Analysis of the Cutting Abilities of the Multilayer Grinding Wheels—Case of Ti-6Al-4V Alloy Grinding

This paper presents an effectiveness analysis of the grinding process with the use of a new multi-layer abrasive tool. The designed abrasive tool consists of external layers with a conventional structure, whose task is to decrease the grinding wheel load and ensure high grinding volumetric efficiency. The inner layer of the grinding wheel contains a 30% addition of abrasive aggregates. The task of the inner layer is to provide lower roughness of the machined surface. The aim of the research presented in this paper was to evaluate the topography of the designed abrasive tool and to analyze the middle layer properties influencing the machined surface roughness. The differentiation of the active surface features of the abrasive tool was determined for the conventional layer and the layer with the addition of abrasive aggregates. The machining potential of the layers was also determined using the Shos parameter. The surface topography of Ti-6Al-4V alloys ground with the use of a multi-layer wheel and a conventional grinding wheel was analyzed. With the application of the bootstrap hypothesis, the set of roughness parameters differentiating the topography of ground surfaces was determined.

Anodic Dissolution Behaviour of Passive Layer During Hybrid Electrochemical Micromachining of Ti6Al4V in NaNO3 Solution

Titanium and its alloys are considered as difficult to cut material classes, and their processing through the traditional machining methods is a painful task. These materials have an outstanding combination of properties like high specific strength, excellent corrosive resistance, and exceptional bio-compatibility; therefore, they have broad fields of application like aerospace, MEMS, bio-medical, etc. Electrochemical micromachining (ECMM) is a very vital process for the production of micro-domain features in difficult-to-machine materials. The machining issue with ECMM for titanium and their alloys is the passive layer formation, which hinders the dissolution and causes stray removal. To overcome these issues, a hybrid ECMM approach has been proposed by using a diamond abrasive tool combined with ECMM. The present study focuses on the detailed characterization of the passive layer formed using the hybrid approach. Through the use abrasive tool, the abrasive grits scoop the passive layer by the mechanical grinding action, formed in micro-drilling on the Ti6Al4V alloy to expose a new surface for further dissolution. The micro-holes were produced incorporating the abrasive tool and then compared by the holes created using a cylindrical tool (tool without abrasive). The taper and the stray dissolution of the micro-holes were also compared, produced at different applied potentials. The minimum average entry overcut and exit overcut of the hole were obtained as 29 µm and 3 µm, respectively, also a micro-hole with the lowest taper of 2.7°, achieved by the use of the abrasive micro tool.

Scythian Burial-Mound 7 in the “Vodovod” Group in the Lower Reaches of the Dniester River

Materials obtained during investigation of Scythian burial-mound 7 in the “Vodovod” group in 2017 near the village of Glinoye in the Slobozia District on the east bank of the Lower Dniester are published here for the first time. The burial-mound contained five burials – four in pits and one in a catacomb. The burials in pits had been deposited at the turn of the 4th century BC and the catacomb burial dated from the first third of the 3rd century BC. The graves belonged to ordinary members of the community but contained a fairly distinctive range of grave goods. It was made up of weapons (arrowheads and an axe) and horse harness (a bit and a cheek-piece), vessels (a wooden dish, hand-moulded pot and a hand-moulded bowl), tools (knives, awls, a needle, spindle whorls and an abrasive tool) and jewellery (rings, a metal bracelet, beads, pendants made of shell, oolitic limestone and canine teeth of dogs). In addition tassel-holders, a bronze mirror and a flint strike-a-light were found. A bronze ring from burial 7/2 reflects La Tène influence and the hand-moulded cup from burial 7/4 reflects Thracian influence on the material culture of the Scythians in the North-West Pontic region. In general the funerary rite and range of grave goods demonstrate the transformation of Scythian culture during the second half of the 4th and first half of the 3rd century BC.

Technological fundamentals of polymer-composite parts with flexible abrasive tool

There are presented investigation results of polymer-composite parts abrasion. The dependences for the definition of surface roughness at polymer-composite material hydro-abrasive cutting are shown. The results of theoretical and experimental investigations of hydro-abrasive cutting processes are presented. A procedure for their carrying out, tool and equipment used is described. The results of experimental investigations on polymer-composite parts preparation to splicing are shown. A procedure for designing a technological process of polymer-composite parts abrasion is offered.

SURFACE ROUGHNESS IMPROVEMENT OF PARTS MADE OF POLYMERIC MATERIALS OBTAINED BY MEANS OF ADDITIVE TECHNOLOGIES

In the paper there is under consideration an effort to achieve the roughness index of Ra <0.8 with the aid of soft abrasive tool use. As a result the purpose of this work became development of the technology for surface quality improvement of parts manufactured with the aid of additive technologies. The authors carried out a number of experiments with the samples manufactured with the aid of the method of FDM print. With the aid of 3D Ultra 3 printer of EnvisionTec company. The samples were made of ABS-plastic in the amount of 6 pieces. On each sample there were defects after printing which contributed to the deterioration of surface quality in products. By means of TR220 profilometer there was measured roughness before and after the experiment. There was carried out dry processing and with the use of SCL. As a result, dry processing resulted in worsening surface quality, heavy wear of an abrasive tool and grain contamination. Analyzing the data obtained from the profilometer in the experiment and SCL use a considerable improvement of the surface layer quality at minimum allowance is observed. Investigation methods: in the work basis there are experimental methods of investigation. The investigations are carried out with the use of a microscope and profilometer. Processing investigation results was carried out as a result of the comparison of the measuring data obtained. Work Novelty: there are defined conditions of soft abrasive tool operation and SCL impact upon Ra indices. The results obtained indicate a possibility of Ra improvement on a part surface which is achieved due to a combined shaping with the aid of additive technologies and further machining carried out on a single technological basis. The experience without SCL use has shown the overheating possibility the result of which is a meltback and plastic sticking both on the surface, and on abrasive grains of the cutter which is inadmissible and results in considerable worsening of Ra on the surface machined and cutter wear. In view of this the SCL use in finishing is promising, but to achieve better results SCL chemistry must be improved.

Simulation of the stock removal in the contact zone during internal grinding of brittle non-metallic materials

Introduction. Finishing operations, in particular, cylindrical grinding, essentially form the quality parameters of products, its performance characteristics and functional suitability. At the same time, the cost of grinding work increases significantly in comparison with grinding metals, reaching an average of 20 ... 28% of the total cost of manufacturing products. The selection of the optimal parameters of the technological system based on the process simulation can improve the reliability, productivity and economic efficiency. To describe the processing of brittle nonmetallic materials, empirical dependences are mainly used, and the existing analytical models do not take into account the stochastic nature of the grinding operation and the combination of microcutting and brittle chipping when removing particles of brittle nonmetallic material and wear of the surface of the grinding tool. Purpose of the work: simulation of stock removal in the contact zone during internal grinding of brittle non-metallic materials. The task is to study the features and patterns of change in the probability of material removal when the treated surface comes into contact with an abrasive tool. In the work, the theoretical and probabilistic models are obtained, allowing to reveal the patterns of material removal in the contact zone. The models make it possible to trace the regularities of the interaction of cutting and piercing grains on the surface of the workpiece and the process of removing the allowance in the contact zone due to a combination of the phenomena of microcutting and brittle chipping, considered as a random event. The research methods are mathematical and physical simulation using the basic provisions of the theory of probability, the laws of distribution of random variables, as well as the theory of cutting and the theory of a deformable solid. Results and discussion. Data are obtained that provide a clear illustration of the patterns of material removal along the contact zone at various levels. Analysis of the results obtained shows that the peripheral speed of the tool and the rotation speed of the workpiece, which are directly included in the equation for calculating the probability of material removal, significantly affect the rate of material removal. The cross feed also has a significant effect on stock removal. A qualitative picture of the change in the probability of material removal in the contact zone during grinding of holes in brittle nonmetallic materials is obtained. The obtained patterns of change in the probability of material removal when the machined surface is in contact with an abrasive tool and analytical dependences are valid for a wide range of grinding modes, tool characteristics and other technological factors.

STABILIZATION OF QUALITY AND PRODUCTIVITY OF GRINDING OF EXTENDED CYLINDRICAL SURFACES OF SHAFTS WITH PETAL CIRCLES

Статья посвящена проблеме стабилизации показателей лепесткового шлифования протяженных цилиндрических заготовок для исключения влияния изнашивания инструмента на качество и производительность данной обработки. Представлены результаты исследований влияния изнашивания абразивного инструмента на процессы съема металла и формирования шероховатости обрабатываемой поверхности при лепестковом шлифовании. Более интенсивно изнашиваются круги большей зернистости, причем стойкость инструментов зернистостью 12…20 (ГОСТ 3647- 80 (в ред. 1995 г.)) в 2…3 раза выше кругов зернистостью 40…50 и составляет 5...10 минут. Приведены данные по стойкости лепестковых шлифовальных кругов с учетом основных факторов процесса обработки. Установлено, что скорость съема металла при шлифовании неизношенными лепестковыми кругами зернистостью от 12 до 40 составляет 130...270 мм/мин, параметр шероховатости Ra находится в пределах от 0,4 до 3,0 мкм, Sm - от 0,08 до 0,20 мм. Значения параметров шероховатости обрабатываемой поверхности вследствие изнашивания инструмента возрастают до 2-3 раз, а скорость съема материала с течением времени непрерывно уменьшается и может стать равной нулю. Предлагается стабилизировать показатели лепесткового шлифования путем непрерывного или периодического увеличения деформации (натяга) инструмента в процессе абразивной обработки, что позволит поддерживать на необходимом уровне требуемое число режущих зерен The article is devoted to the problem of stabilization of indices of petal grinding of extended cylindrical billets in order to exclude the effect of tool wear on the quality and productivity of this treatment. We present the results of studies of influence of abrasive tool wear on processes of metal removal and formation of roughness of treated surface during petal grinding. Circles of greater grain wear more intensively, and the resistance of instruments with grain 12... 20 (GOST 3647- 80 (ed. 1995)) is 2...3 times higher than circles with grain 40...50 and is 5...10 minutes. We give the data on resistance of blade grinding wheels taking into account the main factors of the processing process. We found that the rate of metal removal when grinding with unworn petal circles with grain size from 12 to 40 is 130...270 mm/min, the roughness parameter Ra can vary in the range from 0.4 to 3.0 μm, Sm - from 0.08 to 0.20 mm. The values of the roughness parameters of the treated surface due to wear of the tool increase by 2-3 times, and the rate of material removal over time continuously decreases and can become zero. We proposed to stabilize the indicators of petal grinding by continuous or periodic increase of deformation of the tool during abrasive processing, which will allow one to maintain the required number of cutting grains at the required level

Grinding of Titanium Alloys

X-ray spectroscopic microanalysis was used to determine the concentration of titanium on the surface of the wear spot of a silicon carbide crystal during micro-scratching and the concentration of silicon on the treated surface after grinding by a wheel of silicon carbide. The wear resistance and grinding coefficient of titanium alloys under micro-scratching with single crystals and grinding with wheels made of corundum, silicon carbide, cubic boron nitride and diamond were determined. The morphology of the treated surface and the regularities of changes in the indicators of the grinding process of titanium alloys with circles of various characteristics were studied. The features of the process of grinding titanium alloys using various lubricants and coolants are shown. The influence of the characteristics of the abrasive tool and grinding modes on low-cycle fatigue on the operation of flat and round grinding of samples made of titanium alloys VT9 and VT22 was studied. The influence of abrasive material, grinding speed, feed and sparkout during finishing on low-cycle fatigue was analyzed. Based on the research, recommendations were given for choosing a rational characteristic of the abrasive tool and processing modes.