Insights into basic fundamental and details topic

1. Presentation
on
TIG Welding
By
A V Abhishek

2. Joining process 1. Welding
2. Soldering
3. Brazing
Soldering: Process of joining of
metals with non-ferrous filler metal at
temp below 427 C and below MP of
metals being joined.
Brazing: Joining the metals with non-ferrous filler material at above
427C and below MP of metals being joined i.e., liquidus temp of filler
metal should be less than solidus temp of base metal.
Mechanism of joint formation:
Wetting and Surface alloying
Capillary action and filling the joint

3. Welding: Joining of two or more, similar or dissimilar metals, with
or without the application of heat, with or without the application of
pressure, with or without the application of filler material.
Classification of Welding

4. TIG WELDING
Tungsten Inert Gas
Gas Tungsten Arc
Wolfram Inert Gas
WHY Tungsten?
A metal with a fusion point of
3380 C, which means more
than double the fusion point
of metals we use

5. Principle
Process in which fusion energy is produced by an electric arc
burning between work piece and tungsten electrode.
During the process electrode, the arc and the weld pool are
protected against the damaging effects of atmospheric air by
shielding gas.
By means of gas nozzle the shielding gas is lead to the welding
zone, replaces the atmospheric air.

6.  In DC, the electrode is usually connected to negative polarity
and the work piece to positive polarity.
 According to the theory of electrons the negatively charged
electrons and positively charged ions will migrate when the arc
is ignited.
 The electrons migrate from negative to positive pole while the
ions will travel in the opposite direction and collision occurs
then produces heat energy.
Power Supply
 Alternating current is characterized by
the fact that voltage changes polarity a
certain number of times, usually 100
times per second.
The electrode has positive polarity and
workpiece has negative polarity in a semi
period.

7. In the next semi-period the polarity is reversed, which means
that the heat energy distributes with 50% on the electrode and
50% on the workpiece.
Welding Aluminum, Magnesium and their alloys possible with
AC only.
The adhering oxide film on the aluminum surface which
influences the welding behaviour and has to be removed in
order to prevent oxides from being entrapped in the weld.
The oxide film can be removed by varying the current type or
polarity or use of inert gases.

8. Torch set up:
Main Parts :
Collet body
Collet
Back Cap
Ceramic Cup
 Purpose of torch is to carry the welding current and shielding gas to the weld.
 Set up is constructed with an electrically insulated material.
 Constructed that the current transfer to the electrode takes place very close to
the electrode point.
Gas Nozzle:
 Function is to lead the shielding gas down around the welding zone and thereby
replace the atmospheric air.
 The gas nozzle is screwed onto the TIG torch so it can be exchanged if required
 The size of the gas nozzle is often indicated by a number that refers to the
interior diameter of the orifice in 1/16”.

9. Water cooled Welding Torch:
Depending on the magnitude of thermal stressing, the torches can
be air or water cooled(for > 100 A).
The water cooling cools both torch and current cable.
A flow meter registers any water shortage, switching off the current
in this case and thus preventing torch overheating.
The torch should be airtight since humidity has a negative influence
on the welding result (hydrogen absorption).
A torch cap prevents any inadvertent contact with the electrode

10. Electrodes
Mainly made of tungsten.
Pure tungsten is a very heat resistance material with a fusion point of
3380oC.
By alloying tungsten ,the conductivity of the electrode can be increased
thereby resist a higher current load and have longer life ,better ignition
properties
Alloying of tungsten
Zirconium oxide ZrO2
Lanthanum oxide LaO2
Thorium oxide ThO2
Cerium oxide CeO2
Colour Indications on Electrodes
The electrodes are marked with a particular colour on the last 10 mm.
Pure tungsten -Green colour-AC Welding in Aluminum and its alloys.
Tungsten+2% thorium -Red colour-Non alloyed and low alloyed steels
Tungsten +1% lanthanum-Black colour- for all TIG weldable metals.

11. Electrode Dimensions
Tungsten electrodes are available in different diameters from 0.5 to 8 mm.
Commonly used are 1.6 - 2.4 - 3.2 and 4 mm.
The diameter of the electrode is chosen on basis of the current intensity, which
type of electrode is preferred and whether it is alternating or direct current
Grinding Angle
The point of the tungsten electrode must be ground correctly for good result.
With DC and negative polarity, the electrode point should be conical in order to
obtain a concentrated arc that will provide a narrow and deep penetration profile
Thumb rule -the relation between the diameter of the tungsten electrode and
the length of its ground point.
Blunting the electrode point to make flat area with dia 0.5 mm can increase the
lifetime of the tungsten electrode.
For AC TIG welding the tungsten electrode is rounded as during the welding
process it is so heavily loaded that it is melted into a half globular form.

12. Shielding Gases: Inert gases used Argon and Helium
The amount of shielding gas required depends on the material
used and its thickness.
The gas consumption for titanium is higher than for steel, since a
gas absorption by the former material must be prevented even at
lower temperatures.
Because of its lower density, the amount of argon required is
larger than the helium amount needed
 Argon+H2(2 -5%)for SS and Ni
base alloys.
 He+Ar gives, greater heat
input, deep penetration.

13. Gas flow rate is regulated in CFH(Cubic Feet per Hour).
Depends on the cup size and any draft/wind conditions.
For example If there is no drafts, a rate of 5 CFH may be enough.
Sometimes 60CFH may not be enough if working in outdoors.
A higher gas flow rate is not good either because causes turbulence
that pull air into weld.
The pressure in steel cylinder is between 200-300 bar .
A pressure reducing valve is fitted with a gauge where the actual
cylinder pressure can be read.
Helium
Faster travel speeds
Increased penetration
Difficult arc starting
Less cleaning action
Less low amp stability
Flared arc cone
Higher arc voltages
Higher flow rates (2x)
Higher cost than argon
Argon
Good arc starting
Good cleaning
action
Good arc stability
Focused arc cone
Lower arc voltages
10-30 CFH flow rates

15. Welding Parameters

16. Advantages :
TIG welds are stronger and more ductile.
As shielding gas is transparent, welder can clearly observe the weld.
Wide variety of joints can be made because no flux is used.
It provides a concentrated heating of Workpiece
Areas of application
The offshore industry
Combined heat and power plants
The petrochemical industry
The food industry
The chemical industry
The nuclear industry
Materials used for TIG welding
Welding of thin materials in stainless steels
Mild steel
Aluminum, Magnesium and its alloys
Nickel
Copper and others.

17. Features :
Non Consumable Electrode
Argon supplied continuously to cover the welding pool , to
protect from atmospheric contamination.
Highly reactive metals like Al and Mg alloys can be welded
easily.
Limitations:
Cost is high because of inert gas usage, coolant and coolant
pump.
Maximum Thickness of plate can be joined upto 5 mm, for
above filler rod must be used.
Even though tungsten is not melting but at high temp atoms of
tungsten may get diffused from tip and enters weld pool which
increases brittleness of weld bead.

18. 18
Safety
Electric shock can kill.
Insulate yourself from work and ground
Do not touch live electrical parts
Always wear dry insulating gloves
Keep all panels and covers securely in place
Fumes and gases can be hazardous to your health.
Keep your head out of the fumes
Ventilate area, or use breathing device

19. Welding can cause fire or explosion.
 Do not weld near flammable material
 Watch for fire; keep extinguisher nearby
 Do not locate unit over combustible surfaces
 Do not weld on closed containers
Arc rays can burn eyes and skin; Noise can damage hearing.
 Wear welding helmet with correct shade of filter
 Wear correct eye, ear, and body protection

20. Hot parts can cause injury.
 Allow cooling period before touching welded metal
 Wear protective gloves and clothing
Magnetic fields from high currents can affect pacemaker
operation.
Flying metal can injure eyes.
 Welding, chipping, wire brushing, and grinding cause
sparks and flying metal; wear approved safety
glasses with side shields

21. Welding current can damage electronic parts in vehicles.
 Disconnect both battery cables before welding on a
vehicle
 Place work clamp as close to the weld as possible

22. Manual Torch Movement

23. Butt Weld and Stringer
Bead
Be sure to center weld
pool on adjoining edges
When finishing a butt
weld, torch angle may be
decreased to aid in filling the
crater

24. Lap Joint
Pool is formed so that the
edge of the overlapping piece
and the flat surface of the
second piece flow together
Torch angle is important
because the edge will become
molten before the flat surface
Enough filler metal must be
added to fill the joint as
illustrated on the right

25. T-Joint
Edge will heat up and melt
sooner
Torch angle illustrated will
direct more heat onto the
flat surface
Electrode may need to be
extended further beyond
the cup in order to hold a
short arc

26. Corner Joint
Both edges of the
adjoining pieces should
be melted and the pool
kept on the joint
centerline
Sufficient filler metal is
necessary to create a
convex bead as shown

27. Troubleshooting
 Excessive electrode consumption
 Erratic arc
 Inclusion of Tungsten or oxides in weld
 Porosity in weld deposit
 Cracking in welds
 Inadequate Shielding
 Arc Blow
 Short Parts Life

28. Types of Cylinders for TIG
Generally, Argon & Helium mixture of gases used as per industrial and
type of application used
ARGON(AR), Industrial Grade, 99.995 purity, T Style Cylinder

29. Industrial Gas Cylinder Specifications
Oxygen – A black cylinder with a white shoulder
Colourless, odourless and tasteless
Generally considered non - toxic at atmospheric pressures
Oils, greases and solvents may react violently with oxygen and metals may
burn.
You should never use oil or grease to lubricate oxygen or oxygen enriched
equipment as they can spontaneously burn with explosive violence.
Nitrogen - A grey cylinder with a black shoulder
Colourless, odourless, and tasteless
Does not support combustion or life
Non-toxic
Non - reactive except at high temperature
Argon - A green cylinder with a bright green shoulder
Colourless and odourless.
Inert - does not generally react with other materials
Does not support combustion or life.

30. Industrial Gas Cylinder Specifications
Acetylene - A maroon cylinder
Distinctive garlic like smell - recognisable above 2% concentration in the air
Considered non - toxic but may cause dizziness at high concentrations
Fire and explosion hazards
Will ignite and burn instantly from a spark or piece of hot metal
Lighter than air, so less likely to collect in pits, ducts, trenches and other
low-lying areas.
CO2 - A black cylinder with a grey shoulder
Odourless but can cause the nose to sting
Colourless
Toxic at high concentrations
Slightly corrosive in the presence of moisture
Can cause serious cold burn

31. Additional details on Cylinders
The cylinder label is the primary means of identifying the properties of the gas in a
cylinder, the colour coding of the cylinder body provides a further guide.
The colour applied to the shoulder, or curved part at the top of the cylinder, signifies
the European standard colour coding.
The aim of the new standard (EN 1089-3), which has replaced the old cylinder colour
scheme (BS349), is to help improve safety standards within the gas industry.
The shoulder colours inform about gas properties, but the most common pure gases
have their own colours.
Gas Mixtures
Toxic and / or corrosive gases - Yellow
Flammable gases - Red
Oxidizing gases - Light blue
Inert gases - Green
Pure Gases
Acetylene - Chestnut
Oxygen - White
Argon - Dark green
Nitrogen - lack
Carbon Dioxide - Grey
Helium - Brown
Hydrogen - Red
Nitrous Oxide - Blue