Ensuring an efficient turning process by means of desirability index optimization for correlated quality criteria
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Date
2012-09-19
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Abstract
The desirability index (DI) is a method for multi-criteria optimization accepted
widely in industrial quality management. The DI integrates expert knowledge into the
optimization process by setting up desirability functions (DFs) of the quality criteria
regarding their objective regions and aggregating them into a single performance
index. However, the independence assumption of DFs rarely holds true in real turning
applications, and a number of studies have been conducted proving the existence of
dependencies between tool wear, surface roughness, tool life and cutting forces. As
a consequence, the optimal solution obtained might be biased towards the group of
performance measures, which have a high level of association (positive correlations).
In this thesis, modfications of DI for handling correlated multi-criteria optimization
are developed. By integrating principal component analysis (PCA) into the
optimization procedure, the correlations of DFs can be eliminated, and the overall
performance index, PCA-based DI, is formulated as a strictly monotonically increasing
transformation of DFs; thus, the optimality of solutions can be guaranteed
through the research of Legrand [26]. Apart from the PCA-based procedure, the
weight-adjustment method provides an attractive alternative approach which is simpler
and more
exible, by introducing the weight-adjustment cofficients into the
original formulas of DIs.
The proposed procedures are demonstrated by means of case studies of a turning
process optimization, and the optimization results are benchmarked with the traditional
DIs. It has been shown in results that optimizations should be also subjected
to the correlation information of performance measures. In addition, the procedure
for determining correlation is found to be the second important key for a successful
optimization.
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Keywords
Correlated quality criteria, Desirability index, Turning process