The Effects of Structured Grinding Wheel Designed Parameters On The Geometries of Ground Structured Surfaces

This study investigates the effects of the structured wheels’ geometrical parameters on the geometries of structured surfaces machined by grinding operations. First, the geometrical parameters of the structured wheels were determined. The resultant geometrical parameters of structured surfaces were defined and related to the designed operating condition, including the structured wheel and grinding process by mathematical and simulation models. The results showed that each wheel’s geometrical parameter affects the structured surface geometry at different rates. Grinding experiments were then performed to explore experimentally how the geometrical parameters of the structured wheel affect the geometry of structured surfaces and verify the modeling and simulation results and explanations. The results showed a remarkable compatibility between the predicted and machined surfaces and reflected the accuracy of the presented method for machining the structured surfaces by grinding.

OPTIMUM WORKHOLDING CONDITIONS FOR PRECISION CYLINDRICAL GRINDING OPERATIONS

Grinding process is a very important process in machining industry being one of the most popular processes when high quality parts must be manufacture. Likewise, workholding is a critical issue on cylindrical grinding. The use of the driving dog is common when the workpiece is held between centers. However, one of the handicaps of this workholding is that the cylindrical workpiece cannot be ground along the complete length. In order to tackle this issue, in the present work the workpiece is held between centers avoiding the use of the driving dog. To this end, a methodology to obtain the grinding limit parameters that ensure that the transmitted torque is higher that the resistance torque is presented, being the aim of these tests is to avoid the sliding between the point and the workpiece. Finally, non-destructive tests are designed, which, using a safety coefficient of about 0.77, the tests allow the correct design of each specific grinding process. Keywords: cylindrical grinding, workholding, driving dog, sliding

Methodology for Evaluation of Treated Steels and Alloys in Abrasive Processing

One of the critical physical and mechanical properties of metals and alloys is the suitability for abrasive machining. Machining by abrasive tools is the final operation that sets the desired macro-geometry parameters of processed blanks and microgeometry parameters of processed surfaces such as roughness and length of a bearing surface. Abrasive machining determines the most important physical and mechanical parameters of a blank surface layer, i.e. stresses, phase composition, structure. Machinability by abrasive tools depends on the machining performance affected both by the blank material properties and various processing factors. In our previous studies, we proved that during abrasive machining the metal microvolume affected by abrasive grains accumulates energy. This energy is used for metal dispersion and is converted into heat. According to the theoretical studies described herein, one may note the absence of a reliable and scientifically valid method as well as measuring instruments to determine the machinability of metals and alloys by abrasive tools. For this reason, we suggested a method simulating the effect the multiple abrasive grains produce in a grinding wheel, and enabling us to identify machinability of metals and alloys, select the most efficient abrasive materials for machining of the same, and form the basis for development of effective grinding operations.

Evaluation of the Possibilities of Processing High-Alloy Corrosion-Resistant Steels during Grinding Operations

The issues of processing high-alloy corrosion-resistant steels by the method of centerless cylindrical grinding are considered in the article. Experimental data on changes in the parameters of roughness and hardness of a workpiece depending on the depth of cut, the speed and the design features of a control wheel are presented. The change in the microhardness of a part depending on the depth of cut is analyzed. Much attention is paid to the study of thermal stress of the grinding process. Images of temperature changes in the cutting zone depending on the grinding wheel characteristics are shown. Conclusions in the form of practical recommendations for improving high-alloy steel processing by the method of centerless grinding are formulated on the basis of the results obtained.

EQUIPMENT MODIFICATION FOR FINE GRINDING OF MINERAL RAW MATERIALS

Introduction. The huge energy costs of fine and ultrafine grinding operations have led to numerous studies aimed at developing new devices and methods for producing powdered materials. The first way leads to an increase in specific productivity while maintaining energy consumption at approximately the same level. The second way allows not only to increase the specific productivity, but also to reduce the specific energy consumption, since with a decrease in the exposure time, the body is more easily deformed and destroyed. The grinders in which the intensification of the destruction process is carried out in the first way can include planetary and vibrating mills. The second method of intensification is used in jet and various types of centrifugal mills. It is determined that vertical centrifugal mills are the equipment of a new type that can effectively perform grinding operations at high technological indicators and low energy consumption. The purpose of the research. Development of measures for obtaining a finely dispersed product by destroying mineral raw materials in vertical centrifugal mills by mechanical means. Research methodology. The paper uses a comprehensive research method: analysis of the state of grinding equipment according to literary and patent sources; development of mathematical models of the movement of bulk material in the working space of a vertical centrifugal mill based on the Navie-Stokes equations; computer modeling of the movement of the crushed material using the OpenFOAM package for solving hydrodynamic equations; a solver program was created to perform calculations, implementing the SIMPLER algorithm and using the MRF model; laboratory experiments; granulometric method for the analysis of grinding products; fractional analysis of crushed material with a grain size of 0.08 mm using an X-ray analytical centrifuge ВrооkhаvеnBI-ХDС. The development of measures for the effective evacuation of the crushed product from the working space of a centrifugal mill was evaluated by comparative tests of mills using various design solutions. Research results and discussion 1. It is established that vertical centrifugal mills are the devices of a new type capable of effectively performing grinding operations at high technological indicators and low energy consumption. 2. A mathematical model of the movement of bulk material in the working space of a vertical centrifugal mill has been developed based on the Navier-Stokes equations, which allows determining the speed and direction of movement of material layers at any point in the working space, the energy costs for their movement, the influence of the height of the material column on the nature of its movement in the space above the rotor. 3. The directions of increasing the efficiency of grinding mineral raw materials in a vertical centrifugal mill are determined by reducing the number of radial ribs installed in the cavity of the mill rotor; making cutouts in the radial ribs of the rotor, in the area near the rotor hub; installing coaxial rings in the working space of the mill above the rotor. 4. A method of effective evacuation of the crushed product from the mill body by installing additional screening surfaces in the peripheral part of the working space of the mill has been developed. 5. For the first time, the distribution of the granulometric composition of fine and medium - dispersed crushed product obtained as a result of processing lump dolomite in a centrifugal mill was obtained. It was found that particles with a size class of -0.08 + 0.03 mm are absent in the output of the crushed product from the mill. Conclusions. A mass-produced vertical centrifugal mill will find its effective application at enterprises of the Russian Federation for the preparation of powdered materials and will allow to obtain a significant effect by reducing the price of the final product, simplicity of design and maintenance of equipment, as well as small occupied production areas.

MODERN METHODS OF GEAR MILLING OF HARDENED LARGE-MODULE GEARS

The latest developments of modern methods of high-speed gear milling of large-module cylindrical gears, both for preliminary grinding of teeth and for final blade processing of gears, are considered. For high-speed blade gear processing, promising designs of worm carbide cutters have been developed, manufactured and implemented. The technological regulations of blade gear processing for the operation of each of the design solutions of worm carbide cutters have been developed. The design of a special double-body worm cutter for double-sided cutting has been developed. It is shown that the carbide cutting elements of the milling cutters, which are placed only along the lines of the machine engagement of the tool and the workpiece, make it more economical compared to the known designs of similar tools. The application of the developed technological methods of pre-blade processing of the teeth of hardened wheels with carbide cutters reduces the labor intensity of low-performance gear grinding operations, depending on the wheel module, by 3-4 times by reducing the allowance from 1.5–2.5 mm on the tooth side to 0.3–0.5 mm, and also allows you to ensure the gear processing process is economical by reducing the consumption of carbide plates. The developed technological studies of ensuring the quality of gear processing of large-module cylindrical wheels allow us to solve the scientific and technical problem associated with the production of large-module gears with high-hardness teeth while improving the quality of their manufacture, reducing labor costs and reducing material consumption.

WEDM as a Replacement for Grinding in Machining Ceramic Al2O3-TiC Cutting Inserts

Small-size cutting inserts for assembly cutters are widely used to manufacture a variety of parts for the aerospace, automotive and mechanical engineering industries. Due to their high hardness and chemical stability, cutting Al2O3-TiC ceramics significantly outperform hard alloys in machining heat-resistant and difficult-to-machine materials. However, grinding on CNC machines, the most common technology for manufacturing ceramic inserts, is associated with numerous issues when it comes to manufacturing small-size cutting inserts. For example, high cutting forces and high grinding wheel wear rates cause a rapid loss of dimensional accuracy and deterioration of the quality of the surface being machined, while the interference of the grinding wheel with the surface being treated imposes serious limitations on the geometry of the small-size ceramic inserts to be grinded. Here we show that Wire Electrical Discharge Machining (WEDM), which is a contactless and, thus, a more flexible method in terms of the size and geometrical properties of a workpiece to be machined, can be used as a replacement for grinding operations in machining small ceramic inserts. A composite of 70% aluminum oxide and 30% titanium carbide was chosen as a ceramic material because a further increase in the TiC fraction causes a marked decrease in wear resistance, while its decrease results in an undesirable loss of electrical conductivity. While in order to replace grinding with WEDM, WEDM has to be stable in the sense of occurring without frequent wire breakages, achieving WEDM stability is not an easy task due to the low electrical conductivity of Al2O3-TiC ceramics and high operational temperatures, which promote the diffusion of dielectric and electrode products in the surface layer of the cutting inserts being machined. These factors may lower the quality of the final product due to damage to the insert surface, marked increases in the roughness RA and in diffusion in the surface layer, which increases the friction coefficient and, hence, reduces the life of the manufactured cutting inserts. We have increased stability of the WEDM process by identifying and applying rational process conditions that lead to a reduced, by a factor of 2.63, roughness Ra and also a reduced, by a factor of 1.3, depth of craters. Performing a chemical and structural analysis, we found that the application of high energies combined with an increasing interelectrode gap (IG) (technological parameter SSol, a complex indicator that determines the speed of the wire electrode depending on the number of pulses per unit of time and the IG size, is set at 80, EDM3 technology) causes increased surface damage and contamination, while a small IG (SSol = 45, EDM1 technology) reduces the material removal rate due to contamination of the working zone between the surface being machined and the electrodes. After reducing the IG by lowering SSol from 80 to 45, the roughness Ra of 0.344 µm was achieved, which allows for replacing grinding operations with WEDM in machining hardening chamfers, front surfaces and, to a lesser degree, the rear and support surfaces of cutting inserts. In this case, when the IG is reduced to SSol = 45, the electroerosion products in the dielectric promote local breakdowns, which in turn produce a large number of deep craters which adversely affect the performance of cutting inserts. However, we found that a slight increase in SSol from 45 to 55 (EDM3 technology) significantly reduces the number of craters and lowers their depth from 50 μm to 37 μm. Although in this case the roughness grows to 0.534 μm due to increased discharge energy, the improved flushing of the IG and the reduced occurrence of local high-temperature breakdowns—evidenced by a decrease in the depth and number of deep craters formed due to current localization during short circuits—significantly reduced contamination of the surface layer and the crater formation rate. Therefore, WEDM can be recommended for use in machining reinforcing chamfers and, to a lesser degree, front surfaces. These considerations lead us to conclude that WEDM is a viable alternative to grinding in machining Al2O3-TiC ceramic cutting inserts of a small size and a complex shape, and that its application to manufacturing cutting inserts from poorly conductive cutting ceramics should be studied further.

Determining Surface Topography of a Dressed Grinding Wheel Using Bio-Inspired DNA-Based Computing

Grinding is commonly used for machining parts made of hard or brittle materials with the intent of ensuring a better surface finish. The material removal ability of a grinding wheel depends on whether the wheel surface is populated with a sufficiently high number of randomly distributed active abrasive grains. This condition is ensured by performing dressing operations at regular time intervals. The effectiveness of a dressing operation is determined by measuring the surface topography of the wheel (regions and their distributions on the grinding wheel work surface where the active abrasive grains reside). In many cases, image processing methods are employed to determine the surface topography. However, such procedures must be able to remove the regions where the abrasive grains do not reside while keeping, at the same time, the regions where the abrasive grains reside. Thus, special kinds of image processing techniques are needed to distinguish the non-grain regions from the grain regions, which requires a heavy computing load and long duration. As an alternative, in the framework of the “Biologicalisation in Manufacturing” paradigm, this study employs a bio-inspiration-based computing method known as DNA-based computing (DBC). It is shown that DBC can eliminate non-grain regions while keeping grain regions with significantly lower computational effort and time. On a surface of size 706.5 μm in the circumferential direction and 530 μm in the width direction, there are about 7000 potential regions where grains might reside, as the image processing results exhibit. After performing DBC, this number is reduced to about 300 (representing a realistic estimate). Thus, the outcomes of this study can help develop an intelligent image processing system to optimize dressing operations and thereby, grinding operations.

Electro-pulse method for obtaining raw materials for subsequent flotation enrichment of ore

The main method of enrichment of polymetallic ores is flotation. The peculiarity of solid mineral processing is the preliminary preparation of raw materials. The essence of this stage is the grinding and sorting of raw materials in order to fully reveal the useful substance from the waste rock. The article is devoted to the study of the effect of electric pulse discharges on the grinding of ore containing non-ferrous metals. This article proposes an electro-pulse method for obtaining raw materials for subsequent flotation enrichment of ore in order to extract valuable components. This method of grinding ores is based on the use of the energy of a pulsed shock wave that occurs as a result of a spark electric discharge in a liquid. An experimental electric pulse unit with a crushing unit is described. When electrohydraulic action on solid particles in an aqueous solution increases the intensity of the grinding process under the influence of additional pressure associated with cavitation. The object of the study was the natural ore of the Akbastau mine. Ore grinding operations were performed at various parameters of the electric pulse plant. The dependences of ore grinding on the electrical and geometric parameters of the electric pulse installation, the value of the interelectrode gap on the switching device, the pulse repetition frequency and discharge energies are determined. It is found that with increasing discharge energies introduced into the discharge channel, the fraction of the crushed fraction increases.

Hybrid spotted hyena–Nelder-Mead optimization algorithm for selection of optimal machining parameters in grinding operations

In this research, a novel optimization algorithm, which is a hybrid spotted hyena-Nelder-Mead optimization algorithm (HSHO-NM) algorithm, has been introduced in solving grinding optimization problems. A well-known grinding optimization problem is solved to prove the superiority of the HSHO-NM over other algorithms. The results of the HSHO-NM are compared with others. The results show that HSHO-NM is an efficient optimization approach for obtaining the optimal manufacturing variables in grinding operations.