Compared with copper electrode, graphite electrode has the advantages of small electrode consumption, fast processing speed, good machinability, high processing precision, 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, graphite materials used as EDM electrodes must have sufficient strength to avoid damage during handling and EDM processing, while electrode shapes (thin walls, small rounded corners, sharp changes) Etc.) also imposes high requirements on the grain size and strength of the graphite electrode, which results in the graphite workpiece being easily broken during the processing and the tool being easily worn.
Tool wear is the most important issue in graphite electrode processing. The amount of wear not only affects the tool loss cost, processing time, processing quality, but also affects the surface quality of the workpiece material processed by the electrode EDM, which is an important parameter for optimizing high-speed machining. The main tool wear areas for 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 sliding debris along the tool surface produces sliding friction wear.
The main factors affecting tool wear include:
1 tool material
Tool material is the root that determines the cutting performance of the tool
This factor has a great influence on processing efficiency, processing quality, processing cost, and tool durability. The harder the tool material is, the better its wear resistance is. The higher the hardness, the lower the impact toughness and the brittle material. Hardness and toughness are a pair of contradictions and a key issue that should be addressed by tool materials. For graphite tools, ordinary TiAlN coatings can be selected to have a relatively better toughness in the selection of materials, that is, the cobalt content is slightly higher; for diamond-coated graphite tools, the hardness can be appropriately selected on the material selection, That is, the cobalt content is slightly lower.
2 tool geometry angle
The choice of a suitable geometry for the graphite-specific tool helps to reduce the vibration of the tool and, in turn, the graphite workpiece is not easily collapsed.
2.1 Front angle
When the graphite is processed by the negative rake angle, the cutting edge strength is good, and the impact resistance and friction performance are good. With the decrease of the absolute value of the negative rake angle, the wear area of ​​the flank face does not change much, but the overall trend is decreasing. When the positive rake angle is used, the tool edge strength is weakened as the rake angle increases, which in turn causes the flank wear to increase. When the negative rake angle is processed, the cutting resistance is large, and the cutting vibration is increased. When the large positive rake angle is used, the tool wear is severe and the cutting vibration is large.
2.2 Back angle
If the relief angle is increased, the tool edge strength is reduced and the flank wear area is gradually increased. When the back angle of the tool is too large, the cutting vibration is strengthened.
2.3 helix angle
When the helix angle is small, the cutting edge of the graphite workpiece at the same cutting edge has the longest blade length, the maximum cutting resistance, and the maximum cutting impact force the tool bears, so the tool wear, milling force and cutting vibration are the largest. When the helix angle is large, the direction of the milling force is larger than the surface of the workpiece, the cutting impact of the graphite material is increased due to the collapse, and the tool wear, the milling force and the cutting vibration are also increased. Therefore, the influence of the tool angle change on the tool wear, milling force and cutting vibration is the combination of the rake angle, the back angle and the helix angle, so it is necessary to pay more attention when selecting.
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