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.