No 3 (2017)
- Year: 2017
- Articles: 6
- URL: https://journal-vniispk.ru/1994-6309/issue/view/19972
- Description:
Full Issue
TECHNOLOGY
Analysis, modeling and prediction of surface roughness of copper, obtained by selective laser melting
Abstract
Unlike traditional methods of material removal, rapid prototyping technologies are aimed at creating complex products by sequentially adding material (materials). By now, a large number of rapid prototyping methods, which differ in the material used and in the method for shaping the article, are known. Innovative is the method of selective laser melting of physical copies of various objects from metals, alloys and metal-matrix composite materials to meet the requirements of the Aerospace, Defense, Automotive and Biomedical Industries. An important direction in the development of selective laser melting technology is improving the quality of the product being formed. This is a complex multi-parameter process, in which it is possible to isolate about 130 parameters that affect the final result. The paper presents the results of experimental studies of the influence of argon shielding gas, mechanical activation of powder and the effect of technological melting modes: laser radiation power, laser beam travel speed, scanning step, preheating temperature of the powder material on the surface roughness obtained from copper powder material by selective laser melting. Melting experiments of copper powder are implemented in a layer-by-layer laser melting unit of the original design, which allows regulating all technological melting modes. The surface roughness is determined by the Olympus LEXT OLS4100 digital non-contact microscope. A mathematical dependence of the roughness of the surface layer from copper powder on the technological melting regimes is obtained on the basis of the theory of experimental planning and static processing of the results. Significant parameters of the regime are determined: laser radiation power, laser beam moving speed, scanning step, affecting the layer roughness. As well as the range of its change from 480 to 725 microns with an increase in power from 14 to 30 watts, the laser beam travel speed is 1400 mm/min, the powder heating temperature is 114 oС, the scanning step is 0.2 mm. From 750 to 480 μm with an increase in the speed of the laser beam from 200 to 3000 mm/min, power 22 W, powder heating temperature 114 °C, scanning step 0.2 mm. An increase in the scanning step from 0.1 to 0.3 mm leads to a decrease in the roughness from 740 to 525 μm with a laser beam moving speed of 3000 mm/min, a power of 30 W, a powder preheating temperature of 200 °C. The positive influence of the protective atmosphere and mechanical activation of the powder material on the quality of the surface layer is shown.
Obrabotka Metallov / Metal Working and Material Science. 2017;(3):6-16
6-16
Enhancing the effectiveness of the diamond metal bond instrument when grinding high-strength materials
Abstract
The objective is to identify the nature of the clogging process at the implementation of abrasive instrument in the processing of tough materials and to propose the technology recommendations to minimize the clogging, which will enable the enhanced use of the diamond metal bond instrument during grinding and reducing the costs of advanced and competitive products manufacturing. The research provides the analysis of the diamond metal bond wheels cutting capacity. It also gives a brief overview of the reasons for the loss of the abrasive instrument working capacity as well as evaluates the adhesive and diffusion processes in the cutting zone. The clogging of the grinding wheel is noted to be the main reason for the low working capacity of the diamond instrument. Methods: The experimental research was carried out on the 3D642E machine modernized for the process of the electric discharge diamond grinding and corresponding to the metrological requirements for the verification of product quality indicators. Structural research was carried out using optical and scanning microscopy, spectral and X-ray analysis. The samples were investigated on ARL X'TRA X-ray diffractometer, Carl Zeiss EVO50 scanning electron microscope with the EDS X-Act Integrated Chemical Analyzer and Carl Zeiss Axio Observer A1m optical microscope. The surface of the samples was additionally investigated by optical interferometry techniques using the surface topography complex Zygo Newviewtm 7300 which is designed to define the microrelief and structure parameters of the objects of technical and biological origin. Results and discussion: The proposed technology for the grinding of high-strength and nanoreinforced materials by the diamond metal bond wheels is based on maintaining the wheel high cutting properties by a continuous electrochemical dressing. The use of combined grinding technology makes it possible to significantly increase the working capacity and scope of the diamond metal bond abrasive instrument as well as to improve the processing of various hard alloys containing tungsten, cobalt, titanium or tantalum, oxide and carbide metal ceramics and nanostructured material based on zirconium boride.
Obrabotka Metallov / Metal Working and Material Science. 2017;(3):17-27
17-27
Enhancing the effectiveness of the diamond metal bond instrument when grinding high-strength materials
Abstract
Welded rail joints are integral part of continuous welded rail. However, its reliability during the operation is no sufficiently high. The influence of the grinding process of aluminothermite welded rail joints, performed at different values of the residual post-weld temperature of the weld, on the physical and mechanical properties and roughness of the rolling surface is investigated. The process of grinding is carried out at different values of residual post-weld temperature. The interval of post-weld temperatures in the zone of grinding of welded joints was 600…850 ° C. It is established that, different temperature regimes, when performing the technological operation of grinding aluminothermite joints, lead to the formation of non-identical mechanical properties of the metal surface of the rail head in the weld zone. Grinding at a residual post-weld temperature of the weld surface of 850 ℃ or 600 ℃ allows the highest hardness values of 33 ... 36 HRC to be achieved, while grinding at a residual temperature of 800 ℃ or 700 ℃ results in a decrease in the hardness of the weld metal to 25 ... 30 HRC. However, after grinding when the residual post-weld temperature is 800…700 ℃ hardness of the welded metal decreases from 25 to 30 HRC. Reducing the temperature of the metal surface of the railhead before grinding from 850 ℃ to 600 ℃ allows reducing the roughness of the rolling surface from 2.5 microns to 0.7 microns. The received results indicate that the highest values of hardness and surface finish can be reach when temperature of rail welded joint head metal is 600 ℃ during grinding when carrying out process of welding. It can be claimed that grinding of rails welded joints in a hot state is the perspective direction in the field of improvement of post-weld technological process of welded joints.
Obrabotka Metallov / Metal Working and Material Science. 2017;(3):28-34
28-34
EQUIPMENT. INSTRUMENTS
Dynamic instability of the flight control connecting rod in technological tests
Abstract
For technological control strength of the flight control connecting rod (further rod) selective destructive tests of ready details in static and pulsating axial loads are used. In order to decrease the time and to use non-destructive control methods rods are tested on the experimental installation, which has the two-mass oscillating system. The oscillating system consists of a rod with two identical tipweights and hanging on a thin steel string vertically. A rod under action a longitudinal force P ( t )= = P cos Ω t has the resonant longitudinal oscillations which occur in actual use. A rod is the resonant longitudinal oscillations for the second natural form. The first natural form corresponds to the movement of a rod with end loads as a rigid body and has no practical interest. Experiments showed that there is a dynamic instability in the form of parametric resonance of longitudinal oscillations. In this case, besides the longitudinal oscillations further transverse (bending) oscillations appear. It is interesting to determine the conditions for the emergence of parametric resonance of a rod in the process of technological tests. The analytical solution of the problem results in the Mathieu’s equation. The results of solving this equation for various combinations of the coefficients of the equation represented as Ince-Strutt diagram. The calculation of the Mathieu’s equation of the rod with dimensions D × d × l = 35 × 32 × 1200 (mm) shows that at operating stress of 10 MPa the rod works in the zone of dynamic instability. This fact is confirmed experimentally. Experiment with the short rod by dimensions D × d × l = 25×22×600 (mm) showed that the rod is experiencing longitudinal oscillations without transverse oscillations up to stress 68 MPa. Thus, the short rods have a bigger range of working stresses at the experimental installation. The Mathieu’s equation is valid for all rod sizes. The equation allows determining such parameters of the oscillating system, in which the rod would experience only the longitudinal oscillations, which takes place in real conditions.
Obrabotka Metallov / Metal Working and Material Science. 2017;(3):35-41
35-41
MATERIAL SCIENCE
Structure features of B4C-Ni-Р plasma coatings
Abstract
Purpose: This paper considers the structural features of B4C-Ni-P coatings obtained by air-plasma spraying with the unit for annular injection of powder. Materials and methods: (B4C) boron carbide powder clad with 30 wt. % Ni-P is used. The powder is deposited on pipes of low-carbon steel (0.2 % C) by air-plasma spraying with the unit for annular injection of powder. The structure and phase composition of coatings are studied by optical microscopy, scanning electron microscopy with the microanalyser EDS, transmission electron microscopy and X-ray diffractometry. The microhardness measurements results are also presented. Results and discussion: The high-quality composite coatings with low porosity can be formed using plasma spraying. The combination of the optical and scanning electron microscopy as well as X-ray diffractometry revealed the composition of the plasma coatings. It consists of B4C particles up to 30 μm sizes that are equally spaced in a metal matrix. The metal matrix consists of nickel borides (Ni3B, NiB and Ni3B4). Areas with roundish inclusions about 500 nm diameter are surrounded by boron carbide particles. These areas are characterized by a higher content of nickel, phosphorus and boron. B2O3 boron oxide and NiO nickel oxide are also presented in the coating. The microhardness local measurements demonstrated that the microhardness of boron carbide particles is 3000…4000 HV, the metal matrix is 400 ... 550 HV and the areas with roundish inclusions is 200 HV. According to the transmission electron microscopy data thin interlayers with an amorphous-crystalline structure up to 1 μm width are formed between the boron carbide particles and the metal matrix. The metal matrix constitutes areas with a nanocrystalline structure and columnar crystals that located in the coatings volume at random.
Obrabotka Metallov / Metal Working and Material Science. 2017;(3):42-50
42-50
Modification of Al-Si alloys with particles of ultrafine tungsten powder
Abstract
Purpose: A widespread method, exerting the influence on the homogeneous formation of the microstructure and enhancement of strength properties of Al-Si alloys, is a modification by super- and nanodispersed particles of different chemical compositions. Despite the significant advances in the studies of the influence of various modifying compositions on the structure and mechanical properties of casted silumins, there are no data about the influence of nanodispersed tungsten powder on the formation of the structural-phase state and mechanical properties of the Al-Si alloy in the literature. Materials and methods: The paper investigates the influence of the tungsten nanopowder in the amount of 0.01…0.5 mass.% on the structural-phase state and mechanical properties of the Al-12%Si alloy with different soaking time of the modified melt. Metal smelting is conducted in the muffle furnace. Modification of the melt by the ultrafine powder is carried out before pouring. Before introducing the powder into the melt, its chemical, phase and granulometric composition is studied. For the obtained samples, metallographic examinations are made and the chemical composition, as well as impact toughness are determined. Results and discussion: The results of the conducted experiments showed that a part of the powder is not assimilated by the melt, but precipitated on the walls and the bottom of the crucible. The amount of the powder, not assimilated by the melt, depends on the soaking time. The assimilated powder influences significantly the cast structure; silicon plates are significantly refined; the sizes of the first-order axes and the distances between the axes of the second order decrease for the matrix crystals of casts. These changes in the structure influence largely the properties. Modification of the Al-12%Si alloy by the tungsten powder and soaking it in the furnace during 10 minutes allow increasing impact toughness by ~15%. By the results of the experiments, it has been established that addition of 0.1 mass.% of tungsten into the melt and soaking it in the heated condition before pouring is an optimal mode. Such mode leads to a uniform distribution of eutectic (α-Al + Si), a 1.5-time reduction of eutectic silicon plates, a change of the form of coarse plates into a fine fibrous form and enhancement of mechanical properties by 15…20 %.
Obrabotka Metallov / Metal Working and Material Science. 2017;(3):51-58
51-58