Materials Science Forum Vol. 973

Abstract: A technique and supporting software were designed to select optimal conditions for turning of ductile materials. Selection of optimal cutting parameters is based on a number of process requirements, including achieving the favourable chip form.

Abstract: The paper provides the results of experimental studies of changes in the depth of the defective layer during milling of various structural materials; shows the convergence of the experimental results with the data published in open-access publishing; substantiates a logical change in the depth of the defective layer at various stages of multi-stage machining; and builds probabilistic tables of milling accuracy.

Abstract: The study analyzes physicomechanical and thermophysical properties of hard alloys with due regard to their chemical composition; reveals the dependence of both the cutting properties and regularities of carbide tool wear from cutting conditions and thermophysical properties of tool material; describes a significant impact of not only mechanical but, first and foremost, thermophysical properties of instrumental and structural materials on tool wear; and identifies ways to reduce the wear rate of a cutting tool.

Abstract: The article is about the increasing of the shape accuracy of a roller bearing during the processing by the abrasive tool without a sheaf.

Abstract: The article is about the study of the obtaining process of the abrasive tool without a sheaf and the processing accuracy.

Abstract: Geometrical characteristics of a discrete grinding wheel, which influence on a mechanical strength of the segments, formed during a high-frequency discretization of the cutting surface by highly concentrated energy flow, were defined. The analytical dependences, which establish interrelation of actual stresses in dangerous sections of a discrete grinding instrument with geometrical and mechanical characteristics of a segment, were determined. On a base of these analytical dependences a designing of a discrete grinding wheel with highly frequency discretization of a cutting surface is executed. The scientific recommendations for choice of dimensional characteristics of discrete cutting surface were proposed. Observance of these recommendations allows getting the abrasive segments with a high mechanical strength.

Abstract: This article studies dry hobbing of external cylindrical wheels by worm wheel hobs and reasons why some gear manufactures use hobbing without cutting fluids. Cutting fluids reduce frictional wear, provides temperature cooling of the tool or workpiece and helps flush away the chips from the cutting zone. But uneven cooling and different cutting conditions on the engaging and disengaging sides of a gear mesh provoke intensive wear of the teeth of the worm wheel hob, thus decreasing the life of worm hobs and increasing both the consumption of cutting tools and expenses for them. In this context, it becomes rather difficult to achieve efficiency and stability for the hobbing process. In the recent times, the cost of coolant disposal has been raised; in some cases, it accounts for 15-20% in terms of shop costs. Research was carried out under the following experimental conditions: a hobbing machine equipped with an automation system of high efficiency and with basic units of high static and dynamic stiffness; a high-accuracy worm hob from powdered metal wear-resistant high-speed steel of grade Р6М5К5; a workholding device with an elastic bush, and various cutting modes. Recommendations are given on using the multi-cycle hob-shifting strategy rather than the strategy of single-cycle shifting; and advantages gained by this technique are observed. Best cutting conditions and precision attained by dry gear-hobbing are described.

Abstract: The paper describes a cause of the geometric accuracy degradation of slender metallic products during their operation, which consists in the relaxation of residual stresses accumulated while product manufacturing. The most promising technology among the existing technologies of residual stress relaxation is based on the use of vibromechanical vibrations. This technology has high performance and low energy consumption. The reason for the relaxation of residual stresses under the action of vibromechanical vibrations is the gradual accumulation of internal energy, which leads to plastic dislocation shifts upon reaching a critical level. The dislocation motion under the action of vibromechanical vibrations continues until the dislocations take a more compact layout that corresponds to the equilibrium energy state. For technological implementation of the process there was developed a method of ultrasonic stabilization of elastic plates, which serve as sensing elements in differential-pressure transducers. The experimental studies of ultrasonic stabilization are carried out. According to the results of the studies, there have been conducted tests of the microstructure of the control samples. It is established that the samples of steel 20CH13 subject to ultrasonic treatment have a more uniform structure than the samples after the factory technology of long "aging". This confirms the assumption about the structural-energy processes occurring during vibromechanical relaxation of residual stresses. The technology of ultrasonic stabilization can be recommended as a replacement to the "aging" technology on the basis of the obtained results.

Abstract: In conventional machining, the process of shaping of products from such new materials as alloys with special properties, composite materials and ceramic materials is rather challenged because of low ductility, intense hardness, diversity of physical and mechanical properties of definite components, etc.

Abstract: This study investigates the possibility of electrochemical removal of the defective layer formed on the surface of the product after its electrical discharge machining. A set of experiments was conducted in different electrolytes based on aqueous and aqueous-organic solvents. The experiments were to trace the influence of such settings of electrochemical machining as current density, electrolyte pumping speed, electrolyte temperature, and an electrode gap upon both the dynamics of metal removal and surface quality. Morphology of the obtained surface was examined by an Olympus BX-51Microscope. The dynamics of removing material (stock) from the work piece was inspected. Appropriate adjustments were made to the machining parameters during the machining of 65G steels, and a preferred composition was selected for the working medium. A sufficient design for production tools was proposed. Pitting corrosion was discovered on the surface of the samples in all studied modes of electrolysis. It was observed that switching from aqueous electrolyte to aqueous-organic electrolyte gave lower material removal rate and longer machining time accordingly. At the same time, a reduction in surface roughness was visualized, together with smaller pits and lower density of their distribution. The obtained results may be applied in operation design for electrochemical machining of steels with relatively high carbon contents.