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Cutting tool
A cutting tool is a tool used in machining. Most of the cutting tools are machine tools, but some are hand tools. According to the "China cemented carbide industry market outlook and investment strategic planning analysis report outlook" analysis believes that at present, China's cutting tool manufacturing industry opportunities and challenges coexist, but overall, the industry development of favorable factors occupy the dominant position. Combined with the domestic and foreign economic development and the development of China's cutting tool industry, it is expected that during the "12th Five-Year plan" period, China's cutting tool industry will maintain an annual growth rate of more than 25%. It is expected that by 2015, the sales revenue of the industry is expected to break through 140 billion yuan. Cemented carbide demand in the cutting tool field has a good prospect.
define
A cutting tool is a tool used in machining. Most of the cutting tools are machine tools, but some are hand tools. The word "tool" is generally understood to mean a metal cutting tool, since the tools used in mechanical manufacturing are generally used to cut metal materials. The tools used to cut wood are called woodworking tools.
The development of
According to the "China cemented carbide Industry Market Outlook and Investment Strategic Planning Analysis Report" [1], it is believed that at present, Opportunities and challenges coexist in China's cutting tool manufacturing industry, but generally speaking, favorable factors for the industry development occupy a dominant position. Combined with the domestic and foreign economic development and the development of China's cutting tool industry, it is expected that during the "12th Five-Year plan" period, China's cutting tool industry will maintain an annual growth rate of more than 25%. It is expected that by 2015, the sales revenue of the industry is expected to break through 140 billion yuan. Cemented carbide demand in the cutting tool field has a good prospect.
Tool material
Tools must be made of materials with high temperature hardness and wear resistance, necessary flexural strength, impact toughness and chemical inertness, good manufacturability (cutting, forging, heat treatment, etc.), and not easily deformed.
Usually when the material hardness is high, wear resistance is also high; When the bending strength is high, the impact toughness is also high. However, the higher the hardness of the material, the lower its bending strength and impact toughness. Due to its high bending strength and impact toughness, as well as good machinability, high-speed steel is still the most widely used tool material, followed by cemented carbide.
Polycrystalline cubic boron nitride is suitable for cutting high hardness hardened steel and cast iron etc. Polycrystalline diamond is suitable for cutting non-ferrous metals, alloys, plastics and fiberglass etc. Carbon tool steel and alloy tool steel are now used only for files, dies and taps.
Carbide indexable blades are now coated with hard or composite layers of titanium carbide, titanium nitride, alumina and titanium carbide inserts. Physical vapor deposition is being developed not only for carbide tools, but also for high speed steel tools, such as drills, hobs, taps and milling cutters. As a barrier to chemical diffusion and heat conduction, the hard coating slows down the wear rate of the cutting tool, and the life of the coated blade is about 1 ~ 3 times longer than that of the uncoated one.
Due to the high temperature, high pressure, high speed, and in the corrosive fluid medium of the parts, the application of more and more difficult to process materials, cutting automation level and the requirement of machining accuracy is more and more high. In order to adapt to this situation, the tool development direction will be the development and application of new tool materials; To further develop the technology of tool vapor deposition coating, to deposit higher hardness coating on high toughness and high strength matrix, to better solve the contradiction between hardness and strength of tool material; Further develop the structure of the indexable tool; Improve the precision of cutting tools, reduce the difference of product quality, and make the use of cutting tools to achieve the best.
Tool materials can be divided into the following categories: high speed steel, hard alloy, cermet, ceramics, polycrystalline cubic boron nitride and polycrystalline diamond.
Cause of wear
First, abrasive wear
Although the hardness of the chip, the workpiece is lower than the hardness of the tool, but they often contain some of the very hard micro hard point, can be engraved on the tool surface groove, this is abrasive wear. Hard points include carbides (such as Fe3C, TiC, VC), nitides (such as TiN, Si3N4), oxides (such as SiO2, Al2O3) and intermetallic compounds. Ti(N, C) particles in cutting act as ploughs on the tool. In addition to the abrasive wear on the front surface of the knife, grooves caused by abrasive wear can also be found on the back surface of the knife. Abrasive wear exists at all cutting speeds, but for low speed cutting tools (such as broach, grinding teeth, etc.), abrasive wear is the main cause of wear. This is due to low speed cutting, cutting temperature is relatively low, other causes of wear is not significant, so it is not the main. The hardness and wear resistance of high speed steel tool is lower than that of hard alloy and ceramics, so its abrasive wear accounts for a larger proportion.
Cold welding wear
When cutting, there is a lot of pressure and friction between the chip, the workpiece and the front and rear surface of the knife, so there will be cold welding between them. Due to the relative motion between the friction surfaces, the cold welded joints will break and be taken away by one side, thus causing cold welded wear.
Generally speaking, the hardness of the workpiece material or chip is lower than the hardness of the tool material, and the fracture of the cold welding junction often occurs in the workpiece or chip side. However, due to the alternating capacity, contact fatigue, thermal stress and defects in the surface structure of the tool, the fracture of the cold welding joint may also occur on the tool side, the tool material particles are taken away by the chip or the workpiece, thus causing the tool wear.
Cold welding wear is more serious at medium and low cutting speed. The results show that brittle metals have stronger resistance to cold welding than plastic metals. The cold welding tendency of metals with the same metal or lattice type, lattice spacing, electron density and similar electrochemical properties is small; Metal compounds have less tendency to cold welding than single phase solid melts. Group B elements in the periodic table are less prone to cold welding than iron.
At the normal working speed of high-speed steel tool and low working speed of cemented carbide tool, the condition of cold welding can be satisfied, so the proportion of cold welding wear is relatively large. After increasing the cutting speed, the cold welding wear of carbide tool is reduced.
Diffusion wear
Diffusion wear occurs at high temperatures. When cutting metal, the chips, the workpiece and the tool contact process, the two sides of the chemical elements in the solid state of mutual diffusion, change the original material composition and structure, so that the tool material becomes fragile, thus exacerbating the wear of the tool. For example, when cemented carbide is cutting steel, starting from 800℃, the chemical elements in cemented carbide are rapidly diffused into the chips and workpieces, and WC is decomposed into W and C and then diffused into steel. Because the chips and workpieces are moving at high speed, the surface of the cutting tools and their surfaces maintain the concentration gradient of the diffusing elements in the contact area, so that the diffusion phenomenon continues. As a result, the cemented carbide surface is carbon - and tungsten - poor. The bonding phase CO decreases, and the bonding strength of WC (TiC) in cemented carbide decreases. The Fe in the chip and workpiece diffused into the hard alloy, diffused into the hard alloy Fe, will form a new hardness, high brittleness of the composite carbide. All of these, make tool wear aggravate. In addition to the nature of tool and workpiece material itself, temperature is the most important factor affecting diffusion wear. The diffusion wear is often accompanied by cold welding wear and abrasive wear, and the wear rate is very high. The working temperature of HSS tool is low, and the diffusion action between the chip and the workpiece is slow, so the proportion of diffusion wear is far less than that of cemented carbide tool.
Oxidation wear
When the cutting temperature reaches 700 ~ 800℃, oxygen in the air will oxidized with cobalt, tungsten carbide, titanium carbide, etc., and produce soft oxides (such as Co3O4, CoO, WO3, TiO2, etc.) which will be wiped off by chips or workpieces and form wear, which is called oxidation wear. The oxidation wear is related to the adhesion strength of the oxide film. The lower the adhesion strength is, the faster the wear will be. The reverse can reduce the wear and tear. Generally, the air is not easy to enter the knife chip contact area, and the oxidation wear is most likely to form at the working boundary of the main and auxiliary knife cutting edge.
5. Thermoelectric wear
Due to the different materials of workpiece, chip and tool, the thermoelectric potential will be generated in the contact area when cutting. This thermoelectric potential has the effect of promoting diffusion and accelerating tool wear. This diffused wear under the action of thermoelectric potential is called "thermoelectric wear". It is proved that the thermoelectric wear can be reduced if the electromotive force contrary to the thermoelectric force is applied at the contact of workpiece and tool.
In conclusion, the cause and strength of wear are different in different workpiece materials, tool materials and cutting conditions. For a given tool and workpiece material, cutting temperature has a decisive influence on tool wear. The height of the cutting temperature depends on the heat generation and outgoing situation, it is affected by the cutting dosage, workpiece material, tool material and a few. Therefore, through the reasonable choice of cutting parameters, cutting tool material and Angle, can reduce the production of cutting heat and increase the heat out. It is an important way to reduce tool wear to reduce cutting zone temperature effectively.
Trends in cutting tool development
According to the needs of the development of manufacturing industry, multifunctional composite tools, high speed and high efficiency tools will become the mainstream of tool development. In the face of the increasing number of difficult-to-process materials, the tool industry must improve tool materials, develop new tool materials and more reasonable tool structure.
■ Increased application of cemented carbide materials and coatings. Fine grain and superfine grain cemented carbide materials are the development direction. Nano coating, gradient structure coating, new structure coating and material coating will greatly improve the tool performance; The application of physical coating (PVD) continues to increase.
■ New cutting tool materials are more widely used. The toughness of ceramic, cermet, silicon nitride ceramics, PCBN, PCD and other cutting tool materials is further enhanced, and the application occasions are increasing day by day.
Cutting technology develops rapidly. High speed cutting, hard cutting and dry cutting continue to develop rapidly, the application range is expanding rapidly.
classification
The cutter can be divided into five categories according to the form of the workpiece surface:
■ Processing all kinds of external tools, including turning tool, planer tool, milling cutter, external surface broach and file;
■ Hole cutting tools, including drills, reaming drills, boring tools, reamer and inner surface broach, etc.;
■ Threaded cutting tools, including taps, die, automatic opening and closing thread cutting head, thread turning tool and thread milling cutter;
■ Gear cutting tools, including hob, gear shaver, bevel gear cutting tools, etc.
■ Cutting tools, including insert circular saw blade, band saw, bow saw, cutting tool and saw blade milling cutter, etc.
In addition, there are combination knives.
According to the cutting motion mode and the corresponding blade shape, cutting tools can be divided into three categories:
■ General purpose tools, such as turning tools, plane knives, milling cutters (excluding forming turning tools, forming plane knives and forming milling cutters), boring tools, drills, reaming drills, reamer and saws, etc.;
■ Forming tools, whose blades have the same or close to the same shape as the section of the workpiece to be processed, such as forming turning tool, forming plane tool, forming milling cutter, broach, taper reamer and various thread machining tools;
■ Developing cutting tools are used to process the tooth surfaces of gears or similar workpieces, such as hob, gear shaper, bevel gear planer and bevel gear milling cutters.
Tool structure
The structure of all kinds of cutting tools is composed of clamping part and working part. The clamping part and working part of the whole structure tool are done on the cutter body. The working part of the insert structure cutter (cutter tooth or blade) is mounted on the cutter body.
The clamping part of the cutter has a hole and a handle. The holed cutter is arranged on the spindle or mandrel of the machine tool by means of the inner hole, and the torsional moment is transferred by means of the axial key or end key, such as cylindrical milling cutter, sleeve type face milling cutter, etc.
Tools with a handle usually have three kinds: rectangular handle, cylindrical handle and conical handle. Turning tools, plane knives, etc. are generally rectangular handle; The taper shank bears axial thrust and transmits torque by means of friction. Cylindrical shank is generally suitable for smaller twist drill, end milling cutter, etc., during cutting, the torque is transferred by means of the friction force generated during clamping. Many tools with a handle are made of low alloy steel at the handle, while the working part is welded together with high speed steel.
The working part of a tool is the part that produces and treats the chips, including the blade, the structure that breaks or wraps the chips, the space for chip removal or storage, the channel for cutting fluid and other structural elements. Some of the working part of the tool is the cutting part, such as turning tool, planer, boring and milling cutter; The working part of some tools includes cutting part and calibration part, such as drill bit, reamer, inner surface broach and tap. The role of the cutting part is to cut the chip with the edge, and the role of the calibration part is to smooth the machined surface and guide the tool.
The cutter working part has three kinds of structure: integral type, welding type and mechanical clamping type:
■ The overall structure is to make cutting edges on the cutter body;
■ The welding structure is to braze the blade to the steel body;
■ There are two kinds of mechanical clamping structure, one is to clamp the blade on the tool body, the other is to clamp the brazed tool head on the tool body.
The carbide tool is generally made of welded or mechanically clamped structure. Ceramic tools are mechanically clamped.
The geometric parameters of cutting tool have great influence on cutting efficiency and machining quality. By increasing the front Angle, the plastic deformation of the front cutting surface when it squeezes the cutting layer can be reduced, and the frictional resistance of the chip flowing through the front can be reduced, thus reducing the cutting force and cutting heat. However, increasing the front Angle will reduce the strength of cutting edge and reduce the heat dissipation volume of the cutting head.
In the choice of tool Angle, need to consider the impact of a variety of factors, such as workpiece material, tool material, processing properties (rough, finishing), etc., must be selected according to the specific circumstances. Generally speaking, the tool Angle, refers to the manufacturing and measurement of the marking Angle in the actual work, due to the different installation position of the tool and the change in the direction of cutting motion, the actual work of the marking Angle and the Angle is different, but usually the difference is very small.
Current situation of precision hardware processing and manufacturing industry
Metal cutting, grinding, punching and shearing, stamping, drawing, cleaning, rust prevention and other applications
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