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Module 1: Machining of Advanced Materials

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Unbonded Conventional Abrasive Processes

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Video 1: Lapping ProcessNow we are moving in this particular class to un-bonded conventional abrasive finishingprocesses.Like lapping, super finishing, sand blasting, vibratory bowl feeding and drag finishingand we summarised about the abrasive finishing processes.So, the first thing that I was saying is un-bonded conventional abrasive finishing processes.Wherein the first process comes is a lapping process.In the lapping process the parameters are like lapping wheels, are the plates that arethere, at the same time lapping medium and abrasives that are there which are used inlapping process.So, the lapping if at all the if you want to finish any particular ah sample or theworkpiece you will have a lap; that is plate, wherein you have abrasive particles carryingmedium and all those things.So, we will see what is this lapping process and all those things.Lapping is basically an abrasive finishing process, machining process.If at all people are talking about machining; that is material removal, it is machiningprocess; otherwise it is a finishing process.Mostly lapping process is comes as a finishing process, only you do not bother about, whatis the material removal.We always go for the finishing that is achieved on the final product.So, which is the loose abrasives for cutting points for the this one.Lapping involves the cutting and the shearing action.This is of the loose abrasive particles in order to fine finish the components materialremoval.Generally it ranges from 0.003 to 0.03 mm that is the thickness and, but maximum itmay reach 2.1 mm also, that is the material removal; that means, that it is not a materialremoval process, because the material removal is very very minuteSo, the characteristics of lapping process, it uses the loose abrasive particles betweenlap and the workpiece which you have seen in the previous slide . So, lap and the workpieceare not positively driven, but it is guided in contact with the each other, because theretwo contacts will be there.So, in between the fluid as well as the abrasive particles will be there and it will be donelike this.So, there will be a fixed one, there will be a lap in between the medium will be thereand the workpiece is fixed on the bottom and you can do the lapping process, relative motionbetween the lap and the workpiece.This is the most important, should change continuously.So, that the path of the abrasive grains of the lap is not repeated.Assume that if the ah path is not changed what will happen? the finishing takes placeon the same path, the workpiece is like this.If I have a lap on top and abrasive particles are there, if it rotates there itself, thereis a possibility that the abrasive particle will follow the same track and create thescratch in the same.So, you need to change the relative motion, you need to change the path.If if at all the path has to be changed then you should change, continuously change thepath.So, for that purpose you should change the relative motion between the workpiece as wellas the lap continuously t in order to change the path of the abrasiveLapping normally the tool which is a flat disc or a plate made up of, normally the softof type of materials such as cast iron, aluminium alloy, copper and brass.The abrasive mediums are carried out by medium basically.Medium is nothing, but an agent which carries the abrasive particles like grease oil, waterand high viscosity means a high abrasion.Normally if you are going for grease, if you are going for the grease what will happen?The viscosity will be very high.If the viscosity is very high, the material removal will also will be very high; thatis what the meaning of the sentences There are two varieties of lappings are there;one you just have the work pieces on the bottom like the red ones.If you see the figure one and this is figure 2.In the figure one what is the thing that I want to say is the work pieces are placedon the green one, these are the work pieces and the lap will come on the from the topand it try to finish.This is uh with respect to one lap it, you can do on the both sides like you will havea lower lap.If you see the figure 2 and there will be a upper lap.So, you will have two laps in between you are holding the work pieces.So, you can do the both ways, both the second one.Figure 2 is a quite economical, because for the same input you can do on both sidesSo, the main function of the lapping process is the finishing process.If you see the before finishing and after finishing, the finishing that you are goingto get is better and better.So, the before finishing this is a surface and after finishing this is the surface.So, what will happen that you are going to get a good aesthetic appeal, you are goingto get better surface finish that is low roughness.At the same time you will have a high load bearing capacity and all those things, thatthis is a common for most of the finishing process.And lapping is one of the finishing process that is why mostly you go for the finishingusing lapping if at all.If it is a flat surface or if it is a cylindrical surface and all those things, normally peoplego in a small scale industry for the lapping processSo, lapping process if you see in D, there are the mechanism goes by 2 D and 3 D abrasions,whatever I want to say is 2D abrasion.2D abrasion means if there is no relative motion between two surfaces, assume the grinding.In a grinding process what will happen?You have a grinding wheel where you have abrasive particles are fixed and you have a workpieceon the bottom.So, there is no relative motion between abrasive particles and the grinding wheels.So; that means, that whatever the abrasion, if I give the depth of cut and all those thingswhat will happen?Same, approximately same depth of cut will be removed from the workpiece ok.So, that is nothing, but the 2D abrasion Here 3D abrasion means . In a 3D abrasionwhat will happen?Lapping is good example you have a workpiece on the bottom and you have a particles, abrasiveparticles which are carried by the carrier medium . So, you have a lap and the topsidein that circumstances what will happen.These particles are loosely bonded or these are un-bonded in that circumstances.The abrasive particles not only follow the path of the lap, but also has its own orientationor rotation about own axis.In that circumstances the abrasion takes place in the 3 dimension that is why it is calledthe 3D abrasion So, in the grinding, process is a bonded abrasivesand the lapping process is a un-bonded abrasive.So; that means, the un-bonded abrasives ah have the freedom or independent to move aboutor rotate about its own axis, also along with the axis of rotation of the lap for that purpose.Normally this lapping process is considered to be the three abrasion processThe lapping tool is rotated or oscillated moved irregularly across the machined surface,so that the random motion can be generated.If the random motion is generated the surface finish will be better.So, there are two types of methods which are equalising lapping, another one is formedlapping.So, equalising lapping ah removes the previous shapes or the flattening, this is the mainpurpose normally.If at all somebody I want to remove certain micro-layers or nano-layers, you can use atthe same time, you you can use for the flattening the surface.For the form lapping, the lap is a negative shape of the surface what will happen?If at all I want to generate particular shape, assume that I want to generate certain shapeon a flat workpiece what will happen?You will have a lap like this, and you will rotate what will happen?This negativeness will generate basically.So, this portion you you are going to get, this is called the form lapping process.Negative shape will be there and you can generate; that is the difference between equalisinglapping as well as the form lapping The lapping process mechanism for the brittlematerials and ductile materials goes like this.Just first we discuss about the ductile materials.Always ductile materials will go by chipping process only; that means, that shearing processuh like metal cutting process, whenever you are seeing the continuous chips in ductilematerial and all those things similar fashion, the material removal takes place by the shearingof the surface of the workpiece by the abrasive particles that are involved in the lappingprocess.So, there is a workpiece and your abrasive particle will come and it will take out achip.So, that is how the shearing takes place in this one and gradual shearing takes placethe surface peaks, this is about the ductile mode of removing materialBut in case of brittle materials, if the workpiece is like a glass or if the workpiece is likea silicon.These are the brittle materials, normally material removal.Brittle materials is just first it will have a crack, then it will remove the in termsof the fragments as a chips ok, you are, chips are like fragments of the brittle material,this is how the material removal takes place.In the most of the brittle materials like cracking, then followed by the fragments inthe ductile materials, it is like a shearing operation by the abrasive particles.This is the difference between ductile as well as brittle materials material removalSo, lapping materials, if you see the lapping abrasive types.Normally the abrasive types of ah like alumina chromium oxide and boron nitride, boron carbide,diamond.These are the mostly or commonly used abrasives in the lapping process medium; that is carriermedium, like whatever it carries and all those things that is like machining oil, rape oil,grease.Mostly people will use the grease if at all material removal want to be more, if at allmaterial removal is requirement is less, in that circumstances you can go for low viscousliquids The technical parameters that is unit pressure,how much pressure you are going to apply on the workpiece, the gain size of the abrasivethat what is the grain size, whether you are going for coarse grain, whether you are goingfor a fine grain and a medium grain and all those things that will decide your materialremoval.If the grain size is coarse, the material removal will be very high.If the grain size is less what will happen? the material removal is very low.So, the concentration of abrasive particles in the vehicle; that means, that agent aremedium, vehicle is also a word some of the people will uses.So, the alternatively you can use, say that medium rs.So, the concentration of the medium, if the concentration of the abrasive medium in theagent; that means, that if I am using 50 percent of the abrasive particles among the concentration,then material removal will be very high.If I compare to, if the abrasives we are, you concentration, if I am using like 20 25. So, its all required by the what type of requirement the particular operator have.If the requirement is finishing, you do not need to go for higher amount of abrasive particles.If you are going for the higher material removal rate, you have to go for coarse as well ashigh concentration.So; that means, coarse particle you have to go and you have to go for higher concentrationalso The lapping speed if the less speed increaseswhat will happen?The number of times the abrasives come in contact with respect to the workpiece willbe a very high.So, the material removal also will increase.Since it is, we are considering this particular course as machining as well as the machiningfluids course, we should talk about mostly about machining that is why the, if I am goingto increase pressure material removal rate will increase.If I am going to increase the particle size material removal rate is going to increase.If I am going to increase the concentration material removal rate increases.If I am going to increase speed then material removal will be increased; that means, materialremoval is primary concern, if you are, then you have to increase all the four parameters.If you are finishing is your requirement then you have to play according to the requirementsof yours custom raised requirements ok.Brittle workpiece is normally the abrasive is like diamond, you can use carbon CBN, youcan use silicon carbide, alumina and corubdum.These are the workpiece materials you can ah do the lapping.I mean to say these are the workpiece materials, these are all also as a tool materials; thatmeans, abrasive materials also, but you can also do these work pieces, but only thingis that, whenever you are use this workpiece materials as silicon carbide or aluminiumoxide, then you have to choose your abrasive particles slightly higher than the hardnessof workpiece material.In that circumstances you have to go for CBN; that is called cubic boron nitride and allthose things.
Video 2: Super Finishing ProcessNow we move on to the super finishing.This is one of the conventional finishing process where you will use the coolant, whereyou can use the bonded abrasives partially as per your requirement.So, super finishing is also known as the micro nano finishing.Thus this is achieved by removing just a thin amorphous layer; that is about 1 micron inmagnitude left by the previous process.If at all I want to use the super finishing process, I am going to use the previous process;that is like a grinding or I am going to use the hard turning process.If at all then I am going to do this finishing process then you can achieve the surface;that means, that whatever the layers that are left by the previous processes can beremoved by the super finishing operation.The super finishing is unlike polishing which produces the mirror finish and creates a patternon the workpiece; that means, that you have seen the picture.In that picture it has rotating workpiece and a brush type of, that is nothing, butthe plunge type of thing is there.So, if it is rotating that only polishes the surface, but also it can generate its ownpattern; that is nothing, but the lay predominate direction of the surface finishedPeople you might have seen in the first or second class, where there directrix and generatrix.So, that directrix will be formed on the, which is like a circle will form on the.Not directrix, it is generatrix which will form on the workpiece surface.There are two varieties.These are the two varieties which are the there in the super finishing operation.One is a plunge type, another one is a roller type will come across that.One is a plunge type of super finishing.If you see this type used to finish irregularly shaped surfaces; that means, that if you haveany type of irregular surface you can go for this particular super finishing type.This workpiece is rotated while the abrasive plunge is into the desired shape; that means,that this is a plunge you are going to apply the pressure on it and you are going to rotatethis particular workpiece.So, you will get the finishing operation So, for this purpose this, whatever the stonewhich is there, this may be flexible, this may be a solid.At the same time people you can also go for liquid abrasives here by putting it and youcan rotate it, people uses like that also.So, you can see some of the advanced varieties of super finishing where they can use theporous stone and they just put the abrasive slurry, then they will, you rotate the workpiece.Some of the advanced varieties they are doing like this, like we can take the porous plungeand they put abrasive slurry, then rotate the workpiece in the circumstances the finishingwill be slightly better.So, there are lot of parameters that place the finishing operation performance like whatare the abrasive particle size, carrier, medium abrasive particles concentration.The carrier medium and all those things will play a major roleThe another one is the wheel type or the roller type.So, this abrasive cups are the wheels, basically are used to super finish flat and sphericalsurfaces.You can go for the flat surface as well as a spherical surfaces using this wheel typesuper finishing.
Video 3: Sand Blasting ProcessNow, we move on to sand blasting.The sand blasting is one of the mass production process ok.So, if you see sand blasting, normally it uses the sand particles which are senior.Sand blasting is one of the most effective way to shape or strip or smooth surface byany foreign material.Normally this process you can give the some shaping or normally if there is a big castorproduct is there, if I want to remove some casting layer, the surface of the castingproduct you can use this sand blasting.This process can be used to finish the nooks and crannies and you can also generate virginlike of surface, not the virgin surface.So, you can use the compressed air to blast the fine sand or other abrasive particles.What I mean to say is that, there will be compressed air, there will be sand.You just mix internally and send to the component to be finished at with very high pressure.So, that the finishing will takes place all the that particular object or productMaterials other than the sand can be like a steel grits, steel shots or glass beads,the groundnut shells, many things you can use aluminium oxide; that means, that theAl2O3 also you can use, but depend on your requirement of your particular application.So, the particles, the particles you can use variety of particles here, you can see thesand particles different different the type of abrasive particles like Al2O3, coal slag,brown aluminium oxide.This is the black aluminium oxide, this a will be black aluminium oxide and c will bebrown aluminium oxide.You can also go for beads like of thing.So, you can see these are the spherical bowls where you can do the burnishing operation,see sand blasting, you can do by, it is one type of burnishing operation whenever youjust impinge this particles with high pressure on the workpiece what will happen?This will go and deform the surface roughness peaks which are formed during the previousprocess, this is how the sand blasting works The main purpose of the sand blasting is,it is used to clean the work pieces and also use for removing the impurities and the suspendedparticles.You can see here, these are the rings of the vehicles before and after.So, how it is clean perfectly, so that you can reuse this one by painting it again andagain clearly, you can see here the difference between before and after, this is before,this is after.So, how beautiful the sand blasting worked here before and after.So, you can remove the rusted; that is oxide layer clearly ah gives like a virgin surface,it is may not be a virgin surface, it looks like a virgin surface sand blasting.It uses the compressed air at the same time, it is you take the abrasive particles yousee with as per your requirement what is the size that you want and all those things thenyou can go for the using in the sand blasting, basically sand is a silica.So, on a silica dust the basic problem with this one is silicosis problem.So, the this is a chronic lung disease due to the continuous inhalation of silica dustparticles, because you are sending with high pressure gas along with the silica dust; thatis the sand, what is the problem people if they are not going to use proper precautionarythings like mask operon and all those things what will happen?The silica particles, the dust will go into the lungs of the person; however, this preventedby using a protective clothing and breathing supply.So, if at all the people take care or the operator take care about its operon mask andall those things you can prevent it.Alternatives to send are glass beads metal pellet us dry ice, many things also can beused like these are the particles that you use.
Video 4: Vibratory Finishing and Tumbling ProcessNext one we are going to the vibratory finishingand tumbling process.So, vibratory bowl finishing the finished products in bulk, basically in a container,usually in the presence of a abrasive media.You just put a abrasive media, you put a components, then you apply the vibrations are the oscillatorymotion to the bowls mixing causes parts to rub against the media; that means, that abrasiveparticles are there.This will rub against the components and do the finishing operation, parts are usuallyvery small; therefore, uneconomical to finish individually.Basically here the components are very small, if at all I want to finish individually thatis not economic, the cost of the production, cost of the component goes very high.So, though for that circumstances you can go for vibratory bowl feeding.Another one is tumbling process, it is normally horizontally oriented barrel basically andif the mechanism will be used like a land sliding.So, whenever you have a abrasive particles as well as the components, you just rotateit, what will happen?land sliding type of material removal action will takes place.The basic drawback of this process is, this is the slow process at the same time noisy.If at all the tumbling or the vibratory bowl finishing is going on this interaction ofabrasive particles with a components, at the same time rotation of the bowls will givelarge noises and it occupies large floor area also.This is the tumbling you can see here, this is the process for the mass finishing andthe good shaping process, but not the finishing process I have, a assume that I have a componentswith the cascade components, I want to remove a layer on top.So, you can go for this, you can get the shape, but not the final finish ah, assume that ifI want the nano-finish you may not achieve, but you can get the similarSo, non-uniform finishing due to random contacts.So, abrasives are loosely bonded; that means, that these are individual and you are rotatingit, what will happen? the contact will be random.So, the surface finish that you are going to get on the component will be random ok.So, this is the one variety; that is called centrifugal disk tumbling.Another one is a centrifugal barrel tumbling.These are the two varieties one goes vertical, another this is about this axis, another onewill go for a horizontal axis; like this is the one axis, this will go like horizontalaxis ok.So, this is about the tumbling, again if you see the diagram of tumbling at is nothing,but the barrel finishing operations showing the landslide action.This is how the sliding will takes place; that means, that medium what is the abrasivemedium will takes place like a landslide like this and the finishing will takes placeIn a vibratory finishing process what will happen?Alternative to the tumbling, this is one of the alternative you can go for and vibratoryvessel, subjected to all parts agitation with a abrasive media, opposed only the top layerin the barrel finishing, what will happen?You just put it here and you just rotate it and you will get the finishing process.Vibratory finishing, the process times for vibratory finishing a significantly reduced;that means, that the products are finished in a mass production.So, the time will be very less, at the same time open tub permits the inspection of theparts during the processing and the noise is reduced.