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WELDING 05 – 08 JULY 2010

Zainal Nazri Mohd Yusuf

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Course Outcome

1. To describe and conduct the joining process using arc based welding equipments.

2. To identify and analyze causes of weld defect as a result of welding process.

3. To Indentify destructive testing method used in weldment test.

4. To apply non-destructive inspection methods to detect the surface and subsurface defect.

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SAFETY IN WELDINGSAFETY IN WELDING

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Safety precautions that should be observed in the use of the arc

welding equipment.

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Make sure machine is properly grounded.

Never permit “live” parts of the electric welder to touch bare skin or wet clothing.

Do not cool electrode holders by emersion in water.

Turn off power supply when welder is not in use.

Do not stand on wet areas while welding.

Wear leather gloves.

Make sure cable are covered and in good condition.

Make certain that electrode holders are properly insulated.

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Protect eyes and face from flying particles of slag by use of safety glasses or face shield.

Wear adequate protective clothing.

Always wear leather gloves.

Wear high top shoes.

Keep collar, shirt pockets, etc buttoned.

Do not touch the electrode or metal where welding has taken place.

Handle hot metal with pliers.

Keep electrode stubs properly disposed of.

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Use a welding helmet with the correct shade lens in good condition.

Wear suitable clothing—do not leave bare skin exposed to the rays of the arc.

Do not strike the arc without covering the face and eyes. Give warning to others before striking the arc.

Avoid looking directly at the arc where others are welding without proper eye protection.

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Work only in well-ventilated areas.

Use great care when working on metals covered with lead or zinc.

If working in a confined area use respirator or other approved breathing devices.

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Keep shop clean in areas where welding is to be done.

Do not weld near combustible materials of any kind.

Place at least 10 meter away from the welding area.

Never weld on covered containers which may have held combustible materials without first taking adequate safety precautions.

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Be familiar with location and types of fire extinguishers.

Report any unsafe conditions that might start a fire.

Do not weld near inflammable materials.

Do not weld on containers that have held inflammable materials.

Do not weld near electrical fittings or lines.

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WELDING WELDING

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Welding is a material joining process in which two or more parts are coalesced (joined together) at their contacting surfaces by a suitable application of heat and/or pressure.

Metals that is to be joined is called base metal

Most of the welding uses arc welding – process in which fusion is obtained by heating base metal to form a weld puddle filler material is added to facilitate coalescence.

DefinitionsDefinitionsDefinitionsDefinitions

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Terms Arc voltage – the voltage across the welding arc

Arc Length – the distance between the tip of the electrode and the weld puddle

Bead – Result of the weld deposited on the metals being joined.

Weld puddle – the molten metal form a pool

Slag – outer layer of the weld bead deposited during welding (SMAW)

Deposited Metal- Filler metal that has been added during a welding operation

Depth of Fusion – the distance from the original surface of the base metal to that point at which fusion ceases in a welding operation.

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Weld puddle / weld pool

Arc length

Weld BeadDepth of fusion/ weld penetration

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leg The distance from the root to the toe of the fillet weld. The size of the fillet weld is determined by the length of its legs.

Throat The shortest distance between the weld root and the weld face. The throat determines a fillet weld's size and strength.

Toe A point at which the weld face and the base metal meet.

Face The exposed surface of a weld on the side from which welding occurs.

RootThe depth that a weld extends into the joint root

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Welding Position

There are essentially 4 different fundamental welding positions, namely flat, horizontal, vertical and overhead.

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Definition of welding position for fillet and groove weld as given in BS EN 287-1 AWS designation.

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Horizontal position 2G

Incline position 6G

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Vertical position Overhead position

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Type of Joint

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Alternating Current (AC)

Alternating current constantly change its polarity 120 times, producing 60 positive half cycle and 60 negative half cycle.

This can reduce the arc blow due to magnetic field.

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DCEP (DCRP)In direct-current arc welding, the arrangement of leads where the surface to be welded is the negative and the electrode is thepositive relative to the welding arc.

+ve -ve

Work pieceCurrent flow

deeper penetration is needed

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DCEN (DCSP)

the arrangement of direct current arc welding leads in which the electrode is the negative pole and the work piece is the positive pole.

Shallow penetration

+ve -ve

Work piece

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Welding TechniquesWelding TechniquesWelding TechniquesWelding Techniques

There are two techniques for moving the torches, gun or electrode holder;– Forehand – the flame is directed against the base metal ahead of the completed weld.

– Backhand – the flame is directed towards the completed weld.

Base metal

Base metal

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• Manipulation techniques can control bead size, shape, penetration

• Bead results depends on the weave motion applied during welding operation.

• There are few types of weave patterns could be practiced to obtain the good weld bead.

– Straight drag – Number 8 style– Crescent style– Z style– Whip and pause styleAnd etc.

Manipulation Techniques Manipulation Techniques Manipulation Techniques Manipulation Techniques

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Welding Symbol

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Welding Symbol

• Reference Line• Leader and arrow• Basic weld symbol (location & depth of weld)• Finish symbol• Weld symbol• Dimensions• Supplementary symbols• Tail and specifications

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Cont’d

Leader

Reference Line

Tail

Welding symbol is based on ANSI/AWS A2.4, Standard and symbols for welding , Brazing and Non-destructive testing

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Frequently Used Symbol Elements For Structural Welding

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Example

Fillet Weld

Weld around

Arrow side

Opposite side

Specification Result

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Butt Joint

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Weld symbol (Fillet joint)

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Weld symbol (Corner Joint)

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Arc Welding Process

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SMAW

Shielded Metal Arc Welding (SMAW) is a welding process in which the base metals are heated to fusion or melting temperature by an electric arcThe arc is created between a covered metal electrode and the base metals.

A shielding gas is use to protect the weld area from the atmosphere. The gas is not pressurized. As the flux covering on the electrode melts, it creates the shielding gas. The melting electrode were furnishes filler metal to the weld.

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Application of SMAW

Principle of SMAW

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1. Ability to weld in all position2. Ease in welding many different

metals and alloys3. Ability to weld thin and very thick

metals4. Very portable and good for field

work5. Good choice for repair work6. Low-cost, low maintenance

equipment7. Good arc visibility8. Good accessibility in restricted

areas

1. Ability to weld in all position2. Ease in welding many different

metals and alloys3. Ability to weld thin and very thick

metals4. Very portable and good for field

work5. Good choice for repair work6. Low-cost, low maintenance

equipment7. Good arc visibility8. Good accessibility in restricted

areas

1. High potential for weld contamination

2. Frequent interruptions due to electrode length

3. Need to remove spatter, smoke and slag

4. Unsuitability for very thin material

5. Electrode requires special care to prevent moisture pickup

1. High potential for weld contamination

2. Frequent interruptions due to electrode length

3. Need to remove spatter, smoke and slag

4. Unsuitability for very thin material

5. Electrode requires special care to prevent moisture pickup

Advantages Limitations

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GMAW

GMAW uses a continuous, consumable electrode wire, fed from a spool, to provide the needed filler metal. Shielding of hot and molten metal is provided by a protective gas flowing from proper containers.

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• Increase arc time • Improve productivity• Reduced operator

fatigue• No need to chip away

slag• Reduced smoke and

fumes• Skills easily learned• Cleaner work area

• Increase arc time • Improve productivity• Reduced operator

fatigue• No need to chip away

slag• Reduced smoke and

fumes• Skills easily learned• Cleaner work area

Possible lack of fusion Material thickness

limitation Porosity when there is no

shielding gas.

Possible lack of fusion Material thickness

limitation Porosity when there is no

shielding gas.

AdvantagesAdvantages

LimitationsLimitations

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Shielding gas

Regulator

Power source

Cable

Gun / Torch

Ground Clamp

controller

49Electrode wire Wire feeder

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Shielding Gas

Trigger the button will activate the gas and current delivery

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Gas Tungsten Arc Welding (GTAW)

Non consumable arc welding processes use tungsten electrodes and shielding is provided by an inert gas around the weld area. Once such process, the Gas Tungsten Arc Welding (GTAW) is also called as Tungsten Inert Gas (TIG) welding.

It uses tungsten alloy electrode and helium gas shield. Because of inert gas atmosphere tungsten is not consumed. Filler materials supplied by a separate rod or wire.

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• THE WELD ARE VERY CLEAN AND HAVE GOOD QUALITY

• ARC HEAT IS INTENSE AND HIGHLY CONCENTRATED

• NO SMOKE, FUMES, SPATTER, OR SLAG IS CREATED

• WELD ZONE IS HIGHLY VISIBLE

• GTAW CAN BE USED TO WELD MOST INDUSTRIAL METALS

• THE WELD ARE VERY CLEAN AND HAVE GOOD QUALITY

• ARC HEAT IS INTENSE AND HIGHLY CONCENTRATED

• NO SMOKE, FUMES, SPATTER, OR SLAG IS CREATED

• WELD ZONE IS HIGHLY VISIBLE

• GTAW CAN BE USED TO WELD MOST INDUSTRIAL METALS

• SLOW WELDING SPEED• EXPENSIVE EQUIPMENT• COSTLY USED OF INERT

GASES• REQUIREMENT OF HIGHLY

SKILLED WELDER FOR MANUAL WELDING

• SLOW WELDING SPEED• EXPENSIVE EQUIPMENT• COSTLY USED OF INERT

GASES• REQUIREMENT OF HIGHLY

SKILLED WELDER FOR MANUAL WELDING

Advantages Limitations

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AC current DCEN

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Welding Defect

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Undercut

undercutting is a defect that appears as a groove in the parent metal directly along the edges of the weld. It is most common in lap fillet welds, but can also be encountered in fillet and butt joints. This type of defect is most commonly caused by improper welding parameters; particularly the travel speed and arc voltage.The arc length should be kept short, not only to avoid undercutting but to increase penetration and weld soundness

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Porosity

The most common causes of porosity are atmosphere contamination, excessively oxidized work piece surfaces, inadequate deoxidizing alloys in the wire and the presence of foreign matter. Atmospheric contamination can be caused by:

1)   Inadequate shielding gas flow. 2)   Excessive shielding gas flow. This can cause aspiration of air into the gas stream.3)   Severely clogged gas nozzle or damaged gas supply system (leaking hoses, fittings, etc.)

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Incomplete Fusion

Incomplete fusion – weld pool did not wet surface of workpiece due to

fast traveling speed. The molten material solidified rapidly and not enough

Fusion form.

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Overlap

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Under fill

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Spatter

Spatter- surface damage caused by molten metal from arc or weld pool.

Arc length too long.

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EXCESSIVE CONVEXITY

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EXCESSIVE CONCAVITY

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Excessive weld reinforcement

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Slag inclusion

pieces of slag trapped inside solidified weld pool; may result from

excessive stirring in weld pool, or failure to remove slag from prior weld

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Incomplete Penetration

This type of defect is found in any of three ways: 1)   weld bead does not penetrate the entire thickness of the base plate. 2)   Two opposing weld beads do not interpenetrate. 3)   weld bead does not penetrate the toe of a fillet weld but only bridges across it.

Causes:

Low welding current. Slow a traveling speed and an incorrect torch angle. Both will allow the molten weld metal to roll in front of the arc, acting as a cushion to prevent penetration. The arc must be kept on the leading edge of the weld puddle.

68Excessive penetration

Incomplete penetration – insufficient heating during welding for weld pool to penetrate

to opposite side (or centerline) of weld; results in a gap behind/under weld

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THE ENDTHANK YOU

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