No 1 (2015)
- Year: 2015
- Articles: 7
- URL: https://bakhtiniada.ru/1994-6309/issue/view/19978
- Description:
Full Issue
TECHNOLOGY
Quantitative assessment of burns while flat grinding hardened parts made of steel 37Cr4 by abrasive wheels of different porosity
Abstract
A method for quantitative assessment of grinding burns is developed on the basis of digital technology. It is tested in conditions of pendulum grinding of hardened parts made of steel 37Khr4 by abrasive wheels of different porosity: 25AF46L10V5KF35 (i=1), 25AF46M12V5PO3 (i=2), EKE46K3V (i=3), 5A46L10VAX (i=4). Abrasive wheels with i=1;2 relate to high-porous wheels, while the abrasive wheels with i=3;4 are made of monocrystal carborundum and have standard porosity (producer - company Dorfner schleifmittelwerk (Germany)). To confirm the reliability of the proposed methodology for assessing burn marks a study of details microhardness is undertaken. In consideration of grinding stochastic character, statistical methods (particularly - rank): parametric and nonparametric are used to reduce the observations. They give opportunity to evaluate the reliability of decisions as well as the cuttability of wheels not only by the measures of position but by measures of dispersion. The second characteristic of the marginal frequency distribution is more important while grinding of critical parts on adapted machines with manual control for eliminating rejected probability. The statistical results have shown that in the infringements of homoscedasticity and normality of observations’ allocation, the parametric method reduced to dislodgement of measures of position and confidence intervals. A correlation between measures of position for percent burn content and microhardness is established. Tool 25AF46L10V5KF35 grinding with regime: v c = 35 m.s -1, s l = 7 m.min -1, s c = 1 mm.(d.s.) -1, t = 0.015 mm, z=0.15mm secures the greatest microhardness of parts made of steel 37Khr4 in the minimum burns. This investigation has shown that grinding parts by wheels runs in the softening of their surfaces, but no re-hardening burn. The wheel i=2 with pore-forming ПО3 is probably used for decrease of rejected parts.
Obrabotka Metallov / Metal Working and Material Science. 2015;(1):6-19
6-19
The effect of length of thick-walled cylinders on the residual stresses generated during the single-cycle mandrelling
Abstract
The methodology and results of experimental study by Sachs method of the effect of length of mandrelled thick-walled steel (0.5 % C) cylinders with inner diameter of 5 mm, outer diameter of 15 and 25 mm on residual stresses are studied. It is shown that such effect can take place both due to the uneven process of mandrelling along the cylinder length, and due to zero axial residual stresses on its ends. It is found that the length of cylinders has the strongest influence on axial residual stresses. With allowances between 1.9 and 13.7 % and length reduction from 40 to 10 mm, the largest absolute value of axial residual stresses decreases from 210 to 50 MPa. It is noted that when the outer diameter of cylinders is 15 mm its length significantly influence on both hoop and radial residual stresses. With the above-mentioned reduction in cylinders length, absolute values of hoop and radial residual stress in the region adjacent to the hole, depending on the mandrelling allowance, can increase (from -135 to -205 MPa and from -45 to 55 MPa respectively with 7.1 % allowance), decrease (from -315 to -235 MPa and from -135 to -95 MPa respectively with 0.9 % allowance) and remain almost unchanged (with 3.4 % allowance). The effect of length on these stresses is weak when the outer diameter of cylinders is 25 mm.
Obrabotka Metallov / Metal Working and Material Science. 2015;(1):20-26
20-26
The research of the effect of laser sintering modes on the thickness of the sintered cobalt-chromium-molybdenum powder layer
Abstract
In the modern economic paradigm to reduce the term of the new product launch the technology of layer-by-layer laser sintering is used. Technological development is moving towards the introduction of new powder materials and definition of rational technological modes of formation of the surface layer of a given quality. The creation of applicative product is possible only within a certain range of laser exposure, which is chosen experimentally for particulate material. The accuracy of the product is greatly influenced by the layer thickness. The results of experimental studies of the effect of technological modes of powder materials sintering (the laser power, the velocity of the laser beam scanning step, pre-heating temperature of the powder material) on the thickness of the sintered cobalt-chromium-molybdenum powder layer. The studies are conducted using the technological laser complex for formation of the surfaces of the parts with a complex spatial form. The thickness of the sintered layer is determined by a specially developed technique using a digital engineer microscope. The mathematical dependence of the thickness of the sintered surface layer on cobalt-chromium-molybdenum powder sintering conditions based on the theory of experimental design and statistical treatment of results is obtained. Graphs with superposition of experimental values of the sintered layer thickness depending on the sintering conditions are plotted using mathematical relationship. Characteristic curves analysis identifies the relevant modes parameters: lasing power, laser beam traversing speed, laser beam scanning step. All these parameters affect the thickness of the sintered layer and also limits its change from 0.65 to 1 mm by increasing the laser power from 10 to 20 watts; from 0.65 to 0.88 mm by reducing the moving speed of the laser beam from 300 to 100 mm/min; from 0.9 to 1.27 mm by reducing the laser beam scanning step from 0.15 to 0.1 mm; from 0.88 to 0.91 mm by increasing the heating temperature of the powder material from 26 °C to 200°C.
Obrabotka Metallov / Metal Working and Material Science. 2015;(1):27-32
27-32
Experimental determination of energy-power parameters and components of deformation during cyclic forming of material
Abstract
Production of special types of rolled nonferrous alloys using the combined technology of casting and deformation is a relatively new trend in resource-saving metallurgy. In domestic practice such techniques are implemented in the device for continuous casting and metal deformation. The key features of this device are cyclicity of process and the presence of large irreversible deformations of the workpiece (a strip of rectangular cross section in movable crystallizer, closed on four sides). These features lead to the problem of experimental data obtaining on the energy-power parameters of deformation, as well as the distribution and intensity of the strain state of the workpiece. In this paper, we propose a method for determining the instantaneous power of irreversible form changing by means of indirect measurements. The technique based on the detection and analysis of changes in the electrical characteristics of the motor drive in two modes of operation of the plant: cyclic deformation of the specimen and the motion of plant components without specimen deformation. We propose a method for directly measuring the components of the plastic deformation of the workpiece based on the method of knurled dividing grid with subsequent calculations by the Zibel's method. The experimental results indicate the expressed triaxial strain state of the workpiece because of the combined action of elongation and shifts in two mutually perpendicular planes. Verification of software package LS-DYNA carried out based on obtained experimental data by solving the problem of constrained shear, which coupled with the large plastic deformations.
Obrabotka Metallov / Metal Working and Material Science. 2015;(1):33-41
33-41
EQUIPMENT. INSTRUMENTS
Rational design of the column of a heavy multipurpose machining center
Abstract
The main purpose in the design of supporting constructions of heavy multipurpose machining center is the reduction of mass at the given precision and productivity of machining. Accomplish these ends the technology of rational design of supporting constructions is offered. This technology is based on the decomposition method and the finite elements method in the combination with optimization methods. The technology has four stages: 1) calculation (computation) of external all forces and loads, 2) as a result of the boundary conditions (force, kinematics) for individual supporting constructions are formed, 3) a problem about final optimal distribution of a material by the individual supporting constructions with the real cross-section is solved; 4) dynamic analysis. By the example of design of the column of a heavy multipurpose machining center the main stages of rational design of the individual supporting construction are shown. At a design stage of the carrying system consisting of load-bearing structures with simplified geometry, optimum overall dimensions of the column are identified. For the admitted system of preferences, it is necessary to accept the fact that the carrying system with the column with the sizes of cross section of 1.8 m (on an axis x) and 2.6 m (on an axis y) is the best. The analysis of the work of the column under the torsion condition with the use of method of mechanics shows that the column with square cross section = 2.46 ∙ 2.46 m which rigidity on torsion is 26 % higher in comparison with a production version is the best. Results of calculation show that a production-release design of the column with longitudinal and transverse edges of rigidity is 24 % heavier than the column with the edges located on a diagonally at equal rigidity. However, the serial-hour less rigid than stand with slanted edges.
Obrabotka Metallov / Metal Working and Material Science. 2015;(1):42-50
42-50
MATERIAL SCIENCE
The degree of breakdown of the cemented and borated surfaces on details of the cutting pair of the hydromechanical slot perforator
Abstract
In connection with the intensification of the operation of machines and mechanisms, elevated temperatures and pressures of the surfaces increases significantly. In terms of contact loading in all types of wear parts and machine components fail not due to failures, but because of an unacceptable change in size and shape, as always wear occurs on the surface. In this connection, the structural state and geometric characteristics of the working surfaces of machines and mechanisms play a crucial role in ensuring its reliability and durability. The condition of the surface of the cutting pair knives and axles of hydromechanical slot perforator designed for the opening of boreholes in order to increase their useful life is investigated. A strengthening thermochemical treatment of the surface layers of steel 18HGT, U8, 4H5MFS, 6H6V3MFS is studied. Three friction pairs after the same operating conditions are investigated. The first cutting pair is presented by the axle of mild structural steel 18HGT after cementation and knife of carbon steel U8 with diffusion boride coatings. The second cutting pair is presented by the axle of steel 4H5MFS and knife of steel 6H6V3MFS with the diffusion boride coating. The third cutting pair is presented by the knife made of steel 6H6V3MFS and the axle made of steel 4H5MFS after a full cycle of strengthening treatment (diffusion borating, quenching and tempering). It is shown that the degradation of the boride coating on carbon tool steel takes place in response to the development of oxidative processes. The service life of cemented axles is determined by the thickness of the hardened layer. Maximum durability have boride coatings on axles made of steel 4H5MFS and knives made of steel 6H6V3MFS. In this case, the chromium boride doping of the bases leads to increased heat resistance and ductility of the protective layer that ensures high durability. It is shown that diffusion borating with a full cycle of strengthening treatment (quenching and tempering) is the best way to strengthen a cutting pair of hydromechanical slot perforator.
Obrabotka Metallov / Metal Working and Material Science. 2015;(1):51-59
51-59
The improvement of wear resistance of cast iron products by application of diffusion titanium coatings
Abstract
The cast iron is rather popular structural material for products and elements, operating in a sliding friction conditions. Nevertheless, functionability of cast iron in friction pairs is significantly limited by loads and speeds, acting on them. The analysis of the causes of failure of cast iron products is given. The reasons of cast irons wear resistance decrease are presented. It is shown that the effective way to improve the wear resistance of cast iron products is a diffusion titanizing. But the process of the application of diffusion titanium coatings have problematic nature, because diffusion layers consist of very fragile titanium carbides, that break off from surface even during process of cooling after process of titanizing. The results of studies of the process of diffusion titanizing of cast iron from the environment of fusible liquid metal solutions is given. The technology of formation of workable coatings, including decarbonizing anneal before the process of tetanizing is developed and patented. This technology provides a high quality functional wear-resistant titanium coating on the surface of the cast iron. Coating formed during 2 hours had the thickness of more than 30 μm. The microhardness of the coating is 25000 MPa, of substrate - 4000 MPa. A transition layer of low hardness (3200 MPa) is detected under the coating. The influence of diffusion titanizing on the wear resistance of cast iron products is investigated. The microstructure and composition of the obtained titanium coatings is investigated. The tribological properties of titanium coatings are investigated, the tribological properties of the friction pairs are investigated. The studies of tribological properties conducted by comparative “pad-roller” is given. The linear wear of coated part with titanium coating is zero, and the uncovered sample wear is 0.02 mm.
Obrabotka Metallov / Metal Working and Material Science. 2015;(1):60-68
60-68