Grinding Cycle Research Articles

Optimization of internal plunge grinding using collaboration of the air-grinding and the material removal model based on the power signal

This paper introduces a new optimum method for internal plunge grinding by using the material removal model based on the power signals that were extracted from machine wheel spindle. An automatic grinding cycle optimization functional module is proposed to improve the process grinding efficiency while ensuring component quality requirements. Aiming at the productivity, the functional module encompasses a more comprehensive set of realistic constraints and the manufacturing values. By combining both the air-grinding reduction method and the grinding process optimization method, the functional module has been integrated to provide a new algorithm for analysis and optimization of bearing grinding process. In the paper, an experimental optimization example demonstrates a 33.6% reduction in production cycle time for bearing grinding process. The results confirm that this functional module can be used to save the total grinding cost greatly in industrial implication.

Designing optimal automatic cycles of round grinding based on the synthesis of digital twin technologies and dynamic programming method

Abstract. The article presents methodology for designing optimal feed control cycles resistant to unstable machining conditions for a batch of parts in round grinding operations performed on CNC machines. To improve the quality and reliability of control programs for CNC machines, a digital twin (DT) is proposed to be used. It performs virtual testing of a given grinding cycle for the possibility of defect occurrence at some combination of variable technological factors. To design the optimal grinding cycle by calculating the optimum trajectory of the radial feed change cycle, we propose the dynamic programming method (DPM) used in solving the classical transport problem, in which a network of roads with intermediate stations is specified. In the task it is necessary to find the optimal trajectory of transport. The conditions for the appearance of defects detected by the DT are introduced into the system of restrictions, and the feed cycle is again optimized in the DPM optimization system. A new optimized cycle is again tested by the DT. These iterations are repeated until the DT fixes the present of a defect for the operation. The methodology proposed in the article for the synthesis of digital twin and DPM technologies at the stage of preparation of control programs for CNC machines makes it possible to guarantee the maximum productivity of the grinding operation while ensuring the specified quality of the machined surface under varying processing conditions that vary within the specified limits.

Analysis of separator operating conditions in a technological module with vibration-centrifugal closed-cycle grinding unit for obtaining high-dispersity materials

The demand for up-to-date building materials and components for their production is constantly growing. The purchasing of foreign analogues is often unreasonable and costly, and the domestic products not always meet the high requirements specified for them. In light of this, it is necessary to develop up-to-date knowledge-intensive technologies of producing building materials of various purpose, as well as materials and products of ceramic, varnish- and-paint, glass and other industries, the basis of which is the application of high-dispersive powders. The extensive use of fine-ground and ultrafine-ground materials resulted in designing a wide range of grinders of various types (ball, vibration, planetary, centrifugal, jet grinders etc.). In each certain unit the special conditions for grinding are created, which allows using them for processing materials with various physical and mechanical characteristics. In this work the mathematical model of closed grinding cycle with combined-action air separator is suggested. In this model the integral functions of partition in air separator have been obtained. The calculated and experimental values of the integral functions of partition in air separator have been compared.

Microstructure and physical properties of nano charcoal ash as binder

Waste coconut shell (CS) was used to produce nano charcoal ash (NCA) as a potential modifier material in an asphalt binder. This study focused on the microstructural and physical properties of NCA. Thermogravimetric analysis and derivative thermogravimetric analysis (TGA/DTA), field emission scanning electron microscopy (FESEM), X-ray fluorescence, particle size analysis (PSA), penetration tests, softening point tests and dynamic shear rheometer (DSR) tests were performed. The TGA/DTA results revealed 490°C to be a suitable CS burning temperature to form carbon and to reduce impurities. The morphology determined by FESEM showed that charcoal CS presents a smooth, porous and irregular shape. The carbon content on the surface of the material was 77·6%, as indicated by energy-dispersive X-ray spectroscopy. PSA showed that the optimum size of the charcoal CS obtained after several grinding cycles was 148 nm. Test results indicated that adding NCA from coconut shell to bitumen improved the binder stiffness up to 47% and significantly increased the softening point up to 12% compared with virgin binder. The DSR test revealed that the optimum size of NCA enhanced the bitumen by increasing the resistance to rutting until a temperature of 76°C was reached, prior to failure at a temperature of 82°C.

Some Aspects of Surface Integrity after Hard Milling

This paper deals with surface integrity after hard milling of bearing steel 100Cr6. Surface integrity is expressed in terms of shape deviation as well as Barkhausen noise emission. Furthermore, components of cutting forces are also measured as a function of tool wear. Non homogeneity of cutting force distribution within the contact between the milling cutter and workpiece is discussed. The results of measurements indicate that shape as well as structure remarkable non homogeneity should be expected after hard milling due to missing full contact between milling cutter and workpiece. This non homogeneity can be monitored via Barkhausen noise technique. On the other hand, the competitive grinding cycles produced more homogenous surface and surface state is a function of infeed speed.

ВИРТУАЛЬНОЕ ФОРМООБРАЗОВАНИЕ ОБРАБАТЫВАЕМОЙ ПОВЕРХНОСТИ ПРИ КРУГЛОМ НАРУЖНОМ ШЛИФОВАНИИ С ОСЕВОЙ ПОДАЧЕЙ

PURPOSE. The paper deals with the model of shaping a processed surface in the operation of external cylindrical grinding with a traverse feed performed in an automatic cycle on CNC machines. The developed model of surface formation allows to conduct a step-by-step calculation of the current values of the actual radial in-feed and radii sizes in the different sections of the machined surface and predict the values of grinding surface dimensions throughout the whole grinding cycle for the given processing conditions. METHODS. The basis for the creation of computer-aided design systems serve the data presented in the regulatory literature that makes their use inefficient for the development of cycles for CNC machines. Existing engineering techniques also based on the recommendations of regulatory literature or on particular empirical data do not take into account the changes in variable processing conditions. RESULTS AND THEIR DISCUSSION. The paper discusses the simulation features of grinding cycles along the length of the machined part surface, shows a calculation scheme that establishes the relationship between the graphs of the accumulated software (tп k,i,z ) and actual (tф k,i,z ) feeds, tension (tн k,i,z ), elastic strain (у k,i,z ) of the technological system with the radii of the machined surface (R k,i,z ) when grinding a non-circular workpiece with the maximum radius (Rзаг max ), original workpiece radii (Rзаг k ) and initial radial run-out, which is calculated by formulas. CONCLUSIONS. Presented in the article formation model of the grinding surface in the operation of external cylindrical grinding with a traverse feed performed on a CNC machine allows to predict the actual dimensions of the machined surface for a given cycle and technological conditions of machining as well as to construct a model of the machined surface.

Possibility of implementation of dry technology of gold-bearing ores roughing: case study of “Gurbey” deposit

The aim of the research is to identify the ability/feasibility of dry roughing of ore taking as the example “Gurbey” deposit in Irkutsk Region and to develop a rational scheme for processing ores containing free gold. Studies of the dry processing technology of gold-bearing ore at “Gurbey” deposit with the initial weight of 1,123.8 kg were carried out by semi-industrial plants: the DKD-300 combined shock impact crusher, the CMVU-800 centrifugal mill and the POS-2000 air separator developed by CNMI SD RAS. The sample was subjected to two cycles of crushing and four cycles of grinding followed by pneumatic separation. The circulating load is class +12 mm after the DKD-300 crusher, and for the mill, all screening products are +3 mm, as well as the products of classification -3 + 1 mm of the POS-2000 concentrate. As a result of treatment of the concentration products, 23.93 grams of free gold was recovered (concentration on tables: control, recleaning, concentration of the Mosely minerals by analyzer, magnetic separation, heavy medium separation on bromoform). At the same time, it was established that gold from the ore with initial size of 150 mm can be completely stripped and recovered with the POS-2000 air separator with a particle size of up to 100 microns. At the same time gold extraction into the primary concentrate is up to 60%. Based on the results of the research, a basic scheme for dry roughing of “Gurbey” ore containing “free” native gold was developed using the ore treatment devices: RD-MDV-900, DKD-300 crushers, CMVU-800 centrifugal mill and POS-2000 air separator. The technological scheme is fundamental for gold-bearing ores containing "free" gold of fineness over 100 microns.

Tool Condition Monitoring Of Cylindrical Grinding Process Using Acoustic Emission Sensor

In this work, an experimental setup has been established consisting of a cylindrical grinding machine with piezo-electric sensor for capturing acoustic emission and its related hardware and software for signal processing. Acoustic signals are captured for the entire grinding cycle until the abrasive grains of the girding wheel become dull. Surface roughness produced by the process is recorded at fixed time intervals from the beginning to the end of the grinding cycle. Various features of the acoustic emission signatures such as root mean square, amplitude, ring-down count, average signal level are extracted from the time-domain are compared and correlated with the surface roughness generated by the grinding wheel on the work-piece. Good condition and dull condition of the grinding wheel is predicted using machine-learning techniques such as decision tree, artificial neural network, and support vector machine. Results indicate that there is a strong correlation exiting between the acoustic emission features and the surface roughness produced by the grinding process. Support vector machine trained with cubic kernel is appears to be predicting the grinding tool condition with greater accuracy comparing with decision tree algorithm and artificial neural network considered in this study.

Thermal modeling and optimization of interrupted grinding

Finishing parts such as blade tips of assembled engine rotors is an interrupted grinding process. Thermal issues such as burn often become more prominent for interrupted grinding because of the low thermal capacity during the entry and the exit of each interruption. This paper presents models to calculate the transient and steady state temperatures for interrupted grinding. The developed models are then used to investigate the influence of grinding process parameters and cooling on the transient temperature rise. The model results can be used to develop new grinding cycles with variable work speed to increase material removal rate while maintaining temperature below burn limit.

Improvement of the quality of designed cylindrical grinding cycle with traverse feeding based on the use of digital twin options

In practice of automated mechanical adjustment of cutting conditions for internal grinding operations at the CNC Machine, is carried out on many of control parameters (ccutting regimes, characteristics and geometric parameters of the wheels, etc.) and absence of effective methods of treatment and design of cycles (a normative reference, methods engineering techniques and Automated Design Systems). All this leads to the fact that cycles for CNC machines are selected the same as for manually processing of a number of workpieces in a single cycle. In order to meet the accuracy requirements and quality design optimized for manually initially cycles, which have low regime’s parameters. Therefore, the cycles obtained by the method of selection are not high-performance and they do not provide minimal processing time. This article discusses the use of a digital twin, which performs virtual testing for a specified grinding cycle, on the possibility of spoilage appearance at some combination of variable technological factors to improve the quality and reliability of control programs for CNC machines. Virtual testing of the digital twin is carried out by modelling the process of allowance removal for the whole processing cycle of the workpiece batch with different variables of technological factors, changing in the specified ranges of variation.

Non homogeneity of surface integrity after hard milling of high tempered bearing steel

This paper deals with surface integrity after hard milling of high tempered bearing steel 100Cr6. Surface integrity is expressed in terms of shape deviation as well as Barkhausen noise emission. Furthermore, components of cutting forces are also measured as a function of tool wear and their non homogenity within the contact between the milling cutter and workpiece is discussed. The results of measurements indicate that shape as well as structure remarkable non homogeneity should expected after hard milling due to missing full contact between milling cutter and workpiece. This non homogeneity can be monitored via Barkhausen noise technique. On the other hand the competitive grinding cycles produced more homogenous surface and surface state is a function of infeed speed.

Real-Time Acoustic Monitoring of Cutting Blade Sharpness in Agricultural Machinery

Cutting processes are among the most important crushing procedures in harvesting technology. Common practice attempts to identify the time for regrinding crop cutting blades do not often lead to the desired results. Continuous monitoring of the cutter bars in harvesting machines could provide the optimal regrinding time to maintain cutting performance and to achieve preferably long maintenance intervals. In this study, a method for real-time acoustic monitoring of the sharpness of crop cutting blades is shown based on an analytical simulation, acoustic measurements, and statistical analysis. These measurements were performed with piezoelectric accelerometers and signals were recorded at a sampling rate of 51 kHz. Structure-borne sound was measured on the counter blade, knife drum, and cabin of a self-propelled field chopper during harvesting. A good interrelation was found between the condition of the blades and the structure-borne sound. The statistical classification analysis with the support vector machine method allows an attribution of the blade sharpness (described by means of executed grinding cycles) with an accuracy of 0.76. Further development steps and the optimization potential of the design of system components are also discussed.

Role of Temperature Parameters in Achieving Precision Traverse Cylindrical Grinding of Chrome-Plated Ferrous Metal Rolls

This work considered the finishing precision grinding process at a small ferrous metal roll manufacturer. A design of experiments (DOE) methodology was used to evaluate the process and ascertain whether the degree of confidence gained from the process offers an acceptable level of risk in the conformance of end products to customer requirements. A thorough identification of the process variables and measurement considerations relevant to the process was carried out, before assessing and categorizing these variables using the grinding cycle as a “black box” system. Coolant temperature, environment temperature, work speed, and traverse speed were all considered against measured size change, surface finish, and circular run-out in a full factorial experimental design. The experiments were carried out on a manual cylindrical grinding machine retrofitted with digital encoders on the driven axes, with a chrome-plated roll 300 mm in diameter as the workpiece. Experiments were conducted over a period of 11 months during which the machine used was part of ongoing production environment. The results show that control of temperature, both of the coolant and of the environment in which the machine was operated, was the most important of the variables studied, but the skill of the machine operator remains dominant in the process overall.

Effect of rail corrugation on metro interior noise and its control

Rail corrugation is very common in metro systems, and serious noise problems produced by rail corrugation, especially short-wavelength corrugations (25–50mm), are a common cause of passenger complaints. For metro trains, the wheel-rail interface is the main source of noise, and the wheel-rail roughness, especially in the presence of rail corrugation, is the main excitation source. Rail grinding is a fast, economical, and effective control measure for reducing vibration and noise. However, the existing grinding cycle is not sufficient to meet the requirements of interior noise. There is no rail grinding standard based on interior noise limits for metro trains running on slab tracks in tunnels, which covers the vast majority of situations in China. Therefore, there is an urgent need to understand the effects of rail corrugation on interior noise for metro trains running on slab tracks in tunnels. At the same time, a rail grinding standard based on interior noise limits for such metro trains is very important. In this paper, the characteristics of the serious noise problems caused by rail corrugation are identified and suitable rail grinding controls based on noise limits are presented.

Mechanical pretreatment of cellulose pulp to produce cellulose nanofibrils using a dry grinding method

Cellulose nanofibrils (CNFs) are typically produced via wet milling pretreatment method to facilitate efficient disintegration of cellulose fibers by pre-fibrillation and fiber size reduction. However, the use of high energy and presence of water during wet milling methods leads to the increase in overall energy consumption during CNFs production and pose challenges during storage and handling. The objective of this study is to investigate the dry grinding of cellulose fluff pulp using the shear cutting method to determine the specific energy required to produce cellulose precursors and their characteristics for manufacturing CNFs. The specific energy required to grind cellulose fluff pulp with a screen size of 0.25mm in three cycles was measured. The ground sample received after each cycle was sampled to characterize its properties and its potential to produce CNF hydrogels. As the number of grinding cycles increased, the specific energy required per cycle decreased with an overall net energy consumption of 894kWh/Mg for three grinding cycles. The cellulose powder from the third grinding cycle was successfully disintegrated into cellulose nanofibrils with an average diameter of 119nm without any fiber clogging. In conclusion, the three-cycle shear cutting process was sufficient to produce dry cellulose precursors for CNFs production, while reducing the overall energy consumption and handling and storage problems.

Effects of microstructural orientation on the abrasive wear resistance of subfossil elm wood in three orthogonal planes

The research is part of a more extensive project in wood science, and its aim was to identify the effects of microstructural orientation on the two-body abrasive wear of sub-fossil wood. Samples to be tested were prepared from an approximately 670 year-old sub-fossil elm trunk retrieved from the Sava River bed in the northern part of Bosnia and Herzegovina. The samples were mounted to present three orthogonal planes (transverse, radial, and tangential) to a rotating disk of sandpaper. The effects of three average grit sizes (35, 82, and 201µm) were also investigated. The rate of abrasive wear for each microstructural orientation grew linearly with the number of grinding cycles. The lowest wear rate was observed on the transverse cross-section and the highest on the radial cross-section. As the sandpaper grit size was decreased, the wear rate values decreased for all cross-sections and became similar to one another. The wear resistance appears to be less affected by the heterogeneity of the wood microstructure than it is by a decrease in diameter of the abrasive grains. It was therefore concluded that the abrasion response of subfossil elm wood exhibits the same characteristics as the hitherto researched, more recent wood samples.

Modeling of Discontinuous Surfaces Intragrinding Processing Peculiarities

The analysis of the technological features of internal grinding revealed that a majority of internal grinding operations in the automotive and machine-tool industries are related with the processing of the discontinuous surfaces, including splined and dowel holes, internal surfaces having different notches, grooves and holes. Grinding of these holes causes the greatest difficulties due to the high process instability, increased fluctuations of the cutting forces and elastic deformations; it leads to diminution of processing accuracy. Models of the metal removal process and calculation of the processing errors were proposed to consider the specifics of the internal grinding of the discontinuous surfaces when modeling the optimal grinding cycles; they allow calculating the changes of the current value of the cutting force, actual allowance removal, radii of the machinable holes and other parameters. The developed model of the metal removal process allows considering fluctuating processing conditions of batch of details (initial radial runout of the billet, spread of processing allowance, blunting the grains of the grinding circle, etc.). Based on the metal removal model the modeling technique of the optimal cycles in the multidimensional space of the control parameters and the technological limitations of the criterion function was developed.

Complex optimization of parameters for controlling the cycle of internal grinding by the method of dynamic programming

The technique of designing the optimal cycles of intragrinding processing which allows performing complex optimization of control parameters is presented. As a mathematical optimization technique the method of dynamic programming is used; it allows to take into account any number of optimized control parameters and constraints of the objective function. In this case, this optimization method is not sensitive to the type of mathematical models of the process and the constraints of the objective function. Complex optimization can simultaneously optimize the parameters of the grinding cycle (the number of cycle stages, feed and allowance for the stages), the cutting speed (billet and circle speed of rotation), parameters of the circle characteristics (hardness, granularity, structure, material of grains and bundle) and parameters of technological adjustments (diameter and height of the circle, circle overtravel).

Optimal internal grinding cycles in multidimensional control-parameter space

A method is proposed for the design of optimal internal grinding cycles in multidimensional control- parameter space, under numerous technological constraints. This method is based on stepwise modeling of metal removal in terms of specified machining properties, with allowance for elastic deformation and the cutting kinematics. Optimization is based on dynamic programming, which permits any number of technological constraints to be taken into account and is not sensitive to the type of mathematical models employed or the constraints on the target function.

Pilot plant tests of technology of gold leaching in grinding cycle using underwater acoustic projector

Pilot plant tests of technology of gold leaching in grinding cycle using underwater acoustic projector