Welding Metals Essay Example | Topics and Well Written Essays - 2500 words

Welding Metals - Essay Example (www.wikipedia.org). A weld is defined as a blend or coalescence of two or more metals by heating then until they reach a critical temperature and flow together. The piece of metal to be welded is called the base metal, work piece, or work. The edges of the base metal are often specially prepared for welding by, for example, machining, shearing, or gouging. There are five basic weld joints: butt, lap, corner, "T," and edge. The American Welding Society has developed a system of symbols that are added to mechanical drawings, to convey precisely how a welding site should be prepared, what type of weld should be made, and any other considerations. Arc welding is a very popular method of joining metal together for many different applications. It is the processes of joining metal together through fusion which is done by the electric Arc, by electrical current (Arc 1994).An electric arc between the electrode and the work piece generates heat. Sufficient heat is generated to melt the pieces together. The arc reaches temperatures of around 6,000 degrees Celsius which is concentrated at the tip of the electrode (Weldwell 2003). The range of welding current used varies from 5 to 500 amps. The voltage ranges from 20 to 30 volts. The current can be either AC or DC. The type of current is dependent on material thickness. The electrodes have a metal core surround by flux, which melts with the work piece creating a fusion weld. The flux coating forms a gas and slag that shields the molting metal pool. This flux materialis cleaned off once the weld has cooled with a wire brush. The weld should be as strong or stronger then the metal that i t is fusing together. There are four common types of welding namely Stick or SMAW(Shielded Metal Arc Welding) Mig or GMAW(Gas Metal Arc Welding) Tig or GTAW (Gas Tungsten Arc Welding). Flux-Core or FCAW (Flux Core Arc Welding). Shielded metal arc welding or stick welding is one of the most commonly used types of welding. (Repp 1994).this is because it is one of the easiest methods and the equipment used is inexpensive. It is used in mobile welding due to its ease of portability. In this process the flux covering the electrode melts during welding. Due to this gas and slag are formed that form a protective layer around the molten weld pool. The slag is chipped off the weld bead after welding. The flux provides a method of adding scavengers, deoxidizers, and alloying elements to the weld metal. Advantages The equipment is simple, inexpensive and portable. It has a moderate welding speed. This process is flexible i.e. in order to tackle different tasks, metals and thickness change of rods or welding parameters is sufficient. Flux provides excellent cleaning action in cases where weld metal preparation is less than ideal (rust, scale, dirt, etc.). It is less sensitive to wind and drifts. Discontinuities Considering the weld discontinuities stick welding suffers from undercut where a groove melted into the base metal adjacent to the weld toe or weld root and left unfilled by weld metal. Secondly it suffers from incomplete fusion i.e. a weld discontinuity in which fusion does not occur between weld metal and fusion faces or adjoining weld beads. Other discontinuities include porosity of the weld formed, cracks and slag inclusions in the weld. Problems The main problem concerning stick welding is Arc Blow. It is a problem that exists with most electric welding processes. It is caused by the preferential magnetic fields developed near the arc. These are most often caused by the arc current ground path or in the