RU2131468C1 - Process of hardening of cutting edges of parts of machines and tools - Google Patents

Abstract

FIELD: mechanical engineering, making of cutting edges of parts of machines and tools. SUBSTANCE: in process of manufacture of part there is left technological allowance on "soft" surface of cutting faces mating at blade, chemical and thermal treatment is conducted to depth of layer exceeding technological allowance, thermal hardening treatment (hardening and annealing) of core and diffusion layer are carried out, part of thickness of diffusion layer of "soft" surface is ground off removing technological allowance subject to greater wear. "Soft" surface is polished (sharpened) later with keeping of margin of diffusion layer as defects of wear develop. EFFECT: expanded technological capabilities of manufacture and hardening of cutting parts of machines and tools with effect of self-sharpening, their improved maintainability and lasting qualities. 2 dwg

Description

 The invention relates to mechanical engineering and can be used in the manufacture of steel cutting parts of machines and cutting tools in order to increase its durability.

 To ensure sufficient durability of machine parts and tools, select the appropriate steel grade, heat treatment methods, surface hardening. In this case, attention is not always paid to the ratio of the hardness of the planes in contact with the cutting blade (see Yu.A. Geller, “Tool steels.” - M .: Metallurgizdat, 1961 - p. 64, p. 458 - p. 480 and others) . Ensuring the strength and durability of the parts, they strive to harden the surface layer, leaving a viscous core. Blades, for example, made of damask steel, have a variable hardness along the cross section of the blade and its length ("MiTOM" 1989, No. 9, article by VR Nazarenko et al. "On the technology of production of damask steel"). The disadvantage of all these methods is that the hardness of the planes in contact with the blade is usually the same, which leads to premature blunting of the blade. Surface hardening is applied over polished cutting edges or even finished ones.

 Another solution, more effective, provides a method for designing and hardening "self-sharpening" cutting parts (V. N. Tkachev, B. M. Fishtein, V. D. Vlasenko, V. A. Ulanov "Methods to increase the durability of machine parts." - M .: Mechanical engineering, 1971, pp. 87-90) This ensures that the wear of the side surfaces of the blade outpaces the wear of its tip.

 The "hard" layer here is ensured by the use of bimetal or is applied by special methods: surfacing, electroplating, thermal diffusion alloying. The hardness of the “soft” layer remains constant as the basis. This method is taken as a prototype.

 The disadvantage of the prototype is the limited technological capabilities of creating a sharp hardness, and hence the wear rate of the surfaces mated at the blade, as well as the inability to restore the cutting edge by grinding or sharpening in the case of a thin (micrometers) hard layer, i.e. lack of maintainability.

 The purpose of the invention is to expand the technological capabilities of manufacturing and hardening of cutting parts of machines and cutting tools manufactured using the method of self-sharpening, and to ensure maintainability.

 This goal is achieved by creating a technological allowance during manufacture, by creating by means of chemical-thermal treatment on the surfaces of the mating surfaces of the blade a massive hardened (“hard”) layer with a hardness higher than that of the core of the part, and then removing part of such a layer by its thickness from the surface exposed the greatest wear ("soft" surface), to a hardness equal to the intermediate value between the hardness of the surface of the diffusion layer and the hardness of the core. Maintainability is provided by periodically grinding (sharpening) the "soft" surface to remove defects in blade wear.

 Common features with the prototype: the blade is formed of metal of two mating surfaces with different hardness. Distinctive features: instead of an additional increase in hardness (strength) of the “hard” layer, on the contrary, they lower the hardness of the “soft” layer, because the hardness of the diffusion layer falls from the surface to the core of the part, and grinding (sharpening) reduces the hardness of the surface.

 To implement the method perform operations.

 1. Choose the type of cutting machine parts, mainly flat (plate) knives, easily amenable to "dosed" grinding along the thickness of the working plane, or a cutting tool that lends itself to a "dosed" sharpening by thickness of the cutting part.

 2. Prepare samples for step grinding after chemical-thermal treatment (XTO).

 3. Assign a steel grade and XTO method so as to create a surface diffusion layer with a thickness of several tenths of a millimeter or more, up to 1 mm or more (nitrocarburizing, cyanidation, etc.), and a strong and viscous core.

 4. Assign the modes of subsequent heat treatment after HTO (quenching, tempering — TH) so as to provide sufficient hardness of the core of the parts and increased, in comparison with it, hardness of the diffusion layer by several units, for example, “according to Rockwell”. XTO and MOT regimes must guarantee high resistance to contact fatigue and the absence of fragility.

 5. They make parts, providing technological allowance on a "soft" surface, intended for compulsory removal after XTO and TO, with a thickness less than the diffusion layer.

 6. Perform XTO and TO parts and samples.

 7. Determine the actual thickness of the diffusion layer on the sample. The surface hardness of the diffusion layer is determined by its thickness, for which the sample is ground-steply ground with a step, for example, a depth of 0.1 mm and determination of the hardness of each step and core of the part.

 8. The soot remaining from the CTO is removed by, for example, waterjetting or chemically, but not mechanically or by sandblasting, which can remove part of the diffusion layer.

 9. Grind (sharpen) the "soft" surface, removing the allowance, to a depth calculated according to the schedule "hardness - removed thickness of the diffusion layer" and set as optimal to ensure the durability of this part or tool for specific operating conditions.

 10. If necessary, as the damage to the blade accumulates, they additionally grind (sharpen) the "soft" surface, leaving a diffusion layer with a hardness higher than that of the core of the part.

 The invention is illustrated by a photograph and a graph: FIG. 1 - microstructure of carbonitrides of a diffusion layer on the cross section of a knife blade: on the left - the surface of the knife is polished, on the right - without polishing x 1000, FIG. 2 - hardness (HV) on the grinding steps (ΔH) of the diffusion layer of the knife blade.

 The method was tested practically in the manufacture of lamellar knives of super scissors (steel grade 40X) and guillotine knives from steel 40X. Knives are made in compliance with all standards for ensuring the structural strength of high-strength parts.

 Example 1. Lamellar knives of super scissors 16 mm thick are made of forgings of steel 40X. Technological allowance for grinding a "soft" surface is 0.4-0.5 mm. The diffusion layer with a thickness of 0.8-1.1 mm was created by nitrocarburizing (positive decision from 10.17.95 on the application N 94045206 priority from 12.27.94 patent N 2082820) with subsequent hardening and tempering. The surface hardness without grinding the diffusion layer is 585 HV. Technological allowance on the working "soft" surface of the knife is ground (Fig. 1). The distribution of hardness over the thickness of the diffusion layer is shown in FIG. 2. The surface hardness after grinding is 542 HV. The knives were tested by cutting a bar with a diameter of 20 mm of steel grade 20 with a hardness of 140-180 HB. The operating life without destruction of the knives is 400 or more cut blanks at normal temperature and more than 500 at negative. According to the stable mechanism of contact fatigue, arched cracks appear on the blade of a knife on a supporting “hard” surface with a hardness of 585 HV and “swelling” (plastic deformation) on a “soft” surface.

 Example 2. From forgings of steel 40X made plate guillotine knives (set of 6 pieces) with a thickness of 20 mm and a length of 625 mm. The technological allowance for the “soft” surface was 0.3-0.4 mm. A diffusion layer with a thickness of 0.75-1.0 mm was obtained by nitrocarburizing, as in Example 1. After quenching and tempering, the hardness HV is distributed over the thickness of the diffusion layer as follows: 0.2 mm - 492; 0.4 mm - 432; 0.6 mm - 392; 0.8 mm - 359; 1.0 mm - 357 HV. After shallow grinding of the supporting "hard" surface, its hardness is 492 HV. The hardness of the “soft” surface after removal of the technological allowance is 432 HV. Guillotine knives were tested in the procurement section of the machine shop with intensive loading, but it did not break, no cracks were found, there were no chips on the blade, but only wear (blunting), which can be deduced by additional grinding of the "soft" surface (there is a margin of thickness for the layer ) The operating life exceeded the resource of knives made of tool steel with volume hardening by 1.5 times. At the same time, knives successfully chopped both thick sheets of carbon steel and thin sheets with a thickness of 0.5 mm stainless steel.

 The technical result of the implementation of the proposed method is to expand the technological capabilities of manufacturing and hardening of the cutting parts of machines and tools with the effect of self-sharpening. Creating a massive hard layer, it is possible to grind part of its thickness in order to reduce the hardness of the “soft” layer, to ensure self-sharpening. In addition, the removal of a surface layer with increased hardness, and hence more brittle, increases the viscosity of the remaining diffusion layer. A favorable mechanism of resistance to contact fatigue of the “hard” layer, especially the tip of the blade, is created, because partially, the thickness of the blade, the most “brittle”, is polished. ”The nucleation of fatigue cracks on the blade from the“ hard ”layer is slowed down. The“ soft ”layer serves as a buffer for contact destruction of the blade, the metal of this layer can bulge, but not crack. negative temperature, ie in the "northern version", as evidenced by tests of super scissors.

 The proposed method can be used not only for plate knives, scissors, but also for curly tools, where tool sharpening of a “soft” surface with normalized removal of layer thickness is possible. This is the fundamental novelty of the manufacture and hardening of the cutting tool with increased durability. In addition, there are tools that lend themselves to flat grinding of cutting edges, for example, chamfers with a chamfer on the front face.

 Manufactured and tested knives of super scissors and guillotines confirm the effectiveness of the proposed method. The method is implemented on standard equipment.

Claims (2)

 1. A method of manufacturing cutting parts of machines and tools, including obtaining a part or tool with a blade having mating surfaces, one of which is with the greatest wear, hardening of mating surfaces to provide different hardness, characterized in that upon receipt of the part or tool, the most wear surface is performed with technological allowance, chemical-thermal treatment is carried out with the formation of a diffusion layer on mating surfaces with a thickness exceeding the technological allowance, Then, hardening heat treatment of the diffusion layer and the core is carried out, a part of the diffusion layer is removed from the surface of greatest wear to a depth corresponding to the hardness of the intermediate value between the surface hardness of the diffusion layer and the core hardness.  2. The method according to claim 1, characterized in that as the accumulation of defects in the wear of the blade, the surface of greatest wear is further processed to remove the layer while maintaining its thickness margin.

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