Traditional machining methods for graphite materials include turning, milling, grinding, sawing, etc., but they can only achieve the processing of 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. Practice has shown that due to the hard and brittle nature of graphite matrerial, tool wear is severe during machining. Therefore, carbide or diamond coated tools are recommended.
1 cutting processing measures
Due to the special nature of graphite, in order to achieve high-quality processing of graphite parts, corresponding technological measures must be taken. When the graphite material is rough-processed, the tool can be directly fed into the workpiece and relatively large cutting parameters are used. In order to avoid the occurrence of chipping during finishing, the tool with good wear resistance is often used to reduce the cutting amount of the tool, and Ensure that the pitch cutting amount of the cutting tool is less than 1/2 of the tool diameter, and perform the deceleration processing and other technical measures when machining both ends. During cutting, it is also necessary to arrange the cutting path reasonably. When machining the inner contour, it is necessary to use the contour height cutting as far as possible, which can make the stressed part of the cut part always thicker and the strength higher to prevent the workpiece from breaking. When processing planes or grooves, choose oblique lines or spiral feeds as much as possible; avoid forming islands on the working surface of the part and avoid cutting off the workpiece on the working surface. In addition, the cutting method is also an important factor affecting the graphite cutting machining. The cutting vibration during down milling is less than the cutting vibration during down milling. The cutting thickness of the cutting tool during down milling is reduced from the maximum to zero, and the tool will not appear after cutting into the workpiece, so the general graphite processing selects milling.
When processing complex graphite workpieces, in addition to optimizing the machining process according to the above considerations, special measures must be taken according to the specific conditions in order to achieve the best cutting results.
2 cutting tool
In the high-speed processing of graphite, due to the hardness of the graphite material, the interruption of chip formation, and the influence of high-speed cutting characteristics, the alternating cutting stress is formed during the cutting process and a certain shock vibration is generated. The tool is prone to rake face and flank face. Abrasion seriously affects the service life of the tool. Therefore, the tool for high-speed machining of graphite requires high wear resistance and impact resistance. Diamond coated tools have the advantages of high hardness, high wear resistance, low friction coefficient, etc. Currently, diamond coated tools are the best choice for graphite processing.
Graphite machining tools also need to select a suitable geometric angle, which will help reduce tool vibration, improve machining quality, and reduce tool wear. German scholars have shown that the graphite removal mechanism has a close relationship with the tool rake angle in the graphite cutting process. The negative rake angle increases the compressive stress, which helps to promote the crushing of the material, improves the processing efficiency, and avoids the generation of large-size graphite fragments. Common types of tool construction for high-speed cutting of graphite include end mills, ball nose knives, and corner mills. End mills are generally used for surface machining with relatively simple shapes and shapes. Ball-end milling cutters are ideal for machining curved surfaces, while round-corner milling cutters combine the characteristics of ball-end and end mills and can be used on surfaces and planes processing.
3 cutting parameters
Choosing reasonable cutting parameters for high-speed cutting of graphite is of great significance for the improvement of workpiece processing quality and efficiency. Because the cutting process of high-speed machining of graphite is very complicated, when selecting the cutting amount and processing strategy, the workpiece structure, machine tool characteristics, tools, etc. need to be considered. Many factors, which mainly rely on a large number of cutting experiments. For the graphite material, it is necessary to select cutting parameters with high rotation speed, rapid feed, and large knife during the roughing process, which can effectively improve the machining efficiency; however, graphite is prone to chipping during processing, especially at edges and the like. The position is easy to form zigzag, in these parts should be properly reduced feed speed, not use large engagement. For thin-walled structural graphite parts, the cause of edge cracking is mainly caused by the impact of cutting, the knife and the spatula, and the fluctuation of the cutting force. Reducing the cutting force can reduce the use of knives and shells, improve the surface quality of thin-walled graphite structures, and reduce the disintegration and breakage of corners. The spindle speed of the high-speed graphite machining center is generally large. If the power of the spindle of the machine tool is allowed, a higher cutting speed can be selected, which can effectively reduce the cutting force, and the machining efficiency can also be significantly improved; under the condition that the spindle speed is selected The amount of feed per tooth should be adapted to the spindle speed to prevent the blade from being fed too quickly due to the large amount of knife. Usually, graphite cutting is performed on a graphite machine. The machine speed is generally 3000 to 5000 r/min, and the feed speed is generally 0.5 to 1 m/min. A relatively low speed is selected during rough machining, and a high speed is selected during finishing. For the high speed machining center of graphite, the machine speed is relatively high, generally it is chosen between 10000 and 20000r/min, and the feed speed is generally between 1 and 10m/min.
Author: LUO Heping，JIJun，MIN Li
