Die-casting molds are a method of casting liquid die forging, which is a major category in molds. The die-casting plastic mold is required to have high heat fatigue resistance, thermal conductivity, wear resistance, corrosion resistance, impact toughness, red hardness, good mold release, etc. The surface treatment technology requirements for die-casting molds are relatively high.In recent years, various new technologies for surface treatment of die-casting molds have been emerging, but in general they can be divided into the following three categories:
(1) Improved technology of traditional heat treatment process;
(2) Surface modification technology, including surface thermal expansion treatment, surface phase transformation strengthening, electric spark strengthening technology, etc .;
(3) Coating technology, including chemical plating.
The traditional heat treatment process of die-casting molds is quenching-tempering, and later surface treatment technology was developed. Due to the variety of materials that can be used as die-casting molds, the same surface treatment technology and process applied to different materials will produce different effects. Shikov recently proposed a substrate pretreatment technology for mold substrate and surface treatment technology. Based on the traditional process, suitable processing techniques for different mold materials were proposed to improve mold performance and increase mold life. Another development direction of heat treatment technology improvement is to combine the traditional heat treatment process with the advanced surface treatment process to increase the service life of die-casting molds. If the method of chemical heat treatment is carbonitriding, combined with the conventional quenching and tempering process, NQN (i.e., carbonitriding-quenching-carbonitriding) compound strengthening, not only get a higher surface hardness, but also effective hardening Increasing the depth of the layer, reasonable distribution of the hardness gradient of the infiltrated layer, improving the tempering stability and corrosion resistance, so that the die-casting mold has a good core performance, while the surface quality and performance are greatly improved.
This type includes carburizing, nitriding, boronizing, carbonitriding, sulfur carbonitriding, etc.
The carburizing process is applied to cold, hot work and plastic mold surface strengthening, which can increase the life of the mold. Such as 3Cr2W8V steel die-casting mold, carburized first, then quenched at 1140 ~ 1150 ℃, tempered twice at 550 ℃, the surface hardness can reach HRC56 ~ 61, so the die life of die-cast nonferrous metals and their alloys is increased by 1.8 ~ 3.0 times . When carburizing, the main process methods are solid powder carburizing, gas carburizing, as well as vacuum carburizing, ion carburizing and carbonitriding formed by adding nitrogen in carburizing atmosphere. Among them, vacuum carburization and ion carburization are technologies developed in the past 20 years.This technology has the characteristics of fast carburization speed, uniform carburization layer, gentle carbon concentration gradient and small workpiece deformation.It will be on the mold surface, especially precision molds. Surface treatment plays an increasingly important role.
289Views
