No 3 (2015)

One of the major reasons of failure of the hydraulic cylinders is scratches and teases on the barrel mirror surface. The methods of recovery of the hydraulic cylinder barrel mirror surface are examined. These methods include methods of size repair and methods of plate applications. The galvanic method might allow the recovery of defects associated with the break of tightness. For the experiments the samples sizes 25х25х5 mm made of steel 45 GOST 1050-88 are used. Preparation of samples before the coating includes mechanical (grinding operation and polish) and chemical treatment (deoiling, descaling and activation dipping). Experimental investigations of the electrolyte temperature and cathodic current density effect on galvanic coating quality and thickness have been carried. Current densities varied from 3 to 12 A/Dm 2 with the step 3 A/Dm 2. The temperature is varied from 20 to 80° C with the step 20° C. It is found that at a temperature of 40 ° C highest thickness of the coating received in the investigated range of current densities. When the temperature of electrolyte is 80° C the coating have dendrite structure, associated with a reduction cathodic polarization. It is shown that when current density is 9 A/Dm 2 coating uniformly distributed over the surface of the sample and the porosity of coating is minimal. Increasing of porosity of the coating is associated with decreasing of the current density. When current density is 12 A/Dm 2 the coating have spongioid deposits, due to the low amount of metal ions in the electrolyte near the cathode.

Purpose: The required operating features of machine parts are mainly formed at the final stage of its production process. In this regard, the objective is to investigate the features ensuring the quality characteristics of the surface layer of products, achieved at the last step of the integrated processing - diamond smoothing. Methods: The experiments were performed on a lathe equipped with an additional source of energy, in the function of which the external quenching circuit providing high-energy high-frequency heating was used. Structural studies were carried out with appliance of optical and scanning electron microscopy. Stress-strain state of the surface layer part was evaluated by X-ray and mechanical methods for the determination of residual stresses. The surface roughness assessment was implemented on the profilograph-profilometers Form Talysurf Series 2 and Zygo New View 7300. Results and Discussion: It is found that the diamond smoothing of samples of steel 45 under the proposed principle of integration, which allows processing of parts from one technological base, makes it possible to increase the surface microhardness and residual stress level of compression achieved during the transition surface hardening by high frequency. The formation in the surface-hardened sample a hardened (cold-worked) layer having a thickness of 0.01 ... 0.02 mm after diamond burnishing is experimentally confirmed. Its microhardness is ~ 868 HV, while the level of compressive stress in the surface layer increases to values s t = -678±20 МPa. The rational range of the smoothing power Рy Î [100; 150] N, which guarantees a minimum value of roughness Ra = 0.18±0.08 mm, is determined. The functional dependence of the parameter Ra on processing modes which can be used during the diamond smoothing, based on the high performance and the desired surface roughness is obtained.

The problems of the cut microgeometry formation during aluminum and copper alloys high-precision plasma cutting, which is a promising technology for blank production, are considered. Experimental studies were conducted on samples of aluminum A5M and copper M1 made of a sheet metal with a thickness of 3 mm and 2 mm, respectively. As technological scheme for cutting aluminum alloy a Hi-Focus mode with current I = 35 A at the processing speed V = 1.2 m / min is used. To study the characteristics of cutting copper alloy the Hi-Focus technological scheme, designed for cutting carbon steels, mode with current I = 35 A at a processing speed V = 1.5 m / min. The formation of the surface morphology of the aluminum cutting process is defined as the interaction of the plasma arc column with the material being treated, and the deposition portion of the melt at the bottom of the cut. This is explained by a lack of efficiency of gasdynamic flows to completely remove the product of melt from the channel the cut due to the high kinematic viscosity of the material being processed. It is shown that the deposition of the melt on the cut surface deteriorates the microgeometry forming roughness Ra = 12.1 microns. High kinematic viscosity of aluminum does not exclude burr formation on the edges of the cut. When high-precision plasma cutting copper surface morphology of the cut is uniform in character without any traces of deposition of melt. With regular character of the surface topography of cut it reaches its roughness values Ra = 5.98 microns. Formation of the channel cut copper is not accompanied by the formation of burr at its edges.

A great number of parts which are used in in machine building industry contain deep holes. Its production requires a special tool with a large length-to-diameter ratio boring bar. The boring bar significantly changes its length during lengthy blanks processing. Therefore, natural frequency of the tool changes too. Deep hole boring is inevitably accompanied by the appearance of the resonance, when the forced oscillation frequency, dependent on the operating mode, multiples the natural oscillation frequency of the tool. There is another phenomenon accompanying the deep holes’ machining, called chatter. This kind of self-excited vibration can also lead to resonance. It causes various working errors to appear, the one hardest to reduce being the wall thickness variation, which is presented due to the tool axis deviation in relation to the axis of the hole. Authors suggested a boring bar equipped with gyroscopic stabilizer. It contains a frame mounted on the body of stabilizer by the means of cardan suspension, which provides two degrees of freedom for the gyroscope. The third degree of freedom is offered by the boring bars’ body. Gyroscopic stabilizer mounted inside the boring bar and behind the tool. Thus, when the boring bar starts to bend the frame simultaneously starts to swing and it achieves the lateral vibration suppression. The paper covers the proposed method of deep holes manufacturing. A structure of gyroscopic stabilizer for boring bars with a large length-to-diameter ratio is presented. The experimental stand for the study of the process of damping by the proposed method is described. Ninefold reduction of the amplitude of the resonant vibrations is achieved in the forced oscillations frequency range of 152...1100 rad/s for following values of the natural oscillations frequency of the tool model: rad/s, rad/s, rad/s, rad/s. It is established, that achieving lower values of the vibrations amplitude requires the tool to be maintained in a resonant or near-resonant state. It allows minimizing tool axis deviation and its consequences, which reduce the accuracy of the deep hole machining.

The main difficulties in austenitic steels welding are associated with the need to increase the resistance of the weld metal and heat affected zone to formation of hot cracks, which are usually divided into crystallization and subsolidus ones. Increased resistance of metal to formation of crystallization cracks is achieved by suppressing the columnar crystallization and structure refining by increasing the cooling rate, alloys purity, using the doping elements-modifiers or elements contributing to the formation of high-temperature second maximally plastic phases (e.g. δ-ferrite). These methods narrow the temperature range of brittleness and increase the plasticity reserve. To increase the resistance of austenitic steels to formation of subsolidus hot cracks during welding, the following methods are recommended: alloying with elements that contribute to creating a fragmented cast structure, increasing the purity of the base metal of interstitial impurities, reducing the time spent by the metal at a high diffusion mobility (increasing the cooling rate of the weld metal), restricting deformations by selecting a rational design of joints, etc. The methods listed above are realized in laser welding, which is characterized by high rates of heating and cooling, a little time of stay of the metal in the molten state. It reduces the diffusion interaction and contributes to formation of fine fragmented cast structure of the joint material. Intense convective stirring of the melt in the weld pool helps to remove non-metallic inclusions. A special role can be played by adding refractory nanopowders (NP) into the forming material the welds. Specially prepared well-wettable refractory nanopowder particles, being introduced into the melt, form a dispersed system in which the solid phase serves as the core of each suspension particle. As a result, each nanoparticle becomes a potential seed for the emergence of the new phase. Due to this, during cooling of the melt, a fine crystalline structure is formed in it, thereby increasing the mechanical characteristics of the solidified alloy. The paper addresses the problem of increasing the strength of the weld on the example of AISI 321 (12Kh18N10T) steel. One-piece welded joints are made by laser welding with the use of nanopowder additives. The values of fatigue strength of the welded joints of the steel under investigation produced with a CO 2 laser and additives of nanopowders TiN and Y 2O 3 clad with titanium and iron are determined. The role of the microstructure, grain size, the nature of distribution of microhardness in the formation of the fracture surface under chosen test conditions is studied. It is found out that the average value of tensile strength for the weld is 690 MPa, which exceeds its value for the steel itself (650 MPa). Even the presence of micropores in the material of the welds did not reduce the mechanical properties compared to the base ones. The relief of the sample fractures corresponds to the viscous failure. The additives of nanopowders increased durability of the material of the joints obtained 2.8 times at the maximum cycle stresses above 460 MPa. At that, the zones of complete fracture by the mechanism of viscous failure constituted 65% of the total area of samples fractures with nanopowders and 78% without them. At lower values of the maximum cycle stresses, share of the complete fracture zone was about 50% of the area of sample fractures.