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. These surface properties are: abrasion resistance, corrosion resistance, friction coefficient, fatigue properties, and the like. These performance improvements, which rely solely on the improvement and improvement of the matrix material, are very limited and uneconomical, and surface treatment techniques can often achieve twice the result with half the effort, which is why surface treatment technology has developed rapidly.
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. From the way of surface treatment, it can be divided into: chemical methods, physical methods, physical and chemical methods, and mechanical methods. Although new treatment technologies are being developed to improve the surface properties of molds, most of the applications in mold manufacturing are nitriding, carburizing and hardening film deposition.
The nitriding process has the methods of gas nitriding, ion nitriding, liquid nitriding, etc. In each nitriding mode, there are several kinds of nitriding techniques, which can adapt to the requirements of different workpieces of different steel types. 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.
The purpose of mold carburizing is mainly to improve the overall toughness of the mold, that is, the working surface of the mold has high strength and wear resistance, and the technical idea introduced is to use a lower grade material, that is, by carburizing and quenching. Instead of higher grade materials, it reduces manufacturing costs.
The most mature sclerosing film deposition technology is CVD and PVD. In order to increase the bonding strength of the surface of the film workpiece, various enhanced CVD and PVD technologies have been developed. The hardened film deposition technology was first applied to tools (tools, cutting tools, measuring tools, etc.), and the results were excellent. A variety of tools have been used as a standard process for coating hardened films. 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.
