Discussion on the wear mechanism of the hottest di

2022-08-21
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Discussion on the wear mechanism of diamond tools

1 wear patterns of diamond tools

the wear patterns of diamond tools are commonly seen in the wear of the front face, the wear of the rear face (see Figure 1) and the cracking of the cutting edge (see Figure 2)+ 1

Figure 1 front and rear wear of diamond tools

(a) single crystal diamond electric carving knife edge cracking (b) polycrystalline diamond wheel hub knife edge cracking

diamond tool edge cracking

2 diamond tool wear mechanism

diamond tool wear mechanism is relatively complex, which can be divided into macro wear and micro wear. The former is mainly mechanical wear and the latter is mainly thermochemical wear. The basic law of macro wear is shown in Figure 3. Early wear is rapid, while normal wear is very slow. Through high-power microscope observation, the worse the quality of the cutting edge and the greater the serration, the more obvious the early wear. This is because when the circular arc of the diamond blade is ground by mechanical method, the actual result is an irregular broken line (see Figure 4). Under the action of cutting force, the pressure on the unit broken line increases rapidly, resulting in accelerated wear of the blade. Another reason is that when the grinding pressure of diamond tools is too high or the grinding speed is too high, and the temperature exceeds a certain critical value, oxidation and graphitization will occur on the surface of diamond tools, which will reduce the hardness of the surface of diamond tools and form a hardness softening layer. Under the action of cutting force, the softening layer wears rapidly. It can be seen that the grinding quality of diamond tools will seriously affect its service life and dimensional accuracy

Figure 3 macro wear law of diamond tools

Figure 4 diamond tool edges ground by two methods

when the macro wear is in the normal wear stage, the wear of diamond tools is very slow. Practice has proved that the wear in the crystal direction or (1, 1, 1) direction of diamond is even slower. With the extension of cutting time, the tool still has wear of tens to hundreds of nanometers, which is micro wear. After long-term observation with high-power microscope and analysis with X-ray spectrum and X-ray diffraction, the micro wear of diamond tools may be caused by the following three reasons:

with the continuous extension of cutting time, the energy in the cutting area continues to accumulate and the temperature continues to rise. When the thermochemical reaction temperature is reached, a new metamorphic layer will be formed on the tool surface. Most of the metamorphic layers are oxides and carbides with poor strength, which continue to form and disappear with the chips, gradually forming a worn surface

under the continuous action of cutting force, especially under the alternating pulse load, one C atom after another obtains enough energy and escapes from the lattice, causing crystal defects. The attraction between atoms is weakened. Under the action of external force, shearing and spalling occur between the lattices, gradually forming the wear of the lattice layer. After a certain number of lattice layers are worn, the wear surface of the tool will be gradually formed

when the diamond tool is cutting non-ferrous metals and their alloys at high speed, under the action of high temperature and high pressure for a long time, when the distance between the diamond crystal and the metal lattice of the workpiece reaches the distance between molecules or even atoms, it will cause mutual penetration between atoms. The surface composition of diamond crystal is changed, and the hardness and wear resistance of diamond tool surface are reduced. This phenomenon is called diamond dissolution. The wear degree and speed of diamond tools depend on the dissolution rate of diamond atoms in non-ferrous metals or other non-metallic materials. Practice has proved that diamond tools have different dissolution rates when cutting different materials, that is to say, diamond tools cut different workpiece materials under different cutting conditions, and the wear speed and degree are different. The greater the dissolution rate, the faster the wear of diamond tools

3 some problems to pay attention to

(a) negative chamfering and rounding (b) double chamfering and rounding

c) vibration damping edge and rounding (d) vibration damping edge, crowding edge and rounding

Figure 5 forms of common edge areas of diamond tools

when using diamond tools, in addition to sharp edges, appropriate forms of edge areas should also be selected (see Figure 5) to enhance the strength of the edges

when the diamond tool made by mechanical method is used for mirror cutting, it often needs a running in period, that is, it needs a period of cutting process to achieve the best machining effect. In order to shorten or eliminate the running in period, generally, ion beam splashing method, non-destructive mechanochemical polishing method, vacuum plasma chemical polishing method and thermochemical polishing method can be used to solve the problem

single crystal diamond is anisotropic. The performance of the equipment used to display the pressure of the oil pump varies greatly in different crystal planes and directions. Cutting different materials should have different orientations (see the attached table)

6. Pay attention not to plug and unplug the power cord with electricity

attached table directional crystal surface of single crystal diamond tool

wear form of workpiece material tool directional crystal surface

micro fragmentation of hard and brittle materials (ceramics, glass, etc.)

mechanical wear of silicon aluminum alloy ()

thermochemical wear of frm, FRP, CFRP, etc. ()

in order to improve the brazing quality of diamond tools, alloys with good wettability to diamond should be selected as brazing materials, Ti, Cr, V, Mo and other elements can also be appropriately added to improve the wettability of the alloy solder on the diamond surface in the liquid phase and realize the firm bonding of the solder to the diamond. In addition, brazing must be carried out under the protection of inert gas in vacuum. The brazing temperature should be lower than the graphitization transition temperature of diamond (800 ° C), and the brazing action should be fast to avoid blade cracking and other phenomena. After brazing, the holding time can be appropriately extended to eliminate the brazing stress

pcd tools should adopt the grinding process of gradually reducing the load, which can not only maintain a high grinding efficiency, but also reduce the softening layer depth of the surface hardness after grinding, so as to prolong the service life of the tools. The single crystal diamond tool is ground on a high-precision grinding disc, and smaller grinding is selected. 1 Before use, first make sure whether the surrounding environment is a safe angle Q and an appropriate deviation angle W. use very fine diamond grinding powder and adopt a grinding machine with high precision, smooth operation and low vibration (such as aerostatic bearing grinder)

diamond tools are suitable for cutting non-ferrous metals and their alloys, fiber reinforced metals (FRM), fiber reinforced plastics (FRP), carbon fiber reinforced composites (CFRP) and other continuous surfaces on modular machine tools or machining centers with sufficient rigidity, high speed, high power, low vibration and good stability of machine tool workpiece tool system. Non contact measurement methods such as optical instruments should be used for the detection and adjustment of diamond tools. (end)

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