In the work of the mold, in addition to the requirement that the substrate has a reasonable match of high enough strength and toughness, its surface properties are crucial to the working performance and service life of the mold. These surface properties refer to wear resistance performance, corrosion resistance, friction coefficient, fatigue performance, etc. The improvement of these properties, relying solely on the improvement and enhancement of the base material is very limited and uneconomical, and through the surface treatment technology, can often receive twice the result with half the effort, which is the reason for the rapid development of surface treatment technology.
Surface treatment technology of mold is a system engineering to change the morphology, chemical composition, organizational structure, and stress state of mold surface through the surface coating, surface modification, or composite treatment technology to obtain the required surface properties. From the way of surface treatment, it can be further divided into the chemical method, physical method, physical-chemical method, and mechanical method. Although new treatment techniques aimed at improving the surface properties of the mold are emerging, in-mold manufacturing, the application of more major nitriding, carburizing, and hardening film deposition.
The nitriding process has gas nitriding, ion nitriding and liquid nitriding, and other ways. In each nitriding method, there are several nitriding techniques, which can adapt to the requirements of different steel types and different workpieces. Because nitriding technology can form excellent performance surface, and the nitriding process has good coordination with the quenching process of die steel, at the same time, the nitriding temperature is low, after nitriding does not require intense cooling, the deformation of the mold is extremely small, therefore, the surface strengthening of the mold is the use of nitriding technology earlier, but also the most widely used.
The purpose of die carburizing is mainly to improve the overall toughness of the die, that is, the working surface of the die has high strength and wear resistance. The technical idea thus introduced is to use lower grade materials, i.e., by carburizing and quenching instead of higher grade materials, thus reducing manufacturing costs.
3. Hardening film deposition
Hardened film deposition technology, currently more mature in CVD and PVD, to increase the film layer and the workpiece surface bonding strength now developed a variety of enhanced CVD, PVD technology.
Hardened film deposition technology was first applied to tools (tools, sharpening tools, gauges, etc.) with excellent results, and a variety of tools have been coated with hardened film as a standard process.
Molds have been using the hardened film coating technology since the 1980s. Under the current technical conditions, the cost of hardening film deposition technology (mainly equipment) is high and still only applied on some precision and long-life molds, if the way of establishing a heat treatment center is adopted, the cost of coating hardening film will be greatly reduced. More molds if the use of this technology, can improve the overall level of China's mold manufacturing.
4. Mould material pre-hardening technology
Mould in the manufacturing process, heat treatment is the vast majority of molds for a long time along a process. Since the 1970s, the international pre-hardening idea, but due to the rigidity of the processing machine tool and cutting tool constraints, the hardness of pre-hardening can not reach the hardness of the mold use, so the pre-hardening technology is not much investment in research and development.
With the improvement of processing machine tools and cutting tool performance, the development of pre-hardening technology for mold materials has accelerated, and by the 1980s, the proportion of pre-hardening modules used in plastic mold materials in internationally industrially developed countries has reached 30% (currently above 60%), and China began to use pre-hardening modules in the mid to late 1990s (mainly with foreign imported products).
Pre-hardening technology for mold materials is mainly developed and implemented by mold material manufacturers. By adjusting the chemical composition of the steel and equipping the corresponding heat treatment equipment, pre-hardening modules of stable quality can be produced in large quantities. China's pre-hardening technology for mold materials started late and on a small scale, and is not yet able to meet the requirements of domestic mold manufacturing.
The use of pre-hardening mold materials can simplify the mold manufacturing process, shorten the manufacturing cycle of the mold and improve the manufacturing accuracy of the mold. It can be foreseen that with the progress of processing technology, pre-hardened mold materials will be used for more mold types.