Chapter 3 Introduction to Welding

CHAPTER 3 INTRODUCTION TO WELDING In the Navy as well as private industry, welding is widely used by metalworkers in the fabrication, main- tenance, and repair of parts and structures. While there are many methods for joining metals, welding is one of the most convenient and rapid methods available. The term welding refers to the process of joining metals by heating them to their melting temperature and causing the molten metal to flow together. These range from simple steel brackets to nuclear reactors. Welding, like any skilled trade, is broad in scope and you cannot become a welder simply by reading a book. You need practice and experience as well as patience; however, much can be gained through study. For in- stance, by learning the correct method or procedure for accomplishing a job from a book, you may eliminate many mistakes that otherwise would occur through trial and error. This chapter is designed to equip you with a back- ground of basic information applicable to welding in general. If you take time to study this material carefully, it will provide you with the foundation needed to be- come a skilled welder. WELDING PROCESSES Welding is not new. The earliest known form of welding, called forge welding, dates back to the year 2000 B.C. Forge welding is a primitive process of joining metals by heating and hammering until the met- als are fused (mixed) together. Although forge welding still exists, it is mainly limited to the blacksmith trade. Today, there are many welding processes available. Figure 3-1 provides a list of processes used in modern metal fabrication and repair. This list, published by the American Welding Society (AWS), shows the official abbreviations for each process. For example, RSW stands for resistance spot welding. Shielded metal arc welding (SMAW) is an arc-welding process that fuses (melts) metal by heating it with an electric arc created between a covered metal electrode and the metals being joined. Of the welding processes listed in figure 3-1, shielded metal arc welding, called stick welding, is the most common welding process. The primary differ- ences between the various welding processes are the methods by which heat is generated to melt the metal. Once you understand the theory of welding, you can apply it to most welding processes. The most common types of welding are oxyfuel gas welding (OFW), arc welding (AW), and resistance welding (RW). As a Steelworker, your primary concern is gas and arc welding. The primary difference between these two processes is the method used to generate the heat. GAS WELDING One of the most popular welding methods uses a gas flame as a source of heat. In the oxyfuel gas welding process (fig. 3-2), heat is produced by burning a com- bustible gas, such as MAPP (methylacetylene-propadi- ene) or acetylene, mixed with oxygen. Gas welding is widely used in maintenance and repair work because of the ease in transporting oxygen and fuel cylinders. Once you learn the basics of gas welding, you will find the oxyfuel process adaptable to brazing, cutting, and heat treating all types of metals. You will learn more about gas welding in chapter 5. ARC WELDING Arc welding is a process that uses an electric arc to join the metals being welded. A distinct advantage of arc welding over gas welding is the concentration of heat. In gas welding the flame spreads over a large area, sometimes causing heat distortion. The concentration of heat, characteristic of arc welding, is an advantage be- cause less heat spread reduces buckling and warping. This heat concentration also increases the depth of pene- tration and speeds up the welding operation; therefore, you will find that arc welding is often more practical and economical than gas welding. All arc-welding processes have three things in com- mon: a heat source, filler metal, and shielding. The source of heat in arc welding is produced by the arcing of an electrical current between two contacts. The power 3-1