Analysis of Heat Treatment Technology for Casting Die

It refers to a metal thermal processing process in which materials are heated, insulated and cooled in solid state to obtain expected structures and properties. This technology plays an extremely important role in the flat plate platform industry. In order to make metal workpieces have the required mechanical, physical and chemical properties, in addition to reasonable selection of materials and various forming processes, heat treatment process is often essential. First, the quick screening editor introduces:

1、 Surface treatment technology of mould

In addition to the reasonable matching of the matrix with high strength and toughness, the surface performance of the die is critical to the working performance and service life of the die. These surface properties refer to wear resistance, corrosion resistance, friction coefficient, fatigue performance, etc. It is very limited and uneconomical to rely solely on the improvement and enhancement of matrix materials to improve these properties. However, through surface treatment technology, we can often get twice the result with half the effort, which is the reason why surface treatment technology has been developed rapidly.

The surface treatment technology of mould is a system engineering that changes the shape, chemical composition, structure and stress state of mould surface through surface coating, surface modification or composite treatment technology to obtain the required surface properties. From the way of surface treatment, it can be divided into chemical method, physical method, physical chemical method and mechanical method. Although new treatment technologies aiming at improving the surface performance of dies are emerging, the main nitriding, carburizing and hardening film deposition are widely used in die manufacturing.

Nitriding process includes gas nitriding, ion nitriding, liquid nitriding, etc In each nitriding method, there are several nitriding technologies, which can meet the requirements of different steel grades and different workpieces. As the nitriding technology can form a surface with excellent performance, and the nitriding process is well coordinated with the quenching process of the die steel, at the same time, the low nitriding temperature does not require intense cooling after nitriding, and the deformation of the die is very small, so the nitriding technology was used earlier for the surface strengthening of the die, which is also the most widely used.

The purpose of die carburizing is mainly to improve the overall strength and toughness of the die, that is, the working surface of the die has high strength and wear resistance. The technical idea introduced here is to replace the higher level material with a lower level material, that is, by carburizing and quenching, so as to reduce the manufacturing cost.

At present, CVD and PVD are mature hardening film deposition technologies. In order to increase the bonding strength of the film workpiece surface, a variety of enhanced CVD, ‘PVI) technologies have been developed. Hardened film deposition technology was first applied to tools (tools, cutting tools, measuring tools, etc.) with excellent results. Many tools have adopted the coating of hardened film as the standard process. The mould has been coated with hardened film since the 1980s. Under the current technical conditions, the cost of the hardening film deposition technology (mainly equipment) is relatively 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 hardening film will be greatly reduced. If more molds adopt this technology, the overall level of mold manufacturing in China can be improved.

2、 Vacuum heat treatment technology of mould

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 oxidation and non decarburization, vacuum degassing or degassing, eliminating hydrogen embrittlement, so as to improve the plasticity, toughness and fatigue strength of materials (parts). Slow vacuum heating, small temperature difference between the inside and outside of the parts and other factors determine the small deformation of the parts caused by the vacuum heat treatment process.

According to different cooling media, vacuum quenching can be divided into vacuum oil cooling quenching, vacuum gas cooling quenching, vacuum water cooling quenching and vacuum nitrate isothermal quenching. Vacuum oil cooling quenching, vacuum air cooling quenching and vacuum tempering are mainly used in the vacuum heat treatment of moulds. In order to maintain the excellent characteristics of vacuum heating of workpieces (such as moulds), the selection and formulation of coolant and cooling process are very important. The quenching process of moulds mainly adopts oil cooling and air cooling.

For the die working face that will not be machined after heat treatment, vacuum tempering shall be adopted as far as possible after quenching, especially for the workpiece (die) that is vacuum quenched, which can improve the mechanical properties related to surface quality. Such as fatigue performance, surface brightness, corrosivity, etc.

The successful development and application of computer simulation technology of heat treatment process (including tissue simulation and performance prediction technology) make it possible to intelligentize heat treatment of dies. Due to the characteristics of small batch (even single piece) and multiple varieties of mold production, as well as the high requirements for heat treatment performance and the fact that no waste products are allowed, the intelligent processing of molds has become necessary. The intelligent heat treatment of the mould includes: defining the structure, material and heat treatment performance requirements of the mould; computer simulation of the temperature field and stress field distribution during the heating process of the mould; Computer simulation of temperature field, phase transformation process and stress field distribution during mold cooling; Simulation of heating and cooling process; Formulation of quenching process; Automatic control technology of heat treatment equipment. Industrial developed countries abroad,

For example, the United States, Japan, etc. have carried out technology research and development in this field in the vacuum high-pressure gas quenching, mainly targeting the mold.

3、 Pre hardening technology of die materials

Heat treatment of molds during manufacturing is a process that has been used by most molds for a long time. Since the 1970s, the idea of pre hardening has been put forward internationally. However, due to the constraints of machine tool stiffness and cutting tools, the hardness of pre hardening cannot reach the hardness of molds, so the research and development of pre hardening technology has not been invested much. With the improvement of the performance of machining tools and cutting tools, the development speed of the pre hardening technology of mold materials has accelerated. By the 1980s, the proportion of the international industrial developed countries using the pre hardening module on plastic mold materials has reached 30% (more than 60% at present). In the middle and late 1990s, China began to use pre hardening modules (mainly imported products).

Pre hardening technology of die materials is mainly developed and implemented in die material manufacturers. By adjusting the chemical composition of steel and equipping corresponding heat treatment equipment, the pre hardening modules with stable quality can be produced in large quantities. In China, the pre hardening technology of die materials started late, and the scale is small. At present, it can not meet the requirements of domestic die manufacturing.

The use of pre hardening die materials can simplify the die manufacturing process, shorten the manufacturing cycle of the die, and improve the manufacturing accuracy of the die. It can be predicted that with the progress of processing technology, pre hardening die materials will be used for more die types.