Introduction
D1.3 welding code was developed to encompass structural arc welding of strip or sheet steels, incorporating other members of cold formed processes collectively known as sheet steel. The nominal thickness of the sheet steel worked on should be less than or equal to 4.8 millimeter. Furthermore, this code incorporates three categories of welding that are distinctive to sheet metal. They include arc plug, arc seam and arc spot welds.
This welding code is appropriate to the welding of mechanical sheet steels to similar structural steels or other supporting members.
The general stipulations of the code are relevant to a wide range of situations as provided for in the code’s fundamental premise. Approval principles for fabrication of welds diverse from those postulated in the code would be authorized for specific application, as long as they are appropriately authenticated by the nominator and ratified by an Engineer. These substitute accession standards shall be centered upon assessment of correctness for service by employing past experience, effects of service load, environmental factors, experimental evidence and material type engineering analysis.
In addition, the D1.3 welding code makes available that all recommendation that require authorization shall be taken to mean endorsement by the Engineer. That is, the duly delegated person who may act for and/or on behalf of the proprietor on issues pertaining to this code. Consequently, any deviation from the requirements and specification of the welding code must be authorized by the Engineer.
When a base metal of steel save for those contained in the code is permitted by the provisions of the product specification or project specification, and as such it is recommended for welding, its weldability ‘shall be authorized by conformance with all the necessary requirements of other sections of the code and as may be advised by the Engineer’ Craig, 2001).
The D1.3 welding code specifies for welding with gas metal arc welding, submerged arc welding, flux cored arc welding and shielded metal arc welding processes.
Gas metal arc welding (GMAW)
This type of welding is also commonly known as metal active gas welding or metal inert gas welding. It is defined as a welding process where there is formation of an electric arc between the sheet metal work-piece and an expendable wire electrode which heats the sheet metal work piece. As a result of the high temperature, they all melt and get joined on cooling. Besides the wire electrode, a welding gun is used to feed the work piece with a shielding gas. According to Weman (2001), ‘the purpose of the shielding gas is to protect the whole welding process from possible contaminants present in the air’ (pp. 118-119).
Normally, the welding process may be automatic or semi-automatic. In most applications, direct current power supply or constant voltage are widely used with gas metal arc welding process. This notwithstanding in special cases, alternating current or constant current sources can also be utilized. As Cary and Helzer, examine, metal transfer in gas metal arc welding is known to take place through four main methods. These include short circuiting, pulse spray, globular and spray method. Each of these methods possesses unique properties and merits and demerits.
GMAW was initially developed as a welding process for aluminum and similar non-ferrous substances. It soon got application in the steel industry since it proved to offer a comparatively faster time for welding against other welding methods. Unfortunately, its application was limited by the fact that inert gas was costly. Semi-inert gases like carbon dioxide ‘have boosted the application of this method in industrial use’ (Minnick, 2007). In addition, other technological developments in the 1960s contributed towards wide spread acceptance and use of the process in core welding applications industrially. Currently, the process is preferred for its speed, relative ease of automation of the process and its versatility. GMAW is rarely used in areas prone to air volatility or outdoors.
Necessary equipment for Gas Metal Arc Welding
The basic essential equipment necessary to carry out a gas metal arc welding comprise of; a source of shielding gas, an electrode wire, a wire feed unit, a welding power source, and a welding gun.
Gas metal arc welding process is quite simple to learn and master the basic techniques of welding. Usually, it takes fresh learner duration of one to two weeks to be conversant with the process. The weld quality, even if carried out by professionally qualified persons, it varies since it primarily is affected by many external factors. It is important to note that gas metal arc welding process is dangerous and hazardous, therefore, one has to be careful at all times.
The elemental procedures for GMAW is relatively simple, this is because the feeding of the electrode is automatically carried out through the head of tip. This is in contrast to gas tungsten arc welding, in which the welder handles the welding torch and filler wire in separate hands’ (Kalpakjian and Schmidt, 2003). Gas metal arc welding of sheet steel requires that the operator guides the welding gun’s orientation and position along the welding area. It is important to maintain a constant stick out distance because a wide variation in the stick out distance (if long) may cause overheating of the electrode and wastage of the shielding gas. There is no one particular stick out distance for the gas metal arc welding applications and processes.
Furthermore, it is of paramount importance to maintain the best possible gun orientation position. The gun should be held in such a manner as to bisect the work piece at either 45 degrees or 90 degrees for a fillet weld and flat surface weld respectively. The lead angle or travel angle refers to ‘the angle made by the torch with regard to its travel direction, and it ought to remain nearly vertical, generally’ (American Welding Society, 2004).
Conclusion
Gas metal arc welding process has generally gained enormous applicability in many industrial applications because of the short welding time it offers. However, it has two predominant quality problems. These include porosity and dross. If these problems are not adequately addressed, they can result into less ductile and weaker welds. The main methods of transfer taking place in gas metal arc welding are spray, globular and short circuiting, with a few variations among them. The process of GMAW can be highly dangerous if appropriate safety measures are not adhered to. Welders should wear the necessary personal protective equipment at all times when welding, even on simple tasks.
Works Cited
American Welding Society Welding Handbook, Welding Processes, Part 1. Miami: American Welding Society, 2004. Print.
Craig, Ed. Gas Metal Arc & Flux Cored Welding Parameters. Chicago: Weldtrain, 2001. Print.
Cary, Howard B.; Helzer, Scott. Modern Welding Technology Upper Saddle River, New Jersey: Pearson Education, 2005. Print.
Kalpakjian, Serope; Schmidt, Steven R. Manufacturing Engineering and Technology Prentice Hall, 2003. Print.
Minnick, William. Gas Metal Arc Welding Handbook Textbook Tinley Park: Goodheart–Wilcox, 2007. Print.
Weman, Klaus. Welding processes handbook. New York: CRC Press LLC, 2001. Print.
