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In addition to requiring sufficient strength and toughness, the surface performance of hardware mold parts is crucial to the working performance and service life of precision mold parts during operation. The improvement of these performances is very limited and uneconomical to rely solely on the improvement and enhancement of the base material. However, through surface treatment technology, it is often possible to achieve twice the result with half the effort. This is precisely the reason why surface treatment technology has developed rapidly. Mold polishing technology is an important component of mold surface engineering and a significant post-treatment process in the mold manufacturing process. Due to the fact that there are still certain problems in domestic polishing technology and materials, a large part of injection molds for point-and-shoot camera lenses, CDS, VCDS and tools with high transparency requirements still rely on imports.

The material of mirror mold is not merely a matter of chemical composition. More importantly, during the smelting process, a series of advanced techniques such as vacuum degassing, argon-protected ingot casting, vertical continuous casting and continuous rolling, and flexible forging are required to be adopted, which makes the mirror mold steel have a series of advantages such as few internal defects, fine impurity particle size, high dispersion degree, fine metal grain size, and good uniformity, so as to meet the requirements of polished mirror mold steel. The surface treatment technology of mold parts is a systematic engineering that changes the morphology, chemical composition, microstructure and stress state of the surface of precision mold parts through surface coating, surface modification or composite treatment techniques to obtain the required surface performance. Nitriding processes include gas nitriding, ion nitriding, liquid nitriding, etc. Within each nitriding method, there are several nitriding techniques that can meet the requirements of different steel grades and different workpieces. In terms of surface treatment methods, they can be further classified into: chemical methods, physical methods, physicochemical methods and mechanical methods.

It is worth noting that the surface polishing of molds is not only influenced by polishing equipment and process technology, but also by the mirror finish of the mold material. This point has not received sufficient attention, that is to say, the polishing itself is restricted by the mold material. Although new treatment technologies aimed at improving the surface performance of precision mold parts are constantly emerging, the ones mainly applied in the manufacturing of precision mold parts are nitriding, carburizing and hardening film deposition. Due to the fact that nitriding technology can form a surface with excellent performance, and the nitriding process has good coordination with the quenching process of precision mold parts steel, as well as the low nitriding temperature and no need for intense cooling after nitriding, the deformation of precision mold parts is extremely small. Therefore, the surface strengthening of precision mold parts is the earliest to adopt nitriding technology and also the most widely used.