International Journal of Applied Engineering Research

In the present study an electroless deposition technique has been used for strengthening the surface of pure copper (99.99%) treated as a substrate material. High electrical and heat conductive copper is generally used in optics and electronic industries. However, due to lower strength and poor wear resistance it cannot be used directly in special applications. Thus to increase wear as well as corrosion resistance of pure copper a number of methods have been developed such as chemical vapor deposition, electroplating and many others. Amongst these methods the electroless deposition technique has been found widely used for simplicity and feasibility over others in changing the different properties of pure copper surface. Electroless nickel describes the plating of nickel deposits, which may contain phosphorous and boron, onto metallic or non-metallic substrates by chemical reduction. Unlike electronically plated nickel coatings, electroless nickel coatings produce very uniform, hard and lubricious coatings, without an externally applied electric current, and are normally identified according to their phosphorous or boron content. By varying the percentage of phosphorous or boron in the coating, deposits can be produced to exhibit non-magnetic and high corrosion resistant characteristics or hard deposits with excellent wear resistance. There are several process parameters in electroless Ni-P coating which influence deposition thickness, rate of deposition, deposited percentage of Ni and P; and right combination of them may lead to the most favorable process environment capable of producing required yields. This invites the situation of multi-objective optimization problem which seeks immense interest. To address this issue, in this investigation, preliminary experiments have been performed to obtain the autocatalytic deposition of electroless Ni-P coatings have been evaluated by energy dispersive X-ray analysis (EDAX) and these percentages along with deposition thickness have been considered as response variables for optimization.

Many methodologies have been proposed in the past research to address optimization issues related to various process/product. However, a good number of past works seeks to optimize process parameters under consideration with one response only. In practical situations, attempt should be made to optimize more than one response simultaneously. It has been found that optimization of one quality feature may cause severe loss to other quality indices beyond the expected tolerance level. Therefore, an efficient methodology is indeed required for solving simultaneous optimization problem of these multi quality attributes. In the present work multi-objective optimization problem has been addressed to select the best process environment for obtaining optimal output features in electroless Ni-P coating. In view of the fact that traditional Taguchi approach fails to overcome multi-response optimization problem; to overcome this shortcoming Weighted Principal Component Analysis (WPCA) has been coupled with Taguchi method in the present investigation.

Optimization of various production processes highlighted in literature assumed that individual quality indices are independent to each other i.e. they are not correlated. But in practice the assumption may not be valid always. Therefore, hybrid Taguchi based optimization approaches like grey Taguchi, desirability function based Taguchi, utility concept based Taguchi methods those do not account response correlation may lead to erroneous results.

To overcome this limitation the study applies application of Weighted Principal Component Analysis (WPCA) to eliminate response correlation and to convert correlated response into uncorrelated quality indices called principal components. These principal components have been accumulated further to calculate the composite principal component (Multi-Response Performance Index MPI). Finally, a Combined Quality Loss (CQL) has been defined as the deviation of MPI from its ideal desired value. This CQL serves as the single objective function for optimization with the aim to minimize it. Thus, the multi-objective optimization problem has been converted into an equivalent single objective optimization situation which has been solved by Taguchi method. Detailed methodology of the proposed optimization technique has been highlighted in this paper. The study reveals effectiveness of the proposed method in optimizing multiple response features of electroless Ni-P coating and highlights its effectiveness through confirmatory test.