Method providing an increase of wear resistance of metal-cutting tools made out of tool steels by magnetic-pulse treatment with a preheating and an installation for its realization

FIELD: mechanical engineering.

SUBSTANCE: the invention presents a method providing an increase of wear-resistance of the metal-cutting tools made out of tool steels by magnetic-pulse treatment with a preheating and an installation for its realization. The invention is dealt with the field of mechanical engineering, in particular with production of metal-cutting tools made out of tool steels by preheating and magnetic-pulse treatment. The technical result is increased wear-resistance of the metal-cutting tools made out of tool steels due to removal of internal stresses, increase of thermal conductivity, ordering of magnetic structure of a material. For achievement of the technical result conduct a preheating of the tools by high-frequency currents (HFC) with consequent action by a pulse of a magnetic field of high magnetic intensity. The method is realized by an installation containing a combined inductor with windings. At that a winding of the inductor, powered by high-frequency currents, is placed inside the winding powered by a magnetic-pulse device.

EFFECT: the invention allows to increase wear-resistance of the metal-cutting tools made out of tool steels.

3 cl, 1 dwg

 

The invention relates to the field of processing of cutting tools, namely, to increase the wear resistance of cutting tools made of tool steels, by acting on the tool heat and pulse of a magnetic field.

The wear resistance of cutting tools depends on a number of factors. The main factors are: the material of the tool, the shape of the cutting edges, the cutting conditions, the condition of the crystalline structure of the material and the presence of sites of residual stresses caused by thermal processing.

There are many ways to improve the wear resistance of the cutting tool by changing the internal structure of the material, the state of magnetization, and by changing the chemical composition and state of the surface layer. These methods include: hardening, mechanical hardening, chemical heat treatment, wear-resistant coatings, magnetic-abrasive machining, magnetic-pulse processing.

Most tool steels, and in particular high-speed steel, respond well to training. In the process of hardening the tool hardness increases with 40-45 HRC to 63-69 HRC, which increases its resistance to wear. For cutting tools increased hardness on some units HRC promotes wear in on the tens of percent. The tool made of high speed steel, tungsten and wolframmathematica group (P9, R, R18; RM, R6M5) after quenching and subsequent low-temperature tempering (aging) is obtained hardness 63...67 HRC. The negative side of the hardening process is the occurrence of the hosts on the internal stresses in the structure of the tool, which completely fails to capture even the low-temperature tempering. The nodes of the internal stress is concentrated, the excess internal energy, which causes warping of the tool and the formation of microcracks. These factors sometimes play a major role in the wear and breakage of the tool, and make the necessary additional machining (edit, auto body) before applying the tool.

Chemical and thermal processing relates to methods, which are based on the chemical composition of the surface layer of the tool at elevated temperatures. The main methods of chemical and heat treatment are: cyaniding, nitriding and carbonitriding. A major influence on the improvement of wear resistance has a layer representing at cyanidation thin mixture of martensite, carbides and turbidometric phase, the hardness of which is 69-70 HRC, when nitriding complex nitrides of tungsten and density phase, which have a hardness 1300-1400 HV, when neither is recementation also forms a layer of carbides, with high hardness and wear resistance. With all the advantages of chemical-heat treatment it has also disadvantages. The main disadvantages include: embrittlement of the treated layer, preservation layer to the first retargeting tool. These drawbacks limit the application of this method.

Mechanical hardening of the cutting tool is rounding its edges to the desired size and training of the surface layer by the vibration treatment. The variation of geometrical parameters is expressed in the rounding of the cutting edges and to improve the quality of their surface, the change in physical and mechanical properties is to create in the surface layer of compressive residual stresses. This method of treatment because of its high performance and efficiency, and low cost, widespread in tool manufacture. At the same time it has its drawbacks. These include the fact that the tool is hardened only on the surface, and the structure of the core is not changed, while the cutting edges effect persists only till retargeting.

In recent years have spread the way of wear resistant coatings on the surface of the tool. Industrial there are two techniques of application etc is rd. This technology vapour deposition of titanium carbide and technology of cathodic sputtering and ion bombardment. As a result of precipitation of carbides of titanium on the working surface of the instrument achieves high hardness 2500-4200 HV. This allows to significantly improve the resistance to wear. When the coating is significantly lower coefficient of friction. While many positive factors you can point to some drawbacks of these methods. The main disadvantage is the complexity and high cost process coating. It should also be noted that due to the small thickness of the coating layer it is also saved to the first reshaping.

Recently received wide distribution of magnetic-abrasive machining tool. The essence of treatment is as follows: between the poles of a magnet is the magnetic-abrasive powder, which under the action of a magnetic field of varying intensity forms a cutting tool with variable stiffness. Machined tool is placed between the poles of a magnet in the body of the abrasive tool. Processing is carried out by rotating or moving a handled tool, and the poles of a magnet. In addition to direct abrasive action on the workpiece the tool are fixed and variable magnetic field of varying intensity, as well as the surface pressure from the collision with abrasive particles. The method of magnetic-abrasive machining has many positive sides. First, due to the lack of hard cutting tool processing can be products with any configuration of surfaces. Secondly, by changing the magnetic field strength and rotation frequency of the poles of the magnet and the workpiece tool, you can adjust any of the settings. When the magnetic-abrasive processing in the processing tool, the following changes occur: improving the quality of the surface, the concentration of residual stresses in the surface layer, the change of the internal magnetic structure. Improving the quality of the surface reduces friction between the tool and chip, which prevents clogging of chip grooves and jamming tool. The concentration of residual stresses in the surface layer increases its hardness. It is beneficial to the improvement of wear resistance. When there is a planned change of the internal magnetic structure of the tool increases its conductivity and some other parameters that are also beneficial to wear. The method of magnetic-abrasive machining has one disadvantage in that the structure of the core material remains unchanged, and the layer with increased hardness is very thin. So after regrinding in which trument its processing has to be repeated.

Magnetic-pulse processing (m & e) of the cutting tool is also widespread. This type of processing is successfully applied in modern technique and technologies to control the properties of tool materials. Minor cost and high performance installations of magnetic-pulse treatment, as well as the simplicity of the technology allows to recommend it for various engineering industries. The use of m & e can reduce the residual and fatigue stresses in the structure of the cutting tool. When the magnetic influence of a substance changes its physical and mechanical properties. The interaction of the magnetic field of the instrument is the more intense, the higher the structural and energetic heterogeneity of the. Therefore, the higher concentration of surface and internal stresses in the material of the tool, the more likely the local concentration of microwire external field. In the manufacture of the tool in the material unevenly concentrated a certain amount of excess energy, which increase the probability of its destruction. By reducing excess energy of material external physico-technical ways it is possible to improve the reliability of operation of the cutting tool. The use of m & e can significantly mind what nishith excess energy of the material, associated with the concentration of the internal and surface stresses, thereby increasing the strength and durability of the tool.

There is a method of processing tool [2], including the effects of pulsed magnetic field with a predetermined intensity and frequency, based on the effects of pulsed magnetic field strength of 0.8 to 2 kA/m and frequency 700-800 Hz for 3/4-5/4 π period frequency. The disadvantages of this method of processing tool is a low probability of changes in the structure of the tool after exposure to a single pulse, as well as a strong feedback in the system, the inductor is a tool which determines the oscillation frequency, and hence the energy required magnetic-impulse installations.

On the use of magnetic-pulse treatment is based is another way to improve the basic characteristics of the cutting tool[3]. This method of magnetic-pulse processing tools, machine parts and Assembly units comprises a pulsed magnetic field with the given parameters intensity, shape, and pulse duration on pre-coated with a layer of graphite surfaces of the product. The main disadvantage of this method is similar to the previous, the low probability of changes in the structure of the material due to the impact of only one pulse is inanaga field.

There is a method of heat treatment of high speed steel [1 - prototype], including volumetric hardening, tempering and laser hardening, in order to enhance hardness, hot hardness, wear resistance and reduce processing time after laser hardening additionally perform a vacation in a magnetic field at 540-560°and leave after volumetric hardening is carried out at 300 to 400°C.

The technical result of the invention is to improve durability of the cutting tool.

To achieve a technical result in the known method of increasing the wear resistance of cutting tools made of tool steel by magnetic field of high intensity in the preheated tool workpiece the tool is heated by high frequency currents in the temperature range from 400 to 500°with the subsequent impact of a single pulse of a magnetic field.

In a known installation for increasing the wear resistance of cutting tools, including a composite inductor windings fed from the magnetic-impulse installations (Miu) and the installation of high-frequency currents (currents), the winding of the inductor is fed from the HDTV installation, located inside the winding, powered by a magnetic-impulse installations that allows reinstallation of the tool, the wire is to be heated tool and exposing it to a pulse magnetic field.

For carrying out this method of treatment uses a special installation (figure 1). The unit consists of a high-frequency generator 3, the magnetic-impulse installations 7, springy support collet tool 4, the composite inductor 2, 5. One winding of the compound eductor, with an average of 450 turns 5, is connected to the magnetic pulse unit (Miu), the second containing 5 coils located inside the first 2, is connected to the installation by high-frequency heating.

The process is as follows: machined tool on a special spring clip is placed inside a composite inductor. Then the internal inductor from the installation of high-frequency current heats the tool along the entire length to a temperature below the temperature of phase transitions. Then immediately followed by a magnetic pulse of high intensity. A specially designed control unit controls a joint operation HDTV and Miu, allowing you to change the temperature of the heating tool and synchronously feeding the pulse magnetic field.

In the process of cutting tools offer a way in the structure of the tool material undergoes a number of physical processes, which result in change of some physical and mechanical properties. First, change the magnetic structure, which increases thermal conductivity of the material is a, accelerating the dissipation of heat from the cutting zone. Secondly, under the action of heat and pressure pulse magnetic field reconcentrated nodes internal stresses, increased mechanical strength.

Theoretical justification of this method of hardening is the preservation of the material of the cutting tool ferromagnetic properties almost unchanged when heated to a certain temperature. Because when the temperature in the metal structure increases the amount of internal energy, it is more easily understood by any external influence.

The dependence of magnetic properties on temperature is described by the Curie law. A dependency graph for tool steels is a line that up to 550°C is at 100% magnetic susceptibility, and then drops sharply to 0% at a temperature of 768°C. it is Theoretically possible to predict that the greatest effect on m & e will be observed at a temperature of from 400 to 550°because this interval corresponds to the maximum obtained in the internal energy while maintaining ferromagnetic properties. Theory of heat treatment of tool steels also indicates that to reduce residual stresses in hardening high-speed steels, it is necessary to conduct low-temperature tempering by heating from 300 to 500°C. When heated in this range, the effect of the decomposition of martensite is insignificant, that allows you to preserve the original hardness.

The proposed solution, according to the authors, is one of the most promising and effective ways of increasing the resistance of the cutting tool.

Currently, the method of magnetic-pulse treatment of cutting tools using pre-heating is applied for processing of cutting tools in the workshops and laboratories of the Institute. The proposed method is experimental and research base for the learning process in engineering specialties. At the same time discusses the manufacture of magnetic-impulse installation capable of operating in continuous long-term mode and will be included in the process of manufacturing cutting tools.

Sources of information

1. USSR author's certificate No. 1479525, C 21 D 1709, 1987 [prototype]

2. Patent RU No. 2009210 C 21 D 1/04, 1992

3. Patent RU No. 2153006, C 21 D 1/04, 1999

4. Malygin B. C. Magnetic hardening of tools and machine parts. - M.: Mashinostroenie, 1989. - 112 S.: ill.

5. White IV, FOP S.M., Khymenko LT Reference magnetic pulse treatment of metals. Kharkov: high school, 1977. 320 S.

6. Bernstein M., Pustovoit NR. Heat treatment of steel products in a magnetic field. M.: Mashinostroenie, 1987. 256 C.

1. Ways which improve the wear resistance of cutting tools made of tool steel, includes pre-heating the tool to a certain temperature and the effect on tool magnetic field of high intensity, characterized in that the preheating of the tool carried out by high frequency currents from 400 to 500°and affect tool one pulse of magnetic field of high intensity.

2. Installation to improve wear resistance of cutting tools containing compound inductor windings fed from the magnetic-impulse installations (Miu) and the installation of high-frequency currents (currents), characterized in that the winding of inductor-powered HDTV installation, located inside the winding fed from the Miu to provide heat and impact pulse of magnetic field without reinstalling tool.



 

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