Chapter 1 Introduction to Welding. Objectives Explain each welding process List factors affecting welding process selection Discuss the history of welding.

Chapter 1Introduction to Welding

Objectives

• Explain each welding process• List factors affecting welding process selection• Discuss the history of welding• Describe various welding positions

• Define the terms: – Weld, forge welding, resistance welding, fusion

welding, coalescence, and certification

Introduction

• As civilization developed, materials, tools, and machinery improved

• Egyptians fastened stones with gypsum mortar • In ancient times adhesives joined wood and

stone• Bronze and Iron Ages - forming, casting, and

alloying metals• Early metal-joining methods

– Sand molds for casting – Pouring molten metal between two pieces of metal

Figure 1-1 Direct casting using a sand mold

Introduction (continued)

• Industrial Revolution (1750 – 1850) forge welding– Also known as hammer welding– A forge was used to heat metal– The ends of the iron were hammered together

• Elihu Thomson - resistance welding (1886)– Faster, more reliable

• Riveting was replaced by fusion welding• Welding considered vital to military security• Welding repairs to ships damaged during World

War I were done in secrecy

Welding Defined

• Weld: a localized coalescence• Coalescence: the fusion of the grain structure of

the materials being welded• Produced by heating materials to required

temperatures– With or without pressure

• Can be created by applying pressure alone• Filler added as needed to form a completed weld• Can be made from plastic, glass and ceramic

Uses of Welding

• Ships, bridges, recreational rides, machines to manufacture new products

• Commercial and military aircraft • The space program

– Modern techniques enabled space exploration– The space shuttle's construction required the

improvement of welding processes• And more…

Welding Processes

• The number of welding processes has grown recently

• Processes differ in the manner in which heat, pressure, or both are applied

• Popular welding processes:– Oxyacetylene welding (OAW)– Shielded metal arc welding (SMAW)– Gas metal arc welding (GMAW)– Flux cored arc welding (FCAW)– Torch brazing (TB)

Welding Processes (continued)

• Shielded metal arc welding (SMAW)– Makes high-quality welds rapidly– Excellent uniformity

• Gas tungsten arc welding (GTAW) – Provides high- quality welds– Requires little or no postweld finishing

• Gas metal arc welding (GMAW) – Easily used for thin-gauge metal and heavy plate

• Flux cored arc welding (FCAW)– Does not use an external shielding gas

• GMAW and FCAW most commonly used

Figure 1-7 Oxyfuel welding and cutting equipment.

Figure 1-8 Shielded metal arc welding equipment.

Figure 1-9 Gas tungsten arc welding equipment

Figure 1-10 Gas metal arc welding equipment

Welding Processes (continued)

• Skilled workers use regional terms• Names used for oxyacetylene welding:

– Gas welding– Torch welding

• Names used for shielded metal arc welding:– Stick Welding– Rod Welding– Welding

Selection of the joining Process

• Selection depends upon many factors– Availability of equipment– Repetitiveness of the operation– Quality requirements– Location of work– Materials to be joined– Appearance of the finished product– Size of the parts to be joined– Time available for work– Skill or experience of workers– Cost of materials– Code or specification requirements

Selection of the joining Process (continued)

• The welder must also select the application method:– Manual – the welder manipulates the process– Semiautomatic – filler is added automatically– Machine – done mechanically under observation – Automatic – no interaction with the operator – Automated – performed repeatedly by a robot

programmed for multiple tasks

Occupational Opportunities in Welding

• Welders perform the actual welding• Tack welders make small welds to hold parts in

place• Welding operators operate automatic equipment • Welders' helpers clean slag, position weldments • Welder assemblers position the parts

– Interpret blueprints and welding procedures– Knowledge contraction and expansion of metals

Occupational Opportunities in Welding (continued)

• Inspectors hold a special certification • Shop supervisors have good management skills• Salespersons have understanding of welding and

marketing skills• Shop owners are often skilled welders with

knowledge of small-business management• The test for welding inspector certification covers:

– The welding process, blueprint reading – Weld symbols, metallurgy– Codes and standards, Inspection techniques

Training for Welding Occupations

• Both school and work experience are required• An entry-level welder must have workplace skills• Some welding jobs require theoretical knowledge • Robotics and computer-aided manufacturing

(CAM) require computer literacy• Employers prefer high school or vocational

training in welding processes

Training for Welding Occupations (continued)

• A formal apprenticeship is usually not required• The American Welding Society (AWS)

– Three levels of certification for welders– Entry Level Welder ids for beginner welders– Level II and Level III for more skilled welders

• SkillsUSA – Sponsors welding skill competitions for students – Emphasizes community service and citizenship

Figure 1-13 Skills USA welding assembly. Courtesy of Larry Jeffus.

Experiments and Practices• Chapters contain both experiments and practices

– Intended to develop welding knowledge and skills• Work in small groups as you try experiments• Practices are designed to build welding skills• Welding is developed in stages from basic to

complex• Each practice gives evaluation or acceptable

limits

Welding Video Series

• Each of the four tape sets covers specific equipment setup and operation for:– Welding– Cutting– Soldering– Brazing

• Read the material, watch the video, and practice to develop your welding skills

FIGURE 1-14 Close-up of GMA welding. Courtesy of Larry Jeffus. View Welding Video

Metric Units

• Both standard and metric (SI) units are given• SI units are in brackets () following the unit• SI units rounded to the nearest whole number

– Rounded to agree with the standard value – Whole numbers are easier to work with

• Rounding metric units makes the system easier• Sometimes conversions must be exact

– Many calculators have standard-metric conversions

Summary

• Welding is diverse, used in almost every manufacturing process

• Welded products range from small objects to buildings and space shuttles

• The art and science of joining metals has been around for centuries

• With minor changes it will be around through the 21st century