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Module 1: Machining of Advanced Materials

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Machining of Smart, Brittle and Bio-Materials

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Video 1: Machining of Bio-MaterialsIn today's class, we are going to study about machining of advanced materials.What are the advanced materials that we are going to see is few materials only, especiallywe are talking about machining of biomaterials, machining of aerospace material and machiningof smart materials.We take one-one example and deal with the conventional machining process, because themost of this advanced materials are machined by the advanced machining process, but verylittle amount of work is done in the conventional machining process, especially in the electronicmaterials.Normally, electronic materials you cannot directly do the machining operations.You have to do using some hybridisation then you have to do like, laser assisted machiningand all those things.We will see in particular about each and everything.So, first we will start with machining of the biomaterials.Today's world people are moving around the biomaterials and it is application, becausemany things are happening to the people.So, they need bone materials to the vascular materials to the artificial muscles and allthose things.Since, the biomaterials that can be machined should be either metal or the ceramic materialsthat is why we look into the, mostly we look into the orthopaedic materials.What is the biomaterial?Biomaterial is used to make the device to replace a part or a function of the body ina safe reliable economic prisoners in a acceptable manner.So, it is the biomaterial, is used to make a device to replace, a part or a functionof a body in a safe reliable economic and physiological acceptable manner that is acommon definition for a biomaterial.The materials of synthetic as well as a natural origin contact with the tissue blood and biologicalfluid.Normally, it can be a synthetic material or it can be a natural material, whenever youplace inside the body, it goes in contact with the tissue blood and the biological fluids.Whenever it is in contact, with this type of fluid, it should be safe ok, it shouldnot cause any damage to the cells, it should not make the blood to not flow or something,it should be either, it should be inert or it should do the positive aspects to the body.Normally, in the forms of diagnostic therapeutic are the storage applications without adverselyaffecting the living organisms and it is components; that means, that body fluid, there are whiteblood cells.Red blood cells at the same time tissues osteoblast cells and all those things are there.This whenever you are going to put a particular material things at a body, it should not damageor it should not affect in a adverse manner that is what the biomaterials has to do.If you see the first and foremost material.Normally, whenever you deal is a dental materials, dental ceramics are there.You have to do the casting operation, when you have to do the finishing operation thenyou have to do the polishing operation and all those things.So, next orthopaedic implants, the hip implants, knee implants and all those things.The acetabular socket, it is also known as the acetabular cup.So, it will have a multiple layers or a single layer or normally it can be made out of compositematerial or a single material and all those things.So, knee implant materials and other, these are the some of the examples, where conventionalmachining process play a major role.There are stands and all the things, where the advanced machining processes, such asa laser micro-machining and all those things will play a major role.The characteristics of biomaterials physical requirements, it should be hard materialsdepend on your replication.It can also be a flexible material.The chemical requirements, it should be a non-reactive with any tissue of the body;that means, that it should be bio-inert material, non-toxic.It should not cause any type of toxic elements or any damage to the surroundings, it mustnot be biodegradable.People nowadays, are coming up with respect to the biodegradable also.I mean to say, it can be biodegradable.It cannot be biodegradable depend on your application, if I want a implant to be permanentlyplaced inside the body, in that circumstances, the implant should not degrade, if I wantto heal certain thing, assume that you have a bone fracture, I want to put a plate orpin or something.It should be degradable, because after two months or three months, after getting thehealing, what you should not go for the secondary operation to take up this plate in that circumstances.If it is degradable normally, it will be better.So, it is application oriented, what is the requirement oriented biomaterials are there.So, for the long-term replacement biomaterials, it should not biodegrade for the long-termreplacement.Normally, the material should not be degrade the main, a features of the medical applications.It should be, have bio functionality, that is specific function in physical and mechanicalterms.The bio compatibility normally, biocompatibility mean it should have absence of carcinogenicity;that means, a cancer should not cause immunogenicity, absence of immunogenicity and absence of teratogenicityand absence of toxicity.These are all things is required for a particular biomaterial.Now, you may be getting, why we are studying all these things, the problem is wheneverwe are going to do the machining operation with the parent material, assume that I amgoing to machine, a titanium, which is a bio-inert material.What will happen?The temperature rises and the metallurgical changes will come.Where?Where the metallurgical changes will come into a component?It may, I am saying, it may create problem by, it is elemental change ok.So, it may become carcinogenic.It may act as a toxic things and all those things that is why whenever I am going toput a particular material, it is property, should be checked, before you are placinginside a human ok.So, further purpose, whenever you want to machine particular material, the problem isyou should make sure that you are input conditions and you are tool selection should be sucha way that, that the work piece should not change.It is elemental properties or it should not experience any heat affected zone recast layerand all those things.So, what I mean to say that bottom line of the story is, it should maintain it's parentalform applications of biomaterials.If you see the biomaterials, there are varieties of biomaterials are there.For example, ceramics, you have the heart valves, bone replacement, a dental replacementand all those things, if you see the composite materials, you will have biosensors and implantablemicroelectrodes.If you go for the metals, you will have again dental implants and orthopaedic screws andfixations, whenever you go for the polymers, you have a drug delivery devices skin or cartilageand osculate implants and all those things.These are some of applications of biomaterials in different varieties of forms that is rangingfrom polymers to ceramics ok.So, machining is carried out mostly in the orthopaedic and dental implants for the internaland external fixation devices ok.So, because the machining normally, as a mechanical engineer, what we do is, we talked mostlyabout machining of metals ceramics and polymers and all those things.That is why, in this particular course, we are not dealing with any advanced things,such as a laser beam machining or very complicated shapes finishing or something.We are not going to talk, we are just going to talk about the simple some of the materialsor the metals or the ceramics, which are biocompatible and which you can use inside a body for themostly dental as well as orthopaedic application.I mean to say, we are going to look machining in terms of dental and orthopaedic ok.These two, we are going to study ok.Since, these two involved mostly the mechanical machining; these two involve mostly machiningoperations . So, that is why, we deal with these particular biomaterials, which are machinable.So, if you see the implants, you clearly see normally, the dental things our teeth inside,it will be look like this.So, the similarly, we are also going to develop or the people, who are doing the researchwill also develop in the similar trend for you, need to fix it.So, the external portion should be same that as the internal thing or whatever, you requiredto a particular patient, but the internal situation should be like screw that is tobe fixed into the jaw.These are to be fabricated very precisely and it should be biocompatible and all thosethings.Similarly, for hip implant, plant also.So, hip implant, you will have acetabular socket.Acetabular head will be there and the stem, hip stem will be there and all those.This is the knee, knee implant, if you see, you have a knee, upper side, lower side andin between, you will get the cartilage are, that is as artificial cartilage and all thosethings normally, artificial cartilage materials will be developed with ultra-high molecularweight materials and all those things ok.Apart from the orthopaedics, there are other implants for the heart applications that isheat valves and all those things and intraocular lenses for the eyes and all those things willalso be developed, but this involves very less type of conventional machining processes,that is why we are not going to deal with this type of sophisticated implants, justwe are going to talk about mostly orthopaedic oriented.Now, we have to see what is the difference between normal, that is the conventional machiningand machining of a particular material.Normal machining, I mean to say machining of common materials like mild steel and allthose things even though component is medium precision, you can accept, but in terms ofbio, you need not to take any tolerances, because I mean to say exact, I cannot say100 percent, but the only thing is that you should go for high precise components, inmicron gap also plays a major role.Surface finish is acceptable up to 500 manometers, but here the surface requirements are toohigh that is 50 manometers that is why the cost of bio implants normally, goes up.The product surface structure does not have much significance, but here surface textureplays a major role, if it is a hydrophobic surface, if it is a hydrophilic surface, itplays a major role Normally, you have seen a dental crone inthe previous slide, you need to have the hydrophilic surface, because it should interact with theosteoblast cells or the nearby cells.So, so that, what will happen?Protein exchange will takes place.At the same time, the cell will easily occupy the space and it will tight your particularteeth, that is placed inside, if it is a hydrophobic then what will happen?The cell culture on that, one may not be the , because it is the, phobicity will be there.Generally, high feed and high depth of cut will be given so, but here low feed and lowdepth of cut will be given, because you require very great precise components.That is why, you always go for the better surface finish.Normally, better surface finish, you will get with respect to low feed rate and allthose things, if you are going to use more depth of cut, what will happen?Temperature generation will be slightly higher, because your material removal per unit timewill be very high, that is why the temperature may damage the work product ok.So, the workpiece should not damage for that purpose.You should always play with low depth of cut and low fluid rate.So, machining of dental implant.The procedure goes like this.First, you just fix the dental implant material.Normally, this will be done on the titanium, then using a CNC multi-tool machining process,just you do the turning operation.Normally, patterning operation and all those things, then you generate the threads as peryour requirement, then you can do the post processing like coating and all those thingsalso.So, then you can do the galvanising of the dental implants followed by the spray coatingsof the dental implant, because whenever you want to coat the biomaterial then it willbe good for you, because you are cells, which are there nearby compatible to the biomaterials,then you are dental implants are ready.So, you can see, how the dental implants are ready here, for the deployment in to a humanmachining of knee implant.
Video 2: Machining of Aerospace MaterialsNow, we move on to the machining of aerospace materials.So, aerospace materials, the basic requirements goes like many things and the basic aircraftmaterials here from structures and all those things.Normally, these are the materials that are used in this one, a properties of the superalloys.Mostly, super alloys are used in the aerospace applications, if you see super alloys consumptionin the market, the structural application is 10 percent, chemical industry 10 percent,medical industry 10 percent, but aerospace industry is 70 percent.That is why super alloys like, nickel based alloys and all those things are play a majorrole in the aerospace industry.that is why we see how to machining the super alloys?What are the problems and we also see the other materials also.Nickel based super alloys, nickel based super alloys are the most complex and widely usedin the aerospace industry and nickel based super alloys contribute over 50 percent ofthe weight of the advanced aircraft engines.Especially, this materials are used in the aircraft engines basicallySo, principal characteristics, it is high phase stability and of the face centred cubicnickel matrix and capability of the strengthening by variety of direct and indirect means andthe surface stability of nickel is readily improved by the alloying with the chromiumor aluminium.That is why, you can improve the properties as per your requirement.The machining of the nickel based alloys conventionally.So, high ductility work hardening low material, removal rate high tool wear.Basically, it is a super alloy material in that circumstances, the tool wear will bevery high, the phase transformations will takes place quality that you are going toget on the surface is very poor and the cost goals are difficult to achieve quality andall those things ok.If you see particular thing, that is what I was talking about, the tool wear and allthose things, if you see here tool wear.So, this is the tool wear that is observed on the cutting tool.So, the crater wear also, you can see here and you can see also flank wear.So, at the same time you can also see the basic problem is adverse chip formation here,itself.The chips are entangled in the machining region itself ok.So, this is one of the adverse effect, at the same time formation of burrs.So, whenever I am doing the machining operation, the burrs is nothing, but the pieces bitsand pieces that are not dismantled from the work piece.You can also see these problems will hamper the final product that is, why you need tomachine very precisely, very efficiently?Here, you can see the conventional machining.The basically problem is the surface damage in machining of nickel titanium alloys; metallographicmicrostructure after the turning operation, you can see the carbide particles are thereand all those things; that means, that whenever you do machining with a carbide base cuttingtool, there is will be a diffusion taking place on to the surface; that means, the toolmaterial higher concentration to the lower concentration.That is the workpiece material is transferred.That is why, carbide particles are seen here.So, lay pattern after the dry milling, the predominant direction or surface roughnessis clearly observed at the same time metal debris, after the turning operation how themetal debrises are still there on the surface smeared material and feed box.The smeared material is here, at the same time, these are the feed marks that are observedduring the billing of these super alloys.Applications I said that this is the mostly important material for the aerospace engine.This is a engine and this is the turbine blades that are made and this is the engine.You can see 50 percent on the literature.It is evident that the more than 50 percent are approximately, 50 percent will be usedin the aerospace engines or the other material, which is mostly used in aerospace industry,is the titanium and the titanium based alloys.The properties it will have a lower density, comparing to steel high specific strengthat elevated temperatures, also high strength at temperatures below the freezing temperaturealso good static resistance, excellent corrosion resistance, due to stability of the Ti oxidelayer.Good cold formability of this particular material and low thermal coefficient of expansion,these are an lower thermal stresses also.These are the beautiful properties that one can see in the titanium based alloys.These are the physical properties as well as the mechanical properties of the titaniumbased alloys.You can go through the table for your convenience, what are the various values like hardens tensilestrength modulus of elasticity and all those things.If we see the machining process, it is looks like a ductile and material, because it isa soft material.Even though it is a super alloy type of material, but it, it is a basically a ductile material.That is why, you always see a thick zone ok.You people have studied already thin zone models and thick zone models.If the shear plane is like a line, it is thin zone model.But here, if you see a black thing, this is an area that is occupied, that is nothing,but it is a thick zone is forming here and between the thick zone is formed between theundeformed thickness to the chip thickness.So, chip tool interface, the basic problem in machining the titanium is, it cannot conductthe temperature assume that a here 100 percent temperature is generated in this particularregion.The 80 percent is carried by chip and 10 to 15 percent will be carried out tool and 5percent will be carried by this one ok.In that case what will happen?5 to 10 percent assume ok.In this case what will happen?The tool is the only body where, it will absorb the temperature, because the, if it is a titaniumalloy workpiece is a titanium alloy, it cannot dissipate the heat, to whatever the heat thatis generated, stay on this particular portions only.So, that it will import into the tool.So, the thermal softening of the tool will takes place very fast and the tool will fail,that is the basic drawback of this particular material.The titanium-based turbine blades also will be used, because this adverse effect, whateverI said, the temperature will stay on the surface itself, if you talk in terms of turbine blades,what will happen?Whenever the flight takes off to the higher altitudes, what the temperature.Normally, it will be minus degrees, the whatever the heat is generated on the surface willbe cooled by the way that is coming ok.What is the advantage that you are going to get here is the, it cannot dissipate the temperatureinside ok; that means, that whatever, because of the rotational speed, if there is any temperaturegenerated on the surface, it will be cooled by incoming air ok.The adverse effect in the machining is a good property for aerospace turbine blades developmentand all those things.So, properties causing the difficulty in machining the first property is as I said lower thermalconductivity.If the thermal conductivity of this particular material is 15 and high machining temperatureduring the machining process.If the temperature is very high, it cannot conduct the temperature inside the workpiecematerial.So, it will impart to the tool.So, the thermal softening of the tool takes place and tool melting will takes place thermaland tool will fail.Another one is high reactivity.So, if it is high reactivity, what will happen?The tool wear will be very high, at the same time chemical wear; that means, that it willchemically affect with respect to the temperature gases and all those things and at the sametime it also will have high adhesion effects.So, high strength at high temperatures; that means, that whenever, you are doing the machiningoperation the temperature goes up, if the temperature goes up, still it maintains itstrength, then it is very difficult for the cutting tool to do the machining operation,in that circumstances you will experience high forces, because the strength of thatparticular material even though you are at elevated, temperatures is very high.So, the forces experience will also will be high and the tool breakage will occur as earlyas possible.So, now no elastics modulus, because of this normally chattering will takes place.Poor surface finish will come and at all Ti alloys normally, will have 110 GPA comparedto steels the segmented chips.The type of chips that the operator is going to experience during the machining of thistitanium alloys is shear band formation.Cyclic load of the tool and most importantly, you are going to get the segment type of chips,we will see what are the segment type of chips and all those things.So, the characteristics of Ti 6 Al 4 V, this is the one of the common material that aerospaceindustry uses.So, segmented chips, you are going to get strains, are approximately 4 to 6 strain ratesare 1 naught 5 for second ah, the machining temperature will be very high, that is 200to 600 degrees and you can see here, the primary deformation zone and the machining effectedzone.Basically, the primary shearing zone, this is and the machining affected zone, the lotof temperature that is generated here will be important to the tool ok.That is why tool will experience a lot of temperature, that is the drawback and thetool thermally softens and fails at the same time.You can clearly observe, this is the shear bands ok.These are the shear bands; that means, that you are going to get a segmented chips ok.The proof for this one, you can clearly see the shear bands here.
Video 3: Machining of Smart and Brittle MaterialsNow, we move on to the machining of smart materials basically or very sophisticatedmaterials and most of the smart materials are done by the advanced machining processesonly ok.So, very little chances are there, for the conventional machining processes.That is what we will discuss.Here the smart materials are the materials that have one or more properties, that canbe significantly altered in a controlled fashion by external stimuli that is, whenever yougive certain external stimulus like temperature and all those things, it will change it'smajor properties ok.Change in material can also be reversible.It can go martensite to austenitic phase, austenitic to martensite phase, whenever.If you, if somebody wants to study about what is smart material and all those things, youcan go through some of the videos or some of the books, you can refer it.The examples normally shape memory, piezoelectric magnetic mid shape memory, many materialsare there at the, say and you can also see here same thing the machining difficultiesduring machining of the smart materials ok.So, metallographic microstructure, after the one you can see here, wherever the surfacecavities are formed and all those things and the carbide particles also stays here ok.Whenever people are using here, nickel titanium alloys are more one of the common examplesfor the smart materials.These are the materials that will be used for stent applications and all those thingsnot only stent applications, you can use for many-many applications, whenever the nickeltitanium alloys, that is called nitinol or machine conventionally using the carbide tools.You can see, there is a diffusion of the carbide.Particles will take place into the workpiece that is diffusion is taking place here ok.Lay pattern after the dry milling.You can see the lay patterns that is the surface roughness and even metal debrises are also,you can see in which, at the same time smeared material.Also you can see in this particular workpiece material as I said, there is not much scopein terms of shape memory materials, there is very-very minute area is there, becausethe feature that you are going to generate on shape memory materials, assume that I wantto generate some features on stents, stent itself is very small in that, because it hasto go into the artery of the human.So, artery diameter is approximately 2 MM or something.So, the diameter of that one will be less than 2 MM.This conventional machining process are less preferred for the smart material.That is why, we do not have much things, but you can do the some of the milling operationsand you can generate some of the features on itAnd now, you can see how the slot generation, how the surface finish is there and you cancut on austenitic steel and martensite steel and you can observe milling with minimum quantitycutting fluid, also you can do.So, that the metallurgical changes will be very less.If the metallurgical changes is there, what will happen?Whatever the phase change, you have to do or you are expecting may not be 100 percent.Now, we move on to the electronics materials, machining of electronic materials, the electronicmaterials like silicon material . I am going to talk about most, which is a brittle material.Since, till now, we have seen the ductile materials and the high strength materials,super alloys and all those things.That is why, we are missing the brittle material.That is why in this particular electronic materials, I am going to talk about the brittlematerials.Basically if I want to do the machining of brittle material assume that I have a class,I want to do the machining using the milling operation in that circumstances.How can I do?Basically, the problem comes is, if the interaction forces between tool and workpiece is veryhigh.