Key Engineering Materials Vol. 910

Abstract: The competitiveness of engineering products in the world market is often determined not only by the quality and operational characteristics of products, but also by the cost saving level and labor intensity of their manufacture. This became especially relevant when a wide range of high-strength and difficult-to-machine construction materials appeared, the processing of which by conventional methods is difficult and ineffective. In recent years, various methods are increasingly used for the shaping of parts made of these materials, the efficiency of which is higher due to the combination of several types of effects on the processing object - combined methods. So, for example, the methods of electrolytic abrasive machining with abrasive disks on a conductive bond have replaced the traditional grinding. One of the particular cases of method implementation is processing with a periodic change in the current pulse direction: direct polarity for electrochemical softening of the processed surface, reverse polarity for restoring the cutting ability of an abrasive tool. Whereanent, the purpose of the work is to establish the effect of dressing current pulses duration on the surface roughness of products made of corrosion-resistant steel of 12H18N10T grade. For laboratory research, a bench was designed and manufactured to simulate the conditions of combined processing. It has been experimentally proved that the smallest roughness value Ra = 0.26 μm is observed at the following values of the current pulse duration: the current pulse of direct polarity duration τ_st = 1 s and the current pulse of reverse polarity duration τ_re = 1 s. This allows us to recommend the indicated values in order to ensure high quality of processed surfaces of products made of corrosion-resistant steel 12H18N10T of grade

Abstract: Two schemes of thermomechanical processing of F420W cold-resistant steel to produce sheets with thickness of 5 and 15 mm for manufacture of wind turbine towers, were developed and tested in laboratory conditions. The first scheme simulated hot rolling on a continuous mill, including reductions with minimal inter-deformation pauses and subsequent slow cooling. The second one corresponded to hot rolling on a reverse mill with accelerated cooling. Mechanical properties were analyzed taking into account the related structural features. Technological recommendations for hot rolling of a thin sheet made of high-strength cold-resistant steel were proposed.

Abstract: Stainless steel 304 is one of the most promising materials for many industrial applications. Its machinability is poor whether machined in any environment. Conventional machining causes environmental degradation as well. In this paper, sustainable machining of SS304 using green lubricant is presented. Experiments have been conducted on Taguchi’s robust design of experiment technique. For machinability enhancement, a hybrid optimization technique VIKOR-Regression-PSO is employed. Machinability indicators that have been considered are tool wear, surface roughness, and chip reduction coefficient. Cutting speed, depth of cut, and feed rate have been considered as the variable machining parameters in this work. The hybrid optimization has been found very effective and provided a set of optimum machining parameters i.e. cutting speed-70m/min; feed rate-0.1mm/rev; depth of cut-0.5mm for the best values of machinability indicators i.e. tool wear-249.22 μm, roughness-11.08 μm, chip reduction coefficient-2.26.

Abstract: The requirements of gears are increasing rapidly in the global market for applications from micro electro mechanical systems (MEMS) to aerospace. Gears of various profiles and types including spiral-conical are used for motion as well as torque transfer in microsystems. The development of such gears is a challenging task because no compromise in their quality is acceptable. It necessitates highly accurate gear manufacturing process. This article presents such a process i.e. wire-assisted electrical discharge machining (WEDM) and development of stainless-steel made spiral-conical gears of miniature size. All minute aspects of spiral-conical gear development by WEDM are reported in this paper. In order to investigate the impact of process parameters and gear quality, an experimental study has been conducted based on Taguchi’s robust design of experiment technique. The developed gears are found with good manufacturing quality characteristics.

Abstract: An approach to the development of the full-scale specimens for an experimental method to determine the residual stresses in the circular grooves of body parts is described. The selection of the specimen shape is based on the fulfillment of the geometric and force similarity conditions. The form of a surveillance specimen and loading conditions are proposed, during which all the equally-spaced points of the specimen experience an equal stress-strain state. This approach enables to correctly determine the residual stress levels for various methods of the part machining by cutting.

Abstract: This article investigates the automatic welding of Ø4.5 mm high carbon steel wire frame. Using spring steel wire frame in car seat fabrication reduces its weight and helps to maintain rigidity. The thermal effect during the welding process can unacceptably deteriorate the mechanical properties of the material. It is proposed to use preheating and heat treatment to obtain a joint with required mechanical properties. To reduce of effect on entire product rigidity the thermal treatment was carried out locally in the zone of joining. Heating was carried out using a gas flame. Metallographic and microhardness measurements were used for the structural study. Mechanical properties were evaluated by static tension and free bending test. The recording of thermal cycles during the welding and heat treatment was carried out using chromel-alumel and tungsten-rhenium thermocouples.

Abstract: The simulation of hydro-mechanical billet pressing of bimetallic composite is performed. Using mathematical modeling and simulation exercise, the influence of the main operational parameters, which include: draw-forming, the cone angle of the working die and the conditions of contact friction, on the strain heterogeneity, damage to the fibers (cores), and the extrusion stress, is studied. A method and an expert system were developed that allowed to carry out a computational experiment and a multi-criteria choice of rational values of the technological experiment is carried out. The results of the study are used to improve the industrial production of multi-core bimetallic wires for electrical purposes.

Abstract: This article is devoted to establishing the relationship between the state of the material, phase transformations, and the formation of the microstructure of structural steels widely used in mechanical engineering, as well as for the manufacture of welded sealed bulk structures including capsules for hot isostatic pressing.

Abstract: The results of a technological process development for obtaining a wear-resistant powder coating of Ni-Mo-Al system, applied by cold gas-flame spraying to the surface of a critical unit of compressor equipment in the oil and gas industry, within the framework of repair production are presented. Using scanning electron microscopy (SEM), the features of the structure and distribution of alloying elements in the coating are determined. The authors rationalized mechanical processing of the surface layer in order to obtain minimum roughness of the working area of the compressor cylinder. It is shown that the sprayed coating of Ni-Mo-Al system has a satisfactory adhesion strength in the range of 30-50 MPa, microhardness of 200-210 HV, which provides an increased running-in rate of piston rings of 6-10 mm³/Nm when operating the compressor in the temperature range of 350 - 400 °C. The parameters of finishing machining process of the finished coating are worked out, which makes it possible to ensure the minimum possible roughness of the coating of Ni-Mo-Al system in the range of 0.08-0.15 Ra in order to reduce wear of the working surface and extend service life.

Abstract: As a result of implemented modernization of known electrode composite material based on Cu-3% wt BN copper powder successfully used for electrical discharge machining of high-strength alloys, composite material (Cu - 3% wt BN) – 0.5 % wt Al – 0.25 % wt in the form of high-density long thin-wall plates for operations of electrical discharge cutting and piercing of hard-to-machine materials was obtained. The new material was obtained with the use of the method of reactionary mechanical alloying of initial powder components in the attritor. Tool electrodes made of the new material during electrical discharge piercing of rectangular holes in titanium alloy sheets ensure a 1.6 times higher machining rate comparing to tool electrodes made of the Cu-3% wt BN prototype material. After replacement of rolled copper in tool electrodes with the new composite material the machining rate will increase 4.1 times. The tool electrodes made of this material have significantly lower electrical discharge wear comparing to the wear of tool electrodes made of the prototype material and rolled copper.