Shield Metal Arc Welding (SMAW) is one of the earliest and most common welding techniques. The process uses simple equipment to shield the metal arc, and the welding is fairly uncomplicated. The SMAW is easy to learn and is one of the best starting points for beginners. The main technique involves using a flux covered electrode that helps to create a joint. Filler material melts to form a weld pool that solidifies and joins previously separated metal sections. Getting a good weld requires that one consider different parameters. The main parameters that can impact the process of SMAW include the root gap, tensile strength of the material, type of electrodes, and electric current.
Welding Process
The SMAW involves different materials and components. The main materials include a power supply, the SMAW machine, a coated electrode, welding cables, and the workpiece. The power supply used for the welding can be in the form of an alternating current (AC) or direct current (DC). The current is used to form an arc between the electrode and the base metal, which creates the required heat. The filler material melts through the heat in the electric arc. The process of heating causes the flux coating to disintegrate, and it gives off vapors that serve as the shielding gas, which provide a layer of coating. Most of the filler material is usually provided by the electrode. Moving the electrode steadily along the surface of the base metal creates a uniform layer of metal deposit.
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Parameters
Welding Circuit Power
The two power supply sources are DC or AC current. DC current requires a proper determination of the polarity of the electrode while AC current can be connected to any terminal. The power supplied by the welding circuit is usually expressed in the form of current and voltage. The voltage is dependent on the arc length, which depends on the type and diameter of the electrode. The circuit power usually stated in the form of amperes and is dependent on the electrode diameter and thickness of the metal section being welded. Thick metal sections require a larger current and thicker electrodes require greater current.
Electrode
The type of welding electrode can have a significant effect on the strength of the weld. The electrode in the SMAW usually has a covering with substances that facilitate the alloying elements and welding process that impart useful properties to the weld. In case the electrode is too long, the current created will be too high, and the amount of heat created in the SMAW will be excessive. According to Sumardiyanto and Susilowati (2019), for all types of electrodes, when the amount of current increases, then the mechanical properties like the tensile strength and hardness decrease. The optimal tensile strength for welding material for electrode E7016 and E7018 is produced at 90A with a tensile strength of 617.155 Mpa, and E6013 is produced 100A with a tensile strength of 505.215Mpa. Different electrodes will thus require different currents for optimal strength.
Root Gap
The root gap is usually provided as a path to facilitate the escape of gases and improve welding by avoiding defects created by blowholes. The gap is usually in the form of a narrow opening at the bottom of mating plates to ensure that there is a full penetration of the arc to create a sound welding joint. According to Setiawan & Pradana (2020), the root gap was the most significant SMAW parameter that impacted the tensile strength of the materials. The robust parameter design was identified as a 2mm root gap for a 100A in welding current, a 90-degree electrode angle, and an electrode type E7018. The study also showed that the percentage of contribution for the different parameters were 31.41% for root gap, 20.20% for electrode type, 11.7% for welding current, and 8.85% for electrode angle.
Electrode Angle
Other parameters can impact the quality of the weld. The electrode angle is measured as the plane containing the weld axis and the electrode axis. The electrode angle can impact the tensile strength of the weld. The angle between the electrode determines the direction of the arc force and point of impingement, which can have a direct effect on the depth of penetration. Weerasekralage (2018) observed that tensile strength increases with the increase in the electrode angle. The optimal electrode angle level was identified as 90 degrees.
Engineering Applications
SMAW is one of the most popular welding processes because of its simplicity and versatility. The welding process is thus dominant in the repair and maintenance industry. It is heavily used in industrial fabrication and steel structures. SMAW is specifically used for welding stainless steel, low and high alloy steel, carbon steel, ductile iron, and cast iron. The process finds minimal application in non-ferrous materials and is rarely used on nickel, copper, and their alloys. The process is a preferred method for small businesses and amateurs that have economic considerations. The process has thus declined in the construction industry, where SMAW gas metal arc welding has become more popular (Sachajdak et al., 20180). Nevertheless, the SMAW still has a wide application in various engineering processes.
In conclusion, the analysis of the SMAW process showed that the process is impacted by different parameters like the electric current, type of electrode, root gap, and electrode angle. The electric current and type of electrode can determine the heat generated in the welding process, which impacts the overall strength. The process requires a low cost to set up and is simple to use, meaning that it will likely remain popular in various engineering applications.
References
Sachajdak, A., Słoma, J., & Szczygieł, I. (2018). Thermal model of the Gas Metal Arc Welding hardfacing process. Applied Thermal Engineering , 141 , 378-385.
Setiawan, M. D. I., & Pradana, Y. R. A. (2020, December). Robust parameter design of shielded metal arc welding (SMAW) for optimum tensile strength. In Journal of Physics: Conference Series (Vol. 1700, No. 1, p. 012047). IOP Publishing.
Sumardiyanto, D., & Susilowati, S. E. (2019). Effect of Welding Parameters on Mechanical Properties of Low Carbon Steel API 5L Shielded Metal Arc Welds. American Journal of Materials Science , 9 (01), 15-21.
Weerasekralage, L. S. K., Karunarathne, M., & Pathirana, S. (2018). Optimization of Shielded Metal Arc Welding (SMAW) process for mild steel. IJSRST , 4 , 1536-1543.
