So, good

morning everybody, now, ah I will start ah the introductory level of this course advances in

welding and joining technologies. So, ah to some extent we know about the different welding

techniques and we have seen in the several places the materials are joining ah simply gas welding

processes or some other welding processes, but if we look into the signs behind this

welding and joining technologies and then we can find out that, ah most of the subjects are

involved ah in welding and joining technologies. For example, here ah will be able to know that,

heat transfer analysis the involvement in welding processes, material flow and any kind of stress

analysis distortion level and metallurgical changes; that means, structural changes

microstructure; that means, material science, metallurgical engineering, as well as mechanical

manufacturing ah some design and all are basically involved ah in this in the welding processes.

So, we will try to get some idea some basic idea ah about this process. So,

that we will try to cover the welding science and what are the technological development of

this process till that? That we will try to cover ah in this module. So, the module

consists of this following ah sections the we we can say that, first is the classification of

the welding processes then what are the physics of welding processes? And then mostly use the

fusion welding processes their development and different types of the ah welding processes.

What are the brazing and soldering processes? Soldering processes in regular life we we can

see that to , we can use an some electric circuit board, that is typical application

of the soldering processes, but brazing also industrial scale application also there, but we

will try to look into that what is the typical mechanism of brazing and soldering processes?

Then adhesive bonding is one kind of the joining processes,

we will try to cover this ah topics also physics of welding arc because, so far,

much development has been done in the arc welding processes. So, we will try to get some idea about

the physics involved the formation of the arc and in very specific to the welding processes.

Then more advanced topics ah in this section that is, what is the influence of the surface-active

elements? And based on that what are the different welding processes has been developed

or maybe existing welding process? What way we can modify this welding processes ah by

considering the effect of the surface-active elements? And finally, we will try to cover

the magnetically impelled arc welding process. So, these are the module of this ah different

section of this module and that, name of this module has been given in such the way that,

fundamentals of welding and joining we will try to get some idea basic physics involved

in the welding processes or most conventional welding processes the different ah technology

of the welding processes we will just get some broad idea about the processes.

If we see that, almost all sector of the industry there is a need of joining of the materials,

that can be done either fusing of the metals or may be using some adhesive or some other joining

techniques. If we listed some of the applications area, so electrification, automobile, airplane,

water supply and distribution, electronics, radio and television, agricultural sector, computer,

telephone, air conditioning and of course, almost all sector it it is covering this thing. So, it is

indeed is very much important to know about, the fundamentals of the different welding processes.

Now, if you see the mostly use ah this technology in the or in the air aeroplane

or aerospace industry, highway, the health technologies, spacecraft, and the reselling,

the different welding processes has been developed looking into the application

of the high-performance materials. So, it covers almost all the sector. So,

here the importance of the welding processes and well before going into details, much details about

all the welding processes, we will try to get some ah basic mechanism of all this process, probably

it can be a review of the different welding processes, that mechanisms are only will be

focusing in this part. You know how you can define that, what is the welding and joining? So, there

is no precision definition of ah welding processes or joining processes rather we can say that,

when 2 metals specifically metallic materials are joined by fusing ah with the application

of ah different type of the heat source. So, that in general, that is called the

welding processes normally, welding involvement there is a fusion is there and joining processes

may be in other way ah that for example, that when you some first inert mechanical

riveting and use the first inert to joining the ah 2 components, that is also that is also termed as

a joining processes, but there is no need of any kind of ah fusion or may be atom to atom

violence's is not required ah in that cases. So, that can be considered as a joining process

for example, even in adhesive bonding also if you use some glue and to join 2 materials,

that can be also called joining process, but here the mechanism on joining process different from

the fusion processes. So, that fusion is happening in the welding and joining processes specifically,

that is termed as the fusion welding process of course, we can say that, solid state welding

processes also can be considered we generally say some say solid state welding process,

sometimes also we can say which the solid state joining processes even the soldering and brazing,

that is also the application of the 1 3rd 3rd metal try to join the 2 different material by

fusing the 3rd metal, but not necessary to meld the parent metal. So, that is the basic mechanism

of the soldering and brazing mechanism. So, that is that also we can say one typical

joining mechanism. So, in general we can say that, it is a not only welding or not only joining

process we can say, it is a welding and joining processes ah of the materials irrespective of

materials or irrespective of any non-metals also. Now, critical technologies in manufacturing mainly

recent ah or maybe huge application or I ah can say the maximum application of welding and joining

technologies, we observed the construction industry and as well as the mining industry

and specifically in this case the joining or welding of the materials involves, ah there

is a huge large amount or may be thickness or this thickness of the metal is very high in this case.

But, at the same time if we find out the very precision application of the welding

and joining technologies that, we observed in the weld technologies by medical devices ah there, we

can find out the requirement of the joining of the very small thickness may be, less sometimes it is

requirement is may be less than 100 micrometre. So, we say that, as such the application of

the welding and joining observed from the very precision instrument ah in the level of ah 100

micrometre or less than that to a large extent that, we observe in the huge thickness of the bulk

joining of the material we can find out in the construction and the construction specifically,

if you try to make bridge there also apart from the rubber join the welding join can

also be done ah for the construction industry specifically the example is the making the

bridge the river bridge and then, another cases is the mining industry also we can find out,

that is huge application of the large scale welding processes. So, apart from very large

scale to very small case there is importance of the different welding and joining technologies

So now, here we will try to focus in general of the welding technologies

and there is a separate module of the micro joining and ah nano joining section where,

we will try to focus on the very precision ah welding processes in very small scale.

But, why it is important? The welding and joining analysis of all this welding and joining because,

from the past it has been observed that, if the technologies of welding and joining are

not proper probably we can find out, there is a formation of the defects and presents of the

defects may leads to the catastrophic failure of the whole structure, and that can lead to the loss

of property as well as the human life. So, here is the important to analyse the different welding

processes and if there is a permission of the defects or whether, we can ah chose the different

welding technologies for ah without any defects. So, this is not only the problem in the welding

industry the permission of the defects by the improper choice of the welding materials or

improper selection of the materials ah in the sense that, with respect to the material the

if welding process has not proper then, there may be the problem of the formation of the ah welding

defects not only this finally, if we use ah any kind of ah ah welding processes whether,

it is solids welding processes or fusion welding processes we can found out that, there may be the

formation of the some amount of the residual stress and distortion, that can be controlled

what that cannot be completely avoided? So, presence of residual stress also affect

the life of the ah welded join. So, always we try to target to reduce the the nature of distortion

and nature of the ah residual stress. So, that is also another problem or maybe I

can say that , it is the ah inherit ah that is the that, comes by inheritance the presence of

the any kind of residual stress and defects ah during the welding process. So, in that

sense ah it is also necessary to analyse the or to know ah basic mechanism or basic engineering

of the ah different welding processes. Now, before that which welding and joining

processes can be ah classified in the following way that, based on the different types of welding

of course, the classification can be done from the different perspectives, so with respect to

that one perspective you can say that, there a ah 3 different 1 is the fusion welding,

pressure welding and friction welding. So, here basically the difference is

that, ah nature of the heat source and how we can control the heat source? Or how heat can be

generated to join 2 different or similar kind of materials? Fusion welding definitely the we

apply the source of heat source in such a way that, it should cross the melting point of the

subset material. So, that it can fused together and upper solidification it makes the structure.

Pressure welding simply application of the pressure or may be application of the load

is the main mechanism to do the joining of the materials. Friction welding of course, the heat

is generated in this case due to the friction. So, in friction welding normally, we generally keep

the friction welding ah the maximum temperature is below the melting point ah temperature.

So, in that in that, case they can they can be ah consider as a ah solid state welding

process as well. So, this 3 types of welding processes and we can see further that, fusion

welding processes can be classified as the ah homogeneous and heterogeneous welding processes.

And if you see other part is the heterogeneous welding processes, that brazing and soldering.

The heterogeneous welding processes means that, we use the ah some another 2nd or 3rd material ah to

join the similar kind of metal or 2 different type of material. So, in that sense it is called the ah

heterogeneous welding processes and in the other case the homogeneous welding processes here,

you can find out that not may not be necessary to using the ah 3rd material may be, 2 similar kind

of material they can join ah it is a and can form kind of homogeneous structure. Even for dissimilar

materials also they can join together, but finally, they can from the homogeneous structure.

So, in that sense it is the it is called the homogeneous and the heterogeneous joining

processes. So, homogeneous there are several types of welding process we can see that,

gas welding process, electro flag welding process, high beam energy and the electric arc. So,

all this all these cases the ah generation of the heat mechanism are in the all these cases are

different, but common thing is that anyhow that, ah when you try to join 2 ah materials may be,

there is must be some amount of the heat generation should be there. So,

that the materials can be ah joined together. So, but all these cases the source of the heat

are different, 1st cases the gas welding simply bounding the gas is the that, actually converted

the basically chemical energy and the converted to the heat energy and that, heat energy utilize

to weld the materials then, electro flag welding also similar kind of may be in this case that,

arc can be generated then, high beam energy also the beam means the either laser or electron beam,

that is the high source of energy can be used and electric arc based on the electric

arc ah can be ah can also be used in this case. So, all this ah different types of the

homogeneous welding processes, but in this case the heterogeneous welding processes mechanism are

different from the homogeneous welding processes. So, heterogeneous process in case in generally

generally, we conventional we can find out the 2 different types of welding process, one is the

brazing another is the soldering. So, in details we will discuss about all this processes. Now,

other things we can see that, electric arc welding ah there are 3 different types of mig welding,

metal inert gas welding or gas metal arc welding then, T welding, ah tungsten inert gas welding

or gas tungsten arc welding and shielded metal arc shielded metal arc welding also,

that is sometimes it is called the stick welding, that most of the cases we observe the metal arc

welding process and we ah practically we can observe and the in any kind of construction site,

that using of the different types of the welding processes. So, that can be that are categorised

as the electric arc welding because, in this all these cases they produce the ah electric arc.

So, in general that generic types can be classified of the welding and joining processes

or rather I can say the, what are maybe? You can say the rather than classification here,

we can say what are the different types of welding processes here? So,

in this case fusion welding process see the arc, gas, power beam, resistance that, actually can

be categorised as a fusion welding processes, thermo mechanical processes can be considered as

the friction flask ah explosive welding process. So, in this case the ah not only thermal condition

may be, some mechanical ah energy also required in this case and in general, that is called the

thermo mechanical energy utilized for all this cases and fusion welding only heat

energy or may be, thermal energy is utilised ah to conduct all this type of welding processes.

Then mechanical joining processes. So, it is not the welding, but it is the joining process

because, frost inert can be used simply joining of the 2 components. So, ah that is called the

mechanical ah mechanical joining process or may be in general, that is the joining processes,

ah solid state welding process another generic type of ah welding ah or and joining process,

that is called solid state, that is adhesive soldering and brazing can be categorised as ah

distance because, ah in this case the temperature actually below the melting point temperature of

the substrate material. So, in that sense it is called the solid-state welding processes.

Even for friction state welding process, that is there also the mechanical steering , as as well as

frictional heat generation are responsible for the welding of the materials. So,

that can be or can also be categorised as the um in that, solid state welding process.

So, point is that, when we try to classify the different welding process. So, we need

to consider the different perspective to ah classify the different welding process. So,

this is these are the one way, the different types of welding process normally exist. If we

see in other prospective whatever, we can classify the welding process. So,

before that we look into that, what the different types of welds we generally ah observed?

In the first figure if you see that, that is the 3 types of welds the first one is the

2-common application of for the hot surfacing basically surface welding means; that means,

the it is application of the heat and making the joining of violences of the

materials is happening only over the surface. Second one is the groove welding making a groove

between the 2 plate and that, can be ah that groove is fill using some filler material. So,

the primary use of the groove welds is to be ah complete the butt joints. So,

configuration the butt joint because, ah in this case 2 plates are flat and they are join ah at the

edge and either use using any filler material or not. So, that can be ah that also one type

of joint that is in general, that is called the butt joint. Butt also can be considered

as a groove joint ah if we try to make some groove before, the welding ah of this 2 metals.

So, another types ah types of weld, that is also fillet weld. So, fillet weld ah the configuration

of the geometry ah or of the base metal are different in this case. If we see although,

it waking the kinds of T section, but one side it is weld or fill filled by the welding material.

So, that is call the ah fillet fillet weld. So, have a triangular cross section used or

that are at 90-degree ah 90-degree ah angle. So, filler weld it can be done for a T cross

section and the ah lab joint lab to different metals of joint and then, that can be welded

using the materials or it can edge joints or it can be ah 2 edges having 90 degree perpendicular

they can be join using the ah fillet. So, these are the type of welds different

welds butt type of the joints can be other way we can observe that, butt joint simply joining of

the ah 2 materials ah over the edge and then, lap joint when the lapping lap joint the 1 plate is in

over the another plate and any 1 of the contact is can be join using the filler material. So,

that is called or without the without using the filler material, that is called the lap joints.

So, here the geometric configuration of the joint are different in this case here, if you see

that T joint, T joint means, that ah 1 plate is horizontal plate is there and over this 190-degree

vertical plate ah kept and then, both side can be join or single side can be joint, ah that is that

is called the T type of joint corner joint. So, ah the 2 plates are keeping ah perpendicular with

each other and that, corner are joined using the welding processes and edge joint. So, over on the

edge the geometric configuration different, but over the edge the weld can be done.

So, from the figure it is obvious that, there are there are different types of welds and or there

are different types of the joints we can observe practically, ah by simply by by ah what way we

can configure the ah different materials? We can say, ah different substance materials in that,

way we can find out the this ah this the different nature of the ah types types or

nature of the weld joints observed practically. Now, again we come back to that, classification of

the welding and the joining processes may be other way we can in general we can say that,

joining joining processes. So, joining processes itself include the welding processes ah also.

So, ah in the joining processes we can see the there are 2 different one is the permanent joint,

another is the non-permanent joint, another is the semi-permanent.

So, from that way, we can categorise the different joining processes, first is the

permanent joint may be, welded joint can be considered as a permanent joint and because,

violences of the material happen in this case it can it may happen either in the liquid state;

that means, cross the melting point is above the melting point temperature or it can happen

the in solid state as well also. So, both can be considered as a permanent joint.

Second is the soldering and here also soldering the soldering is when soldering is done joining

between the 2 components, the solder material needs to melt and it can join the 2 materials ah,

but not necessary to make the parent metal. So, this also creates the permanent joint. So,

similar philosophy also for brazing also and this also call the permanent joint and of course, may

riveted, riveted joint ah this one kind of I can say the mechanical joint also, but this is also a

this can be considered as a ah permanent joint . But non-permanent joint in the sense, that bolted

joint and the screw joint because, it is possible whenever, requirement required this possible the

disassemble of the ah joining materials. So, in that sense it is considered as a non-permanent

joint where in, other way welds is riveted has been when riveted joint can be considered as a

permanent joint in the sense that, if you want to disassemble the components then,

you needs to break the ah the riveted part, that is why it it is considered as a permanent joint,

but it is not necessary for the bolted joint or screw joint.

Semi-permanent joint can be categorized as the ah adhesive bonding because, adhesive bonding when we

joining 2 materials, we put the adhesive between these 2 metals and ah at a curing of the after

certain curing time the 2 components or 2 metals ah can be joint. So, that is the joint by using

the adhesive bonding, but these adhesive bonding having some life after certain ah time they

can ah ah they can disassemble, but the depends on the what type of adhesives we are using.

So, in general ah this adhesive bonding can be considered as a semi-permanent joint. So, in

that prospect for the different ah ah permanent, non-permanent or the semi-permanent joint. So,

this is the one way of the classifying the different weld joining processes. So,

in other other way, the welded joint. So, that is the classification of the welded joint.

So, several joining processes the fusion welding then, metal deposition process and pressure

welding this 3-main categorisation can be done, when you try to classified of the weld joint. So,

if you look into that, what are the different types of the welding process include in fusion

welding process? That gas welding, arc welding, high beam energy welding and thermit welding. So,

all these cases ah the we apply the heat source intensity in such a way that,

it try to melt the ah basic material or base material and then, after solidification the

permanent joint can be done. So, in this case. So, here nature of the heat source is applied in

such way that, it will try to fuse the base material. So, that is why it is comes under

the category of the fusion welding. So, that fusion welding the source of the energy here,

in the in the by creating the arc or chemical in the using the gas or uh using the high

beam energy like, laser and electron beam. But, in case of metal deposition process the

sense of the classification is different in this case of course, we use the ah source of

the energy ah different energy is it try to ah fuse the ah material, ah which solder material,

but it is does not fuse the based material. So, that is way the metal deposition process in the

sense, that we use the another extra material to join between the 2 metals, without ah reaching

the melting point of of the 2 material. So, soldering, brazing and adhesive bonding

also ah comes into under this category. So, that; that means, we use some extra material

to join between the 2 components, ah without melting the parent components. Pressure welding

other categorisation is that, here you can see that, what are the different welding processes

includes in the pressure welding process? That friction welding, ultrasonic welding,

explosive welding, diffusion welding, resistance welding and magnetic in arc welding.

So, in this case normally the pressure welding means, the application of the load is required.

So, that actually try to ah create the joint or deep bonding between the 2 components or

2 materials. So, friction welding of course, apart from the pressure some frictional heat

also generated in this case, ah that actually helps to ah violences of the ah components or

materials similarly, ultrasonic energy can be used in this case to joining explosive when the

using sub explosive in this case the using some explosive and then, highly deform the components

is highly deform the high high rate of plastic deformation happen with the component and then,

these 2 components can join in the solid state ah creates the solid state welding processes also.

Ah similarly, ah resistance welding also ah resistance welding ah in this case that,

we apply that resistive heat also, but at the same time to make the joining process we need

to apply some mechanical load as well ah. So, in that sense the resistance welding of

resistance the ah it creates the due to the ohmic heating, it creates the uh generates the heat,

but at the same time we need to apply some constant pressure or may be some variable

pressure also. So, that the welded can be done. So, apart from the various kind of the source of

the heat or generation of the heat, there is also some mechanical loading condition is also

required in case of the pressure welding. Anyway, we will try to discuss of all the

different types of the welding processes as well individually. So, by looking into that,

different way of classification of the Ah welding processes. Now, we will try to focus on the,

that physics of the ah welding process. So, how ah the joining of the 2 materials comes

and what way the different development of the in the welding industry has been terms. So, what the

type? So, first question is that, if it is possible to being 2 metallic surfaces together,

is it possible to join these 2 surfaces or 2 components, if that is possible then I think

they are may not be necessary, that such kind of all this ah development in the welding processes.

But, let us look into that things since the only grain boundary separate them; that means, between

the 2 metals, if that in that case 2 metals come in contact with the metallic surface come in

contact then, joining adherence with the large force is possible, but this is the very ideal

case. Because, that types of metallic surface ah may not be possible in practically because,

that metallic surface most of the cases we can find out they are contaminated with the oxide

layer. So, ideally it is not possible to may bring the 2-metallic surface if it is not contaminated

with any kind of ah layer of the metals. So, in that sense in absence of that layer,

that 2 metallic surface in come in to the contact then it is possible to join between

these 2 metals, but apart from this if there is a no if there is ah any presence of the

oxides layer then, in ideal in that ideal cases it is possible to join, but practical

cases most of the metallic surface equisetum with some of the oxide layer and it is not

possible to join ah possible to join them, until unless there is a removal of the oxide layer.

So, that presence of that oxides layers is basically brings the concept of the different

weld ah development of the different welding processes by the mainly by the application of

the amount of the ah or the some kind of creation of the generated heat between the surfaces. So,

that actual practical ah that surfaces presence that, deals with the phenomena associated with the

different welding processes and development of the different welding processes.

Now, the formation of the weld bead bones basically that fusion welds or even

solid-state welding commonly differentiated by the physics of the metallic bonding mechanism. So,

that is only difference the ah in weld bond or that is the only metallic bonding the nature

of the metallic bonding ah what way we try to explain the fuse or solid-state welding

processes ah either in the fused welding processes or the solid-state ah weld?

So, we will try to look into that, deviation from the ideal cases and what are the development

of the welding processes can be done? Now, before that we will look into that,

what is the physics ah principle of the fusion welding processes? So,

in fusion welding processes basically they are created by the coalescence of the molten base

metals and mixed with the molten filler metals not necessary always the filler metals are required?

So, ah in this case the fusion welding happens by the way, the metals must be heated to the to

raise the melting point temperature for fusion weld to be produced. So,

in this case what happens raise to the molten temperature and they mix up the molten metal

mix up and then finally, they solidify to the ambient temperature and then, actually

makes the ah bonding between the 2 materials. So, that bonding may happen either similar type

similar type of materials or maybe 2 different types of the materials, but in this case the

typically the fusion welding process it is characterised by the molten pool pool zone

basically the molten zone and then, heat affected zone. So, heat affected zone also occurs because,

the heat is applied to the to melt the surface, but up to a certain extent there may occur the

phase transition or phase transformation happens, and that is inherent to the processes. So,

that phase transformation ah ah measure the phase transformation affect is basically

indicated by the heat affected zone, and that heat affected zone is basically ah identified the

ah microscopically or macroscopically as well. But, after after solidification or may be after

cooling down of the molten pool and then, when the it is cool down ah to the room temperature then,

there may be the possibility or definitely there must be some amount of the distortion and residual

stress and over the solidification period the some metallurgical changes also happen. So, like the

phase transformation also happens in this way. So, that metallurgical transformation of this ah this

can be better identified by the different size of the molten zone or different size of the weld zone

or different size of the heat effected zone. So, in this case what we understand that,

in fusion welding process there is a necessary to apply some intense heat ah to the ah focus

zone. So, that intense heat basically melts the selective part of the material where, uh about to

join between the 2 components and after melting it subsequently solidify and creates some different

metallurgical zones, may be that is called the fusion zone or heat effected zone and of course,

remaining part is unaffected the base metal. So, these are the typical characteristics, but

other way also after solidified of the molten zone it is accustomed to some amount of the distortion

and residual residual stress. So, this is the principle of the fusion welding processes. Now,

what is the solid-state welding process? So, solid state welding process definitely the

temperature should be below the melting point temperature and ah arc created by

either the microscopic or the ah ah ah this is the basically created either the macroscopic

or the microscopic violences of the materials, and that remains in the solid state of course,

phase transformation may also happen in the solid state, but the team that that

phase transformation is the happens below the melting point temperature of the materials.

So, apart from this the fusion welding and ah sorry that, principle of the fusion

welding we discussed and that principle of the solid-state welding process. Now, we come to that,

point the physics of the arc welding process in the sense that when you try to ah because,

arc welding is the ah mostly used ah process and most common processes also and in arc

welding process we generally, ah control the separate parameters first is the voltage.

So, electrical ah potential or the pressure that, causes the current flow that voltage is the the

potential, that is required to flow the current and basically the current can be defined is the

movement the movement of the charged particles in a specified direction. So, voltage decides

the flow of the current and current actually is basically in terms of the charged particle,

and that flow one direction and then, that when the current flowing in specified direction and

when it is creates the arc between the ah positive and ah negative charge work

piece on the electrode material and then, it try to complete the ah electrical circuit.

So, that electrical circuit makes the ah development of the arc welding process,

but in this case this electrical circuit or nature of the voltage and current ah is

basically different from the ah other common ah electricity what we use in the 2 use in the

this thing that ah normal current; that means, for a specifically for ah in ah in a bulb here,

you can see that common electrical connection were is the the supply is basically that high voltage

and ah low current normally the voltage around 240 volt and low current may be 5 rams like that.

But, when you try to use this electric current in the welding purposes the we use in different way,

here the current requirement is very high and the voltage requirement is the low maybe

standard or typical say 20 volt or 24-volt ah is required, but current may be depending upon the

process arc welding processes or depending of the size of the work piece it can varies

from 100 amps to say 200 amps like that. So, that way the common electrical circuits

is different different from the ah what we use in kind of welding purpose, but point is

that ah voltage current, that actually decides the power of the arc ah, but polarity also is another

important factor. So, polarity means what way we can use a positive and negative cathode and how

what we decide the cathode and anode? Which one should be positive? Which one should be negative?

So, there are several way to decide the polarity one is the DC; that means, ah DC minus; that

means, direct current electrode negative, DC plus direct current electrode positive and we

can use also alternating current depending upon the application ah of the application

or maybe depending upon the materials and they are typical characteristic how is uh interact

typical characteristics of the molten pool? what it is interacted with the surrounding

materials or surrounding atmosphere? So, here specifically the heat ah that,

different type of polarity; that means, whether it is DCEP direct current electrode positive or DCEN

direct current electrode negative or it may be AC depending upon the polarity the amount of the

heat is generated in the electrode or amount of the heat is generated to the work piece. So, that

depends on the in general the type of the polarity we can use for the ah in this welding purpose.

So, that maybe it is not necessary for the different welding processes follow the different

type of the polarity, but for example, GTAW and GMAW the gas tungsten arc welding process and

gas metal arc welding. In these 2 processes there that we have the choice of the using the DCEN or

DC or AC polarity depending upon the application or depending application on on the materials.

So, I will come to that one later on ah the what is the typical utilization of all this thing? But,

thing is that ah if electrode negative and work piece is positive in general in that case,

the kinetic amount of the energy electrode is basically exposed more on the work piece surface.

So, in that case we can expect the more amount of the heat generated in the work piece surface. So,

our if our objective is to melt the work piece material more in that case,

we should use the DCEN polarity; that means, work piece positive and electrode should be

negative in that in that, polarity around 70 percent it will be generated in the work piece.

But, our objective is to melt the consumable electrode for example, in case of gas metal arc

welding process we use the consumable electrode. So, objective is to consume more electrode. So,

more amount of the heat general is more preferable on the on the electrode. So,

in that case direct current electrode negative is more preferable in that sense uh. So,

in this mode DCEP, that more amount of the heat will be generated on the electrode than,

the work piece material and also AC current. So, certain typical material for example,

aluminium this low melting point material ah, which is having high affinity to form the oxides.

So, in that case the AC current is more preferable. So, in this case may be in

alternatingly the 50 percent amount of the heat generated in general in the local 50 percent in

the work piece. So, the AC current basically helps to cleaning the oxide layer and the remaining 50

percent amount ah heat is generated on the surface. So, in that sense the if cleaning

action is required or maybe to remove the oxides layer. So, AC current is more preferable in

that sense , that generally observe in the application of the ah welding of aluminium.

So, electrical circuit basically the decides, that the ah nature amount of the generation of

the heat. So, we can see the electricity flow from the power source and through the electrode

basically if we consider the circuit in such way that, the through the power source the electricity

flow and then, it comes to the electrode we use electrode and then, it again it passes through

across the arc and then, that flow through the base material and again back to the power source,

in that is way it actually creates the ah electrical circuit here.

So, formally we can say the electrical energy is basically converted to the thermal energy

in the arc welding process. So, arc created by the electric current here the converted

heat into because, of the resistance of the electric flow. So, resistance of the

electric flow that actually responsible for the creation of the heat and the heat

melts the metal to fuse it together, after that heat melts the metal and to fuse it together.

So, that physics of the arc welding process then, just we will try to cover here the basic

concept of the which generally use in the arc welding processes next to that point enthalpy

of melting basically energy required to melt the material what we can estimate? Or what are the

factors is responsible for the to estimate the melting of the enthalpy of melting?

So, straightforward we can find out what is the amount of the energy required? That heat

energy required to melt are given volume of the weld, we estimate in that way we can separate

on these 2 part the heat required to melt the solid and then, latent heat of fusion

that actually to change the phase from liquid phase ah sorry from solid phase to liquid phase

some amount of the latent heat is required. So, in that way we can estimate that Q equal

to that, first component is basically the latent heat ah sorry the heat capacity or

may be in this case, that is called the ah specific based on the specific heat,

that component can be the melting point temperature based from the ambient temperature

to the melting point temperature and the total heat content to raise the or heat required to

raise the ambient temperature up to the melting point temperature, with the same phase solid

phase that is the amount of the heat required. And then, second part is the latent heat required

to change the phase. So, that is why the total amount of the heat can be ah considered ah that

is required ah to the volume required to melt a given volume of the material. So, once we

estimate the amount of the heat and typically we can find out the weld zone is like that,

first is the fusion zone that is the molten zone of course, molten zone not exactly the amount of

the heat generated just to melt, but here the application of the heat says it goes up to the

some super heat temperature as a also. So, we are neglecting basically the enthalpy melting

we are neglecting, that super heat ah that amount of the heat required to super heat the material.

Now, apart from the fusion zone it some part is affected up it is the solid solid state,

but that is defined in the heat affected zone. So, that zone is affected by the heat, and that

can be identified simply the by phase transition with this zone and of all these happens over the

in the solid state; that means, without the less than the melting point temperature. So, that zone

is the heat affected zone and other part is the base metal that is, the unaffected base it is not

affected by the application of the heat in the source. So, this is the typical characteristics

of a basically the zone of the different weld zones in in specific fusion welding process.

Now, what are the different energy sources are generally used in case of welding processes? So,

of course, the energy here is used to produce the bond in form in the form of the heat first

making the heat application the heat to melt the metals and then, cooling the cooling of

the metals through solidification process. So, here we will try to the what are the different

categorisation of the heat source may be used ah for the fusion welding processes?

So, first is the electrical sources of course, use the electrical energy either available in

the form of the AC alternative current or in the form of the direct current sources for example,

the different welding processes arc welding processes, resistant resistance welding process,

electro electro slag welding all the different welding processes,

we just use the ah source we use the different electrical sources to create the thermal energy.

Second is the another source of the energy for the welding is the chemical sources. So,

here the chemical energy uh is stored ah within a cylinder and the in the different form we

can use the ah chemical energy for example, the oxyfuel gas welding. So, oxyfuel gas welding we

can use the ah the fuel cylinder and to make the gas welding processes even for thermit

welding processes in this case also that, we can use the chemical energy or of course,

we use the some ah in this case we use the thermit is the mixture of oxides and other materials and

that, create some ah chemical reaction and the reacts that, exothermic reaction and that creates

the some amount of the heat and that, heat can be utilized for the welding processes.

So, in these cases the chemical sources actually acts as to produce the generated heat. Optical

sources we can categorize the optical sources in this way that fused beam of the electron or laser,

which is operated is actually operated according to the law of optics. So, in this case that it

can achieve a high-power density creates it possible to the high-power density ah; that means,

high concentrated heat can be possible as compared to the other welding processes.

So, typical example is the laser welding laser beam welding processes and electric beam welding

processes in these 2 cases ah we can use the heat source from the optical sources then,

mechanical sources the in involve the some amount of the mechanical movement of the that, mechanical

movement of the ah movement that, actually produce the amount of the energy for example, friction

welding if you friction welding basically if we try to give the mechanical motion of the substrate

material the high rotational speed ah then, even if it is contact with another material, ah that at

the contact surface they are may be the generation of the heat ah due to the friction and that,

friction happens due to the mechanical motion of the ah substrate material. So, in that way that,

some mechanical source can be used ah to generate the amount of the heat. So, that friction welding,

ultrasonic welding and explosion welding all these kind of welding processes the mechanical source is

the actually produce the amount of the heat. Solid state sources we can separate category

the solid state sources in this case is the categorises it is categorised by a lack of

the motion in contrast to the mechanical source is that is, in that sense we are not using the

any mechanical ah sources here, ah may be we do not use the mechanical motion as a source

of the generated heat rather, in this case may be the application of the concentrated

load or may be distributed load is applied, and that is responsible for the joining of

the material. So, that is one example is the diffusion welding and, in this case,

may be the source of the ah energy source of the energy can be considered as a solid-state source.

Now, when you analysing the different energy sources is required for the welding process now,

we will look back to the what are the different different physical properties of the material?

And which may be significant ah in very specific to the ah welding processes or to analyse the

different welding processes? So, physical welding properties basically of the materials influence

the applicability of the different various joining processes. So, that is why we need to know the

different physical properties of the materials, and that actually decides what that actually

relates to the applicability of the different welding processes. So, that is why it is necessary

to analyse the different physical properties of the metals, first is the electrical resistivity.

So, electrical it is having the maximum effect in the resistance welding and significant role

in other processes like, ah gas metal arc welding process or gas tungsten arc welding processor. So,

that is why we should know the, what is the electrical resistivity of the material

decide the applicability of the different welding processes in principle thermal conductivity. So,

what way the materials can transfer the heat that, depends on the thermal conductivity.

So, for example, some material is having very high thermal conductivity ah for example, copper,

copper is having high thermal conductivity. So, sometimes it is very difficult to ah weld in the

sense the application of the heat immediately the conduct away the amount of the generated heat. So,

concentration of the heat is maybe is probably less in this case to melt the the material. So,

that is why, it is necessary to know the thermal conductivity of the it is

a very significant parameter, that this is the applicability of the different welding processes.

So, in general pure metal is happen good thermal conductivity, but if we try to allow

if we add on the alloying elements generally the thermal conductivity reduces. Next is the

coefficient of of expansion the thermal expansion coefficients in welding of the materials also it

equally important to analyse the distortion of the welded specimen because, the application of the

thermal energy or there may be the thermal strain will be produce and the thermal strain is that,

amount of the strain is that, depends on the distinguish or expansion coefficient. So,

or maybe if there are 2 different material there is huge difference in the thermal

expansion coefficients probably in this case there is the difficulty of joining

these 2 materials or maybe the 2 materials having the similar range of the 2 dissimilar

materials having the similar range of the expansion coefficients. So, probably in that

case the joining must be little bit ease. Ah. So, that thermal expansion coefficient

is another important parameter, and that directly linked to the distortion analysis

of a welded join specific heat we understand the measure or amount of the heat content or

it can observer amount or it can store the heat the amount is basically decided by the

specific heat of a pacific material, ionisation potential. So, different materials the ease of

arc initiation basically when we try to do the arc welding processes how is we can create the

arc? And what way easily we can maintain or arc can be stable, that actually relates to

the ionization potential of a specific material. So, to get a initiation of the arc easily and we

can stability as minimum as possible ionization potation material is required in this sense metal

oxides of course, oxidation rate is another critical problem in the welding process. So,

different materials the oxidation rate are different and the effective stability,

when this meeting the metal oxides the stability of the metal oxides during the

welding is basically affects the transfer of the heat from the any source or it also

depends on the different alloying elements ah alloying elements of the parent metal.

So, that is why it is very important to the know the ah oxidation rate of a specific material ah or

or the nature of the metal oxides and when you try to weld when you try to select the

an alloying process for a specific material it is necessary to analyse the metal formation of

the metallic oxide just give the example that, aluminium oxide aluminium is having high rate

of oxidation and easily form the aluminium oxide. So, that is why when you try to choose the welding

process we generally use the alternative current AC current such that, it clears or it removes

the oxide layer in the half of the cycle and remaining time of the cycle cycle time it is

the simply heat the material. So, in that sense the analysis of the metallic oxides is required .