Machining is one of the most basic, widest and most important processes in the wood industry, directly affecting production efficiency, processing costs and energy consumption. With the advancement of the wood industry technology, various wood composite materials, plywood, wood, bamboo glulam, especially melamine impregnated paper plywood, PVC plywood, Al 2 O 3 reinforced plywood and other materials are increasingly used. For furniture, flooring, roofing panels and engineered wooden pieces. These materials are difficult to cut, simple cutting operations, conventional tool construction, and common tool materials are difficult or impossible to achieve. In addition, with the development of the wood industry technology, artificial board production equipment, manufacturing equipment, furniture manufacturing equipment, etc. are moving in the direction of high degree of automation, full functionality, fast feed, and high production efficiency. Both advances in technology have promoted the development of cutting tool materials and manufacturing technology. Whether the cutter can perform normal cutting, the cutting quality is good or bad, and the degree of durability is closely related to the material of the cutter cutting part. The various physical phenomena in the cutting process, especially the wear of the tool and the nature of the tool material, are of great relevance. With the machine tool allowed, the productivity of the tool depends essentially on the cutting performance that the material itself can perform. The requirements for woodworking tools are to maintain the sharpness of the cutting tool for a long time under high speed and impact conditions. For this reason, the material of the woodworking tool must have the necessary hardness and wear resistance, sufficient strength and toughness, and a certain degree of workmanship (such as welding, heat treatment, cutting and grinding).
1. Carbide tool material
Cemented carbide is a powder metallurgy product made of a highly rigid, refractory metal carbide (WC, TiC) sintered with Co, Ni, etc. as a binder. Its performance mainly depends on the type, performance, quantity, particle size and binder amount of the metal carbide. The hardness of the hard alloy is HRC74~81.5, and its hardness decreases as the binder
content increases. The content of high-temperature carbide in cemented carbide exceeds that of high-speed steel, so it has good thermoplasticity and can withstand cutting temperatures of up to 800-1000°C. The room-temperature hardness of high-speed steel is exceeded at 600°C, and exceeds the room-temperature hardness of carbon steel at 1000°C. The cutting tools for wood and wood composites mainly use YG cemented carbides with metal cobalt (Co) as the binder and tungsten carbide (WC) as the hard phase. Although various new types of cutting tool materials have emerged in recent years, with the development of automation in the wood-based panel industry and the wood processing industry, hard-aluminum alloys, which are highly wear-resistant materials, have become the main woodworking tool materials, and will be for a long time to come. The inside will still occupy an important position in the wood cutting tool material. Since cemented carbide is a brittle material, its bending strength is about 1/4 to 1/2 that of ordinary high-speed steel, impact toughness is about 1/30 to 1/4 of ordinary high-speed steel, and the cutting edge cannot be polished like high-speed steel. As sharp as that, it is necessary to research and develop new material preparation techniques to further improve and improve the cutting performance of carbide cutting tool materials.
2 Carbide cutting tool materials research and application status
As the wear resistance and toughness of carbide cutting tool materials are not easily taken into account, users can only select suitable tool materials among many carbide grades based on specific machining objects and processing conditions. This brings inconvenience to the selection and management of cemented carbide tools. In order to further improve the comprehensive cutting performance of carbide cutting tool materials, the current research hotspots mainly focus on the following aspects.
2.1 Grain Refinement
By refining the grain size of the hard phase, increasing the surface area between the grains, and enhancing the bonding force between the grains, the strength and wear resistance of the carbide cutting tool material can be improved. When the grain size of WC is reduced below the submicron scale, the hardness, toughness, strength, and wear resistance of the material can be increased, and the temperature required for full densification can also be reduced. The grain size of ordinary cemented carbide is about 3~5μm, the grain size of fine grained cemented carbide is 1~1.5μm, and the grain size of ultrafine grained cemented carbide can reach 0.5μm or less. Compared with ordinary hard alloys with the same composition, ultrafine grained carbides can increase the hardness by more than 2HRA, and the bending strength can be increased by 600~800MPa. Ultrafine grained carbide has been increasingly used.
2.2 Surface, Overall Heat Treatment and Cyclic Heat Treatment
The treatment of nitriding, boronizing, etc. on the surface of hard alloy with good toughness can effectively improve the surface wear resistance. The overall heat treatment of hard alloys with good wear resistance but poor toughness can change the composition and structure of the binder phase in the material and reduce the adjacency of the WC hard phase, thereby improving the strength and toughness of the hard alloy. The use of a cyclic heat treatment process to relieve or eliminate the stress between the grain boundaries can comprehensively improve the overall performance of the hard alloy material.
2.3 Add rare metals
The addition of TaC, NbC, and other rare metal carbides to cemented carbide materials allows the additives to combine with the existing hard phase WC to form a complex solid solution structure, which further strengthens the hard phase structure and also suppresses the hard phase. Grain growth, enhance the uniformity of the organization and other effects, will greatly improve the overall performance of cemented carbide. This type of cemented carbide with Ta(Nb)C added to the ISO standard P, K, and M carbide grades.
2.4 Add rare earth elements
Adding a small amount of rare earth elements such as tantalum in the cemented carbide material can effectively improve the toughness and bending strength of the material, and the wear resistance is also improved. This is because the rare earth element can strengthen the hard phase and the binder phase, purify the grain boundary, and improve the wettability of the carbide solid solution to the binder phase. Carbide alloys containing rare earth elements are most suitable for rough machining, and are particularly suitable for the cutting and processing of wood and wood composite materials. China’s rare earth resources are abundant, and such carbide cutting tools will have broad application prospects. At present, carbide cutting tool materials are developing in two directions. On the one hand, the applicable surface of general-purpose brands is getting wider and wider, and the versatility is becoming stronger; on the other hand, special-purpose brands are increasingly targeted and more adaptable. The nature of the material being processed and the cutting conditions, so as to achieve the purpose of improving the cutting efficiency.
3. Coated carbide
On a tough, tough carbide substrate, a layer can be applied by CVD (Chemical Vapor Deposition), PVD (Physical Vapor Deposition), PVCD (Plasma Enhanced Chemical Vapor Deposition), HVOF (High Speed Thermal Coating), etc. Very thin wear-resistant metal compounds such as TiN, TiC and other materials. High TiC hardness (HV3200), good wear resistance, so the coating thickness is generally 5 ~ 7μm. The low TiN hardness (HV1800~2100) has a low binding force to the substrate, but it has good thermal conductivity and high toughness. The coating thickness can reach 8~12μm, and the toughness of the substrate can be combined with the wear resistance of the coating. In order to improve the overall performance of carbide cutting tools. The coated carbide cutting tool has good wear resistance and heat resistance, and is particularly suitable for high-speed cutting. Due to its high durability and versatility, it can be used to reduce the number of tool changes when it is used in small batches and varieties of flexible automatic processing. Times, improve processing efficiency.
The coated cemented carbide tools have strong anti-crater wear ability, stable blade shape and groove shape, chip breaking effect and other cutting performance, which are conducive to the automatic control of the processing process. After the passivation and refinement of the substrate of the coated cemented carbide cutting tool, the dimensional accuracy is high, which can meet the requirements of automatic machining to the positioning accuracy of tool change. The above characteristics determine that coated cemented carbide tools are particularly suitable for automated processing equipment such as FMS (Flexible Manufacturing System), CIMS (Computer Integrated Manufacturing System). However, the use of coating methods still fails to fundamentally solve the problem of poor toughness and impact resistance of cemented carbide matrix materials. It was found that when the TiN-coated carbide saw blades were used to saw the teeth, the wear performance of the rake face of the saw teeth was improved.
The PVD-coated woodworking saw cutting test proves that when the TiN-coated WC hard alloy saw blade (pre-coating tooth surface) saws the hard fiberboard, the amount of saw tooth wear is reduced. However, the higher temperature of the CVD coating results in the formation of a brittle binder phase between the substrate and the coating.
The coating on the cutting edge quickly peels off under the influence of residual stress of the coating, cutting heat and cutting force. Compared with the CVD method, PVD coating temperature is low, therefore, the PVD coating tool can obtain a better coating structure and high coating hardness, tool edge sharpness has also been improved. In addition, PVD coated tools have better crack resistance. After the mid-1990s, researchers conducted research on carbide-size, binder content, and coating materials for PVD-coated carbide woodworking tools.
The carbide particle size was 0.8, 1.2, 1.5, and 1.7 μm, respectively. The corresponding cobalt contents were 3%, 4%, 6%, and 10%, respectively; the coating materials were TiN, TiN-Ti (C,N)-TiN, respectively. The thickness of the coating corresponding to TiAlN 2 is 3.5 μm, 5.5 μm and 3 μm, respectively, which are applied to the rake face of the tool. The results showed that the coating peeled off in all three coating materials, but TiN and Ti (N, C, N) were much lighter than TiAlN 2 , and the wear resistance of the tool with fine particles and low cobalt content increased by 10%. ~30%, but the high cobalt content of the tool coating reduces the wear resistance. The study also pointed out that low coating adhesion is the main reason for coating spalling. 2 times longer tool life under cutting conditions. In the coating, the surface finish of the coating is improved by the grain refinement technology, so that the coating surface is smooth, so as to improve the ability of the coated tool to resist friction and resist adhesion is also a development direction of the coating technology. Toughness and wear resistance, the outer surface of a layer of titanium compounds, the coating surface is smooth, flank surface is ultra-smooth coating to ensure the stability of the tool wear. Diamond has extremely high hardness and excellent chemical stability. Its wear resistance is 100 to 250 times that of cemented carbide. It also has the ability to resist strong acids and alkalis, but its toughness is very poor. If the tougher tool material is used as the substrate, apply a layer of high hardness, wear resistance and chemical inertness, so that the tool not only has a certain strength and toughness, but also has good wear resistance and cutting. Performance, to meet the characteristics of woodworking tool wear, diamond coating is an ideal means of anti-wear.
In the 1950s, while high-temperature and high-pressure synthetic diamonds were being developed, low-pressure gas-phase synthetic diamonds were also explored, but the deposition rate was slow. Low-pressure gas-phase synthetic diamonds were produced in the metastable zone of diamond and the stable phase of graphite phase. Graphite and amorphous carbon are easily precipitated. Therefore, inhibiting the formation and removal of graphite and amorphous carbon is the key to vapor-deposited diamond films. In the late 1980s, in order to reduce costs and achieve industrial production, high-speed deposition methods such as DC plasma jets have become the fastest growing method for diamond film deposition. Cutting experiments on particleboards using CVD diamond film coated carbide inserts with a rake face (coating thickness of 20 μm) showed that the spalling of the coating was a fatal drawback. As long as the coating does not peel off, the wear of the tool hardly changes and is maintained at 40 to 50 μm. Milling tests on MDF with diamond-coated carbide indexing inserts showed that the diamond films had different degrees of peeling, but the unpeeled film played a “bank” protection and reduced the wear of the matrix material, thus the tool The wear resistance has increased nearly 1 times. With the improvement of the coating process and equipment, the bonding force between the diamond film and the substrate is further increased and the film peeling will be controlled. At present, diamond-coated cemented carbide materials have been used to manufacture tools for strengthening the floor, which are used to cut the Al 2 O 3 wear-resistant layer on the surface of the reinforced floor. However, the purity of the CVD diamond polycrystalline film is very high, the hardness (HV9000~10000) is close to that of natural diamond, and its machinability is very poor, and it is difficult to process it by conventional machining or electrocorrosion. Therefore, the diamond coated hard alloy material is suitable for manufacturing indexing blades that are not regrind.
After 2000, the performance of diamond CVD coated tools has been further improved. The products cover indexable tools and solid carbide tools.
Carbide cutting tool materials have become the main cutting tool materials in the current wood processing industry, and will occupy an important position in wood cutting and processing for a long period of time in the future. With the continuous improvement of various hard alloy performance improvement technologies and coating technologies, the cutting performance of carbide cutting tool materials will continue to increase, and the wood processing industry will apply various modifications to the cutting characteristics of wood and wood composite materials. The coating technology obtains new materials, and the hard alloy and hard alloy tools are reasonably selected to maximize the cutting performance, product quality, and production efficiency of carbide cutting tools.