INTRODUCTION TO WELDING - GlobalSecurity.org

1 CHAPTER 3 INTRODUCTION TO WELDINGIn the Navy as well as private industry, WELDING iswidely used by metalworkers in the fabrication, main-tenance, and repair of parts and structures. While thereare many methods for joining metals, WELDING is one ofthe most convenient and rapid methods available. Theterm WELDING refers to the process of joining metals byheating them to their melting temperature and causingthe molten metal to flow together. These range fromsimple steel brackets to nuclear , like any skilled trade, is broad in scope andyou cannot become a welder simply by reading a need practice and experience as well as patience;however, much can be gained through study.

2 For in-stance, by learning the correct method or procedure foraccomplishing a job from a book, you may eliminatemany mistakes that otherwise would occur through trialand chapter is designed to equip you with a back-ground of basic information applicable to WELDING ingeneral. If you take time to study this material carefully,it will provide you with the foundation needed to be-come a skilled PROCESSESW elding is not new. The earliest known form ofwelding, called forge WELDING , dates back to the year2000 Forge WELDING is a primitive process ofjoining metals by heating and hammering until the met-als are fused (mixed) together.

3 Although forge weldingstill exists, it is mainly limited to the blacksmith , there are many WELDING processes 3-1 provides a list of processes used in modernmetal fabrication and repair. This list, published by theAmerican WELDING society (AWS), shows the officialabbreviations for each process. For example, RSWstands for resistance spot WELDING . Shielded metal arcwelding (SMAW) is an arc- WELDING process that fuses(melts) metal by heating it with an electric arc createdbetween a covered metal electrode and the metals beingjoined.

4 Of the WELDING processes listed in figure 3-1,shielded metal arc WELDING , called stick WELDING , is themost common WELDING process. The primary differ-ences between the various WELDING processes are themethods by which heat is generated to melt the you understand the theory of WELDING , you canapply it to most WELDING most common types of WELDING are oxyfuel gaswelding (OFW), arc WELDING (AW), and resistancewelding (RW). As a Steelworker, your primary concernis gas and arc WELDING . The primary difference betweenthese two processes is the method used to generate WELDINGOne of the most popular WELDING methods uses a gasflame as a source of heat.

5 In the oxyfuel gas weldingprocess (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 iswidely used in maintenance and repair work because ofthe ease in transporting oxygen and fuel cylinders. Onceyou learn the basics of gas WELDING , you will find theoxyfuel process adaptable to brazing, cutting, and heattreating all types of metals. You will learn more aboutgas WELDING in chapter WELDINGArc WELDING is a process that uses an electric arc tojoin the metals being welded.

6 A distinct advantage of arcwelding over gas WELDING is the concentration of gas WELDING the flame spreads over a large area,sometimes causing heat distortion. The concentration ofheat, characteristic of arc WELDING , is an advantage be-cause less heat spread reduces buckling and 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 andeconomical than gas arc- WELDING processes have three things in com-mon: a heat source, filler metal, and shielding.

7 Thesource of heat in arc WELDING is produced by the arcingof an electrical current between two contacts. The power3-1 MASTER CHART OF WELDING AND ALLlED PROCESSESF igure 3-1. We1ding 3-2. 0xyfuel gas WELDING (OFW).source is called a WELDING machine or simply, a should not be confined with the same term that isalso used to describe the person who is performing thewelding operation. The welder ( WELDING machine) iseither electric- or motor-powered. In the Naval Con-struction Force (NCF), there are two main types ofarc- WELDING processes with which you should becomefamiliar.

8 They are shielded metal arc WELDING and gasshielded arc Metal Arc WELDING (SMAW)Shielded metal arc WELDING (fig. 3-3) is performedby striking an arc between a coated-metal electrode andthe base metal. Once the arc has been established, themolten metal from the tip of the electrode flows togetherwith the molten metal from the edges of the base metalto forma sound joint. This process is known as coating from the electrode forms a covering overthe weld deposit, shielding it from contamination;Figure 3-3.

9 Shielded metal arc WELDING (SMAW).therefore the process is called shielded metal arcwelding. The main advantages of shielded metal arcwelding are that high-quality welds are made rapidly ata low cost. You will learn more about shielded metal arcwelding in chapter Shielded Arc WeldingThe primary difference between shielded metal arcwelding and gas shielded arc WELDING is the type ofshielding used. In gas shielded arc WELDING , both the arcand the molten puddle are covered by a shield of inertgas.

10 The shield of inert gas prevents atmospheric con-tamination, thereby producing a better weld. The pri-mary gases used for this process are helium, argon, orcarbon dioxide. In some instances, a mixture of thesegases is used. The processes used in gas shielded arcwelding are known as gas tungsten arc welding3-3 Figure 3-4. Gas tungsten arc WELDING (GTAW).(GTAW) (fig. 3-4) and gas metal arc WELDING (GMAW)(fig. 3-5). You will also hear these called TIG and MIG. Gas shielded arc WELDING is extremely usefulbecause it can be used to weld all types of ferrous andnonferrous metals of all that we have discussed a few of the weldingprocesses available, which one should you choose?