BOC Smootharc MMA 170 User manual

Smootharc
MMA 170
OPERATING MANUAL

2
Welcome to a better way of welding
Congratulations on puchasing the Smootharc MMA 170
welding machine.
The products in BOC's manual metal arc range perform with reliability and have
the backing of one of South Pacific's leading welding suppliers.
This operating manual provides the basic knowledge required for MMA and
DC TIG welding, as well as highlighting important areas of how to operate the
Smootharc MMA 170 welding machine.
BOC equipment and technical support is available through our national BOC
Customer Service Centre or contact your local Gas & Gear outlet.
Important Notice: This document has been prepared by BOC Limited ABN 95 000 029 729 ('BOC'),
as general information and does not contain and is not to be taken as containing any specific instructions.
The document has been prepared in good faith and is professional opinion only. Information in this document
has been derived from third parties, and though BOC believes it to be reliable as at the time of printing, BOC
makes no representation or warranty as to the accuracy, reliability or completeness of information in this
document and does not assume any responsibility for updating any information or correcting any error or
omission which may become apparent after the document has been issued. Neither BOC nor any of its agents
has independently verified the accuracy of the information contained in this document.The information in this
document is commercial in confidence and is not to be reproduced.The recipient acknowledges and agrees
that it must make its own independent investigation and should consider seeking appropriate professional
recommendation in reviewing and evaluating the information.This document does not take into account the
particular circumstances of the recipient and the recipient should not rely on this document in making any
decisions, including but not limited to business, safety or other operations decisions.
Except insofar as liability under any statute cannot be excluded, BOC and its affiliates, directors, employees,
contractors and consultants do not accept any liability (whether arising in contract, tort or otherwise) for any
error or omission in this document or for any resulting loss or damage (whether direct, indirect, consequential
or otherwise) suffered by the recipient of this document or any other person relying on the information
contained herein.The recipient agrees that it shall not seek to sue or hold BOC or their respective agents liable
in any such respect for the provision of this document or any other information.

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Welcome to a better way of welding 2
1.0 Recommended Safety Precautions 4
1.1 Health Hazard Information 4
1.2 Personal Protection 4
1.3 Electrical Shock 6
1.4 User Responsibility 6
2.0 Manual Metal Arc Welding Process
(MMAW) 7
2.1 Introduction 7
2.2 Process 7
2.3 Welding Machine 7
2.4 Welding Technique 8
2.5 Electrode Selection 8
2.6 Types of Joints 11
2.7 Fillet Welds 12
2.8 Typical Defects Due to Faulty Technique 15
3.0 Gas Tungsten Arc Welding (GTAW/TIG) 17
3.1 Introduction 17
3.2 Process 17
3.3 Process Variables 18
3.4 Welding Techniques 19
3.5 Shielding Gas Selection 20
3.6 Consumable Selection 21
3.7 Typical Welding Joints for Gas Tungsten
Arc Welding 25
4.0 Machine Specifications and Contents 28
4.1 Operating Controls 28
5.0 Operating Functions 29
5.1 Welding selections 29
5.2 Earthing 29
6.0 Technical Specifications 30
7.0 Periodic Maintenance 31
7.1 Daily Maintenance 31
7.2 Troubleshooting 31
8.0 Terms of Warranty 32
8.1 Terms of Warranty 32
8.2 Limitations on Warranty 32
8.3 Warranty Repairs 32
9.0 Recommended Safety Guidelines 33
Contents

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1.1 Health Hazard Information
The actual process of welding is one that
can cause a variety of hazards.
All appropriate safety equipment should be
worn at all times, i.e. headwear, respiratory,
hand and body protection. Electrical equipment
should be used in accordance with the
manufacturer’s recommendations.
Eyes:
The process produces ultra violet rays that
can injure and cause permanent damage.
Fumes can cause irritation.
Skin:
Arc rays are dangerous to uncovered skin.
Inhalation:
Welding fumes and gases are dangerous to
the health of the operator and to those in
close proximity.The aggravation of pre-existing
respiratory or allergic conditions may occur in
some workers. Excessive exposure may cause
conditions such as nausea, dizziness, dryness
and irritation of eyes, nose and throat.
1.2 Personal Protection
Respiratory
Confined space welding should be carried out
with the aid of a fume respirator or air supplied
respirator as per AS/NZS 1715 and AS/NZS
1716 Standards.
•Youmustalwayshaveenoughventilationin
confined spaces. Be alert to this at all times.
•Keepyourheadoutofthefumesrisingfrom
the arc.
•Fumesfromtheweldingofsomemetalscould
have an adverse effect on your health. Don’t
breathe them in. If you are welding on material
such as stainless steel, nickel, nickel alloys
or galvanised steel, further precautions are
necessary.
•Weararespiratorwhennaturalorforced
ventilation is not good enough.
Eye protection
A welding helmet with the appropriate welding
filter lens for the operation must be worn at all
times in the work environment.The welding arc
and the reflecting arc flash gives out ultraviolet
and infrared rays. Protective welding screen and
goggles should be provided for others working
in the same area.
Clothing
Suitable clothing must be worn to prevent
excessive exposure to UV radiation and
sparks.An adjustable helmet, flameproof loose
fitting cotton clothing buttoned to the neck,
protective leather gloves, spats, apron and steel
capped safety boots are highly recommended.
Recommended filter shades for
arc welding
Less than 150 amps Shade 10*
150 to 250 amps Shade 11*
250 to 300 amps Shade 12
300 to 350 amps Shade 13
Over 350 amps Shade 14
*Use one shade darker for aluminium
1.0 Recommended Safety Precautions

5
Cylinder Safety
1Cylinder valve hand-wheel
2Back-plug
3Bursting disc
Backview of typical cylinder valve
1
2
3
Operator wearing personal
protective equipment (PPE)
in safe position
Ten Points about Cylinder Safety
1Read labels and Material Safety Data Sheet
(MSDS) before use.
2Store upright and use in well ventilated,
secure areas away from pedestrian or vehicle
thoroughfare.
3Guard cylinders against being knocked
violently or being allowed to fall.
4Wear safety shoes, glasses and gloves when
handling and connecting cylinders.
5Always move cylinders securely with an
appropriate trolley.Take care not to turn the
valve on when moving a cylinder.
6Keepinacool,wellventilatedarea,away
from heat sources, sources of ignition and
combustible materials, especially flammable
gases.
7Keepfullandemptycylindersseparate.
8Keepammonia-basedleakdetection
solutions, oil and grease away from cylinders
and valves.
9Never use force when opening or closing
valves.
10 Don’t repaint or disguise markings and
damage. If damaged, return cylinders to BOC
immediately.
Cylinder Valve Safety
When working with cylinders or operating
cylinder valves, ensure that you wear
appropriate protective clothing – gloves, boots
and safety glasses.
When moving cylinders, ensure that the valve is
not accidentally opened in transit.
Before operating a cylinder valve:
•Ensurethatthesystemyouareconnecting
the cylinder into is suitable for the gas and
pressure involved.
•Ensurethatanyaccessories(suchashoses
attached to the cylinder valve, or the system
being connected to) are securely connected.
A hose, for example, can potentially flail
around dangerously if it is accidentally
pressurised when not restrained at both ends.
•Standtothesideofthecylindersothat
neither you nor anyone else is in line with the
back of the cylinder valve. This is in case a
back-plug is loose or a bursting disc vents. The
correct stance is shown in the diagram above.
When operating the cylinder valve:
•Openitbyhandbyturningthevalvehand-wheel
anti-clockwise. Use only reasonable force.
•Ensurethatnogasisleakingfromthecylinder
valve connection or the system to which the
cylinder is connected. DO NOT use ammonia-
based leak detection fluid as this can damage

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the valve. Approved leak detection fluid, can be
obtained from a BOC Gas & Gear™centre.
•Whennishedwiththecylinder,closethe
cylinder valve by hand by turning the valve
hand-wheel in a clockwise direction. Use only
reasonable force.
Remember NEVER tamper with the valve.
If you suspect the valve is damaged, DO
NOT use it. Report the issue to BOC and
arrange for the cylinder to be returned
to BOC.
1.3 Electrical Shock
•Nevertouch‘live’electricalparts.
•Alwaysrepairorreplacewornor
damaged parts.
•Disconnectpowersourcebefore
performing any maintenance or service.
•Earthallworkmaterials.
•Neverworkinmoistordampareas.
Avoid electric shock by:
•Wearingdryinsulatedboots
•Wearingdryleathergloves
•Neverchangingelectrodeswithbare
hands or wet gloves
•Nevercoolingelectrodeholdersinwater
•Workingonadryinsulatedoorwhere
possible
•Neverholdtheelectrodeandholder
under your arm.
1.4 User Responsibility
•ReadtheOperatingManualpriorto
installation of this machine.
•Unauthorisedrepairstothisequipmentmay
endanger the technician and operator and will
void your warranty. Only qualified personnel
approved by BOC should perform repairs.
•Alwaysdisconnectmainspowerbefore
investigating equipment malfunctions.
•Partsthatarebroken,damaged,missingor
worn should be replaced immediately.
•Equipmentshouldbecleanedperiodically.
BOC stock a huge range of personal protective
equipment.This combined with BOC’s extensive
Gas and Gear network ensures fast, reliable
service throughout the South Pacific.
PLEASE NOTE that under no circumstances
should any equipment or parts be altered
or changed in any way from the standard
specification without written permission
given by BOC.To do so, will void the
Equipment Warranty.
Further information can be obtained
from Welding Institute of Australia
(WTIA) Technical Note No.7
‘Health and Safety Welding’
Published by WTIA,
PO Box 6165 Silverwater NSW 2128
Phone [phone].

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2.1 Introduction
Arc welding, although in the past principally
the tool of tradesmen and fabricators, has
in recent years found increasing usage with
small workshops, farmers, handyman-hobbyists
amongst others.This has been brought about
by the introduction of low-cost portable arc
welding machines and the ready availability
of small diameter electrodes and thinner
section construction materials. Provided the
operator is familiar with the basic principles and
techniques, arc welding can be a fast, efficient
and safe method of joining metals.
The main purpose of this manual is to help
the welder with limited experience to obtain
a better understanding of the process, and to
acquire a reasonable degree of proficiency in
the least possible time. Even welders with some
experience will benefit from the information in
this manual.
2.2 Process
Manual Metal Arc welding is the process of
joining metals where an electric arc is struck
between the metal to be welded (parent metal)
and a flux-coated filler wire (the electrode).
The heat of the arc melts the parent metal and
the electrode which mix together to form, on
cooling, a continuous solid mass.
Weld Metal
Slag
Core Wire
Flux Covering
Arc
Weld Pool
Workpiece
Before arc welding can be carried out, a suitable
power source is required.Two types of power
sources may be used for arc welding, direct
current (DC) or alternating current (AC).
The essential difference between these two
power sources is that, in the case of DC, the
current remains constant in magnitude and
flows in the same direction. Similarly, the voltage
in the circuit remains constant in magnitude and
polarity (i.e. positive or negative).
In the case of AC however, the current flows
first in one direction and then the other.
Similarly, the voltage in the circuit changes from
positive to negative with changes in direction
of current flow.This complete reversal is called
a‘halfcycle’andrepeatsaslongasthecurrent
flows.The rate of change of direction of current
owisknownasthe‘frequency’ofthesupply
and is measured by the number of cycles
completed per second.The standard frequency
of the AC supply in Australia is 50 Hz (Hertz).
2.3 Welding Machine
The most important consideration when
contemplating the use of arc welding for
the first time is the purchase of a suitable
welding machine.
BOC supplies a popular range of arc welding
machines. Machines range from small portable
welders that operate from standard 240 Volt
household power to heavy-duty welders used
by the largest steel fabricators.
2.0 Manual Metal Arc Welding
Process (MMAW)

8
Lift-TIG
Basic Welding Machine and Cables
The choice of welding machine is based mostly
on the following factors:
•primaryvoltage,e.g.240Voltor380Volt
•outputamperagerequired,e.g.140amps
•outputrequired,e.g.ACorDC+/-
•dutycyclerequired,e.g.35%@140amps
•methodofcooling,e.g.air-cooledor
oil-cooled method of output amperage
control, e.g. tapped secondary lugs
•orinnitelyvariablecontrol.
For example, the Smootharc 170 connects to 240
Volt supply (15 amps Input), has an output of 170
ampsDC@50%dutycycle.
Having decided on a welding machine, appropriate
accessories are required.These are items such as
welding cables, clamps, electrode holder, chipping
hammer, helmet, shaded and clear lenses, scull cap,
gloves and other personal protective equipment.
BOC stocks a huge range of personal protective
equipment.This combined with BOC’s
extensive network ensures fast reliable service
throughout the South Pacific.
2.4 Welding Technique
Successful welding depends on the
following factors:
•selectionofthecorrectelectrode
•selectionofthecorrectsizeofthe
electrode for the job
•correctweldingcurrent
•correctarclength
•correctangleofelectrodetowork
•correcttravelspeed
•correctpreparationofworktobewelded.
2.5 Electrode Selection
As a general rule the selection of an electrode
is straight forward, in that it is only a matter of
selecting an electrode of similar composition
to the parent metal. It will be found, however,
that for some metals there is a choice of several
electrodes, each of which has particular properties
to suit specific classes of work. Often, one
electrode in the group will be more suitable for
general applications due to its all round qualities.
The table (page 9) shows just a few of the wide
range of electrodes available from BOC with
their typical areas of application.
For example, the average welder will carry out
most fabrication using mild steel and for this
material has a choice of various standard BOC
electrodes, each of which will have qualities
suited to particular tasks. For general mild steel
work, however, BOC Smootharc 13 electrodes
will handle virtually all applications. BOC
Smootharc 13 is suitable for welding mild steel in
all positions using AC or DC power sources. Its
easy-striking characteristics and the tolerance it
has for work where fit-up and plate surfaces are
not considered good, make it the most attractive
electrode of its class. Continuous development
and improvement of BOC Smootharc 13 has
provided in-built operating qualities which
appeals to the beginner and experienced
operator alike. For further recommendations
on the selection of electrodes for specific
applications, see table page 9.

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Electrodes andTypical Applications
Name AWS Classification Application
BOC Smootharc 13 E6013 A premium quality electrode for general structural and
sheet metal work in all positions including vertical down
using low carbon steels
BOC Smootharc 24 E7024 An iron powder electrode for high speed welding for
H-V fillets and flat butt joints. Medium to heavy structural
applications in low carbon steels
BOC Smootharc 18 E7018-1 A premium quality all positional hydrogen controlled
electrode for carbon steels in pressure vessel applications
and where high integrity welding is required and for
free-machining steels containing sulphur
BOC Smootharc S 308L E308L Rutile basic coated low carbon electrodes for
welding austenitic stainless steel and difficult to weld
material
BOC Smootharc S 316L E316L
BOC Smootharc S 309L E309L Rutile basic coated low carbon electrode for welding
mild steel to stainless steel and difficult to weld material
Electrode Size
The size of the electrode is generally dependent
on the thickness of the section being welded,
and the larger the section the larger the
electrode required. In the case of light sheet
the electrode size used is generally slightly
larger than the work being welded.This means
that if 1.5 mm sheet is being welded, 2.0 mm
diameter electrode is the recommended size.
The following table gives the recommended
maximum size of electrodes that may be used
for various thicknesses of section.
Recommended Electrode Sizes
Average Thickness
of Plate or Section
Maximum Recommended
Electrode Diameter
≤1.5 mm 2.0 mm
1.5–2.0 mm 2.5 mm
2.0–5.0 mm 3.15 mm
5.0–8.0 mm 4.0 mm
≥8.0 mm 5.0 mm
Welding Current
Correct current selection for a particular
job is an important factor in arc welding.
With the current set too low, difficulty is
experienced in striking and maintaining a stable
arc.The electrode tends to stick to the work,
penetration is poor and beads with a distinct
rounded profile will be deposited.
Excessive current is accompanied by overheating
of the electrode. It will cause undercut, burning
through of the material, and give excessive
spatter. Normal current for a particular job may
be considered as the maximum which can be
used without burning through the work, over-
heating the electrode or producing a rough
spattered surface, i.e. the current in the middle
of the range specified on the electrode package
is considered to be the optimum.
In the case of welding machines with separate
terminals for different size electrodes, ensure
that the welding lead is connected to the
correct terminal for the size electrode being
used. When using machines with adjustable
current, set on the current range specified.

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The limits of this range should not normally
be exceeded.
The following table shows the current
ranges generally recommended for BOC
Smootharc 13.
Generally Recommended Current Range
for BOC Smootharc 13
Size of Electrode (mm) Current Range (Amp)
2.5 60–95
3.2 110–130
4.0 140–165
5.0 170–260
Arc Length
To start the arc, the electrode should be gently
scraped on the work until the arc is established.
There is a simple rule for the proper arc length;
it should be the shortest arc that gives a good
surface to the weld.An arc too long reduces
penetration, produces spatter and gives a rough
surface finish to the weld.An excessively short
arc will cause sticking of the electrode and rough
deposits that are associated with slag inclusions.
For downhand welding, it will be found that an arc
length not greater than the diameter of the core
wire will be most satisfactory. Overhead welding
requires a very short arc, so that a minimum of
metal will be lost. Certain BOC electrodes have
beenspeciallydesignedfor‘touch’welding.These
electrodes may be dragged along the work and a
perfectly sound weld is produced.
Electrode Angle
The angle which the electrode makes with the
work is important to ensure a smooth, even
transfer of metal.The recommended angles
for use in the various welding positions are
covered later.
Correct Travel Speed
The electrode should be moved along in the
direction of the joint being welded at a speed
that will give the size of run required.At the
same time the electrode is fed downwards
to keep the correct arc length at all times.
As a guide for general applications the table
below gives recommended run lengths for
the downhand position.
Correct travel speed for normal welding
applications varies between approximately
125–375 mm per minute, depending on
electrode size, size of run required and the
amperage used.
Excessive travel speeds lead to poor fusion, lack
of penetration, etc.Whilst too slow a rate of
travel will frequently lead to arc instability, slag
inclusions and poor mechanical properties.
Run Length per Electrode –
BOC Smootharc 13
Electrode
Size (mm)
Electrode
Length (mm)
Run Length (mm)
Minimum Maximum
4.0 350 175 300
3.2 350 125 225
2.5 350 100 225
Correct Work Preparation
The method of preparation of components to
be welded will depend on equipment available
and relative costs. Methods may include
sawing, punching, shearing, lathe cut-offs, flame
cutting and others. In all cases edges should be
prepared for the joints that suit the application.
The following section describes the various
joint types and areas of application.

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2.6 Types of Joints
Butt Welds
A butt weld is a weld made between two
plates so as to give continuity of section. Close
attention must be paid to detail in a butt weld
to ensure that the maximum strength of the
weld is developed. Failure to properly prepare
the edges may lead to the production of faulty
welds, as correct manipulation of the electrode
is impeded.
Butt Welding
WELD FACE
FACE REINFORCEMENT
ROOT FACE ROOT GAP
Two terms relating to the preparation of butt
welds require explanation at this stage.
They are:
•RootFace:theproportionoftheprepared
edge that has not been bevelled.
•RootGap:theseparationbetweenroot
faces of the parts to be joined.
Various types of butt welds are in common
use and their suitability for different thickness
of steel are described as follows:
Square Butt Weld
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
The edges are not prepared but
are separated slightly to allow
fusion through the full thickness
of the steel. Suitable for plate up
to 6 mm in thickness.
Single‘V’ButtWeld
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
This is commonly used for plate up
to 16mm in thickness and on metal
of greater thickness where access
is available from only one side.
Double‘V’ButtWeld
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
Used on plate of 12 mm and over
in thickness when welding can
be applied from both sides. It
allows faster welding and greater
economy of electrodes than a
single‘V’preparationonthesame
thickness of steel and also has less
of a tendency to distortion as weld
contraction can be equalised.
Butt Weld with Backing Material
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
Whensquarebuttweldsorsingle‘V’
welds cannot be welded from both
sides it is desirable to use a backing
bar to ensure complete fusion.
Single‘U’ButtWeld
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
Used on thick plates an alternative
toasingle‘V’preparation.Ithas
advantages as regards speed
of welding. It takes less weld
metalthanasingle‘V’,thereis
less contraction and therefore a
lessened tendency to distortion.
Preparation is more expensive
thaninthecaseofa‘V’,as
machining is required.The type of
joint is most suitable for material
over 40mm in thickness.
Double‘U’ButtWeld
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
For use on thick plate that is
accessible for welding from both
sides. For a given thickness it is
faster, needs less weld metal and
causes less distortion than a single
‘U’preparation.
Horizontal Butt Weld
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
The lower member in this case is
bevelled to approximately 15° and
the upper member 45°, making
an included angle of 60°.This
preparation provides a ledge on
the lower member, which tends
to retain the molten metal.

12
General notes on Butt Welds
The first run in a prepared butt weld should
be deposited with an electrode not larger than
4.0 mm.The angle of the electrode for the
various runs in a butt weld is shown.
It is necessary to maintain the root gap by
tacking at intervals or by other means, as it will
tend to close during welding.
Allsingle‘V’,single‘U’andsquarebuttweldsshould
have a backing run deposited on the underside of
thejoint;otherwise50%maybedeductedfromthe
permissible working stress of the joint.
Before proceeding with a run on the underside
of a weld it is necessary to remove any surplus
metal or under penetration that is evident on
that side of the joint.
Butt welds should be overfilled to a certain
extent by building up the weld until it is above
the surface of the plate. Excessive build-up,
however, should be avoided.
In multi-run butt welds it is necessary to
remove all slag, and surplus weld metal before
a start is made on additional runs; this is
particularly important with the first run, which
tends to form sharp corners that cannot be
penetrated with subsequent runs. Electrodes
larger than 4.0 mm are not generally used for
vertical or overhead butt welds.
The diagrams following indicate the correct
procedure for welding thick plate when using
multiple runs.
Electrode Angle for 1st and 2nd Layers
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
Electrode Angle for Subsequent Layers
WELD BEADS
LAYERS
70˚ - 85˚
WELD BEADS
LAYERS
ELECTRODE
SLAG
WELD POOL
WELD METAL
ARC
DIRECTION OF WELDING
Welding Progression Angle
Weld Metal
Slag
Electrode
Arc
Weld Pool
Workpiece
70–85˚
Direction of Welding
2.7 Fillet Welds
A fillet weld is approximately triangular in
section, joining two surfaces not in the same
plane and forming a lap joint, tee joint or
corner joint. Joints made with fillet welds do
not require extensive edge preparation, as is
the case with butt welded joints, since the weld
does not necessarily penetrate the full thickness
of either member. It is important that the parts
to be joined be clean, close fitting, and that all
the edges on which welding is to be carried
out are square. On sheared plate it is advisable
toentirelyremoveany‘falsecut’ontheedges
prior to welding. Fillet welds are used in the
following types of joints:

13
‘T’Joints
A fillet weld may be placed either
on one or both sides, depending
on the requirements of the work.
The weld metal should fuse into
or penetrate the corner formed
between the two members.
Where possible the joint should
be placed in such a position as to
forma“Natural‘V’llet”since
this is the easiest and fastest
method of fillet welding.
Lap Joints
In this case, a fillet weld may be
placed either on one or both
sides of the joint, depending on
accessibility and the requirements
of the joint. However, lap joints,
where only one weld is accessible,
should be avoided where possible
and must never constitute
the joints of tanks or other
fabrications where corrosion is
likely to occur behind the lapped
plates. In applying fillet welds to
lapped joints it is important that
the amount of overlap of the
plates be not less than five times
the thickness of the thinner part.
Where it is required to preserve
the outside face or contour
of a structure, one plate may
be joggled.
Corner Joints
The members are fitted as
shown,leavinga‘V’-shaped
groove in which a fillet weld
is deposited. Fusion should be
complete for the full thickness
of the metal. In practice it is
generally necessary to have a
gap or a slight overlap on the
corner.The use of a 1.0–2.5 mm
gap has the advantage of assisting
penetration at the root, although
setting up is a problem.The
provision of an overlap largely
overcomes the problem of
setting up, but prevents complete
penetration at the root and
should therefore be kept to a
minimum, i.e. 1.0–2.5 mm.
The following terms and definitions are
important in specifying and describing
fillet welds.
Leg Length
A fusion face of a fillet weld, as shown below.
All specifications for fillet weld sizes are based
on leg length.
Throat Thickness
A measurement taken through the centre of a
weld from the root to the face, along the line
that bisects the angle formed by the members
to be joined.
Effective throat thickness is a measurement
on which the strength of a weld is calculated.
The effective throat thickness is based on a
mitre fillet (concave Fillet Weld), which has a
throatthicknessequalto70%oftheleglength.
For example, in the case of a 20 mm fillet, the
effective throat thickness will be 14 mm.
Convex Fillet Weld
A fillet weld in which the contour of the weld
metal lies outside a straight line joining the toes
of the weld.A convex fillet weld of specified leg
length has a throat thickness in excess of the
effective measurement.
Convex Fillet Weld
ACTUAL THROAT
EFFECTIVE THROAT
CONVEXITY
LEG
LENGH
THEORETICAL THROAT
CONCAVITY
ACTUAL THROAT
AND EFFECTIVE
THROAT
LEG
SIZE
SIZE LEG
THEORETICAL THROAT

14
Concave Fillet Weld
A fillet in which the contour of the weld is
below a straight line joining the toes of the
weld. It should be noted that a concave fillet
weld of a specified leg length has a throat
thickness less than the effective throat
thickness for that size fillet.This means that
when a concave fillet weld is used, the throat
thickness must not be less than the effective
measurement.This entails an increase in leg
length beyond the specified measurement.
Concave Fillet Weld
ACTUAL THROAT
EFFECTIVE THROAT
CONVEXITY
LEG
LENGH
THEORETICAL THROAT
CONCAVITY
ACTUAL THROAT
AND EFFECTIVE
THROAT
LEG
SIZE
SIZE LEG
THEORETICAL THROAT
The size of a fillet weld is affected by the
electrode size, welding speed or run length,
welding current and electrode angle.Welding
speed and run length have an important effect
on the size and shape of the fillet, and on the
tendency to undercut.
Insufficient speed causes the molten metal
to pile up behind the arc and eventually to
collapse. Conversely, excessive speed will
produce a narrow irregular run having poor
penetration, and where larger electrodes
and high currents are used, undercut is
likely to occur.
Fillet Weld Data
Nominal
Fillet Size
(mm)
Minimum
Throat
Thickness
(mm)
Plate
Thickness
(mm)
Electrode
Size (mm)
5.0 3.5 5.0–6.3 3.2
6.3 4.5 6.3–12 4.0
8.0 5.5 8.0–12 & over 4.0
10.0 7.0 10 & over 4.0
Selection of welding current is important. If it is
too high the weld surface will be flattened, and
undercut accompanied by excessive spatter is
likely to occur.Alternatively, a current which is
too low will produce a rounded narrow bead
with poor penetration at the root.The first run
in the corner of a joint requires a suitably high
current to achieve maximum penetration at
the root.A short arc length is recommended
for fillet welding.The maximum size fillet which
should be attempted with one pass of a large
electrode is 8.0 mm. Efforts to obtain larger leg
lengths usually result in collapse of the metal
at the vertical plate and serious undercutting.
For large leg lengths multiple run fillets are
necessary.These are built up as shown below.
The angle of the electrode for various runs in
a downhand fillet weld is shown below.
Recommended Electrode Angles for
Fillet Welds
1st Run 2nd Run
3rd Run Multi-run Fillet

15
Multi-run horizontal fillets have each run made
using the same run lengths (run length per
electrode table). Each run is made in the same
direction, and care should be taken with the
shape of each, so that it has equal leg lengths
and the contour of the completed fillet weld
is slightly convex with no hollows in the face.
Vertical fillet welds can be carried out using
the upwards or downwards technique.The
characteristics of each are: upwards – current
used is low, penetration is good, surface is
slightly convex and irregular. For multiple run
fillets large single pass weaving runs can be
used. Downwards – current used is medium,
penetration is poor, each run is small, concave
and smooth (only BOC Smootharc 13 is
suitable for this position).
The downwards method should be used for
making welds on thin material only. Electrodes
larger than 4.0 mm are not recommended for
vertical down welding. All strength joints in
vertical plates 10.0 mm thick or more should
be welded using the upward technique.This
method is used because of its good penetration
and weld metal quality.The first run of a vertical
up fillet weld should be a straight sealing run
made with 3.15 mm or 4.0 mm diameter
electrode. Subsequent runs for large fillets may
be either numerous straight runs or several
wide weaving runs.
Correct selection of electrodes is important
for vertical welding.
In overhead fillet welds, careful attention to
technique is necessary to obtain a sound weld
of good profile. Medium current is required for
best results. High current will cause undercutting
and bad shape of the weld, while low current will
cause slag inclusions.To produce a weld having
good penetration and of good profile, a short
arc length is necessary. Angle of electrode for
overhead fillets is illustrated above.
Recommended Angles for Overhead
Fillet Welds
30˚
15˚ 45˚
2.8 Typical Defects Due to
Faulty Technique
Shielded metal arc welding, like other welding
processes, has welding procedure problems
that may develop which can cause defects
in the weld. Some defects are caused by
problems with the materials. Other welding
problems may not be foreseeable and may
require immediate corrective action.A poor
welding technique and improper choice of
welding parameters can cause weld defects.
Defects that can occur when using the shielded
metal arc welding process are slag inclusions,
wagon tracks, porosity, wormhole porosity,
undercutting, lack of fusion, overlapping, burn
through, arc strikes, craters, and excessive
weld spatter. Many of these welding technique
problems weaken the weld and can cause
cracking. Other problems that can occur which
can reduce the quality of the weld are arc blow,
finger nailing, and improper electrode coating
moisture contents.
Defects caused by welding technique
Slag Inclusions
SLAG INCLUSIONS

16
Slag inclusions occur when slag particles are
trapped inside the weld metal which produces a
weaker weld.These can be caused by:
•erratictravelspeed
•toowideaweavingmotion
•slagleftonthepreviousweldpass
•toolargeanelectrodebeingused
•lettingslagrunaheadofthearc.
This defect can be prevented by:
•auniformtravelspeed
•atighterweavingmotion
•completeslagremovalbeforewelding
•usingasmallerelectrode
•keepingtheslagbehindthearcwhichisdone
by shortening the arc, increasing the travel speed,
or changing the electrode angle.
Undercutting
UNDERCUTTING
Undercutting is a groove melted in the base
metal next to the toe or root of a weld that
is not filled by the weld metal. Undercutting
causes a weaker joint and it can cause cracking.
This defect is caused by:
•excessiveweldingcurrent
•toolonganarclength
•excessiveweavingspeed
•excessivetravelspeed.
On vertical and horizontal welds, it can also
be caused by too large an electrode size and
incorrect electrode angles.This defect can be
prevented by:
•choosingtheproperweldingcurrentforthe
type and size of electrode and the welding
position
•holdingthearcasshortaspossible
•pausingateachsideoftheweldbeadwhena
weaving technique is used
•usingatravelspeedslowenoughsothatthe
weld metal can completely fill all of the melted
out areas of the base metal.
Lack of Fusion
LACK OF FUSION
Lack of fusion is when the weld metal is not
fused to the base metal.This can occur between
the weld metal and the base metal or between
passes in a multiple pass weld. Causes of this
defect can be:
•excessivetravelspeed
•electrodesizetoolarge
•weldingcurrenttoolow
•poorjointpreparation
•lettingtheweldmetalgetaheadofthearc.
Lack of fusion can usually be prevented by:
•reducingthetravelspeed
•usingasmallerdiameterelectrode
•increasingtheweldingcurrent
•betterjointpreparation
•usingaproperelectrodeangle.

17
3.1 Introduction
The Tungsten Inert Gas, or TIG process, uses
the heat generated by an electric arc struck
between a non-consumable tungsten electrode
and the workpiece to fuse metal in the joint
area and produce a molten weld pool.The arc
area is shrouded in an inert or reducing gas
shield to protect the weld pool and the
non-consumable electrode.The process may
be operated autogenously, that is, without filler,
or filler may be added by feeding a consumable
wire or rod into the established weld pool.
3.2 Process
1
2
3
4
5
6
7
1Shielding gas
2Arc
3TIG filler rod
4Weld pool
5Collet
6Tungsten Electrode
7Workpiece
Schematic of the TIG welding process
Direct or alternating current power sources
with constant current output characteristics
are normally employed to supply the welding
current. For DC operation the tungsten may
be connected to either output terminal, but
is most often connected to the negative pole.
The output characteristics of the power source
can have an effect on the quality of the welds
produced.
Shielding gas is directed into the arc area by the
welding torch and a gas lens within the torch
distributes the shielding gas evenly over the
weld area. In the torch the welding current is
transferred to the tungsten electrode from the
copper conductor.The arc is then initiated by
one of several methods between the tungsten
and the workpiece.
During TIG welding, the arc can be initiate by
several means:
Scratch Start
With this method, the tungsten electrode
is physically scratched on the surface of the
workpiece and the arc is initiated at the full
amperage set by the operator.The incidence
of the tungsten melting at the high initiation
amperage is high and tungsten inclusions in the
weld metal are quite common.
High Frequency Start
DuringHighFrequencystart,thearcwill‘jump’
towards the workpiece if a critical distance
is reached.With this method, there is no
incidence of tungsten inclusions happening. High
Frequency is only available on certain types of
machines and it can affect nearby electronic
equipment.
3.0 Gas Tungsten Arc Welding (GTAW/TIG)

18
Lift Arc™
During this method of arc initiation, the
tungsten is actually touching the workpiece.
This occurs at very low amperage that is only
sufficient to pre-heat, not melt the tungsten.
As the tungsten is moved off the plate, the arc
is established.With this method, there is little
chance of tungsten inclusion occurring.
3.3 Process Variables
DCEN
When direct-current electrode-negative
(straight polarity) is used:
•Electronsstrikethepartbeingweldedata
high speed.
•Intenseheatonthebasemetalisproduced.
•Thebasemetalmeltsveryquickly.
•Ionsfromtheinertgasaredirectedtowards
the negative electrode at a relatively slow rate.
•Directcurrentwithstraightpolaritydoesnot
require post-weld cleaning to remove metal
oxides.
Use of DCEN
For a given diameter of tungsten electrode,
higher amperage can be used with straight
polarity. Straight polarity is used mainly for
welding:
•Carbonsteels
•Stainlesssteels
•Copperalloys
The increased amperage provides:
•Deeperpenetration
•Increasedweldingspeed
•Anarrower,deeper,weldbead.
DCEN - Narrow bead - Deep penetration
Nozzle
Ions Electrons
DCEP
The DCEP (reverse polarity) are different from
the DCEN in following ways:
•Highheatisproducedontheelectroderather
on the base metal.
•Theheatmeltsthetungstenelectrodetip.
•Thebasemetalremainsrelativelycool
compared to sing straight polarity.
•Relativelyshallowpenetrationisobtained.
•Anelectrodewhosediameteristoolargewill
reduce visibility and increase arc instability.
Use of DCEP
•Intenseheatmeansalargerdiameterof
electrode must be used with DCEP.
•Maximumweldingamperageshouldbe
relatively low (approximately six times lower
than with DCEN).
DCEP - Wide bead - Shallow penetration
Nozzle
Ions Electrons

19
3.4 Welding Techniques
Welding techniques
A= Torch travel angle – forehand technique
– push angle 10–20° (to the vertical)
B= Work angle: 90°
C= Filler metal feed angle: 10–20°
D= Arc length: 1–1.5 x electrode diameter
Flat position (1G) Vertical position (3G)
Upwards progression
Horizontal position (2G)
Torch and filler metal manual control guidelines
60–75°
15–30°
Nozzle
Direction of travel
Welding Rod
Shield gas
Vertical
Tungsten electrode
The suggested electrode and
welding rod angles for welding
a bead on plate.The same
angles are used when making
a butt weld.The torch is held
60–75° from the metal surface.
This is the same as holding the
torch 15–30° from the vertical.
Take special note that the rod
is in the shielding gas during
the welding process.

20
3.5 Shielding Gas Selection
Brass With argon, the arc is stable and there is little smoke.
Cobalt-based alloys Argon provides a stable, easy-to-control arc.
Copper nickel (Monel) Argon gives a stable, easy-to-control arc. Also used for welding copper nickel
to steel.
Deoxidised copper Helium is preferred as it helps greatly in counteracting thermal conductivity of
copper.Amixtureof75%heliumand25%argon(AlushieldHeavy)producesa
stable arc, less heat than an arc produced with helium alone.
Nickel alloys
(Inconel)
Argon produces a very stable arc. Helium is recommended for automatic welding
at high speeds.
Mild steel For manual welding, argon is recommended. Successful welding depends on the
skill of the welder. Helium is preferred for:
•highspeedautomaticwelding
•wheredeeperpenetrationthanwithargonisrequired
•smallHAZ
Magnesium alloys Argon recommended with continuous high frequency AC. Produces good arc
stability and good cleaning action
0.5%Molybdenum Pure argon or helium is recommended. For good welding ductility, welding must
be carried out in a draught-free area.
Silicon bronze Argon decreases internal tension in base metal and in the weld since there is less
penetration with this gas compared to helium.
Stainless steel Argon is the most commonly used gas for stainless steel. Helium can be used if
better penetration is required.
Titanium alloys Argon produces a stable arc. Helium is recommended for high speed welding.