Graphite end mills use carbide or super-hard alloy tool materials, combined with diamond coating or PCD tool heads, which have higher hardness and wear resistance, can effectively reduce tool wear, and improve processing accuracy and efficiency. The emergence of graphite end mills provides an efficient and reliable solution for the processing of graphite electrodes, and plays an important role in the fields of electronics, automobiles, aerospace, etc.
Graphite electrodes have been widely used in the field of electrospark machining (EDM) due to their unique physical and chemical properties. Compared with traditional copper electrodes, graphite electrodes have the advantages of low electrode loss, fast processing speed, good mechanical processing performance, high processing accuracy, small thermal deformation, light weight, easy surface treatment, high temperature resistance, high processing temperature, and electrode bonding. However, the brittleness of graphite also makes it easy to break during processing. At the same time, the strong abrasiveness of graphite will cause the tool to wear faster, affecting the processing accuracy and efficiency.
How to Choose a Suitable End Mill for Graphite Processing
End Mill Tool Material
End mill tool material is an important factor in determining the cutting performance of the tool, and has a great influence on processing efficiency, processing quality, processing cost and tool durability. The harder the tool material, the better its wear resistance. However, the higher the hardness, the lower the impact toughness, and the more brittle the material. Hardness and toughness are contradictory, which is a problem that tool materials should solve. For graphite end mills, ordinary TiAlN coatings can be appropriately selected with relatively better toughness, that is, with a slightly higher cobalt content; for diamond-coated graphite end mills, relatively higher hardness can be appropriately selected, that is, with a slightly lower cobalt content; for polycrystalline diamond PCD tools, coarse-grained grades with better wear resistance can be selected.
End Mill Tool Geometry
Selecting appropriate geometry for graphite-specific tools can help reduce tool vibration, and in turn, graphite workpieces are not prone to chipping.
End Mill Ttool Coating
Diamond-coated end mills have the advantages of high hardness, good wear resistance, and low friction coefficient. At this stage, diamond coating is the best choice for graphite processing tools, and it can best reflect the superior performance of graphite tools.
Passivation of the Cutting Edge of the End Mill
The purpose of passivation of the end mill is to solve the defects of the microscopic notches on the cutting edge of the tool after grinding, reduce or eliminate the edge value, and achieve the purpose of smoothness, sharpness, firmness and durability.
Machining Conditions of End Mill
Choosing appropriate machining conditions has a considerable impact on the life of the tool. Combining the above points, the material, geometric angle, coating, edge reinforcement and machining conditions of the tool play different roles in the service life of the tool, and they are indispensable and complementary. A good graphite tool should have a smooth graphite powder chip groove, a long service life, be able to perform deep engraving, and save processing costs.
Factors to Note When Determining the Geometric Angle of Graphite Machining Tools
Rake Angle of Graphite Machining Tools
When using negative rake angle to machine graphite, the tool edge strength is better, and the impact and friction resistance is good. As the absolute value of the negative rake angle decreases, the wear area of the back tool face does not change much, but it generally shows a decreasing trend. When using positive rake angle for machining, as the rake angle increases, the tool edge strength is weakened, which leads to increased wear of the back tool face. When machining with negative rake angle, the cutting resistance is large, which increases the cutting vibration. When machining with large positive rake angle, the tool wear is serious and the cutting vibration is also large.
Back Angle of Graphite Machining Tools
If the rake angle increases, the tool edge strength decreases, and the wear area of the back tool face gradually increases. When the tool rake angle is too large, the cutting vibration is enhanced.
Helix Angle of Graphite Machining Tools
When the helix angle is small, the blade length of the same cutting edge that cuts into the graphite workpiece at the same time is longer, the cutting resistance is larger, and the cutting impact force borne by the tool is large, so the tool wear, milling force and cutting vibration are relatively large. When the helix angle is large, the direction of the milling force deviates greatly from the workpiece surface, and the cutting impact caused by the collapse of the graphite material is aggravated, so the tool wear, milling force and cutting vibration are also increased.
Therefore, the influence of tool angle change on tool wear, milling force and cutting vibration is a combination of rake angle, back angle and helix angle, so more attention should be paid when selecting.
Structural Form of Graphite Processing Tools
Different graphite-specific tools need to be selected according to different processing procedures and processing requirements. The tool structure forms of graphite milling tools include rod-shaped milling cutters and milling inserts, including: PCD end mills, PCD ball head milling cutters, PCD single-edge milling cutters, PCD double-edge milling cutters, PCD slot milling cutters, PCD chamfering cutters, diamond PCD face milling cutters, PCD milling inserts and CVD diamond coated milling cutters, etc. The tool structure of graphite turning tools is divided into composite PCD blades and welded turning tools, including PCD sheets, PCD welded turning tools, PCD slotting tools, PCD external turning tools, PCD slotting tools, etc. The forms of graphite hole processing tools include PCD drills, PCD internal turning tools, PCD boring tools, PCD milling cutters, CVD diamond coated drills, etc.
