Knife material
Choose the tooling material according to the design brief, considering factors such as processing volume and cost. For solid cutters, alloy tool steel or high speed steel can be selected for small batches, for large batches, the tooth part can be selected from carbide, and for the cutter body, No. 45 steel, which can be used to make a welded tooth structure.
Woodworking tools are characterized by the need to maintain sharpness of cut for a long time in conditions of high-speed and impact cutting. The material of woodworking tools must have the necessary hardness and wear resistance, sufficient strength and toughness, a certain manufacturability (for example, productivity in welding, heat treatment, cutting and grinding, etc.).
Carbon tool steel (carbon structural steel) refers to high quality high carbon steel with a carbon content of 0.65% to 1.35%. According to the content of S and P in steel, it can be divided into high-carbon steel. quality steel and advanced high quality steel. High quality steel is used to make hand tools with light load and low cutting speed, and high quality high quality steel is used to make machine tools. Carbon steel has the advantages of low price, sharp edge, good thermoplasticity and good cutting performance. The temperature at which the cutting ability is maintained is below 300 ° C, and the normal temperature hardness after quenching is HRC 60-64. The disadvantages of this type of steel are high thermal denaturation, poor hardenability, low thermal hardness.
10.1.2 Alloy tool steel (alloy steel)
Cr, W, Ni, V, Co, Mo, Si, Mn and other alloying elements are added to tool steel to obtain alloy tool steel such as 9CrSi, CrVIMn and so on. In recent years, instead of alloy tool steel, GCr15 bearing steel, etc. can also be used.
Alloy tool steel for woodworking tools, alloy content range: Cr<1%, W=1%-2%, Ni=1%-1.5%, V<0.3%.
HSS
When the content of w, Cr, V, Mo, etc. in alloy steel increases, the steel becomes high speed, also known as face steel. By mass, high speed steel contains about Cr4%, W and Mo1.0%-2.0%, V1% or more. The role of W and Mo in high speed steel is basically the same. the content of alloying elements in steel, part of w and Fe, Cr together form high hardness carbides, and part of W is dissolved in the matrix. At a quenching temperature close to the melting temperature, a fine-grained and highly alloyed martensitic structure is obtained. Therefore, its thermal hardness and wear resistance are higher than those of carbon tool steel and alloy tool steel. The hardness after quenching is HRC62-70, and the cutter retention temperature can reach 540-600°C.
In order to improve the performance of high speed steel, foreign countries mainly increase the content of Co and C. My country's diamond resources are relatively poor. In order to save expensive diamond resources, the method of adding Al and C, that is, adding 1% Al based on W6Mo5 Cr4V2, is adopted, and increase C from 0.8%-0.9% to 1.05-1.2%. Cheng 501 steel, its high temperature hardness, bending strength and toughness are equivalent to M42, and the price is cheap (the price is about 20% of the price diamond high speed steel).
Carbide
Carbide is a powder metallurgy product made from extremely hard and refractory metal carbides (wC, Tic) sintered with Co, Mo, Ni, etc.speaking. Its performance mainly depends on the type, performance, quantity, particle size and amount of metal carbide binder. The hardness of the cemented carbide is HRC74-81.5, and its hardness decreases with increasing binder content. The content of heat-resistant carbides in the hard alloy exceeds that in high-speed steel, so it has good thermoplasticity and can withstand cutting temperatures up to 800-1000°C. At 600°C it exceeds the normal temperature hardness of high speed steel, and at 1000°C it exceeds the normal temperature hardness of carbon steel.
With the development of automation in the woodworking and woodworking industry, cemented carbide, a material with high wear resistance, has become the main material for woodworking tools.
However, cemented carbide is a brittle material, its bending strength is 1/2 to 1/4 that of conventional high speed steel, and its toughness is 1/4 to 1/30 that of conventional high speed steel. - high speed steel, and the blade cannot be sharpened as sharp as high speed steel.
Cubic boron nitride (CBN)
Cubic boron nitride is a new type of superhard material that is only harder than diamond. The disadvantage of cubic boron nitride is that its bending strength is lower than that of conventional hard alloys, high cost, poor welding performance, and easy chipping. It is still in the experimental stage and its characteristics are yet to be explored.
Diamond
The diamond used in the industry to make knives is actually a type of man-made polycrystalline diamond (polycrystalline diamond called PCd). It does not change with direction, the material is stable, and the cutting ability can be predicted. Although the hardness is less than that of natural diamond, its strength and toughness are better than natural diamond, and it is not easy to be broken and damaged, so the service life is longer .
The PCD blade is a composite sintered body formed by sintering diamond particles (surface layer) of a certain size and cemented carbide (substrate liner) at high temperature and high pressure. Polycrystalline diamond composite blades are mainly used for cutting products such as laminate flooring, solid wood multi-layer composite flooring, bamboo flooring and solid wood doors.
The smart choice of materials for woodworking tools
In order to save precious metal materials and economic feasibility, the cutting part and the body of the cutting tool of a conventional tool can be made of different materials and combined by welding or mechanical clamping.
The above factors must be taken into account in the judicious choice of materials for cutting tools. Obviously, they are not isolated from each other, but are connected or even mutually limit each other. For example, the hardness and thermal hardness of the tool material are adequate, but poor toughness or large heat treatment deformations may not necessarily be used in woodworking tools. For this reason, with a particular choice of tool materials, you can focus on fulfilling the basic requirements, and other aspects can be ignored as long as they have little effect.
Woodworking machine knives, blades used in the processing of wood-based panels, as well as blades for band and circular saws are also widely made from alloyed tool steel. This is due to the fact that the addition of alloying elements w, Mn, Mo, Cr, V, Si, Ni, Co, etc. to the alloyed tool steel affects the phase transformation process of the steel, increasing the hardenability, wear resistance, toughness, etc. e. Steel performance improved.
Tungsten (w) mainly increases the hardness of steel, improves hardenability without reducing ductility, manganese (Mn) can improve the hardness and hardenability of steel, eliminate sulfur in steel, but reduce the toughness of steel; molybdenum (Mo) can improve the ductility, hardenability and hardness of steel; chromium (Cr) can improve the hardenability of steel and the wear resistance of high carbon steel; vanadium(V) can improve the hardness, ductility and hardenability of steel. the steel structure is thinner and reduces thermal sensitivity; silicon (Si) can improve the elasticity of steel, improve hardenability, but reduce the ductility of steel, nickel (Ni) can improve toughness, and ductility improves corrosion resistance, but the hardness of steel is slightly reduced; drill (Go) can improve the wear resistance of steel, but reduce the hardenability.
When choosing a carbide for woodworking tools, you should pay attention to the following points:
(1) Woodworking knives must use YG carbide with high strength.
(2) In YG grade, there are large particles, small particles and ordinary particles. With the same composition, the strength of the alloy with large particles is high, but the hardness and wear resistance are slightly reduced. Fine-grained alloys can increase hardness and increase wear resistance without a significant reduction in strength.
(3) The carbide is brittle, and can only be used for woodworking after a reasonable choice of the wedge angle according to the grade, workpiece material, feed rate and other cutting conditions.
(4) After selecting the right grade of cemented carbide, it is necessary to intelligently select the model of cemented carbide products.
Improve the wear resistance technology of woodworking tools
1 surface heat treatment
Different metallographic structures have different wear resistance. Appropriate surface heat treatment methods can transform the metal structure, improve the surface hardness of the tool, and enhance the wear resistance. Common surface heat treatment methods include: ① laser hardening, ② high frequency hardening, ③ electrical contact hardening.
2 layer infiltration technology
Infiltration layer technology is a chemical-thermal treatment method to change the chemical composition of the tool surface and improve the wear and corrosion resistance of the tool. Boriding is the penetration of boron into the surface of the tool to give it high hardness. and chemical stability Good protective layer.
3 coating technologies
Electroplating is a traditional method of protecting materials. It has high adaptability and is not limited by the size and batch of workpieces. It can be electroplated on iron, non-ferrous metals, powder metallurgy, plastics and graphite parts. substrates. .
4 Thermal Spray Technologies
Thermal spray technology uses gas, liquid fuel or electric arc, plasma arc, etc. as a heat source to heat spray materials such as metals, alloys, cermets, oxides, carbides, etc. Spray method, spraying and applying to the surface of a pre-treated workpiece with the formation of a strongly adherent surface layer.
5 Coating technology
Apply a thin layer (5-12µm) of a highly wear-resistant refractory metal (or non-metal) to the tool base to improve tool life, corrosion resistance, and high temperature oxidation resistance.
6 Plasma enhanced chemical vapor deposition technology:
In a vacuum furnace with a certain pressure and temperature, the correspondingthe proportion of the working gas H2, N2, Ar2, TiCl" and under the action of high voltage, a thin gas glow discharge is generated to form a plasma physical field. Among them, electrons with high kinetic energy will activate the atoms of the cold coating material to form active Ti+, N2+ ions or free radicals and form a hard TiN coating on the surface of the base material at a temperature of about 500 °C.
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