Graphite is a common non-metallic material, black in color, with high and low temperature resistance, good electrical and thermal conductivity, good lubricity and stable chemical properties, good electrical conductivity, and can be used as an electrode in EDM. Compared with traditional copper electrodes, graphite has many advantages such as high temperature resistance, low discharge consumption, and small thermal deformation. It shows better adaptability in the processing of sophisticated and complex parts and large-scale electrodes. The mainstream of processing electrodes. In addition, graphite wear-resistant materials can be used under high-speed, high-temperature, and high-pressure conditions without lubricating oil. Many equipment widely use graphite-made ring cups, sealing rings and bearings.

At present, graphite materials are widely used in machinery, metallurgy, chemical industry, national defense and other fields. There are many types of graphite parts, complex structure of parts, high requirements for dimensional accuracy and surface quality. Domestic research on graphite machining is not deep enough. During machining, it is prone to severe tool wear, cracks or breakage of the workpiece, and chipped corners.

Machining Performance Analysis of Graphite

Graphite is a brittle material with a heterogeneous structure. Graphite turning is achieved through the brittle fracture of graphite materials to generate discontinuous chip particles or powder. Scholars at home and abroad have done a lot of research on the turning mechanism of graphite materials. Formation process of graphite chips is roughly when the turning edge of the tool is in contact with the workpiece, there is extrusion and crushing at the tip of the tool, forming fine chips and small pits, and A crack is generated, and the crack will extend to the front and bottom of the tool tip to form a fracture pit, and a part of the workpiece is broken due to the advancement of the tool to form chips. Graphite particles are extremely fine, and the arc of the turning edge of the tool is relatively large, so the turning edge acts like extrusion, and the graphite material in the tool-workpiece contact area is squeezed by the rake face and the tip of the tool. Effect, resulting in brittle fracture, thus forming chipping chips.

Performance Analysis of Graphite Turning

Graphite is a brittle material with a heterogeneous structure. Graphite turning is realized by generating discontinuous chip particles or powder through brittle fracture of graphite material. Regarding the cutting mechanism of graphite materials, the formation process of graphite chips is roughly that when the cutting edge of the tool contacts the workpiece, there is extrusion and crushing at the tip of the tool, forming small chips and small pits, and a crack is formed, which will move forward to the tip of the tool. The lower part extends and expands to form a fracture pit, and a part of the workpiece is broken by the advancement of the tool to form chips. Graphite particles are extremely fine, and the arc of the cutting edge of the tool is relatively large, so the cutting edge acts like extrusion. The graphite material in the tool-workpiece contact area is squeezed by the rake face and the tip of the tool, resulting in Brittle fracture, thus forming chipping chips.

During the graphite turning process, due to the change of the cutting direction of the workpiece fillet or corner, the change of the acceleration of the machine tool, the change of the direction and angle of the cutting in and out of the tool, the turning vibration, etc., a certain impact is caused to the graphite workpiece, resulting in the edge of the graphite workpiece. Corner brittleness and chipping, serious tool wear and other problems. Especially when processing angular and thin and narrow-ribbed graphite parts, chipping and chipping of the workpiece are more likely to occur, which has also become a difficulty in graphite machining.

Graphite material processing technology

The traditional mechanical processing methods of graphite materials include turning, milling, grinding, etc., but they can only process graphite parts with simple shapes and low precision. With the rapid development and application of graphite high-speed machining centers, cutting tools and related supporting technologies, these traditional processing methods have been gradually replaced by high-speed machining technologies. Due to the hard and brittle nature of graphite, tool wear is severe during machining. Therefore, it is recommended to use diamond-coated tools (PCD tools).

Processing technology

Due to the particularity of graphite, in order to achieve high-quality processing of graphite parts, corresponding technological measures must be taken to ensure. During rough machining of graphite materials, the tool can be fed directly on the workpiece, using relatively large cutting parameters; in order to avoid chipping during finishing machining, a tool with good wear resistance is often used, and the cutting amount of the tool is reduced. And ensure that the pitch of the cutting tool is less than 1/2 of the tool diameter, and take deceleration processing and other technological measures when processing both ends. During cutting, it is also necessary to arrange the routing of the tool reasonably. When processing the inner contour, contour cutting should be used as much as possible, so that the stressed part of the cut part is always thicker and the strength is higher, preventing the workpiece from breaking. When machining planes or grooves, choose oblique or helical feed as much as possible; avoid forming islands on the working surface of the part and avoid cutting away from the workpiece on the working surface. In addition, the cutting method is also an important factor affecting the graphite cutting process. The cutting vibration during down milling is smaller than that of up milling. The cutting thickness of the tool during down milling is reduced from the maximum to zero, and the tool will not bounce after cutting into the workpiece. , so general graphite processing chooses down milling.

When processing graphite workpieces with complex structures, in addition to optimizing the processing technology according to the above considerations, some special measures must be taken according to specific conditions to achieve the best cutting effect.

Cutting tools

Graphite is a non-metallic material, so diamond tools are generally used for processing. Diamond tools have extremely high hardness and wear resistance, low friction coefficient, high elastic modulus, high thermal conductivity, low thermal expansion coefficient, and low affinity with non-ferrous metals. And other advantages, diamond tools are divided into four types of structures: natural diamond, single crystal diamond, PCD diamond and CVD diamond, among which PCD tools are mainly used for processing graphite.

---EDITOR: Doris Hu

---POST: Doris Hu