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Module 1: Machining of Advanced Materials

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Advances in Metal Cutting / Machining Processes

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Video 1: High Speed MachiningIn this class we are going to see advances in metal cutting or machining processes.If you see what various processes that are come under the metal cutting or the machiningprocesses which are called as the advanced in particular to the current day is concerned,that as called some of the things; that is high speed machining, hard machining, diamondturning, double tool machining and thin wall machining.Some of the things are already known to many of the you, at the same time these are alsonot called as so advanced, but it these are all few of the advancement that are made bythe researchers in the arena of conventional machining processes.First we will move on to the high speed machining.So, high speed machining as the word the speed specifies that, it is deals with cutting speedof the machining processes.If you see the history the, this is the first definition of high speed machining was proposedby Carl Salomon in 1931.Later on what happen it has the assumed that the certain cutting speed which is 5 to 10times higher than the conventional machining processes, where the chip tool temperaturegoes down; that is what the proposed thing and that it was the some of the people theyhave invented . So, if you see this particular diagram, wherethe conventional machining processes will go up to 600 normally.This is the range where the conventional machining processes will take care and the machinablematerials and other things.If you go beyond this, this is called as a high speed machining or you can, you can seethat what is happening there is the forces; that is conventional temperature which isseeing here is gradually decreasing also.As a speed is increasing the temperature that you you can see on the y axis, is graduallydecreasing.So, if the temperature decreases; that means, that the part accuracy goes up, because youknow the difference between cold holding and hot holding.The part accuracy the component accuracy in the cold holding is much better than hot holdingprocess.Similarly if the temperatures are lower; that means, that the process will become much saferfrom the point of machining.If you see the different different materials; like a steel, cast iron and and bronze whichis comes under the nonferrous materials, all these things the temperature goes down.So, there are some advantages about this one; that is why we proceed towards the high speedmachining.The high speed machining, normally there are ah many varieties are there, some of the peoplethey say high cutting speed machining, some people they say high spindle speed machining,some they say high speed machining, I and people they clubbed both and they termed itas a high speed and feed machining and the high productive machining.So, these are that the synonyms are some of the variance in the high speed machining orallied processes.Finally high speed machining is termed as, it is a powerful machining method that combinesthe high feed rates with high spindle speed and the specific cutting tools and the specifictool motion.If you are clubbing most of the things which are specified above, these all lead to a commonword called high speed machining ok.So, this is about the high speed machining.This contains high feed rates as well as high speeds that are there, used by specially madecutting tools.So, what are the cutting tools, what are the materials and all those things we will seein the upcoming slides.If you see particularly about the cutting force versus cutting speed, e as the speedis increasing what is happening?The cutting force basically Fc is gradually decreasing, but this is up to certain velocity.Whatever you have seen the previous graph is beyond the range that inner zone.The basic mechanism here is, whenever you are going to cut the workpiece material ifthe temperature is high the basically problem is the workpiece becomes thermally softened,if the workpiece become thermally softened up to particular temperature only.I am not talking about 16,000 meter per minute and all those things up to certain, what willhappen this will work as a preheating for the upcoming material; that is why the cuttingforces will decrease.So, various materials will have various transition ranges of high speed machining, because ifyou take a aluminium, if you take the hard steel, both assume that if I am rotating forthat same RPM tool with help of head stock.You cannot say the same is considered as a hard machining.In steels, hard steels you may consider as hard, high speed machining, but not in caseof the aluminium, because there is a hardness variation okThe hardness variation also play a major role, whenever you are deciding particular processas a high speed.So, for that every material there is a transition range, when you call it as a high speed machining,when you call it as a conventional machining.If you see particularly reinforced plastics are the polymer based materials, if the rangeis approximately 1000 metres per minute, still you can call it is a conventional machining.If you are crossing some more then only you can call it as a high speed machining.If you see the aluminium at 1,000 degrees still you can call it as a conventional machiningbeyond which slightly ahead like 13,00 meters per minute, 1400 4 meters per minute, thenyou can call it as the high speed machining.Bronze and brass on the edge it is exclusively on the edge it is there.So, you can call it beyond 1100 degrees and 1200 1100 degrees around, you can call itis a high speed machining cast iron, 1,000 degrees itself cast can be named as a high-speedmachining and the steel, titanium, nickel based alloys which are called the high-temperaturealloys and all those things, have very less speeds.If you see the steels approximately the temperature is around 700 degrees or something you cansay it is a high-speed machining; that is the transition from the conventional machiningto the high-speed machining.If you take a around the titanium, normally titanium will be around 200 to 300 degrees,the 300 meters per minute.And if you see about nickel alloys, the transition will come below 100 metres per minute.This is about the transition where particular material if you are using as a workpiece material,heat properties strength, its hardness and all the properties will also matter, willalso can decide whether you are in the high speed region or the conventional region.If you see the features of high-speed machining, the high-speed machining, the features youwill get is good accuracy and the efficiency, because you are going to machine many partsin less time, because your speed is very high; that means, that you are efficiency or theperformance is very high, reduced machining time, because you are machining at very highspeed, so the part to be manufactured will take very less time.Assume that you have two components one is machine conventionally, another one is machineah using high-speed machining.You are going to complete the second part in less time; that means, that the time isreduced, time is money.So, you can sell the particular component at less price.The quality of the work pieces is very good and decreased cost.These are all on an average the final destiny for any company is, how to sell a market competitiveprice.So, that the buyers or the customers will purchase the product, a quality product ateconomic price; that is what the motive for the people are going regularly continuously,the research towards the betterment and betterment of the products by reducing the cost of theproduct.If you see the features and its effects, reduce the heat transfer into the workpiece, becauseof which you will get the good part accuracy; that means, that tolerances will be good andthe surface finish will be good and all those things.Reduction of cutting forces, if the cutting forces are reduced what will happen?The part accuracy and surface quality is good.If the forces are less what will happen?The penetration and all those things will be less, at the same time temperature generationwill be less.So, the part accuracy and surface quality will be more.Increased cutting speed, if you increase the cutting speed what will happen?The stability of rotating tool will be good and feed rate of the material will be increasedand material removal all and average.What I mean to say is that, if you are going to increase the cutting speed your MRR, MRRstands for material removal rate.There is a difference between material removal and there is a difference between materialremoval rate.Sometimes B.Tech students may confuse with this respect to these two words; that is materialremoval is how much material you are removing and material removal rate is how much materialyou are removing per unit time, so time factor comes in this particular.So, if the speed is very high your time taking is very less ok.For less time I am going to remove more material; since this particular process is a machiningprocess, you are mostly worried about how much material I am removing per unit time,so that the production rate will increase.So, comparison between conventional and high speed machining, if you see the typicallycutting speed in the normal machining and high-speed machining.So, aluminium if you seem it is less than 305 and normally it will be multiple times.So, similarly if we, if we can see the cast iron, steel, titanium super alloys and allthose things, the speed normally that you will use here is this one.The conventionally normally people will use this much.Assume that let me take the super alloy.
Video 2: Hard MachiningSo, hard machining, the word stays, the word says hard; that means, that the workpieceis hard.The workpiece hardness is very high if you are going to machine that material, then youcould call it as a hard machining.Now we will see what is the range of that hardness.Introduction to the high-speed, introduction to the hard machining.So, machining of hard materials, people can go for many things; that is one of the optionsyou have is a hard machining, another option is a non-traditional machining that is advancedmanufacturing processes, another one is the grinding process and there is a option forcryogenic also.So, these are varieties there, among which particularly we talk about hard machining.So introduction to hard machining.So, hard machining is the machining of hardened materials, over 45 HRC, workpiece materialwhich have the rock well hardness scale see above 45, then typically you can call it asthe hard machining process, but the hardness if it is in the range of 56 to 68 you caneasily call.Some of the people they do not call even the HRC is 45, but there is a slight contradictoryis there, some people they call it as a hard machining with 45 also some people they donot call it as.So, it is a time dependent, because if you see the old papers other time they do nothave most sophisticated cutting tools, from that point they called it as a hard turningor hard machining process.As the world grows or the time passes what is happening is, that the hardness is goingto increase in terms of work pieces, at the same time the people are inventing new andnew cutting tools, it is raising the bar.Continuously the bar is raising, because the tools which are sophisticated are coming intothe market; that is why the hardness is, as you know the nanotechnology peoples stay.People say about once upon a time they say that below one micron is a nano, but nowadayspeople say about below 10 nanometre is a nano.So, there is,because the world is progressing.If the world is progressing, the world become advanced and advanced and the values are goingto increase increase increase ok.From this point of view for hardness values for the hard machining is increasing gradually.Tomorrow this particular 56 to 68 may also increase, there is a chance, because the worldgrows.When you students will become faculty you may teach to your student saying that if youare going to use the hardness of your workpiece above 70 called as hard machine, there isa chance, I am not saying that is going to be true, but there is a chance or there isa probability, using this specially prepared tools with geometrically defined cutting edgeswith a negative rake angle, normally uses in the hard machining process.Polycrystalline cubic boron nitride that is called PCBN and mixed ceramics; Al2O3, titaniumcarbide and sometimes ceramics also used as a cutting tool materials for machining ofthis hard workpiece materials.You can also see it eliminates the distortion problems from the heat treatment and unclampingand reclamping of the workpiece in many cases, expensive polishing operations and save thetime and money, because the hard machining is one of the advanced process, where youcan go for slightly higher sites.This machine tools are specially prepared for the special application, so you can evengo for slightly higher depth of cuts and feeds; that is why your time and money saved, becauseyou may not required to operate the post processing like polishing and all those things.You can do instead of grinding, here itself you can do the turning operation or the millingoperation the, whatever the operations that you can do for the particular component tomake it as a final product.If you see here the turning operation or the milling operation, whenever you are operatingagainst the workpiece material, the lot of fire type of things spark will come into picture.If you see this particular video, you can clearly visualise what is hot turning.In particular this is taken at our laboratory, but this is not that much hard workpiece materialto show you how the spark or the fire that will going to generate at the machining region,for that purpose we are showing this particular video.You can clearly see the hardness of this particular material is around 48 to 50, which is stillcalled in the range of hard only.The spark at the fire that you are going to see is purely because of the interaction forces.If you are interaction forces at the same time speed plays a major role, if the interactionforces is very high and severe what will happen?The fire type of spark will generate.The difference between normal machining or the conventional machining and the hard machining.This is machining of material possess the hardness less than 45 HRC normally, this isabove 45 to 68 HRC, this may still may increase with respect to time.Generative forces are less compare to the hard machining.Here the cutting forces are generally 30 to 80 percent greater than the hard turning,normal turning process.It requires setup that providers normal dynamic stiffness, but it requires maximum dynamicstiffness.All operation steps are to be executed, it provides a reduction in the operational steps;that means, that if the people are using a post processing techniques, you may not requiresthose post processing techniques in terms of hard machining.
Video 3: Diamond Turning ProcessNow, we move on to the diamond turning.So, how the diamond tools are fabricated and all those things we do not see, but if yousee particularly, the mirrors.If you see the figure 1 the mirrors are finished by using the diamond turning operation andthese are the components super quality finish.Normally these diamond turning is costly process, because you are tool itself in this particularprocess is a diamond one.So, widely used for manufacturing of high quality aspheric; that is called non pore,aspheric optical elements from the crystals metals and acrylics.Acrylics such as PMMA and all those things.Turning with diamond tool, so you are going to use the diamond as a cutting tool here.There are many varieties of diamonds, artificial diamond and a natural diamond.In this particular thing people mostly use artificial diamond, mechanical machining processfor the precise works, whenever you require the precise work in that circumstances, normallyyou go for the diamond turning operation.You can see here what is happening?The mirrors are finished.If I want to make a mirror; that means, that the image should be clear; that means, thesurface quality that you are going to get on the particular components should be sohigh.The diamond turning is a multistage process and the diamond tipped lathe tool is usedto in the final stages, you will use a diamond tip, assume that here what is happening hereis diamond tip is there and you can even see the mirror image inside the workpiece also.So, that much super quality products are to be fabricated.These are the materials, normally plastics, infrared crystals, metals.These are the materials which are readily machinable and you can see the plastics, howthe people have used it and the materials not readily machinable or like a silicon based,ferrous based.Ferrous based normally do not use for the diamond, you need to take some of the precautions.So, silicon based also glasses and all those things you need to take some precautions beforeyou are going to use this particular diamond turning process.Diamond tools which are used for the cutting operation.This turning is performed with the use of cutters made of diamond; that is we have alreadyshown in the previous slides.Diamond are carefully ground and polished to generate the geometrically defined cuttingedges, at the specific crystallographic orientation, you cannot do the grinding of the or the polishingof this diamond as you wish.You need to follow certain procedures, you need to follow certain metallographic or thecrystallographic access only.Otherwise you cannot do the process.The cutting performance and surface finishing produced using the diamond turning is greatand edge sharpness of the diamond is greatly depend on the cutting edges; that means, thatif you can maintain the cutting edge sharper and sharper, you are going to get a very goodquality of the surface finish on the particular component.You can see here, this is the diamond tip that is there and if you see the exaggeratedview, how sharp is the cutting tool.The edge sharpness and quantitatively defined as the tool edge radius.So, this edge radius is most important, key properties of the diamond, you also know thatthis is the hardest and coefficient of friction is very low and the strength is also high,electrical resistivity is very high.So, thermal coefficients of expansion is low and high abrasion and corrosion resistance.This is one of the stable materials that is why the corrosion and all those things arevery minimal.
Video 4: Double Tool Turning and Thin Wall Machining ProcessesSo, double tool turning process.Normally this particular process where you will use the two tools on both sides of theturning process.Like you can see here; one tool is from this side, another tool you are feeding from thisside.So, there should be some offset, so that we can do the process safely.Simultaneous machining by two single point cutting tools in the turning process, so tomodify a conventional lathe and to enhance the productivity.basically if at all I want to give the depth of cut heavily in a single guided is not possible,for that purpose you can divide that particular ah depth of cut into two and you can giveon the both sides.So, normally multi-tool turning or the parallel turning is normally attempted for heavy materialremoval, minimising the cost and maximising the rate of material removal.In this particular circumstances you can go for double tool turning process.So there are three varieties; one is a parallel turning with two cutting tools on the sameside, one is here, another one is here.This is the one.The second is parallel turning with two tools on the opposite direction; one is here anotherone is here.The synchronous turning process two tools on opposite direction; one is here anotherone is here.Whatever we are going to see in the next slides is the variety c, but slight offset is required.In the schematic it is not shown properly, but you required slight offset, so that youcan do the machining process with safe.You can see here one tool is mount on this side, another tool is mount on this side,so that the machining process is taking place.The schematic image, if you see here, the tool one is here and tool two is here, sothat the machining is taking place.At the same time you are dividing the depth of cut, you are not wearing any other parameter,for the same thing you are doing what you are doing is, you are dividing your depthof cut into two segments and you are giving to one tool some depth of cut another toolsome depth of cut The advantage of this one you are going touse the rotational speed same; that means, that the power that you are going to feedto the lathe machine is same ok.For the same revolution or the for the same workpiece rotation, the two tools are operatingsimultaneously by dividing the depth of cut or if at all I want to remove more and morematerial, you can go for the single rotational speed requirement power for particular latheusing this particular process.In a single tool what will happen if you are going to use the RPM, certain RPM, you haveto give some power to the lathe machine, but you are able to remove only certain material.If at all I am using two tools I can go for the higher material removal rate; that means,that my production rates are very high.But your tools are mounted on the opposite direction, because of which one will experiencepositive, another will experience the negative forces.The tool one; that is called the front tool and rear tools.The front tool will experience higher and the rear tool experience the lower, becauseof the thermal softening of the workpiece; that is done by the first tool, the forcesexperienced in the second tool will be normally low; that is why as you increase the speedthe feed forces are slightly low.You can see the temperature on the tool workpiece interface.If the temperatures also the rear tool as well as the first tool.So, the temperatures normally will be very high, because already the temperature is therein the workpiece that will be imparting to the tool; that is why the temperatures inthe rear tool will be slightly higher compared to the first tool.The cutting tool wear life and all those things.Normally the tool wear if you talk in terms of the front and the rear tool.Rear tool; obviously, the flank wear will be very less, because the workpiece is gettingthermal softened and all those things.In the machining the, if you talk about the tool wear in the front cutting tool and therear cutting tool, the tool wears normally if you talk.The front tool wear will be slightly higher, because you are removing the original material.In the rear what is happening is, the workpiece is getting pre-temperature; that means, thatthe heating is taking place that is why the thermal softening of the workpiece is there,because you are offset is too less between the two cutting tools.Assume that my cutting tool is here another cutting tool is here, there is a slight offsetbecause the time travel is very less that mean that the first tool cuts and goes offsecond tool come into action; that means, that there is no much is sufficient time tocool down.In that particular case what will happen, the thermal softening of the workpiece takesplace, so that the rear cutting tool experiences very less temperature.Rear tool experiences the thermal softened workpiece material; that is why the flankwear is less.If you see all the speed, if you see all the cutting times, for every condition, normallyfront tool as well as rear tool follow the similar trend; that means, that front toolhave higher flank wear compared to the rear tool.Double tool versus the conventional, double tool process produces the superior surfacefinish.This is a maybe may not be that is depend on your second tool feed conditions and depthof conditions.If you are going to use less in terms of the second tool; that is the final tool that iscoming.In that circumstances you are going to get good surface finish.Tool separation distance do not have much effect on the average surface roughness , butit will have effect on the temperature.Double tool turning is advantages and it leads to reduction of machining cost, because thesame power of the workpiece spindle is you are using in both, same power that you aregiving to the spindle; that is head stock, you are using for machining with two tools;that means, that; obviously, the power consumption is less.The cutting forces and feed forces are lower compare for the rear tool.Basically the thermal softening of the workpiece takes place, because of which rear tool experienceslow forces.The coefficient of friction on the rear tool is reduced due to clearing effect, the frontof the front tool.This is attributed to the reduction of the forces of the rear cutting tool.Distance between the cutting tools are not affected, the cutting force, feed force andthe temperature significantly, but in practical there will be a some temperature raise, becauseof the machining of the front tool, because of that there is a slight variation that youhave seen in the previous one, where the ah tool life is or the tool wear is less in therear tool.Some similarities in terms of conventional as well as the double tool turning.The average surface roughness becomes lower at higher cutting speed and higher at lowercutting speed.The average surface roughness becomes lower at higher cutting speed, this is holds goodfor the both double tool as well as single tool, with the increase in the feed, the averagesurface roughness increases.This is the same in terms of conventional as well as double tool.Average surface roughness increased with increasing depth of cut.This is not so, but the problem is whenever you decrees that depth of cut what will happen,temperature raises, if the temperature raises there will be a problem with surface roughnessalso in the nano-scale, not into very big scale, but very minute level.Advantages of this particular process; short machining time, because you are doing withtwo tools high productivity and superior surface finish subjected to the machining conditions.Tool life increases due to superior surface finish.Tool life normally will be increased in terms of the rear tool, machining accuracy alsoincreases.This is about the advantages.The domination cooling properties based cutting fluids will be used for the both the thingsor you can use if the speed is very high you can go for the cooling based also.The here you can see here; one tool is doing the machining here, another tool is doingmachining here, for the rotation is same.