Introduction to Grinding | Abrasive Machining Processes | Alison
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Module 1: Abrasive Machining Processes

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Introduction to Abrasive Process-Grinding

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Video 1: Grinding ProcessWe are going to see about the Abrasive Processes, we completed some of the machining processesas well as the machining fluids.So, we are in the area of one of the multipoint cutting tool processes, you can say it ismillions of millions of cutting edges will be there in this process.So, the surface roughness are the surface that you are going to get is completely randomin nature because, the orientation of the abrasive particle as well as the shape andsize of the abrasive particles will vary for process to process.So, let me enter into the ah process, till now we have seen the practical machining processessuch as milling drilling other processes, at the same time this is also one of the practicalmachining process, as per the present scenario is concerned the grinding, or the conventionaltype of grinding is considered to be one of the machining process only, but if you seeas such it is one of the finishing processes in a olden age, or nowadays also some of theindustries they follow it as the finishing process, how you are looking at that perspectivedecides, whether it is a machining process, or a finishing process.If you are looking for this process lie material removal process, you can say that it is amachining process, if you are looking like a if this process as a surface finish processare the final finishing process.So, it is as a finishing process, how you are .looking that perspective decides whethertoday's lecture you are going to take or you are going to grasp as a machining processare the finishing process.We will see now about the introduction to abrasive processes various abrasive processeswe deal in which mostly the common physics are the common example of the abrasive finishingprocess is the grinding process, ok that is why we talk in (Refer Time: 02:38) of thevarieties or the advantages types and all those things grinding process and when, wego on to the honing process, lapping process, super finishing, drag finishing, vibratoryfinishing and all other processes, which are also considered to be one of the conventionalfinishing processes will see a little bit little bit of this processes ok.In particular about this particular class, we deal with the grinding process only.If time permits we will also see advanced finishing process, if time is there becausenumber of hours also has a constraint.So, if time permits we will also see the glimpse just how and what are these process and allthose things.So, in the grinding process today we are going to deal with introduction to the grinding,in grinding wheel specification and the what are the problems and the solutions to theproblems what is robotic belt grinding process, at the same time we will see what are theadvantages as well as applications of grinding processes.So, the grinding process the grinding process is one of the ancient process, where peopleused to make it the grind the materials to make medicine.So, on if you go to the villages also mothers normally they, do the chutney and all thosethings using rock as well as one of the woods.So, they also grind that because so, that you can swallow it easily rather than swallowingcomplete leaf, just they do it the chutneys the red chillies and all those things, theywill just that is the conventional way of the grinding grinding into the powder particles,or grounding into the semi solid where the particle size is very less that is also calledas a grinding process.One of the example is ball milling is one of the grinding process, where you can crushthe bigger particles into smaller particles.So, not only the particles reducing we also uses this process for finishing applicationor the machining application.If you see this particular process, where the shown is surface grinding, what is surfacegrinding and other things you will come across ok so, the surface grinding just there isa work piece, this is the work piece and, ah this is a wheel the wheel is rotating atcertain speed 2350 per RPM, it is rotating it is taken from the laboratory or laboratoryonly.So, various variables that you can give and you can generate, or you can get the outputresponses.So, the variables that normally you can give is depth of cut that is nothing, but how muchdepth you are going to give so, that on the work piece.The second thing is number of grindings cycles that is complete rotation is 1 cycle.So, number of cycles you can give 1000 cycles 2000 cycles and all those things you can.So, another important parameter is wheel speed how much speed you can rotate, if you wanthigher speed you can give the wheel speed higher.If you want lower lower speed all those things this are the some of the common variables,apart from the wheel designations like, you can also vary the abrasive particles sizeand abrasive particle type and all those things also you can vary at the same time you canuse the flood cooling, since you have the knowledge of flood cooling NQL and all thosethings.You can also vary their volume flow rate as well as the pressure and all those thingsalso can be variable ok, those are apart from the basic machining process of grinding ok.So, if you see the 3 mechanisms of material removal, one is cutting or shearing of thematerial that is dominating here, the cutting of the material is nothing, but if you havesufficient depth of cut what will happen the abrasive particles, will shear the surfaceand takes the chip that is nothing, but the cutting or shearing operation normally thisis the dominant mechanism of material removal in the grinding process, there is a ploughingaction also ploughing means, if you see the farmers whenever they do with ah hull whatwill happen though material will come and it will fall in the previous one.So, there material will be not completely removed that is material will go into thepreviously existing surface this is called the ploughing.Another one is rubbing if you do not give sufficient amount of depth of cut and allthose things what will happen, the rubbing will takes place, you might have seen themechanism of ball burnishing and all those things, that is what is happening and thechips will again mere on the surfaces and it will destroy the surfaces.So, you also if some people are working in the area of grinding, or abrasive grindingprocess, or abrasive processes you come across the critical surface roughness and all thosethings.Since the roughness which I have told, in the previous lectures has some relevance here,turning, boring these are the processes where you may not get good surface finish if atall you want to get good surface finish normally you can go for this particular process, butthe critical surface roughness is the surface roughness beyond which even though you changethe input parameter, you may not improve the surface finish assume that if I am going toincrease the wheel speed beyond.
Video 2: Grinding WheelNow, we are moving into the grinding wheel, which is most important part of ah our grindingprocess is grinding wheel, there is a variety of grinding wheel tool and cutter grindersurface grinder grinding wheel, tooler cuter grinder grinding wheel, there are ah someother cylindrical grinding wheels many many more, the if you see the depend on your requirementthere are variety of grinding wheels are there.So, wheel specification, the wheel specification in a common terminology like goes like this,but it may be prefixed or super fixed by some other things like company name company theyhave their own codes.So, this that may be possible in of the some of the cases; however, we do not bother aboutcompany or something.So, we bother about what is the basic specification of a grinding wheel ok.So, if you see A 36 M 7 I am taking a example and I will explain ok.So, A stands for abrasive type, 36 stands for your grit size, or particle size and Mstands for the grade, 7 stands for the structure, and V stands for the bond type.So, if you see the abrasive type there are varieties of abrasives, if there is A herethat means, it is Al 2 O 3 that is alumina type of abrasive particle, if C is there itis silicon carbide, if D was there in that place of a it was diamond so; that means,I mean to say that type of abrasives, which are going to use in that particular grindingwheel which I am specifying as A 36 M 7 V.So, next goes the grit size that is nothing, but if the grit size is 10 to 24 course coursemeans very big or rough, normally course size of grits are normally used whenever you aregoing to machine the material; that means, that where your material removal is a criterianot the surface roughness is the criteria.So, if you go 30 to 60 it will be medium, 70 to 8 will be fine and 220 to this 1 willbe super fine.If your particle size goes seventy and above normally you can go for the finishing process,these two you can go for finishing processes, these two normally you can go for machiningprocesses.So, grit size course means very big, if it is big the material removal will be also bigthe surface roughness will be too high; that means, that surface finish will be very bad.So, if you see the M, M stands for the grade, I tell what is the grade and all those thingsin the upcoming slides.So, the grade specifies the bond strength, how firmly you are holding the abrasive particlethat is nothing, but the grade ok.So, there is A to H stands for soft grade, then J to P stands for medium grade and, Qto Z stands for hard grade; that means, the soft grade means the abrasive particle isheld very lightly.So, it can be loosely delaminates from the bot.So, if the hard means it is firmly hold the abrasive particle is firmly hold by the bondmaterial.Next structure structure there are 2 varieties of structures one is open structure, anotherone is a dense structure, if it is 0 to 8 normally, it is dense structure 9 to 16 itSi a open structure open.Structure means structure means what the particles distribution, abrasive particles how the abrasiveparticles are distributed on the grinding wheel, if it is too nearer to the consecutiveparticles; that means, dense if it is there is a gap then; that means, it is open structure.Next comes the bond, V stands for vitrified bond and type of bond, normally the bond materialis there clay is there, the metal is there, this type of things are there.So, if the vitrified bond is there that is one type of bond, if V here it is representingthe V that means, that it is going to be vitrified bond and, if in case of V it will it is Dresinoid bond, if it is S silicate bond, R is rubber bond and E is a shellac bond ok.So, what are these bonds and all those things will see in the upcoming slides.So, mesh size there is slightly confusion for the basic people who are looking at thepresentation that, ah there will be a difference between mesh size and grit size, or the particlesize.Assume that I want to convert the mesh size, mesh mesh mesh means you know our mothersnormally whenever you have a wheat flour or some flour, they will you to sieve this oneok that is nothing, but the mesh the square holes which are there on the net where themothers used to sieve is nothing, but the mesh for a unit area how many that squareholes are there that is decides the mesh number.If your mesh number is very high for a square for a same area; that means, that the particlespasses through that mess will be very small; that means, your abrasive particle size isinversely proportional to your mesh size, assume that if I want to calculate normallythere is a formula that is called 15.2 mm by mesh size normally represented by hashmultiplied by 1000 gives your abrasive particle size in terms of micro meters ok.So, assume for example, I have a thousand mesh size ok let me take a 1000 mesh size.So, it is there already I am given here.So, 15.2 multiply by 1000, why I am multiplying is to convert into microns divided by 1000mesh size, if it goes what will happen you will get 15.23 micro meters; that means, myabrasive particles size if I take the mesh size is 1000.So, my abrasive particle size is 15.2 microns.In this way one can calculate the abrasive particle size.So, that is a relation if I am increasing my denominator; that means, my particle sizeif I go assume that 1000 particle size what will happen, it will be 1.52 micro metersso; that means, that if I am going to increase mesh size that the particle size is graduallydecreasing, that is the relation between the mesh size as well as particle size.Again the same thing just to show you the prefix and suffix just I took this one matchnormally the some of the companies, they will show the symbols indicating exact type ofabrasive used which is in optional basically, at the same time at the end also some of themanufacturers they will give, their private marking which is also a optional.So, that is why I telt in this particular thing about this particular portion, whichis a constant for all of the manufacturers, but this one and this one is optional forthe manufacturers.So, you do not worry, but this is what the commonly followed grinding wheel specificationfor any type of grinding wheels.So, the selection of grinding wheel if you see the shape and size of the grinding wheelis important, the kind of abrasive material which is whether it is a silicon carbide orAl 2 O 3, or for the high material strength grain size, whether it is a coarse grain sizethese are the particle size 1 has to know, if at all I want to machine it or materialremoval normally the grain size should be coarse and finer are better for the surfacefinish applications.So, if you also see that the coarse are wheels are normally used in the softer material and,fine grains normally used in the hard and brittle materials, this is a common conceptfollowed by the grinding process grade, hard grade normally uses for the soft wheel softmaterials machining and softer grades are used for the machining of the harder workpiece materials, structure open structure any how bond material these are all thingswill come.So, among the wheel specification normally A 36, whatever we have seen grades as wellas the structure the two things if you see here, you are there is no much problem aboutanything here, if you see abrasive type there is no confusion because, you are saying whatare the abrasive type of abrasive particle, if you see the grid size; that means, thatyou are talking about the particle size.If you see the grade I will explain if you see the structure ok; that means, that A and36 do not have any confusion, let me go into directly into the grade structure and bondok.So, I will explain you grade structure and bond.So, what is the grade define the degree of strength at which the bond holds the abrasiveparticles so; that means, that how firmly the abrasive particle is held by the bondmaterial, whether it is a vitrified bond, or any bond hard grade means it is held veryhardly; that means, tightly.It bond posts very strong strength, if it is a soft grade grains are released rapidlyduring the grinding process.
Video 3: Grinding Wheel Problems and SolutionsThe first problem is glazing; glazing is nothing, but normally whenever if you see the hardwork piece material versus hard wheel that hard grade, normally you will get a glazingproblem ok what is the glazing high strength material hard metals abrasive wheels get dullbecause of their edges get rounded off; that means, if I have a hard wheel; that means,my abrasive particles are firmly bonded, if you are using against the hard work piecein that circumstances my abrasive particles are unable to remove the material and theybrake, because these abrasive particles are ceramic particles, they will have a brittlefracture and it loses it cutting edges and become dull.Then the surface will become smooth and shining and creates it will become less effective,that is if you see in this particular picture, there the difference you can clearly see herewhere ever the work piece is attacking, or where they are contacting, there the surfaceis completely shining other area, if you see here the other area is not shining; that means,that this shining portion is glaze you can say glazing.This also have good abrasive particles, this particular portion is good this particularportion is good, but this particular portion is glazed ok, that is about the glazing.If you can also see the practically how it look like, because of the hard grade versushard work pieces the surface become smooth, I mean not the work piece surface become smooththe surface of the grinding wheel become smooth, that is what you can clearly see in this wheelas well as same thing, if you can exaggerate can see here how the abrasive particles arebecome dull and inefficient ok this is called the glazing.The second problem is wheel loading, if this is the process where the tiny chips are beingaccumulated in the gap between two successive grains that is called gullet, two abrasiveparticles are there in between there is a gap that is called gullet, if the abrasiveparticles are too near and, if you are going for the machining of softer materials; thatmeans, whenever you are machining a softer material with dense structure, then this problemwill comes.If you see this one what will happen this white 1 is nothing, but the material is occupiedthat means nothing, but material is loaded inside the grinding wheel.Whenever you have a softer work piece and dense structure, then you do not have sufficientspace between two abrasive particles to accommodate the chips.So, I mean to say there is no I am not saying, there is a gap very minimal gap in that circumstancesvery less time the wheel loading takes place because, the material removal of the softerwork piece is very high, that is what you can also see here how the material is occupyingbetween two abrasive particles ok.So, this is about the wheel loading Now, how to resolve this problems these arethe common problems of the grinding wheel and, the solutions if you see here one isdressing.So, dressing defines the process of re sharpening of the grinding wheel this process used tofracture or tear away, the glazed or loaded outer surface that means, that it is applicablefor both the problems that is the glazing, if you see the glazing that mean that thesharp edges are gone and it becomes smooth on the wheel.So, I have to remove that layer and I have to get a new layer that is what intensionis in other case if abrasive particles are loaded or; that means, that gap between twoabrasive particles are consecutive abrasive particles are loaded by the work piece material,then also you have to remove because in a both cases wheel loading as well as wheelglazing the wheel become inefficient.So, you have to find some suitable solution that is what you will do is you just put astar dresser there is one type of dresser and, you just drawn the grinding wheel process.If you do the just you have to run the grinding wheel, then outer surface of the grindingwheel will remove by the star dresser, you can also use some of the diamond dresser,where it will be a like a point, this will particular grinding one will remove the outerlayer and, you will get a new surface which is having abrasive particles ready to go forthe grinding process, these are the two varieties of dressers, when is a star dresser is thereanother one is a diamond dresser will be there both will remove the glazer layer, or theloaded surface and gives the fresh surface for the grinding operation that is how youcan come up.Next one is truing basically truing means because of the sudden jerks, or somethingwhat will happen the grinding wheel will loses its true geometry that means, that if I wanta geometry circular geometry certain parts of circular T will goes off assume that Iwant a grinding wheel like this.Because of the sudden shock or something if I the grinding wheel will become like thiswhat will happen, this particular portion, this particular portion become a straight,I want to do the truing operation; that means, that I want to make into a true geometricallycircle shape.
Video 4: Types of Grinding ProcessSo, type of grinding process we since we are talking about introduction of particularlyto the machining and machining fluid, I am not talking about any mechanics, or somethingbecause I already told many times that particular chlores is floated, or may be floated in thenext semester.So, people can take up that one that is why I am not talking about any mechanics likeany mathematical equation or something ok.So, types of grinding if you see horizontal grinding vertical grinding in as you see,in the milling process also you will have the horizontal grinding and vertical grindingwhere the your Arber axis where you will mount, if it is parallel to your work piece thatis called horizontal, if it is perpendicular then it is called vertical.So, the first one is flat grinding process are the surface grinding process, if you seethis the surface is there and the wheel is there just the flat surface grinding wheel,if you see here it will rotate about its own axis while the work piece is fed beneath itnormally; that means, that it is fed beneath the grinding wheel and it will do only onthe surface you can clearly see here how the surface because of the high speed the surfaceis getting machined and, we will get a very perfect flat surfaces for the perfect flatsurfaces normally you can go for surface grinding operations ok.Cylindrical grinding is another one where you can see here, if at all I want the goodgeometry you can get even by turning the operation also, but the problem with the turning processis your surface roughness that is f square by 8 R equal to your R a will be; that means,that it is will be a function of your feed as well as nose areas here, there is nothingbecause your abrasive particle is too tiny and it will remove the material.But only 1 point you should clearly notice in the grinding process is the abrasive particlesall will poses the negative rake angles, no abrasive particles will be like concave surfacelike that all the abrasive particles mostly it will be like abrasive convex particle;that means, that you will have the negative rake angles, but the size of abrasive particleis too small compared to your nose radius the ah surface roughness which you are goingto get is very fine, as the particle size goes down you will get very very good surfacefinish.If you see there is another cylindrical process that is called internal cylindrical process,if you are working on outside surface it is external cylindrical grinding process, ifyou are working inside that is called inner cylindrical grinding process.So, external and internal just if you see that is a schematic diagram, these are thepractical diagram, that is the schematic diagrams and this is the practically visible diagramsthat we have taken.So, if you see cylindrical grinding process there are 4 motions which are involved inthe cylindrical grinding process.Rapid motion of the grinding wheel will be 1, this is the grinding wheel ok, normallythe RPM will be about 2000 slow rotation of the work piece against the grinding wheel.So, the work piece also will be rotated against the grinding wheel.So, that ah machining will takes place and finishing will takes place horizontal traverseof the work bench and which is back and forth of the grinding wheel.And another one is in feed wheel control this is nothing, but depth of cut; that means,that you will give depth of cut like this.This will also move in this direction.So, that is this are the 4 motions for the this is external and this is internal grindingok, you can see the grinding wheel here the grinding wheel is fed in this direction thegrinding wheel is rotated inside the work pieces.So, this is how practically the internal cylindrical grinding and external cylindrical grindinglook like.The profile grinding, if you see the profile grinding, normally this are used to grindintricate profile; that means, that if I want to machine or if I want to finish a profileassume that I want to machine this particular profile, what I want is I need to generatea profile which is converse to that surface ok.So, if you can generate a wheel which is converse to my surface normally, if it comes in contactwith uniform surface of the cylindrical rod what will happen it will generate your specifiedform.These wheels rotate at very high speed while the work piece is given rotation in the oppositedirection to get because, since we have seen the cylindrical grinding operation this alsowork in the similar lines, but only thing is that there the surface of the grindingwheel is same here, the surface of the grinding wheel will be converse of what you want productthat is what the profile grinding.If you see some of the examples, you can go by like this also this also and, this alsolike this you can this one of the profiles, if you have a grinding wheel you have to takeinto convership and just you have to give so, that you get a proper profile.Centre less grinding is another variety of grinding process, where there are two varietiesone is given here, this is a external and internal both surfaces you can do by thiscentre less grinding process; that means, that there is no center if at all I want todo the machining process and turning process, you have to hold the work piece between thecenters that is nothing, but normally the centered process.If there is no centers then; that means, if at all I want to finish ah the machine theirregular surfaces normally you go for the centre less grinding process, if you see thisis the grinding wheel and, this is the regulating wheel and work piece will be there and workrest will be there.So, it will work piece will be kept on a work rest and grinding wheel will be removing thematerial and the regulating wheel will be assisting the process.So, two things are there one is centered grinding as well as centre less grinding, if you seehere in the centered grinding there it is the work piece held between the centers.So, perfectly only I can do it for the normal regular shape, if at all I have a irregularsurface, then I have to go for center less grinding process that I have told in the previousslide also.There is called another one is internal center less grinding also is available, where ifyou see internal center less grinding there are 2 wheels, one is bigger wheel, anotherwhich is actually is the grinding wheel, while the smaller one is used to as a regulatingwheel.So, this is ah regulating wheel actually the ok and the pressure rolls are there supportingrolls are there and all those things, in that regulating wheel is made up of rubber bondabrasives and has good frictional characteristics.So, that it will be intact.Normally if you see here the angles are not given any how this is about the simple centerless grinding wheel process, where you can do the internally if there is a irregularsurface also.So, normally tilted angles also there some of the things are there, in the mechanicswhich for the basic introduction you may not required.So, what I mean to say is that if at all I have a irregular shapes like camps for example,I want to grind normally you will go for external center less grinding process, if you havesimilarly hollow things you can go for internal center less grinding process.There is another variety which is called creep feed grinding where the depth of cut is so,high.

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