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Cutting machining is a basic and commonly used precision machining method. It plays an important role in various industrial sectors such as machinery, electric motors, and electronics. The factors that determine cutting machining efficiency are many such as machine tools, cutting tools, and workpieces, among which the cutting tools are the most Active factors. The degree of tool durability, tool consumption and processing cost, processing accuracy, and the quality of the surface quality, etc., depend to a large extent on the mechanical properties and processing performance of the tool material, so people are constantly researching and developing new ones. Tool material. However, the development speed of new materials is often indistinguishable from that of modern cutting processing. For example, high-speed cutting of 300-1000m/min cutting steel and 90-200m/min cutting of titanium alloys must achieve such a high cutting speed. With more excellent high-temperature mechanical properties, high chemical stability and thermal stability and high temperature thermal vibration resistance of the tool material, accelerate the research and development of tool materials, the rational choice of tool materials is an important prerequisite for promoting the wide application of high-speed cutting technology.
Laser processing is the primary field of laser application. In this field, laser processing of the object material occupies a very important position, especially for the material surface can be a variety of enhanced treatment.
The main application of the tool material modification is the melting process. The melting process is the melting of the surface of the metal material under the irradiation of the laser beam, and it rapidly solidifies to produce a new surface layer. According to the changes in the surface texture of the material, it can be divided into alloying, coating, remelting and refining, glazing and surface composites. Laser fusing is to irradiate the surface of a material with a laser beam of a suitable parameter to rapidly melt and rapidly condense the surface of the material to obtain a surface modification technique that refines the homogeneous structure and the desired properties. It has the following advantages:
1. When the surface is melted, no metal element is generally added, and the melted layer forms a metallurgical bond with the material matrix.
2. In the laser fusion process, impurities and gases can be eliminated, while the magazine obtained by quenching recrystallization has higher hardness, abrasion resistance and corrosion resistance.
3. The molten layer is thin and the thermal area is small, which has little effect on surface roughness and workpiece size. Sometimes it can be used without further polishing.
4. To increase the limit of solid solubility of solute atoms in the matrix, ultrafine grain and second-phase particles, to form a metastable phase, to obtain a single crystal structure without diffusion or even amorphous, so that the resulting new alloy obtains the traditional method. Unable to get good performance.
5. The light beam can be guided by the light path, so that it can handle special parts and complex shapes of the surface.
Second, the tool material laser surface modification research at home and abroad
There are many related documents at home and abroad, such as the use of XeCl excimer laser (wavelength 308nm) irradiation of Al2O3-SiC nanocomposite ceramic samples, energy density in the range of 0.8J/cm3 ~ 6.0J/cm3, after irradiation, the surface The defects are eliminated, a smooth and smooth molten layer is formed continuously, and the metastable phase γ-Al2O3 appears. The surface toughness is improved due to the improvement of surface morphology and structural changes. After W18Cr 4V lath tool is coated by laser, the wear resistance is obviously improved for deep cutting, rapid cutting and special hard cutting. If the blunt surface of the blade is used as standard, it will increase by nearly 250%; The blunt standard is an increase of 200%; if broken, it is increased by nearly 100%. In addition, the wear resistance of the flank is significantly increased after the laser treatment of the rake face of the turning tool. After the flank surface is treated with laser, the flank wear resistance of the rake face is also improved, but the growth rate is less than the former. Xuan Chongwu and Zhang Lianbao from Beijing University of Technology used laser surface alloying technology to change the surface composition of the wood processing blade to increase the toughness of the blade. The alloying layer obtained by laser surface alloying is a kind of metallurgical bond with the substrate of the insert, and the binding force is better than various sprayed layers. The average yield of the best product once sharpened is less than 20t, but the breakage rate of the blade itself is more than 30%. After the laser alloyed blade, the life of one-time sharpening is about three times higher than that of the best product, and the cutting edge does not collapse, roll or break, and it can be used with a sharp edge. Li Liangfu of Wuxi Metallurgical Machinery Factory has confirmed that using laser processing to improve the tool's durability, laser hardening has a good effect on improving the working ability of various tools. For example, the durability of T8A, T10A, CrWMn, and 9Cr steel molds can be increased several times. The service life of the mold can be increased by 15-19 times compared with that after general heat treatment, and is 0.5-1 times higher than that of the cobalt nitride wear layer. . The former Soviet Union had conducted laser cladding tests on WC85%+Co15% and WC92%+Co8% hard alloy powders using a 35-30J solid pulsed laser and 0.1,0.5,1-3Kw continuous CO2 lasers. 2.2-17mm/s, the highest microhardness obtained by cladding (WC92+Co8) powder on Y8A tool steel is HV1180. KJ.Schmaxtjko used an excimer laser to directly remelt the surface of ceramic materials (Al2O3, ZnO2, Si3N4). The results showed that the surface roughness of ceramic materials decreased from 10-15 μm before laser modification to 1-4 μm. , And the porosity is greatly reduced. A.Detitbon's remelting method can reduce surface cracks and pores by at least 50%.
In recent years, lasers have reported various degrees of surface hardening of various tool materials[5,6]. Some people have directly studied the laser surface hardening of high-speed tools. Although laser alloying and cladding ceramic layers have achieved the key The progress of sex, but the actual batch application in industry is less, especially in the tool material modification.
Third, the current laser enhancement technology in civilian tool manufacturing applications
There are a large number of tools for civil use, including: kitchen knives, scissors, razors, and crushers. Currently, tool failures are mainly caused by cutting edges, such as edge wear, chipping, and corrosion. In order to achieve long-lasting durability, they are generally manufactured. The process methods are: 1) The use of high-performance alloy materials, such as high-speed steel, etc. 2) The use of composite steel, such as composite steel knife and scissors, etc. 3) Inlay welding of hard alloy materials, such as carbide, ceramics, high-speed steel, etc. . The first two methods have higher raw material requirements and higher manufacturing costs; while the latter are often hard and brittle materials due to inlay welding, which brings difficulties to the manufacturing process, such as the inlay strength of cemented carbide and the substrate, and the length of hard alloy inlays. Limited, etc., service life is affected.
Laser cladding is a new laser processing technology developed after laser cladding technology. It draws on the advantages of traditional overlay welding technology, uses high-power laser as a heating source, and simultaneously melts the simultaneously fed alloy wire and the surface of the substrate. , to get a complete metallurgical bonding with the substrate and has a special performance (wear, corrosion, heat, etc.) of the surface layer, forming a composite layer for the manufacture of bimetal knives. The laser alloying is to add alloying elements in the surface molten layer of the substrate to form a new alloy layer based on the substrate to achieve surface modification and edge toughening.
Combining the advantages of the above technologies, applying this technology to the surface treatment of tool materials is one of the important ways to improve the wear resistance and service life of tools, especially for high hardness and heat resistance of ceramic and carbide tools. The advantages of good performance, etc., are conducive to improving the processing efficiency and processing accuracy, and can perform cutting processing on difficult-to-machine materials such as quenched steel under unfavorable processing conditions. Due to their relatively low strength, toughness and poor performance, which severely limit their application, laser surface hardening technology has a profound research significance and broad application prospects for ceramic, carbide cutting tools. .
At present, the methods for improving tool wear resistance at home and abroad are mainly divided into two categories: one is a conventional surface treatment method, such as an unconventional surface quenching method and a laser cladding method. (The coated alloy powder is mostly Ni, Co. Base-self-fluxing alloys or coarse-grained tungsten carbides or laser thick-layer claddings are more suitable for abrasive wear conditions such as mines, petroleum, agricultural machinery and other mining tools. The disadvantage is that it is easy to produce cracks and other defects. The other is the recently developed coated tool. The disadvantage of this method is that the deposited coating is thin. Both methods have their disadvantages to varying degrees. The former is to improve the hardness and wear resistance through the transformation of the microstructure of the material itself, so it is only effective for carbon steel, while the effect is not obvious for the tool materials of cemented carbide and high-speed steel materials. The latter is not only coated. The thin layer has a long deposition time, and peeling often occurs in actual use.
The following is an application example of laser surface hardening technology in tool material modification.
1. Laser Cladding Surface Modification of Household Kitchen Knife
Laser cladding is used to quickly and thinly cover the surface of the commonly used stainless steel kitchen knife to obtain uniform, high wear-resistant cutting edge of the coating layer. Instead of the traditional tool production process, the industry is improved to improve the tool (kitchen knife) products. Intrinsic quality and added value. Through the analysis of coating material ratios, laser coating properties, etc., kitchen knives with the same level as "Lazy Knife" were developed and put into practical use. Through optimization of the process, the use of a preset-type alloy powder results in a blade with no cracks, a certain hardness coating thickness, small deformation, and a narrow tempering zone. It can be seen that the cladding layer uniformly covers the blade edge.
Cross section analysis can be clearly seen from the outside to the inside is divided into four areas: cladding layer, hardening transition zone, tempering zone and matrix materials.
1.1 Cladding area
The area is mainly composed of coating materials, with a high hardness of HV990-1300 and a thickness of 0.02-0.08 mm, in which a large number of unmelted hard particles play a role in dispersion strengthening. The coating is too thick and easy to form cracks, which affects the use. By optimizing the process parameters, a coating with no cracks, high hardness, smooth surface and good metallurgical bonding with the substrate is obtained, and this coating is to improve the edge wear performance. key.
1.2 Hardened transition area
This area contains an alloyed layer in contact with the cladding layer. The quench zone in contact with the tempering zone accounts for 80% of the hardened layer. The hardness of the hardness layer is smooth and excessive. The microstructure is mainly over-refined martensite and carbonization. Things.
1.3 Tempered area
As the scanning speed increases, the tempering zone becomes narrower and the structure is sorbite and carbide. The presence of a tempering zone helps maintain the toughness of the cutting edge and does not break under high hardness impact conditions.
2. Laser infiltration nano modified strengthening tool
Laser infiltration is a surface modification method that combines a laser cladding process and a laser alloying process. Applying it to the garden tool production process, laser surface modification and strengthening can be performed on different types of tools. Nanomaterials have better mechanical properties than micron-sized materials. The nanoalloy powder coated on the surface of the substrate is rapidly melted under the action of a high-density laser beam, and some of the nano-particles of tungsten carbide penetrate into the matrix material. Micro-alloying, and the surface of the tool can be obtained nano-crystalline coating, which not only improves the toughness and wear resistance but also deepens the hardness depth of the cutting edge of the tool, extending the service life of the tool.
After the blade is laser-treated, a hardened layer is formed on the surface layer, the hardness shows a gradient change, and the heart still maintains the original structure. This makes the surface layer hard and wear-resistant, the core maintains toughness, and the operation process has a "self-sharpening" effect, making the blade life longer. The thickness of the blade is 1.5mm, the depth of the hardened layer is 0.18mm, the bright white layer of the surface layer is alloy carbide, martensite, hardness is HV0.2 820-766, the core is tempered troostite, hardness is HV316.
Fourth, the laser enhancement technology in the tool material modification application prospect
At present, the research on engineering ceramics and cemented carbide materials at home and abroad has made certain progress. On the other hand, the laser surface treatment for cutting tools is a frontier in the field of mechanical processing, and it is effective to replace some heat treatment with a strong laser beam pair. The method, combined with the current development of nanotechnology, finds their combined points on the basis of these three directions. With reference to similar research methods, the laser-enhanced mechanism and technology of ceramics and hard alloys are studied and proposed for future research. The work will include the development and blending of highly wear-resistant/corrosion-resistant/heat-resistant nano hard powders (ceramics, composites, etc.), the performance of laser nano-reinforced layers, laser thick surfacing technology, and cemented carbide materials. In terms of analysis and research, new tools for improving cutting edge toughness, wear resistance, and service life are developed using common tool materials for different tools, and various types of tool materials are obtained by laser cladding and nanotechnology. The overall process technology of alloy infiltration and productization makes it possible to meet the complex requirements of actual production, in particular to overcome pottery Tool material brittleness, reliability and low defects, to improve carbide and ceramic materials adds an effective way.
It is believed that the laser alloying surface strengthening technology has a wide range of applications and broad application prospects in the modification of tool materials.
Application of Laser Strengthening Technology in Tool Material Modification
I. Introduction