routine manual metal arc welding

Metals and Engineering Industry5.12AB Perform Routine Manual Metal Arc Welding

ContentsTraining Record 3Introduction 7

Topics 7Prerequisites 7Instructions 7

Competency assessment 7

Section 1 - Introduction to Manual Metal Arc Wdding 9Aim 9

Acti vity 9MMAWelding video response 10

Arc welding 10

Section 2 - Operating Principles for Manual Arc Welding 13Aim 13

Activity 13Electricity 14Hazards 14

Protective clothing 17Maintenance of welding equipment.. 2021Welding machines 23Power source 26

Rating of power sources 29Current range 29Electrodes 30

Basic symbols 33Welding symbols 33\Velding procedures 35Joint preparation 37

Review questions - Operating principles for manual arc welding38Review questions - Weld symbols 42Review questions - Electrode identification - Current settings .. 44

Section 3 - Manual Metal Arc Welding - Basic Welds 45Aim 45

Acti vity 45Manual metal arc welding - basic welds .46

Material preparation 46HOViTto strike an arc 47

Laying down a weld bead 48Weld cleaning 49

Review questions - Material preparation and weld cleaning 50

5

6

Metals and Engineering Industry

5.12AB Perform Routine Manual Metal Arc Welding

Practical exercise 1 - Beads on plate - flat 52Procedure sheet 1 - Beads on plate - flat 54

Practical exercise 2 - Pad welds - flat.. 55Procedure sheet 2 - Pad weld - flat 57

Section 4 - Fillet Weld Joint Terms and Faults 59Aim 59Activity 59

Fillet weld joint terminology and faults 60Fillet weld terminology 60Weld Defects 62Workshop tests 67

Review questions - Fillet weld joint terminology and faults 69Practical exercise 3 - Fillet weld, single run - horizontaL 78

Procedure sheet 3 - Fillet weld, single run - horizontal 80Practical exercise 4 - Fillet weld, 3 run 2 layer - horizontal.. 81

Procedure sheet 4 - Fillet weld, 3 run 2 layer - horizontal. 83Practical exercise 5 - Outside corner fillet - horizontal 84

Prooedure sheet 5 - Outside corner fillet - horizontaL 86Practical exercise 6 - Fillet weld - horizontal 87

Prooedure sheet 6 - Fillet weld - horizontal 89

Seotion 5 - Butt Weld Terminology and Faults 90Aim 90Activity 90

Butt weld terminology and faults 91Weld preparation 91Preparation types 93Weld defects 96

The principle of expansion and contraction in a metal 101Angular distortion 101

Review questions - Butt weld terminology and faults 102Practical exercise 7 - Butt weld, flat sheet steel 108

Procedure sheet 7 - Butt weld, flat sheet steel 110


S.12AB Perform Routine Manual Metal Arc Welding

Introduction

This training guide is designed to support training for the Metal and

Engineering Training Package.

Topics

• Operating principles for manual arc welding

• Manual metal arc welding - basic welds

• Fillet weld joint terms and faults

• Butt weld terminology and faults

Prerequisites

Nil

Instructions

1. Study the information for each topic and complete review

questions

2. Complete the practical exercises.

note

The pr~ctical exercises are suggested only and may be replaced

by any other suitable training activity.

3. The Training Record must be signed by your trainer on

completion of each activity.

4. Complete the theory test. (The test results may be

recorded as part evidence of competency.)

Competency assessment

To achieve competency other approved activities must be entered in theAssessment and Evidence Record section.

7


S.12AB Perform Routine Manual Metal Arc Weldiug

Section 1 - Introduction to Manual

Metal Arc WeldingAim

To understand the operating principles, equipment, consumables and

safety requirements for general purpose welding using the manual metal

arc welding process.

Activity

1. View video No. 47 Arc Welding.

2. Complete the video response questions during or

immediately after watching the video.

3. Ask your supervisor or teacher if the information is not

clear to you.

4. Ask your trainer to check and sign your Training Record.

S. On completion of this section you must attempt the test

on this topic and reach the required level of competence

before proceeding to the next section.

Safety

• Wear safety glasses at all times while in welding workshops.

• Follow safe working practices to avoid electric shock.

• Weld in well ventilated areas.

• Wear protective clothing.

9


Section 2 - Operating Principles forManual Arc WeldingAim

Topractice manual metal arc welding exercises in order for you to develop

the manipulative skills for striking an arc and depositing weld metal on

low carbon steel plate.

Activity

1. Read and study the resource material following.

2. Complete the review questions.

3. Ask for assistance if the information or instructions are

not clear to you.

4. Ask a teacher or your supervisor to check and sign your

Training Record.

Safety

• Follow OHS workshop procedures.

• Protect your eyes from the welding arc and wear the proper

eye protection.

• Wear suitable protective clothing including dry leather gloves.

13

14

Metals and Engineering IndustryS.12AB Perform Routine Manual Metal Arc Welding

The welding process uses electricity and generates heat and fumes. Safety

precautions including wearing protective clothing are important.

Maintenance of equipment and supplies and a thorough understanding of

safety aspects of welding will minimise the risk of accident and injury.

Electricity

Electricity is the flow of electrons through a conductor at a certain pressure

and speed. It's like water running through a hose. Some of the terms

associated with electricity are explained here.

Conductor In welding an electrical conductor is a metal through which

electricity will easily flow. Copper is the most used conductor.

Voltage This is the unit of electrical pressure. The voltage at the terminals

of an AC welding machine is never more than 80 volts for safety reasons.

This electrical pressure (or force) is responsible for the current flow in a

welding circuit.

Amperage This is the measurement of the electron flow,or current, through

an electrical conductor. Amperage is measured in amps. An amp is a unit

quantity of electricity passing through a given point per second. This is

similar to the rate water flows through a pipeline.

Electric arc welding process This is also called manual metal arc welding

or MMAW. In MMAW a high output amperage (low voltage) is passed

through a consumable flux coated electrode and the work piece. This sets

up an electrical resistance between the tip of the electrode and the workwhich causes the electrode to melt off and form a weld bead.

Hazards

Working with electrical equipment can be hazardous. Youmust take proper

precautions and follow the set safety procedures. Hazards in the welding

workshop include electric shock, fumes, heat, glare and harmful rays.


Electric shocks - low voltage

Electric shocks are possible on the secondary (low voltage) side of the

welding circuit. They may be caused by:

• working on wet floors - a shock may be felt when putting an

electrode in the holder. Always stand on insulated mats or

wooden boards to reduce the risk and wear dry leather gloves

• working in a very humid climate or rainy weather - a shock

may be felt when changing electrodes. Keep electrodes and

gloves dry.

Electrical shocks • high voltage

High voltage shocks shouldn't happen if precautions are taken such as

ensuring welding machines are maintained by licensed electrical tradesmen

and that you never interfere with the inside parts of the welding machines.

Symptoms of electrical shock

Often electric shock stuns but doesn't kill. However when electricity passes

through the body it causes muscles to contract and can stop the heart

from beating or cause breathing to stop.

Electricity can also cause serious burns.

Fumes

Fumes can result from:

• the production of oxides and nitrous gases from incomplete

combustion or oxidation of nitrogen from the atmosphere

• the surface coatings on steel such as galvanising, cadmium

or chrome plating and paints and solvents such as red oxide

parts/degreasing solvents

• elements within the parent metal

• electrode flux coatings.

15

16



Safety

Welding should be carried out in well ventilated areas. When welding high

fuming materials such asga1vanised steel, use extraction systems to carry

away the fumes. If an extraction system is not available, an approved

respirator should be used to filter out the fumes.

Respirators should only be used as a secondary protection.

Dangerous fumes

Gases, dusts and vapours are given off during welding. They can cause:

• gassing or asphyxiation because the oxygen has been used

up in the work area (common in confined spaces)

• build up of poisonous metals in the body, such as lead,

cadmium, zinc, beryllium or mercury

• respiratory ailments from wheeziness to serious lungdisorders.

Heat

Heat is a form of energy. When a substance is heated the molecules vibrate

or move more rapidly. Heat may be generated by various means. In manual

metal arc welding it is generated by the passage of an electric current

across an arc;:gap.

The electric arc (about 6000°C) generates the heat to melt and fuse themetal surfaces.

Heat is transferred in two ways, by conduction and by radiation.

Conduction Solid bodies must be in physical contact for heat to travel

through them. Some materials conduct heat more rapidly than others.

Metals are generally good conductors but, because of their different

properties, some have a greater conductivity rate than others, for example

copper and aluminium are very good conductors while cast iron and

stainless steel are poorer conductors.


Radiation This is the transfer of heat through space by wave motion. No

physical contact is needed. Allbodies at a higher temperature than their

surroundings radiate heat, for example, the sun radiates heat energy in

the form of cosmic rays and an electric radiator transfers heat through

space across a room.

Protective clothing

Protective clothing will help to protect you from heat, hot metal and

harmful rays.

Helmet

Gauntlets

Leather apron

Gaiters,'''-.

Spats ~--..~

Full protective clothing

Protection against hot metal

Molten droplets have a way of getting into boots. You can avoid this by

wearing proper protective clothing and footwear. When welding out of

position wear spats over your boots and under overall legs.

17


Protection from harmful rays

The harmful rays given off from an electrical welding process are ultra

violet rays and infra-red rays.

These rays can damage the skin. Ray burn is like very severe sunburn;

your skin reddens and then peels. If the ray burn is very severe, there

may be blisters and sores. Rays will also harm the eyes causing a condition

called a flash or arc eye. The first symptom of a flash is an itchy feeling in

the eye. Afterwards a throbbing pain (much like sand in the eye) may

stop you sleeping. There are eye drops that relieve the pain. Continuos

flashes may cause blindness. The use of Safety Glasses will help protect

your eyes from these rays.

Filter lenses These are specially designed glass lenses to filter out harmful

rays and allow you to see what you're welding without causing any changes

in the pupil size or damage to your eyes. Filters come in different shade

numbers, according to the current range or type of welding.

Recommended minimum protective filters

Process

MMAW

ApproximateWelding (AMPS)

Up to 100100 - 200200 - 300300 - 400Over 400

FilterRecommended

810111213

18

Safety

• Wear safety glasses at all times.

• Wear appropriate clothing to protect your eyes and skin, from

welding rays.

• Prevention, is the best policy, avoid exposing eyes to harmful

rays.


5.12AB Perform Routine Manual Metal Are Welding

Wear a welding shield or helmet, fitted with the correct filter to protect

you from arc rays, heat and the spatter from molten metal. The filter

reduces the intensity of the radiation, but allows sufficient light through

for you to see the weld pool and the end of the electrode.

Clear glass

Head shield

Swivel filter

hand held shield

19

20

Metals and Engineering lndustry5.12AB Perform Routine Manual Metal Arc Welding

Maintenance of welding equipment

Before carrying out any maintenance on electrical equipment, it's

important that you first switch off the power and remove the plug. If there

isn't a plug, lock off the machine or danger tag the isolator switch.

Transformer

Never do maintenance work inside the case of the welding machine.

Operators can care for the machine by:

• keeping the case clean and dust free

• maintaining the secondary circuit in good condition

• sending the machine to a licensed electrician for any

maintenance on the internal parts, the primary lead and plug.

Machine terminals

Keep terminals clean and tight to ensure that the current will flow freely.

If you don't check nut tightness now and then, you may get arcing and/or

overheating of the terminal and lug connections. This will also be

detrimental to weld quality and machine performance. This can lead tofire or cause burns.

Joints

Loose joints or bad contacts cause cable, clamps and other parts of the

welding plant to overheat and may give you unstable arcing. Use properly

designed cable connectors when you make any joints in cables. Make

sure that good electrical contact is made when you connect cables to the

power source, electrode holder and the return work clamp

Secondary leads (electrode/return lead)

Damaged leads may cause the operator discomfort from overheating, and

poor arcing characteristics. Maintain leads by:

• rolling them up after use

• unroll prior to using


5.12AB Pedorm Routine Manual Metal Arc Welding

• making sure that the ends are fixed correctly into the

electrode holder, work-clamp or terminal lugs

• covering lug connections with insulation tape when necessary.

The size of the cable must suit the output of the welding power source at

the maximum duty cycle (refer to Australian Standard AS1995 on welding

cables for the cable size).

Electrode holders

Electrode holders should suit the minimum output current being used.

The holder should be relatively light, comfortable to hold, fully insulated

and sturdy enough to withstand the wear and tear from constant use. The

holder should be rated to withstand the maximum current required for

the activity.

Retumclamp

This is fastened to the work or to the workbench to complete the welding

circuit. Spring pressure and screw type clamps are normally used. Magnetic

type clamps are also available.

Twist handle to

grip electrode

Insertelectrode

Heavy duty type

Spring-loaded jawsto grip electrode

Electrode holders

21

22


Screw Clamp

Work cable attachments

. -: /0'1~/-..., /- /.a

Cable attachments

Safety

Protect yourself by wearing the following safety clothing:

• overalls or work clothes

• leather apron and/or coat

• welding gloves.

Machine location

Welding machines should always be in a dry protected area as close to the

power outlet as possible.

Protection of others

Welding should be done in special welding bays. When this is not possible,

use portable screens to shield others working in the area from the rays

generated from the arc. You should also put up signs to warn people that

you are welding.


Welding machines

Weldingmachines operate with either alternating current or direct current.

Alternating current (AC) welding machines

Alternating current welding machines are transformers which step down

line voltage (240 or 415 volts) to provide a safe welding voltage. The welding

current supplied by the secondary circuit of the transformer is set by the

operator to suit the type and size of electrode and its use.

Transformer welding machines are less complex and slightly less expensive

than other types.

Direct current (DC) welding machines

The direct current output may be supplied by a transformer/rectifier or

generator power source.

Transformer/rectifiers

An efficient and reliable transformer/rectifier is a machine designed to

transform AC input current to DC output current suitable for welding.

Transformer/rectifiers have no moving parts and like the transformer are

quiet to operate, convenient and cost less than motor generated units. If

an AC current is needed from this type of machine, all the operator has to

do is to select the AC output switch.

Transformer/rectifiers are often designed to provide either DC or AC

outputs. DC is normally preferred because of its greater arc stability but

AC may be required at higher currents to avoid arc blow.

23


24

Arc welding power source - AC transforrner

Arc welding power source - mobile engine driven DC generator

Metals and Engineering lndustl)'5.12AB Perlorm Routine Manual Metal Arc Welding

AC transformer setsDC motor generator sets

Portability

These machines generally consist ofMost modern types have features that allowstatic step-down transformers and

portability (especially the self containedthey are considered as stationary

types). They have an undercarriage fitted withtypes.

wheels.

Power supply

The use of these machines isPetrol or diesel engine driven machines canrestricted to the location of the nearest

be used in any location (special applicationsalternating current power point.

may use generators driven by compressed airie mining).

Efficiency

70-90 per cent electrically efficient.40-60 per cent electrically efficient but someMany multi operator sets give higher

modern types compare with alternatingefficiency.

current efficiency.

Polarity

No polarity. A choice of polarity is obtained by a simplereversal of a switch.(DC- or DC+)

Arc blow

Unaffected. Arc blow occurs even in normal currents andthey are difficult to control above 300amperes.

Maintenance

As there are no moving parts to beRevolving and wearing parts add to runningconsidered, maintenance costs are

costs.very low.

Initial costs

Cheaper plant as less construction isMore costly due to generator and motorinvolved.

construction.

Electrodes

Restricted to use of electrodes that areSuitable for all types of electrodes.suitable for alternating current only.

Running

Cheaper running costs due to the useAdded costs due to the use of electric motorscosts

of an installed power supply.or internal combustion engines.

Voltage

Constant open circuit voltage.A variation of open circuit voltage is possiblecontrol

allowing a selection of electrode type andwelding technique.

Arc length

Limited arc length. Greater tolerance in arc length due to thecharacteristics of the machine.

25



Power source

A welding source provides enough current (heat energy) to melt the

electrode and the parent metal. Manual metal arc welding machines have

a variable (adjustable) current output that can be set to suit the job and

type of electrode.

Power source terminals and polarity

Electrical connections for a welding machine are illustrated below.

Output terminals on AC machines are marked electrode and work.

On a DC machine the terminals are marked positive (+) and negative (-)

except in the case where the polarity can be changed by means of a polarity

reversing switch. In such cases the terminals are marked electrode and

work with electrode terminal polarity indicated at the polarity switch.

Most electrodes designed for DCoperate on DC electrode terminal positive

(+) while some types of electrodes should be operated on DC electrode

negative (-). Refer to the manufacturer's instructions for polarity selection.

Main voltage415 or 240 volts

WeldM/C

45-80V

26

Open circuit 'Voltage (no currentjlowing)

Mctals and Enginccring IndustryS.12AB Perform Routine Manual Mctal Arc Welding

Main voltage415 or 240 volts

Arc voltage (currentjlowing)

Welding cables

A multiple-strand, insulated flexible copper or aluminium lead conducts

the welding current from the power source to the work. A return cable is

needed to complete the welding circuit between the work and the powersource.

Electrode holder

Power source

Cable connections (secondary circuit side)

27


Open circuit voltage - arc voltage

Power sources may supply direct current (DC) or alternating current (AC)

to the electrode. AC transformers and DC generators supply only one

type of current, but many transformer/rectifiers can be switched between

AC and DC output.

AC power supply is used more often because the cost is lower and the

welding machines are simpler in design. However, DC current has some

advantages. The DC arc is much more stable with certain types of electrode.

DCis better for working with sheet metal because a stable arc is produced.

Engine driven DC models provide welding power where there are no

electrical supply lines available, for example on site work.

The current should remain nearly constant during welding where the

operator's movements tend to vary the arc length. These movements may

be accidental, or deliberate, to control the weld pool. An increase in arc

length win increase the voltage across the arc, however the machine is

designed to control the current close to the amperage set by the operator.

Melting of the electro<i~ is then uniform in spite of the normal variations

when welding.

The open circuit voltage (OGV) is located and measured at the power

source terminals with the machine switched on but no welding current

flowing. This voltage must be high enough to establish an arc, but not so

high that there is risk of dangerous electric shock.

The welder makes the arc by striking the tip of the electrode on the work

to cause a momentary short circuit. This is at the point on the graph

where V = O. With current flowing, the electrode is drawn away by the

welder to establish the arc. The amperage and voltage for a typical arc

length are shown at point x. For a longer arc length, there is significant

increase in arc voltage and a sman decrease in welding current (point y).

The welding machine is designed to avoid noticeable changes in current

output when the welder varies the arc length.


60

60:l!! 40

0:>

200

SO

100150200250

Amps

Output curvefor constant current power source, adjustedfor minimum current'Variation

Rating of power sources

Australian Standard AS1966 rates the output (duty cycle) of electric arc

welding power sources. The machines are classified according to the type

of service for which they are designed, for example: continuous duty, heavy

duty, light industrial or limited output cycles.

The standard defines each of the classes according to the output (load

current, load voltage) needed for a nominated duty cycle. The duty cycle

allows for the Jact that in any five minute period, current for welding may

be drawn for only part of that time. For example, if welding is for a

maximum of three minutes in any five minute period, the machine only

operates up to 60% duty cycle (3/5 of 5 minutes). A much lower current

must be selected for continuous (100%) operation.

All power sources must display a name plate stating the equipment class

and the rated output and duty cycle for its class (eg 300 amps, 32 volts,

60%duty cycle). The 100%duty cycle output current must also be noted.

Current range

The manufacturer's recommendations on the range of current for different

types and sizes of electrodes will only give you their lower and upper

current range.

29

Packet of electrodes

130-170

185-235140-200

105-150100-130

130-170

95-150

140-200

90-140

130-190

You should use the recommended amperage and electrode type and size

as stated in the procedure sheets for the practical exercises. This will

help you gain the experience to select the electrode type and size for

future welding exercises.

Electrodes

Electrodes are available in different types.

4113~~

The choice of current will depend on such factors as weld position,

thickness of the joint parts, root gap and access to the structure.


5.12AB Perform Routine Manual Metal Aro Welding

EXX12 Electrodes These have rutile coatings with other constituents

added to form a gaseous shield and slag modification. These electrodes

are easy to use in any positions (including vertical do\'\rn).They operate

with a quiet, medium penetrating arc able to bridge gaps or misalignedsections. These electrodes are general purpose electrodes used forstructural and sheet steel fabrication.

EXX13 Electrodes These also have a rutile coating, similar to the EXX12

type, but they produce a more fluid and easily removed slag (not suitable

for vertical down) with a very neat and flat profile. They are generally

Typical current ranges for the electrode classifications

130-160

75-1253.25

4.0

30


5. 12AB Pertonn Routine Manual Metal Arc Welding

more suited to overhead and vertical welding in an upwards direction

than EXX12. They have good X-ray and impact qualities. (these qualities

vary dependant on the impact grading number)

The effect of moisture on electrodes

Any electrode that absorbs excessive moisture into the coating may cause

one or more of the following problems:

• porosity

• excessive spatter

• arc instability

• poor weld contour

• undercut

• difficulty in slag removal

• cracking through hydrogen embrittlement.

Storage

All types of electrode should be stored in their original packaging in a

weather proof area on racks clear of the floor. They should be stored away

from moistvre and high humidity and possible damage.

Storage in an unheated room is satisfactory for a period of less than six

months. If storing for more than six months, or if in tropical or very wet

climates, all electrodes except cellulose types (EXXIO,EXXll) should be

stored in a room or insulated building heated to 15°C to 20°C room (or

ambient) temperature, but at no time more than 40°C. Electrodes stored

in hermetically sealed (airtight) boxes need not be kept in such anenvironment.

31

32



Never tear electrode information data from the boxes. This can lead to

confusion and/or improper use of electrodes.

Storing electrodes

Welders are responsible for the care and handling of electrodes on the

shop floor or work site.

Electrodes should be kept clean and dry.

Defective electrodes should not be used. Discard electrodes or which are

wet or seek manufacturer's advice. Don't use electrodes showing signs of

rust or of damaged coating.

Only remove from the packet the number of electrodes you need for the

next few hours or the immediate job in hand. This reduces the risk ofcontamination and waste.



Unseal packets of electrodes just before you use them and not before.

Basic symbols

Basic symbols which are used to denote the type of weld are illustrated in

Backing strip Weld allField orSurface shapeor bar

roundsite weldFlushConvex

0 ~ C\.

the table below. Also shown are a number of instructional symbols used

to impose certain requirements on the actual welding operation.

Welding symbols

Arrow connectingreference line

to joint

SrS

/::!Fi'eld or site of weld4eld all round

r--t~'-lI L1J WUJ rI 0 :I:o II _ ~_ t

I U'} Ot/) I

I :r: ~ I

I b Ow If m 0:::0 II 0:::_IL__ ~lflJ

F(N)

Number of stud, plug,slot,spot or projection welds

Basic weld symbol area

Spacing between intermittent welds

Tail of reference line (omittedwhen reference P is not used)

The standard welding symbol used to represent welds on drawings is shown

below. The symbol can be used in many ways.

33

34



note

Information relating to a particular weld, such as S, (N), F, W,

(M) must be placed on the same side of the reference line as

the symbol for that weld.

Symbol belowreferenceline

Symbol abovereferenceline

Application of the standard welding symbol

When applying the standard welding symbol, thought must be given as to

whether the actual weld is situated on the same side of the joint as thearrow or on the other side.

Arrow 1

W is called the arrow side of joint 1

X is called the other side of joint 1

Arrow 2

Z is called the arrow side of joint 2

Y is called the other side of joint 2

Arrow 1 bears no relation to arrow 2 as they refer to different

joints.

For weld A, the basic fillet symbol is placed underneath the reference line

indicating that the weld is on the arrow side of joint 1.

For weld B, however, the basic fillet symbol is placed above the reference

line indicating that the weld is on the other side of joint 2.


Wherever possible, the arrow should be positioned adjacent to the weld,

as with joint 1, with the symbol underneath the reference line.

Welding procedures

It is sometimes necessary to specify certain procedures or requirements

about a weld. The standard symbol used in such cases should be provided

with a tail as shown on the previous page and the information inserted

where shown, for example, at P.

In order to control a welding process more fully, a procedure sheet may

be added to the drawing. The sheet should contain the following generalinformation.

• type of material being welded;

• form of weld (to include plate preparation such as angle of

bevel, root penetration, root radius, etc.);

• set-up details such as welding position, alignment, gap

required;

• number and order of runs;

• electrode size, type and make (consultAS1552, Classification

of Covered Electrodes);

• electrical supply data such as polarity, current and voltagevalues;

• preheating requirements;

• pre- and post-weld cleaning procedures;

• treatment of joint after welding;

• preparation and/or procedures to apply in between runs.

The arrow is cranked as shown below and points towards the plate

which has to be prepared. The crank is omitted when the edge to

be prepared is abvious, for example, a tee but joint.

35



Symbol below the horizontal reference line.This indicates that the weld is to be placedon the same side as the arrow.

Symbol above the horizontal reference line.This indicates that the weld is to be placedon the opposite side to the arrow.

Symbol below and above the horizontalreference line. This indicates that the weld is to

be placed on both sides of the arrow.

Weld ISymbolICross SectionIDrawing ApplicationIDrawing Explanation

a) Seal bead weld at the

Jkt1 LEarrow side

Bead

ICsI

~b) Bead weld at the arrow side

c) Single bevel butt on

the arrow side with aNo edge preparation

abc bead weld on the other side

,bk;~~

a) Filet weld at the arrow side

Fillet

I1"- II'...'f~ b) Filet weld on the other side

of the jointc) Filet weld on both sides of

a

bcthe joint

a) Single V butt weld on

I~~ 11the arrow side

Single IVI~\}m b) Single V butt weld onVthe other side

c) Single V butt weld onthe other side groundEdge preparation required I a bcflush

~;v;

IOrll~""\.::'::::? ~

36


Joint preparation

The arrow may also be used to indicate when one plate only of a joint is to

be prepared in welding single bevel and single J butt joints.

The arrow is cranked as shown below and points towards the plate which

has to be prepared. The crank is omitted when the edge to be prepared is

obvious, for example, a tee but joint.

Actual weld

Plate to bebevelled

End view

Crankedarrow

Front view

~~:~~ooeclfue~o~m~~~~u~d

37


5.12AB Perform Routine Manual Metal Arc WeWing

Section 3 • Manual Metal Arc Welding •Basic Welds

Aim

Topractice manual metal arc welding exercises in order for you to develop

the manipulative skills for striking an arc and depositing weld metal on

low carbon steel plate.

Activity


2. Complete the practical exercises.

3. Ask for assistance if the information or instructions are

not clear to you.


Training Record.

5. These are skill practice exercises which are assessed. You

must reach the required standards to enable progressionto the section .

Safety


• Protect your eyes from the welding arc and wear the propereye protection.

• Wear suitable protective clothing including dry leather gloves.

45


Manual metal arc welding - basic welds

The following instructions will provide you with basic information about

material preparation, striking an arc and laying down a weld bead. The

cleaning requirements for a finished weld will also be identified along with

the equipment used for this task. Read them carefully before attempting

the four practical exercises in this section.

Material preparation

Cleaning

A welded joint on low carbon steel (mild steel) requires the material to be

cleaned in such a way as to remove all matter that may contaminate the

weld runs (beadlbeads). This can be in the form of Mechanical or Chemical

cleaning. If chemical cleaning is to be carried out it is critical that all

safety factors are adhered to as chemicals may produce dangerous

substances when heated by the arc. Consult the Material Safety Data

Sheet (MSDS) or the manufacturer/distributor if you are not sure about

using any cleaning agents.

Mechanical cleaning

The weld area may be machined. This preparation will generally require

minimal cleaning. If the material is flame cut or hot rolled it will have an

oxide skin that will need to be removed. This will usually require grinding

as wire brushing may not be aggressive enough to bring the material backto bare metal.

Aggregate blasting such as sand or other particles may be also used toclean the weld area.

Tools used for cleaning

The hand held power tools that are used for material removal may include:

46

Angle grinder

Straight portable grinder

Die grinder

Belt sander

Grinding or sanding

Grinding or wire brushing

Aleta!s and Engineering Industry

5.12AB Perform Routine Manual Meta! Arc Welding

These tools can be either pneumatic (air driven) or electric. A floor

mounted pedestal grinder may also be used for material removal.

The practical exercise in this module will require you to use an electric

angle grinder.

How to strike an arc

Preparation

1. Select a piece of steel and after material preparation placeit on the work bench.

2. Select a 4.0 mm E4112 or E4113 Manual Metal Arc

electrode.

3. Set amperage on power source to approximately 165

amps.

4. It is important that you get yourself into a comfortable

and relaxed position when welding to counter the effects

of body sway, movement restrictions and heat generated

by the arc. To get comfortable you can be seated, lean

against the bcnch or lean against a wall in the welding

bay.

Striking the arc

1. Turn on the power source.

2. Lightly touch the end of the electrode on to the work and

you will complete the circuit and current will flow.

3. The electrode end rapidly heats, melting sufficiently to

momentarily weld the electrode on to the work.

4. Due to the low voltage current we are using the arc will

not jump an air gap (as in a spark plug). Wemust therefore

establish an arc by first touching the end electrode onto

the work and then immediately, lengthen the distance

between end of the electrode and work allowing droplets

of metal and flux to cross the ARCGAP(3 mm approx.) to

form a molten pool.

47

48


5. If you fail to do this, droplets will bridge the arc gap,

causing a short circuit and a freezing of the electrode endonto the work.

6. If your action is incorrect and the electrode freezes onto

the work, that is becomes welded or stuck to it, a sharp

backward angling of the electrode should break it free.

7. Keep your head shield over your face, as an arc flash willoccur as the electrode breaks contact.

Laying down a weld bead

1. Once the arc has been established, reduce the arc length

to about 3 mm and note that molten metal is beginning

to mount up under the end of the electrode.

2. Start moving the tip of the rod slowly away to the right,

(if you are left- handed, to the left) endeavouring to

maintain a molten pool approximately 8mm wide behindthe arc.

3. You will have to feed in the electrode as it burns off,

maintaining a steady rate across the plate using the correct

arc length.

4. Continue to deposit a beadlbeads across the plate.

5. Remove the slag cover and wire brush and inspect yourweld.

6. A little more practice and some of these actions will begin

to happen automatically.

7. Remember, not all people are born natural welders.

8. Welding requires practice to gain the necessary skills to

lay down consistent welds. You only obtain these skills

by running lots of electrodes and concentrating on what

you are doing.


S.12AB Perform Routine Mauual Metal Arc Welding

Weld cleaning

It is important that the finished weld is of an acceptable standard free of

slag and adhering spatter. The finished appearance may be given in job

specifications and may require additional work. This may need to be

ca.rried out before the final finish is added to the completed job/component.

Cleaning may just require you to use a chipping hammer and a wire brush.

It could also require you to use the following tools.

Angle grinder

Straight portable grinder

Die grinder

Belt sander

Chisel (hand, electric, air)

File

Grinding or sanding

Grinding or wire brushing

Peening gun (electric, air) used to remove slag.

By the removal of slag and spatter many welds on fabrication work are left

as cleaned. Additional treatment such as machining, sand blasting, grinding

and sanding are after treatments that may be carried out by other personnel

in the manufacturing process. The practical exercises in this module will

require you to use a chipping hammer, chisel and wire brush.

49


Practical exercise 1 - Beads on plate flatAim

To develop the skills to deposit uniform weld beads to the standards below.

Material

1 piece low carbon steel 75 x 10 x 225 mm

Consumables

Mild steel electrodes 4.0 mm E4112 or E4113 at approx. 165 amps.

Instructions

Check the following points:

Amperage setting and heat input, position of the plate on the

bench, correct method of arc striking, correct arc length, correct

welding speed arid travel, electrode angles. Your teacher will

demonstrate if required.

1. Obtain your MMA welding board, safety equipment (head

shield, gloves), material, and consumables (if necessary)from the store.

2. Position the plate on the bench so that a right handed

operator would weld across the body from left to right

(left hand opposite direction).

3. Deposit a weld bead along the plate length, maintaining

the angles as shown, and an arc gap of approximately 2-3mm.

4. Deposit additional runs parallel to the plate edge

approximately 10mm apart.

5. When the top surface of the plate has been covered, turn

the material over and repeat the exercise.


6. Evaluate the weld exercise and complete the proceduresheet.

7. Submit your completed weld and procedure sheet forassessment.

Economy

Materials and consumables are expensive. Use electrodes to 50 mm

maximum stub length.

Standards

Your work should have:

• uniform beads with consistent, even restarts, free from slagand spatter

+2

• bead height 3 -1 mm.

53



Procedure sheet 1 - Beads on plate - flat

Electrode

View A

11- Start,.

~B

A~

VlewB

Weld current dataRun 1

23

Electrode dataSize

Type Rutile

Brand Name

Electrode AnglesLead

60°' 80°Lateral

90°

Material data

TypeThickness

Low carbon steel

10mm

Assessment Complies

Workshop safety

54


Practical exercise 2 - Pad welds - flat

Aim

To deposit a pad weld on low carbon steel plate in the flat position.

Safety


• Use an approved shade 10 welding glass filter.

• Wear suitable protective clothing to stop ray burn.

• Always wear your safety glasses when removing slag.

Material

1 piece low carbon steel 75 x 10 x 225 mm

Consumables

Mild steel electrodes 4.0 mm E4112 or E4113 at approx. 165 amps

Instructions

Check the following points.

Setting of amperage and heat input, position of the plate on the

bench,' correct method of arc striking and arc length, correct

welding speed and travel, electrode angles. Your teacher will

demonstrate if necessary.

1. Obtain your MMAwelding board, safety equipment (head

shield, gloves), material, and consumables (if necessary)from the store.

2. Outline, with chalk, a rectangular shape 40 x 200 mm.

3. Position the plate on the bench.

4. Deposit a weld bead along the plate length, maintaining

the angles shown.

55

56



5. Remove all slag from each individual weld bead before

depositing subsequent runs. Each run must have a

staggered stop and restart.

6. Build up the pad to the required dimensions and on

completion, evaluate your weld with the given standards.

7. Fill in all the relevant information on the procedure sheet.

8. If it meets the standard, submit your work for assessment.

Economy

Use electrodes down to a stub length of SOmm maximum.

Standards


+2

• pad weld height 3 -1 rnm

• a maximum of four significant surface defects on a unit area

of 40 x 150 mm with the accumulative area not exceedingthe square of the plate thiclmess

• no adhering slag or spatter.


Procedure sheet i-Pad weld - flat

First run Subsequent runs

Weld current data

Run 123

~B

View A

View B

Electrode data

Size

TypeBrand Name

Electrode AnglesLead Lateral.. .

Material data

TypeThickness

Assessment

Low carbon steel

10mm

Complies

Workshop safety

57

Metals and Engineering Industry5.12AB Perform Routine Manua! Meta! Arc Welding

Section 4 - Fillet Weld Joint Terms andFaults

Aim

To learn the basic terminology (technical language) used to describe weld

positions, areas and locations of a welded joint, and common defects andtheir causes.

Activity



3. Ask for assistance if the information is not clear to you.

4. Complete the practical exercises at the end of the section.


Training Record.

6. On completion of this section you must attempt the test



Safety

Wear the right clothing to protect you against rays and hot metal

spatter.

59

Metals and Engineering Industry5.12AB Perform Routine Manual Metal Are Welding

Fillet weld joint terminology and faultsIt is important for you to know the terms used to describe fillet weld

joints and fillet weld defects so that you are able to talk to other trades

persons, clients and inspection authorities in an informed way. An

understanding of the technical terminology will also assist you to get the

most out of your training.

Fillet weld terminology

60

Positions of welds

Overhead

Lap weld-

Fillet weld

Weld names

[vertic.al

·.]1~1

\I.•..~-

r "--... .•

/ Vertical/

Horizontal

Single v.,~ butt weld

Intermittentfillet welds

'....- Plug weld/'-.--- Slot weld,/

-'--- Corner weld



Definition of a fillet weld

A fillet weld is a weld of approximately triangular cross-section which is

formed in the corner between surfaces of two components.

0--

Parts of a fillet weld Fillet weld contours and

measurements1.

Parent metal 7.Heat affected zone

2.

Reinforcement 8.Root

3.

Fusion zone 9.Penetration

4.

Weld face 10.Leg length

S.

Weld metal 11.Nominal throat thickness

6.

Toe 12.Throat thickness (convex fillet)

13.

Throat thickness (concave fillet)

Parts of a welded structure

Parent metal

Fillet weld

/penetration/fUSion. Weld face

61


Fillet weld dimensions

The size of a fillet weld is determined by the following dimensions. These

can easily be checked with a fillet gauge. Note that the strength of a welded

structure is determined by the type of metal, leg length and the effectivethroat thickness.

62

Fillet weld dimensions.

Fillet weld profiles

Weld Defects

Weld defects are either external or internal.

External defects can be detected by visually inspecting the finished weld

for plate misalignment, incomplete penetration, weld craters, blowholes,weld spatter and correct weld size.

Internal defects can only be detected by destructive or non destructive

testing, which may reveal slag inclusions, porosity, cracks and incomplete

fusion or incomplete penetration.


Common weld defects

The most common weld defects are:

Undercut

A sharp groove at the toe of a ron between the weld and the parent metal

or in previously deposited weld metal, due to welding. It may be continuousor intermittent.

This is caused by using the wrong electrode angle, excessive welding

current, incorrect operating technique or excessive arc length.

~Undercut~

Over roll (overlap)

Weld metal at the toe of a weld which covers the parent metal surface but

is not fused to it. It is caused by overflowing molten weld metal on the

surface of unmelted parent metal which leaves an unwelded area. This is

caused by using too Iowa current or too slow welding speed, or by using

too large an e!ectrode.

63


Misalignment

Misalignment is any variation from line or dimension of a welded joint. It

is caused by faulty setting up of job, distortion or lack of tack welds.

Misalignment

Incomplete penetration

Incomplete penetration may be classified as an internal or external weld

fault. Incomplete penetration is the failure of the weld metal to fill and

fuse the root of the joint. It is caused by faulty preparation of work, using

too Iowa welding current or poor operating technique.


Slag inclusions

Slag inclusions are non-metallic particles trapped in the weld metal. They

may weaken the weld joint. Inclusions result from not removing slag from

previous runs, using too Iowa current or using too long an arc length.

64

Inclusions

Metals and EngIneering Industry'


Porosity

Gaseous substances such as oxygen or nitrogen trapped in the weld metal

leave a cluster of small holes in the weld. It is caused using wet or damp

electrodes, welding over coated surfaces, over painted oily or greasy

surfaces or by using the wrong type of electrode.

Cracking

A variety of different types of cracks may occur in the welded area of

fabricated products. Identifying the type of crack helps to isolate the

possible causes. Causes are using wrong type of electrode, not applying

preheat to crack sensitive steel, using damp or wet electrodes or weldingover oil, grease or a plated metal surface .

..•.../I..

Lack of fusion

Incomplete fusion between weld metal and weld metal or weld metal and

parent metal is caused by not enough amperage, incorrect joint preparation

and incorrect welding technique.

Lack of fusion

65

66


Undersized and oversize welds

Welded joints are designed by structural engineers to carry loads safely.

The size and type of weld depends on its use. An undersized weld might

not be strong enough to carry the load it supports. A weld that is reinforced

(over welded) too much can make other sections of the work too rigid andcause them to crack or break.

You will be asked to weld to the designer's specification. For example

• a 6 mm fillet weld requires a 6mm leg length and a 4.2 mmthroat thickness

• a butt weld requires an even or slightly curved surface.

You may not be given the weld size for all jobs. If no weld size is specified,

deposit the weld in proportion to the plate thickness. For example:

a 10 mm plate requires a 10 mm weld thiclmess.

Butt welds should always be built up to the thickness of the parent metal.

Oversize

Correctsize

"\\Undersize

Weld assembly (undersized welds)



Workshop tests

These are only some of the tests which call be carried out to check the

weld quality.

Visual

Youcan do a visual check for external weld defects. Internal ones can't be

seen.

Fillet break

A fillet break shows satisfactory fusion, penetration, and inclusions or

porosity.

Summaryof weld defects and how to fix them

When preparing the plate, check that you have:

• correct edge preparation

• clean/smooth surfaces

• correct plate alignment.

When welding, check that you have:

• correct electrode

• correct current (amperage)

• correct speed of travel

67

68



• correct arc length

• correct operation (welder).

When checking the electrode for condition, check for damp or damagedelectrodes.

When inter-run cleaning remove all slag, rust, undercut, and excess weld

spatter before depositing the next pass.

78


5. 12AB Perform Routine Manual Metal Arc Welding

Practical exercise 3 - Fillet weld, singlerun - horizontal

Aim

To deposit 6 mm fillet weld in the horizontal position on 10 mm low

carbon steel plate.

Note

This is a skill practice exercise which is assessed. You must

reach the required standards to enable progression to the nextsection.

Safety

• Youmust wear eye protection .

• Make sure that the centre of the press ram and the highest

point of the exercise are in line when breaking welds.

Material

2 pieces low carbon steel 75 x 10 x 225.

Consumables

4 mm 4112 or 4113 electrodes at 160 to17S amps approximately.

Instructions

Your teacher will demonstrate.

1. Wire brush the material to remove surface rust and loose

scale.

2. Tack both ends of the plate to ensure metal to metalcontact.

3. Complete approximately half the weld, stop, remove slag,restart and finish the weld.

4. Remove all slag and spatter and submit the exercise for

visual inspection.



5. Break the weld and resubmit the exercise for internal

inspection.

6. Relocate the plates for further practice using all edges asshown.


8. Submit your work for assessment.

Economy

Consumables and materials are expensive. Relocate plates for maximum

use. See chart (on earlier page) for suggested plate positioning sequenceto obtain four or more fillet welds from one material unit. Use all electrodes

down to a maximum stub length of 50 mm and return unused material tothe store.

Standards


• correct alignment and assembly

• smooth regular weld contour

• angular distortion 0° to 5°

• a maximum of two significant weld defects per 250 mm of

weld length with an accumulative area of less than twice the

square of the plate thickness

• weld size 8 mm

• complete fusion for the length of the weld joint.

79


Procedure sheet 3 - Fillet weld, single run horizontal

View A ViewB

Weld current data123

Electrode dataSize

TypeBrand Name

Electrode classification

Angles Lead Lateral

80

Material data

Type Low carbon steelThickness 10 mm

Assessment

Alignment and assembly

Angular distortionSurface finish

Weld size

Surface defects

Complete fusion

Workshop Safety

No. of units completed to standard

Complies:

Complies:

Complies:

Complies:

Complies:

Complies:

Complies:

Complies:


Practical exercise 4 - Fillet weld, 3 run2 layer - horizontalAim

To use the fillet welding technique necessary to deposit an 8 mm three

run, two layer fillet weld to the requirements below.

Material

2 pieces low carbon steel 75 x 10 x 225

Consumables

Mild steel electrodes F4112 or E4113 at 160 to 175 amps approx.

Instructions


1. Wire brush or grind the weld fusion faces to remove therust and mill scale.

2. Tack both ends of the plate ensuring metal to metal

contact with no gap. Tack only on the ends or side to bewelded.

3. Complete approximately half the first run, stop, remove

slag, and examine the weld profile.

4. Finish the run and subsequent runs using the sequence

illustrated with at least one staggered stop and start perrun.

5. Submit the exercise for visual inspection then fracture

the weld and resubmit it for internal inspection.

6. Relocate the plates for further practice using all edges asshown.



81

82


Economy

Consumables and materials are expensive. Relocate plates for maximum

use. See chart (on earlier page) for suggested plate positioning sequenceto obtain four or more fillet welds from one material unit. Use all electrodes

down to a maximum stub length of 50 mm and return unused material tothe store.

Standards




• angular distortion 0° to 5°




• weld size 8 mm



5.12AB Petform Routine Manual Metal Are Welding

Procedure sheet 4 - Fillet weld, 3 run 2 layerhorizontal

Weld current data

Amperage used

Run 123

Electrode dataSize

TypeBrand NameElectrode classification

Angles Lead Lateral

Material data

TypeThickness

Assessment

Low carbon steel10 cm

Complies

Workshop safety Complies

83

84


Practical exercise 5 - Outside cornerfillet - horizontal

Aim

To deposit a multiple nm corner weld in the horizontal position using

fillet welding techniques to the requirements below.

Safety

Always wear safety glasses when chipping slag deposits away from theweld.

Materials

Material from the single or 3 run fillet (crucifixes) exercises or 2 pieces 25x lOx 225 111111 low carbon steel.

Consumables

Mild steel electrodes E4112 or E4113 , 3.25 m at approx 120-130 amps.

Mild steel electrodes E4112 or E4113 4.0 mm at approx 160-175 amps.

Instructions

Your teacher will demonstrate if required.

1. A-ssemble and tack plates using a suitable spacer to

maintain root gap.

2. Position the plates and deposit approximately 50 mm ofthe root run.

3. Examine the bead shape and penetration before

continuing the weld.

4. Completely fill the remainder of the weld using 3.2

diameter electrodes and a logical weld sequence.

5. Seal the reverse side with a 6 mm horizontal vertical fillet

weld.



6. Add additional plates as required and repeat the exercise.



Economy

Maximise the use of electrodes and return all unused material to the store.

Standards




• angular distortion 00 to 5°




• weld size 8 ~6mm

• complete fusion for the length of the weld joint

• full radius weld.

85



Procedure sheet 5 - Outside corner fillet horizontal

86

Weld current data

Amperage used

Material dataTypeThickness

Assessment

Workshop safety

Electrode dataSize


Angles Lead

Complies

Lateral



Practical exercise 6 - Fillet weld horizontal

Aim

To fillet weld 3 mm low carbon steel sheet assembled in the horizontal

position to the requirements below.

Safety

• Always use tongs to position tacked and welded work.

• Never leave hot work unattended in the workshop.

Material

6 pieces low carbon steel 50 x 3 x 225 mm.

Consumables



Instructions

Your teacher will demonstrate. Students must attend this demonstrationbefore beginning the exercise.

1. Clean, assemble and tack weld at three locations for each

joint.

2. Use E4112 electrodes and stop each run at least once.

3. Weld both sides of the horizontal fillet.

4. Repeat the exercise with E4113 electrodes.

87

88


Economy

Materials and consumables are expensive. use electrodes down to amaximum total length of 50 mm.

Standards

Your weld should have:



• angular distortion 00 to 50



square of the sheet thickness.

• weld size equal to the sheet thickness ::.~mill


note

Watch for these points.

Distortion tack at regular intervals, assembly and 'fit up' of

cornerjoint.



Procedure sheet 6 - Fillet weld - horizontal

Outsidecornerweld

Weld current data

Amperage used

Material data

TypeThickness

Assessment

Workshop safety

Electrode dataSize


Angles Lead

Complies

Lateral

89

90

Metals and Engineering Indust/)·5.12AB Perform Routine Manual Metal Arc Welding

Section 5 - Butt Weld Terminology andFaults

Aim

To learn the technical terms used for butt welds and to be able to identify

typical weld defects.

Activity

L Read and study the resource material following.


3. Ask for assistance if the information is not clear to you.


Training Record.

5. On completion of this section you must attempt the test



Safety

Wear the proper clothing to protect your skin and eyes.

Do not·try to take short cuts or risks


Butt weld terminology and faults

In this section you will learn about the different types of butt welds and

how to identify some of the faults which can occur in butt welds.

Butt welds are used to join metal products such as sheet, plate, rolled and

pressed sections. This type of joint has the advantage of giving high strength

without changing the profile of the structure.

Industrial uses for butt welds include:

• boiler and pressure vessel construction

• ship building

• earth moving equipment

• aircraft and submarines.

Butt weld joints can be designed for full penetration welding to give

maximum strength or for partial penetration welding in places where the

strength of the joint is not so important.

Weld preparation

Reinforcement

Weld components

Toe

Fusionzone

Root penetration

Parentmetal

Joint edges have to be prepared before plates are welded together. Joint or

edge preparation is essential for complete fusion and penetration.

91



\ ~ ; Root face: fa supporf fhe

~ _~_=========::~ fltst run of weld-JL- Roof gap: to allow complefeweld penetration

Weld preparations

On thick plate

use double V or U preparations. Less weld =less heat = less distortion.

U preparations

less weld metal than V preparations but aremore difficult to prepare.

V preparations

usually done by flame cutting or machining.

Single butt welds

back gouge and deposit a backing run formaximum strength.

Double butt welds and

need to balance joint to minimise distortion.multi-run fillet welds

{

.~

'j( )

~L

92

Plate thickness

DCJDCJ


Preparation types

There are several preparation types and details are given below.

Closed butt joint

This is used when the edges do not need preparing. They are placed

close together and single or double welded. The closed butt joint is

suitable for sheet up to 3 mm thick.

j~ -~-

Sr [ I~--~S

Open butt joint

This is used when the edges do not need preparing. They are separated

slightly to allow fusion of the full thickness of material. An open butt

joint is suitable for material up to 5 rom thick.

~mm ~ JI sr- -1L-'.S-2.S

Single V butt joint

This is commonly used on material up to 12 rom thick.o?2\/,---~?-~12m~

1.5mmm~JL f1.5 mm

93

94


S.12AI3 Perform Routine Manual Metal Are Welding

Double V butt joint

This is used on plate 12 mm to 38 mm in thickness when both sides

are welded.

Single bevel butt joint

Used only when one member of the joint can be prepared as in the case of

a T joint.

~5°~Minimum",

15M~imu~JL

Single U butt joint

The single U butt is used as an alternative to single V butt joint.

~inimumr-\ 1-'

\ I r Radius5mm Minimum\1 ~ __ t

;'-1=V;r- -~-UPto 25mm. II t3 mm Maximum--i+-- 3 mm J

Metals and Engineering Indnstry5.12AB Perform Routine Manual Metal Arc Welding

Double U butt joint

This is used on material over 2S mm thick where welding can bedone from both sides.

iO~ Minimum

___ "/_1_r -===RadiUS 5 mmMitmLl====---"~L ;Up to 25mm

3 mm Maximum L 3 mm r

When you need to butt weld two sections of different thickness, you should

taper the thicker one to match the other. The length of the tapered sectionshould be at least three times the difference in the thickness between the

plates. This type of butt weld is used to join dished ends to pressure vessels.

Uneven section" butt joint

95


5.12AB Periorm Routine Manual Metal Arc Welding

Weld defects

Common weld defects are detailed below.

Excesspenetration

Definition Too much weld metal extending through the root of the weld .

•••••• --- u u'-etration

Causes are:

• incorrect preparation

• amperage too high

• incorrect welding technique.


Definition Failure of the weld metal to extend into the root of a joint.

7

S'

Causes are:

~.....:-..;:,." " .;:..::- :'-':.~"

",:.,

---------Incomplete penetration

~., .

..•- .

•••••• M'.'1·••·-'··-

// .• "_;1

96

• incorrect preparation

• amperage too low

• arc length too long.


5.12ABPerform Routine Manual Metal Arc Welding

Lack of fusion

Definition Incomplete fusion between weld metal and weld metal or weld

metal and parent metaL

)

Lack of fusion

Causes are:

• not enough amperage

• incorrect joint preparation


Inclusions

Definition Slag or other foreign matter trapped during welding.

Causes are:

• faulty joint preparation

• not enough amperage

• poor cleaning of prior runs.

97

98



Porosity

Definition A group of gas holes in the weld metal.

Porosity ~., '. ..,":.'? O';'~<".. ,':. '~'...

• ~~t'

Causes are:

• damp or old electrodes

• composition of parent metal

• incorrect electrode type.

Cracking

Definition Discontinuity produced from tearing of the weld metal while

in a plastic condition when hot or a fracture when cold.

HAZ cracking

Causes are:

• insufficient weld deposit

• insufficient pre-heat

• incorrect electrode.


Undercut

Definition A groove or channel in the parent metal at the toe of the weld.

Causes are:

• too much current

• welding too fast

Undercut


Overrall

Definition A section of unfused metal extending past the toe of the weld.

~verrOI1~w/ove~OIl

Causes are:

• electrode too large

• welding speed too slow

• incorrect electrode angle.

99


Misalignment

Definition Any variation from line or dimension of a welded joint.

Misalignment

Causes are:

• incorrect weld procedure

• careless preparation

• too few tack welds.

Incompletely filled joint

~ ~comPletelY filled joint

~.=- -~~~----(

100

Causes are:

• not enough weld metal

• welding too fast

• too few beads.



The principle of expansion andcontraction in a metal

Metals expand when heated and contract when cooled. For example, a

piece of low carbon steel, if not restrained in any way, will increase its

dimensions in all directions for every degree Celsius the temperature rises.

On cooling, the steel will return to its original size.

Angular distortion

There is distortion when unequal contractional forces cause angular changein the parent metal position.

j Outward movement~ caused by expansion

i

Inward movement

caused by contraction

Transverse distortion by butt weld

6 4 2 '3 5 7

Tack weld sequence

101

108

Metals and Engineering lndustryS.12AB Perfonn Routine Manual Metal Arc Welding

Practical exercise 7 - Butt weld, flatsheet steel

Aim

To deposit single run butt welds in the flat position on 3.0 mm low carbonsheet steel.

Materials

4 pieces 40 x 3.0 x 150 mm low carbon flat bar.

Consumables



Instructions


1. Assemble and tack weld sheets using the sequenceillustrated.

2. Position the plates with a sligh t slope and weld

approximately 50 mm of the joint.

3. Examine weld profile and penetration before completingthe weld.

4. Complete the weld and submit for inspection.

5. Cut sheets and relocate for further practice as illustrated.




Economy

Cut and relocate sheets for maximum use. Return all unused material to

the store.

Standards




• weld penetration for a minimum of 20% of the weld length

• angular distortion 00 to 50



square of the plate thickness.

109


S.12AB Perlorm Routine Manual Metal Arc Welding

Procedure sheet 7 - Butt weld, flat sheet steel

Weld current data

Amperage used

1.6mm 3.0mm

Electrode data

Size

TypeBrand nameElectrode classification

Material data

Type

Thickness

Assessment

Workshop safety

110

Angles Lead Lateral

routine manual metal arc welding

Documents