The surface strengthening technology in the mold manufacturing refers to the professional strengthening technology that allows the mold working parts to obtain the required surface or comprehensive performance after being pretreated and processed by single or composite surface technology. The advantages of the technology, such as functionality, environmental protection and efficiency enhancement, play a particularly important role in mold manufacturing cost, mold quality and mold life. In production, considering the characteristics of the technology, the working conditions of the mold and the economics of production, and selecting the best matching point of all factors can significantly improve the life and quality of the mold and obtain outstanding economic benefits.
1. Carburized surface chemical heat treatment
The carburizing process is a more commonly used (more than 80%) mold surface strengthening technology, which is mainly aimed at the surface strengthening of plastic mold cavities. After carburizing, the working parts of the mold can achieve the effect of “outer hardening and inner toughness”, that is, the surface of the working parts has improved hardness, wear resistance, fatigue strength and other properties, while the core still maintains the original plastic toughness and strength , Meet the requirements for the performance of mold working parts. It has fast infiltration speed, deep infiltration layer, low cost, and has a perfect bonding performance between the infiltration layer and the base part, and realizes a smooth transition between the bonding layers. However, the operating temperature is relatively high (900 ~ 950 ℃), especially the ion carburizing temperature can reach 1100 ℃, and the corresponding heat treatment is required after carburizing, which leads to an increased possibility of mold deformation, so high-precision plastic molds are not This technique is recommended.
The gas carburizing temperature is generally 920 ~ 950 ℃, comprehensive evaluation by Wang Rongbin test: the most reasonable carbon content on the surface of the carburized layer is w (C) 0.85% ~ 0.95%, the carbon mass gradient from the outside to the inside should be even and smooth In the quenching structure, coarse strip martensite, excessive residual Olympics, network carbide and black troostite are not allowed. Too high a carbon mass fraction is likely to cause malignant tissues such as mesh carbides in the mold part structure, which affects the quality and life of the mold. In the subsequent processing, stress concentration and cracks are likely to occur.
Ion carburizing temperature is generally 900 ~ 960 ℃, compared with gas carburizing, ion carburizing has the advantages of high efficiency, small deformation, little pollution, and can handle any shape of the surface of mold parts, etc. It is more suitable for plastic mold and stamping mold surface Strengthen the application in processing.
2. Thermal spraying technology on flame surface
Thermal spraying technology is a very rapidly developing new technology for surface strengthening. It uses a heat source (arc, ion arc, flame, etc.) to heat the sprayed material to a molten or semi-melted state and atomize it, spraying at a certain speed. To the surface of the pre-treated substrate, the physical and chemical changes are combined with the substrate. This combination layer can improve the wear resistance, corrosion resistance and heat resistance of the mold parts, and the operation is simple and the cost is low.
The life of the die is increased by 3 to 10 times. At the same time, the application of this technology has also made great progress in mold repair. For example, Zhang Xianglin of the State Key Laboratory of Material Forming and Mold Technology of Huazhong University of Science and Technology used supersonic flame spraying (HVOF) technology to prepare nanostructured steel on the surface of Cr12MoV mold steel. For WC12Co cermet coating, the measured average shear strength of the coating is 150.8MPa, the bonding strength of the coating is greater than 80 MPa, and the coating hardness is higher than 1000HV. After repairing the cold extrusion die with HVOF technology, it can fully meet the use requirements of the enterprise.
3. Composite surface plating technology
Electroplating technology is a technology that uses electrochemical methods to deposit metal or metallize the surface of the substrate. Electroplating hard chromium and hard nickel is the traditional technology of plastic mold surface treatment in China. The technology is carried out at near room temperature, the mold performance is almost not affected, and there will be no serious deformation,
At the same time, the surface roughness of the plating layer is low, and the hardness is increased to 800HV. However, there are still many problems, such as: the corrosion resistance is not high, and the grooves and deep holes cannot be processed, which limits its application in mold strengthening. At present, it can only be used to strengthen the wear resistance of ordinary plastic molds, not suitable for Plastic molds with complex shapes and high corrosion resistance.
4. PVD, CVD, PCVD surface coating technology
Coating technology, which is vapor deposition technology, is to deposit stable compounds with special properties on the surface of the mold working parts to form a super-hard coating, so that the mold working parts have excellent performance. The stable compounds with high frequency of use in industry mainly include TiC, TiN, SiN and so on.
5. High-energy beam strengthening technology
The high-energy beam strengthening technology has comprehensive advantages such as non-contact, precise controllability, wide material adaptability, strong flexibility, excellent quality, resource saving and environmental friendliness. It can be used for high-volume and high-efficiency automated production, but also suitable for multiple varieties and small batches Processing, even the customization of personalized products, is an indispensable important technology in the mold manufacturing industry. Among them, the ion implantation technology is widely used in the fields of cold work molds, hot work molds and plastic molds with its almost perfect strengthening effect, and its average life can generally be increased by 2 to 10 times. It has significant application value.
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