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WELDING TECHNOLOGY

Dr. S.Thiru PhD.,

ENME 102Full Lectures

Mechanical engineering department

http://www.uj.edu.sa/Home.aspx

CONTENTS

➢ Fundamentals of Welding.

➢ Safety and Health of Welders.

➢ Arc Welding with a Consumable Electrode.

➢ Electrodes and Filler Materials.

Introductions

 Reasons for and benefits of joining (by design goals)

 Achieve functionality

 Facilitate manufacturability

 Minimize costs

 Allow complex shapes to be formed

joining Processes and Equipment

 Overview:

 Joining processes fall into three major categories：

1. Welding

2. Adhesive bonding

3. Mechanical fastening

 Welding processes, classified into three basic

categories:

1. Fusion welding

2. Solid-state welding

3. Brazing and soldering.

AWS Master chart of welding and allied

processes

Major categories

Allied processes, which use similar energy sources

AWS designation

AMERICAN WELDING SOCIETY

Welding Processes Listed by Energy Source

Electric Arc Fusion Welding

 Arc welding ▪ For workpieces that are electrical conductors, it can be made part of the

electric circuit with an electric power supply. ▪ As part of the electric circuit, electric current is passed to the conductive

workpiece through an arc from an electrode across a gap in a gas

 Resistance welding If the electric current can be passed directly through the workpiece as an integral part of the circuit.

 High Energy beam welding A beam of intense, high-density electrons are applied to heat a workpiece (whether an electrical conductor or not).

Advantages and Disadvantages of Welding

Advantages  Joints are permanent,

precluding accidental (or even intentional) disassembly and loosening

 Wide variety of process embodiments

 Applicability to many materials within fundamental class

 Allows manual or automated operation

 Can be portable

 Reasonable overall cost, usually

 Provides leak tightness with continuous welds

Disadvantages  Prevents/precludes disassembly for any

purpose

 Heat of some welding (especially involving fusion) disrupts base material properties

 Precludes joining between materials from different classes

 Unbalanced heat input leads to distortion or residual stresses

 Requires considerable operator skill

 Can be expensive due to skilled labor rates or due to labor intensity for thick, long, or critical welds

 Capital equipment can be expensive, especially for some automated processes

Modes of Arc Welding

 Direct current straight polarity (DCSP): Arc heating when the workpiece is positive and the welding electrode is negative. Also called as dc electrode negative (EN) or dc-.

 Direct current reverse polarity (DCRP): Arc heating when the workpiece is negative and the welding electrode is positive. Also called as dc electrode positive (EP) or dc+.

 AC mode: One-half of the voltage cycle operates as dc-/DCSP, while the other half operates as dc+/DCRP.

Arc Welding Processes

 Nonconsumable Electrode Arc Welding

 Gas tungsten arc welding (GTAW)

 Plasma arc welding (PAW)

 Stud arc or simply stud welding (SW)

 Magnetically-impelled arc butt welding (MIAB)

 Consumable Electrode Arc Welding Processes

 Shielded metal arc welding (SMAW)

 Flux-cored arc welding (FCAW)

 Gas metal arc welding (GMAW)

 Submerged arc welding (SAW)

 Electrogas welding (EGW)

 Electroslag welding (ESW)

GTAW PAW

SMAW FCAWSAW

https://www.youtube.com/watch?v=4hqTJHFOHY8

https://www.youtube.com/watch?v=jRmqrqIGOIY

https://www.youtube.com/watch?v=LXBz2ZPeGnY

https://www.youtube.com/watch?v=LcqbmywaLxA

https://www.youtube.com/watch?v=QMFDpZwbPwg

https://www.youtube.com/watch?v=pVyYvcEqkcQ

https://www.youtube.com/watch?v=twUAa5LWUvk

https://www.youtube.com/watch?v=H6QGLGJ-BOE

https://www.youtube.com/watch?v=SlJBLNVLAOA

CODES, STANDARDS AND PRACTICE

 American Welding Society

The AWS multi-volume Welding Handbook is a comprehensive treatment of the art and technology of welding [AWS].

It includes:  Volume 1 - Fundamentals of Welding

 Volumes 2 and 3 - Welding Processes

 Volume 4 - Engineering Applications - Materials

 Volume 5 - Engineering Applications - Design

 The welding of structural (non-pressure boundary) members typically complies with either AWS D l.l or AWS D1.6. The American Welding Society  (AWS) standards of interest to welding piping and pipelines include:

 AWS A 3.0 - Welding terms and definitions, including terms for brazing, soldering, thermal spraying and thermal cutting.

 AWS A 5.01 - Filler metal procurement guidelines.

 AWS A 5.XX - Series of filler metal specifications.

 AWS Dl.l - Structural welding code – steel.

General Requirements

 Welder’s protective clothing

General Requirements

 Minimum warning label for Arc welding processes and equipment

Protection in the general area

 Protective screens  Persons adjacent to welding and cutting must be

protected from radiation and hot spatter by flame resistant shields or screens with suitable eye and face protection clothing.

 Wall reflectivity  Where arc welding or cutting is regularly carried out

adjacent to painted walls, the walls should be painted with low reflective pigments for UV radiation such as Titanium dioxide or Zinc oxide.

 Fire  Open flames, electric arcs, spatter, hot metal and sparks

are the potential fire igniting elements related to welding.

 The risk of fire is greatly increased by combustible floor, partitions, ceiling etc and also by the presence of combustibles in the working area such as wood, paper, trash, cotton, textiles, chemicals, paints, and flammable liquids and gases. For outdoor, dry grass and brushes highly ignite potential to welding.