Current status and prospects of stone processing tools

The rise of diamond processing technology and the application of diamond technology have brought a "revolution" to the world stone industry. In the Mohs hardness level based on relative scoring, diamond is listed as the hardest level. It is a superhard material tool made by combining it with sintering agent, electroplating, etc., and is widely used in various fields such as geological exploration, stone, machinery, automobile and defense industry. The combination of various diamond tools and other high-tech tools makes stone mining and processing easier and less expensive. Therefore, the stone production has gone from the extensive form to the road of large-scale, large-scale and civilized and safe production of automation, mechanization and continuous.  

Main factors affecting the processing of stone  

    The processing of stone is mainly sawing, cutting, grinding and throwing. The machinability of stone refers to the difficulty of sawing, cutting, grinding and polishing. Saw, cut the same, grinding, throwing, although different, but very similar. Therefore, the workability of general stone generally refers to sawability and grindability [1]. The main factors affecting the processing of stone are:  

    (1) Hardness  

    In general, the greater the hardness of the stone, the more difficult the processing and the greater the wear on the tool.  

(2) Mineral composition and chemical composition  

    The material components of stone include mineral composition and chemical composition, different mineral components and chemical composition, and different processability. For example, marble rock minerals are mainly calcite and dolomite, and their Mohs hardness is 3 and 3.5-4 respectively. It is lower in hardness than granite and easy to process. The main rock-forming minerals of granite are quartz, feldspar, and plagioclase, which have a Mohs hardness of 6.5-7. Its processability depends to a large extent on the content of quartz and feldspar, the higher the content, the more difficult it is to process. In chemical composition, such as higher SiO2 content, the more difficult the processing.  

    (3) Structural structure of rock  

    In general, the grain is more uniform than the uneven stone, the fine grain is higher than the sheet-like polishing quality, and the dense stone has higher gloss than the loose stone. The degree of crystallization of the mineral is good, and the orientation and alignment of the optical axis will greatly improve the gloss after polishing. The cleavage, grain boundaries and initial cracks of the rock are also important factors influencing the processability.  

    In addition, the selected processing tools and process parameters are a factor that must be considered.  

    The decorative stone used for building decoration mainly consists of marble and granite. The finished stone block material is processed into a building decorative plate, and the main processes are sawing, grinding and polishing, cutting finished plate, trimming chamfering and slotting. The sawing process is the most critical, which determines the output and quality of the product [2]. In the sawing process, there are the most used diamond saw blades. According to statistics at home and abroad, about 50% of the world's industrial diamonds are currently used in the manufacture of stone processing tools, mainly stone processing saw blades. The issue of diamond saw blades is discussed below.  

Systematic Analysis of Factors Affecting the Use of Diamond Saw Blades  

Judging the effectiveness of the use of diamond saw blades is mainly based on three indicators, namely sawing efficiency, service life and processing quality. The above three performance indicators depend first on the performance of the saw blade itself, such as sharpness and durability. On the other hand, it also depends on whether it is reasonably selected and used correctly. The reason why the use of the saw blade is not good is not only the quality problem of the saw blade itself, but also in many cases due to improper use. As far as the current domestic situation is concerned, the responsibilities of both parties are roughly half.  

The factors affecting the performance and use of diamond saw blades are summarized, including manufacturing factors (raw materials, manufacturing processes and equipment) and usage factors (reasonable selection and proper use).  

Manufacture of diamond saw blades  

The essence of a diamond saw blade is that the base is inlaid with diamond by appropriate carcass material. It is a composite sintered body composed of diamond particles and a carcass material, which is often referred to as a cutter head, on a steel substrate. At present, the connection methods adopted in China are mainly brazing and cold pressing sintering. Cold-pressed sintering is mainly used for small pieces. The base of the brazing saw blade and the joint surface of the cutter head are connected by melting and penetration of the brazing material, and the bending strength is low. The bending strength is only 350-600 N/mm2, and the bearing capacity is poor, especially dry. When cutting, the saw blade is softened by the solder when it is heated to high temperature, which often causes the cutter head to fall off, which may cause harm to the operator. Therefore, foreign countries have developed laser welding instead of brazing since the late 1980s. Compared with brazing, laser welding has many significant advantages. Because the laser heat receiving area is small and the heat affected zone is small, the stress and the deformation of the matrix are greatly reduced; there is no influence on the diamond, which ensures the best performance of the product, especially the laser. Welding is a fusion welding with high bonding strength and a bending strength of 1800 N/mm2, which can be applied to dry cutting applications.

Research on cutting of diamond saw blades
The flourishing development of the stone processing industry places higher demands on the performance of diamond cutting tools. Not only does it require faster cutting speeds and longer lifespans; it also requires a wider range of tools for cutting stones and better cutting quality. To this end, relevant scholars at home and abroad have carried out a large number of targeted work.  

1. Improve the performance of diamond tools  

(1) Adding rare earth elements  

Diamond products are mainly made by powder metallurgy. The carcass components are mostly hard alloys. The improvement of the properties of rare earth elements on cemented carbides is expected to play a role in the performance of diamond tools: the addition of rare earth elements can improve the carcass. The wetting property of metal to diamond enhances the bonding ability; the addition of rare earth elements can improve the flexural strength, wear resistance and impact toughness of the carcass material, and improve the quality of the diamond tool; the rare earth element can lower the melting point of the bonding metal. , reducing the sintering temperature of the diamond product, thereby reducing the diamond quality degradation caused by the high temperature of the hot pressing method.  

(2) Application of self-propagating high-temperature synthesis technology  

Self-propagating high-temperature synthesis referred to as SHS is also called combustion synthesis. It is a new technology developed in the past 20 years and relies on the chemical reaction itself to generate heat. Usually, after the diamond is added to the carcass, the bending strength of the carcass decreases due to the "inclusion" effect of the diamond, but the carcass bending strength decreases after the formation of the carbide transition layer between the diamond and the carcass by reaction hot pressing. The magnitude is much smaller.  

(3) Pre-alloyed carcass metal powder  

The pre-alloying of the carcass metal powder has the following advantages: the melting point of the alloy is lower than the melting point of the single element, which can lower the melting point of some high-strength metals after alloying to meet the requirements of sintered diamond products; the alloy has the same as the single-element metal High physical and mechanical properties, easy to meet the performance requirements of diamond product carcass; alloy oxidation resistance is stronger than single element, good sintering performance, easy to preserve; pre-alloyed powder is more uniform than mechanically mixed powder, good wettability to diamond; alloy powder It has a single melting point, thus avoiding the most frequently occurring component segregation in mechanically mixed powder carcass sintering and the melting and enrichment of low melting point metals and the defects of oxidation and volatilization, thereby ensuring the quality of diamond products and the mechanical properties of the products. Also greatly improved.  

(4) Application of activation sintering  

Activated sintering is a chemical or physical measure that reduces the sintering temperature, speeds up the sintering process, or increases the density and other properties of the sintered body.  

(5) Design a reasonable structure  

(6) Diamond surface metallization  

In a diamond tool made of a bonding agent mainly composed of Fe, Cu, Co, Ni, etc., since the covalently bonded diamond crystal has no chemical affinity with the above bonding agent, the interface is not wetted, etc., the diamond particles can only be mechanically The ground is embedded in the binder matrix. Under the action of the grinding force, before the diamond abrasive grains are ground to the maximum cross section, the carcass metal loses the bond of the diamond particles and falls off by itself, which reduces the service life and processing efficiency of the diamond tool. The cutting action is not fully utilized. Therefore, the diamond surface has metallization characteristics, which can effectively improve the service life and processing efficiency of the diamond tool. The essence is that a bonding element such as Ti or an alloy thereof is directly plated on the surface of the diamond, and a heat bonding heat treatment is performed to form a uniform chemical bonding layer on the surface of the diamond. By plating the treated diamond abrasive grains, during the hot-press solid phase sintering or cold-press liquid phase sintering process of the diamond tool, the plating layer reacts with the diamond to form a chemical bond to metallize the diamond surface. On the other hand, the metallized diamond skin layer can smoothly achieve metallurgical bonding between metals with the metal matrix bond. Therefore, titanium-plated and alloyed diamonds have wide applicability to cold-pressed liquid phase sintering and hot-pressed solid-phase sintering. In this way, the solidification force of the carcass alloy on the diamond abrasive grains is improved, and the falling off of the abrasive particles during use of the diamond tool is reduced, thereby improving the service life and efficiency of the diamond tool. At present, methods for changing the surface properties of diamond mainly include electroless plating, vacuum evaporation, and ion plating.  

(7) using ultra-fine or nano-scale materials  

The finer the particle size of the powder, the larger the surface area and the higher the surface energy, the easier the sintering process and the higher the mechanical properties.  

Nanoscale materials use nanoscale objects made of nanotechnology. Due to the extremely small size of the nano-materials, the surface area is sharply increased and the surface activity is very strong. It has broad application prospects in many fields such as powder metallurgy, petrochemical, aerospace, military, energy, machinery, electronics and prospecting.  

2. Wear of diamond saw blades  

The wear performance of the diamond saw blade is one of the important indexes for the rationality of the sawing process parameters, the performance of the sawing tool and the machinability of the stone.  

The wear condition of the diamond saw blade has an important influence on the sawing ability and the stability of the sawing process. Keeping the cutting edge sharp is the decisive factor for obtaining the stability of the sawing process. The stone sawing process is the abrasive cutting process. Therefore, the mechanical micro-crushing of the diamond abrasive grains and the corresponding carcass wear should be continuously performed during the sawing process to produce a new sharp blade to ensure a certain sawing efficiency.  

The diamond abrasive grains from the carcass to the edge of the carcass to completely lose the cutting ability to undergo a certain wear process. The typical diamond wear process is: diamond cutting edge → reaching working height → crushing → bonding agent abrasion → diamond re-blade → abrasive particle crushing → abrasive particles completely falling off. Due to the irregular distribution of diamond abrasive grains on the saw blade working surface, the wear stages experienced vary. The whole process of diamond wear can be divided into three stages: initial wear (outper edge), normal wear and sharp wear. In the normal wear stage, there are three different wear routes:

(1) Initial wear → partial wear → large area crushing;  

(2) Initial wear → polishing → partial damage → large area crushing;  

(3) Initial wear → polishing → overall crushing.

The wear of diamond saw blades can be divided into the wear of diamond abrasive grains and the wear of diamond agglomerates. The research on the wear mechanism of diamond saw blades focuses on the wear mechanism of diamond abrasive grains. MW, Bailey et al. microscopically observed the wear process and wear morphology of diamond abrasive grains on the sawing tool, and divided the wear patterns of diamond abrasive grains into four forms: good edge, smooth, broken and shedding. Liu Quanxian et al. further divided the wear patterns of diamond abrasive grains into five main forms, namely initial blade cutting, polishing, partial crushing, large-area or overall crushing, shedding, and considered the mechanical load and thermal load alternating during sawing. And the internal defects of the diamond determine the abrasive wear pattern. Through research, Wang Chengyong and others proposed a new classification method of diamond wear morphology, which is divided into three types: wear and shape of diamond abrasive grains: good and micro-crushing, end crushing, smoothing, partial shedding, shedding pits and cutting edges. . This new classification method better describes the wear process of diamond abrasive grains during sawing. The wear pattern of the diamond determines the sawing performance of the saw blade. The more the number of diamond abrasive grains on the saw blade working surface is slightly broken, the more the saw blade is sharper, the cutting efficiency is correspondingly improved, but the saw blade has a low service life; The more polished diamond particles, the greater the cutting force, the lower the cutting efficiency, and the longer the saw blade life. Therefore, many researchers believe that there is a diamond wear pattern on the saw blade working surface. The optimum ratio makes the sawing performance of the saw blade optimal, but the ratio depends on the stone material and the requirements of the sawing process.  

During the wear process of the diamond abrasive grains, the continuous micro-crushing and partial crushing process causes the new cutting edge to be continuously generated, and the saw blade is in a sharp cutting state, and the cutting efficiency is high. Cutting power consumption is reduced, but continuous micro-crushing, partial crushing will lead to large-scale crushing of diamond abrasive grains, and the life of the saw blade is reduced. The continuous grinding and polishing of diamond will passivate the cutting edge, increase the cutting force and reduce the cutting efficiency. However, the service life of the saw blade has been improved.  

3. Force analysis of diamond circular saw blade  

(1) Establishment of mechanical model of saw blade  

In general, the thickness of the circular saw blade is relatively small, so that it can be treated as a plane stress problem when analyzing the force. The saw blade is placed on the spindle of the saw and tightened by the flange, so the six degrees of freedom of the central hole of the saw blade are limited. The saw blade is mainly subjected to a force on the diamond serration that is in contact with the stone cutting. The number of sawtooths involved in the cut is related to the depth of the cut.

The greater the depth of cut, the more teeth involved in cutting. The force acting on the serrations is the tangential force, so the tangential force is decomposed into two component forces in the X and Y directions and acts on the serrated nodes in a concentrated force. When the saw blade motor power is determined, the tangential force is determined by the blade line speed.  

    (2) Static method for analysis of sawtooth force  

Sawing force is an important data to measure the rationality of the sawing process parameters, the durability of the diamond saw blade, the quality of the cutting and the cuttability of the stone material.

When sawing, the sawtooth of the diamond saw blade has two cutting forces on the stone: one is the normal force Fn and the other is the tangential force Ft along the line speed direction. The sawing force Ft is the main cutting force of the saw blade, which directly affects the sawing power. The vertical force Fn directly affects the stiffness, stability and wear resistance of the saw blade. However, since the direct measurement of Fn and Ft is difficult, the tangential force Ft and the vertical normal force Fn are decomposed into the cutting force Fx along the feed direction and the vertical force Fy in the cutting depth direction. At a certain moment, Fn and Ft can be projected onto the x and y axes. Through the above geometric relationship, we can get:  

FX=Fnsinθ+Ftcosθ,                     Fn=-Fcosθ+Ftsinθ  

In the formula, θ is the angle between the diameter of the cutting point and the vertical direction of the cutting stone, and the angle between the saw blade and the cutting point from the cutting point to the midpoint of the cutting.

(3) Research on processing mechanism  

Stone processing is a new branch of discipline derived from traditional metal cutting. Although people have done a lot of work around stone processing equipment, tools and techniques for many years, but the history of stone processing is not long, the related mechanism research work is still significantly behind the production application, coupled with fierce competition in the stone market, some Most of the valuable research results are regarded as trade secrets and there is very little open communication. Therefore, whether in foreign countries or at home, the new branch of stone processing has not yet formed a theoretical support system that effectively guides the actual production. In fact, regardless of the type of granite stone, they can be regarded as a non-homogeneous anisotropic hard brittle natural composite. When the actual cutting of granite stone is possible, the following three conditions are possible: the interference depth of the abrasive grain relative to the stone is too small, and the corresponding interference force is not enough to cause the cleavage and destruction of the stone, and between the abrasive grain and the stone Intense squeezing and ploughing, the material removed at this time is mostly powdery. The sawing in this state not only has a very low material removal rate, but also because the sawing ratio is high, the temperature rise is obvious, and the abrasive wear is extremely serious, so the life of the saw blade is extremely low; the interference of the abrasive grains with respect to the stone is deep Large, the interference between the abrasive particles and the stone is too large. In this state, the sawing can obtain a high material removal rate, but at the same time, the abrasive grains will be broken and peeled off prematurely due to the overload work. The life is also very low; there is a reasonable and appropriate interference depth between the abrasive grains and the stone and the corresponding interference force. In this state, the sawing can not only obtain a very high removal rate due to the ideal cleavage of the stone. And because the cleavage-based sawing process is easy and smooth, the saw blade itself can also achieve the highest life.

    The research on the mechanism of sawing processing has been gradually developed from the early use of the single-granular upper surface topography method to the comprehensive use of polarized light microscopy and scanning electron microscopy to observe the mineral composition and scratch morphology, and the acoustic state is used to evaluate the cutting state. In recent years, this has intensified the study of the influence of rock mineral characteristics on various phenomena of sawing engineering such as sawing force, tool wear and sawing process.  

(4) Research on the matrix  

The saw blade cuts the stone at a high speed. The line speed of cutting granite is usually 25-40 m/s, and the cutting marble is 45-60 m/s. The substrate with a certain vibration frequency increases the vibration frequency during the cutting process. When the additional frequency and the natural frequency coincide, resonance occurs, which requires the matrix to have a high elastic limit and a yield ratio. Secondly, due to the unevenness of the body, Or the saw blade is not properly installed, and side pressure is generated during cutting to repeatedly bend the base body, resulting in a decrease in the rigidity of the base body or fatigue strength. Therefore, the matrix should also have high stiffness and fatigue strength; in addition, the saw blade should withstand the cyclic cutting pressure and impact force during the cutting process. Therefore, the base body also has high tensile strength and certain impact toughness. degree.  

The chemical composition and heat treatment state of the steel determine the mechanical properties and service life of the product. For products requiring high mechanical properties with a saw blade base, it is usually made of carbon steel or alloy steel with high carbon content, and is quenched and moderately tempered to ensure the tempered tortoplast structure meeting the performance requirements. . The carbon content of the steel has a great influence on the mechanical properties of the product. When the carbon content is low, properties such as tensile strength, elastic limit, and fatigue strength are lowered. On the contrary, the brittleness increases. The type and content of alloying elements also have a great influence on the mechanical properties and process properties of the products. Through research and practical exploration, it is known that the material suitable for manufacturing the saw blade substrate is silicon manganese steel.  

Heat treatment specifications are one of the key factors in determining the mechanical properties and service life of a saw blade substrate. The medium-frequency induction heating austempering process effectively solves the problem of salt bath quenching of the 65Mn steel diamond saw blade [13]. In addition, stress relief annealing and stabilization treatment are also processes that cannot be ignored in the matrix manufacturing process [11].  

4. Development of diamond saw blades  

With the development of technology, the family of diamond saw blades is getting larger and larger, and new saw blades are constantly being applied to production.  

(1) Noise saw blade  

When the diamond saw blade is used to cut hard and brittle materials, the matrix generates severe vibration due to mutual friction and impact with the workpiece, and the noise intensity reaches 100-110 dB, which greatly exceeds 80-85 dB required by national noise hygiene standards. In order to reduce noise, low-noise saw blades have been sold very early in foreign markets, while China is in its infancy. The development of low-noise saw blades generally follows two approaches: one is to change the structure of the substrate, the laser is used to machine a specific groove on the substrate, and the groove is filled with damping material; the other is to divide the substrate into three layers, the middle The layer is made of a damping material. According to reports, one of the world's largest diamond tool manufacturers, Finland's LevabtoOy company's low-noise saw blade has recently begun to supply Addtek GroupCo, the world's largest concrete parts manufacturer. LevabtoOy's low-noise saw blade uses a German base with a laser-machined ring groove on the base and a damping material in the ring groove. Its cutter head is designed in the form of a sandwich. After testing, the noise intensity can be reduced from 100dB to 81~83dB.  

(2) Composite base diamond saw blade  

The composite-based diamond saw blade adopts the low-temperature electrodeposited alloy carcass and the diamond inlay process, which effectively solves the problem that the mechanical properties of the carcass are poor and the holding power of the diamond is weak. The mechanical properties of the carcass prepared by the technical process are equivalent to the carcass prepared by metallurgical method, have excellent bending strength and can adjust the formula composition according to various stone characteristics, so as to have suitable hardness and toughness, suitable for diamond. Inlaid fixed.

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