the fluidity of the molten metal is improved, and even mold grooves with complex shapes can be filled easily, effectively avoiding the appearance of liquid boundary marks .

Limitations of Traditional Die Casting

In traditional high-pressure die-casting, even if the mold is equipped with a slag bag and an exhaust groove, the molten liquid will still come into contact with the air in the mold cavity during high-speed injection, resulting in an increase in porosity, thereby reducing the air tightness of the casting. This phenomenon makes it difficult for products to meet the mechanical performance requirements of seals and structural parts.

Advantages of Vacuum Die Casting

1. Improve mechanical properties and surface quality : Vacuum die casting can significantly reduce the pores inside the casting, enhance its mechanical strength and surface quality, and is suitable for manufacturing high-performance parts.
2. Improve filling conditions : Under vacuum, the back pressure in the mold cavity is significantly reduced, and the liquid metal flows faster, which helps fill the overall mold shape.
3. Increase fluidity : The vacuum environment provides adhesion to the metal liquid and improves its fluidity, which is especially significant for materials with poor fluidity such as pure aluminum and high thermal conductivity aluminum.
4. Extend mold life and reduce costs : Since the filling pressure of vacuum die-casting is 30% to 50% lower than that of ordinary die-casting, the mold life is greatly extended; in addition, the proportion of flow channels and slag bags in vacuum die-casting is lower, and the recycled materials are reduced by more than 20%. , significantly reducing production costs.

Future Development

As the market demand for high-performance structural parts increases, XY-GLOBAL ‘s requirements for pore control standards are getting higher and higher. Vacuum die-casting, as a new generation process, will become the core technology of the die-casting industry.

Advantages of Vacuum Die Casting

1. Our precision die-casting factory can perform welding;
2. The internal structure of the casting is dense and the air tightness is good;
3. The porosity is low, and there will be basically no exposed pores after post-processing;
4. After surface treatment (anodizing, electroplating, powder spraying, etc.), the risk of surface blistering and other defects is low;
5. XY-GLOBAL can undergo T6 heat treatment to obtain higher mechanical properties such as tensile strength, yield strength and good elongation.

Vacuum die casting applicable process range

1. Zinc, aluminum, magnesium and copper die casting.
2. Semi-solid die casting, low pressure casting.
3. Liquid die forging, extrusion casting.
4. Plastic, resin molding, etc.

Vacuum die casting application range

1. High-strength structural parts
2. Airtight parts
3. Auto parts
4. Communication filter
5. Pure aluminum/anodized aluminum parts
6. Electroplating parts
7. Power Tools
8. Other high quality die castings.

Comparison between traditional die casting, ultra-low speed die casting and vacuum die casting

1. Traditional die casting produces many pores during molding, which has great limitations in making high-demand products;
2. Ultra-low speed die casting. There are fewer pores during molding, but it has great limitations on product structure;
3. Vacuum die casting. There are fewer pores during molding, but the limitation on product structure is small;
4. Ultra-low speed vacuum die casting. Based on ultra-low speed die casting and vacuum die casting, the product quality is further improved, and products with higher requirements and higher quality can be made.

Classification of vacuum die casting exhaust components

1. Corrugated plate exhaust (steel, copper, beryllium), can be used for vacuum and ordinary exhaust;
2. Use vacuum valve closed at injection position/time;
3. Rely on mechanical/liquid filling to close the vacuum valve.

Vacuum Valve Body Components

Factors affecting vacuum die casting include:

The design and production of vacuum die-casting molds are the key to determining the quality of the castings after molding.

1. Since the clamping force of the die-casting machine is very large, the mold parting surface is prone to stress deformation after being squeezed, and the flatness and sealing of the mold processing have very high requirements.
2. The control of air leakage such as the gap between the side of the mold slider and the gap between the ejector pin and the melting cup gate sleeve will directly affect the effect of high vacuum extraction;
3. Melting technology: control of degassing, slag removal and hydrogen content;
4. Setting of process parameters of die-casting equipment, etc.;
5. Maintenance frequency of molds and vacuum components.

The impact of air leakage in vacuum die casting applications:

For example, the deformation of the mold core plane will cause gaps (including the gap between the synchronous valve and the exhaust plate), the gap between the mold slide, the gap between the mold ejector, the gap between the material pipe and the plunger head, the gap between the material pipe and the gate sleeve and the mold, and the air in the mold end of the gas pipeline. When this reason directly causes the pressure loss of the gas tank to exceed the preset theoretical value, it will be impossible to ensure that each mold can obtain a high vacuum degree.

Mold requirements

1. Mainly for the design layout and processing accuracy of mold cavity, gate, runner and vent; as well as the design layout and processing accuracy of ejector and slider.
2. For molds with extremely high requirements for reuse rate, their quality directly affects the quality of castings.
3. If the mold material and production quality are poor, the high vacuum requirements cannot be achieved.

The main difference between ordinary vacuum die casting and high vacuum die casting lies in the vacuum degree and equipment configuration. The following is a summary of the two processes:

1. Ordinary vacuum die casting

Working principle and function:

• Ordinary vacuum die casting sets a slag bag on the side of the mold cavity to squeeze the cold material and air in the cavity generated during the filling process into the slag bag, and exhausts the air through the exhaust groove.
• The vacuum system is connected to an exhaust plate or a mechanical synchronous shut-off valve to extract the cavity air after the mold is closed.
• During the injection process, the injection rod moves forward to form a closed state between the mold cavity and the material tube, and at the same time the valve of the vacuum system is opened to evacuate air.

Equipment configuration:

• A high-speed, low-noise rotary vane vacuum pump is usually used, and the volume ratio of the air tank to the mold cavity is not less than 200:1.
• The vacuum degree can reach -0.1MPa or -101.3KPa, and the mold cavity detection value is within the range of -75 – 250mbar).

2. High vacuum die casting

Process requirements:

• High vacuum die casting requires the vacuum degree in the mold cavity to be below -95KPa (50mbar), and a large air pumping speed must be ensured to quickly remove the gas in the cavity.

Device configuration:

• The design uses a larger buffer tank to quickly extract gas under high vacuum conditions.
• You can use a single-pump, single-tank system with a vacuum in the range of 100mbar-200mbar, or a dual-pump, dual-tank, dual-gas source system that uses multiple pumps and gas storage tanks to pump in sections to achieve a high vacuum below 50mbar.

Effect of Vacuum Degree on Casting Quality

• Vacuum degree has a significant impact on the elongation and surface quality of castings. Especially in high vacuum die casting, good vacuum degree helps to improve the performance of castings.

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