Reasons for graphite electrode replacing copper electrode

2020-12-1757

            Graphite material is a kind of carbon material composed of graphitic carbon. It is one of the rapidly developing materials in today's industrial materials. It is not only used in the traditional industrial industries (metallurgy, chemical industry, machinery), but also has been extended to a wider range of high-tech fields, such as aerospace, aviation, electronics, electrochemistry, communication, nuclear industry, machinery, bioengineering and environment Protection and other fields. The graphite material studied in this paper is an isotropic high performance graphite electrode material formed by cold isostatic pressing for EDM (unless otherwise specified, all graphite materials studied in this paper are referred to as graphite). It is widely used abroad. More than 95% of EDM users in the United States choose graphite as electrode material. In other developed industries such as Japan and Switzerland, graphite is used in EDM Industrial electrode materials also play an important role. In recent years, graphite as an electrode material has been widely used in the field of die EDM manufacturing of automobile, household appliances, communication and electronic industries. The density of graphite is about 1.55-1.859/em3, which is only 1 / 5 of that of copper. At the same time, graphite can be bonded, so it can be used to make large electrodes with complex shapes. Compared with copper electrode material, graphite has the advantages of high strength, low electrode consumption and small thermal deformation. It is especially suitable for manufacturing electrodes with complex cavity mold with thin wall, fin and micro hole. Graphite electrode material has gradually replaced copper electrode and become the mainstream electrode material for EDM.

        The traditional processing methods of graphite include turning, milling, grinding and sawing, but they can only realize electrode machining with simple shape and low precision. With the rapid development and application of graphite high-speed machining center, cutting tools and related supporting technologies, these traditional processing methods have been gradually replaced by high-speed machining technology. The spindle speed of the graphite high-speed machining center is usually between 10000 and 60000r / min, the feed speed can reach 60m / rain, the processing wall thickness can be less than 0.2ram, the small fillet can be less than 0.2ram, the surface processing quality and machining accuracy are high, which is the main means to realize the high-precision processing of graphite. With the rapid development of the product structure of the die and mold industry to large-scale, complex and effective direction, the demand for the mold with deep groove, narrow slot and micro group hole and other micro structure increases sharply, which also puts forward a huge demand and higher update requirements for the high-speed processing technology of graphite electrode used for manufacturing complex mold. Graphite is a typical heterogeneous brittle material. The graphite chips produced in high-speed milling are usually granular fine dust. Even if there is a dust collection system, it is very easy to scatter, accumulate and adhere to the front and rear cutter surfaces and machined surfaces. Together with the processed graphite materials, the cutting tools will have severe wear and damage. Usually, the tool cost caused by tool wear accounts for more than one-third of the total machining cost, which also makes the dimensional accuracy and surface quality of the workpiece difficult to be guaranteed. In the process of graphite high-speed milling, the following reasons may cause cutting impact on graphite workpiece, resulting in brittle fracture of graphite electrode corner: (1) change of milling direction at workpiece corner or corner; (2) sudden change of machine tool acceleration; (3) change of cutting direction and angle of cutting tool in and out; (4) cutting vibration in intermittent milling; (5) tool wear and breakage. At present, in the actual production process of graphite electrode high-speed machining enterprises in China, the selection of process parameters mainly depends on the practical experience of programmers. Due to the lack of systematic graphite high-speed milling technology theory to guide, it is difficult to make timely and reasonable selection of high-speed milling process parameters for different processing methods, tool materials, workpiece materials and shapes, which is also one of the key factors restricting the further promotion and application of graphite electrode. Therefore, how to explore the mechanism of tool wear and the mechanism of workpiece breakage in the process of graphite machining from the basic theoretical research, and reasonably select the high-speed milling technology to realize low-cost and high-precision graphite processing is an important application basic research problem in graphite processing. In order to solve the problems in the process of high-speed milling graphite with cemented carbide micro milling cutter, such as serious tool wear, broken graphite electrode edges and corners, and lack of theoretical guidance in the selection of cutting tools and geometric parameters, this paper adopts the theories of tribology, cutting mechanics and materials science, as well as on-line photography technology, material micro analysis technology and test analysis technology In this paper, the mechanism of chip formation in orthogonal cutting and high-speed milling of graphite is deeply studied. The model of graphite cutting mechanism is put forward. The sliding friction and wear behavior of graphite / cemented carbide pair are systematically studied. The friction and wear mechanism of cemented carbide tool matrix material and coating with graphite are revealed. The tool material and geometric angle are analyzed and studied On the basis of the optimization of the technological parameters of high-speed milling of graphite, the low-cost machining of typical thin-walled graphite electrode is realized. These studies are of great significance to improve the processing technology level of graphite electrical speed milling, and will also bring a greater role in promoting the development of China's mold manufacturing industry and certain economic benefits.