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.
Some things that affect tool wear:
1. Tool material Tool material is the fundamental factor determining the cutting performance of the tool. It has great influence on machining efficiency, machining quality, machining 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 to the tool material. For graphite tools, ordinary TiAlN coatings can be selected with a relatively good 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;
PARA tool combines many years of experience, using the tool materials of famous European brands.
2, the geometric angle of the tool graphite tool to choose the appropriate geometric angle, help to reduce the vibration of the tool, in turn, the graphite workpiece is not easy to collapse;
(1) The rake 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. As the absolute value of the negative rake angle decreases, the flank wear area 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 leads to increased wear on the flank. 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) Back angle, if the back angle increases, the tool edge strength decreases, and the flank wear area gradually increases. When the back angle of the tool is too large, the cutting vibration is strengthened.
(3) When the helix angle is small, the blade length of the graphite workpiece is the longest at the same cutting edge, the cutting resistance is the largest, and the cutting impact force of the tool is the largest, 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, and the cutting impact caused by the collapse of the graphite material is intensified, so that the tool wear, the milling force and the cutting vibration are also increased.
Therefore, the influence of tool angle change on tool wear, milling force and cutting vibration is the combination of front angle, back angle and spiral angle, so we must pay more attention to the selection.
Through a large number of scientific tests on the processing characteristics of graphite materials, PARA tools optimize the geometric angle of the relevant tools, so that the overall cutting performance of the tool is greatly improved.
3. The coated diamond coated tool of the tool has the advantages of high hardness, good wear resistance and low friction coefficient. At present, the diamond coating is the best choice for graphite processing tools, and it can best reflect the superior performance of graphite tools. The advantage of the diamond-coated cemented carbide tool is that it combines the hardness of natural diamond with the strength and fracture toughness of the cemented carbide; however, the domestic diamond coating technology is still in its infancy, and the cost investment is very large. Therefore, the diamond coating will not develop much in the near future, but 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 some extent, it can be processed in graphite. Applied.
There is a fundamental difference between the geometric angle of the diamond coated tool and the ordinary coated tool. Therefore, when designing the diamond coated tool, due to the particularity of graphite processing, the geometric angle can be appropriately enlarged, and the groove can be enlarged. Reducing the wear resistance of the tool front; for ordinary TiAlN coatings, although the wear resistance is significantly improved compared to uncoated tools, the geometric angle of the graphite coating should be compared to the diamond coating. Appropriately put small to increase its wear resistance.
For diamond coatings, many coating companies in the world have invested a lot of manpower and material resources to research and develop related coating technologies, but so far, mature and economical coating companies abroad are limited to Europe; PARA as a The excellent graphite processing tool also uses the world's most advanced coating technology to surface the tool to ensure the processing life and ensure the economical and practical tool.
4, the enhancement of the cutting edge of the tool cutting edge passivation technology is a problem that has not been universally recognized, but also very important. The edge of the carbide cutter after sharpening of the diamond wheel has microscopic notches of different degrees (ie, micro chipping and sawing). Graphite high-speed cutting tool performance and stability put forward higher requirements, especially diamond coating tools must be passivated by the knife edge before coating to ensure the firmness and service life of the coating. The purpose of tool passivation is to solve the defect of the micro-notch of the cutting edge of the above-mentioned sharpened blade, so that the front value is reduced or eliminated, and the smoothness and rigidity are achieved.
5. Machining conditions of the tool Choosing the appropriate machining conditions has a considerable impact on the life of the tool.
(1) Cutting method (shun milling and up milling), the cutting vibration during down milling is smaller than the cutting vibration of up milling. The cutting thickness of the tool during down-cutting is reduced from the maximum to zero. After the tool is cut into the workpiece, there is no knives caused by cutting the chip. The rigidity of the process system is good and the cutting vibration is small. When cutting the thickness of the tool during the reverse milling From zero to maximum, the cutting edge will be scratched on the surface of the workpiece due to the thin cutting thickness. At this time, if the cutting edge encounters hard spots in the graphite material or chip particles remaining on the surface of the workpiece, it will cause the tool. The knives or flutter, so the cutting vibration of the up-cut milling is large;
(2) Blowing (or vacuuming) and impregnating EDM liquid processing, timely cleaning the graphite dust on the surface of the workpiece, which is beneficial to reduce the secondary wear of the tool, prolong the service life of the tool, and reduce the graphite dust on the screw and guide rail of the machine tool. influences;
(3) Select the appropriate high speed and the corresponding large feed.
In summary of the above points, the material of the tool, the geometric angle, the coating, the reinforcement of the cutting edge and the machining conditions play different roles in the service life of the tool, which are indispensable and complementary. A good graphite tool should have a smooth graphite powder chip flute, long service life, deep engraving processing, and can save processing costs.
6, application examples Workpiece size: 600 × 400 × 90
Graphite material: ISO-63 (Toyo Carbon)
Electrode shape: Home appliance heat sink cover Tool: PARA ¢6 RO (finished bottom)
PARA ¢6 R3 (finished side wall)
S=17 000 F= 6000mm/min
Processing time: continuous processing for 15 hours Wear condition: tip tip <0.02mm, good coating S=17 000 F= 6000mm/min
Processing time: continuous processing for 8 hours
Application of PARA tool in graphite processing
Compared with the copper electrode, the 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, the graphite material used as the EDM electrode must have sufficient strength to be damaged during handling and EDM processing, while the electrode shape (thin wall, small rounded corners, sharp change) 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.