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Joining Processes

WELDING


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WELDING

Definition: Material joining process. Two parts

connected at their contacting surfaces by suitable

heat and pressure.

Many welding processes are accomplished

by heat alone, some others by heat and pressure,

and some with pressure only.In some welding operations a filler material

is used.

Welding operation usually applied to metalsbut also used for plastics.


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Parts produced by any of the manufacturing processes can be

made into larger, more complex bodies via Joining processes

Creating a metallurgical bond by adhesion and diffusion

Joining by fusion with the use of various heat sources

Brazing or soldering with a lower-melting metal

Mechanical fastening

Joining Processes


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Fusion Welding Processes


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Sources of Energy for Fusion Welding

Chemical reactions Burning gases

GAS WELDING

Heat from electricity Arc ARC WELDING SYSTEMS

Resistance welding

Light

LASER


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Three Specific Types of Welding Modules

In this Welding, Cutting, and Brazing

module, three specific types of welding are

covered. These are listed below:

Oxygen-fuel gas welding and cutting

Arc welding and cutting

Resistance welding


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Resistance Welding Definition:

This is a group of fusion welding processesthat use heat and pressure to make thecoalescence.

The heat comes from electrical resistance

to current flow at the site of the weld. The processes include:

Spot Welding

Projection Welding

Seam Welding

Note: FP&M only does spot welding.


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Welding/Cutting Hazards

Potential Hazards

Firesmay start by hot materials igniting nearby

combustibles.

Burnsto the operator may occur if unprotected

skin comes into contact with the extremely hotwork.

Magnetic fields could easily

destroy/disrupt electroniccomponents, stored data if notcareful.


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Welding/Cutting Hazards

Potential Hazards Cont.:

Metal fumesfrom vaporizing of the work with theextremely hot arcs may be inhaled into the workers lungs.

Certain metals and metal oxide fumes, including zinc,

cadmium and beryllium, produce serious illnesses when

inhaled. Fluxes used with welding to create inert atmospheres at

the point of the weld also present inhalation hazards.

All welding and cutting must have adequate ventilationto

protect the person doing the welding and those workingaround the welding area.


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Weld Joint StructureCharacteristics of a typical fusion-weld zone in oxyfuel-gas and arc welding.

Microhardness (HV) profile across a

weld bead.

A fusion joint is far from homogenous. Degree ofinhomogeity increases from pure metals tomultiphase alloys.


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Typical weld zone in arc and gas welds

The base material adjacent to the melt boundary is exposed to hightemperatures, and the properties and structure are changed within the heat-

affected zone.

Cold worked base material will show recrystallization in HAZ, with coarse grainsizes.

In either case, a coarse-grained structure of lower strength exits at the meltboundary.

Melt

W ld bilit d W ld Q lit


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Weldability and Weld Quality

- Welding Defects-


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1. Preheating the weld zone reduces energy input, coolingrates in the weld and HAZ, reduces differential shrinkage,

residual stresses, and distortion.

2. Postwelding heat treatment of the entire welded structure

a. Stress-relief anneal reduces residual stresses to

acceptable level.

b. Normalizing a steel wipes out most undesirable effects of

welding.

c. Full heat treatment (quenching and tempering of steels)

3. Peening (hammering or rolling) of weld bead improves the

strength of welds.

Metal Treatment


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Oxyacetylene Gas Welding

Three basic types of oxyacetylene flames used in oxyfuel-gas weldingand

cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or

reducing, flame. The gas mixture in (a) is basically equal volumes of oxygen

and acetylene. (d) The principle of the oxyfuel-gas welding operation.


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Oxyacetylene Torch

The acetylene valve is opened first; thegas is lit with a spark lighter or a pilot

light; then the oxygen valve is opened

and the flame adjusted.

Basic equipment used in oxyfuel-gas welding. To ensure correct connections, all

threads on acetylene fittings are left-handed, whereas those for oxygen are right-

handed. Oxygen regulators are usually painted green, and acetylene regulators red.


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Oxyfuel gas welding


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Oxygen-fuel gas welding & Cutting

The elements of Oxygen-fuel gas welding

and cutting:

General Requirements

Cylinders

Service Pipe Systems

Pipe System Protection


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General Requirements

Focuses on using Acetylene Safely Flammable

Unstable

Cannot be adjusted above 15 psi

Safe Work Practices

Blow out cylinder valve

Turn on cylinder valve first and

then adjust the regulator pressure screw. Never stand in front or behind

a regulator when opening the cylinder valve

Open cylinder valve slowly

The pressure adjusting screw:

Turning clockwise allows the gas

allows to flow.

Turning counterclockwise reduces

or stop the gas flow.


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General Requirements Cont.: Safe Work Practices

Purge oxygen and acetylene passages

Light the acetylene Never use oil or grease

Do not use oxygen as a substitute for air

Keep your work area clean


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Cylinders

Cylinder approval and marking marked for the purpose of identifying the gas content,

with either the chemical or trade name of the gas

Storage of cylinders

Storage area must be well ventilated Cylinders must be at least 20 feet from combustibles

Valves must be closed

Valve protection must be in place

Inside storage must be limited to 2,000 cubic feet.

Cylinders must be stored in upright position

Oxygen must be at least 20 feet from fuel gas

or 5 feet with a 1/2 hour fire barrier

Separate oxygen from fuel gas


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Cylinders Cont.:

Operating Procedures

Operation must emphasize the absence of

oily or greasy substances. Follow these rules

of operation:

Cylinders, cylinder valves, couplings, regulators,

hose, and apparatus shall be kept free from oily or

greasy substances.

Oxygen cylinders or apparatus shall not be

handled with oily hands or gloves.

A jet of oxygen must never be permitted to strike

an oily surface, greasy clothes, or enter a fuel oil

or other storage tank.


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Service Pipe Systems

There are special requirements for service pipe

systems when using oxygen or acetylene.

Oxygen

Acetylene or Acetylene Compounds


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Pipe System Protection

The entire service pipe system must be protected

against build-up of excessive pressure and leaks.

This protection is accomplished with: Protective equipment

Regulators

Proper hose and hose connections.


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Pipe System Protection Cont.: Protective equipment is divided into the two

categories listed here:

Pressure Relief Devices

The pressure relief device should discharge upwards to a

safe location.

Pressure relief valves are required in fuel-gas piping systems

to prevent excessive pressure build up within the system.


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Pipe System Protection Cont.:

Approved protective equipment shall be

installed in fuel-gas piping to prevent:

Backflow of oxygen into the fuel-gas supplysystem

Passage of a flash back into the fuel-gas supply

system Excessive back pressure of oxygen in the fuel-

gas supply system.


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Weld joint

There are 5 basic joint types in welding

Butt joint: Two materials are in the sameplane, joined from the edges.

Corner joint:The corners of two materials

form a right angle and joined. Lap joint: Two parts overlaps.

Tee joint: One part is perpendicular to the

other, making a T shape. Edge joint: Edges of the two materials

joined.


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Weld Joints


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Types of weld

1. Fillet weld: Used in T joints,corner joints, lap joints.

2. Groove weld:Used in butt joints.

3. Plug weld: Used in lap joints.

4. Slot weld: Used in lap joints.

5. Spot weld: Used in lap joints.

6. Seam weld: Used in lap joints.

7. Flange weld:Used in edge joints.

8. Surfacing weld:Not a joining process, it is used to

increase the thickness of the plate, or provide aprotective coating on the surface.


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Fillet Weld

Groove weld

Slot and Plug Weld
http://www.mig-welding.co.uk/plug-weld.htm


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Arc Welding


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Arc Welding and Cutting

Definition:

A fusion process wherein the coalescence of the

metals is achieved from the heat of an electric arc

formed between an electrode and the work.

Application

Installation

Operation & Maintenance

t

Electric Arc Welding


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Electric Arc Welding

- Classification -

The Electrode

Consumable: melts and serves as a filling material

Non-consumable: does not melt, parent metal is used, or aseparate filler rod

Coated or Uncoated

Coating

Provides a gaseous shield to prevent oxidation

Lowers the voltage needed to establish the arc

May provide slag-blanket to protect the joint

Add alloying elements to enhance the properties of the joint.

C bl El d A W ldi P


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Consumable Electrode Arc Welding Processes

Shielded metal arc welding

Submerged arc welding

Gas metal arc welding

Consumable Electrode Arc Welding


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Schematic illustration of the shielded metal-arc welding process.About 50% of all large-scale industrial welding operations use this

process.

Consumable Electrode Arc WeldingShielded-Metal Arc Welding


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Consumable-Electrode Welding:


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Consumable-Electrode Welding:Gas Metal-Arc Welding (GMAW) - MIG

Consumable gas metal-arc welding (MIG)

Consumable electrode is metal which meltsto become part of the weld seam.

Weld zone is protected by a gas or a flux

No slag is formed

Several layers could be build with little or

no intermediate cleaning

It is suitable for most metals

Wire electrode can be supplied in long,

coiled lengths which allow uninterrupted

welds in any welding position.

Consumable Electrode Arc Welding Gas


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(a) Schematic illustration of the gas metal-arc welding process,

formerly known as MIG (for metal inert gas) welding. (b) Basic

equipment used in gas metal-arc welding operations.

Consumable Electrode Arc Welding Gas- Gas Metal-arc Welding Process-


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Non-Consumable Electrode Arc Welding

Gas Tungsten Arc Welding ( TIG)

Plasma arc welding

Atomic hydrogen welding

Non-Consumable-Electrode Welding:


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Non Consumable Electrode Welding:

Gas Tungsten-Arc Welding (GTAW) Nonconsumable gas tungsten Inert

gas welding (TIG)

Weld zone is protected by inert gas

DC with straight polarity is usedwith steel, cast iron, and stainless

AC with Al, Mg alloys where ac

helps in stripping the oxide Both hand and automatic

operations are possible

The process demands considerableskill but produces very high-quality

welds on almost any material No weld spatter or slag formation

t er e ng rocesses


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Electron Beam welding (EBW) Heat is produced by high velocity electron

gun in a narrow beam

No filler material

High rate of heating results in greater depth

and heat-affected zone is very small

Suitable for welding refractory materials like:

molybdenum and zirconium

Requires a vacuum (limitation)

x-ray will be generated around the welding

gun which may be cancerous

t er e ng rocessesHigh Energy Beam Welding

High Energy Beam Welding


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High Energy Beam Welding

LASER Beam welding (LBW) Uses a focused high power monochromatic light

beam as a source of heat to the metal

Beam can be directed to the welding spot with a

lens

Depth of welding similar to electron beam

welding

Vacuum is not necessary (advantage)

Workpiece usually needs protection by a gas

Process is suitable for automation Welding speeds can be upto 7 m/min

Laser beam welding


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Laser beam welding


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Thermit Welding

E l i W ldi


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Explosion Welding


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Resistance welding

F ldi


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Forge welding

PCB printed circuit boards


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Soldering

Circuit Board

Resistor

Solder Pads

Side View

Top View

PCB printed circuit boards


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Soldering

Iron


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Move soldering iron until tip is

touching wire & solder pad


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Move solder to touch edge of tip.

Solder


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Hold until solder melts

on tip by wire

Solder


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Move solder back to touch wire only

Solder


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Move solder in to form a

small pocket

Solder


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Move soldering iron tip up. Thiswill drag solder up with it.

Solder


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Look for

shinny fillets


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Brazing

Definition:

A process which a filler metal is placed at or between the

faying surfaces, the temperature is raised high enough to

melt the filler metal but not the base metal.

The molten metal fills the spaces by capillary attraction.

Torch Brazing

Oxy-fuel torch with a carburizing flame

First heat the joint then add the filler metal

S f W k P ti


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Safe Work Practices

Electric & Gas Welding Safety Check:

Ensure electrical cord, electrode holder

and cables are free from defects No cable splices within 10 feet of electrode holder.

Ensure welding unit is properly grounded.

This helps to avoid over heating.

All defective equipment shall be repairedor replaced before using.

Safe Work Practices


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Safe Work Practices

Electric & Gas Welding Cont.: Safety Check:

Remove all jewelryrings, watches, bracelets,etc

Ensure PPE e.g.. welding hood, gloves, rubberboots or safety shoes, apron are available and in

good condition. Ensure fire extinguisher is charged and available.

Ensure adequate ventilation and lighting is in place.

Set Voltage Regulator to Manufacturesspecifications Avoid electrical shock ONTwrap cables around

any body part.

Ensure fittings are tight.


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Safe Work Practices

Electric & Gas Welding Cont.: Safety Check:

Inspect hoses for cuts and frayed areas.

Set gauges to desired PSI.

Ensure that sufficient PPE is madeavailable.

Locate welding screens to protect

employees ONTblock your exit.

Ensure that adequate ventilation andlighting are in place.

Fire Protection & Prevention Cont :


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Fire Protection & Prevention Cont.:

Welding areas should meet the following

requirements: Floors swept & cleared of combustibles 35 ft. radius

of work area.

Flammable and combustible liquids kept 35 ft. radius

of work area. At least one fire extinguisheron site

Protective dividers to contain sparks and slag

Welding curtains

Non-combustible walls Fire resistant tarps & blankets

UW-Eau Claire

Facilities Planning & Management

Proper Ventilation for Welding


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Proper Ventilation for Welding

Ventilation

Proper ventilation can be obtained either naturally ormechanically.

Natural Ventilationis considered sufficient for welding and brazing

operations if the present work area meets these requirements:

Space of more than 10,000 square feet is provided per welder

A ceiling height of more than 16 feet.

Mechanical ventilationoptions generally fall into two basic

categories.

Low vacuum system which takes large volumes of air at low velocities.

High vacuum system that are captured and extracted fumes as near tothe work as possible.

Fi P t ti & P ti


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Fire Protection & Prevention

Fire hazards must be removed, or

Guards installed, or

Welding/cutting must NOT take place

Hot work permit should be used outside

designated areas to ensure that all firehazards are controlled

Use of fire watch

1/2 hour after operation ceases


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Welding Operators Protection


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Welding Operators Protection

Welding involves specialized personal

protection that must be worn every time you

perform welding operations. The following is a

list of basic PPE:

Fire-resistant gloves

Aprons

Safety shoes

Helmet

Ultraviolet radiation filter plate (arc welding)

Goggles with filter lenses

U


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Welding, Cutting and Brazing

Summary Major hazards include:

Fire

Burns

Shock

Toxic Exposure

Follow proper procedures to prevent fires

Use appropriate engineering controls

Wear appropriate PPE


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