1. About Graphite milling cutter
Compared with copper electrodes, graphite electrodes have advantages such as 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 adhesion.
Although graphite is a material that is very easy to cut, the graphite material used as an EDM electrode must have sufficient strength to avoid damage during operation and EDM processing. At the same time, the electrode shape (thin-walled, small rounded corners, sharp changes, etc.) also puts high requirements on the grain size and strength of the graphite electrode, which leads to the graphite workpiece being prone to fragmentation and tool wear during the processing.
2. Graphite milling tool material
The tool material is the fundamental factor determining the cutting performance of the tool, which has a significant impact on machining efficiency, quality, cost, and tool durability. The harder the tool material, the better its wear resistance, the higher its hardness, the lower its impact toughness, and the more brittle the material.
Hardness and toughness are contradictory and a key issue that tool materials should address.
For graphite cutting tools, ordinary TIAIN coatings can choose materials with relatively better toughness, that is, those with slightly higher cobalt content; For diamond coated graphite cutting tools, materials with relatively higher hardness, i.e. with lower cobalt content, can be selected appropriately.
3. Tool geometry angle
Special graphite cutting tools Choosing the appropriate geometric angle helps to reduce tool vibration, and conversely, graphite workpieces are also less prone to breakage.
anterior angle
When using negative rake angle to process graphite, the tool edge strength is good, and the impact resistance and friction performance are good. As the absolute value of negative rake angle decreases, the wear area of the rear tool surface does not change much, but overall shows a decreasing trend. When using positive rake angle to process, as the rake angle increases, the tool edge strength is weakened, and instead, the wear of the rear tool surface is intensified. When machining with a negative rake angle, the cutting resistance is high, which increases the cutting vibration. When machining with a large positive rake angle, the tool wear is severe, and the cutting vibration is also high.
relief angle
If the back angle increases, the strength of the tool edge decreases and the wear area of the back tool surface gradually increases. When the back angle of the tool is too large, cutting vibration increases.
helix angle
When the helix angle is small, the length of the cutting edge that simultaneously cuts into the graphite workpiece on all cutting edges is longer, the cutting resistance is greater, and the cutting impact force borne by the tool is greater, resulting in greater tool wear, milling force, and cutting vibration. When the helix angle is large, the direction of the milling force deviates greatly from the surface of the workpiece. The cutting impact caused by the fragmentation of graphite material intensifies wear, and the impact of milling force and cutting vibration is a combination of the front angle, back angle, and helix angle. Therefore, it is necessary to pay more attention when selecting.
3.end mill for graphite coating
PCD coating cutting tools have advantages such as high hardness, good wear resistance, and low friction coefficient.
At present, diamond coating is the best choice for graphite machining tools and can best reflect the superior performance of graphite tools. The advantage of diamond coated carbide tool is that it combines the hardness of natural diamond with the strength and Fracture toughness of carbide
The geometric angle of diamond coated tools is fundamentally different from that of ordinary coatings. Therefore, when designing diamond coated tools, due to the special nature of graphite processing, the geometric angle can be appropriately enlarged, and the chip holding groove can also be enlarged, without reducing the wear resistance of the tool edge. For ordinary TIAIN coatings, although their wear resistance is significantly improved compared to uncoated tools, compared to diamond coatings, the geometric angle should be appropriately reduced when machining graphite to increase its wear resistance.
4. Blade passivation
The passivation technology of cutting edge is a very important issue that has not been widely recognized yet. Its importance lies in the fact that the passivated tool can effectively improve the edge strength, tool life, and stability of the cutting process. We know that cutting tools are the “teeth” of machine tools, and the main factors affecting cutting performance and tool life. In addition to tool material, tool geometric parameters, tool structure, cutting parameter optimization, etc., through a large number of tool edge passivation practices, we have realized that having a good edge form and edge passivation quality is also a prerequisite for the tool to be able to perform good cutting processing. Therefore, the condition of the cutting edge is also a factor that cannot be ignored
5. Cutting method
The selection of cutting conditions has a significant impact on the tool life.
The cutting vibration of forward milling is smaller than that of reverse milling. During forward milling, the cutting thickness of the tool decreases from maximum to zero. After the tool cuts into the workpiece, there will be no bouncing phenomenon caused by the inability to cut chips. The process system has good rigidity and low cutting vibration; During reverse milling, the cutting thickness of the tool increases from zero to maximum. In the initial stage of cutting, due to the thin cutting thickness, a path will be drawn on the surface of the workpiece. At this time, if the cutting edge encounters hard points in graphite material or residual chip particles on the surface of the workpiece, it will cause the tool to bounce or vibrate, resulting in significant cutting vibration during reverse milling.
Blowing (or vacuuming) and immersion in electric discharge fluid machining
Timely cleaning of graphite dust on the surface of the workpiece is beneficial for reducing secondary tool wear, prolonging tool service life, and reducing the impact of graphite dust on machine tool screws and guides.
Post time: Jun-19-2023