Current status and trend of mold heat treatment technology

Mold heat treatment is an important process to ensure the performance of the mold, which has a direct impact on the manufacturing precision of the mold, the strength of the mold, the working life of the mold, and the manufacturing cost of the mold. Since the 1980s, the field of rapid development of international mold heat treatment technology has been vacuum heat treatment technology, surface strengthening technology of molds and pre-hardening technology of mold materials.

Vacuum heat treatment technology for mold

Vacuum heat treatment technology is a new type of heat treatment technology developed in recent years. Its characteristics are urgently needed in mold manufacturing, such as preventing heating oxidation and non-decarburization, vacuum degassing or degassing, eliminating Hydrogen embrittlement improves the plasticity, toughness and fatigue strength of materials (parts). Factors such as slow vacuum heating and small temperature difference between the inside and outside of the part determine the small deformation of the parts caused by the vacuum heat treatment process.

The main application of mold vacuum heat treatment is vacuum oil quenching, vacuum gas quenching and vacuum tempering. In order to maintain the excellent characteristics of vacuum heating of workpieces (such as molds), it is very important to select and formulate coolants and cooling processes. The mold quenching process mainly uses oil cooling and air cooling. For the working face of the mold which is no longer machined after heat treatment, vacuum tempering is used as much as possible after quenching, especially vacuum hardened workpiece (mold), which can improve the mechanical properties related to surface quality, such as fatigue performance, surface brightness, Corrosion resistance, etc.

The successful development and application of computer simulation technology in the heat treatment process makes the intelligent heat treatment of the mold possible. Due to the small batch (even single piece) and multi-variety characteristics of the mold production, as well as the high requirements for heat treatment performance and the fact that waste products are not allowed, the intelligent heat treatment of the mold becomes a necessity. Foreign industrialized countries, such as the United States, Japan, etc., in the vacuum high-pressure gas quenching, the development is also very fast, mainly aimed at the mold.

Mold surface treatment technology

In addition to the reasonable cooperation of the mold with sufficient strength and toughness, the surface properties of the mold are crucial to the working performance and service life of the mold. The surface treatment technology of the mold is to systematically change the morphology, chemical composition, microstructure and stress state of the mold surface by surface coating, surface modification or composite treatment technology to obtain the desired surface properties. At present, most of the applications in mold manufacturing are nitriding, carburizing and hardening film deposition.

Because the nitriding technology can form a surface with excellent performance, and the nitriding process has good coordination with the quenching process of the die steel, and the nitriding temperature is low, there is no need for intense cooling after nitriding, and the deformation of the mold is extremely small, so the mold is Surface strengthening is the earliest and most widely used nitriding technique.

Mold carburizing is to improve the overall strength and toughness of the mold, that is, the working surface of the mold has high strength and wear resistance. The most mature sclerosing film deposition technology is CVD and PVD. Molds have been coated with hardened film technology since the 1980s. Under the current technical conditions, the cost of hardened film deposition technology (mainly equipment) is still high, and it is still only applied to some precision and long-life molds. If the method of establishing a heat treatment center is adopted, the cost of coating the cured film will be greatly reduced. If more molds adopt this technology, they can improve the overall level of mold manufacturing in China.

Pre-hardening technology for mold materials

Since the 1970s, the idea of ​​pre-hardening has been proposed internationally. However, due to the rigidity of the machine tool and the constraints of the cutting tool, the hardness of the pre-hardening cannot reach the hardness of the mold, so the research and development of the pre-hardening technology is not large. With the improvement of the performance of machine tools and cutting tools, the development of pre-hardening technology for mold materials has accelerated. By the 1980s, the proportion of pre-hardened modules used in plastic molds in industrialized countries in the world has reached 30% (currently More than 60%).

In China, the pre-hardening technology of mold materials started late and has a small scale. At present, it cannot meet the requirements of domestic mold manufacturing. The use of pre-hardened mold materials can simplify the mold manufacturing process, shorten the manufacturing cycle of the mold, and improve the manufacturing precision of the mold. It is foreseeable that as processing technology advances, pre-hardened mold materials will be used for more mold types.