Apr 072012
 

The theory of relativistic heat conduction (RHC) claims to be the only model for heat conduction (and similar diffusion processes) that is compatible with the theory of special relativity, the second law of thermodynamics, electrodynamics, and quantum mechanics, simultaneously. The main features of RHC are:

  1. It admits a finite speed of propagation, and allows for relativistic effects when heat flux transients approach that speed.
  2. It removes the possibility of paradoxical situations that may violate the second law of thermodynamics.
  3. It, implicitly, admits the wave–particle duality of the heat-carrying “phonon”.

These outcomes are achieved by (1) upgrading the Fourier equation of heat conduction to the form of a Telegraph equation of electrodynamics, and (2) introducing a new definition of the heat flux vector. Consequently, RHC gives rise to a number of interesting phenomena, such as thermal resonance and thermal shock waves, which are possible during high-frequency pulsed laser heating of thermal insulators. The main appealing feature of the theory is its mathematical elegance and simplicity.

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  1. Y.M. Ali, Relativistic heat conduction, Wikipedia, 2008.
Apr 072012
 

Impact abrasive machining is a broad class of manufacturing processes that include surface cleaning, descaling, deburring, sand-blasting, shot-peening, abrasive water or air jet micromachining, and abrasive waterjet (AWJ) cutting, milling, turning, and drilling. Starting from the basic principles of fluid and solid mechanics, this chapter describes the underlying physical processes and mechanisms affecting jet formation and material removal, and leads to a practical discussion of factors affecting process performance. Adaptations of the basic cutting process to operations such as milling, turning, micromachining, surface cleaning, or surface treatment are explained; and various means for process improvement are discussed. Throughout, focus is on AWJ cutting as the common generic process, from which all other processes are treated as special cases. This chapter is suitable for practicing engineers and researchers, and includes an extensive list of references to guide further study.

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  1. Y.M. Ali, J. Wang, Impact abrasive machining, in: J.P. Davim, M.J. Jackson (Eds.), Machining with Abrasives, Chapter 9, Springer, New York, 2011, pp. 385-419.
Apr 072012
 

An experimental study of a radial-mode abrasive waterjet (AWJ) turning of AISI 4340 high tensile steel is presented. The major process parameters, i.e. feed speed, waterjet pressure, abrasive flow rate, nozzle tilt angle, and workpiece surface speed, are considered in a statistical experimental design. The advantages of the radial-mode AWJ turning over the offset-mode turning include maximum jet energy utilization, high surface speed, a variety of nozzle tilt angles and small nozzle standoff distance, to enable high material removal rate (MRR). It is found that the depth of cut is considerably increased when large nozzle tilt angle and high surface speed are used. It also shows that feed speed and waterjet pressure are the two most significant parameters to control the MRR. This preliminary study suggests that the radial-mode AWJ turning is feasible and can yield high material removal rates. Future research to advance the knowledge about this new machining process is also proposed.

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  1. W.Y. Li, J. Wang, Y.M. Ali, An experimental study of radial-mode abrasive waterjet turning of steels, MATER SCI FORUM 697-698 (2012) 166-170.
Apr 072012
 

Most existing models for abrasive jet machining (AJM) are based on erosion models for either ductile or brittle materials. This classification imposes some limitations, because most materials are neither absolutely ductile nor absolutely brittle, but lay within the continuous spectrum between those two idealizations. This work reports recent progress in the modeling of erosion processes for real materials, and discusses the implications of a new model in estimating the performance of AJM. The new model is more capable in explaining the effects of jet velocity, abrasive particle size, and various material properties on the efficiency of the cutting process.

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  1. Y.M. Ali, P. Mathew, J. Wang, Progress in the modeling of abrasive jet machining, AMR 126-128 (2010) 3-8.
Apr 072012
 

Owing to its various distinct advantages over the other machining technologies, abrasive jet machining has become a promising machining technology for brittle and hard-to-machine materials. An experimental study is presented on the micro-grooving of quartz crystals using an abrasive airjet. The effect of the various process parameters on the major machining performance measures are analysed to provide a deep understanding of this micro-machining process. Predictive models are then developed for quantitatively estimating the machining performance. The models are finally verified by an experiment. It shows that the model predictions are in good agreement with the experimental results under the corresponding conditions.

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  1. A. Moridi, J. Wang, Y.M. Ali, P. Mathew, X.P. Li, A study of abrasive jet micro-grooving of quartz crystals, KEY ENG MATER 443 (2010) 645-651.
Apr 072012
 

Mono crystalline silicon wafers are important materials in the semiconductor industry for fabricating integrated circuits and micro electro mechanical systems. To ensure high surface integrity of polished wafers, the effect of pad texture and its variation on the pad performance needs to be understood. This paper studies experimentally the dependence of pad performance on its texture deterioration by investigating its correlation with polishing time, polishing pressure, and material removal rate. The study concludes that material removal rate decreases as the cylindrical cell structure of a pad is gradually deteriorated, that there is a pad life limit beyond which polishing quality can no longer be maintained, and that the workable pad life can be extended to a certain degree by applying higher polishing pressure.

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  1. L.C. Zhang, A.Q. Biddut, Y.M. Ali, Dependence of pad performance on its texture in polishing mono-crystalline silicon wafers, INT J MECH SCI 52 (2010) 657.
Apr 072012
 

This paper presents a comprehensive model for predicting surface roughness due to grinding. Fuzzy rules are provided, to estimate roughness for any practical combination of (1) wheel hardness grade, (2) abrasive grain size, (3) dressing condition, (4) table speed, (5) wheel depth of cut, and (6) coolant application. The rule-base can be adapted to account for the effect of (7) different workpiece material hardness, (8) wheel rotational speed, and (9) equivalent wheel diameter. The 86 rules are intuitive, and are particularly useful for production and/or embedded control applications.

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  1. Y.M. Ali, L.C. Zhang, Fuzzy rules for surface roughness of ground steels, KEY ENG MATER 389-390 (2009) 120.
Apr 072012
 

This paper experimentally investigates the effect of time and pressure on the condition of polishing pads and the material removal rate (MRR) of single crystal silicon. It was found that as the pad deteriorates with time, MRR decreases. Surfaces with a required quality can only be achieved before the texture deterioration reaches a critical limit. At a higher pressure, 25 kPa, deterioration is slower, and the effective life of pads and MRR is enhanced.

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  1. A.Q. Biddut, L.C. Zhang, Y.M. Ali, Effect of polishing time and pressure on polishing pad performance, KEY ENG MATER 389-390 (2009) 510.
Apr 072012
 

This paper experimentally investigates the micro-structural changes in mono-crystalline silicon induced by abrasive polishing with abrasive grain size and applied pressure. It was found that while the large abrasives of about 15 μm and 300 nm in diameter induce both residual amorphous phase and various residual crystalline structures and dislocations, the finer abrasives of about 50 nm in diameter only produce residual amorphous phase in the top subsurface of polished silicon. With the fine abrasives, reducing applied pressure reduces the amorphous layer thickness,and a damage-free polishing can be achieved at the pressure of 20 kPa.

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  1. A.Q. Biddut, L.C. Zhang, Y.M. Ali, Z. Liu, Achieving a damage-free polishing of mono-crystalline silicon, KEY ENG MATER 389-390 (2009) 504.
Apr 072012
 

This investigation explores the possibility and identifies the mechanism of damage free polishing of monocrystalline silicon without chemical additives. Using high resolution electron microscopy and contact mechanics, the study concludes that a damage free polishing process without chemicals is feasible. All forms of damages, such as amorphous Si, dislocations and plane shifting, can be eliminated by avoiding the initiation of the b tin phase of silicon during polishing. When using 50 nm abrasives, the nominal pressure to achieve damage free polishing is 20 kPa.

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  1. A.Q. Biddut, L.C. Zhang, Y.M. Ali, Z. Liu, Damage-free polishing of mono-crystalline silicon wafers without chemical additives, SCRIPTA MATER 59 (2008) 1178.
Apr 072012
 

The relativistic heat conduction (RHCE) model is particularly important in the analysis of processes involving moving heat sources (MHS) at speeds or frequencies comparable with those of heat propagation in the medium. This paper establishes a unified framework for solving heat conduction problems using the RHCE model. It offers ‘‘Fundamental Solutions’’ in one, two, and three spatial dimensions, for the transient response due to an instantaneous point MHS. Moreover, it presents the transient response due to a continuous point MHS, the quasi-steady response due a periodic point MHS, as well as guidelines for solving the RHCE equation under various loading and boundary conditions.

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  1. Y.M. Ali, L.C. Zhang, Relativistic moving heat source, INT J HEAT MASS TRAN 48 (2005) 2741.
Apr 072012
 

The hyperbolic heat conduction equation (HHCE), which acknowledges the finite speed of heat propagation, is based on microscopic evidence from the kinetic theory and statistical mechanics. However, it was argued that the HHCE could violate the second law of thermodynamics. This paper shows that a HHCE-like equation (RHCE) can be derived directly from the theory of relativity, as a direct consequence of space time duality, without any consideration of the microstructure of the heat conducting medium. This approach results in an alternative expression for the heat flux vector that is more compatible with the second law. Therefore, the RHCE brings the classical field theory of heat conduction into agreement with other branches of modern physics.

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  1. Y.M. Ali, L.C. Zhang, Relativistic heat conduction, INT J HEAT MASS TRAN 48 (2005) 2397.
Apr 072012
 

Existing analytical thermal models for predicting surface burns due to grinding have limited use because of their reliance on parameters that are not readily obtainable in practice. This paper presents a practical and consistent fuzzy rule based model for estimating the grinding conditions at which ‘‘burn limits’’ occur. The model consists of 37 absolute and eight relative rules. It has a wide range of applications over many types of steels, Alundum wheels, and grinding conditions. It is also simple to implement, from a rule chart mode to an intelligent online adaptive control mode.

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  1. Y.M. Ali, L.C. Zhang, A fuzzy model for predicting burns in surface grinding of steel, INT J MACH TOOL MANU 44 (2004) 563.
Apr 072012
 

This paper describes a systematic approach to the modeling of engineering systems using a fuzzy formulation that is independent of human knowledge. The computer algorithm described here operates on a set of experimental observations of the system and constructs an optimum fuzzy model for these observations. The program automatically selects membership functions, deduces inference rules, constructs logical relations, and determines the formulae for conducting union and intersection operations. Membership functions, rules, and logical operations are defined parametrically. Model parameters are optimized so that the model can, at least, re-produce with minimum error the data that were used in obtaining the membership functions and rules. Therefore, model parameters are optimized to minimize error or entropy of the back-inferences of the observations from which the model was constructed. To reach the global minimum and avoid entrapment in a local minimum, a random search is carried out, then followed by a systematic Hooke-Jeeves search optimization algorithm. It has been found that this technique is more successful, compared with other statistical techniques.

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  1. Y.M. Ali, L.C. Zhang, A methodology for fuzzy modelling of engineering systems, FUZZY SET SYST 118 (2001) 181.
Apr 072012
 

In this paper a total of 16 variables, which are most influential on surface roughness in grinding, are considered. The variables are classified into three groups depending on their significance and effect on surface roughness. A three-layer fuzzy model is used to correlate these variables to surface roughness using the fuzzy rules generated based on experimental observations and recommendations from wheel manufacturers. Membership functions, fuzzy rule bases, and a worked example are presented in detail to demonstrate the strength of fuzzy logic in modeling such a complex system in an efficient manner.

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  1. Y.M. Ali, L.C. Zhang, Surface roughness prediction of ground components using a fuzzy logic approach, J MATER PROC TECH 89-90 (1999) 561.
Apr 072012
 

This paper proposes a fuzzy logic approach for the prediction of residual stresses induced by surface grinding. The surface residual stress of a ground component is considered as a function of ten variables including properties of the workpiece material, grinding wheel and the variation of operation parameters. The system extracts, from experimental results, experience and knowledge about the grinding processes and makes better prediction of residual stresses for a given grinding situation. It is shown that the fuzzy logic method provides a flexible framework for modeling the residual stresses induced by the grinding processes, in spite of the existence of experimental errors.

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  1. Y.M. Ali, L.C. Zhang, Estimation of residual stresses induced by grinding using a fuzzy logic approach, J MATER PROC TECH 63 (1997) 875.
Apr 072012
 

A large set of orthogonal metal-cutting tests has been conducted for Aluminum 2014-T6 using carbide and HSS tools over a wide range of cutting variables such as: spindle speed, fed and width of cut. The transient dynamic force behavior during the first few spindle revolutions after tool-workpiece contact was recorded and later analyzed in the time and frequency domains. Results show that, depending on the cutting conditions and in most of the tests carried out, the cutting and thrust forces reached their steady-state values in a number of spindle revolutions ranging from one and a half to two. This result indicates that the application of existing metal-cutting force models can not predict the actual behavior of the forces during transient cutting conditions. A new dynamic force model is proposed in which the instantaneous force and depth of cut as well as their first-order time derivatives are involved. This first-order linear differential equation is particularly important for advanced modeling for adaptive control purposes. Physical implications of these results are briefly discussed.

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  1. A. Abdel Hamid, Y. Ali, Experimental determination of dynamic forces during transient orthogonal cutting, J MAT PROC TECH 55 (1995) 162.
Apr 072012
 

This paper presents a fuzzy logic model for the selection of grinding wheels for surface grinding. The model is based on the qualitative knowledge obtained from various physical and empirical models of the grinding process, practical experience in the form of rules-of-thumb, and recommendations given by grinding wheel manufacturers. It is found that the selection of a proper grinding wheel, in terms of the type and size of abrasive grits, bond material and wheel grade, depends on seven parameters: (1) properties of work material, especially its hardness, (2) material removal rate, (3) required surface roughness, (4) effect of coolant application, (5) grinding wheel speed, (6) area of wheel-workpiece contact, and (7) machine power available. Recommendations by the model are compared with those by leading wheel manufacturers. The model can be applied to other grinding processes with some modification of the rule base.

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  1. Y.M. Ali, L.C. Zhang, A fuzzy logic approach for grinding wheel selection, in: N. Narutaki, C. Dingchang, Y. Yamane, A. Ochi (Eds.), Pro. 3rd Int. Conf. Prog. Cut. Grind., JSPE, Osaka, 1996, pp. 488-493.
Apr 062012
 

This work presents a complete fuzzy model for surface grinding of steel using aluminium oxide grinding wheels. Six independent variables—wheel grade, grit size, table speed, depth of cut, dressing, and coolant application—are input, and eight dependent variables—two force components, two residual stress components, two surface roughness parameters, change in surface hardness, and the onset of surface burns—are output model predictions. Thesis StatementThe entire model is automatically extracted from experimental data, without human intervention.

Chapter 1 is a brief introduction to the technological and economical importance of the grinding process. It provides a motivational foundation for the desirability of better understanding, predictability, and control of this important manufacturing process.

It is argued that our current portfolio of engineering sciences were not intended for describing behaviour under conditions prevailing during grinding. Before attempting to model the grinding process, analytically, there is a need for revamping engineering sciences and extending their reach to those extreme conditions. Moreover, there is a need for significant advances in material testing procedures, in order to acquire constitutive models and material properties under those extreme—not the idealized laboratory—conditions. As neither frontiers—fundamental theories or testing procedures—are likely to make quantum leaps in the near future, we seek alternative solutions, outside the classical analytical paradigm. This argument is promoted in Chapters 2 and 3.

Chapter 2 discusses the fundamental physical processes occurring during grinding. It is shown that several mechanisms take place during a typical grinding process, with varying degrees of intensity and interdependent nonlinear interference. Not only we do notunderstand the extent of each mechanism and its interplay with others, but also we do not have satisfactory basic knowledge of each individual mechanism, under the conditions prevailing in grinding. This lack of knowledge manifests itself in a number of conflicting reports by various research groups.

Chapter 3 is a road map of research in grinding over the last five decades, and a general review of various research efforts. It is shown that analytical research for grinding has had limited practical utility, because it (1) is based on simplified physical models, (2) applies many unrealistic assumptions, for the convenience of numerical solvability, and (3) requires input values that are not readily available to the user. It is estimated that grinding models include, typically on average, ± 30% uncertainty in their predictions, when tested over wide range of testing environments. At such a level of uncertainty, the computational demand by many analytical models is unjustifiable. Practicing engineers, often, find it easier to just rely on skills and experience of their grinding machine operators.

Fuzzy modelling is, therefore, offered as an interim pragmatic solution to modelling the grinding process. It may lack the intellectual superiority and mathematical robustness of an analytical model, but it offers meaningful answers to practical questions at the workshop level.

However, a major difficulty with fuzzy modelling is the acquisition of reliable fuzzy rules. Human experiences are known to be victim to bias, misconception, and misinformation, and are confined to a limited range of current and recurrent observations, with no possibility for extension beyond established operating conditions. It would be advantageous to fuzzy modelling, if we develop a methodology for fuzzy rules generation that is independent of human experts, and derive rules automatically from experimental data. Such fuzzy models would have the same—or better—credibility and extensibility as other empirical models, but would be much easier to use and comprehend.

Chapter 4 is concerned with the process of constructing objective fuzzy models that do not require any human input. This is achieved by extracting rules from experimental data directly, not from heuristic human experience. Further, no human contribution is required for defining membership functions, selecting inference mechanisms, number of rules, etc. A basic requirement for model parameters is that they should enable a model to predict data from which it was originally extracted, with minimum error. Hence, fuzzy modelling is reduced to a problem of non-linear optimization over a vast dimensional space, and innovative algorithms for solving such a problem are introduced. Chapter 4 describes a set of algorithms that, starting from a given empirical data set, produce a complete fuzzy model that is optimized to an arbitrary level of precision, determined by the user. The methodology and algorithms are applicable to any set of data, and any engineering system, including grinding.

Quality of a model is as good as the data used in its construction. Therefore, it is of utmost importance that experimental data are produced with greatest precision, reliability, and reproducibility, over the largest number of pertinent variables and the widest range of variation. Equally important is to have an estimate of model quality and the degree of confidence in its prediction, by measuring confidence in quality of the underlying experimental procedures.

Chapter 5 is an experimental investigation into surface grinding. An extensive set of grinding tests are performed on annealed A4140 steel, under a wide range of grinding conditions. A number of important product characteristics are measured and reported for each test point. Attention is given to detailed description of the experimental setup, calibrations, procedures, and standards followed. This is to help users of the fuzzy model identify the differences between their respective work environments, and the environment from which this model is extracted, and to estimate the likely effect of those differences on predictions made by the model.

Particular emphasis is placed on estimating the range of error, scatter, or uncertainty in the experimental data obtained. It is found that an average ±20% uncertainty in all grinding quantities can be expected. This uncertainty is irreducible by refinement or stricter control on the experimental environment, because it is an inherent characteristic of the grinding process itself. This provides further support for the fuzzy modelling paradigm.

Chapter 6 applies the algorithms in Chapter 4 to the experimental data from Chapter 5, and presents a complete, six dimensions eight variates, fuzzy model for the surface grinding process. Implementation of the model is demonstrated by two worked examples. This model is useful in the grinding environment from which it was extracted. Therefore, guidelines are offered on means of transporting, and optimizing the model for usage within other grinding environments.

The model developed in this work is original in (1) the way it was automatically extracted from data, (2) the large number of variables included, (3) the compact and efficient structure of the rule-base and its presentation, and (4) that the complete functional model is available for other users to impalement, e.g. within their machine control systems. Finally, Chapter 7 is a summary of main topics where further research may be needed. Brief discussions and proposals for conducting those future research tasks are also provided.

Apr 052012
 

A large set of orthogonal metal cutting tests was carried out, for Aluminium 2014_T6 using HSS and carbide tools, with the main objective of observing transient dynamic response during the first few revolutions after tool-workpiece engagement. Thesis StatementThe parametric study covers a wide range of various combinations of depth, width of cut as well as spindle speed. Depth of cut is assumed to rises linearly to its nominal steady state value after one spindle revolution (the wedge effect). Both of the two force components as well as tool acceleration in the thrust direction are monitored, and recorded on FM tape recorder for further analysis. Experimental results show that forces rise up to their quasi-steady state values, but not necessarily after one spindle revolution. Often, more than one revolution is taken. This rise duration increases with decreasing depth of cut and increasing spindle speed. This behaviour can not be explained using classical quasi-static models.

Steady state force values are found to be in agreement with established models in the literature. Root mean square of acceleration in the thrust direction was found to be a good measure of energy involved in the process and to be very sensitive to cutting conditions and their dynamic changes. It is shown that with reasonable simplifying assumption and using standard system identification techniques, experimental cutting force transient response can be fitted to a first order model. This model states that the forces depend not only on depth of cut but on the rate of change of depth of cut and rate of change of force as well.

In order to explain this transient force response on physical bases, it is proposed that metal cutting, usually, occurs under adiabatic shear band conditions. This comes in agreement with earlier views about the dual nature of metal cutting as a shearing-cracking process. Yet, for adiabatic shear banding to occur, metal deformation is to be modelled as a Thermo-Visco-Plastic large deformation large strain rate process.

Finally, a simplified one-dimensional verification of the proposed time dependent force model is presented. Possible implications of using such a model in more practical metal cutting situations is discussed. Moreover, some applications of the obtained results in adaptive control, material testing, and machinability data prediction are briefly discussed. Possible extensions and continuation of the present work are also suggested. The appendices include a comprehensive graphical report of most of the cutting tests performed as well as a literature survey in support of this new physical model.

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  1. Y.M. Ali, Experimental Investigation on The Dynamics of Orthogonal Metal Cutting, Master Thesis, The American University in Cairo, May 1993.