International Journal of Machine Tools and Manufacture
A multi-objective genetic algorithm (GA) approach for optimization of surface grinding operations
Introduction
Optimization analysis of machining process are usually based on either minimizing production cost, maximizing production rate, or obtaining the fitness possible surface quality by using empirical relationships between the tool life and the operating parameters. Optimization analysis are applicable also to grinding process provided the suitable tool life equations are available. Fortunately, many researchers have published a number of such equations for the practical grinding process in which numerous process variables are involved. The development of comprehensive grinding process models and computer-aided manufacturing provides a basis for realizing grinding parameter optimization.
Previous work on the optimization of grinding parameters has concentrated on the possible approaches for optimizing constraints during grinding [1]. The technique of optimizing both grinding and dressing condition for the maximum work piece removal rate subjected to constraints on workpiece burn and surface finish in an adaptive control grinding system can be found in ref. [2]. The use of quadratic programming for the optimization of grinding parameters subject to multi-objective function has been reported in ref. [3]. In the previous work of the authors, genetic algorithm (GA) based optimization procedure has been successfully implemented for solving surface grinding process problem by considering single objective function [4].
This paper describes a GA based optimization procedure to optimize grinding conditions, viz. wheel speed, workpiece speed, depth of dressing, and lead of dressing, using a multi-objective function model with a weighted approach for surface grinding. The procedure evaluates the optimal grinding conditions subjected to constraints such as thermal damage, wheel-wear parameters and machine-tool stiffness. Initially a detailed description of the mathematical model of the grinding process is given. Then the optimization procedure is described. Finally an example taken from the literature [3] is used to illustrate new approach.
Section snippets
Mathematical model of the surface grinding process
The aim of carrying out a grinding operation is to obtain the finished product with minimum production cost, maximum production rate, and the finest possible surface grinding finish. The mathematical model proposed by Wen [3] is used in this work.
Solution methodology
Most of the researchers have used traditional optimization techniques for solving machining problems [10]. The traditional methods of optimization and search do not fare well over a broad spectrum of problem domains.
Traditional techniques are not efficient when practical search space is too large. These algorithms are not robust. Numerous constraints and number of passes make the machining optimization problem more complicated. Traditional techniques such as geometric programming, dynamic
Genetic algorithm
GA form a class of adaptive heuristics based on principles derived from the dynamics of natural population genetics. The searching process simulates the natural evaluation of biological creatures and turns out to be an intelligent exploitation of a random search. A candidate solution (chromosome) is represented by an appropriate sequence of numbers. In many applications the chromosome is simply a binary string of 0 and 1. The quality of its fitness function, which evaluates a chromosome with
Numerical illustration
The following data [3] is used as the input data for this optimization problem.Description Symbol Value No. of work piece on table (pc) P 1 Length of the work piece (mm) LW 300 Empty length of grinding (mm) Le 150 Width of work piece (mm) bW 60 Empty width of grinding (mm) be 25 Cross feed rate (mm/pass) fb 2 Total thickness of cut (mm) aW 0.1 Down feed of grinding (mm/pass) ap 0.0505 Number of spark out grinding (pass) Sp 2 Diameter of wheel (mm) De 355 Width of wheel (mm) bS 25 Grinding ratio G 60 Distance of wheel idling (mm) Sd 100
Implementation of GA
The implementation of the GA technique for the multi-objective optimization problem is discussed below.
Result and comparison
The operating parameters, optimum production cost, optimum production rate, surface finish and combined objective function obtained by GA and quadratic programming are given in Table 1, Table 2.
From these tables, it is observed that the combined objective function obtained by GA is 47.27% better than those obtained by quadratic programming for rough grinding and 6.3% better for finish grinding. For rough grinding, cost is 14.62% higher but the work piece removal parameter is higher by 24%. For
Conclusion
For solving the machining optimization problems, various conventional techniques have been used so far. It is observed that, the conventional methods are not robust, because of the following reasons:
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The convergence to an optimal solution depends on the chosen initial solution.
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Most algorithms tend to get stuck to a sub-optimal solution.
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An algorithm efficient in solving one machining optimization problem may not be efficient in solving a different machining optimization problem.
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Algorithms are not
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