Cutting tool materials
With the continuous progress of global machining level, the manufacturing technology of cutting tools is also developing gradually. In terms of cutting tool materials, modern metal cutting tool materials have developed from carbon tool steel and high-speed steel to superhard tool materials such as cemented carbide and cubic boron nitride today, which makes the cutting speed soar from a few meters per minute to a kilometer or even ten thousand meters. With the continuous development of CNC machine tools and difficult-to-machine materials, cutting tools are really difficult to cope with. To realize high-speed cutting, dry cutting and hard cutting, it is necessary to have good tool materials. Among many factors affecting the development of metal cutting, tool material plays a decisive role.
1. High-speed steel
High-speed steel was introduced from 19 to 2. Although various superhard materials emerged continuously, it still failed to shake its dominant position in cutting tools. After 2, cemented carbide has become the "natural enemy" of high-speed steel, which is constantly eroding the market share of high-speed steel tools. However, for some tools that require high toughness, such as thread tools and broaching tools, high-speed steel can still compete with cemented carbide.
It is customary to divide high-speed steel into four categories:
1) General-purpose high-speed steel (HSS)
HSS, represented by W18Cr4V, has been brilliant for a century and made outstanding historical contributions to China's tool industry, but it has gradually faded out of the market due to many disadvantages; 9341 is a self-developed HSS in China, with a market share of about 2%. The output of other HSS such as W7 and M7 is relatively low. HSS has accounted for more than 6% of the total high-speed steel. Due to HSS's excellent properties such as toughness, high wear resistance and red hardness, it will firmly hold a site in the field of tools such as taps and broaches, but the position is decreasing year by year.
2) High-performance high-speed steel (HSS-E)
HSS-E refers to the steel with alloy elements such as Co and Al added on the basis of HSS composition, and the carbon content is appropriately increased to improve the heat resistance and wear resistance. The red hardness of this kind of steel is relatively high, and the hardness remains above 6HRC after 625℃×4h, and the durability of the tool is 1.5~3 times that of HSS tool.
the output of HSS-E, represented by M35 and M42, is increasing year by year. 51 is a high-performance high-speed steel made in China, which is widely used in form milling cutter, end milling cutter and other aspects, and it is also successful in complex cutting tools. Due to the rapid development of CNC machine tools, machining centers and high-difficult-to-machine materials, HSS-E tool materials are gradually increasing.
3) Powder high-speed steel (HSS-PM)
Compared with smelting high-speed steel, the mechanical properties of HSS-PM have been significantly improved. Under the same hardness, the strength of the latter is 2%~3% higher than that of the former, and the toughness is 1.5~2 times higher, so it is widely used abroad. In the 197s, China developed various brands of HSS-PM and put it into the market, but somehow it died, and all the materials used in various tool factories were imported. It is gratifying that Heye Technology Co., Ltd. (formerly Hebei Metallurgical Research Institute) has been able to produce HSS-PM and supply it in small quantities, with good results. Due to the depletion of resources, the excellent comprehensive performance of HSS-PM and the market demand, HSS-PM is bound to make a great progress.
4) Low-alloy high-speed steel (DH)
Due to the shortage of alloy resources, the export of complete sets of twist drills and the need of low-speed cutting tools, steel mills and tool factories have jointly developed DH of 31, F25, D11 and other brands. In 23, China produced 6, tons of high-speed steel, including 2, tons of DH, accounting for 1/3 of high-speed steel. In 24, DH accounted for 4% of high-speed steel, and it was still increasing in 25 and 26. However, some of them are not high-speed steel at all, and their hardness can't reach 63HRC. They are also labeled as HSS.
2, and cemented carbide
machinery manufacturing industry needs "high precision, high efficiency, high reliability and specialization". In the field of contemporary tool manufacturing and use, the concept of "efficiency first" has replaced the traditional concept of "performance-price ratio", which is a high-tech change.
cemented carbide not only has high wear resistance, but also has high toughness (compared with superhard materials), so it is widely used. Looking forward to the future, it is still the most widely used tool material. It can be seen from previous machine tool fairs that cemented carbide rotary cutter covers almost all kinds of tools. With the development of science and technology and the progress of cutting tool technology, the properties of cemented carbide have been greatly improved: first, fine cemented carbide with 1~2μm particles to improve toughness has been developed; The second is to develop coated cemented carbide. Compared with high-speed steel tools, the market share of cemented carbide coated tools has increased more, because high strength is more important under high temperature and high speed cutting parameters.
in modern cutting tools, cemented carbide shows its great power. Looking forward to the future, the tool material is undoubtedly the world of cemented carbide.
3. superhard tool materials
superhard materials refer to substances with high hardness represented by diamond. Although there is no strict regulation on the category of superhard materials, people are used to calling diamonds and materials with hardness close to that of diamonds superhard materials.
1) diamond
diamond is the hardest material found in the world at present. Diamond tools have high hardness, high wear resistance and high thermal conductivity, and are widely used in non-ferrous and non-metallic machining, especially in the high-speed cutting of aluminum and silicon-aluminum alloy, such as the processing of car engine cylinder block, cylinder head, gearbox and various pistons, etc. Diamond tools are the main cutting tools that are difficult to replace. Due to the popularity of CNC machine tools and the rapid development of CNC machining technology, the application of diamond tools with high efficiency, high stability and long life is becoming more and more popular.
2) Cubic boron nitride (CBN)
Cubic boron nitride is an isom of boron nitride, and its structure is similar to that of diamond, with hardness as high as 8~9HV, heat resistance as high as 14℃ and good wear resistance. It is not only competent for rough turning and fine turning of hardened steel (45~65HRC), bearing steel (6~64HRC), high-speed steel (63~66HRC) and chilled cast iron, but also competent for high-speed cutting of superalloy, thermal spraying materials, cemented carbide and other difficult-to-machine materials.
3) Ceramic tool
Ceramic tool is one of the most promising tools. Has attracted the attention of the world tool industry. In industrially developed Germany, about 7% of the process of processing castings is completed by ceramic tools, and the annual consumption of ceramic tools in Japan has accounted for 8%~1% of the total tools. Because of CNC machine tools, efficient and pollution-free cutting, hard materials, and other factors, the cutting tool materials must be updated. Ceramic cutting tools are just following the trend and constantly innovating. Adding 2%~3% SiC crystal liquid into Al2O3 ceramic matrix to make whisker toughened ceramic materials. SiC whiskers act like steel bars in reinforced concrete, which can be an obstacle to stop or change the direction of crack propagation and greatly improve the toughness of the cutting tool. It is a promising cutting tool material. In order to improve the toughness of pure alumina ceramics, metal with content less than 1% is added to form the so-called cermet. This kind of tool material has strong vitality and is developing with strong momentum, and may become a new member of the tool material family in the future.
The main raw materials of ceramic tools are Al2O3, SiO2, carbide, etc. They are the most abundant resources in the earth's crust, and there is no problem in the source of raw materials to develop such tools. Therefore, the development and application of ceramic knives has important strategic significance and far-reaching historical significance.
Lathe and its machining
Turning machining uses the rotation of the workpiece and the linear movement of the cutter to machine the workpiece, and various revolving surfaces can be machined on the lathe. Because turning has the characteristics of high productivity, wide process range and high machining accuracy, lathe accounts for the largest proportion of metal cutting machine tools, accounting for about 2-35% of the total number of machine tools, and lathe is one of the most widely used metal cutting machine tools. Take the common CA614 common machine tool as an example to analyze the composition and processing characteristics of the lathe. A, CA614 ordinary machine tool
CA614 ordinary machine tool is an ordinary precision machine tool.
(1) Composition of the machine tool
Its main components are as follows:
(1) The headstock is used to support the spindle, and by changing the position of the external handle of the headstock (speed change mechanism), the spindle can obtain various speeds. The spindle in the spindle box is a hollow piece for passing through the bar. The spindle drives the workpiece to rotate through the chuck or other fixture installed at its end.
(2) The change gear box transmits the rotation of the spindle to the feed box, and the gears in the box are changed and matched with the feed box, so that various feeds can be obtained or various threads can be processed.
(3) The rotation of the spindle of the feed box (feed box) is transmitted to the polished rod or lead screw through the gear mechanism in the feed box. Changing the position of the handle outside the box can make the polished rod or lead screw get different speeds.
(4) The carriage box changes the rotation of the polished rod or lead screw into the movement of the carriage through the conversion mechanism in it. The longitudinal or transverse feeding movement is realized by the carriage. The big carriage makes the lathe tool move longitudinally; The middle carriage makes the turning tool move laterally; Fine adjustment of the tool can also be realized by turning short workpiece longitudinally by small carriage or turning a certain angle around the middle carriage to process the cone.
(5) The tool rest is used to clamp the tool.
(6) The tailstock is installed on the guide rail at the right end of the lathe bed, and its position can be adjusted left and right as required. Its function is to install the rear center to support the workpiece and install various tools.
(7) The lathe bed is the basic part of the lathe, which is used to support and install various parts of the lathe, so as to ensure the accurate relative position between the parts and bear all cutting forces. There are four precise guide rails on the car body to guide the carriage and tailstock to move.
in addition, there are cooling and lubricating devices, lighting devices and liquid trays.
(II) Movement on the lathe
To process all kinds of revolving surfaces on a lathe, you must have the following movements.
(1) The main motion is the rotation of the workpiece on the lathe.
(2) The feed movement, that is, the longitudinal and lateral movement of the tool rest, is expressed by the spindle turning once, and the moving distance of the tool relative to the workpiece, and the speed of the feed movement is relatively low, expressed in mm/r..
in addition, there are auxiliary transportation such as cutting, withdrawing and returning of tools. (III) Transmission system of lathe < P > II. Application scope and machining characteristics of horizontal lathe < P > The technological scope of lathe is quite extensive, and all kinds of work can be completed without adding other devices: drilling the center hole (A) with a center drill; Exterior circle (b); The vehicle end face (c); Drill a hole (d) with a twist drill; Boring (e); Twist the hole (f) with a reamer; Grooving and cutting (g); Turning thread (h); Knurling (i )； with a knurling knife; Turning cone (j); The lathe profile (r )；; Coil the spring (l).
1. Turning excircle
Turning excircle is the most basic and simple cutting method. Generally, the excircle of a car goes through two steps: rough turning and fine turning. The purpose of rough turning is to make the workpiece close to the shape and size on the drawing as soon as possible. And leave a certain amount of finishing allowance. Roughing accuracy is IT11 and IT12, and roughness is 12.5μm m.. Finishing is to cut off a small amount of metal to obtain the required shape, size and small surface roughness on the drawing. Precision turning is IT6～IT8.
2. Turning the end face
When turning the end face, there are two commonly used turning tools: offset turning tool and elbow turning tool. When turning, the turning tool can be fed from the outer circle to the center. However, because the eccentric cutter is used to cut from the outside to the center, and influenced by the cutting force direction, the tip of the cutter is easy to penetrate into the workpiece to form a concave surface, which affects the quality of the workpiece. Therefore, when finishing the end face, the eccentric cutter should feed outward from the center for the last time, so as to avoid the following shortcomings, as shown in the figure. When turning the end face with an elbow tool, because the main blade is used for cutting, the cutting is smooth and suitable for machining larger end faces.
when turning the end face, the tip of the turning tool should be aimed at the center. Otherwise, it will not only change the front and back angles, but also leave an inextricable boss in the center of the workpiece, crushing or damaging the tool tip.
3. Cutting and grooving
The so-called cutting refers to the processing method of cutting a bar with a cutting knife on a lathe or cutting a workpiece from a raw material. When cutting, the forward cutting method is generally adopted, and at the same time, the feed speed should be uniform and the cutting continuity should be maintained. Tangent is prone to vibration, causing the cutting knife to break. Therefore, when cutting large workpieces, the reverse cutting method is often used for cutting. The reverse cutting method has the same direction of the tool's force on the workpiece as the gravity g of the workpiece, which effectively reduces the vibration, and is easy to remove chips, reduces the tool's wear and improves the processing conditions. Because the tool bit cuts deeply into the workpiece and the heat dissipation condition is poor, coolant should be added when cutting steel parts.
Generally, grooves with various shapes on the cylindrical surface are machined with turning tools corresponding to the groove. The wide groove can be finished by cutting the knife several times, and finally finish turning according to the requirements of the groove.
4. Turning the conical surface
When the conical surface is used, the coaxiality is high and it is convenient to assemble and disassemble. When the cone angle is small, it can transmit large torque. Therefore, conical surfaces are widely used in cutting tools and tools.
there are three processing methods for the conical surface:
(1) turning the conical surface with a small tool holder
When turning the inner and outer conical surfaces with large and short taper, loosen the nut that fixes the carriage of the small tool holder, turn the axis of the rotary table of the small tool holder around a certain angle (half taper angle of the workpiece), and then lock the nut. Shake the handle of the small carriage to make the turning tool move along the generatrix of the conical surface, thus machining the required conical surface.
The advantage of this method is that it can process the outer conical surface with large cone angle, and it is easy to operate and adjust, so it is widely used. However, due to the limit of the travel of the small carriage, it is impossible to process a long conical surface and do motor feed, so it is only suitable for processing a short conical surface and single piece and small batch production.
(2) Turning the conical surface with a wide-edged turning tool
Machining a short conical surface with a wide-edged turning tool, the length of the conical surface is L2～25mm. When the turning tool is installed, the cutting edge should be parallel to the cone generatrix. The longer conical surface cannot be cut with a wide-edged knife, otherwise, it will cause vibration and ripple on the surface of the workpiece.
(3) Offset the taper surface of the tailstock
When machining a small taper external taper surface on a long workpiece, the tailstock center can be offset outward by a certain distance s, so that the generatrix of the taper surface is parallel to the longitudinal feed direction of the turning tool, and the required taper surface can be turned by using the automatic longitudinal feed of the turning tool.
This method can be used to process a long conical surface and adopt motorized feed. But only the outer conical surface with smaller half cone angle can be machined. Because when the cone is too large, the center will be skewed in the center hole of the workpiece, with poor contact and uneven wear, which will affect the machining quality.
in addition, for some parts with long conical surface and high precision, and large batch, the copying method can also be used for turning.
5. Drilling and boring
When drilling on a lathe, the workpiece is usually mounted on a chuck and the drill bit is mounted on a tailstock. At this time, the rotation of the workpiece is the main movement. In order to prevent drilling deviation, the end face of the workpiece should be turned flat first, and sometimes a small pit should be turned out at the center of the end face to center it. When drilling, the action should not be too violent, so as not to impact the workpiece or break the drill bit. When drilling deep holes, cutting is not easy to discharge, so the drill bit should be withdrawn frequently to remove chips. Coolant should be added when drilling steel, but not when drilling cast iron.
boring is drilling.