Effect of different parameters on grinding efficiency and its monitoring by acoustic emission

Grinding efficiency is one of the most important considerations in the selection of grinding operation conditions because it has a significant impact on the productivity, quality, energy consumption and cost of production. Focusing on the core issues of grinding process, the paper presents some fundamental research findings in relation to grinding material removal mechanisms. The grinding efficiency is analysed by considering the rubbing, ploughing and cutting three stages of a single grit grinding process. By analysing the features of acoustic emission in single grit grinding tests, an evidence based scientific foundation has been established for monitoring grinding efficiency using acoustic emission. Accordingly, the energy consumption in the grinding is considered with the grit shape. Following the discussion of the models of temperature elevation and thermal stresses in grinding, the paper provides a logic depiction that explains why acoustic emission in grinding can be used for grinding thermal performance monitoring. As a result, the paper introduces a novel acoustic emission monitoring method that is capable to monitor grinding temperature and grinding wheel wear status

Análise de Sinais de Emissao Acústica e Estatística Counts na Detecção da Alteração Microestrutural na Retificação de Aço 1045

Grinding is a high-precision, high-value-added finishing process as it is usually the last stage of the manufacturing chain. However, unsatisfactory results may occur, mainly due to changes in the microstructure of the ground workpiece. Such changes are caused by the high temperatures involved in the process due to the grinding conditions in which the part was subjected. In this way, the main objective of this work is the monitoring of the grinding process in order to detect changes in the signal and to relate them with damage occurred in the ground workpiece. The tests were carried out on a surface grinding machine, aluminum oxide grinding wheel and ABNT 1045 steel parts. Metallography was performed on the parts for a more further analysis of their microstructure. The recording of signals was obtained at a sample rate of 2 MHz through an acoustic emission sensor (AE). A frequency study for the selection of the best frequency bands that characterize damage occurred in the ground workpiece. The event counts statistic was applied to the filtered signal in the chosen frequency bands. The results of this work show that the grinding conditions influence the signal and, therefore, its frequency spectrum.Keywords: Manufacturing process; automation, monitoring; grinding process; acoustic emission, damage detectio

Abrasive Feature Related Acoustic Emission in Grinding

Grinding monitoring enables the online supervision of crucial aspects of the process, such as tool state, surface quality, and dimensional accuracy; and possesses a great advantage over traditional post-process quality control techniques by reducing costs and inspection times. Such an advantage relies on a good interpretation of monitored signals in relation to grinding behaviours. This paper presents an experimental study on acoustic emission (AE) features in abrasive grinding scratch experiments. The acoustic emission signals are analysed in both the time and frequency domains. The results show that the signal feature extraction in the frequency domain gives excellent indication in correlation to the surface creation with different abrasive geometrical characteristics. The AE features in the frequency range between 0 and 200 kHz show good correlation with the characteristics of interaction between abrasive and workpiece in scratching tests and could be an ideal data source for the online monitoring of surface creation in grinding processes

Theoretical background of rock failure at hydraulic seam fracture and aftereffect analysis

Purpose. Theoretical substantiation of the methodological foundations of possible effects and aftereffects identification of the hydraulic seam fracture (HSF) technology. Methods. The research structure and procedure includes: studying the power engineering aspect of the rock failure, the acoustical wave effects; thermodynamic analysis of rock failure, analysis of surfaces mechanoactivation at rock failure and aftereffect of the primary pore space self-development at the HSF due to the Rebinder’s effect. Findings. It was established that among the fundamental consistent patterns that determine the formation and development of the HSF technology aftereffects during formations mining, are the methodological provisions and criteria for failure parameters prediction and grinding effects, namely: the average and local energy density of geoenvironment destruction, efficiency of grinding, the average particle and pore size, the specific surface area, the specific energy consumption per unit of the resulting surface. The connection between the parameters of the acoustic wave and the size of the fractures, which forms the basis of the acoustic emission (AE) method, is experimentally confirmed. Originality. It is established that the database for evaluating the expected fracture effects in the working zone of the HSF is: AE activity, specific acoustic radiation, spectrum of signals, characteristic amplitudes under the condition of physical modeling on the model samples of the geoenvironment behavior. It is shown that the critical state of a substance corresponding to the beginning of failure at the microlevel should be considered from the standpoint of thermodynamics as a phase change (evaporation, sublimation) near the critical point, based on the temperature critical values and the specific energy of the phase change. The presence of surfaces mechanoactivation in the rock failure is experimentally proved. The hypothesis concerning the rock pore space development aftereffect during hydraulic seam fracture due to the Rebinder’s effect is presented. Practical implications. It is proposed to size up the degree of geoenvironment destruction in the process of the HSF by the Kd parameter, which is equal to the product of the maximum amplitude of acoustic signals on the total acoustic activity of the destruction zone. It is established that the conditions for rock failure at the HSF are determined by the relationship between the rock pressure P and the volume energy density W of the failure. It is shown that the level of surfaces mechanoactivation can be estimated by adsorption characteristics – the adsorption potential and the pH of the newly discovered surfaces.Мета. Теоретичне обґрунтування методологічних основ встановлення умов прояву можливих ефектів і пост-ефектів технології гідравлічного розриву пласта (ГРП). Методика. Структура та послідовність проведення дослідження включає вивчення енергетичного аспекту руйнування гірського масиву, дії акустичних хвиль, термодинамічний аналіз руйнування гірського масиву, аналіз механоактивації поверхонь при руйнуванні гірського масиву та пост-ефекту саморозвитку первинного пористого простору ГРП внаслідок дії ефекту Ребіндера. Застосовано метод акустичної емісії, потенціометрії та рН-метрії. Результати. Встановлено, що до числа фундаментальних закономірностей, які визначають формування і розвиток пост-ефектів технології ГРП при відпрацюванні продуктивних пластів, відносяться методичні положення й критерії для прогнозу показників руйнування та ефектів подрібнення, а саме: середньої та локальної густини енергії при руйнуванні геосередовища, ККД подрібнення, середній розмір часток і пор, питома поверхня, питомі витрати енергії на одиницю одержаної поверхні. Експериментально підтверджений зв’язок між параметрами акустичної хвилі та розміром тріщин, що складає основу методу акустичної емісії (АЕ). Наукова новизна. Встановлено, що базу інформації для оцінки очікуваних у робочій зоні ГРП ефектів руйнувань складають активність АЕ, питоме акустичне випромінювання, спектр сигналів, характерні амплітуди за умови фізичного моделювання поведінки геосередовища на модельних зразках. Визначено, що граничний стан речовини, що відповідає початку руйнування на мікрорівні, слід розглядати з позицій термодинаміки як фазовий перехід (випаровування, сублімація) поблизу критичної точки, виходячи із критичних значень температури і питомої енергії фазового переходу. Експериментально доведено наявність механоактивації поверхонь при руйнуванні гірського масиву. Висунута гіпотеза щодо пост-ефекту розвитку пористого простору гірського масиву при ГРП у контексті дії ефекту Ребіндера. Практична значимість. Запропоновано оцінювати ступінь руйнування геосередовища у процесі ГРП показником Кр, що дорівнює добутку максимальної амплітуди акустичних сигналів на сумарну акустичну активність зони руйнування. Встановлено, що умови руйнування гірського масиву при ГРП детермінуються співвідношенням між гірським тиском Р і об’ємною густиною енергії W деформації. Показано, що ступінь механоактивації поверхонь може бути оцінена за характеристиками адсорбції – потенціалом адсорбції та показником рН нововідкритих поверхонь.Цель. Теоретическое обоснование методологических основ установления условий проявления возможных эффектов и пост-эффектов технологии гидравлического разрыва пласта (ГРП). Методика. Структура и последовательность проведения исследования включает изучение энергетического аспекта разрушения горного массива, действия акустических волн, термодинамический анализ разрушения горного массива, анализ механоактивации поверхностей при разрушении горного массива и пост-эффекта саморазвития первичного пористого прострагства ГРП в результате действия эффекта Ребиндера. Применен метод акустической эмиссии, потенциометрии и рН-метрии. Результаты. Установлено, что к числу фундаментальных закономерностей, определяющих формирование и развитие пост-эффектов технологии ГРП при отработке продуктивных пластов, относятся методические положения и критерии для прогноза показателей разрушения и эффектов измельчения, а именно: средней и локальной плотности энергии при разрушении геосреды, КПД измельчения, средний размер частиц и пор, удельная поверхность, удельные затраты энергии на единицу полученной поверхности. Экспериментально подтверждена связь между параметрами акустической волны и размером трещин, что составляет основу метода акустической эмиссии (АЭ). Научная новизна. Установлено, что базу информации для оценки ожидаемых в рабочей зоне ГРП эффектов разрушений составляют актитивность АЭ, удельное акустическое излучение, спектр сигналов, характерные амплитуды при условии физического моделирования поведения геосреды на модельных образцах. Определено, что предельное состояние вещества, отвечающее началу разрушения на микроуровне, следует рассматривать с позиций термодинамики как фазовый переход (испарение, сублимация) вблизи критической точки, исходя из критических значений температуры и удельной энергии фазового перехода. Экспериментально доказано наличие механоактивации поверхностей при разрушении горного массива. Выдвинута гипотеза относительно пост-эффекта развития пористого пространства горного массива при ГРП в контексте действия эффекта Ребиндера. Практическая значимость. Предложено оценивать степень разрушения геосреды в процессе ГРП показателем Кр, который равен произведению максимальной амплитуды акустических сигналов на суммарную акустическую активность зоны разрушения. Установлено, что условия разрушения горного массива при ГРП детерминируются соотношением между горным давлением Р и объемной плотностью энергии W деформации. Показано, что степень механоактивации поверхностей может быть оценен по характеристикам адсорбции – потенциалом адсорбции и показателем рН новооткрытых поверхностей.The authors express their gratitude to Doctor of Physical and Mathematical Sciences Vilian Mykolayovych Bovenko for valuable advices when conducting research. In addition, thanks to Doctor of Engineering Sciences Anatolii Dmytrovych Aleksieiev for the opportunity to use a unique research unit of non-uniform triaxial load and research method revision. The authors thank to Candidate of Engineering Sciences Iryna Mykhailivna Yuriivska for consultations on the use of her original method of mechanoactivation study

Fundamental Study of Corrective Abrasive Machining Technology

The presentation give an overview on the research activities undertaken in the AMTG, CPT in the University of Huddersfield

Acoustic image-based damage identification of oxide aluminum grinding wheel during the dressing operation

Abstract Grinding is a finish process of parts that require high precision and tight dimensional tolerance, which owe high value-added. As the grinding process takes place, the cutting surface of the grinding wheel undergoes wear and then its cutting capacity is reduced. On the other hand, the dressing operation is responsible for restoring the cutting surface of the grinding wheel and, therefore, plays a key role in the grinding process. This work aims at obtaining acoustic images of the grinding wheel surface to identify its conditions during the dressing operation. Experimental tests were conducted with a single-point diamond dresser in a surface grinding machine, which was equipped with an oxide aluminum grinding wheel in which specific marks were intentionally made on its surface to simulate damages for identification. An acoustic emission sensor was fixed to the dresser holder and the signal were acquired at 5 MHz. The signal spectrum was investigated and a frequency band was carefully selected, which represented the conditions of grinding wheel surface. The root mean square values were then computed from the raw signal with and without filtering for several integration periods, and the acoustic images obtained. The results show that the proposed technique is efficient to identify the damage on the wheel surface during the dressing operation as well as its location

Monitoring Single-point Dressers Using Fuzzy Models

AbstractGrinding causes progressive dulling and glazing of the grinding wheel grains and clogging of the voids on the wheel's surface with ground metal dust particles, which gradually increases the grinding forces. The condition of the grains at the periphery of a grinding wheel strongly influences the damage induced in a ground workpiece. Therefore, truing and dressing must be carried out frequently. Dressing is the process of conditioning the grinding wheel surface to reshape the wheel when it has lost its original shape through wear, giving the tool its original condition of efficiency. Despite the very broad range of dressing tools available today, the single-point diamond dresser is still the most widely used dressing tool due to its great versatility. The aim of this work is to predict the wear level of the single-point dresser based on acoustic emission and vibration signals used as input variables for fuzzy models. Experimental tests were performed with synthetic diamond dressers on a surface-grinding machine equipped with an aluminum oxide grinding wheel. Acoustic emission and vibration sensors were attached to the tool holder and the signals were captured at 2MHz. During the tests, the wear of the diamond tip was measured every 20 passes using a microscope with 10 to 100 X magnification. A study was conducted of the frequency content of the signals, choosing the frequency bands that best correlate with the diamond's wear. Digital band-pass filters were applied to the raw signals, after which two statistics were calculated to serve as the inputs for the fuzzy models. The results indicate that the fuzzy models using the aforementioned signal statistics are highly effective for predicting the wear level of the dresser