In the die casting production process, the improvement and optimization of the die casting process to improve the quality of die casting has played a significant role in promoting; this article briefly describes the die casting technological innovation and how product quality continues to improve, its various aspects of the characteristics of the increasing attention. Pressure casting is characterized by high speed and high pressure.

In the die-casting plants, the metal liquid is the unavoidable involvement of ga in the process, so the die-casting is unsuitable for heat treatment to enhance the mechanical properties. The vacuum die-casting method can reduce the porosity within the die-casting and improve the mechanical properties of the die-casting effective method. Vacuum die casting is the current high-quality aluminum die casting parts necessary for production conditions.

1. Analysis of the current situation of die-casting technology

Die-casting technology is constantly pursuing technological progress and high-quality production. However, because of its process characteristics of the existence of porosity, some things could be improved. How to avoid these shortcomings, today’s die-casting service provider technology continues to explore the direction of the development and application of new die-casting technology, which will bring opportunities to the die-casting industry.

In recent years, with the rapid growth of new energy vehicles, the automobile industry in various countries has begun to use lightweight designs. The excellent quality of the product is a guarantee of safety, and constantly improving the quality to reduce the product porosity is a road of unremitting exploration.

2. Die casting process advantages and its limitations

Die casting process, and its advantages: the essence of die casting is under the action of high pressure so that the liquid or semi-solid metal and high speed filling into the die casting mold, and under pressure molding and cooling solidification and castings of a forming process. It can be seen that high pressure and high speed filling die casting mold are the two main characteristics of the die casting process. Therefore, the main characteristics of die casting are:

 (1) Molding under high pressure, high densification, high mechanical strength, and surface hardness, but the product elongation is low.

 (2) Fast product filling, short cooling time, high production efficiency, and low cost in mass production.

 (3) The product’s surface is rough, even up to Ra1.6-6.3.

 (4) Thin wall-thickness parts can be produced.

 (5) Fast filling means more internal gas is involved, and the product has more air holes.

 (6) Do not heat treat. When heat-treated, the internal gas expands, resulting in defects such as bulging or cracking of the product.

The porosity problem also exists and constantly promotes improving the die-casting process. To meet the quality of the die casting, people continue to increase the requirements and expand the scope of application of the die-casting process; vacuum die-casting technology is one of the methods.

3. Vacuum die-casting method

Vacuum die-casting technology supplements traditional pressure-casting technology. That is to say, the first use of a vacuum extraction device will be a die casting mold pressure chamber and cavity gas extraction so that the metal melts in relative vacuum conditions to fill the cavity.

In the die-casting process, using vacuum die-casting technology to extract the die-casting mold pressure chamber and cavity gas can eliminate or significantly reduce the dissolved gas and porosity within the die casting, improve the casting internal organization density, and enhance the surface quality of the die casting and the comprehensive mechanical properties of the purpose.

To obtain ideal die-casting alloy components, it is necessary to minimize the contact between the sprayed hot metal and the air and fumes inside the cavity; in other words, it is to reduce the gas pressure of the air and fumes inside the cavity as much as possible during the whole process from the beginning to the end of the die-casting and to reduce the gas content of the entire process to a near-ideal condition. Vacuum is used to solve this exhaust problem.

4. Vacuum die casting characteristics

The vacuum die-casting method is currently one of the many process methods, mainly the mold cavity gas extraction, so that the liquid metal in the vacuum state filling cavity, so the die-casting process involved in less gas, casting mechanical properties have been significantly improved. High vacuum law is in the ordinary vacuum die-casting based on the development of new technology, characterized by the mold cavity vacuum being less than 90 millibars.

The die-casting process removes the die-casting mold cavity gas. It eliminates or significantly reduces the porosity and dissolved gases within the die-casting, improving the mechanical properties of the die-casting and surface quality of the advanced die-casting process.

The application of the vacuum die casting method for aluminum and magnesium alloy die casting has been proved to be able to use welding, heat treatment, and other means of processing. Room temperature performance also has a certain degree of improvement.

In general, the vacuum die-casting method has the following advantages:

(1) The Vacuum die casting method can eliminate or reduce the porosity inside the die casting, improve the surface quality of the die casting, and facilitate casting size stability in the production process.

(2) The Vacuum die-casting method dramatically reduces the cavity’s counterpressure. The specific pressure of the injection can be reduced by 40%. It is possible to use a small machine to die-casting larger castings.

(3) Improved mold filling conditions enable the production of castings with thin wall thicknesses and large structures.

(4) Increase heat treatability and weldability of die castings.

The disadvantages of the vacuum die-casting method are:

(1) The mold seal is complex and difficult to manufacture and install, resulting in higher costs.

(2) The vacuum die-casting method is only very effective if adequately controlled.

(3) Vacuum valves require maintenance and spare parts.

A comparison of the above advantages and disadvantages can be seen. As long as proper control is maintained, manufacturers of vacuum die-casting methods can improve their die-casting performance. Mold sealing and pressure chamber sealing caused by cost enhancement, with the popularization of technology and mass production brought about by cost sharing, will be a good solution.

5. Heat treatment of die castings

Porosity is the most common internal defect in aluminum alloy die casting. The use of a vacuum die-casting process reduces the appearance of internal porosity. The purpose of aging treatment is to eliminate internal stress and improve the mechanical properties of the product. The aging process for this product is: heating temperature is 300±10℃, and holding time is 2 hours.

After aging treatment, if the internal organization is not good and there are a lot of air holes, the product will show some uneven-sized air bubbles. When the vacuum system is not used, many bubbles are evident after aging treatment.

Vacuum technology die casting was used to effectively avoid the generation of such bubbles. The microstructure is shown in Fig. 1 and Fig. 2. Production efficiency has been improved, and the scrap rate has been reduced, which satisfies the customer’s high-volume demand and makes the internal operation continuously standardized.

Fig. 1 Structure of casting without vacuum venting (50 times) / Fig. 2 Structure of casting with vacuum venting (50 times)  

6, vacuum die casting necessary conditions

6.1 Sealed molds

Vacuum die casting to remove the cavity of the form of gas for the mainstream. Only on this form, for the mold cavity air pumping clean to get a better vacuum effect, then there is a vacuum valve installed in the mold and exhaust channel connection (figure 3); there is also a vacuum valve installed in the pressure chamber sprue material mouth, through the pressure chamber pumping out the cavity gas, which will be installed in the vacuum valve in the mold on the method of the more simple and practical.

Its most significant advantage lies in the design of the mold, and the same as the conventional die-casting, mold sealing needs to be considered to protect the sealing ring, mold design step parting surface, etc. (Figure 4).

6.2 Sealing of punches and chambers

The design of the material tube is a central part of the entire pressure injection kit. It is best to use an integrated stock tube to use a sealing ring punch. Advantages include long life, high process stability, easy tube/machine/die alignment, and tolerance and temperature control built into the tube. Successful barrel design is essential for the use of sealing ring punches.

For the production of thin-walled die castings, the vacuum in the cavity needs to be controlled to <90 bar, which requires the following conditions:

1. The punch’s press chamber’s sealing should be high to minimize air leakage (Fig. 5).

2. Do not spray too much mold release agent to avoid moisture residue in the cavity.

3. Sprayer atomization should be good, preferably a micro nozzle.

4. The amount of release agent sprayed should be small to avoid accumulation of residue in the exhaust channel, which may affect the action of the vacuum valve or reduce the area of the exhaust channel.

5. Use less wax as a purity refining mold release agent. Avoid too much residue on the mold surface, resulting in the appearance of burrs, and damage to the seal, affecting production.

6. High injection speeds for thin-walled parts require good punch lubrication.

7. Avoid putting the punch oil directly into the pressure chamber, as this will affect the gas content of the casting. Instead, use the linkage pulse spray method.

8. The punch must be cooled for an extended period, ensuring water pressure and flow (Figure 6).

9. Tolerance and temperature control of the tubes are critical and require careful calculations and reasonable temperature control.

6.3 Large capacity vacuum tanks and pumps

To ensure a high degree of vacuum, it must be equipped with large-capacity vacuum tanks and vacuum pumps; the following figure shows a 2000-ton die-casting machine with a vacuum machine.

6.4 Vacuum valve selection

Vacuum valves are cores of vacuum die-casting. The current vacuum valve has a mechanical structure, a hydraulic solenoid control valve structure, and a cooling exhaust plate structure.

1. Mechanical valves operate by utilizing the kinetic energy of the alloying fluid to close the mechanical valve at the final filling point.

2. The hydraulic electromagnetic control valve working principle is the valve inlaid into the die-casting mold; its advantages are exhaust capacity and anti-pollution ability. The Disadvantage is the need for electromagnetic control and a hydraulic source, closing the response time by the solenoid valve. The die-casting unit control system requires a high; the die-casting equipment controls the valve’s work process.

2. according to the structure, the cooling exhaust block is divided into a flat exhaust piece and a three-dimensional exhaust piece; the three-dimensional exhaust piece is a three-dimensional rubbing plate, and the flat exhaust piece has a larger cross-section area of the pumping channel, improving the pumping efficiency.

The cooling method is divided into water-cooled and self-cooled. The water-cooled usually uses hot work mold steel and a cooling water channel; the self-cooled principle relies on its heat conduction to exhaust the alloy liquid cooling block. Beryllium copper alloy is the most suitable production material. The choice of vacuum valve depends on the equipment interface and the casting quality requirements.

7. Conclusion

With the development of the die-casting industry, vacuum equipment is being used by more and more die-casting manufacturers. The use of vacuum equipment to produce castings has two main advantages: it reduces the product porosity, improving the product qualification rate; and it reduces the pressure of the front end of the metal liquid, conducive to filling and forming.

The main advantage of a vacuum is to reduce the gas content of the product and thus improve the casting qualification rate, as well as the production of thin-walled parts and other products that are difficult to fill, which has a high value of use in actual production.

Of course, the vacuum system is affected by various aspects; first of all, the mold should be sealed, and the mold design should be reasonable; at the same time, in the die-casting process, to maintain the system regularly, taking into account the impact of all aspects. So, no vacuum system is entirely omnipotent.

The quality of die-casting products depends on all aspects of support. The vacuum system, a more advanced technology, is now widely utilized.

Therefore, the promotion of high vacuum die-casting technology will raise the level of die-casting technology and expand its scope of application. With its process, matching technology, as with the market demand, should come into being.

However, using vacuum process die casting, first of all, requires buying equipment and increasing investment. Secondly, using the process requires good maintenance, and using valves also needs to replace wearing parts, increasing the cost of die-casting products.

Therefore, the mechanical properties have no special requirements; the product process is mature and easy to fill the die casting, so it generally can not use vacuum production; for the performance and porosity, which have special requirements of the product, such as high-quality thin-walled parts as well as structural parts, etc., vacuum equipment is a necessity.Therefore, the mechanical properties of no special requirements, product process is mature and easy to fill the die casting, generally can not use the vacuum production; for the performance and porosity have special requirements of the product, such as high quality thin-walled parts as well as structural parts, etc., the vacuum equipment is a necessity.

FAQ

Question 1: What role does vacuum technology play in die-casting?

Answer: To minimize the formation of pores and inclusions during the die-casting process, vacuum technology is mostly utilized to remove air from the mold before the injection of the metal liquid. To ensure that the metal liquid can fill the mold smoothly and to increase the density and mechanical qualities of the casting, this procedure is typically carried out using a vacuum pump and vacuum valve.

Question 2: In contrast to conventional die casting, what benefits does vacuum die casting offer?

Answer: In response, vacuum die casting offers the following benefits over regular die casting:

Lower the number of pores within the casting while raising the material’s density and tensile strength.

Enhance the quality of the surface and lessen flaws such as shrinkage cavities and bubbles.

Boost the castings’ durability and mechanical qualities.

Lower the percentage of defects, increase production effectiveness, and reap financial rewards.

Question 3: What effect does material selection have from vacuum die-casting technology?

Answer: In response, a greater variety of material types, such as zinc, magnesium, and aluminum, may be processed using vacuum die-casting technology. A vacuum atmosphere reduces holes and inclusions, greatly improving material purity and performance. This makes high-performance alloy materials more capable of expressing their properties and fulfilling the demands of high-strength, high-precision parts.

Question 4: What tools are required to use vacuum die-casting technology?
 Answer: The following tools are needed to put vacuum die-casting technology into practice:
 A vacuum environment is created by using a vacuum pump to remove air from the mold.
 Vacuum valve: regulates the creation and preservation of vacuum.
 Sealed mold: guarantees that there won’t be any leaks in a vacuum.
 Die-casting machine: Vacuum-system-compatible specialized die-casting apparatus.
 By utilizing these tools in tandem, casting quality is improved by ensuring that vacuum technology is applied effectively during the die-casting process.

Question 5: What areas does vacuum die-casting technology find application in?

Answer: The answer is that vacuum die casting technology is commonly applied in industries that demand accuracy and high performance, such as:

Gearbox housings and engine parts are among the high-strength parts produced by the automotive industry.

Aerospace: Manufacturing strong, lightweight structural components.

We produce parts with excellent dimensional precision and thermal conductivity for electronic and electrical equipment.

Medical devices: Make components for medical equipment with excellent precision and cleanliness.

Because of vacuum die-casting technology, product performance and quality have increased dramatically in these sectors.