Common problems and solutions of die casting mold?

Die-casting die is a method of casting liquid die forging and a process completed on a special die-casting die forging machine. Its basic technological process is: casting molten metal at low speed or high speed and filling it into the mold cavity, and the mold has a movable cavity surface. It is forged under pressure with the cooling process of molten metal, which not only eliminates the shrinkage and porosity defects of the blank, but also makes the internal structure of the blank reach the forged broken grains. The comprehensive mechanical properties of the blank have been significantly improved.

Die-casting die is a big kind of die. With the rapid development of automobile and motorcycle industries in China, the die casting industry has ushered in a new development period. At the same time, it also puts forward higher requirements for the comprehensive mechanical properties and service life of die-casting dies. It is still difficult to meet the growing demand for performance only by relying on the application of new mold materials. Various surface treatment technologies must be applied to the surface treatment of die-casting dies in order to achieve the importance of high efficiency, high precision and long life of die-casting dies. Among all kinds of dies, the working conditions of die-casting dies are harsh. Pressure casting is a die casting in which molten metal fills the cavity at high pressure and high speed and contacts with molten iron repeatedly during the working process. Therefore, the die-casting die is required to have high thermal fatigue resistance, thermal conductivity, wear resistance, corrosion resistance, impact toughness, red hardness and good demoulding performance.

Therefore, the technical requirements for surface treatment of die-casting dies are higher. In recent years, various new technologies for surface treatment of die-casting dies have emerged, but generally speaking, they can be divided into the following three categories:

(1) Improvement technology of traditional heat treatment process;

(2) Surface modification technology, including surface thermal diffusion treatment, surface phase transformation strengthening and electric spark strengthening technology.

(3) Coating technology, including electroless plating.

The traditional heat treatment process of die casting mold is quenching-tempering, and then the surface treatment technology was developed. Because there are many kinds of materials that can be used as die-casting dies, the same surface treatment technology and technology will produce different effects when applied to different materials. Kefu Shi recently put forward the substrate pretreatment technology and surface treatment technology of mold substrate. On the basis of traditional technology, suitable processing technology is put forward for different die materials, so as to improve die performance and prolong die life. Another development direction of heat treatment technology improvement is to combine traditional heat treatment technology with advanced surface treatment technology to improve the service life of die casting mold. For example, if the chemical heat treatment method of carbonitriding is combined with conventional quenching and tempering processes to strengthen NQN (namely carbonitriding-quenching-carbonitriding), not only higher surface hardness is obtained, but also the depth of effective hardened layer is increased, the hardness gradient distribution of carburized layer is reasonable, and the tempering stability and corrosion resistance are improved, so that the die-casting mold can obtain good core performance and improve surface quality and corrosion resistance.

This kind includes carburizing, nitriding, boronizing, carbonitriding, sulfur carbonitriding and so on.

Carburizing process can be used for cold working, hot working and surface strengthening of plastic mould, which can improve the service life of mould. For example, the die-casting die made of 3Cr2W8V steel is carburized first, then quenched at 1 40 ~150℃ and tempered twice at 550℃, and the surface hardness can reach HRC 56 ~ 6 1, which prolongs the die life of die-casting nonferrous metals and their alloys by/kloc-0. When carburizing, the main technological methods are solid powder carburizing, gas carburizing, vacuum carburizing, ion carburizing and carbonitriding formed by adding nitrogen in carburizing atmosphere. Among them, vacuum carburizing and ion carburizing are technologies developed in recent 20 years, which have the characteristics of fast infiltration rate, uniform infiltration layer, gentle carbon concentration gradient and small workpiece deformation, and will play an increasingly important role in mold surface treatment, especially in precision mold surface treatment.

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