Compared with copper electrodes, graphite electrodes have the advantages of low electrode consumption, 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. Although graphite is a very easy-to-cut material, the graphite material used as EDM electrode must have sufficient strength to avoid damage during operation and EDM processing. At the same time, the electrode shape (thin wall, small fillet, sharp change, etc.) also puts forward higher requirements on the grain size and strength of the graphite electrode. This leads to the easy collapse of graphite workpieces and easy wear of tools during processing.
Tool wear is the most important issue in graphite electrode processing. The amount of wear not only affects the tool loss cost, processing time, and processing quality, but also affects the surface quality of the workpiece material processed by electrode EDM. It is an important parameter for optimizing high-speed processing. The main tool wear areas in graphite electrode material processing are the rake face and the flank face. On the rake face, the impact contact between the tool and the broken chip area produces impact abrasive wear, and the chips sliding along the tool surface produce sliding friction wear.
When Choosing Graphite Machining Tools, You Should Pay Attention to the Following Factors
Graphite Machining Tool Materials
Tool material is the fundamental factor that determines 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, the higher the hardness, the lower the impact toughness, and the more brittle the material. Hardness and toughness are contradictory, and it is also a key problem that tool materials should solve. For graphite tools, ordinary TiAlN coatings can appropriately choose materials with relatively better toughness, that is, slightly higher cobalt content. For diamond coated graphite tools, materials with relatively higher hardness, that is, slightly lower cobalt content, can be appropriately selected.
Graphite Machining Tool Geometry Angle
Choosing the right geometric angle for graphite specific tools helps reduce tool vibration, which in turn makes graphite workpieces less prone to chipping.
Front Angle
When using negative rake angle to process 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 shows a decreasing trend overall. When using positive rake angle to process, as the rake angle increases, the tool edge strength is weakened, which leads to increased wear of the back tool face. When using negative rake angle to process, the cutting resistance is large, which increases the cutting vibration. When using large positive rake angle to process, the tool wear is serious and the cutting vibration is also large.
Rear Angle
If the back angle increases, the tool edge strength decreases and the back tool wear area gradually increases. When the back angle of the tool is too large, the cutting vibration increases.
Ângulo de hélice
When the helix angle is small, the length of the blade that cuts into the graphite workpiece on the same cutting edge is long, the cutting resistance is large, and the cutting impact force borne by the tool is large. Therefore, the tool wear, milling force and cutting vibration are relatively large. When the helix angle is large, the direction of the milling force deviates from the workpiece surface to a large extent, and the cutting impact caused by the graphite material breaking is aggravated. Therefore, the tool wear, milling force and cutting vibration are also increased. Therefore, the influence of tool angle changes on tool wear, milling force and cutting vibration is a comprehensive result of the rake angle, back angle and helix angle. So you must pay more attention when choosing.
Graphite Processing Tool Coating
Diamond-coated tools 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 also best reflect the superior performance of graphite tools. Because it combines the hardness of natural diamond with the strength and fracture toughness of cemented carbide. However, currently in the country, diamond coating technology has made great progress in recent times. We can optimize the angle of the tool, select materials and improve the structure of the ordinary coating on the basis of ordinary tools. To a certain extent, it can still be applied in graphite processing.
The geometric angles of diamond-coated tools are essentially different from ordinary coated tools. Therefore, when designing diamond-coated tools, due to the particularity of graphite processing, the geometric angle can be appropriately enlarged and the chip flute can be enlarged without reducing the wear resistance of the tool edge. For ordinary TiAlN coatings, although its wear resistance is significantly improved compared with uncoated tools. However, compared with diamond coating, the geometric angle should be appropriately reduced when processing graphite to increase its wear resistance.
Tool Edge Strengthening
The passivation of tool edges is an issue that is not widely valued, but is very important. The cutting edge of a carbide tool sharpened with a diamond wheel has microscopic notches (i.e., tiny chipping and sawtooth) of varying degrees. High-speed cutting of graphite places higher demands on tool performance and stability, especially for diamond-coated tools, which must be passivated before coating to ensure the firmness and service life of the coating. The purpose of tool passivation is to solve the problem of microscopic notches on the cutting edge after tool sharpening, reduce its sharpness, and achieve a smooth, flat, strong and durable edge.
Cutting Processing Conditions
The choice of cutting conditions has a considerable influence on tool life.
Corte Method (Down Milling and vocêp Milling)
The cutting vibration of down milling is less than that of reverse milling. In down milling, the cutting thickness of the tool decreases from the maximum to zero. After the tool cuts into the workpiece, there will be no tool bounce due to the inability to cut the chips. The process system has good rigidity and small cutting vibration. In reverse milling, the cutting thickness of the tool increases from zero to the maximum. In the initial stage of tool cutting. Due to the thin cutting thickness, a path will be scratched on the surface of the workpiece. At this time, if the cutting edge encounters hard points in the graphite material or chip particles remaining on the surface of the workpiece, it will cause the tool to bounce or vibrate. Therefore, the cutting vibration of reverse milling is relatively large.
Blowing (Ór Vacuuming) and Dipping EDM euiquid
Timely cleaning of graphite dust on the workpiece surface is beneficial to reduce secondary wear of the tool and extend the tool life. It also reduces the impact of graphite dust on the machine tool lead screw and guide rail.
Outro Matters
Choose the appropriate high speed and corresponding large feed rate.
Combining the above points, the tool material, geometric angle, coating, edge strengthening and cutting processing conditions play different roles in the tool life, and each is 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.
