Boron Ultrahard Material
China cubic boron nitride full industry manufacturer
1. Overview of polycrystalline cubic boron nitride (PCBN) grinding
In recent years, the use of polycrystalline cubic boron nitride (PCBN) has made it possible to perform precise hard cutting of workpieces with a hardness of 58HRC or more, and achieve the surface quality of turning instead of grinding. Compared with high-speed steel and cemented carbide materials, PCBN The tool can greatly improve the surface quality and processing speed of the workpiece, improve the processing efficiency and tool life. At present, the methods of cutting edge processing of PCBN tools at home and abroad mainly include mechanical grinding, electrical discharge grinding and so on.
Mechanical grinding, that is, grinding the machined surface of PCBN tools with high-speed rotating diamond grinding wheels. Mechanical grinding has the advantages of simple process and low surface roughness value of the cutting edge. However, due to the problems of difficult grinding wheel shaping, serious grinding wheel wear and high cost, it is difficult to realize the processing of sharp and thin cutting edge and complex shape cutting edge cutting tools. , the scope of application is limited. EDM is a self-excited electric discharge machining process based on the principle of pulse discharge erosion. The physical process of electric discharge erosion is a process of comprehensive action of electromagnetism, thermodynamics, fluid dynamics, etc. The mechanism of electric discharge machining is an electrical discharge machining process. physical process. EDM is a non-contact machining and has no mechanical cutting force, so it is not necessary to consider its force characteristics when making tool electrodes. It has the advantages of simple tool electrode forming and low relative loss, and can be effectively used in sharp and thin cutting edges and complex Shaped edge PCBN tool processing. In this paper, according to the characteristics of superhard tool products, combined with the principle of EDM, the processing efficiency and machining quality of the electrode rotation speed, peak current and pulse width of superhard tool EDM are discussed in detail. described.
2. Influencing factors of EDM grinding
2.1 Linear speed of electrode rotation
When the electrode does not rotate, the material removal of the workpiece is the lowest, and the surface roughness value of the workpiece is also the largest; after the electrode rotates, the machining speed and machining quality are significantly improved. This is because the rotation of the electrode improves the electrical discharge machining conditions and accelerates the Erosion rate of material; with the increase of electrode rotation speed, the amount of workpiece material removal also increases, but the increase gradually slows down, and the loss of electrode also increases. This is because the wear of electrode mainly occurs in the early stage of electric discharge machining. With the increase of rotation speed, the discharge point is rapidly transferred, and the discharge frequency is obviously strengthened, which leads to the increase of electrode loss; with the increase of electrode rotation speed, the surface roughness value of the workpiece first decreases and then increases. In terms of machining quality and machining efficiency, the influence of electrode linear velocity variation is smaller than that of peak current and pulse width.
2.2 Peak current
With peak current Ip increases, material removal increases, and electrode wear decreases , the surface roughness value of the workpiece material increases. However, the trend of the three changes is different: when the peak current is less than 5A, the workpiece material removal and workpiece surface roughness value both increase slowly, while the electrode loss decreases sharply; when the peak current is greater than 10A, the workpiece material removal and The surface roughness values ??of the workpieces increased rapidly, and the decrease trend of electrode wear became slower. At the same time, when the peak current is below 8A, the PCBN particle size basically has little effect on the processing efficiency and processing quality; but when the peak current is greater than 10A, the PCBN particle size has a certain impact on the processing efficiency and processing quality of the workpiece.
2.3 Pulse width
As the pulse width increases, the removal of PCBN material increases rapidly. The reason for this may be that the longer the pulse width and discharge time, the more energy is generated between the electrode and the PCBN blank, thereby accelerating the removal of PCBN material. At the same time, the electrode loss decreases rapidly with the increase of pulse width. The electrode loss mainly occurs at the front end of the pulse. When the pulse interval constant increases, the larger the pulse width is, the fewer pulses are generated, and the smaller the electrode loss is. With the increase of the pulse width, both the surface roughness value and the thickness of the metamorphic layer of the PCBN blank increase.
3. Summary
The particle size of workpiece PCBN has a certain influence on the machining efficiency and quality of EDM, but it is not as significant as EDM process parameters. Considering the combined influence of cutting efficiency, surface quality and electrode wire loss, a reasonable pulse width should be selected for wire EDM of PCBN composite sheets. liquid.
