what is vacuum casting？

Vacuum casting is the process of injecting molten metal into the mold through air pressure, and then removing the air to form a vacuum. It is a process of ventilating the mold. This casting method is mainly used for small parts or jewelry with delicate details.

Defects of ordinary die casting process

Conventional high pressure casting

(Exhaust for standard die-casting mold with slag bag and exhaust groove)

1. Since the material liquid at the inner gate is sprayed at high speed, 40% to 90% of the material liquid will contact the gas in the cavity and the outside air.

2. In high-speed filling, the more gas the material liquid entrains, the higher the porosity of the casting, and it is difficult to meet the air tightness requirements and mechanical performance requirements of seals, structural parts and other products.

Vacuum die casting

1. Eliminate or reduce the pores inside the product, and improve the mechanical properties and surface quality of die castings;

2. Greatly reduce the back pressure of the cavity, accelerate the liquid flow rate and improve the filling conditions;

3. With the increasing number of structural products, the requirements for the control of pore defects are becoming more and more stringent. The higher the vacuum in the cavity when the molding die is filled, the concept of high pressure casting-high vacuum die casting is gradually becoming Standards accepted and considered by die casting companies.

Advantages of vacuum die casting production

1. Before high-speed filling, 80~90% of the gas in the cavity has been discharged. During the high-speed filling process, the probability of entrainment is low, and the risk of porosity in the casting is small;

2. Negative pressure is formed in the cavity, which has adsorption power to molten metal, which can increase the fluidity of molten metal, and has the most obvious effect on materials with poor fluidity such as pure aluminum and high thermal conductivity aluminum;

3. The filling pressure of vacuum die-casting is 30%~50% lower than that of ordinary die-casting, which greatly improves the life of the mold;

4. The quality of the die-casting pouring system (runner, slag ladle) is lower, and the return charge is reduced by more than 20%, which effectively reduces the cost of die-casting.

Advantages of vacuum die casting

1. Can be welded;

2. The internal structure of the casting is dense and the air tightness is good;

3. The porosity is low, and the pores will not be exposed after the subsequent processing;

4. After surface treatment, anodic oxidation, electroplating, powder spraying, etc.), the risk of defects such as surface blistering is low;

5. T6 heat treatment can be performed to obtain mechanical properties such as higher tensile strength, yield strength and good elongation.

Vacuum applicable process range

1. Die casting of zinc, aluminum, magnesium and copper.

2. Semi-solid die casting, low pressure casting.

3. Liquid die forging, squeeze casting.

4. Plastic, resin molding, etc.

Application scope of vacuum die casting

1. High-strength structural parts

2. Air-tight parts

3. Auto parts

4. Communication filter

5. Pure aluminum/anodized aluminum parts

6. Electroplated parts

7. Power tools

8. Other high-quality die-casting parts.

Schematic diagram of vacuum die casting work

Comparison of ordinary die-casting and vacuum die-casting products

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

1. Traditional die-casting. There are more pores during forming, and it is very limited to make high-demand products;

2. Ultra-low speed die-casting. There are fewer pores during forming, but it has great limitations on the product structure;

3. Vacuum die-casting. There are fewer pores when forming, but the limitation on the product structure is small;

4. Ultra-low-speed vacuum die-casting. On the basis of ultra-low-speed die-casting and vacuum die-casting, the product quality is improved again, and products with higher requirements and higher quality can be made.

Vacuum die casting form

Comparison of Metallographic Porosity of Several Types of Vacuum Die Casting

Vacuum application case

Classification of vacuum die casting exhaust components

1. Corrugated board exhaust (steel, copper, beryllium), can be used for vacuum and general exhaust;

2. Use the vacuum valve with the injection position/time closed;

3. Rely on mechanical/material liquid to fill the closed vacuum valve.

Advantages and disadvantages of mechanical and hydraulically driven synchronous valves

Advantages: The above two models have large diameter, large flow exhaust and air extraction functions.

shortcoming:

1. The production cost is high, the maintenance period is short, and the maintenance workload is large; 2. Regular maintenance is required: It is generally required that the vacuum valve must be removed from the mold for maintenance and cleaning every 12 to 24 hours.

Only regular cleaning and maintenance can ensure the normal operation of the vacuum system. For mass die-casting production, several more sets are needed for easy replacement.

Factors affecting the following aspects of vacuum die casting

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

1. Since the clamping force of the die-casting machine is very large, the parting surface of the mold 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 phenomena such as the gap between the side of the mold slide block and the gap between the thimble and the sprue sleeve of the melt cup will directly affect the effect of high vacuum pumping;

3. Melting technology: control of indicators such as degassing, slagging and hydrogen content;

4. Setting of process parameters of die-casting equipment, etc.;

5. The frequency of maintenance of molds and vacuum components.

In the vacuum die casting application, the influence of the existing air leakage:

For example, the gap between the mold core plane deformation (including the gap between the synchronization valve and the exhaust plate), the gap between the mold slide, the gap between the mold thimble, the gap between the material tube and the plunger head, the gap between the material tube and the sprue sleeve and the mold, Air in the mold end of the gas pipeline, etc., when this cause directly causes the pressure loss of the gas storage tank to exceed the preset theoretical value, it will not be possible to ensure that each mold can obtain a high degree of vacuum.

1. Mainly for the design layout and processing accuracy of mold cavity, gate and runner, and exhaust port; as well as the design layout and processing accuracy of thimble and slider.

2. For molds that require extremely high reusability, the quality of the mold directly affects the quality of the casting.

3. If the mold material and production quality are poor, the high vacuum requirements to be achieved cannot be achieved.