Lesson 2 - Common Electric Arc Welding Processes

COMMON ELECTRIC ARC WELDING PROCESSES 2.1 INTRODUCTION After much experimentation by others in the early 1800's, an Englishman named Wilde obtained the first electric welding patent in 1865. He successfully joined two small pieces of iron by passing an electric current through both pieces producing a fusion weld. Approximately twenty years later, Bernado, a Russian, was granted a patent for an electric arc welding process in which he maintained an arc between a carbon electrode and the pieces to be joined, fusing the metals together as the arc was manually passed over the joint to be welded. 2.1.0.1 During the 1890's, arc welding was accomplished with bare metal electrodes that were consumed in the molten puddle and became part of the weld metal. The welds were of poor quality due to the nitrogen and oxygen in the atmosphere forming harmful oxides and nitrides in the weld metal. Early in the Twentieth Century, the importance of shielding the arc from the atmosphere was realized. Covering the electrode with a material that decomposed in the heat of the arc to form a gaseous shield appeared to be the best method to accomplish this end. As a result, various methods of covering electrodes, such as wrapping and dipping, were tried. These efforts culminated in the extruded coated electrode in the mid-1920's, greatly improving the quality of the weld metal and providing what many consider the most significant advance in electric arc welding. 2.1.0.2 Since welding with coated electrodes is a rather slow procedure, more rapid welding processes were developed. This lesson will cover the more commonly used electric arc welding processes in use today. 2.2 SHIELDED METAL ARC WELDING Shielded Metal Arc Welding*, also known as manual metal arc welding, stick welding, or electric arc welding, is the most widely used of the various arc welding processes. Welding is performed with the heat of an electric arc that is maintained between the end of a coated metal electrode and the work piece (See Figure 1). The heat produced by the arc melts the base metal, the electrode core rod, and the coating. As the molten metal droplets are transferred across the arc and into the molten weld puddle, they are shielded from the atmosphere by the gases produced from the decomposition of the flux coating. The molten slag floats to the top of the weld puddle where it protects the weld metal from the atmosphere during solidification.

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