Grinding Mode Research Articles

Modeling and Simulation Study of Dry Ultrasonic Vibration-Assisted Grinding of Tool Steel With Single Alumina Abrasive Grit

Abstract In the precision fabrication industries, ultrasonic vibration-assisted grinding is widely utilized for the finishing of “difficult-to-cut” materials due to its intermittent cutting mechanism and brittle-to-ductile mode machining. In this study, a two-dimensional finite element model (FEM) of single grit ultrasonic vibration-assisted dry grinding (UVADG) and conventional dry grinding (CDG) of AISI D2 steel has been developed, which taken into account the influence of longitudinal ultrasonic vibration on the workpiece with variable downfeed. The effects of ultrasonic vibration and downfeed on the chip formation mechanism, temperature field, grinding force, and equivalent stress and strain were evaluated by analytical and simulation methods. The results show that the formation of the grinding chips under UVADG is much shorter and straighter than CDG mode at all respective downfeed. The validation experiment compared the simulated and experimental grinding force in both grinding modes to verify the reliability of the FEM results. The validation results demonstrate that the FEM model can accurately describe the single grit UVADG and CDG grinding. At each downfeed, the CDG mode has generated a larger equivalent plastic strain than the UVADG mode, resulting in a higher thermomechanical load on the workpiece. According to the findings, UVADG mode has the least plastic damage on the ground surface, which may improve the surface integrity of the ground component.

The choice of finishing methods and cutting modes in the development of technological operations based on the analysis of data on the quality of the surface layer

In the article, the authors conducted a brief review of the quality indicators of the surface layer of machine parts with various methods of abrasive processing. Recommendations are given on the choice of cutting modes during grinding, recommendations are also given on the refinement of grinding modes based on measurement data in real production conditions. The application of the approaches presented in the article may vary depending on the situation and the current production conditions, it is useful in the implementation of the educational process in the relevant specialized areas of training specialists in the development of course and diploma projects.

DATABASE FOR NUMERICAL SIMULATION OF GAS FLOWS IN A GAS JET GRINDER

The process of material jet grinding is analyzed from the point of view of the granulometric material composition changing in the main elements of the grinding plant. A database of dependencies connecting the technological parameters of the process and the acoustic sig-nal characteristics of the mill operating zones has been created. The advantage of the ap-proach to building mathematical models and creating an automatic control system based on the developed database is the ability to accurately describe most of the factors affecting the grinding efficiency, the possibility of describing with the necessary details for specific mate-rial grinding and obtaining the required size of the ready product. The use of connections between acoustic signals and technological parameters makes it possible to take into ac-count the patterns of changes in the material particle size distribution during the passage of the flow in the grinding plant channels and respond to changes in the product quality or the grinding mode on-line, without wasting time on transport delays.

Влияние на вероятность удаления материала относительных вибраций абразивного инструмента и заготовки при чистовом шлифовании

Introduction. Grinding remains the most efficient and effective method of final finishing that is indispensable in the production of high-precision parts. The characteristic features of grinding materials are that the removal of the material roughness of the workpiece surface occurs due to the stochastic interaction of the grains of the abrasive material with the surface of the workpiece, in the presence of mutual oscillatory movements of the abrasive tool and the workpiece being processed. During processing workpieces with abrasive tools, the material is removed by a large number of grains that do not have a regular geometry and are randomly located on the working surface. This makes it necessary to apply probability theory and the theory of random processes in mathematical simulation of operations. In real conditions, during grinding, the contact of the wheel with the workpiece is carried out with a periodically changing depth due to machine vibrations, tool shape deviations from roundness, unbalance of the wheel or insufficient rigidity of the workpiece. To eliminate the influence of vibrations in production, tools with soft ligaments are used, the value of longitudinal and transverse feeds is reduced, but all these measures lead to a decrease in the operation efficiency, which is extremely undesirable. To avoid cost losses, mathematical models are needed that adequately describe the process, taking into account the influence of vibrations on the output indicators of the grinding process. The purpose of the work is to create a theoretical and probabilistic model of material removing during finishing and fine grinding, which allows, taking into account the relative vibrations of the abrasive tool and the workpiece, to trace the patterns of its removal in the contact zone. The research methods are mathematical and physical simulation using the basic provisions of probability theory, the laws of distribution of random variables, as well as the theory of cutting and the theory of deformable solids. Results and discussion. The developed mathematical models allow tracing the effect on the removal of the material of the superimposition of single sections on each other during the final grinding of materials. The proposed dependencies show the regularity of the stock removal within the arc of contact of the grinding wheel with the workpiece. The considered features of the change in the probability of material removal when the treated surface comes into contact with an abrasive tool in the presence of vibrations, the proposed analytical dependences are valid for a wide range of grinding modes, wheel characteristics and a number of other technological factors. The expressions obtained allow finding the amount of material removal also for the schemes of end, profile, flat and round external and internal grinding, for which it is necessary to know the magnitude of relative vibrations. However, the parameters of the technological system do not remain constant, but change over time, for example, as a result of wear of the grinding wheel. To assess the state of the technological system, experimental studies are carried out taking into account the above changes over the period of durability of the grinding wheel.

Сравнительный анализ механической прочности шлифовальных кругов

The problem of high-strength grinding tool creation is decribed. The possibility of intensifying grinding modes by using prefabricated textured wheels is shown. It is found that high-strength abrasive segments with edge and axial projections should be used, respectively, for narrow and wide prefabricated textured wheels.

Research of the dependence of geometric parameters of holes on electroerosive grinding modes with a changing polarity of electrodes

In this paper are presented the results of electrical discharge diamond grinding with with difference polarities for processing various materials and calculates geometric parameters of erosion holes. The purpose of the study is to determine the volume of holes during electrical discharge diamond grinding using the mathematical method of planning experiments. The experimental plans is a combination of statistical theory and mathematical model, which is very useful in the modelling and analysing the technical problems. As a result of experimental studies, a mathematical model of the volume of holes from electrical modes of the process of electrical discharge diamond grinding was built. The mathematical formula of geometric parameters of holes obtained can be used to determine the volume of holes for different electrical quantities of discharge diamond grinding. It is found that the most significant factors that affect the geometric parameters of holes are the voltage of the igniting pulse and the pulse duration. The dependence of electrical parameters on the hybrid grinding process is investigated. There is a certain volume of holes, at which the discharge acts most efficiently, and the process performance is the most optimal. During the operation of the pulse generator, it is preferable to maintain a certain value of geometric parameters of holes, which results in an unhindered release of metal, since the effect of electrical erosion increases.

Повышение коррозионной стойкости шлифованных деталей рациональным применением энергии ультразвукового поля

The results of experimental studies of the effect of processing conditions on the corrosion resistance of ground parts made of stainless chromium-nickel steel of austenitic class 12X18N9T2 are quoted. It is found that the introduction of ultrasonic field energy into the zone of generation of geometry during grinding makes it possible to increase the corrosion resistance of parts by 12...15%, depending on the grinding mode.

Improving the Corrosion Resistance of Polished Stainless Steel Parts by Introducing the Energy of the Ultrasonic Field into the Forming Zone

This article presents the results of experimental studies of the effect of processing conditions on the corrosion resistance of polished parts made of stainless chromium-nickel steel of austenite class 12X18N10T. It is established that the introduction of the ultrasonic field energy into the shaping zone during grinding can increase the corrosion resistance of parts by 12-15 %, depending on the elements of the grinding mode. The latter is explained by a significantly lower heat-force stress during processing, which, in turn, leads to a decrease in the magnitude and depth of distribution of technological residual tensile stresses along the surface layer.

INFLUENCE OF GRAIN QUALITY INDICATORS ON THE FLOUR QUALITY INDICATORS AT THE LABORATORY MILLING

In the conditions of high competition in the flour market, the development of models that allow to predict the quantitative and qualitative indicators of flour during grain milling and to understand the correlation between grain and flour quality indicators is extremely relevant and requires efforts in this direction. 64 samples of wheat grain from mills situated in different regions of Ukraine, grown in 2019 and 2020 and straight flour obtained from this wheat in the laboratory at the mill MLU-202 were investigated. The data obtained confirmed great variability of grain and flour quality indicators which can depends on many factors: from agro-climatic condition and variety features to milling flow diagram and tempering conditions before milling. Wheat quality indicators are shown next results: test weight values ranged from 727 to 845 g/l, vitreousness – from 25 to 83%, initial moisture content – from 10.4 to 13.7%, protein content – from 11.3 to 17.2%, ash content – from 1.35 to 1.73%, gluten content – from 17.6 to 38.3%, gluten deformation index – from 46 to 96 units and Falling Number – from 309 to 500 seconds. Analyzing of correlations between grain quality indicators and flour quality indicators shown: the direct extra high correlation between grain protein content and flour protein content (r=0.95) and also between grain gluten content and flour gluten content (r=0.87); average correlation between ash content of grain and ash content of flour (r=0.68). According to milling properties was found: average correlation of initial grain moisture content and flour yield (r=0.52), a direct high correlation between grain vitreousness and the ratio of reduction and break flour (r=0.70), and an inverse average correlation of test weight with ratio of break and reduction bran (r=–0.61). It has been established that the flour strength W is affected by a set of grain quality indicators: grain protein content with high coefficient correlation (r=0.70), grain gluten content and grain Falling Number with average correlation coefficients – r=0.53 and r=0.56, respectively. For other rheological indicators, such as stability, water absorption capacity and P/L, no high correlation coefficients were found, since their values depend on a complex of various indicators of grain. The obtained correlations can be used to improve the efficiency of grain blending before milling, to substantiate the modes of tempering, grinding, and flour mixing stage in existing mills, as well as to design a milling flow diagram for new mills.

Оптимизация режимов плоского шлифования деталей малой жесткости типа колец и призматических стержней

The study introduces an algorithm and method for optimization of flat grinding modes for low-rigidity workpieces such as rings and prismatic rods. The proposed solution ensures the specified quality of the machined surface at the maximum process efficiency. The required flatness tolerance of the machined surface is provided at the second stage of optimization modes by limiting the value of the maximum elastic deformation. The variable parameters are the cutting forces, magnetic field attraction of the machine table, and the bending rigidity of the workpiece. The study introduces mathematical models to determine maximum elastic deformation of workpieces when fixing and machining, outlines the conditions for ensuring the required flatness tolerance of the machined workpiece surface, taking into account the maximum elastic deformation of the low rigidity workpiece under the influence of the magnetic field of the machine tool and the radial component of the cutting force.

Determination of the influence of rock and grinding modes on the surface roughness of wood

Experimental studies of the influence of wood species and grinding modes on the roughness of the obtained surface were carried out. It is investigated that the type of wood also affects the magnitude of the irregularities of the surface to be treated, namely the magnitude of the roughness of the treated surface is inversely proportional to the density of the treated material. Regression models are obtained, which characterize the roughness of the surface of oak and spruce wood depending on the cutting speed and the specific pressure of pressing. It is established that the cutting speed has a positive effect on the roughness of the treated surface. This is due to the fact that at high cutting speeds wood fibers (especially relevant for hardwoods with higher density) show proper support to the cutter and do not have time to break under its pressure, and cut with a cutter before it breaks their connection with neighboring fibers. Therefore, the purity of the treated surface will be better. It is established that with the increase of cutting speed from 10 to 30 m / s by grinding skin of oak wood surface roughness decreases by 40-60%, and spruce - by 44-86%. Spruce has a 10-20% roughness dynamics than oak. It was found that with the increase of the specific pressure of pressing the part to the sanding skin on the surface of oak wood, the surface roughness increases by 20-30%, and the surface of spruce wood - by 12-32%. In spruce, the deterioration of roughness is 12-13% greater than in oak. It is established that with the increase of the feed rate on the surface of oak wood the surface roughness increases by 21-30%, in spruce - by 13.63-23.46%. In spruce deterioration of roughness by 9-13% more than in oak. To carry out effective grinding to obtain a quality surface (such as oak and spruce), the following input values are recommended: cutting speed 20-30 m / s; feed speed 6-8 m / min; specific clamping force 2.2-4.4 kPa; grain size of skins: P180-P150; P120-P100; P90-P60.

Modeling of formation regularities of conical surfaces

The scheme of processing conical surfaces by grinding them to a flat tool is considered and a technical solution for the implementation of such processing is proposed. Using the created device allows implementing the group method of forming conical parts with a deviation of the generatrix of the cone from straightness of not more than ± 0.00012 mm. A mathematical model of the patterns of removal of stock from a conical part with a flat tool is developed. A formula is obtained for calculating the modulus of the sliding velocity at any point on the processed conical surface, which implements engineering methods for controlling the shaping of conical parts without conducting preliminary labor-intensive experimental studies. An optimization technique for the adjustment parameters of technological equipment was proposed. The most effective axicon processing modes were revealed at the stages of preliminary, medium and fine grinding, as well as at the polishing stage, depending on the technological heredity of the workpiece from the point of view of distribution of the stock to be removed over its surface. It has been established that changes in the eccentricity between the axes of rotation of the tool and the faceplate as well as the amplitudes of the reciprocating rotational movements of the latter practically do not affect both accuracy and processing productivity, therefore, in practice, these parameters can not be optimized, but their average values can be assigned. The operating modes of the basic lever grinding and polishing machine are established, at which the required accuracy of the working surface of the tool is provided, which directly affects the straightness of the generatrix of the cone. Studies of the regularities of the shaping of the side surface of a conical lens in the conditions of free grinding are carried out and the adjustment parameters of technological equipment that affect the quality and productivity of the processing process are determined.

Effect of flattening wheat grain on grinding modes in roller mill

Introduction. The flattening process is used to intensify the grinding of grain during varietal milling of wheat, while the optimal gap between the rolls of the ivy system remains uncertain. Materials and methods. Flattening was carried out in a laboratory ivy machine with a roller diameter of 144.0 mm; 68.4 mm and a rotation speed of 14.6 s-1. Grinding of wheat grain was carried out in a roller mill. The length of the rollers is 70 mm; the number of rifts per 1 cm circle of rollers is 6, the slope of the rifts is 12%, the ratio of circular speeds is 1:2, the speed of rotation of the high-speed roller is 3.93 m/s, the diameter of the rollers is 150 mm, the interdependence of the rifts is the back on the back, the angles of exacerbation of the rifts are 35°/70°. The mode of grinding wheat grain in the ivy machine and in the roller mill was determined by sifting the products obtained through a sieve with holes of 1.0 mm. Granulometric analysis of crushed products was determined by sifting on a standard set of sieves with module Δ≈1.21. Result and discussion. When grinding ivy products in a roller mill, the total yield of intermediate products is nonlinear in nature and can be approximated by the equation of the second degree. The optimal distance between the rollers of the ivy machine is 1.4 mm, provided that small products after flattening were previously isolated from the mixture of the flattened product. The total product of intermediate products after flattening and grinding in the roller mill has a complex nonlinear nature, which did not allow to establish the optimal value of the gap value between the rollers of the ivy system. The total product of intermediate products obtained in total during flattening and grinding is 2.9 % greater than the total product product yield obtained only in the roller mill with small ivy products previously removed. Differential curves are polymodal and have 5 maximums. Integral curves have an S-shaped appearance. When grinding whole grain, the total yield of intermediate products is greater than when grinding flattened grain in a roller mill under the same conditions. When crushing flattened grain, a greater number of large fractions of products are formed due to small ones. Conclusion. In the range of the established optimal clearance between the rolls of the flattening machine, there are no significant differences between the two methods of grinding wheat.

Increase in productivity and quality based on the control of thermodynamic processes during deep profile grinding of the gas-turbine engine blade

The article provides the system of interaction of dynamic processes during deep profile grinding of complex profiles on a multiaxis machine, the influence of dynamic processes on the quality of the surface layer, the endurance limit of the gas-turbine engine blade. The method presented allows to assign corresponding grinding modes based on the forecast of the dynamics of elastic, thermal and working processes in a thermomechanical system. This technique allows to control the process of deep profile grinding to achieve the specified parameters of surface quality, the endurance limit of the blade and increase process efficiency.

Image Analysis to Optimize Calculations of Grinding Modes

Modeling helps to investigate and analyze the interrelationships of grinding parameters as a single system. The article describes a computer model of the surface layer of a grinding wheel, taking into account the cutting modes and characteristics of the circle. The subsystem of the surface layer of the grinding wheel is the most important subsystem of grinding, since it connects the main characteristics of the circle with the cutting modes and with the parameters of the workpiece. The output characteristics of the model are the parameters of the working layer with a height of several micrometers, in which micro-cutting occurs. It is impossible (or very difficult) to obtain them by conducting full-scale experiments, since the processes are instantaneous, and the cutting elements have micro-dimensions. This problem was solved by creating a simulation stochastic model based on the geometric representation of the surface layer, which clearly displays the result. The analysis of the image of this model allowed us to numerically describe the output parameters of cutting.The article offers a faster algorithm for analyzing the image of the simulation model of the surface layer. It is carried out over a matrix containing numerical information about the projection of the surface layer, the main parameters of each single slice are calculated, and only after that the result is displayed on the graphic screen. To simulate a single grinding mode, it is necessary to repeat the process of "image creation - image analysis– output of results" hundreds of times until a stable state is reached.The use of the algorithm in an automated system will allow you to create a system for automatically searching for optimal grinding modes, as well as to derive analytical dependencies of cutting modes on input parameters, for example, on the parameters of the circle and the workpiece.

Improving the quality parameters of a fibrous pulp in the process of knife milling

Pulp and paper products in the modern world are used in a variety of types and areas, due to which the issue of improving paper production technologies is relevant. The article presents the results of grinding fibrous semi-finished products using the knife method. A disc mill with an original knife set was used as the unit under study. For the most effective modes of grinding were selected to obtain raw materials with high quality indicators.

The Properties of OPEFB Cellulose Nanofibrils Produced by A Different Mode of Ultrafine Grinding

Cellulose Nanofibrils (CNFs) was resulted from deconstruction of the hierarchical structure of cellulose. CNFs are commonly obtained by mechanical fibrillation, such as ultrafine grinding processes and its variation. Nevertheless, the influence of different treatments on the properties of the resulting CNF especially from variety of ultrafine grinding mode has not been reported. This study investigates the properties of cellulose nanofibrils (CNF) produced from bleached pulp oil palm empty fruit bunch (OPEFB) Kraft pulp through an ultrafine grinder with two different treatments in the fibrillation process. These two treatments were: 1) ultrafine grinder with increasing gaps distances; -30, -50, -70, and -90 µm with five cycles in every gap, 2) ultrafine grinder on constant gaps (-30µm) with increasing grinding cycles: 5, 10, 15, 30, and 40 cycles through the grinder. The influence of the treatment was evaluated through particle size distribution, crystallinity index, and morphological properties. The result showed that the increasing gaps treatment efficiently improved the size uniformity of CNFs, length 147-139.5 nm, and scanning electron microscope micrograph confirmed that the diameter of CNF was smaller with the increasing grinding gaps than increasing grinding cycles. However, the increasing cycle’s treatment produced CNF with a higher crystallinity index. The crystallinity index (CrI) of the CNF decreased from 71.27 to 62.25% with increasing gaps, whereas the CrI of the CNF from increasing cycles was 69.35%. This study provides a valuable guideline for determining the appropriate process to produce CNF especially by mechanical grinding using ultrafine grinder from OPEFB according to the desired result.

Grindability study of hard to cut AISI D2 steel upon ultrasonic vibration-assisted dry grinding

Ultrasonic vibration-assisted dry grinding is a sustainable hybrid manufacturing technology that decreases the negative environmental impact of coolant, reduces manufacturing costs, and improves surface integrity. The present investigation analyses the mechanisms associated with ultrasonic vibration-assisted dry grinding of AISI D2 tool steel with an alumina grinding wheel. It also compares the influence of traditional dry grinding and traditional wet grinding modes with the ultrasonic vibration-assisted dry grinding mode at different ultrasonic vibration amplitudes. Ultrasonic vibration was applied to the sample in the longitudinal feed direction. Further, kinematics of the abrasive grit path during the traditional grinding and ultrasonic vibration-assisted dry grinding is presented schematically. In this research, the impacts of ultrasonic vibration amplitude as well as the depth of cut on the process yields such as ground surface topography, grinding force, specific grinding energy, force ratio, surface finish, microstructure, and hardness were investigated experimentally. Experimental results revealed that the highest decline in tangential and normal grinding forces in ultrasonic vibration-assisted dry grinding at ultrasonic vibration amplitude 10 µm and the reduction in surface roughness parameter ( Ra, Rq, and Rz) in ultrasonic vibration-assisted dry grinding was 43.23%, 42.59%, and 33.69%, respectively, in comparison to those in traditional dry grinding and 26.35%, 26.94%, and 27.48%, respectively, in comparison to those in traditional wet grinding. It was observed that ultrasonic vibration-assisted dry grinding is beneficial as the profile produced by ultrasonic vibration-assisted dry grinding has a comparatively flat tip, and profile points are shifted to the bottom of the mean line. This study is expected to assist ultrasonic vibration-assisted dry grinding of hard materials.

Population balance modeling approach to determining the mill diameter scale-up factor: Consideration of size distributions of the ball and particulate contents of the mill

In the past, most of the Population Balance Model-based ball mill scale-up studies were carried out using a mono-size ball charge and a single size fraction of the particulate material as the starting feed. It was reported that the breakage distribution parameters were independent of the mill diameter, specific breakage rate parameters varied with mill diameter as Dγ, and the mill diameter exponent γ was independent of particle size. However, in the industrial grinding operations, we have significantly broad size distributions for both the grinding media and the particulate contents of the mill. Therefore, experimental data generated under these conditions were taken from the literature and analyzed. These data pertain to the dry and wet batch grinding of limestone, quartz, and ores of vanadium and pyrochlore. Our analysis of the data showed that in contrast to the findings of the earlier researchers, the breakage distribution parameters were not independent of the mill diameter, and the value of γ for the specific breakage rate parameters varied with particle size in the case of multicomponent ores. Because of these complications, a single parameter, the specific rate of production of material that is finer than a specified size, was used as the basis for scale-up. It was found that the value of the mill diameter scale-up factor varied quite significantly with the breakage properties of the material, the size distribution of the particulate contents of the mill, the size of the desired product, and the mode of grinding (dry/wet). Therefore, ball mill scale-up models presently available need to be modified in light of these new findings.

Повышение эффективности плоского глубинного шлифования

There is considered a possibility of effectiveness increase of machinery billet flat deep grinding at the expense of high-speed machining use and also grinding on an automatic cycle of grinding mode changes. The application of high-speed deep grinding, for instance, slots or profiles of turbine blade locks allows rejecting their preliminary milling, carrying out single position machining on one machine which increases machining accuracy and its capacity.