IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Computer aided process planning (CAPP) is an important interface between computer aided design (CAD) and computer aided manufacturing (CAM) in computer integrated manufacturing (CIM). Operation sequencing in process planning is concerned with the selection of machining operations in steps that can produce each form feature of the part by satisfying relevant technological constraints specified in the part drawing. A single sequence of operations may not be the best for all the situations in a changing production environment with multiple objectives such as minimizing number of set-ups, maximizing machine utilization and minimizing number of tool changes. This paper demonstrates the application of genetic algorithms as a global search technique for a quick identification of optimal or near optimal operation sequences in a dynamic planning environment. A novel initialization scheme for representing the genetic code and a new crossover operator are designed to retain the local operation precedence for each form feature. Since sequences can be obtained quickly, this approach can actually be used by the process planner to generate alternative feasible sequences for the prevailing operating environment. © 1999 Taylor &amp; Francis Group, LLC.

Department of Mechanical Engineering

GENERAL

International Journal of Production Research

Operation sequencing in CAPP using genetic algorithms

In general, systematic and accidental non-conformities contribute to the non-deterministic nature of the manufacturing processes. The measurement data generated during production and inspection should be further processed to get the desired information contained in it. The measurement data can be considered as the sum of the desired information and certain random errors and variations. Processing requires a method that reduces the effect of wild non-conformities giving due importance to the desired information present in the original measurement data. In this paper an efficient L1-approximation is presented and used for form error evaluation of engineering surfaces to show its effectiveness when the measurement data contains wild points. The result is compared with the least-squares solution. The use of L1-approximation for form error evaluation will also help to identify the wild points present on the surface of the part that can be compensated by further operation(machining) to produce a better quality part. © 1998 Elsevier Science S.A. All rights reserved.

Computer Methods in Applied Mechanics and Engineering

Form error evaluation using L1-approximation

Workpieces make contact on their functional boundaries, not on the best fit surfaces. Better quality products can be made by controlling parameters of the production process and evaluating the workpiece based on functional requirements. A new algorithm is proposed in this paper, based on a sound mathematical background, to obtain the functional boundaries that are best represented by enveloping features. © 1998 Elsevier Science Inc.

World University root node

Precision Engineering

Function-oriented form evaluation of engineering surfaces

The selection of the depth of cut during optimisation in multi-pass turning is an important activity, along with the selection of the speed and feed. A new approach for the optimal sub-division of the depth of cut is presented using a genetic algorithm. The total production-cost minimisation is achieved by adding the minimum costs of the individual rough passes and the finish pass. The resulting sub-division of the depth of cut using the proposed methodology gives a cost that is lower than, or equal to, the minimum cost obtained by the commonly-practiced method of using the minimum depth of cut in the finish pass and a number of rough passes of equal size, or using enumerative search techniques based on integer programming and dynamic programming. © 1998 Elsevier Science S.A. All rights reserved.

Journal of Materials Processing Technology

Optimal sub-division of the depth of cut to achieve minimum production cost in multi-pass turning using a genetic algorithm

In this part, the concept of enveloping tangent planes dealing with gear geometry and normal deviations is applied to bevel gears. Exact spherical involute is established by the procedure outlined in this paper. Straight tooth and spiral tooth bevel gears are considered in this paper. The method of determining the normal deviation from the idealized surface and the validation of the method are reported here. Effectiveness of the proposed method for obtaining normal deviation is established by considering spiral bevel gear geometry based on circular arc. © 1998 Elsevier Science Ltd.

Mechanism and Machine Theory

Establishing gear tooth surface geometry and normal deviation: Part II - Bevel gears

This part reports a preliminary work wherein spur and helical gears are established from first principle using the concept of tangent line and plane, respectively. The coordinates of the ideal surfaces are obtained which can be verified on a Coordinate Measuring Machine. From the measurements, the normal deviations from ideal surfaces can be obtained by the method proposed in this paper. This method is validated by introducing a known error at a specific point on the ideal surface. Significance of the normal deviation method proposed is brought out by considering crowned helical gear surface. © 1998 Elsevier Science Ltd.

Establishing gear tooth surface geometry and normal deviation: Part I - Cylindrical gears

This study investigates the nature of the acoustic emission (AE) generated during the reaming of EN4 steel workpieces. For this purpose, experiments were conducted in a horizontal boring and milling machine to determine the effects of cutting parameters. The results show good correlation between the AE parameters and the severity of the contact conditions during chip formation.

Condition monitoring in reaming through acoustic emission signals

This paper analyses the effect of relief and rake angles on the effective generating profile of the helical gear shaping cutter. In a gear shaping process, the conjugate motion between the gear blank and the cutter, along with the cutting motion generates the gear. The cutter is a modified version of the rack/pinion incorporating rake and relief angles. Effect of different sharpening methods has also been discussed in this paper. Certain design modifications are proposed to minimize the deviation from the ideal profile in case of rack as well as pinion cutters.

Journal of the Institution of Engineers (India): Mechanical Engineering Division

Helical Gear Shaping Cutters - Design and Analysis

A novel model for CMM measurement process using the concept of Self Avoiding Walk is presented. The objective is to find out a sampling lattice which results in reduced measurement time without affecting the precision of the measurement. Sampling in honeycomb lattice is shown to have less mean square displacement than sampling in square lattice as a result of which sampling in honeycomb lattice requires less measurement time than sampling in square lattice. Further it is shown that the sampling in honeycomb lattice resembles the unaligned systematic sampling which again increases the precision of the sampling in honeycomb lattice.

Proceedings of SPIE - The International Society for Optical Engineering

Inspection planning for coordinate metrology

The mathematical modelling of the tooth surface geometry of spiral bevel gears has been done applying the principles of differential geometry and the theory of conjugate surfaces. A comparison has been made with involute spiraloid surface, which is the corresponding theoretical surface. The surface coordinates that can be obtained using CMM inspection of generated surface are computed, to compare with actual surface. This approach can be used in the areas of CAD-CAM, Finite Element Analysis, Tooth Contact Analysis, CNC machining and inspection. © 1994.

Journal of Materials Processing Tech.

Mathematical model for generation of spiral bevel gears

Electrodischarge machining with pulsing relaxation generator using a powder compact electrode and reverse polarity setting modifies the surface properties of a machined surface greatly. Using a hard and wear-resistant material in the compact, the wear resistance of the resultant surface can be improved. In the present investigation, tungsten carbide powder is used in the compact. The wear resistance is evaluated by cutting tests and the results show considerable improvement over the uncoated surfaces. © 1994.

Wear

Improvement of wear resistance by EDM with tungsten carbide P/M electrode

Form error is specified on the basis of an ideal geometric feature established from the actual measurements such that the maximum deviation from the ideal feature is the least possible value. The least squares method of establishing the ideal feature does not yield a minimum value. A few attempts have been made to establish the feature with a minimum value of error. In case of roundness evaluation modern instruments specify the error based on minimum deviation and ring-and plug-gauge circles. However the instrument manufacturers do not reveal the algorithms used. This paper deals with the methods of establishing the enveloping features for different geometric features namely straight line circle plane and cylinder. A non-linear optimization technique is followed to solve simple numerical examples. The values are compared with the values obtained by the least squares and minimum deviation methods. NOMENCLATURE ECF Enveloping crest feature EVF Enveloping valley feature e. Deviation of a point from assessment feature f Function to be minimized K Number of points in a section L Number of sections LSF Least squares feature 1 m Slope values (l'' for transformed values) o o 0 0 MDF Minimum deviation feature N Total number of points r. O. Polar coordinates of a point R. Radius of a circle/cylinder/ x. y. z. Cartesian coordinates of a point(x 1 1 1 1 1 1 for transformed values) x y z Estimated coordinates. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.

Establishing enveloping features for engineering surfaces

A pinion type gear shaping cutter is used to cut both external and internal gears following the generating principle. The cutter has a complex geometry and its inspection poses a number of problems. A Coordinate Measuring Machine (CMM) can be conveniently used to inspect the pinion type cutter. The theoretical basis of the measurements on a pinion type cutter is presented in this paper. Typical results of the measurements obtained using a CMM are also included. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.

Measurements on pinion type gear shaping cutter using coordinate measuring machine

Metal transfer from the tool electrode to the machined surface is appreciable in electrodischarge machining when a powder compact tool electrode is used under reverse polarity conditions. A powder metallurgy bronze electrode was employed in the present work and investigation of the frictional behaviour of the resultant surface showed considerable reduction in the friction coefficient. Reduction in wear was also confirmed by a new method using cutting tests, establishing that the surfaces can be used in applications involving extreme pressure and velocity. © 1993.

Tribology International

Tribological behaviour of an electrodischarge machined surface with a powder metallurgy bronze electrode

Pulse train studies reveal the typical characteristics of the spark discharges associated with EDM. It has been observed that the use of reverse polarity and a powder-compact tool electrode influences the discharge phenomenon and results in an appreciable amount of deposition on the work surface. In the present investigation, electro-discharge machining has been carried out using combined pulse generation and a relaxation circuit which also enhances the tool electrode transfer and the pulse trains have been recorded using a dual-trace storage oscilloscope and an X-Y plotter. © 1992.

International Journal of Machine Tools and Manufacture

Pulse train studies in EDM with controlled pulse relaxation

Gear shaping process is a generation process by which precision gears produced. In some generation motions. cases, because can be of the interference conditions exist in the process. These interferences may introduce preferable conditions on the gears produced, in a few cases. Such limiting conditions are presented here, after allowing for the trimming of the profile due to these interferences. © 1992 American Society of Mechanical Engineers (ASME). All rights reserved.

Proceedings of the ASME Design Engineering Technical Conference

Limiting conditions in gear shaping with allowance for trimming

The dynamic effect of machine tool errors leaves its signature on machined surfaces. This paper proposes an application of data dependent systems (DDS) methodology to recover this signature from the surfaces in a comprehensive manner and provides a realistic basis for machine-tool acceptance. The approach is illustrated by experimental results from three different lathes. It is shown that relative contributions due to the feed wavelength reveal the dynamic performance of the machine tools. The deviation from the nominal and the spread of the estimated feed wavelength quantify the accuracy and rigidity, the feed wavelength being precisely maintained with minimal spread in a machine tool with high accuracy and high rigidity. Presence of other wavelengths and their relative contribution to the RMS surface roughness serve as quantitative indicators of other machine tool errors. © 1992 by ASME.

Journal of Manufacturing Science and Engineering, Transactions of the ASME

Signature of machine tool errors on surface texture by DPS

Dissimilar metal welds between low-alloy ferritic steels and austenitic stainless steels are widely used in power station steam generators. This dissimilar metal joint has got problems and indeed several premature failures have occured well below the designed lifetime. To overcome the above problem a transition metal joint with Alloy 800 as transition piece is used between low-alloy steel and austenitic stainless steel. This paper gives the details of friction welding between Alloy 800 and 2.25 Cr-1 Mo steel. The joints were subjected to different mechanical strength tests, microstructural observation and thermal exposure studies simulating the service conditions.

International Journal for the Joining of Materials

Dissimilar friction welding of alloy 800 and 2.25 Cr - 1 Mo steel

During electrodischarge machining (EDM) the topography and metallurgical and physicochemical properties of the surface layer change considerably. Under certain conditions, the metal transfer from the tool electrode to the machined surface is also appreciable. By employing suitable process parameters, surface modification for desired functional behaviour is possible by EDM. In this paper, the metal transfer from the tool electrode is studied by cross-sectional examination, electron spectroscopy for chemical analysis and X-ray diffraction analysis of the work surface. The associated changes in the surface topography are analysed by scanning electron microscopy and the harmonic contents of the surface profiles. © 1991.

Surface modification in electrodischarge processing with a powder compact tool electrode

ISO defines form error based on the concept of minimum zone, but does not describe the methods to obtain the same. In this paper, drawbacks of the available methods are discussed and a new algorithm is presented. This algorithm is guaranteed to give the minimum value of form error. The algorithm is well-suited for implementation on a computer which may be interfaced with a Coordinate Measuring Machine. © 1991.