Investigation of Material Removal Mechanism in Grinding: A Single Grit Approach

This thesis has investigated material removal mechanisms in grinding by considering single grit workpiece interaction. The investigation was performed both experimentally and using finite element simulation. Rubbing, ploughing and cutting mechanisms occurring during the grinding process were studied at the micro scale. Due to its nature the rubbing phase occurs in a very narrow region of grit-workpiece engagement and is difficult to examine under a microscope and so was investigated using FEM simulation. The ploughing mechanism was thoroughly investigated using both experimental tests and FEM simulations, and a similar trend was observed for the pile up ratio along the scratch path from the experimental tests and the FEM simulations. Ploughing and cutting mechanisms in grinding were found to be highly influenced by grit cutting edge shape, sharpness and bluntness. Cutting is the prominent mechanism when the grit cutting edge is sharp, but ploughing is more prominent when the grit cutting edge becomes flattened. In the case of multiple edges scratch formation, ploughing is dramatically increased compared to single edge scratches. Feasibility of ground surface simulation using FEM is demonstrated using multiple pass scratch formation in a cross direction. Although chip formation mechanism is developed at a relatively higher depth of cut (greater than 10 μm), at small scales down to 1 μm, FEM simulation was not a suitable method to use. To reduce the drawbacks of FEM simulation in micro scale cutting, a meshless simulation technique such as smooth particle hydrodynamics is recommended for future studies

External grind-hardening forces modelling and experimentation

Grind hardening process utilizes the heat generated in the grinding area for the surface heat treatment of the workpiece. The workpiece surface is heated above the austenitizing temperature by using large values of depth of cut and low workpiece feed speeds. However, such process parameter combinations result in high process forces that inhibit the broad application of grind hardening to smaller grinding machines. In the present paper, modelling and predicting of the process forces as a function of the process parameters are presented. The theoretical predictions present good agreement with experimental results. The results of the study can be used for the prediction of the grind hardening process forces and, therefore, optimize the process parameters so as to be used with every size grinding machine

On geometry and kinematics of abrasive processes: The theory of aggressiveness

Due to the stochastic nature of the abrasive-tool topography, abrasive processes are difficult to model and quantify. In contrast, their macro geometry and kinematics are usually well defined and straightforwardly controlled on machine tools. To reconcile this seeming contradiction, a novel unifying modelling framework is defined through the theory of aggressiveness. It encompasses the arbitrary geometry and kinematics of a workpiece moving relative to an abrasive surface. The key parameter is the point-aggressiveness, which is a dimensionless scalar quantity based on the vector field of relative velocity and the vector field of abrasive-surface normals. This fundamental process parameter relates directly to typical process outputs such as specific energy, abrasive-tool wear and surface roughness. The theory of aggressiveness is experimentally validated by its application to a diverse array of abrasive processes, including grinding, diamond truing and dressing, where the aggressiveness number is correlated with the aforementioned measured process outputs

Approach of Characterization of the Grinding Wheel Topography as a Contribution to the Energy Modelling of Grinding Processes

AbstractA major percentage of the kinematic energy during the grinding process is converted into heat. The energy conversion is significantly influenced by the grinding wheel topography. Therefore the distribution and the shape of the cutting edges have to be considered in order to give a general model of energy conversion in grinding. This paper introduces an approach to describe and characterize the cutting edges of a grinding wheel topography, taking the elasto-plastic material behavior of the workpiece into account. Finally, based on experimental results the influence of the grinding wheel topography on energy conversion is shown using the presented model

New insights into the methods for predicting ground surface roughness in the age of digitalisation

Grinding is a multi-length scale material removal process that is widely employed to machine a wide variety of materials in almost every industrial sector. Surface roughness induced by a grinding operation can affect corrosion resistance, wear resistance, and contact stiffness of the ground components. Prediction of surface roughness is useful for describing the quality of ground surfaces, evaluate the efficiency of the grinding process and guide the feedback control of the grinding parameters in real-time to help reduce the cost of production. This paper reviews extant research and discusses advances in the realm of machining theory, experimental design and Artificial Intelligence related to ground surface roughness prediction. The advantages and disadvantages of various grinding methods, current challenges and evolving future trends considering Industry-4.0 ready new generation machine tools are also discussed

Development of Composite Grinding Wheels for Hard and Soft Metals

This research investigates the performance of grinding wheel in terms of its internal granular particles and their effect on the surface finish for both soft and hard metals subjected to both dry and wet conditions of use. The study considers the properties of materials of construction including hardness of the granular particles and their size and distributions that affects the grinding wheel efficiency in abrading of soft and hard metal surfaces. Furthermore, in order to improve grinding performance, the mechanism of clogging the cutting surface of the grinding wheel as a function of for example, the surface properties of granular particles and the chips formed during the grinding operation have been considered. Objective of this project is to study the overall sharpness of the grinding wheel in terms of its internal granular particles and their effect on the surface finish for both soft and hard metals at different conditions of use. The properties of materials of construction including hardness of the granular particles that affects the grinding wheel efficiency in abrading of soft and hard metal surfaces have been studied. During this project two novel grinding wheels, namely single grooved and crossed grooved wheels, have been developed and their performance has been compared with a selected commercial grinding wheel, the design of grinding wheels incorporated an innovative surface profile which has been shown to be capable of taking potentially large depths of cut at high wheel and workpiece speeds to create a highly efficient material removal process. This aggressive processing generated high temperatures in the contact zone between the wheel and workpiece. The voltage measured by oscilloscope during grinding of different workpiece materials including mild steel, brass and aluminium bars was related to the temperature generated between wheels and workpiece materials. Temperatures in the ground surface can be predicted with a knowledge of the specific grinding energy and the grinding parameters used. Specific grinding voltage recorded at high specific material removal rates demonstrated a constant value of specific grinding heat dependent on cutting and contact conditions, improving accuracy of the predictive model. 4 Cutting and contact conditions in the different grinding wheels vary dependent on their surface patterns. This thesis shows how temperature, contact stresses, material removal rates vary with the surface profile, size and orientation of the abrasive particles of the grinding wheel, affecting the performance of the grinding wheel during the grinding operations. Redesigning grinding wheels by making grooves on surface of wheel, material removal rate was increased and less voltage has been recorded. Also, time for redressing wheels was reduced. The wheel surface of crossed grooves shape showed a significant improvement in grinding of soft materials e.g. aluminium. Finally, the different stress distribution, including von_Mises, principal stresses and shear stresses, in the grinding wheels and the three workpiece bars during the grinding process were investigated using Finite Element Analysis (FEA) technique. The maximum von-Mises stress value of the brass bar was found to be 173.2 MPa. Hence the strength of produced grinding wheel calculated as 207 MPa which was extensively higher than the maximum von-Mises stress value obtained from FEA profile, resulting 19.5% higher strength in crossed grooves wheel

Advances in centerless grinding

La lavorazione di rettifica senza centri a tuffo \ue8 un processo ad alta produttivit\ue0 ma che pu\uf2 soffrire di instabilit\ue0 e condizioni mutevoli, dovuti alla propria configurazione geometrica e alle caratteristiche degli utensili abrasivi. Il presente lavoro si propone di presentare un approccio pratico alla scelta dei parametri di processo con uno studio sperimentale dei loro effetti sulle caratteristiche qualitative tipiche di questa lavorazion

An investigation into Vibratory Grinding of hard-to Machine Aerospace Materials

There is an increased demand for high surface finishes and tight tolerances, especially in high value manufacturing processes. However, progress in materials science has led to the development of new materials especially in the aerospace industry, where high heat resistance materials are preferred such as Ti-6Al-4V. These new materials have different mechanical properties from conventional ones. This makes their machinability very unusual when compared to that of conventional materials. Consequently machining these materials poses a significant challenge to industry. Since this alloy has got low density, high strength to weight ratio and also high temperature strength, it is used for aerospace, civil and military aircraft turbine engine compressor blades manufacturing. This research programme sets up an investigation into vibration assisted grinding in a range of frequencies and amplitudes combined with various process parameters in the attempt to grind advanced aerospace materials. Such a novel approach called “Resonance machining” also depends on the Taguchi experimental design method, with the aim of improving the grinding quality and efficiency. The novelty of this new approach is that the vibration assisted resonance was implemented in the axial direction of the grinding feed rate, using an aluminium oxide grinding wheel, with the application of coolant fluid to enhance grinding difficult to machine aerospace materials, this approach is considered to be an alternative to the usage of super abrasive wheels such as CBN and diamond wheels currently been used, with negative effect where damage to the workpiece surface and subsurface crack have been reported. However, the advantages of vibration assisted grinding as a new technique are the reduction of wheel wear and cutting forces. Through over this study it has been proven that vibration assisted grinding allows the wheel to cut in two directions and that will increase the material removal rate reduce the wheel wear, cutting forces and also the power consumption. The purpose of this research is to achieve an optimum performance of vibration assisted grinding processes using difficult-to-machine advanced aerospace materials. The first step in this investigation is to identify the material under investigation. Therefore, the above mentioned aerospace materials have been tested. Initial hardness testing was carried out on two types of materials involved this study, namely Nickel alloy (Inconel 718) and Ti-6Al-4V. This was followed by a chemical element content analysis undertaken on the scanning electron microscope with X-Ray setup. However, this work investigates the grinding performance of titanium and nickel alloys using aluminium oxide (Al2 O3) grinding wheel. Hence, experiments were carried out in wet conditions with/without vibration grinding and the results are provided to confirm the effectiveness of this approach

Modelling of grinding mechanics : a review

Grinding is one of the most widely used material removal methods at the end of many process chains. Grinding force is related to almost all grinding parameters, which has a great influence on material removal rate, dimensional and shape accuracy, surface and subsurface integrity, thermodynamics, dynamics, wheel durability, and machining system deformation. Considering that grinding force is related to almost all grinding parameters, grinding force can be used to detect grinding wheel wear, energy calculation, chatter suppression, force control and grinding process simulation. Accurate prediction of grinding forces is important for optimizing grinding parameters and the structure of grinding machines and fixtures. Although there are substantial research papers on grinding mechanics, a comprehensive review on the modeling of grinding mechanics is still absent from the literature. To fill this gap, this work reviews and introduces theoretical methods and applications of mechanics in grinding from the aspects of modeling principles, limitations and possible future trendencies