# Week-1 Lesson-2 Fundamentals of Welding and Joining Part II

Now, one of the important ah aspect of the
Arc Welding process, that the how to decides or how to design the power sources for different
welding processes. So, that definitely there is a requirement
of a power source to deliver the controllable current and voltage according to the welding
process used. So, ah we know that specifically in welding
process the power source is used in such a way, that high amount of the current and the
low voltage, basically low voltage in the sense that around current raisings may be
more than 100 amps and voltage is around 20 volt. So, as compared to the normal electrical connection
so, but this requirement ah for this requirement specifically used for the welding process
needs to develop the different sources, but there is another aspects also; that during
the process or when you creates the arcs to maintain the arc and to continue the welding
process over the time. So, in that case 2 different characteristics
of the power source can be defined. So, one is the constant current source or
otherwise it is it is also called the falling characteristic power source and second one
is the constant voltage or flat characteristic power source. So, these 2 different type of the power source. How the current or voltage can be adjusted
during the welding process when we use some ah consumable electrode or normal electrode
or in the process if there is some change in the ah arc length, arc length or if there
is a presence of any ah agents or this surface oxides layers present in that ah work piece
surface; that actually tends to ah makes some variation in the either welding current or
voltage. So, based on this the applicability of the
power source in welding process is defined basically in these 2 categorization. Let us see the first one is the constant voltage
ah power source. What are the typical characteristics of this
type of power source? And why it is required? First thing if we look into that this type
of power source can be used in case of semiautomatic arc welding process; that means, semi arc
welding automatic ah semi ah automatic arc welding process there is a probability of
variation of any voltage or current relatively small since is automated process as compared
to the any kind of manual process. So, in that case the typically downward negative
slope type of characteristics. So, that characteristics define the relation
between the voltage and current. If you see from the figure that voltage and
current it is follow almost linear or in other way we can say it is a almost flat characteristic
of the power source; that means, relation between the linear relation between the voltage
and current. So, this type of power source is characterised
by that first is the sufficient internal electrical resistance and inductance uh in the circuit. So, that the just small change in the current
probably there may be the changes accordingly the there may be the try to maintain the ah
almost constant voltage by changing the current. So, change in current is accompanied by the
process is basically the melt the electrode at the required rate. So, the sense of change in current is basically
reflected by melting the electrode. So, that it will try to maintain the constant
voltage of the power source. Speed up also speed of electron as well also
control the average welding current and constant electrode wire feet basically the is the self-regulating
or self-adjusting creates the self-adjusting ah arc length of the system. So, in this case the pre state always try
to maintain the ah desired arc length by by maintaining the constant voltage, but if during
the process if there is a small variation of the change in the arc length that is automatically
adjusted by melting the electrode material, definitely in case of the consumable electrode. So, any change in the welding current occurs
in this case it automatically increase or decrease the electrode melting ah to regain
the design ah desired arc lengths. So, to maintain the desired arc length it
is also to maintain the constant voltage power source. So, figure if we see that from the figure
that it is starts from the open circuit voltage. So, that open circuit voltage is just to start
the arc welding process. And then from the open circuit ah from the
open circuit voltage there is a drop, but drop rate is very low in this case and of
course, it is a negative slope and that actually desirable characteristics of the ah constant
voltage power source. And of course, it is more suitable for the
ah automation of the arc welding process. So, if you look into the another type of the
power source; that is, constant current power source in this case we can see from the figure
the relation between the voltage and current can be represented like that. It is a non-linear way and there is a sharp
dropping of the voltage with a small change in the current. So, that is called the sharply dropping characteristic
of the power source. So, definitely in this case the during welding
process it is always try to maintain the constant current, but by accordingly by changing the
voltage. So, this type of power source is typically
useful in case of manual arc welding process. If you look into the manual arc welding process,
it is starts with the by sticking of the arc; that means, by sticking of the arc; that means,
open circuit voltage is very high. And then after after that after sticking of
the arc then we will after that we try to maintain the ah constant arc ah between the
work piece of electrode. But manually it is not very easy to maintain
always the constant arc. So, there is the highly chance of the desirable
that there is may be the continuous change in the arc load. So, that is accommodated by this type of typical
characteristic ah power source. And if we look into that definitely the high
frequency unit supplies the high voltage and along with the high frequency ah with low
current. So, initially when you try to create the arc,
that that ionizes the medium between the electrode and the work piece material. And so, that it is starts the pilot arc which
ultimately leads to the start of the main arc. So, to maintain a change with the to maintain
this type of ah arc welding process ah to create the arc the it should follow this type
of typical characteristic of the power source; that starts with the very high open circuit
voltage. And then drop of the voltage is actually occurs
means rapidly and that follow very non-linear path and also it is a sharply dropping characteristic
it follow in this case. So, this type of power source is basically
desirable of the manual arc welding process . And it reflects that it in changing the
power source; that means, open circuit voltage adjust and out and also control the output
current. And that basically represented by the change
of the slope; that represented by the change of the slope in this volt versus ampere characteristic
graph ah of this type of power source. So, here you can see that 2 types of the power
source, one is the constant another is the constant current. So, one is suitable for the manual arc welding
process that is the constant current power source is suitable for manual arc welding
process and another is suitable for the ah automatic arc welding process. Uh that is the constant voltage power source
is suitable for the automatic arc welding process. So, basic things is that if we try to sustain
the welding process; that means, after creating the arc and to maintain the ah arc gap between
the work piece an electrode. We need depending upon the application applicability
ah of the whether it is manual or whether it is automatic, based on that ah power source
can be power source can be set accordingly. So, apart from this ah characteristic power
source we can find out that 2 different characteristic of the power source. And then we can find out that there is another
important phenomena which happens in the welding process that is the shielding gas. So, basic role of the shielding gas we use
in the this shielding gas in the welding process, but the main role is that to protect the molten
metal from contamination of by the outside ah atmosphere. That is the main objective of using the shielding
gas. Now, this is the essence of part of the ah
welding process until and unless the welding happens in vacuum. So, in if it happens the vacuum there is a
no question of the contamination of the molten weld pool or with the atmosphere. So, in that sense is an almost every welding
process, normally uh different way we can protect the molten pool from the outside atmosphere
ah ah either using the direct using of the shielding gas or in different way; that means,
we can create the slag coverage and that is by the chemical reaction of the arc that happens
during the chemical reaction of the arc. So, these are the 2 way 2 different ah to
apply the shielding gas or to protect the molten pool. Now, what are the common shielding gas use? We use we have observed that the different
type of the shielding gases like argon, helium, carbon, carbon dioxide and oxygen. These are the typical shielding gas is used,
but oxygen cannot be used alone, but always we use the oxygen mixing with the other shielding
gases. Now, the shielding gases either we can use
is 100 percent. The if we see the shielding gas is mostly
the inert type of gas. So, that it will try to avoid the make the
reaction with the molten pool; that is why argon, helium these are the typical type of
ah shielding gas ah we use during the welding process. First ah either the shielding individual shielding
gas can be used all 100 percent of the, ah shielding gas can be used in the for certain
application or sometimes we use the mixture of the 2 different or more different shielding
gases ah for with different combination to get the certain advantage, but the basic role
of the shielding as or basic principle of the shielding gas actually relates to the
reactivity or shielding gas can be decided based on the reactivity of the shielding gas
with the molten pool or maybe you know during that high temperature environment. And what is the ionisation potential of this
type of shielding gas; that means, how easily ah the it can be organised or not. And what are the thermal conductivity of the
ah ah this type of gas or thermal conductivity of the work piece materials. That also play important this factors also
play important role to choose the shielding gas. But basic ah basic point of choosing the shielding
gas is that; based on the the whether it is very reactive with the at high temperature
environment or not. Or if whether by reacting with the ah work
piece materials subset material whether it can produce some defect in the welded joint
or load. So, based on that we can choose the different
type of the shielding gas. Now, these are the basic role of the shielding
gas, now we will try to discuss the some overall idea, but in general different fusion welding
processes. So, this uh fusion welding processes we know;
that it is a broadly categorized this ah welding processes that fusion welding processes non
pressure; that means, without the application of the any pressure or pressure welding that
non fusion. So, without using any ah with; that means,
pressure welding there is no fusion of the substance material. So, what we will we focus on the only on the
fusion welding processes some general idea about the fusion welding processes. So, that fusion welding is basically we can
categorize this way; that gas welding ah name of the different gas welding processes that
is oxyacetylene here acetylene oxy hydrogen. So, basically chemical sources ah ah by burning
this gases ah they are this can produce the heat. And that heat can be used to fuse the to melt
the ah material. So, this is ah these are the typical gas welding
process we have used ah for joining of the metallic materials. High energy beam see if we look into that
high energy beam welding process normally the electron beam welding process and laser
beam welding process are 2 widely used the high energy beam welding processes. Third is the chemical based the thermit welding
so in that case some oxides is used. And during the reaction it generate the heat
and that heat is basically try to ah fuse the material. So, that is call the welding process, ah that
is chemical based welding process. The one example of this thing is the thermit
welding process. And apart from this other at the other typical
usable welding processes that is arc welding process. So, arc welding process in this case the categories
in the following way that using the consumable electrode or using non consumable electrode. So, consumable electrode the electrode can
be consumed due to the welding process and and it becomes the final part of the weld
joint. So, consumable electrode we can find out that
shielded metal arc welding process that is SMAW process mostly use, GMAW gas metal arc
welding process submerged arc welding process and electro slag welding process. These are the most general the consumable
electrode arc welding processes. And if you look into that non consumable electrode
that is the gas tungsten arc welding process. Plasma arc welding process and carbon arc
welding process these are the typical ah non consumable electrode process, but of course,
which is a non-consumable electrode process; that means, ah in the sense that main electrode
which creates the arc between the work piece ah ah and the ah electrode material. So, in this case that electrode material is
non-consumable, but it is possible to use some extra ah material that can be ah melt
during the creation of the arc between the work piece and the non-consumable electrode. And that extra material becomes the final
part of the weld join. And in this way that using the filler metals
the non-consumable electrode arc welding process can also be developed um for example, in case
of gas tungsten arc welding sometimes we use the extra filler material in this case, but
the main electrode is not consumable in this case in that sense it is call the non-consumable
electrode arc welding process. So, with this fusion welding processes, ah
we will try to give an overview of all this type of fusion welding processes; although
it is the very conventional courses this is this already covered, but I am giving try
gas welding process. So, oxyacetylene is a gas welding process. So, basically the mixing of the oxygen and
acetylene in the different way different way means the in the different proportionate between
ah oxygen and acetylene they can produce the varieties of the envelope of the ah varieties
of the envelope of the flame. And that temperature actually depends temperature
of this flame depends on the what ah ratio ah where mixing between the acetylene and
oxygen. Let us see that the proportional of the gases;
that actually ah decide the nature of the flame. First we will look into the natural flame. So, in this case oxygen and acetylene is mixed
in such way that; almost one to one. And in this case if we see from the figure
the typical nature of the flame that actually produce the some inner cone. And output envelope during the welding process. So, that probably that outer envelope here
actually try to protect the heated zone from the little bit heated zone from the outside
atmosphere, and ah inner cone actually supply the try to may melt the molten material. So, in this case if we see that welding of
the mild steel, welding of the stainless steel, copper, aluminium all these type of materials
can be welded using the simple gas welding ah processes. And here natural flame in that sense that
we assume the copper mixing of the oxygen and ah acetylene can happens here, can happens
here also. Depending of the nature of the flame the applicability
of the 2 different material process actually can be decided .
Second one is that ah carburizing flame. In this case the proportion of the acetylene
in the mixture is higher than that the require to produce the with reference to the neutral
flame so; that means, the acetylene part is more in this case and oxygen part is less
in this case with reference to the neutral flame. So, definitely uh it can be assumed that the
absence of oxygen that can be say that there may be some unborn ah acetylene in this case. So, for this case sufficing sufficient bonding
does not occur. So, it can produce the low temperature with
respect to the neutral flame. And at the same time it can create some excess
carbon can be created. So, typical application of the neutral flame
we can see that welding of the iron and steel and since excess carbon always produce the
hard brittle iron carbide. So, if there is a requirement of producing
the the iron carbide, in that case the use of the carburizing flame is more preferable,
but the maximum temperature is lower than that of the neutral flame in this case and
if you look into this figure the envelope of the flame is like ah 3 different way it
can creates the 3 different envelope. So, if you see the inner cone and outer envelope,
but here if you see the apart from inner cone to outer envelope also created and that can
be created due to the nature of the mixing ratio between the oxygen and acetylene. So, third one is the oxidising flame. So, here if you see the oxidising flame means
in this case the oxygen amount will be the more, and the with reference to the neutral
flame. So, in this case definitely since oxygen amount
is more. So, in this case the temperature will be the
more ah with respect to the neutral flame. And here you can see that ah from the picture
we can see also that inner apart from the inner cone there is the outer envelope and
the outer envelope is basically smaller and narrower as compared to the ah neutral flame. So, this type of flame is used when there
is a high amount of the heat is required. For example, highly conductive material like
copper copper base metals ah and can also be used in case of the zinc base metals. So, this is the very basic types of the gas
welding process. Now we we will try to look into the other
welding processes ah that is called the shield metal arc welding process. So, it is well known that shield metal arc
welding process, but here we are try to focus on the some typical characteristics of this
welding process. First is that definitely shielding metal architecture
welding process is most commonly used and we we can see this welding processes used
in the definitely in the construction site also. So, ah first thing we can see that consumable
electrode; can be used in this case, but if we see precisely look in to the electrode,
electrode is coated with some flux . So, purpose of using this coated flux that actually try
to ah produce the protective gas around the weld. And then it it actually ah helps ah to protect
this molten pool from the atmosphere by creating the outside ah that creating the protective
gas. And finally, the it becomes it creates the
produce the slag. Layer of the one slag that is in in weight
that is lighter as compared to the ah molten material or may be as compared to the base
material. So, that lighter metal becomes on the top
surface and that creates the layer of the slag layer. So, that slag layer also other way until unless
becomes cool down heat also heat also against the protects the this ah molten material during
the solidification process. So, in that case it is very most advantageous
to use, the in the different way basically it is a electrode is basically supplying the
extra material and the same time it it is it is also protecting the the weld zone during
the welding process or as well as during the solidification process also. So, if you look into that figure there is
a power supply and it it is completes the electrical circuit and between the work piece
and the electrode it creates the arc, and the arc is basically surrounded by the protective
gas, and that protective gas actually creates from the coating of the coating over the flux
coating over the ah electrode. And then if we see the solidified metal, over
the solidified metal there is a slag layer. So, after finishing welding process it is
necessary to remove the ah slag layer. So, these are the very, very well-known and
ah very stable welding ah process and we use most of the cases, but here the choice of
the electrodes depends the because electrode material is also important factor here. The what type of material we are trying to
weld and what is the uh that choice can be done according to the metallurgical compatibility
of the electrode material to the base material based on that we can choose the different
types of the electrode material. In simple way what are the advantage of this
process? It is a very simple process and mostly this
process is used manually, it is a ah very simple portable and portable, equipment and
the not very costly equipment as compared to the other welding processes, but if you
look in to the limitation of this process disadvantage of this process is that it is
a discontinuous process because the length of the electrode is limited. So, there is a not continuous supply of the
electrode. So, once the electrode is length of electrode
is over then uh process become discontinued again we have to next we need to fit the another
electrode. And then we can continue the ah process. So, that is the one limitation. Second the weld metal content also the slag
inclusion because it is the height this given this high temperature phenomena molten metal
may contain some kind of the some amount of the slag, slag material may also remain within
this zone. So, that is also another disadvantage and
because during the welding process it creates the protective gets gas and that is very,
that is why it is very difficult to make it as a make the process control. So, in that sense this process can it is not
process this process is not converted to the alternating process that’s why, that’s why
mostly use for the ah manual process. Second if we look into the other welding process
that is gas metal arc welding process. So, with reference to that shielded metal
arc welding process the in gas metal arc welding process here, apart from this we can use the
continuous supply of the electrode material. So, that electrode is basically the electrode
is used ah is a continuous weld and that ah that is wanted in the ah other places and
it is externally or separately it is supplied to the process continuously. So, in that sense it is a very we can say
the it is a continuous process as compared to the shielded metal arc welding process. So, definitely gas metal arc welding process
we use the consumable electrode. And in this case we generally not use the
ah flux, but directly we can use the shielding gas here to protect the molten pool. So, shielding gas like argon, helium, carbon
dioxide or mixing of argon oxygen or any other gas other gas mixture is normally used for
gas metal arc welding process, but commercially we generally use in gas metal arc welding
process for welding of the steels normally carbon dioxide can be used because carbon
dioxide is cheaper as compared to the other inner type of shielding gas. So, if we look into the process that it is
also create the electrical circuit, that to the arc is created between the electrode and
the work piece. And here if you see there is a apart this
along with the supply of the ah consumable electrodes over some drive rolls the same
times ah there is a supply of the shielding gas used to the same nozzle. So, that shielding gas actually protect the
molten pool ah thing and normally copper nozzle is used used here and this wire sometimes
we use, either the electrode wire is either is the solid or solid wire definitely use
and sometimes it is also used in the form of the some coating maybe d1 over the the
solid wire. So, this process if we very precisely look
into what are the advantages of this process. We can find out that it is a very it is a
continuous welding process no interaction, like shielded metal arc welding process. And of course, in the another advantage is
that it is not necessary to remove the slag. So, slag after the finishing of the welding
process slag removal is not required. So, that is why in this way this gas metal
arc welding process is possibly can be ah or can be automated as ah in the ah automated
and in that sense it is advantageous as compared to the shielded metal arc welding process. But if we look into the disadvantage in general
that it is a definitely uh expensive ah as compared to the shielded metal arc welding
process, because it is also necessary to drive the electrode material according to the the
consumption rate. That should be adjusted to the consumption
rate during the welding process. So, in that way it the equipment is little
bit expensive as compared to the shielded metal arc welding process. Then will one of the most widely used welding
process that is submerge arc welding processes. In this case also we use the consumable wire
electrode and, but the difference is that, that shielding is actually provided not by
the shielding gas is a ah provided by the granules of the flux is used. In this case if we look into this picture
though like gas metal arc welding process here also some drive roll is there and that
actually supply the drive roll is basically control the ah consumable electrode and, but
the shielding is happen using the flux granules. And this low and it produce the low ultraviolet
radiation and also fumes as compared to the shielded metal arc welding process. And flux actually acts as the thermal insulator
and suitable for the this this process is mainly suitable for the very thick material. So, it is a large volume of the welding is
required. So, in that case submerged arc welding is
the good choice of that. So, submerged arc welding process also developed
that not only the single wire twin wire 2 wires can be used also so instead of single
wire. So, it is a kind of ah taking the advantage
of the submerged arc welding process ah combining this things that both shielded metal arc welding
process. So, using the flux and takes the advantage
from the gas metal arc welding process. So, here the we use the consumable electrode,
but in the form of the ah wire. And here if you see similar electrical circuit
is put between the consumable electrode on the work piece, but it is a huge flux actually
cover the weld zone. So, that is since the flux granules cover
the weld zone. So, in this case the efficiency of the process
is, ah efficiency of the process is relatively higher as compared to the ah arc welding or
shielded metal ah gas metal arc welding or shielded metal arc welding processes, but
if you look into that typical advantages that it is a very high welding rate. So, ah as compared to the shielded metal arc
welding ah gas metal arc welding or shielded metal arc welding process. And this process is basically it is possible
to do the suitable for the automation or it can be converted to the automatic system and
high quality weld structure is can be produced. And main advantage is the efficiency of this
process is very high as compared to the ah gas metal arc welding or shielded metal arc
welding processes, or at the same time the very high welding rate can also be ah done
using the twin wire also; that means, 2 wires can also be used ah in this process to get
this to improve the ah rate of the welding process or material deposition process. And of course, this process is designed or
developed specifically for the or suitable specifically for the very when there is a
requirement of the very high thickness or large volume of the metal material, but also
having some disadvantages, that weld may contents the as in as in general other processes also. That it content the slag inclusion within
the weld zone also, and mostly used for the or suitable for the horizontally located plate. So, these are the 2 typical at this advantages
of this process. And now we will look into that electro slag
welding process. So, in this process the workpiece is filled
with the welding flux. If you see the welding flux and, but at the
start the arc is created to melt the flux powder and that actually forms the molten
pool. And then after that heat is generated ah the
due to the molten flux become short circuit the arc and then heat is generated due to
the ohmic heating of the slag. So, then slag circulates and the molten ah
circulates within the zone and the melt the consumable electrode and basically finally,
it is join the workpiece edges. So, we look into this figure, that we use
the electrode wire and the power supply; that means, to make is the electrical circuit. The guide tube also there and that actually
wire electrode and guide tubes the flux making this thing and produce the molten. This in this the ah in this case the advantage
is that it produce the molten slag and then indirectly that molten slag is actually produces
the ah weld pool. So, in this case if we look into the main
advantage of this that that high deposition rate is possible, even also welding of the
very thick plates also possible, that slag consumption rate is typically low and low
distortion is possible in this processes; that means, the electro slag welding processes
is uh almost the similar kind of advantage of the submerged arc welding process, but
if you look into the other aspects this thing the distortion point of this thing. First point is that this process can be done
only over the in the design specifically for joining of the in the vertical position of
the place, basically when keep the vertical position of the plate and then keeping 2 plates
as a vertical position and then from the bottom bottom plate we just keep on welding and the
electrode is basically simply keeping upward direction and then upward direction and at
the consequently it make the welding in the backside. So, that this process is specifically advantages
for joining of the vertical to vertical plate and in the large scale; that means, large
volume of the molten pool is required uh in this case this process is more suitable. So, apart from the electro slag welding process
also there are other welding process. That is the more simple welding process that
is call the carbon arc welding process. It is a very oldest welding process shields
may be used for the weld pool, protection depending on type of the metal shielding can
be use also; that means, either natural gas or flux can be used in this processes, but
the basic principle of this process is that powers same as the other welding processes
the workpiece power supply, the work the arc is created between the workpiece and the electrode
using the non-consumable ah carbon electrode. And it is produces the weld pool and in this
case if you see that non consumable ah carbon electrode is basically used and that this
process has been developed long before than the other processes. So, but if we typically look into the advantages
of this process is the first is that; low cost of the equipment. So, simply we can use the ah non consumable
carbon electrode and shielding can also be done either flux or maybe we can use the natural
gas. So, in this process that is one of the advantages
that, ah low cost of the equipment and therefore, not required very high ah operator skill is
not required. And this processes can be easily automated,
but because this process is not very complicated and low distortion work piece can also be
achieve. Since this is one of the one of the oldest
welding process. So, that it is a very simplified way can be
applied, but definitely if we look into the very precision of the welding process in the
sense less defect and other way ah try to produce the less amount of the defects, probably
then looking into that aspect the other welding processes has been better choice as compared
to the carbon arc welding process. But precisely looking into the disadvantage
of this process that; is that mainly the quality of the weld joint. So, in terms of that it is not suitable for
the when you try to expect the high quality welding joint processes has is already there,
but one point of that, one point is that the carbon of the electrode actually contaminates
the weld material with making formation of the carbides, because since carbon is is acting
as an electrode. So, at high temperature there may be the possibility
of the transfer of the carbon atom and that creates the carbides in the work piece metal. So, if it is the requirement of to produce
the any carbides on the work piece metal probably in that sense this welding process is more
suitable as compared to the other welding processes. Now the most usable another one of the most
usable welding process that is gas tungsten arc welding process. In this process we use that non consumable
electrode and of course, non-consumable electrode, but with or without any extra filler material
can be added in this process. And shielding is done generally argon helium
and nitrogen ah that is one type of the ah inert type of the gas and specifically used
for this process when it is a very thin section or very small weld join is required in this
case the gas tungsten arc welding is a good solution. Now, if you look into this ah the from the
figure that, power supply is similar to other welding processes between the arc can be created
between the non non consumable electrode and the work piece material shielding gas is required. And the filler roll may or may not be used
depending upon the application. So, the non-consumable to the along with the
non-consumable electrode that there is a the passes through the nozzle and the ah also
the shielding gas also passes through the nozzle. So, this is the may be without using the any
kind of using the non-consumable electrode this is one of the more simple a simplified
welding process, but more power more usable welding process in the sense that it is having
the typical advantages; that since there is no need of using some ah consumable electrode
or if there is no need of use any ah filler material. So, only by supplying the heat and fusing
these 2 material. So, material composition is almost close to
that of the parent material, but of course, the nature of the solidification behaviour
of the specific material that may be ah bring some structurally different from the base
material, but composition may be the same. Relatively high quality welded structure can
be ah can be possible. So, no slag formation as compared to the other
welding process since we are using only in the shielding gas and it may not become part
of the final weld joint. So, thermal distortion of the workpiece can
be minimised because the heat can be concentrated in a very small zone as compared to the consumable
electrode ah like gas metal arc welding or shielded metal arc welding process. So, in general the shielded metal arc welding
or gas metal arc welding process definitely the concentration of heat depends on the the
size of the electrode, but in that sense the size of the electrode can be control is a
in case of gas tungsten arc welding process, ah that can be done ah the different shape
of the ah nozzle tip and accordingly heat can be concentrated and of course, in other
way heat also depends of the shield gas product also. So, in that point of view that; the gas tungsten
arc welding process is one of the most widely used welding process specifically when you
try to join is the very thin metal and there is no need of any filler material, but disadvantage
is that low melting rate as compared to the other welding when there is uses of consumable
electrode, relatively expensive as compared to the ah I i can say that carbon arc welding
processes and it is also requires high level of the operator skill; that means, to maintain
the arc gap or to move the torch then high operating skill is required ah to get the
successful weld joint from this processes. So, apart from gas tungsten arc welding process
we can look into the other aspects of the gas tungsten arc welding process. One thing is that workpiece in a protective
inert gas workpiece remains in the protective gas atmosphere. And next is the any filler material is used
with which can be used externally. So, there may or may not be required any filler
metal or may be filler metal may not be the part of the ah main welding system. Sometimes to increase the melting rate melting
point of the electrode. So, that since in this process we use the
non-consumable electrode is objective maybe to increase the melting point of the electrode,
and that can be done using the thorium or zirconium is added to the tungsten that actually
ah that is uh is basically useful or helpful to retain the high hot hardness even at very
high temperature. So, in that case we generally use 2 percent
oriented tungsten electrode in gas tungsten arc welding process just because of that in
for this material the melting point is very high. So, that it we will try to reduce the wire
of the electrode, at the very high temperature or melting of the electrode. But in the when we try to look into the that
we use we can see there is a electrical circuit is there power supply. And then ah here work piece and that it is
create the circuit. So, whether the electrode, what is will be
the polarity of the electrode? Uh that can also be changed in gas tungsten
arc welding process. Normally DCEN; that means, direct current
electrode negative is used in this case, but of course, depending upon the application
direct current electrode positive can also be used or ac current can be used instead
of the only of the dc current um. Normally welding of the aluminium and magnesium
and their alloy normally ac current is preferred because alternative current is make the cleaning
action in the half of the cycle during the welding of this material. So, there is a continuous change of the polarity
positive and negative when we use the ah ac current, but typical point of this process
is the most usually shielding gas is the argon material, but sometimes use the nitrogen for
welding of the copper material. So, these are the typical characteristics
or typical points that is related to the gas tungsten arc are welding process. Now, we will look back to the another arc
welding process that is called the plasma arc welding process. Here if we see that plasma arc welding process
it is always it is try to take the advantage of the gas metal arc welding process, almost
similar configuration; that means, they use the non-consumable electrode creates the electrical
circuit, but here we can use that another extra shielding gas that is call the plasma
gas basically that actually creates the arc and maintains the arc. And that actually helps to melt melt the workpiece
material. So, with respect to the gas tungsten arc welding
process ah and ah all the all the general components of the gas tungsten arc welding
process here the addition of the extra plasma shielding gas, but let us look into this figure,
how this process has been developed? The plasma arc welding process here you can
use the DC power supply and create the positive and negative and here in non-consumable tungsten
electrode we can use here and shielding gas also supply, but inside there is a plasma
gas plasma gas also be supplied here. So, basically passing through the electrode,
there is a current when passes through the electrode it creates the pilot arc and then
after that the it creates the arc due to the ah passing of the plasma gas and then high
temperature has been created and finally, it creates the plasma arc between the ah nozzle
tip and the ah workpiece material. So, what is the advantage of with respect
to the gas tungsten arc welding process in case the plasma arc welding process. In general the position of the electrode or
torch of this plasma ah arc welding process can be designed in such way that; it can produce
the very constricted arc as compared to the gas tungsten arc welding process, because
gas tungsten arc welding process the arc is created between the workpiece and the electrode
tip of the electrode. So, depending of the tip of the electrode
the shape of the arc can be decided mainly, but in this case the apart from the electrode
tip there is a the plasma gas is the main ah gas that actually creates the arc between
the work piece. So, that plasma gas application of the plasma
gas can be constricted in a very small zone. So, that is why very constricted arc can be
created using the ah ah plasma arc welding process. So, even from on the other welding on the
arc welding process only in the plasma arc welding process it is possible to produce
the keyhole mode; that means, high depth of penetration can be welded using the keyhole
mode plasma welding process. So, here look in to that typical points of
this arc welding process first is the, what is the plasma? Plasma is a basically gaseous mixture of positive
ions electro and neutral gas molecules. And that plasma gas is actually create the
arc between the workpiece and electrode material. And here also like GTAW here is the non-consumable
electrode by specific advantage is that, it is a good tolerance of the arc to misalignment
if there is a misalignment it can be adjusted by the creation of the arc. And high welding rate can also be done in
plasma and keyhole effect can also be produced this is the only arc welding process, where
keyhole mode effect can be produced. Ah that produce that actually that actually
penetrate is the high penetrate in the for high thickness material. So, this is these are the typical advantage,
but other advantage of this things plasma arc welding can also be, nowadays the plasma
arc welding ah can also be developed in in the the in the micro plasma range in the sense
that that is called micro plasma arc welding processes. So, such that the electrode current that welding
current can also be reduced to less than 10 amperes and even it is can be controlled the
even for the in the range of the milliampere. So, it is controlled arc with this controlled
ah current the arc can also be control in in even in the model of the pulse or continuous
mode; and that small amount of the application of the current here; that means, the indirectly
heat is basically it can controls the heat input. And that input can be created in small way
small amount, that may be are suitable for the any kind of micro welding processes. So, that development has been done also in
plasma arc welding processes. That is the another advantage of this process
can say. But in terms of the disadvantage that expensive
equipment as compared to the other welding process that of course, the expensive equipment
it is a relative term here, probably this is expensive expensive equipment ah as compared
to the gas tungsten arc welding process, but high distortion and weld wide weld as a result
of the high input if there is a requirement of the high input then it can produce the
high distortion. And may be wider weld pool can also produce,
but the width of the weld pool is more con trollable in plasma arc welding process as
compared to the gas tungsten arc welding process. Now, normally plasma arc welding process 2
modes of the plasma arc can be used in the arc welding process. One is the transfer arc another is the non-transfer
arc. So, transfer arc means it is a it is a simple
way the creating the arc between the workpiece and the electrode material . So, that workpiece
being welded that workpiece being welded and it becomes the final part of the electrical
circuit. Ah plasma arc transfers from the electrode
arc basically arc creates or arc transfer from the electrode to the workpiece material
and that can be done is a very high speed of welding. So, this is the normal mode of the plasma
arc welding process that is that we we say the transfer arc it is like a gas tungsten
arc welding process it is a simple way the creating the arc between the workpiece and
the electrode, but other way also it can also be developed, but it is developing the another
mode of the electrode arc that is called the non-transfer arc. So, non-transfer arc is basically arc can
be created between the electrode and the nozzle. So, basically nozzles becomes the part of
the electrical circuit here to complete; and that generate the heat that heat can be the
heat can basically creates the molten of the workpiece material. So, in this non transfer arc basically high
temperature is carried out to the workpiece by the plasma gas. And this is in this case the thermal energy
transfer mechanism is basically like the almost similar to the and oxyfuel, ah where mode
of in oxyfuel welding process or may be oxyfuel transfer of the in oxyfuel welding process
what way it transfer the ah or it is generates the heat. So, basically the non-transfer arc is mainly
used for the welding of the various metal, but it is can be used as a in for the thermal
spring or making the coating of the surface. This non transfer arc is more preferable. So, that is way this is the another development
of the plasma arc welding process the using the non-transfer arc basically create the
coating process then welding processes. So, laser beam welding process this is one
of the most ah precisely controlled ah heat source process and use and when there is a
requirement of the very precision; that means, limited amount of the molten zone heat affected
zone, then this is one of the best solution; that means, using the laser beam welding process. Let us see the laser beam welding process. So, generation of the laser all these things
that the physics of the laser ah, that can be explained or in the different module, but
knowing all this fact about the laser we can say that in this case the laser beam welding
is mainly advantageous to produce the high depth of penetration. And it can creates the ah limited size of
the heat affected zone and the limited size of the molten pool; that means, aspect ratio
between the ratio between the width and depth of penetration is relatively more in case
of laser welding process as compared to the other are welding processes. Other point of laser welding process that
heat can be used either conduction mode or keyhole mode welding process both depending
upon the requirement. So, conduction mode welding process means
relatively the aspect ratio; that means, width and depth of penetration is relatively low
as compared to the keyhole mode welding process. So, conduction mode welding process we can
get the not much depth of penetration, but high amount of the weld width, but just vice
versa in the characteristic of the typical keyhole mode laser welding process, where
high depth of penetration and very small amount of the welding is produce the keyhole mode
welding process. So, depending upon the application both conduction
and keyhole mode laser will be process can also be used. In this of course, like other arc welding
processes here also the laser beam welding also use the shielding gas to protect the
molten pool ah of the material, but if you look in the typical advantages of all this
process; that first is that very narrow weld zone can be obtained using this laser beam
welding process because it is focused on the, it is focused on the very small zone, but
at the same time the intensity is intensity of focus intensity is very high as compared
to the ah arc welding processes. Relatively high quality weld zone can be produced
by simply making the usable of the keyhole mode laser welding process in this case; very
small heat affected zone, dissimilar combination of the materials can be welded using the laser
welding processes more easily as compared to the arc welding process. And of course, laser welding process is one
of the most suitable. So, ah welding process specifically to design
and development of different micro and nano welding process because laser source can be
controlled very precisely. So, taking this advantage there are the several
developments of the micro and nano scale welding process has been done, where other arc welding
process may not be suitable for the micro welding processes. Of course ah since we can use the shielding
gas also there is no need of the vacuum in this case like electrode beam welding processes. And heat can produce the low distortion of
the workpiece. Since, heat is focused on the or in this very
narrow zone that is, that way it can produce the relatively low distortion as other are
welding processes. But if we try to look into certain limitation
of the this welding process, the one limitation is that the cost of the equipment is very
high and as compared to the any other arc welding processes. And of course, it is not completely free from
the contamination of the outside atmosphere therefore; there is a requirement of the shielding
gas even in laser welding processes. So, these are the 2 limitation of welding
processes. And maybe we can we will try to focus discuss
more about on this laser beam welding processes later on. And next we can look into the another ah ah
high beam energy welding process that is call the electron beam welding process. So, in this case so it creates the this is
a high beam of the flow of electrons and this process definitely it carried out under the
vacuum. So, that the flow of the beam cannot be affected
by the atmosphere and definitely it also follow the keyhole in that sense; that means, the
even the high depth of penetration welding process can be achieved in using the laser
beam electron beam welding process as compared to the laser beam welding process. So, if very precisely look into the different
advantages that deep penetration weld can be produced and even narrower zone and heat
affected zone and narrow weld can be produce as compared to the laser welding process very
small distortion ah is the another ah advantage of this process, filler material is not required
and another advantage is that electron beam welding process that; the lot of combination
of the dissimilar materials can be welded more easily as compared to the other welding
processes. But of course, having some disadvantages in
this case is the even more expensive equipment does that than laser welding process. And very high ah production cost is also very
high; that means, when precision is the main requirement ah ah of any kind of welding process
then it is better option; that means, electron beam welding can be used as compared to the
other welding processes. Ah, but another it during the electron beam
welding process, the secondary scattering; that means, x ray irradiation also happens
during the process. So, that needs to protect ah during the welding
process. So, apart from this disadvantage in general
the electron beam welding is normally preferred, when there is a requirement of the high precision
ah ah by compromising the cost of this welding process. Now, other welding processes we can see that
the other type of welding process that is called the thermit welding process, where
the chemical sources can be used as a source of the heat. So, basically the generation of heat is mainly
control by the exothermic ah chemical reaction between the components of a thermit. Thermit can be defined as a mixture of the
metal oxides and aluminium powder. We can look into the example for example,
if you look into this equation ; that aluminium and Fe3O4 they react and forms the more Fe;
that means, pure iron and that aluminium ah aluminium oxide that produce the oxide. So, during this reaction heat also heat also
creates the heat. So, that heat generated is responsible to
weld the 2 different materials, but at the same time that pure iron here becomes the
part of the ah final weld joint. So, therefore, the molten metal produce by
the reactions acts as a basically filler material joining the workpiece after solidification. And that reaction since reaction produce the
aluminium oxides and free elemental iron and large amount of the heat and that exothermic
reaction occurs is basically reduction and oxidation. So, here aluminium oxide is much ah less dense. So, that can be separated out from the ah
molten zone, but it is also possible to include the welding process ah by sometimes by adding
some kind of the other alloying elements. Since, the production of the pure iron becomes
the final part of the weld joint. So, when you try to join the steel. So, that using some adding components can
improve the composition of the steel steel along with the ah molten pure iron. So, if you look into other type of reaction
also in thermit welding that chemical reaction other metal oxides can also be used. Here to produce the copper, here also second
equation we can see that there is a production of the copper. So, copper or copper based alloy can also
be welded using a similar principle. Now, if you look into that advantage of this
thermit welding process we can see that; heat of the chemical reaction is basically utilized
in this process therefore, no need of the extra power source is required. And specifically ah this large heavy sections
can be join in this process. So, typical application we can see the thermit
welding in realer track the joining of the ah component using this process. But of course, having the disadvantage that
one pointed out that only ferrous may be steel, aluminium, nickel materials can be welded
and; that means, we need to chose choose the material. So, that the reaction may happens in such
a way that; that produce the amount of the heat generate can produce the metal, but at
the same time the production of the pure iron from the equation we have seen. That becomes a part of the ah actual welded
join. So, that is why it is having limitation limit
combination of the material and the thermit. Relatively slow welding rate. So, the welding rate is not as much as high
as compared to the other arc welding processes, but high temperature passes may cause the
distortion and that actually affect the grain structure in the weld zone, sometimes the
weld metals may contain the hydrogen and the also the slag in slag inclusions or contamination
is the another difficulties ah may be disadvantage of this ah welding process. So, in summary of all this welding processes
we can see, we can see the few points that is most important points from overall idea
of all the different types of the welding process and their ah basic structure first
is that, heat generation is basically in the electrode that actually depends on the ah
polarity. So, amount of the heat generated on the workpiece
or on the electrode that; depends on the whether we are using the direct current electrode
positive or whether we are using the direct current electrode negative. So, when use the direct current electrode
negative in that case the maximum amount of the heat generated in the workpiece material. So, welding of the highly oxidized material;
that means, having aluminium oxides. So, where the cleaning action of is most important
in that case ac current; that means, alternative current is more preferable. Third point is that thermal conductivity of
the material is very important parameter and that thermal conductivity ah actually decides
that is the, that is the most in influencing ah properties of the material that actually
influence the amount of the fusion zone as well as the more on the, what is the amount
of the or size of the heat affected zone. So, this dimensional of these 2 heat affected
zone fusion zone is mainly depends depends apart from the other parameters the main parameter
is the thermal conductivity of this specific material. Now, if you when we discuss about the type
or nature of the power source is required for different welding process, in general
we can say the flat characteristic of voltage and ampere current curve is suitable for the
semiautomatic arc welding processes, but on other way the such drop characteristics type
of the power source is more suitable for the manual arc welding process. So, if if you look into the what is the nature
of the shielding gas. So, inert type of gas is the most preferable
choice for the shielding gas. And next is that in plasma arc welding process
the non-transfer arc is specifically suitable for the ah thermal spring or the in the coating
purpose rather than the welding processes welding of the different materials. And laser beam welding or electron beam welding
is mostly preferred when there is a requirement high depth of penetration, and the minimum
heat affected zone and the minimum fusion zone. Ah definitely this laser beam welding and
electron beam welding they produce the high depth of penetration through keyhole mode
formation of the keyhole mode welding processes. So, thank you very much for your kind attention,
next we will try to the next part of the ah this module. Thank you .

## One thought on “Week-1 Lesson-2 Fundamentals of Welding and Joining Part II”

1. Deepak Kumar says: