Lec 24 – Ultrasonic welding

Lec 24 – Ultrasonic welding


hello i welcome you all in this presentation
on the ultrasonic welding process related to the subject joining technology for the
metal this ultrasonic welding process is one of
the solid state joining process were very less heat is generated at the interface generated
at interface by friction and another important thing there is no melting or fusion there
is no filler use of filler so the mating surfaces are brought together in metal to metal contact
and then using the vibratory energy ultrasonic vibratory energy the joint is made through
the localized plastic deformation at the interface so very less heat in is generated which at
the most comes out to be like say 35 to 50 percent of the– like say the temperature
rise due to the heat generation is the temperature of a melting point in absolute scale so point
35 to 50 percent of the melting point temperature in kelvin of the metal that is the maximum
temperature rise due to the frictional heat generated in course of the welding and this heat helps to soften the metal facilitate
the plastic flow of the metal at the interface so sequentially we will see now that the what
kind of system is used here let us say this is the base and the component to be joined
is placed over the base the base will support the work piece or the work pieces and the
load which is applied so loading or the clamping forces is supported by the base another component
to be joined in very clean condition is placed over it like this so there is a direct metal
to metal contact between the two components this is part one to be joined with the part
two say and then over this then one member is brought in contact with the surface of
the one of the component which is placed at top this is a tip tip of the sonotrode this
transfers the vibratory energy to the plates the sheets being joined and this is done with
the help of one arrangement where in we will see that– this is the transducer which will
be supplying the ultrasonic vibrations like this this component is vertical and then applied
load so here the load is applied which will apply the necessary clamping force and this
one is called reed through the reed load is applied onto the work piece and this transducer
will be supplying the necessary vibratory energy so it will be at very frequency so
this in turn will be causing the literal movement at the tip so basically the force is applied
through the reed and you can say the shear force is applied
through this vibrations at very high frequency so the tip basically applies both a combination
of compressive force clamping force and the shear force so shear force the clamping force
is static in nature while the shear force is a dynamic acting literally and acting at
very high frequency so when there is a direct metal to metal contact like say this is a
real surface of the upper component and the real surface of the lower component
having the contact at peaks and valleys under the constant static load and the literal shear
force initially the oxide impurities all these are flushed out or removed from the interface
so these impurities are removed and direct metal to metal contact is established in the
initial stage under the effect of the static clamping force and the vibratory shear forces once this contact is established metal to
metal contact is established actual contact area starts to grow and this growth is facilitated
by elastic-plastic flow of the metal at the interface so as the process continues elastic-plastic
flow at the interface will continue to increase and this in turn will keep on increasing the
direct metal to metal contact area and subsequently we will see tható the contact between contact between the two
pieces to be joined is perfect and under this condition what we will see we will see that
due to the elastic-plastic flow of the material especially at the interface so what are the
things involved the friction and elastic-plastic flow all these things will generate enough
heat so heat generation will cause the temperature
rise 03 to 05 times of the melting point of the metal in kelvin right so this increase
in temperature is high enough to cause the recrystallization and the formation of the
new grain and these things actually facilitate the refinement of the grains at the interface
one and the second is cold or work hardening due to the plastic flow of the metal work
hardening although this is very mild or the moderate so the material which is formed at the interface
is moderately cold work and the refined why due to the elastic-plastic flow as well as
the frictional heat generated causes the enough temperature rise for the recrystallization
to take place so if we measure the hardness at the interface
we may find we refine that this is the interface then on approaching towards the interface
we will refine the increase in bit hardness and this increase in hardness is attributed
to the moderate work hardening which is taking place due to the elastic-plastic flow of the
material at the interface and then additionally the grain refinement of the material at the
interface due to the continues deformation in both the direction of the material in course
of the ultrasonic welding process so in this case what we have seen we area
applying the static load which will be basically holding the work pieces to be join and then
literal force literal shear force which will you apply through the ñ in form of vibratory
energy through the transducer — this combination of the two actually facilitates very elastic-plastic
flow very dynamic conditions at the interface and facilitate the elastic-plastic flow of
the material at the interface and that in turn helps in development of the
joint at the interface so keeping this principle in mind if we see that no external heat was
supplied and only- so we did not supplied heat from the outside
and despite of this without any supply of heat only the frictional heat frictional heat
caused enough temperature rise like say 35 to 50 percent of the melting point of the
metal in kelvin scale which is found to be enough for recrystallization of the material
and the plastic deformation coupled with the recrystallization results in the refinement
of the grain structure also so since there has been no melting so not
cost structure no heat and the heat being generated at very small area at the interface
and therefore the issues related with the heat are extremely limited so no heat related issues in case of the ultrasonic
welding and because of this we will since is no melting cost structure and the heat
being generated over a very small volume of the metal so what we will see very less haz
very reduced residual stresses and any dissimilar systems dissimilar metals which are metallurgical
incompatible metals can be joined by this process okay so these are some of the benefits
additionally due to the inherent nature of the process itself now we will see the things which actually
matter in a development of the sound and perfect weld joint so for that what we need to see like this is the upper component and this
is sonotrode transferring the vibratory energy supplying the literal shear force through
the vibrations and the static clamping force and this is the another member with which
it is to be joined so part a and the part b so how much vibrate energy is to be supplied
there are some aspects like how much vibratory energy is to be supplied this is one thing and the second is how much
force force is to be applied for development of the sound weld joint so what is important
here the kind of surface conditions like surface roughness presence of the impurities hardness
of the material so the factors that affect these two vibratory energy and the clamping
force which is to be applied is influenced by thickness of the sheets to be joined this is one thickness of the sheets to be
joined then hardness of the material then we will see under the percentage elongation
also to some extent determined up the plastic flow behavior of the material at the interface
during the process so these factors also affect the amount of energy that it will take before
development of the sound weld joined apart from the presence of the impurities and the
oxides etcetera so since the thickness and the factor that
is governing the ability for the plastic flow influence the success of the process significantly
and that is why these two parameters significantly determine the energy which is required for
development of the ultrasonic joints and which his given by say the vibratory energy need
to be supplied say in joule is found the function of the k multiplied by h into t raise to the
power 3 by 2 so this is the energy in joules or k is constant
for welding system being used for development of the weld joint h is the weakest hardness
of the material which is being jointsóso higher is the– so this because hardness number
will come higher is the hardness greater will higher will be resistance for the plastic
flow and so greater will energy it will take for development of the joint and similarly
the thickness t thickness of the sheets being joined in mm s the thicker is the plate greater will be
the energy requirement for development of the weld joints because these needs to be
transferred across to the interface and then so the thickness of this top sheet will definitely
be mattering here definitely be important so greater the thickness of this plate greater
will be the energy requirement to be welded and similarly higher is the yield strength
higher is the hardness lower is the ductility greater requirement of the energy for developing
sound weld joint so considering this points materials having
low sigma y low hardness they will be easier to be welded and similarly less in thickness
they will be easier to be welded so thin sheet and soft metals soft metals can be easily
softóeasily ultrasonically welded as compare to the harder high strength materials of the
higher sections due to the energy requirement and it is the capacity of the ultrasonic welding
systems that actually limits the maximum thickness which can be welded using this process since
not very high energy ultrasonic welding systems are available so the process is basically
limited to the thin sheet or very thin gages sheets and therefore what we will see limitation
wise as far as the limitation the process is limited to very thin sheets and this limitation
comes primarily from the non-availability of high energy high energy ultrasonic welding
systems so if we have high energy ultrasonic ñ high energy ultrasonic welding systems
then definitely it is possible to join even the sheets of the greater thickness another one is that this is limited for the
lap joint configurations only in other configuration joints are not so easily possible so therefore
the two major things can say associated with this processes in form of the limitations now the kind of joints which can be made using
the ultrasonic welding processes if we have to see the ultrasonic welding process very
common that spot joints are made wherein one sheet is placed over the another and one spot
kind of joint is made at the interface so section will be circular in this case and
its area will determine the shear strength load carrying capacity of the joint so this is most common form which we can say
as a variance of an ultrasonic welding process one is spot joint another is you can say line
ultrasonic joint where primarily if we see this in top this is the this is the upper
plate and this is the lower plate like this to have been joined and then in this case
joint is made at the interface along a particular line like this only so in this case ultrasonically
welded joints like– three joints but in form of the line so of course we have to use the sonotrode
tip according to the shape which is desired it can be of any other particular contour
also like it can be triangular it can be oval or it can be circular shape like spot weld
so in that case like say here this is the top sheet and this is the the bottom one and
if you want to make the joint of a particular configuration in that case the sonotrode tip
is to be made according to the shape desire like say in that case weld line will be made
according to the geometry of the sonotrode tip shape and this will with the kind of a joint along
which it will be made this will be like the contour ultrasonic weld joints where the joint
geometry will be governed by the geometry of the geometry of the ultrasonic sonotrode
tip so these are the different variance and as it has been said the process is limited
to the thin sheets now we will see some other details and few examples of the typical situations
where ultrasonic weld joints are used so we will quickly go through the figures
and specific diagrams this is the dead weight or force through which
mass or the force through which it is applied through the reed and then the wedge will be
supplying the vibratory energy through the transducer to the sonotrode tip and here we
have the sheets to be joint and this is the base or the anvil which will be providing
the support to the clamping force as well the force which is generated being generated
in course of the welding very localized of high frequency vibratory
energy under pressure and metallurgical bond at the interfaces created like there is sonotrode
tip static force and vibratory energy facilitates the the deformation at the interface and that
helps in development of the weld joints ultrasonic vibration are transmitted through
the transducers transducers transmits the vibration through a coupling system and clamping
forces are applied through the reed these are the various process variance as
i have said it maybe spot ring line continuous seam wherein the rotating disk shaped sonotrode
tip is used or the close loop weld like i have explained according to the requirement
of the sonotrode tip is shaped for circular square or oval shape so sonotrode tip in that
case made hollow and the tip is contoured to the shape desired the different variables that affect the success
of the process one is clamping force and shear oscillating force and under the process conditions
due to the friction and deformation heat is generated so the heat generation is moderate
and these factors mean clamping force and oscillating force magnitude is influenced
by means their selection depends on thickness of the sheet to be welded hardness of the
material in yield strength and the surface conditions of course so the combined clamping and oscillating forces
causes elastic-plastic deformation at the interface this is what we can see the clamping force
and the ultrasonic vibrations appearing in form of and the two sheets are welded and
the samples are supported over the anvil so in course of the process what happens initially
the contact at the interface breaks the surface films in oxides disperses them and metal to
metal contact is established gradually the elastic-plastic flow of the material at the
interface continuous which in turn grows the size of the weld base and in this process
itself diffusion at the interface takes place and at the same time frictional heat causes
enough rise in temperature for recrystallization to take place that in turn refines the grain
structure as i have said the success of the process
depends that how effectively energy we can supply and how much energy we need to supply
so energy to be supplied electrical energy to be supplied in course of the process is
found a function of the hardness of the material because hardness and thickness t and this
will be governing the kind of how effectively the sound weld joint will be made so as per the thickness and the hardness of
the material we need to supply the different amount of energies for ultrasonic welding
process advantage of processes i have said that very
less heat is generated that to with the friction only therefore heat affected zone is very
limited rs are very limited no melting so there is no nugget or intermetallic formation
possibility we can weld thin to thick sections but normally thin sections are welded thick
sections are difficult due to the availability of the high energy ultrasonic welding systems variety of dissimilar systems can be welded
and these weldments can be made even through the thickness so means if the base metal is
coated then through the coating also the joints can be made by the ultrasonic process so the
amount of energies which are required for welding aluminum and copper they are much
less as compare to that is required for resistance spot welding similarly the weld cycle is time is very short
pressures which are applied are much lower as compare to those which are used in case
of the resistance spot welding process for joining of aluminum-copper and other high
connectivity; high thermal connectivity metals so thickness deformation in this case also
very limited as compare to the cold welding process limitation wise as i have already talked the
process is limited to the thin gages because of the power limitations of the ultrasonic
welding equipments which are available and the process is limited to the lap joints only
applications the assembly of electronic components because the process is very light it can be
used mainly for the thin gages and then electrical connections broken aluminum foil packaging
applications wherever so thin sections need to be joined of very delicate materials this
process is used very effectively and in structural welding also like in helicopter
access doors this process is effectively used so now here i will summarize this presentation
in this presentation i have talked the basic principles of the ultrasonic welding process
different factors that affect the soundness of the success of the process the process
advantages and the limitations besides the areas where this process can be used thank
you for your attention

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