Parametric Optimization of Shielded Metal Arc Welding Processes by Using Factorial Design Approach

The Shielded Metal Arc Welding (SMAW) process is an arc welding process which produces coalescence of metal by heating them with an arc between a covered metal electrode and the work. Shielding is obtained from decomposition of the electrode covering. Pressure is not used. Filler metal is obtained from the electrode. The prediction of the optimal weld deposit area is an important aspect in shielded metal arc welding (SMAW) process as it is related to the strength of the weld. The goal of this research work is to optimize various parameters for Shielded Metal Arc Welding process, including welding voltage, welding current and welding speed by developing a mathematical model for sound weld deposit area of a mild steel specimen. Factorial design approach has been applied for finding the relationship between the various process parameters and weld deposit area. The study revealed that the weld deposit area varies directly with welding voltage and welding current and inverse relationship is found between welding speeds with weld deposit area. elding is a process of joining different materials. It is more economical and is a much faster process compared to both casting and riveting (1). The weld deposition area is the maximum area of the weld metal deposited. It influences the flux consumption rate and chemistry of the weld metal and hence determines the mechanical properties of the weld (2). SMAW input process parameters like welding current, welding speed; open circuit voltage and external magnetic field are highly influencing the quality of weld joints. (3). A precise means of selection of the process variables and control of weld bead shape has become essential because mechanical strength of weld is influenced not only by the composition of the metal, but also by the weld bead shape. The weld bead width is an important factor of the shape of the weld. The weld quality can be achieved by meeting quality requirements such as bead geometry which is highly influenced by various process parameters involved in the process. Inadequate weld bead dimensions will contribute to failure of the welded structure (4). Among all the welding processes, SMAW is very important. The advantages of this method are that it is the simplest of the all arc welding processes. The equipment is often small in size and can be easily shifted from one place to the other. Cost of the equipment is very less. This process finds a number of applications because of the availability of a wide variety of electrodes which makes it possible to weld a number of metals and their alloys. The welding of the joints may be carried out in any position with highest weld quality and therefore the joints which are difficult to be welded because of their position by automatic welding machines can be easily welded by shielded metal arc welding. Both alternating and direct current power sources could be used effectively. Power sources for this type of welding could be plugged into domestic single phase electric supply, which makes it popular with fabrications of smaller sizes (5). However, non equilibrium heating and cooling of the weld pool can produce micro-structural changes which may greatly affect mechanical properties of weld metal. To get the desired weld quality in SMAW process, it is essential to know interrelationships between process parameters and bead geometry as a welding quality. Many efforts have been done to develop the analytical and numerical models to study these relationships, but it was not an easy task because there were some unknown, nonlinear process parameters. For this reason, it is good for solving this problem by the experimental models. These results showed that arc current has the greatest influence on bead geometry, and that mathematical models derived from experimental results can be used to predict bead width accurately. Nearly 90% of welding in world is carried out by one or the other arc welding process; therefore it is imperative to discuss the effects of welding parameters on the weldability of the materials during the arc welding. Mild steel was selected for work-pieces to be welded because it is the most common form of steel as its price is relatively low while it provides material properties which are acceptable for many applications.