No 1 (2016)
- Year: 2016
- Articles: 7
- URL: https://journal-vniispk.ru/1994-6309/issue/view/19974
- Description:
Full Issue
TECHNOLOGY
Experimental modeling of technological process of pure aluminum alloy (Al-Zn-Mg-Cu) structural elements forming under creep
Abstract
Due to the improvement of the forms of aircraft, methods of complex surfaces forming using rectangular solid plates and elevated temperatures have become popular. Compared with the production of prefabricated elements, such molding techniques allow saving resources, reducing weight, getting rid of assembly and fitting work on the stage of manufacturing. How different will the fatigue life of pre-deformed at different temperatures and deformation rates products be? The answer to this question is relevant to aerospace industry. A pilot study of the issue is conducted. Fatigue life of pure aluminum alloy (Al-Zn-Mg-Cu), depending on temperature of pre-deformation and strain rate is set. Experimental modeling of fatigue life of pure aluminum alloy samples is made. Three series of samples previously plastically deformed at different strain rates (1 - at room temperature, 2 - artificial aging temperature and 3 - at the annealing temperature) were used. Plastically deformed samples were heat-treated using the mode T2 in accordance with the production instruction 1.2.699-2007 PI. The effect of the reverse creep at relaxation is shown. This effect should be considered when designing the formation of large structural components at elevated temperatures. The number of cycles to failure at regular loading depends on temperature and deformation rate. Pure aluminum alloy (Al-Zn-Mg-Cu) fatigue resistance does not decrease after a pre-deformation at the annealing temperature.
Obrabotka Metallov / Metal Working and Material Science. 2016;(1):6-15
6-15
Standardization of oxygen-assisted laser cutting by the surface roughness criterion
Abstract
Laser cutting technology rightly ranks highly in the range of many common types of metals mechanical cutting. High density of laser radiation power permits cutting metal and non-metal materials of different thickness. Low cut width, high speed of processing, and accuracy are the peculiarities of the laser-cutting technology. In spite of many advantages, opposite to the other technologies, the laser cutting still has no position in the processing quality standard system. The paper deals with the investigation of the oxygen-assisted laser cutting of low-carbon steel by the gas-discharge CO2 laser and ytterbium fiber laser with the radiation wave length of 10.6 µm and 1.07 µm, respectively. The sheets of 3, 5, 10, and 16 mm were cut. The laser radiation was assigned as 200 W per 1 mm of the sheet thickness for the both laser types. Initial stage was to optimize the laser cutting by the criterion of the minimal surface roughness. It is shown that the striated structure of the side surface of the cut is not uniform and has its features in the top and bottom parts of the samples. To define the cut quality class, the roughness value measured in the bottom part was used. It is found that the gen-assisted laser cutting of low-carbon steel by the CO2 laser shows the better quality of the cut surface as compared with the treatment by the ytterbium fiber laser. It is also obtained that the laser cutting of low-carbon steel correlates to the 4 - 6 class of roughness. We founded that, as the cut sheet thickness rises, the roughness value changes in accordance with the law Rz=1.15∙t+6.5 for the cutting by the СО2-laser and Rz=3.7∙t+3.8 for the cutting by the ytterbium fiber laser.
Obrabotka Metallov / Metal Working and Material Science. 2016;(1):16-21
16-21
Features of cut channel formation during high-precision plasma cutting of bimetallic compositions made of promiscuous materials
Abstract
The paper discusses the features of formation of the cut channel of bimetallic composition “steel St3 + aluminum A5M” during high-precision plasma cutting. The mechanism of formation of the cut channel is defined as a choice of technological scheme of cutting the composition and appointment of the front side of the cut are identified. It is shown that the different character of the geometry of the cut in the areas of the bimetal is defined by thermal properties of materials composition, and above all, its melting point. Thus, when cutting the package from the side of low carbon steel the undercut, filled with elements of melted steel, is formed on portion of aluminum. This is due to significant differences in melting temperatures of steel and aluminum, as well as the weakening of the gas-dynamic flows in the cut channel, responsible for the removal of the products melt. The formations of heat affected zone in the area of low carbon steel up to 300 microns width are established. The maximum value of microhardness (up to 4000 MPa) is observed at the surface, with a gradual decrease in microhardness up to 1800 MPa, which corresponds to the hardness of the starting material. If you change the front side of the cut with steel to aluminum, deposition of products of aluminum melt in the cut channel, due to its high kinematic viscosity is observed. When cutting a bimetallic composition from the side of aluminum the heat affected zone in the area of steel decreases to 150-180 microns. X-ray and metallographic analysis showed that the products of melt in the cut channel contain elements of aluminum, steel and aluminum oxide.
Obrabotka Metallov / Metal Working and Material Science. 2016;(1):22-30
22-30
EQUIPMENT. INSTRUMENTS
Optimization of multifunction machines constructions with required accuracy and productivity
Abstract
One of the main criteria of the supporting constructions (column, spindle head, bed) of the multifunction machine is the mass of constructions. It is required to find such distribution of material in the supporting constructions whereby conditions of strength reliability are satisfied with minimum possible mass. Supporting system, consisting of these optimum supporting constructions, has to provide the precision and productivity of machining. In order to support business objectives, the technology of rational designing of supporting constructions, offered by us, uses the principle of decomposition and the integrated work of the finite elements method with optimization methods. The main stages of this technology - optimization of the supporting system of the machine with the supporting constructions simplified on geometry and optimum design of the individual supporting constructions for definition of real geometry of cross section are considered. Calculation of the supporting system with the simplified supporting constructions (without edges of rigidity, partitions, etc.) is made for limit and operating conditions of working. Calculations showed that in the stage of the machine supporting system modeling for typical operating conditions the mass of the supporting system due to optimization is 35% less than the production version. Active restrictions in strain of an end face of a spindle in the direction of action increases the cutting force. Due to high dimension of calculation models of the supporting constructions it is offered to use the substructure at a stage of optimum design of the individual supporting constructions on the basis of the principle of decomposition. The calculated strain field of the optimal column substructure is consistent with the strain field of the column, which is obtained when calculating the machine supporting system, consisting of simplified supporting constructions at satisfaction of precision standards of working. Restriction on the allowed strain for knots on an axis of y (0.45 ∙ 10-6) is strictly carried out, and on the rest settlement strains there are less than allowed. The turning angle of the optimal column with real cross-section is less, than the turning angle of the column as part of supporting system with the supporting constructions of simplified geometry - 0.0778 rad and 0.1495 rad, respectively, i.e. torsion rigidity of the optimal column is higher. As a result of optimum design, a mass of the pallet, consisting of the moving-rotary table, is reduced by 35.5 % in comparison with a production version.
Obrabotka Metallov / Metal Working and Material Science. 2016;(1):31-41
31-41
MATERIAL SCIENCE
Investigation of the structure and phase composition of Ti and Nb powders after mechanical activation
Abstract
Features of structure and phase composition of the powders of Ti and Nb after mechanical activation are investigated by the methods of X-ray diffraction, scanning electron microscopy and energy-dispersive microanalysis. The powders were mixed in mass ratio 60 % Ti and 40 % Nb in planetary mill AGO-2C during 10, 15 and 20 minutes. Water-cooled camera was used to reduce the temperature of the process. It is shown that during the process of mechanical activation the powder of two-component composition is obtained. During the process of severe plastic deformation and mixing particles of Ti and Nb are combined into larger objects. The agglomerates with scale structure are formed. The size distribution of powder particles is characterized by bimodal type. Most particles have a size from 10 to microns. A smaller part of formed particles has a size of about 100 microns. As a result of treatment time increasing the scatter of the powder granulometric composition is reduced with shifting to lower values. It was observed that during activation time increase the content of Nb saluted in Ti increases and reaches composition Ti37Nb at 20 minutes of activation. Ti and Nb are equilibrium distributed inside the particles. Herewith the main β-phase forms rom phases of initial components. β-phase is the substitutional solid solution of Ti and Nb. The β-phase quantity increases with the activation time increasing. The phase of initial α-Ti is retained in the alloy throughout the treatment time. Increasing of treatment time or using of additive factors which enhance the effect of mechanical activation is necessary to complete the process of monophase alloy formation. It is shown in conclusion that the form and granulometric composition of obtained Ti-Nb alloy powder, its phase composition with equilibrium distribution of components allow use it in additive technology of selective laser sintering.
Obrabotka Metallov / Metal Working and Material Science. 2016;(1):42-51
42-51
Structure and mechanical properties of the low-carbon steel after severe plastic deformation and forging
Abstract
The effect of the hot forming obtained by multi-directional forging on the structure and mechanical properties of the ferrite-pearlite dual phase steel 09Mg2Si after equal channel angular pressing (ECAP) is studied. Four passes of ECAP were conducted using a route of "Bc" (90-deg rotation after each pass) adjusted to 120° internal angle of channels, 450 °C pressing temperature. Subsequent multi-directional forging (MDF) was performed with accumulated strain of deformation of 60 and 80%. To remove the excess of internal stress after severe plastic deformation (SPD) billets were annealed at 350 °C for 1 hour with following furnace cooling. Thermo mechanical processing by MDF affects not only the shape and structure, but, respectively, the mechanical properties of the billets too, due to the processes of deformation and recrystallization of metal. After ECAP and MDF more fine-grained structure was expected to ensure the best strength characteristics, but there was decrease in values compared to steel, which was processed only by ECAP. Nevertheless its yield point after combined processing by SPD and forging exceeds the initial values by 40-80%, the ultimate tensile strength - by 32-45%. Subsequent MDF also resulted in increase of ductility of the ultrafine grained (UFG) steel 2-3 times in comparison with steel after ECAP. After ECAP and MDF with accumulated strain of deformation 80% ferrite and pearlite grains of the steel were significantly refined to 3.8 and 2,5 μm respectively, that is 2 times less than after ECAP. Research results show the applicability of combined treatment which consists of the ECAP and MDF as manufacturing technology of work pieces with shaped form with sufficient preservation of structural and mechanical conditions obtained after ECAP.
Obrabotka Metallov / Metal Working and Material Science. 2016;(1):52-59
52-59
The effect of normalization on the structure and mechanical properties of rails aluminotermitic welded joints
Abstract
The article is devoted to improving the quality of rail aluminotermitic welded joints. The analysis of the causes of rail aluminotermitic welded joints failure is given. The results of an experimental research of the effect of normalization on the hardness and structure of metal rail welded joints are studied. It is shown that without heat treatment the hardness of rail welded joints increases from 24 HRC to 38 HRC in the fusion zone of the weld metal and rail metal. The hardness is confirmed by microstructural analysis. Microstructural analysis showed the differences in the grains sizes of metal welded zone and heat affected zone. The structure of welded metal is acicular dendritic. Owing to a difference between structures of the welded joint zones the probability of occurrence of cracks on the boundary of fusion weld and metal is increased. It is found that the normalization of rail top aluminotermitic welded joints at temperature 850…900 °C provides the formation of ferrite-pearlite structure in the welded zone. The normalization formed fine-grained metal structure with a hardness, which approximate to the hardness of rail in the heat affected zone (along the fusion line). The normalization eliminates the harmful effects of overheating of the metal during welding. It is noted that heat treatment of rail aluminotermitic welded joints slightly changes mechanical properties, such as hardness, in the welded zone. But, hardness decreased by 8..10 HRC in the heat affected zone. This investigation has shown that the normalization of rail aluminotermitic welded joints reduces the probability of occurrence of brittle destruction in the heat affected zone during the operation of continuous welded rail.
Obrabotka Metallov / Metal Working and Material Science. 2016;(1):60-66
60-66