Pressure casting (referred to as die casting) has the process characteristics of high production efficiency, short production process, high casting finish and strength, less processing allowance, and saving metal materials.
In recent years, the die casting industry has developed rapidly, and the total output has increased significantly. Molds, die casting machines and die casting materials are the three major elements of die casting production. Only high-quality molds can stably and efficiently produce high-quality castings.
The working environment of the die casting mold is very harsh: the cavity is directly in contact with high-temperature, high-pressure, and high-speed molten metal during the die casting production process, and is directly washed by the molten metal, which is prone to wear, high-temperature oxidation and various corrosion. High-efficiency production causes the mold temperature to rise and fall sharply periodically, and thermal fatigue cracks are prone to occur on the working surface. When the metal is forced to deform, it rubs against the surface of the cavity, which is easy to wear the mold and reduce its hardness.
The mold cost is high, the production cycle is long, and it is difficult to repair. It is also particularly important in terms of service life. Therefore, the study of factors affecting mold performance and service life is conducive to improving the quality of castings and reducing economic losses caused by premature mold scrapping.
Generally speaking, the factors that affect the performance and service life of die-casting molds include mold materials, mold design and manufacturing, surface treatment technology and specific mold usage.
Mold material
The performance and service life of die-casting molds are closely related to the material of the mold. High quality die-casting mold manufacturing materials generally have the following characteristics. Good machinability and forging performance. High wear resistance and corrosion resistance. High strength, high red hardness, high temperature oxidation resistance, impact toughness and tempering stability at high temperature. Good thermal conductivity and fatigue resistance. Small thermal expansion coefficient. Small heat treatment deformation rate and good hardenability.
In addition to the temperature and type of casting metal, the selection of die-casting molds should also consider the impact and wear of the various components of the die-casting mold by the casting metal. The higher the temperature, the higher the thermal fatigue performance and high temperature performance the material should have. Parts with more severe wear should have higher hardness.
The increasingly harsh working conditions of die-casting molds have continuously increased the requirements for the metallurgical quality, performance, and life of mold materials, especially the purity and isotropy of materials. Some high-alloy, high-quality, and optimized mold materials continue to appear, which in turn promotes the development of the die-casting industry.
Mold design and manufacturing
Reasonable mold design is an important prerequisite for extending the service life of die-casting molds. Reasonable wall thickness and cooling water channel design can ensure the strength and thermal balance of the mold. In mold design, special attention should be paid to the parts where stress concentration and large abrasion occur during work.
The accuracy of each part selection should be reasonable. If the gap is too large, the heat conduction is poor, resulting in thermal fatigue damage. If the gap is too small, extrusion pressure and tensile stress will be generated. Internal stress is easy to generate during the mold manufacturing process, and internal stress has a great impact on the service life of the mold.
Therefore, internal stress should be avoided as much as possible and eliminated in time during the manufacturing and processing of the mold. For example, timely stress relief and tempering after rough machining, and electric pulses can be used instead of electric sparks to reduce the surface tension of the mold.
Mold surface treatment technology
Through rigorous and reasonable technical treatment of the surface of the die-casting mold, its performance and life can be greatly improved. The surface treatment technology of the die-casting mold can be divided into three categories. First, traditional heat treatment process improvement technology. The second， surface modification technology, such as surface laser treatment technology. The third, coating technology.
- Traditional heat treatment process improvement technology. The traditional die-casting mold heat treatment process is quenching-tempering. The improvement technology of the traditional heat treatment process is to combine quenching-tempering with advanced surface treatment technology.
- Surface modification technology. Surface modification technology refers to the use of physical or chemical methods to change the surface properties of the mold. Generally speaking, there are two types. Surface heat, diffusion, and infiltration technology. The second is surface laser treatment technology.
- Coating technology. Coating technology is to coat the surface with a coating to give the mold a layer of protection, such as polytetrafluoroethylene composite plating. The main purpose is to enhance the mold’s wear resistance, corrosion resistance, and resistance to cold and heat.
Mold Use
Choosing a reasonable die-casting process and maintenance is crucial to the service life of the mold. Most mold damage is caused by improper use and lack of scientific maintenance. First of all, special attention should be paid to the temperature control of the mold.
The mold should be preheated before production, and the appropriate temperature range should be maintained during production to prevent surface cracks or even cracks caused by excessive temperature gradients between the inner and outer layers of the cavity.
Secondly, the selection of high-quality die-casting release agents with moderate thickness and uniform coating of the mold surface plays an important role in protecting the mold material.
Finally, in order to reduce the accumulation of thermal stress and avoid cracking of the die-casting mold, it is necessary to regularly use tempering and other technologies to eliminate thermal stress.
Conclusion
Die-casting mold materials, mold design and manufacturing, mold surface treatment technology and mold use have a comprehensive impact on the performance and service life of the mold. Combining these factors and taking effective measures can effectively improve the performance of the die-casting mold and extend the service life of the die-casting mold.
