Time：2019-11-30| Author：Admin
Mold heat treatment is an important process to ensure mold performance. It has a direct impact on the following properties of the mold. Mold manufacturing accuracy: uneven and incomplete structural transformation and excessive residual stress caused by heat treatment cause the mold to deform during the processing, assembly and use of the mold after heat treatment, thereby reducing the accuracy of the mold and even scrapping it.
Strength of the mold: The heat treatment process is not properly formulated, the heat treatment operation is not standardized, or the heat treatment equipment is in an incomplete state, which causes the strength (hardness) of the processed mold to meet the design requirements.
Working life of the mold: The irrational microstructure and excessive grain size caused by heat treatment, etc., lead to the decline of the main properties such as the toughness of the mold, cold and hot fatigue performance, and abrasion resistance, which affect the working life of the mold.
Mold manufacturing cost: As an intermediate link or final process in the mold manufacturing process, cracks, deformation distortion and performance degradation caused by heat treatment will cause the mold to be scrapped in most cases, and it can continue to be used even after repairing, which will increase man-hours. , Extend the delivery time and increase the manufacturing cost of the mold. It is the heat treatment technology and mold quality that are very closely related, which makes these two technologies promote each other and improve together in the process of modernization. Since the 1980s, the areas of rapid development of international mold heat treatment technology are vacuum heat treatment technology, mold surface strengthening technology and pre-hardening technology of mold materials. Vacuum heat treatment technology for molds Vacuum heat treatment technology is a new type of heat treatment technology developed in recent years. It has characteristics that are urgently needed in mold manufacturing, such as preventing heating oxidation and non-decarburization, and vacuum degassing. Or degassing, eliminating hydrogen embrittlement, thereby improving the plasticity, toughness and fatigue strength of materials (parts). The slow vacuum heating and small temperature difference between the inside and outside of the part determine the small deformation of the part caused by the vacuum heat treatment process. According to the cooling medium used, vacuum quenching can be divided into vacuum oil cooling quenching, vacuum air cooling quenching, vacuum water cooling quenching and vacuum nitrate isothermal quenching.
The main applications of mold vacuum heat treatment are vacuum oil-cooled quenching, vacuum air-cooled quenching and vacuum tempering. In order to maintain the excellent characteristics of vacuum heating of the workpiece (such as the mold), the selection and formulation of the coolant and cooling process are very important. The mold quenching process mainly uses oil cooling and air cooling. For the working surface of the mold that is no longer mechanically processed after heat treatment, vacuum tempering is used as much as possible after quenching, especially for the workpiece (mold) that is vacuum quenched, which can improve mechanical properties related to surface quality, such as fatigue performance, surface brightness, And corrosive and so on. The successful development and application of computer simulation technology (including organization simulation and performance prediction technology) of heat treatment process makes intelligent heat treatment of mold possible. Due to the small batch (or even a single piece) of the mold production, the characteristics of multiple varieties, and the high requirements for heat treatment performance and the fact that scraps are not allowed, the intelligent heat treatment of the mold becomes necessary.
The intelligent heat treatment of the mold includes: clarifying the structure, materials and heat treatment performance of the mold. The computer simulation of the temperature field and stress field distribution of the mold heating process, the computer simulation of the temperature field, phase change process, and stress field distribution of the mold cooling process. The automation control technology of heat treatment equipment for the development of simulation quenching process. Developed foreign industrial countries, such as the United States and Japan, have carried out technical research and development in this area in terms of vacuum high pressure gas quenching, mainly targeting molds. Surface treatment technology of molds In addition to the reasonable cooperation of the matrix with sufficient strength and toughness, the surface properties of the molds are very important to the working performance and service life of the molds.
These surface properties refer to: wear resistance, corrosion resistance, friction coefficient, fatigue performance, etc. These performance improvements relying solely on the improvement and improvement of the base material are very limited and uneconomical. Through surface treatment technology, they can often get more results with less effort, which is why the surface treatment technology has developed rapidly. The surface treatment technology of the mold is a system engineering that changes the morphology, chemical composition, structure and stress state of the mold surface through surface coating, surface modification or composite treatment technology to obtain the required surface properties.
From the way of surface treatment, it can be divided into: chemical method, physical method, physical chemical method and mechanical method. Although new treatment technologies are constantly emerging to improve the surface properties of molds, the main applications in mold manufacturing are nitriding, carburizing, and hardened film deposition. Nitriding processes include gas nitriding, ion nitriding, and liquid nitriding. Each nitriding method has several nitriding technologies, which can meet the requirements of different steel types and different workpieces. Because the nitriding technology can form a surface with excellent performance, and the nitriding process and the quenching process of the mold steel have good coordination, at the same time, the nitriding temperature is low, no intense cooling is required after nitriding, and the mold deformation is extremely small. Surface strengthening is an earlier application of nitriding technology and is also the most widely used. The purpose of carburizing of the mold is mainly to improve the overall strength and toughness of the mold, that is, the working surface of the mold has high strength and abrasion resistance. The technical idea introduced here is to use lower-level materials, that is, quenching by carburizing To replace higher grade materials, thereby reducing manufacturing costs.
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