Mold heat treatment technology

source：宏森    data：2024-05-10

Mold heat treatment is an important process to ensure the performance of molds, which has a direct impact on the manufacturing accuracy, strength, service life, and manufacturing cost of molds. Since the 1980s, the rapidly developing fields of international mold heat treatment technology have been vacuum heat treatment technology, surface strengthening technology of molds, and pre hardening technology of mold materials.

Vacuum heat treatment technology for molds

Vacuum heat treatment technology is a new type of heat treatment technology that has 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, and improving the plasticity, toughness, and fatigue strength of materials (parts). The slow vacuum heating and small temperature difference between the inside and outside of the parts determine the small deformation of the parts caused by the vacuum heat treatment process.

The main applications in vacuum heat treatment of molds are vacuum oil quenching, vacuum gas quenching, and vacuum tempering. To maintain the excellent characteristics of vacuum heating of workpieces (such as molds), the selection and formulation of coolant and cooling process are very important. The quenching process of molds mainly uses oil cooling and air cooling. For mold working surfaces that are no longer mechanically processed after heat treatment, vacuum tempering should be used as much as possible after quenching, especially for workpieces (molds) that are vacuum quenched. This can improve mechanical properties related to surface quality, such as fatigue performance, surface brightness, corrosion resistance, etc.

The successful development and application of computer simulation technology for heat treatment processes have made intelligent heat treatment of molds possible. Due to the small batch (even single piece) and multi variety characteristics of mold production, as well as the high requirements for heat treatment performance and the prohibition of waste, intelligent heat treatment of molds has become necessary. Developed industrial countries abroad, such as the United States and Japan, have also developed rapidly in vacuum high-pressure gas quenching, mainly targeting molds.

Surface treatment technology of molds

In addition to requiring a reasonable combination of high strength and toughness of the matrix, the surface performance of the mold is crucial for its working performance and service life during operation. The surface treatment technology of molds is a systematic engineering process that changes the morphology, chemical composition, microstructure, and stress state of the mold surface through surface coating, surface modification, or composite treatment techniques to obtain the required surface properties. At present, the main applications in mold manufacturing are nitriding, carburizing, and deposition of hardened films.

Due to the ability of nitriding technology to form surfaces with excellent performance, and the good coordination between nitriding technology and quenching process of mold steel, as well as the low nitriding temperature, there is no need for intense cooling after nitriding, and the deformation of the mold is extremely small, nitriding technology is the earliest and most widely used method for surface strengthening of molds.

Mold carburization 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 deposition technologies for hardened films are CVD and PVD. The mold has been using coating hardening film technology since the 1980s {BANNED}. Under the current technological conditions, the cost of hardening film deposition technology (mainly equipment) is relatively high, and it is still only applied to some precision and long-life molds. If a heat treatment center is established, the cost of coating hardening film will be greatly reduced. If more molds adopt this technology, the overall level of mold manufacturing in China can be improved.

Pre hardening technology for mold materials

Since the 1970s, the idea of pre hardening has been proposed internationally. However, due to the constraints of machine tool stiffness and cutting tools, the hardness of pre hardening cannot reach the hardness required for mold use, so there is not much investment in the research and development of pre hardening technology. With the improvement of machining machine tools and cutting tool performance, the development speed of pre hardening technology for mold materials has accelerated. By the 1980s, the proportion of pre hardening modules used in plastic mold materials in industrialized countries internationally had reached 30% (currently over 60%).

In terms of pre hardening technology for mold materials, China started late and has a small scale, which currently cannot meet the requirements of domestic mold manufacturing. Using pre hardened mold materials can simplify the mold manufacturing process, shorten the mold manufacturing cycle, and improve the mold manufacturing accuracy. It can be foreseen that with the advancement of processing technology, pre hardened mold materials will be used for more types of molds