Lec 27 – Magnetic pulse welding

Lec 27 – Magnetic pulse welding


hello i welcome you all in this presentation
this presentation is based on the topic magnetic pulse welding and this presentation is related
with the subject joining technologies for the metals so the topic is magnetic pulse welding this
process is basically solid state joining process so there is no fusion at the faying surfaces
or at the surfaces of the metal being joined so there is no fusion and this unique feature
is exploited for joining the metals which are not compatible metallurgically particularly
metallurgically with each other in molten state so if they are not metallurgically compatible
then such kind of metal combinations can be brought into weather using solid state joining
technologies like magnetic pulse welding right so metallurgically incompatible because such
incompatible metallurgical systems during fusion welding when they come together like
aluminium and iron or aluminium and copper or copper and iron when such systems in molten state brought
together they form unfavorable inter-metallics after interaction or reactions in the molten
state and formation of such brittle poor inter-metallics they lower down the mechanical properties
as well as corrosion resistance of such kind of the weld joined so if we need to bring
together the two metal systems which are otherwise in molten state not metallurgically compatible
then we can use magnetic pulse welding process which is one of the solid state joining techniques this process was invented long back in 1970s
for specially joining of the sheets and for the automotive components so for manufacturing
the automotive parts this process was developed and still it is largely used for joining of
the sheets which are plain or flat form and also thin walled tubes and pipes so we will see how this process works in which
way which other solid state joining process is close to the magnetic pulse welding process
and how it exploits in which way the joint is formed so this process is one of the you can say
is very close to the explosive welding process about which we have already talked this process
works on a very simple principle one system say this is base or anvil on which the component
to be joined is kept so this is stationary and another component is kept movable kind
at some distance over which we place the explosive material and this explosive is detonated so detonation of the explosive accelerates
the movable plate towards the stationary plate and impacts at very high velocity above certain
critical velocity and this in turn results in the development of the joint at the interface
and this interface typically is found to be of very wavy in nature so such kind of wavy
structure at the interface results in the strong bond if this interface is largely flat
then it results in somewhat poor strength of the bond so in case of explosive bonding we need to
be very careful in the sense that since explosive is used and it is the donated in course of
the process this explosive is used to accelerate the process one of the movable component towards
the stationary component so that it can impact with the stationary components presently high
velocity to develop the bond so we need the lot of infrastructure and special
precautions to use the explosive welding process but the magnetic pulse welding is close to
the explosive welding process in the way that the acceleration of the plate towards the
fix plate it also uses one fix plate fixed one and another is movable and in this case
sufficient gap is kept so that when it moves impacts with the work piece and here what
we use basically the coils are used which are fat with the suitable high frequency high
current for very short period so the period is very short may be say like
50-100 microseconds current so this is time for which the current is fed and the current
is of very high magnitude say 500-1000 amperes and it is allowed to flow for a very short
period so when it happens a high strength this such a flow up such a high current for
a short period a develops the high density magnetic field this high-density magnetic field this results
in the development of eddy current in the one of the plates which is movable in movable
plate and the magnitude is so high interaction of these two means the development of a high-density
magnetic field induces the eddy current so high repulsive force start acting on the movable
plate so high force high magnitude you can say high magnitude repulsive force start acting
on the repulsive lorentz force start acting on the plate and which accelerates the plate at very high
velocity towards the fix plate and when it happens the plate accelerated the movable
plate accelerated towards the fix plate and impacts at high velocity which is say 500
up to 500 m/s such kind of impact result in the formation of the bond at the interface in the same way as we have seen in case of
the explosive bonding so as in case of the explosive bonding here the interface also
will be of somewhat wavy in nature one side we may have aluminium and other side it may
be copper and similarly we may have one side the steel and another side we may have copper
and it will result in the interface which is typically wavy in nature greater is a waviness stronger will be the
bond between the two and under such conditions of impact what are oxides or absorbed gases
are present at the surface all these are destructed broken so that the metallic continuity between
the two members dissimilar members being joined is established for developing the metallurgic
bond between the members so this is the process of principle on which it is based so we have seen the high velocity acceleration
is achieved through the pulse of high strength magnetic field pulse of the high frequency
current and a such a high-frequency current for a short period is fed through the discharge
of capacitors because it takes a lot of time for charging of the capacitors and once they
are the discharge such a high magnitude of current is allowed to flow through the coils
so the high-density magnetic field is generated which in turn generates the repulsive lorentz
force that forces the movable plate to move towards the fixed plate so that after impact
after the collision it develops the strong metallurgical bond so if we say the nature of the process and
certain conditions are important for successful welding in this case one is the collision
velocity the velocity at which impact is taking place must be high enough otherwise the bond
will not be formed and the too high velocity also can result in the partial melting so
the important thing is the velocity at which impact is taking place is high enough say
these are the two members which are being joined so whenever there is a impact lot of
interfacial surface layers experience that deformation so due to the impact at such a high velocity
results in the very localized plastic deformation this deformation may be limited to say 50-100
micrometer and such deformation also means this due to the impact temperature rise also
takes place sometimes at very near surface layers it causes the re-crystallization formation
of the new grain at the same time lot of slips and twins and dislocations are also generated
at the near surface layers so near surface layers experience the plastic
deformation over narrow layer the decrystalization is also observed the grain refinement also
takes place and apart from this the microscopically or you can say metallurgical the factors indicating
the deformities due to the deformation the slips twins and dislocations are also generated
near the interface so all these are deformation related effect
and generation of the re-crystalline grain structure
means re-crystallization of the near surface grains coupled with the plastic deformation
and the grain refinement these three factors in fact results in the
somewhat higher hardness of the interface is greater than the base metal so if we take
any typical joint produced using the magnetic pulse velocity welding process it will have
somewhat the deformed layer comprising the re-crystallized zone grain defined zone and
plastically deformed zone having the much higher hardness as compared to that of base
metal so if we plot the hardness variation like
say is the interface and this is the distance distance increasing from interface if you
plot that then we will see that at the interface hardness is higher as compared to that away
from the base metal so mostly in such cases the failure takes place from the base metal
and not from the joint this indicates that the efficiency joint efficiency or joint is
much is stronger than the base metal or efficiency of the joint is greater than hundred percent this is what indirectly we say that if the
joint is stronger than the base metal then efficiency of the joint is greater than hundred
percent because this calculation is based on the this kind of efficiency calculation
is based on the strength of the base metal and strength of the joint itself so whatever
is a weak metal wherever is the weak link in the joint that fills so if the failure
is occurring from the base metal then it will be
indicating that the base metal is weaker than the joint now we will see certain certain advantages
disadvantages and limitations associated with the process so as far as the advantages related
with the process is concerned what we can say the most important advantage that there
is no fusion related to the process means no solidification are related problems
there is no heat affected zone absence of heat affected zone show there is no major
unfavorable haz heat affected zone characteristics there is no external heat application so are
we can say no fumes or radiations or smoke which is generated so process is very clean
and it is green because there are no fumes no radiations the interface has mainly the deformed interface
re-crystallized interface with the grain refined structure so it is largely free from distortion
tendency no residual stresses same time it can combine the similar and dissimilar metals
equally good so similar and dissimilar metals can be joined without any problem similar
and dissimilar metals can be joined equally effectively during the welding then since the heat affected zone is the absent
so there is no metallurgical change near the interface so no corrosion loss related issues
which are typically observed in case of the fusion welded joints the process is very fast
in the sense it takes just 10-100 microseconds for one weld but certainly the time required
for loading unloading and charging of the capacitor is too much so in that way if we
will see the productivity of the process is a still quite good as compared to the other
fusion welding process however the time required for developing the
joint is a very short further repeatability of the process is very good
and that is why this process can be effectively used for development of the joined consistently
of the same quality for the mass production purpose now we will see are certain limitations apart
from that so many advantages associated with the process there are a few limitations also
which need to be considered while selecting the process so that it can be applied effectively
for the given application so the major limitation associated with this process is somewhat same
as that of the explosive welding process and that process is limited to the lap joints so the first major limitation of the process
is this one is limited to the lap joint configuration so this is one thing we need to use the either
sheets like this or we have to use like say the tubes are to be welded and tubes will
have the overlapping zone and then the joint will be formed so the system is limited to
the lap joints mainly it is used for the thin sheets as well as tubes but it can also be
used for a different configurations or the complex designs which are otherwise difficult
to be achieved using other processes so limited to the thin sheets mainly for thin sheets then it is necessary that one part or one
piece of the members to be joined is electrically conducting because the eddy currents are induced
then they will be repulsive lorentz force will be pushing one of the sheets towards
the another member with which it is to be joined so in this case it if the this is one
of the member agrees another will see that the high is strength magnetic field induced
develops the lorentz force and which pushes it towards the another sheet so it has to be conductive otherwise we have
to use some driving plate in that case one member and this will be the driving plate
member this may be non-conducting and this is another member and then this is the driver
one so driver one basically pushing the non-conducting plate when it is brought in close to the another
coil having the high-strength which is capable to deliver the highest strength electromagnetic
field and the induced the eddy currents in the driver plate for realizing the required
movement in the movable plate so one-piece of the members to be joined must
be electrically conducting or otherwise it will require the another driver plate which
will be pushing the movable member and the another thing the work piece or the work pieces
must to be capable to withstand high-pressure generated during the operation or during the
welding so in this case especially like in case of
the flats it is not a big problem flat sheets are well supported with the base and after
the impact they will be formed and the entire load will be taken without any difficulty
but if the shape is such that the pressure being applied on one of the plates will deform
the work piece in that case special supporting members will be used so that they do not deform
under the effect of the lorentz repulsive force which is being applied during the process so is one typical example of this one is like
say the tube joining in case of the tube joining if this is one member and is another member
and here the coils will be applied high-strength electromagnetic fields will be applied from
all the sites in outer coil while which will be moving towards the inside towards the in
the inner surface of the work piece so part two and this is part one so part one
basically will moving towards part two and if the force is too high then part two tube
can get collapsed so to avoid such kind of the deformation we can use the mandrel inside
so the mandrel first and then the outer tube two and then over this tube one can be applied
so this mandrel basically mandrel or such kind of support system can be used to provide
to avoid unnecessary deformation of the work piece if it is very delicate and thin in section then a special supporting units and members
can be used to avoid deformation due to the height lorentz force during the welding and
another one this process is justified only for the high volume production because the
system is a costly and this one is a limited to the factory environment means very heavy
system is needed for developing the joint using the magnetic pulse welding process so it can be are carried out or performed
in the factory environment so although most of the mass production and such kind of the
jobs are produced in the industry only or in the factory environment or in soft floor
environment so this is what now we will be using this
one the ppt here like say this is the outer tube and this is the inner tube which are
to be joined so what we will do the capacitor bank which will be supplying the high current
for a very short period after the discharging so the eddy current when induced the high
strength repulsive lorentz force is generated which moves the surface of the outer tube
towards the inner tube and then the joint is developed the after the impact and you will see the typical photograph or
the interfaces of the joints developed using the magnetic pulse gmew these are the 2 diagrams
which are showing the joining of the aluminium with the copper so the one with the light
itched part is showing the aluminium and this reddish part is showing the copper portion
and here we can see that the typical waviness or the kind of a bond which is more of the mechanical kind is reflecting
is developed in case of the aluminium and the copper one and typical wavy structure
can be seen in these two cases where this one is the bond between the copper and the
mild steel and this is the bond between the copper and the stainless steel and these morphologies
at the interface are similar to that of the explosive weld joints what we have seen earlier so now i will summarize this presentation
in this presentation i have talked about the pulse magnetic pulse welding process this
is one of the solid-state welding process primarily used for joining the thin sheets
component of the dissimilar metal systems which are otherwise not metallurgically compatible
for the fusion welding process we have talked about the basic principle of the magnetic
pulse welding apart from the advantages and limitations associated with this process thank
you for your attention

2 thoughts on “Lec 27 – Magnetic pulse welding

  1. thank you very much for this lecture. I need to know please whats is really happening in the joining area. In the atomic level, are these two material electrically connected to each other ? how ? ?

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