Process parameter selection for optimizing the weld pool geometry in the tungsten inert gas welding of stainless steel

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Abstract

In this paper, the selection of process parameters for obtaining an optimal weld pool geometry in the tungsten inert gas (TIG) welding of stainless steel is presented. Basically, the geometry of the weld pool has several quality characteristics, for example, the front height, front width, back height and back width of the weld pool. To consider these quality characteristics together in the selection of process parameters, the modified Taguchi method is adopted to analyze the effect of each welding process parameter on the weld pool geometry, and then to determine the process parameters with the optimal weld pool geometry. Experimental results are provided to illustrate the proposed approach.

Introduction

Tungsten inert gas (TIG) welding which uses a non-consumable tungsten electrode and an inert gas for arc shielding, is an extremely important arc welding process. It is commonly used for welding hard-to-weld metals such as stainless steel [1]. Basically, TIG weld quality is strongly characterized by the weld pool geometry. This is because the weld pool geometry plays an important role in determining the mechanical properties of the weld. Therefore, it is very important to select the welding process parameters for obtaining an optimal weld pool geometry [2], [3], [4], [5], [6]. Usually, the desired welding process parameters are determined based on experience or from a handbook. However, this does not ensure that the selected welding process parameters can produce the optimal or near optimal weld pool geometry for that particular welding machine and environment. In this paper, the use of the Taguchi method [7], [8], [9] to determine the welding process parameters with the optimal weld pool geometry is reported. This is because the Taguchi method [4], [5] is a systematic application of design and analysis of experiments for the purpose of designing and improving product quality. In recent years, the Taguchi method has become a powerful tool for improving productivity during research and development [10] so that high quality products can be produced quickly and at low cost.

Basically, the geometry of the weld pool has several quality characteristics, for example, the front height, front width, back height and back width of the weld pool. However, the original Taguchi method has been designed to optimize a single quality characteristic. To consider several quality characteristics together in the selection of process parameters, the Taguchi method must be modified to integrate several loss functions corresponding to different quality characteristics. Therefore, the modified Taguchi method is adopted in this paper to analyze the effect of each welding process parameter on the weld pool geometry, and then to determine the process parameters with the optimal weld pool geometry. Experimental results are also provided to illustrate the proposed approach.

In the following, the modified Taguchi method for optimizing multiple quality characteristics is given first. Then, optimization of the weld pool geometry in the TIG welding process is described in detail. Finally, the paper concludes with a summary of this study.

Section snippets

The modified Taguchi method for the optimization of process parameters

Optimization of process parameters is the key step in the Taguchi method to achieving high quality without increasing cost. This is because optimization of process parameters can improve quality characteristics and the optimal process parameters obtained from the Taguchi method are insensitive to the variation of environmental conditions and other noise factors. Basically, classical process parameter design [11] is complex and not easy to use. Especially, a large number of experiments have to

The TIG welding process

The schematic diagram of the TIG welding process is shown in Fig. 1. A non-consumable tungsten electrode, shielded by inert gas, is used to strike an electric arc with the base metal. The heat generated by the electric arc is used to melt and joint the base metal. The traveling speed of the electrode is controlled by a servo mechanism. In the experiments, the welding power source is provided by a thermal-arc AC welding machine (HeroTIG 250P). The shielding gas is argon and the flow rate of the

Optimal selection of process parameters

In this section, the use of the modified Taguchi method to determine the process parameters in the TIG welding of stainless steel is reported step-by-step. Welding process parameters with the optimal weld pool geometry are determined and verified.

Conclusions

In this paper, the selection of the process parameters for TIG welding of stainless steel with the optimal weld pool geometry has been reported. The optimal weld pool geometry has four smaller-the-better quality characteristics, i.e. the front height, front width, back height and back width of the weld pool. The modified Taguchi method is adopted to solve the optimal weld pool geometry with four smaller-the-better quality characteristics. Experimental results have shown that the front height,

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