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Machinability and Thermal Aspects of Machining

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Video 1: Surface Morphology on Cutting Tool and Workpiece
Now we are into the surface roughness in machining. Till now what we have studied is surface roughness, lubrication in machining and all those things .whenever I am talking about surface roughness in material cutting, I am more inclined workswhat is the surface roughness in material cutting ok .So, till now in the previous class, what we have studied is a , what is surface roughness?How do you define the surface roughness ? What is center line average value? What is rmsvalue? What is maximum peak to minimum value? And all these things this is the introductionto surface roughness, as the surface roughness is one of the most important responses thatwe take out from the machining experiments ok.. So, we all study at the lubrication in machining, types of lubrication in tribology and machiningintroduction to surface that is what I was telling , how you measure the surface roughness,profilometers noncontact surface profilometers , and experimental techniques to and the representationof surface roughness and texture . These are all we have studied in the previous classok. So now we will move into exclusively whatis the surface roughness in machining pertaining to this particular course ok.So, the surface morphology and the surface roughness is ah one parameter of the surfacemorphology. Morphology will tell you not only the surface roughness, there is any a waviness,there is any profile cr there and all those things ok .So, for example, if you see the surface morphology of the cutting tool, one the machined , thisis you have already seen, but ah from the angle of ah surface roughness. T previouslyyou have seen this was a sticking region, and the sliding region as the tribologicalaspects. Now if you see , your perspective of ah looking , now in the surface roughness,how do you represent the surface roughness, assume that I want to measure the surfaceroughness of the sticking zone , what I will do is I will just take the surface . JustI plot a line like this, and I will take the surface roughness. Or if I want to take acrossfrom the cutting edge . So, I will take like this ok .So now that you will get in the form of surface roughness . So, similarly in this if you takein the region of this one , sliding region you will get the profile like this. Becauseif you see a flat region is there in this this ok. So, gradually it is going to tendingto the parent material . That is why , this is how we are looking from the surface roughnesspoint of view ok ok . . So now, what are the parameters are inputconditions that will affect the surface roughness. So, what I am going to show you is a fishbonediagram of surface roughness in the machining. So, how the surface roughness will affectby various enormous input conditions that are there in the machining . So, if you cansee the surface roughness , surface roughness is what my output response is ok, there isa difference between parameter and response . If I am seeing an input parameter; thatmeans, that I can vary it. Because I am the person who is operating this machine , I canvary if the feed rate is the input parameter parameter means I can vary ok.The responses when I talk about the surface roughness , surface roughness is a response;that means, that I cannot control it because it is an output response only I can pick it,I cannot change it ; however, I can get different output by changing different input parameterok. So, response is what I will get and input is what he will give. That is why wheneverI speak about parameter ; that means, that that are controllable things , and responsesmeans what I am going to get ok. Surface roughness is for me a responseok . If you see the machining parameters, the firstI will take the machining parameters, the machining parameters are like ah cutting speedis one of the most important feed rate depth of cut , and the tool angles like rake angleflank angle and all those things step overs . In the type of cutting fluids and processkinematics, whether you are holding it proper there . These are the major ah important inputparameters , normally most of the researchers will ok .So, the cutting phenomena, whether it is the acceleration phenomena is there, whether vibrationsare there , the the chip formation, you can see and friction cutting zone and cuttingforce variations ok . These are the other things that normally mostly people would nottouch this; however, the design people who do design of these machine elements are themachine tools , normally thinks about ah if I am giving this this input parameters theywill measure the vibrations forces , and the chip formation as an output parameters ok.However , the surface finish also vary with this intermediate responses . So, if you seethe workpiece properties, the workpiece diameter workpiece length and workpiece hardness . So,these are the another input parameters normally one can work is ah , how much diameter ifmy diameter increases, if the constant rpm if I am using if the diameter of workpieceincreases what will happen ? My cutting velocity goes up ok. Pi dn by 60, if you take thatone de is, function and n is also a function. So, if my diameter increases my cutting velocitywill increase. So, workpiece hardness , if hardness goesup, I will take one some the glimpse of advanced in machining processes, where I will talkabout the hard machining . So, hard machining means if you are working with ah much harderworkpiece material. That is called what ; so, that is one of the studies that ah can takesplace here . Cutting fluid properties is another parameterthat you can one can vary, that is a tool material whether it is a hss cbm ceramic orsomething tool shape , whether the positive or negative , whether run outs are there arenot on the tool, and nose radius whether I am going to use 0.4 or 0.8. For example, ifyou take a carbide tool , TPUN 16, 0, 3, 0, 8 ok so; that means, are the last one representsnormally what is a nose radius ok. So, in case of a one 16, 0, 3, 0, 4, 16, 0,3, 0, 8 normally 0.4 is the nose radius in other case 0.8; where 8 is there if thereis the most radius is about ah point nose radius ok . So, these are all the input parametersthat will influence. So, this is the completely shows how these parameters influence my surfaceroughness .
Video 2: Measuring Surface Morphology 
I will just give you some introduction about , how to check the surface morphology. So, the first one is scanning electron microscopy,how the scanning electron microscopy a characterizes our ah the surface ok . So, if you see thisone . You have a electron gun where electron beam in it is allowed will be there magneticlens, will be there to focus . And it at last you will have a backscattered electron detectoris there and the stage is there where you just place your workpiece, you just placeyour a workpiece on top of it normally you will get ah the electrons which will be detectedbasically. So, what are the electrons that are detected ?See there are various type of electrons that are detected . Among which there are 3 majorthings. One is x ray photons will be detected . Secondary electrons will be detected ; whichwe are mostly worried about, and backscattered electrons we are worried about ok . Theseare the 3 things which normally we want as a mechanical engineer, but if the metallurgypeople material science people they may go in deep of this knowledge . But; however,for the introduction of this course I guess this much is ah sufficient enough .So, secondary electrons from here the secondary electrons are captured , and the detectorwill be there it will detect , backscattered electrons will come up to this one, this backscatteredelectrons are strictly bigger and if you just bombard it and ah and it will go to the detectorof the backscattered electrons . And x rays will be there to detect the elemental analysis. So, most of the time mechanical engineershave a slight difference, because backscattered imaging as well as the secondary electronsimaging are the 2 types of imaging. So, the difference; so, what will be the difference.So, for a be tech students are the basic ah people who are working on the characterizationof the surfaces in the mechanical engineers you may have some of the doubts.. So, if one can understand between the backscatter image as well as secondary electrons image, you will be used this technology for choosing which type of image I want after doing mymachining operation ok . If you see the backscattered image, just Iam if you see there are the aluminum and ah copper 2 faces are there in a alloy . Largeratoms are lot strongers and compare to the light atoms this number of backscattered electronsreaching to detector proportional to their z number ok that is valency number , dependon the number of ah backscattered electrons atomic number helps to distinguish withindifferent faces providing the image . And what I want to tell is the back scatteredimage helps you in terms of differentiating the faces . If I have an alloy ok, if I amdoing a machining on an alloy where copper and aluminum is a part, if my surface is there,whenever I focus , if I want check the what are the faces are available on the surface,I should take the image which is back scattered image, so that you can differentiate aluminumyou can differentiate copper ok. My intention is to check the faces, then Ihave to, but back scattered image also give surface topography ok. It also give surfacetopography if , but conditions are the, quality of this may not be superior to the secondaryelectrons image ok . If you are thing is to find the element I mean to save the facessorry, not the elements, it is is the faces, then you should go for always back scatteredimage ; when you are doing your characterization using scanning electron microscopy.Now, various field enhanced scanning electron microscopies are also there which go beyondwork the scanning electron microscope is nowadays are doing ok .If at all, I want to know about the surface morphology. Then you should go for secondaryelectrons. They in contracts a secondary electrons originate from the surface , are near surfaceof the sample ok. These electrons are emitting if you would have seen clearly in the previousslide where I have shown the scanning electron microscopy , if you see here . So, the secondaryelectrons are coming from the surface. If you see the select , secondary electrons arecoming from the top; that means, that surface topography will be the better one ok.. So, there are interaction between primary electron beam, and the sample have lower energyand the backscattered electron than the backscattered electrons ok . Just I will give you some glimpseok . So, if you see figure a. This is the full backscattered image . I am talking aboutthe image of particular location on a leaf . I it is a taken from the wikipedia . Acknowledgeto the wikipedia. Just I want to differentiate between what is the backscattered image quality, what is the secondary electron image quality ok, for that purpose . The first a this isthe image which I have taken , which is a full backscattered image . If I want to convertthis full backscattered image surface topographically , the final image that I am going to get isthis one that is b . But if I locate the same area and if I amtaking the image from the same area using secondary electrons ok, electrons , this isa topography, you can clearly differentiate between the pictures between a b and c . Thatis why the understanding what a mechanical engineer, we may not be a very good metallurgicalaspects , but whenever you are taking your pictures, you should be cautious to know whatyou want. If you know what you want half of the problem is solved. So, you can go aheadwith this one and you can take ok. So, what do you understood from this forcelights of scanning electron microscopy is , if I want the faces, I should go for backscattered image . If I want the surface morphology are the topography which is there on the surface, I should go for secondary electrons imaging ok . Hope you understand ok.Machined workpiece surface morphology. If I want to see the machine surface morphologyok , this is the surface ah if you at all if I am taking a secondary electrons imageand ah this is taken from a micro turning process .
Video 3: Material Removal Rate and Machinability
now we are going into the materialremoval rate in turning operation, single point cutting tool ok .So, then we followed by the machinability ok .So, why we have to study the material removal rate in conventional machining. Why not inpolishing process. Such as lapping, horning, some other advanced finishing processes andall those things ok. why we want to calculate? The process itselfis called machining process, the machining process and the finishing process differenceis my machining process means how much material I am removing. I am worried about what isthe volume of the material that I am removing. In a polishing process I am not worried abouthow much material I am removing from the workpiece I should look at what is my final output interms of surface finish ok. . So, if my surface finish is 50 nanometersthat is what my requirement is for the finishing or the polishing process, whether I removeone mm or one micron thickness or does not matter for being in a material removal process;that means, that conventional machining process , I worry about the material removal, becauseif I want to do the turning operation and bring a workpiece from 80 mm to 75 mm , Iworry about the thickness material removal I do not worry about the surface finish.Still, I worry about surface finish. But my major concern is material removal ok . Thatis a difference between a machining process, and the finishing process or a polishing process.Here in a machining process, how much materially I removed in a finishing process, what isthe surface that I got ok . That is what I am telling here. That is how much materialI am removing is a concern here what is the final surface roughness is a concern .So, if you see it it is very simple whatever the thing material removal in metal. Cuttingindicates the volume of the chips being removed ok , volume removed per unit time ok . So,normally volume removed is Lw and t naught; where is t naught is nothing but my uncutthickness , w is nothing but my depth of cut, and L is nothing but my length. So, you canwrite time equal to length of cut by the velocity cutting velocity. So, if you can calculatethis normally you will end up with this one ok.if you talk in terms of input parameters, it will be like this ok . So, where you knowall the input parameters, which is ah cutting velocity in, but you know cutting velocity,you can calculate from the pi dn by 60 . You can calculate the cutting velocity , whereyou the input parameter is rpm that is a rotational velocity of the ah workpiece, d is the diameter, and ah other things are kwon to you ok . This is the only thing that you are calculating;however, these 2 are input conditions . Apart from your feed and the depth of cut ok. Justtotal input parameters is diameter , and the rpm rotations per minute . If you know allthese things, you can calculate your material removal rate ok. So, that is what ah is givenhere ok. So, I just divided the cutting velocity also into input parameters .Now, we will move to machinability. So, machinability is nothing but is nothingbut ease of machining . How easily I am going to machine my workpiece is nothing but a machinabilityok . Given material maybe anything to me, rather I have machined it with easy or notis what the machinability ; that means, ease each material can be machined machinabilitydepend on physical properties of the cutting conditions and the cutting conditions ok . Also,mission ability can be expressed in the percent of normalized value, these are the some ofthe standards that ah one can follow machinability is a relative statement ok.. So, what when it is stated that material A is more machinable than material B, it isa I said now it is a relative statement. Whether I have 2 materials assume that I have a mildsteel in one hand and another side I have a silicon carbide . So, which is easy basicallywith the common if you are a machining engineer or basic metal cutting is known to you youcan; obviously, say that mild steel is much easier to cut ok .Why you say you are talking about the relative with respect to the silicon carbide ok. So,it is always relative. So, machinability is all squeezed , which material a having a longertool life compared to b , then you can say that ah material a is more easy to machine. Material a require lower cutting forces , and power compared to b, then I can saymaterial a is easily machinable or machinability of material A is good. Material A is providingbetter surface finish compared to B, to B in this condition also the 3 conditions areindividual conditions if any one satisfies ; that means, that my material A is much bettermachinability compared to material B ok. this is the relatively statement.And the factors affecting the machinability are tool materials , feeds and speeds cuttingfluids and the rigidity of the tool holding device how regidly I am holding . If it isnot hold properly it may deflect. So, if deflect. So, the my machining conditions completelywill destroy the microstructure. That I am going to get on the surface . Grain size ofthe machine surface heat condition chemical composition fabrication methods hardness yieldand tensile strength of the workpiece ok . In many conditions will depend decides. In fact,of the machinability if it is very hard it is very difficult to machine ok. You haveto find some alternative solution to make the machining of that particular materialis easy. So, that is called machinability.
Video 4: Thermal Aspects of Machining
Thermal aspects of machining what ah I wantto show you is , why we are going for the turbine aspects of machining . If you seethe thermal aspects of machining already I have shown you .Just watch the video . If you watch the video; see, lot of ah fire or ah chips with the redred color chips are moving in the machining region that is just going away. So, you canunderstand how much heat is generated . What are the thermal aspects are going on duringthe machining operation if you see the chip , red red chip is accumulating there ok. Youcan see in this area , you clearly see the chips are accumulating in the machining regionwhich are ah very red red hot hot chips. So, the thermal aspects plays a major role. Nowyou can see that chip the continuous chip in red color is accumulating there and goingoff after some time. . So now, you can understand what is the temperaturegeneration, how the heat is affected there, and all those things. You can see now theok . energy dissipated in the machining is convertedinto the 3 zones; that is called the heat in shearing zone. And heat in chip tool interface,that is ah this region. This is called a shearing zone . This is called chip tool interface.Another one is tool work piece this region .As in all material working where the plastic deformation in energy dissipated in the cuttingtool converted to heat , which in turns raises the temperature ok . So, because of the severeplastic deformation, normally the ah heat is generated now heat dissipated which isin terms of which raises the ah heat , raises the temperature with the machining region. There is 2 things , one is ah heat generation, at the same time heat distribution . During the machining of material considerable heatis generated, which converts mechanical energy takes place this occurs in the following distictregion. So, normally the heat is generated 80 to 85 percent in the primary shear zone.And 15 to 20 percent in the chip tool interface and one to 3 percent. Sometimes, it will be5 percent also in that tool work piece interfaces ok, this is the ah generation of the heat. So, normally the distribution; if you seethe distribution and all those things . So, here it is not there, but; however, I willexplain you the distribution. Normally , 80 to 85 percent will be taken by the chip . Thisis the whatever you are showing the figure is ah temperature generation of the heat generation. So, how the distribution normally chip will take 80 to 85 percent . The tool or cuttingwill take ah around ah 10 to 15 percent . So, the workpiece takes around the one to 5 percentok. This is the combination of these things will takes place. This is nothing but temperaturedistribution . This is temperature generation ,this is temperature distribution ok. . So, there is a slightly difference is there. In temperature generation, it is the interfaces are the shearing zones. Here distribution,normally distribution I have given apple to ramu; that means, that I am giving to individualentity, that is nothing but this one. So, I am saying individually how the distributioneven distribute the aspects . The sources of heat generation in the machining.The shear zone where the heat is generated due to plastic deformation . This is aboutthe plastic deformation, where I said 80 to 85 percent is generated. Chip tool interfacewhere the heat is generated due to frictional rubbing between the rake face and the toolchip ok. Though the are second one which is becauseof the ah frictional rubbing. The third one tool work interface where the flank surfacewill ah rub against the workpiece . Which leads to one to 3 percent . Normally, I saidalready it is fine about. 80 to 85 percent of the heat is generated in the shearing zonewhile 15 to 20 percent and about this one already have seen this one .Adverse effect of temperature rise, normally the major disadvantages are what are the affectingthings , whenever this is the temperature rise, that is lowers the strength hardnessand stiffness and wear resistance of the tool; that means, that thermal softening of tooltakes place, because whenever I am cutting . So, the my chip is continuously moving;however, my tool is static ; that means, that continuously the heat is going in. Becauseof it is thermal aspects of will takes place, and the thermal softening of the tool takesplace. That increases the temperature within the 2 which lowers the strength of the tool,hardness of the pool also and stiffness of the tool and wear resistance and ah will allgo down ok. causes uneven dimensional changes. Wheneverthe temperature as very high , what will happen ? Workpieces also may have tendency to increaseit is dimensions by nanometers are sometimes micro meters also . Whenever the thermal conductivityof the workpiece material is very high. Induce thermal damage and metallurgical changes tothe mission surface normally , whenever the cutting tool ah machining region is very high,what will happen as you see the thermal layers will form.There are thermal layers there are 3 thermal layers one is ah if you see in ah edm processor laser beam process, where is ah thermal thermal machining processes , heat effectorzone ah recast layer and the conversion layers. I am not saying that all these layers willinform, but there is a chances of ah these layers that is . Recast layer or ah heat affectedzone and ah conversion layer ok . There is a chance very less chance is there , but becausethe temperature is going up ok . So, the mean temperature in the turning processis normally in the planning process are the lathe is a function of cutting velocity. Andfeed and a and b are the co efficients ok . So, the cutting velocity v and tool feedis nothing but this one. For the carbides approximately, a and b values are point 2and ah , b is 0.125 high speed steel normally these values goes up . Because soft thermalsoftening of this material is faster than compared to the hard ah carbide tool thatis why points 5 and b . So, also not that the relation shows the increasein temperature with the increase in cutting speed and feed ok . So, if the cutting speedincreases, and the feed increases. Ah if the workpiece is softer and that circumstancesmy temperature goes up ok. If you see the cutting speed , and the energy percentagenormally tool is upper side the work piece and the chip ok . So, this is the dissipation.So now you measure this ah temperature. How to tem measure the temperature? That is calledah one is the thermocouple techniques , infrared spectroscopy radiation pyrometers and thosethings; however, just I will tell you processes how experimentally we can measure ok .now thermocouple techniques normally a thermocouple from the junction . See if you see, if I tellI want to cut the orthogonal cutting, normally the best thing is just you take it you andyou take the perfectly the tool and you cut it ok.. So, here you can take the tube is taken . This is the hollow one ok . So, tube andI am cutting here . Now I am having a junction here . Because connection is not showing property. So, this is one connection . Another one connection is given here ok. So, this is alsoconnected . So, what I mean to say is I am cutting orthogonalmachining process; where one junction is on the tool, another junction is here . So, thereis whenever I am cutting this will become hard junction, and this is the cold junction; where I am having a disc here, which is connected basically the head stock will havea hollow structure ; where I can put a rod which is connecting to the work piece, andI am connecting this rod with a disc . This is a disc basically, this is disc which isdipped in a mercury. This is we can see here, this is the mercury this is called my hotjunction . This is called my cold junction; which is connected to this one .So, using the seebeck effect if there is a temperature difference, then EMF will produce,what is called EMF is generated ? Which is measured at the temperature. Normally EMFis generated because of there is a difference in temperature . This is called cold junction, this is called hot junction . When there is a cold junction hot junction is con converted,then EMF will produce from the EMF , you can calculate the by using some relations, youcan calculate the temperature measured and all those things ok .So, the seebeck effect back effect , back effect will be there. So, hot junction andcold junction , you can connect and you can get it. This is what the thermocouples technique. And another one is infrared photography techniques;where the if you are machining, infrared using this one. So, you can see the temperatureregions using the colors that are captured in the infrared ok. Temperature distributioncutting zone from the infrared. So, normally the temperature highest temperature will berecorded in the chip tool interface . Even though the highest energy heat heat isgenerated in the shearing zone, temperature highest region recorded here. Because thechip is taking 80 80 to 85 percent of heat , and the tool is taking 10 to 15 percent. Here what we see is taken one to 5 percent ok . At the same time the noting point thatyou have to see my chip is continuously moving body. So, it continuously moving body at thesame time my workpiece is stationary ok. That means, that my continuously chip whatis taking the heat is moving on the red surface of my tool. At the same time it is impartingcontinuously ok . So, it is imparting continuously the heat . And it is also rubbing here . Becauseof normally the temperature recorded in this region will be very high . That is why thetempareture in this region is very high, because of the friction at the same thing becauseof the chip that is having highest temperature moving on the rake surface ok .