1. Introduction

The improvement of air shrinkage hole research has important theoretical value and practical significance, for promoting the progress of casting technology and the development of die casting industry is of great significance. Die casting gas shrinkage hole phenomenon is die casting production process common quality defects, serious will lead to die casting scrap, on the use of the product performance and aesthetics have a negative impact. Therefore, die casting manufacturer The research on the improvement of the air-shrinkage hole phenomenon is of great practical significance. The background introduction of the phenomenon of air-shrinkage holes mainly involves the following aspects:

The formation of gas shrinkage holes is closely related to a number of factors in the die casting process. In the die casting process, the metal liquid gradually solidifies as the temperature decreases, but due to the formation of a sealed hard shell on the outer surface of the casting, the internal metal liquid may not be adequately replenished during the solidification process, thus forming a hollow space, or shrinkage holes, in the location of solidification. In addition, blocked vent holes or improper use of lubricants may lead to the creation of blowholes.

Gas shrinkage usually occurs in areas where the wall thickness of the casting varies considerably or where the temperature of the liquid metal is too high. Excessive wall thickness leads to slow internal cooling and solidification, which prevents sufficient replenishment of the liquid metal during shrinkage, thus increasing the likelihood of shrinkage hole formation.

The phenomenon of air shrinkage not only affects the usability of the product, but may also lead to problems during processing. The presence of shrinkage and air holes will reduce the strength and sealing of the die casting, and may even lead to cracks; oil leakage, fracture and other more serious defects.

The phenomenon of gas shrinkage hole is an important problem to be solved in die casting mold production. Through in-depth study of the formation mechanism and influence factors of air shrinkage holes, take effective improvement measures (such as: cooling water, high pressure fine core cooling water, vacuum, slag collection package, extrusion, etc.), can significantly improve the quality and performance of die casting, for the production and development of the enterprise to provide a strong guarantee die casting service.

 

2. Analysis of the formation mechanism of gas shrinkage holes

Liquid metal in the cooling solidification process, due to the lower temperature of the mold surface and accompanied by water-cooled air, the liquid metal first from the surface in contact with the mold began to solidify, forming a layer of hard shell. As the temperature is further reduced, the liquid metal gradually solidifies inward. In this process, the liquid metal will occur volume contraction, but due to the sealing effect of the external hard shell, the internal liquid metal can not be pressurized to fully replenish the solidification of the position of the formation of hollow space, that is, shrinkage holes.

Secondly, the gas involved in the die-casting process is also one of the important reasons for the formation of gas shrinkage holes. Liquid metal in the casting process may be involved in too much air, and particles of oil, punch oil combustion gas into the cavity, especially in the molding equipment pressure is insufficient, the air is easy to stay in the casting inside the formation of air holes. In addition, improper design of the mold exhaust system (e.g., insufficient exhaust volume and poor design considerations, etc.) may also lead to gas that cannot be discharged smoothly, resulting in the formation of gas-shrinkage holes.

Dissolution and precipitation of gases in the metal liquid is also another key factor in the formation of gas shrinkage holes. In the die casting process, the metal liquid may be in contact with water or humid air, resulting in hydrogen in the water dissolved into the metal liquid. As the metal liquid cooling solidification, (hydrogen and aluminum alloy easy adhesion is particularly strong and difficult to decompose finished, and then involved in the casting) dissolved hydrogen will gradually precipitate and the formation of gas shrinkage holes.

Factors such as variations in wall thickness of the die casting, alloy composition, and casting process parameters can also have an effect on the formation of gas shrinkage holes. Excessive wall thickness may lead to slow internal cooling and solidification speed, so that the liquid metal in the contraction process can not get the pressurization pressure to make up the contraction. At the same time, different alloy compositions and casting process parameters will also affect the liquid metal fluidity and solidification speed, thus affecting the formation of gas shrinkage holes.

The formation mechanism of gas shrinkage holes in die casting involves a number of factors, including the solidification process of metal liquid, gas involvement, gas dissolution and precipitation, and casting process parameters. In-depth understanding of these mechanisms helps us to put forward effective improvement measures to reduce the generation of gas shrinkage holes and improve the quality and performance of die castings.

3. Improvement strategies and methods for gas shrinkage holes

Improvement of air shrinkage holes in die castings is a complex and critical process that involves the optimization of multiple processes and factors. The following are some of the main strategies and methods for improving air shrinkage:

Control of pouring speed and temperature: Reasonable pouring speed (based on the results of simulation software can be seen in the casting temperature changes, the distribution of gas content) Reasonable temperature can reduce the gas involved in the metal liquid, thus reducing the formation of gas shrinkage holes.

Optimization of cooling system: design a reasonable cooling system to ensure that all parts of the casting cooling rate is uniform to achieve the thermal balance of the mold, reduce shrinkage caused by uneven cooling.

Optimization of mold structure: Reasonable design of mold sprue, exhaust channel and cooling waterway, to ensure smooth flow of liquid metal, gas can be effectively discharged, as far as possible to make the casting of the internal gas content is reduced, increased to achieve qualified castings.

Use of high-quality mold materials: Selection of wear-resistant, high-temperature resistant, erosion-resistant, strength-resistant mold materials to improve the service life of the mold and the quality of the castings.

Adjustment of alloy composition: By adjusting the alloy composition, improve the fluidity and solidification characteristics of the metal liquid, reduce the generation of gas shrinkage holes.

Adoption of refining technology: Adoption of refining technology removes impurities and gases from the metal liquid and improves the purity of the metal liquid.

Vacuum die casting technology:

1. die-casting processing in a vacuum environment, effectively reduce the gas content in the metal liquid, mainly the mold cavity in the start of high-speed gas will be pumped out of the gas, so as to reduce the formation of gas shrinkage holes.

2. Now integrated die-casting molding usually use high vacuum technology, in the punch closed pressure chamber mouth began to pump the air inside the pressure chamber, the mold cavity using sealing strips to close the mold cavity; cavity in the top bar using glue to close, thus reducing the formation of gas shrinkage holes.

Pressurized die-casting technology: in the die-casting process to apply a certain pressure, change the pressure, pressure, pressure speed, pressure when the mold temperature, pressure time, so that the metal liquid more dense filling mold, reduce shrinkage and porosity.

Regularly check the state of the equipment: to ensure that the die-casting equipment is in good condition, to take daily, weekly and monthly maintenance, usually on the equipment spot check scheduling, to avoid quality problems caused by equipment failure.

Strictly control the quality of raw materials: choose high quality raw materials and manufacturing process to ensure the stability and consistency of the metal fluid.

Enhance staff training and operation standardization: Improve staff’s operation skills and quality awareness to ensure that each production process is in line with the norms.

4. Die casting process parameters on the impact of gas shrinkage holes

1. Pouring speed and temperature: Experimental results show that appropriate pouring speed and temperature can effectively reduce the formation of gas shrinkage holes. Too high pouring speed and temperature may lead to the gas in the metal liquid can not be fully discharged, thus increasing the number of gas shrinkage holes.

2. Press and shoot speed: Press and shoot speed will lead to changes in casting gas shrinkage holes, changes in mold erosion, changes in mold sticking.

3. Pressure: Increasing the pressure in the die casting process can make the liquid metal fill the mold more closely and reduce the formation of shrinkage and porosity. But too high pressure may also lead to mold damage or casting deformation.

4. Time: The length of the cycle time will affect the mold temperature changes, resulting in porosity and shrinkage instability.

Influence of mold design on gas shrinkage holes

1. Sprue design: Reasonable sprue design can ensure the uniform flow of liquid metal and mold erosion, reduce the gas involved and the formation of shrinkage holes.

2. Exhaust groove design: Effective exhaust holes can discharge the gas in the mold cavity, thus reducing the generation of gas shrinkage holes.

3. Cooling water circuit design: reasonable cooling water circuit design can ensure that the casting cooling rate of all parts of the uniform, reduce the uneven cooling caused by shrinkage.

Influence of alloy composition on gas-shrinkage porosity

Adjusting the alloy composition can change the fluidity and solidification characteristics of the metal liquid, thus affecting the formation of blowholes. It has been found that changes in certain alloying elements or ratios can significantly reduce the number of blowholes and casting size.

The formation of air-shrinkage holes in die castings can be effectively improved by means of optimizing die casting process parameters, improving die design and adjusting alloy composition. The experimental results provide useful reference and guidance for the subsequent production practice. However, due to the complexity and variability of the die casting process, further in-depth study of the formation mechanism of gas shrinkage holes and improvement methods are still needed to continuously improve the quality and performance of die castings.

5. Conclusion

In this study on improving air shrinkage holes in die castings, we conclude that several critical factors—including die casting process technology, mold design, alloy composition, and production operations—play a significant role in the formation of air shrinkage holes. By optimizing these elements, we can effectively reduce the occurrence of such defects, thereby enhancing the quality and performance of die cast products.

For the die casting process, controlling the pouring rate and temperature, adjusting the pressure, and optimizing the cooling system are key strategies for minimizing air shrinkage holes. Similarly, mold design has a profound impact; proper sprue design, air vent placement, and cooling water layout can significantly decrease both the number and size of these holes.

Adjusting the alloy composition is another crucial approach. By fine-tuning the alloying elements, the fluidity and solidification characteristics of the molten metal can be improved, reducing the likelihood of air shrinkage holes.

As a leading die casting manufacturer, Kingship has implemented these strategies to improve the quality of our die castings. However, while we’ve achieved significant progress, there are still areas that require further investigation:

Understanding the Formation Mechanism: The underlying physical and chemical mechanisms behind the formation of air shrinkage holes need more in-depth exploration. A deeper understanding will provide a stronger theoretical foundation for developing more effective improvement measures.

Optimizing Existing Measures: Although effective, the current improvement measures may face limitations in practical applications. Kingship is committed to optimizing these measures and exploring innovative solutions to better address the challenge of air shrinkage holes.

Integration of Intelligent and Automated Technologies: The advancement of technology opens new possibilities for die casting production. Kingship is exploring the integration of artificial intelligence and machine learning to enhance process monitoring and quality control. The goal is to achieve automated detection and early warning systems for air shrinkage holes, ultimately boosting production efficiency and product quality.

Focus on Green Production and Sustainability: While addressing air shrinkage holes, Kingship also prioritizes environmentally friendly practices. By adopting sustainable materials, energy-efficient processes, and a circular economy approach, we aim to minimize the environmental impact of die casting production, contributing to both economic and social benefits.

In conclusion, the ongoing research and development in improving air shrinkage holes in die casting hold significant potential and practical importance. Kingship remains dedicated to pioneering solutions that drive the sustainable development of the die casting industry.