Stone sawing mechanism and diamond tool wear mechanism research status

1 Introduction Hard and brittle materials refer to materials with high hardness and high brittleness, usually non-conductors or semiconductors, such as various kinds of stone, glass, silicon crystals, quartz crystals, hard alloys, and ceramics. With the development of science and technology and modern industry, the application fields of hard and brittle materials are expanding, and the processing technology of hard and brittle materials is also constantly developing. In various hard and brittle materials processing methods, cutting processing plays an important role. For example, in the processing of building decorative plates and precision parts of rock materials, sawing is the first process of machining, and the cost of sawing accounts for more than 50% of the total processing cost. Currently, various diamond cutting tools are used for cutting and processing hard and brittle materials such as stone. As diamond is the hardest material known in nature, its excellent properties determine its broad prospects for development in the field of cutting and processing of hard and brittle materials such as stone. The processing methods for sawing hard and brittle materials by using diamond tools mainly include: circular saw blade cutting, diamond band saw cutting, diamond frame saw cutting, and diamond bead saw cutting. Although each method has its own different characteristics and application range, its cutting mechanism and diamond wear mechanism are roughly the same. As rock cutting is the most important use of diamond cutting tools, it is of great significance to deeply study the mechanism of stone sawing and the wear mechanism of diamond cutting tools for the rational manufacture and correct use of diamond cutting tools. For a long time, experts and scholars at home and abroad have conducted extensive experiments and research on the processing mechanism of diamond tool sawing granite, the wear mechanism of diamond tools, and the sawing power in the sawing process, and have achieved remarkable results. The research and development of processing and diamond tools have played an active theoretical guiding role. 2 Research on diamond cutting stone sawing mechanism Diamond abrasives are usually made by cutting or sintering. The cutting process of diamond tools is similar to that of grinding. However, due to the influence of materials, the processing mechanism of hard and brittle materials such as rocks and ceramics is different from the metal processing mechanism, and the processing process is more complicated. Since the diamond cutting tool was first applied to stone cutting, there are many researches on the mechanism of diamond cutting stone. Domestic and foreign scholars have conducted long-term research on the processing mechanism of diamond tools sawing granites. From the early application of rock fracture theory under the intrusion of the indenter, single-grain diamond scratch surface morphology observation method has gradually developed to comprehensive application of polarizing microscope and scanning electron microscope. Observe the morphology of rock processing surface and the generation and propagation of cracks, and use acoustic emission signals to evaluate the cutting status of rocks. However, due to the complex cutting and cutting processes of hard and brittle materials such as rocks, the study of its cutting mechanism has not yet formed a unified understanding. Similar to the grinding process, people first studied the mechanism of action between single diamond particles and stone during cutting. Early experimental studies have shown that: When single-grained diamonds cut granites under different conditions, the main failure modes of the rock are brittle collapse; at the same time, according to different mineral compositions, there are still plastic deformations in the rock.

Fig.1 P.Bienert model of single-grained diamond cutting rock

Fig. 2 Improved single particle diamond cutting rock model by M.Meding

P. Bienert proposed a model of single-particle diamond-cut rock in his doctoral dissertation on concrete processing (see Figure 1). The model summarizes the process of sawing the rock as follows: 1 In front of the diamond particles, the rock material is broken due to the shear stress generated by the compressive stress, forming the main cuttings, and is collapsed and extruded in the cutting zone; 2 in the abrasive grain Below, due to high pressure and possible temperature effects, the rock material plastically deforms to form secondary chips, forming a smooth surface in a certain thin layer; 3 behind the abrasive particles, due to the sudden release of elastic stress, resulting in larger chips The formation of it consists of loose blocky chips and secondary cuttings. The P. Bienert model described the chip formation process of diamond abrasive grain cutting rock in detail, but failed to study the stress distribution in the cutting zone during chip formation and the law of crack generation and expansion. It also failed to reflect the blade front lower pressure. The situation of the entity. M.Meding improved the P. Bienert model (see Figure 2), and considered that there are three deformation zones in the cutting process: 1 The first deformation zone is located in front of and near the abrasive particles. The compressive stress generated by the negative rake edge causes shear failure of the rock. The disintegrated rock particles fly out of the front of the abrasive particle and the rock presses against both edges of the abrasive particle. 2 The second deformation zone is located below the abrasive particles. For limestone and marble, a plastic deformation zone is formed on the surface in contact with the abrasive particles, the surface of the workpiece is smooth (mainly caused by compressive stress), and the strong plastic deformation is only a few microns thick; the granite also generates under the high temperature and high pressure in the contact zone. Local plastic deformation. 3 The third deformation zone is located behind the abrasive particles. Some tails composed of fine rock grains are formed in the vicinity of the abrasive grains. It is inferred from the test results that this is mainly due to the change of the surface stress of the scratches after the abrasive grains are scratched to the tensile stress due to the compression stress. Many domestic scholars have also studied the sawing mechanism of granite and other stone materials. Xu Xipeng observed through scanning electron microscopy of the sawing surface of granite: The fracture types of quartzite are mainly intergranular fractures and transgranular fractures. The deformation mode is mainly determined by the deformation mode of quartz, the main component of the rock; The structural components are quartz, orthoclase and plagioclase, so the deformation characteristics are determined by the three. Among them, mica has the most complete dissociation and is the easiest to remove, followed by orthoclase and plagioclase, while quartz is hardly dissociated and fractured, making it difficult to cut. The squeezing effect of diamond cutting granite will cause the brittle fracture of granite. This is because there are various defects and stress concentration in granite stone, which causes the crack to be generated and expanded under the action of extrusion, leading to the brittle failure of granite. As a non-destructive testing method, acoustic emission measurement has been used in the monitoring of breakage and wear of cutting tools, metal and rock fracture analysis. Some studies suggest that the AErms have a good correlation with the rock's machinability, and the rock hardness is proportional to the AErms value. Tests have shown that the greater the AErms value, the worse the machinability of the rock sawing with a diamond disc saw. Wang Chengyong used DIN50103 to measure the Rockwell hardness diamond indenter on the TypFP3 NC milling machine for a single abrasive grinding test, and analyzed the acoustic emission signal and grinding depth, rock types, mineral composition and other factors. The research shows that the acoustic emission signal of single-grain diamond grinding granite is affected by the granite type, mineral composition, grinding depth and other factors. When grinding and sawing good machinability of granite and quartz (or deeper grinding depth), the average AERns is larger, and there are more signals in the high peak range. The AErms value also reflects the fracture mode during grinding. For granites, the AErms mean is small and there are many signals in the low peak range, which means that there are many micro-fragmentation components and the crushing energy consumption is high. Although people have conducted a lot of research on the mechanism of stone sawing from different angles, due to the complexity of the rock sawing process, people still need to further understand the physical nature of the sawing process. The rock sawing process is like a black box, and the corresponding relationship between input and output parameters can only be established through suitable measuring instruments. Therefore, although some sawing models currently established reflect the sawing process to a certain extent, they cannot fully explain the physical nature of the sawing process.

1. Friction between the substrate and the chip 2. The substrate is chipped by the chips and flakes 3. The first chip area 4. The friction between the stone and the abrasive grain 5. The plastic deformation 6. The elastic deformation Figure 3 The mechanical action between the tool and the workpiece when cutting the stone

3 Research on wear mechanism of diamond tools When diamond tools are used to cut hard and brittle materials such as stone, due to high pressure, violent friction and possible high temperature, diamond abrasive and matrix will inevitably wear out. The abrasive wear, shedding, and wear of the matrix determine the sawing effect and tool life. Balogh pointed out that the main factors affecting the life and efficiency of diamond saws include the cutting speed, the characteristics of the material being cut, the quality of the saw blade, and the operator's skill level. Liao YS studied the wear characteristics of diamond agglomerates when the diamond saw blades cut granite. Studies have shown that the failure modes of agglomerates are mainly erosion erosion, cavitation erosion and wear. British scholar Luo SY has carried out effective research on the wear of diamond circular saw blades. As early as 1991, he conducted experimental research on diamond saw blade wear. The diameter of the saw blade used in the experiment was 205mm, the thickness of the core was 5mm, the size of the diamond sintered block was 40×7×10. 5(mm), the external speed of the saw blade was 30m/s, and the feed speed was 1m/min. The depth is 0.2mm; the coolant is water; the workpiece material is Indian red granite; the wear condition of the diamond abrasive grain is analyzed by SEM, and the wear amount and force of the saw blade are measured. The experimental results show that the etched pits on the diamond surface of the block are very small, and the wear of the face is mainly manifested as the microscopic damage and polishing of the diamond grains. At this time, the cutting force is small, and the saw blade is more wear-resistant. On the contrary, when there are a large number of expansion pits on the diamond surface, the main wear patterns are microscopic breakage and particle pullout. At this time, the cutting force is greater and the saw blade is not wear resistant. In 1996, Luo SY further studied the wear characteristics of diamonds when sawing circular saw blades. The research shows that the failure of saw blades is mainly caused by the damage and pull-out of abrasive particles. When more than one third of the abrasive particles are broken or pulled out, The cutting efficiency is significantly reduced. In severe cases, the saw blade may even fail. HK Tönshoff and J.Asche studied the wear of diamond tools when cutting stone, and established a model of single diamond cutting stone. The model describes the mechanical interaction between the tool and the workpiece when the diamond saw blade cuts stone (see Figure 3), including the elastic and plastic deformation of the workpiece under the action of the cutting force, the friction between the stone and the diamond, and between the stone and the substrate. The friction, the friction between the chip and the substrate, etc. The study believes that the diamond wear mechanism can be divided into four types: 1 Adhesive wear: diamond adheres to the stone surface and is cut off; 2 Friction and wear: extremely hard particles in the rock scratch the diamond surface; 3 diffusion wear: The chemical reaction between the workpiece and the diamond reduces the strength and hardness of the diamond; 4 Abrasive fracture: diamond fracture caused by mechanical overload, thermal overload or fatigue. Many scholars in China have also studied the wear and failure modes of diamond saw blades. Song Yueqing of Beijing Nonferrous Metal Research Institute observed the cutting performance and wear surface morphology of different diamond saws, and analyzed the relationship between wear patterns of diamond particles in the tool and wear properties of the tool matrix and the cutting performance of the tool. The effect is that diamonds polished or polished in the tool are detrimental to the cutting performance of the tool, while the increase in the number of newly emerging and micro-fractured diamond particles is beneficial to improving the cutting performance of the tool. Yang Weiguang and others of the Beijing Institute of Powder Metallurgy have studied the wear mechanism of diamond tools. Scanning electron microscope observations show that the wear of diamond tools includes slight wear and severe wear. Slight wear includes diamond furrow, exfoliation, and pitting wear; severe wear includes diamond chip wear, matrix and diamond interfacial extrusion, relief, and detachment. Studies have shown that the edge height h of the diamond tool decreases with slight wear and increases with severe wear. Although the severe wear of diamond can improve the processing efficiency, it will affect the service life of the tool. Wang Dian of Zhongnan University of Technology will study the wear mechanism of diamond saw blades when cutting hard stone. Studies have shown that diamond saw blades have four wear mechanisms: impact shear, fatigue failure, particle pull-out, and thermal effects. Surface erosion is caused by thermal influences. Impact shearing and fatigue can cause microscopic fracture of diamond particles, and the extraction of particles can increase the cutting force of individual particles. Xu Xipeng of Huaqiao University studied the wear mechanism of diamond tools, and believed that while diamonds are subjected to direct friction and wear with granite, they are also subject to the impact and wear of granite chips. Therefore, the wear types of diamond can be classified as abrasive grains. Wear, impact wear, and impact wear caused by solid particles in the fluid. The actual wear process of diamond can go through different paths, either starting from a complete crystal, going through micro-fragmentation to macro-fragmentation, finally falling off, or falling off from the beginning. The specific method of wear depends on the quality of the diamond, the load it bears, and the properties of the binder. In addition, many scholars have studied the friction and wear characteristics of diamond saw blades when cutting stone, and obtained some valuable conclusions. 4 The research of sawing force The sawing force is a very important parameter in the stone sawing process. The sawing force not only determines the power of the processing machine, but also determines the load on the tool, which determines the tool. Sawing ability. Since the sawing force of the diamond tool is the sum of the sawing forces acting on each diamond particle, it is necessary to study the relationship between the sawing force, the geometry of the chip and the diamond abrasive grain, and to study the process parameters for individual diamonds. Particles and the effects of the overall tool's cutting performance. In the early research on the sawing force, Tönshoff obtained the relationship between the force on a single diamond abrasive grain and the grain size, feed rate, and feed pressure. Tönshoff believes that the ratio of feed pressure to tangential force is 5 to 15, so the feed pressure is the main sawing force component; the larger the abrasive grain, the greater the feed pressure acting on the abrasive grain; with the feed When the amount is increased, the feed pressure will be reduced. This is due to the increase of the chip cross-sectional area, which causes the diamond abrasive grains to break. The self-sharpening effect will make the abrasive grains more sharp. Chen Xian through the study that the sawing force includes the crush resistance of the rock, the friction between the diamond and the rock, the friction between the sawdust and diamond and metal carcass. Obviously, the crush resistance of rock is related to the physical properties of rock, chemical composition, mineral composition and sawing process parameters. Although the mechanism of the crushing of granite is not yet fully understood, it is generally believed that the process of sawdust formation is brittle failure and the energy consumed is not large. Therefore, the crush resistance component is very small, accounting for only about 15% of the sawing force component. The power loss caused by friction is about 82% to 87% of the sawing power. Xu Xipeng's research on the sawing force also proved this point. The research results show that the energy of the fracture and the kinetic energy of the chip are negligible in the sawing process, and the energy is mainly consumed in friction. Jerro et al. used the finite element method to analyze the cutting process of diamond saw blades and established a cutting force calculation model for cutting hard and brittle materials. In addition to the machining process and tool parameters, such as the blade circumferential speed, feed speed, saw blade diameter, cutting depth, abrasive grain size, diamond sintered block density and distribution, the model also includes the workpiece material performance parameters, such as Elastic modulus, Poisson's ratio, etc. The finite element method can be used to first calculate the cutting of a single abrasive particle, and then calculate the cutting force of a single agglomerate and the entire saw blade. Due to the complexity and randomness of the sawing process, the research on the sawing force is mostly based on experiments and empirical formulas obtained from experiments, and relatively few theoretical studies. Zhou Canfeng of the Beijing Institute of Petrochemical Technology theoretically studied the sawing power of the diamond circular saw blade when sawing stone materials. The relevant theoretical formula was obtained by referring to the relevant formula deduced by G.Wener. The formula reflects that the microstructure of the workpiece material is not distributed. The effect of uniform and non-linear characteristics on the sawing force, but does not take into account the particularities of sawing brittle materials. 5 Conclusion In summary, people have conducted a lot of research on the sawing mechanism of diamond tools and other hard and brittle materials and the wear mechanism of diamond tools. Many achievements have been made. However, due to the complexity of the sawing process, most of these studies are in the exploratory stage. There are also many major theoretical issues such as the microscopic mechanism of the sawing process, the theoretical calculation of the sawing force, the microscopic wear mechanism of diamond abrasive grains, and the diamond abrasive grains and sintering. The micro-interface analysis of substrates or electroplated coatings is urgently needed for further in-depth exploration and research.