 Welcome you all for the series of lecture on surface in the metrology. Now we will start module number 5 lecture number 1. In this module we will be covering the following aspects of measurement of surface finish. We will learn about basic basics of surface finish and how the surface finish is indicated on the technical drawings and what are the various parameters used in the measurement of surface finish. And then we will move on to the different kinds of measurement of surface finish like contact method and non-contact method. And we will also learn some offline methods and in process gauging of surface finish. And then we will move to care of instruments. Now let us understand what is the meaning of the surface finish. If you take any engineering component it will have a surface which is open to atmosphere here. And there are some valleys and peaks on the outer boundary of the workpiece. And the sometimes the surface will be very rough and sometimes it will be very smooth. In some cases where there are sliding parts for example machine tool guide ways or bearing surfaces. We need to have very fine and smooth surface so that the frictional forces are reduced. And in some cases we need to have somewhat rough surface for example in the cases of mating parts which are not to be moved. There is no sliding between two mating parts for example parts in interference fit. So in such cases to prevent the relative motion between the two parts we need to have a slightly rough surface. This surface finish is also known as surface texture or surface topography. And in some cases we require very fine surface just to improve a look of the component or the product. And we need to measure the finish of the surface to control the machining process also. Now we can see here we have two mating parts. We can see the finish on the face of this cylindrical part and the roughness on the round cylindrical portion. Also we can see the finish of this flat surface. And here intentionally they are made very rough to have proper gripping. And we have another picture of a flat surface which is face turned component. We can see clearly see the rough surface and we can see the circular the concentric circles made by the cutting tool, cutting action. The surface roughness is very important from the point of view of fundamental problems such as friction and wear, surface contact, lubrication, fatigue strength and tightness of joints. It affects the conduction of heat and electrical current, cleanliness, reflectivity of the surface and sealing action. It definitely affects the positional accuracy of mating parts, load carrying capacity, resistance to corrosion and hydration of paint and coatings. And then the accuracy and surface finish requirements for machine parts in the modern industry are becoming more and more stringent. If the machining imperfections exceed the design specifications, then the functionality of the product is definitely affected. So it is very essential to check whether the design of the workpiece complies with the functional requirements of the product. Hence it is necessary to check the geometry and the surface characteristics of the workpiece. So we have a component like this and then I am just showing the details of this particular surface. So now we can see it appears to be some wavy. That means with respect to this point, what is the height of this point, what is the height of this point like this, the relationship between various points on the same surface will be studying. And then every part surface, every engineering component surface will have a sort of texture. It can be a rough texture or a very smooth texture or it can have a very specific type of surface as shown in the previous picture. And then measurement of surface texture is very essential to understand a component's surface and to control the manufacturing process to the degree required in today's modern world. So surface texture parameters are grouped into many basic categories like roughness parameters, waviness parameters and spacing parameters and also the combination of these termed as hybrid parameters. Now what are the various principle elements of a surface? Now you can see here the general term surface, it is the boundary of any engineering component which is exposed to the atmosphere or other kind of media. And then we say a profile, it is the contour of any specified section through a surface. For example, so we have a component which is turned like this. Now you can see here if you take this particular portion, now it has a taper component maybe because of some error in the machine tool slide movement and also it will have some periodic shape like this which is termed as waviness. If you take, if you consider the small portion of this wavy surface and enlarge it, it will have a surface like this which is termed as roughness. That means profile it consists of all the elements like the form error of the workpiece and then wavy surfaces and then roughness of the surface. It is total contour of the surface is known as the profile. And then the roughness is the closely spaced irregular deviations on a smaller portion of waviness as considered here. And then we have the waviness, it is a recurrent deviation from a flat surface. It is like wave on a surface of water. It is measured and described in terms of space between adjacent crusts and peaks and valleys like this. It looks something like this, this is a peak and then this is the valley. And we measure the distance between peaks and valleys and distance between two peaks and such parameters we study. This waviness is caused due to deflection of tools and workpieces. For example, we have the workpiece mounted between two centers and when we use the cutting tool when we press. So if it is slender, it may bend like this. The workpiece may bend like this because of this waviness may occur. And also the cutting forces will cause the waviness and temperature variations cause the variations. And if the lubrication is not proper, then also the waviness may occur and machine tool vibration, charter of the cutting tool. These are some of the reasons why the waviness occurs on the surface. And then maybe there are some flaws like the maybe a blowhole on the surface. On the component surface maybe there is a blowhole or some scratch maybe there or a crack or some depression. So such things are known as flaws. And lay it is the direction of the predominant surface pattern which is visible to the naked eye. So this appears on the surface because of the tool movement of the surface. It is like a tool mark on the machined component. Now we can see all those terminologies in this diagram. So you can see this is the total profile which consists of waviness of the surface and then micro irregularities, micro asperities, valleys and peaks as also the taper and drum shape or barrel shapes. So that total various parameters are combined in this particular shape and which is termed as profile. And here you can see there is a scratch or depression in the surface. This is known as flaw. And we can also see the direction of tool mark which is termed as lay. Now when we remove this micro irregularities or roughness then we will get the waviness like this. And this is the waviness height that is the distance between peak and valley. And also the distance between two peaks or distance between two valleys is termed as waviness spacing. And if we remove the waviness part of the profile then we will get only the micro irregularities which is termed as roughness. And the distance between peak and valley is termed as roughness height and the pitch that is distance between two peaks is termed as roughness spacing. Now we will have another diagram here which will help us to understand the various terminologies. So this is a flat surface and when we closely observe we can see the unevenness. This is the waviness we can observe and then the direction of tool marks we can observe and the flaw also we can observe. And then when we measure the surface finish we will move the instrument. For example if you take a stylus type instrument we move the stylus or the probe on the surface to a particular length which is termed as traversing length. And this portion traversing length the profile is enlarged here you can see the waviness and the waviness height and waviness spacing. And again if you consider the small portion of the waviness then when we enlarge it we can see the micro irregularities, we can see the peaks and valleys. And the distance between two peaks of roughness is known as roughness spacing and we consider a particular length of the wavy profile and then we go for studying or the measuring the roughness. So this particular length is known as roughness sampling length also it is known as cutoff length. And actually when the mechanical engineer specifies the roughness we actually decide, he specifies to have a desired profile like this which is almost a flat and straight. But when we actually cut the workpiece using machine tool and cutting tool we get the profile like this, when we measure it we get the profile like this. These variations are due to many reasons like the vibration of the machine tool and the shape of the cutting tool and then the use of various parameters, machining parameters like speed and feed etcetera. And then here you can see the surface is tapered like this, this is the surface profile and so this is actually the combination of these three, the error of the form, form error which is the taper in this case and then we have waviness and then we have roughness, all these put together we get the profile like this. And now if we take the machining operation very simple very well known machining operation that is turning operation. Now you can see this is the workpiece and then we have the cutting tool with some round nose, this is nose radius and then the cutting tool is fed in this particular direction, this is the feeding direction. And then because of this radius the tool mark appears on the machine surface like this, we get the shape concave shapes like this. So this gap that is distance between peak and valley is known as the surface roughness, this is actually the radial depth of cut and then this is the feed rate per revolution. So when we vary the feed rate then the roughness will change. So if you have a very fine feed then we get the surface roughness like this. So and if the nose radius is more and then we get the surface roughness like this. So the geometry and the machining conditions do affect the roughness of the workpiece. So in this diagram you can see a turned component, we have a turned component here you can see on the face, this is the face portion you can see the concentric circles. And then on the periphery also we see the tool marks. And this is another surface which is face turned, we can see the concentric circles and then burr at the center and then various the flasks burrs on the surface. So when we vary the feed rate this roughness will also vary. Now surface roughness in the machining operation, when we machine the workpiece surface, so we get two kinds of surfaces, one is the ideal surface and another one is natural surface. So ideal roughness is a function of feed and geometry of the tool, we have discussed about this feed and geometry of the tool. When we use a very fine feed, we get a better finish. Also when we have a sharp point, we get a good finish. It represents the best possible finish which can be obtained for a given tool shape and feed rate. It can be achieved only if the built up edge and charter and the inaccuracies in the machine tool movements are eliminated properly. So this diagram shows that from valley to valley, this gap is known as feed per revolution and these are the various angles on the cutting tool. So because of this tool shape and feed rate, we get the surface roughness. This valley to peak distance is the r max, again the parameter used to designate the surface roughness. For a sharp tool without any nose radius, the maximum height of unevenness is given by this expression r max is equal to f is the feed rate divided by these cot phi and cot beta which are the cutting tools on the angles of the cutting tool where f is the feed rate per revolution and surface roughness value is given by r a is equal to r max divided by 4. Practical cutting tools are usually provided with a rounded corner. So if it is very sharp, it will break easily and we get a blunt corner on the tool. The roughness value is closely related to the feed and corner radius by the following expression. We can use this, if you know the radius, corner radius of the tool nose radius and feed rate, we can calculate what is the r a value we are going to get. And then other one is natural roughness. This natural roughness we get because of various inaccuracies in the machine tool and then vibration of the machine tool and cutting tool, charter of the tool and then occurrence of the built up edge of the cutting tool. Because of this we get a surface which is known as natural roughness which will be greater than the ideal surface finish. So if we can eliminate this built up edge and vibration aspects of the machine tool, then we get a better finish. And then what are the factors affecting the surface finish? Say whenever two machine surfaces come in contact with one another, the quality of the mating parts plays an important role in the performance and wear the mating part. That is if two surfaces are very rough, then the frictional force will be more and the more wear will take place. And if the surfaces are very smooth and if we can use some lubricant, then the movement will be very smooth and friction will be less and wear rate will also be less. The height, shape and arrangement and direction of these surface irregularities on the work piece depend on a number of factors such as machining variables which include what is the cutting speed, we hear the cutting speed and finer the feed rate, we get better surface. Also what is the depth of cut? If we give higher depth of cut, then the cutting tool and work piece may vibrate and we get some roughness. And then tool geometry will also affect the surface finish. Some geometric factors which affect the finish or nose radius and then the various angles like crack angle and then side cutting edge angle, cutting edge. These are the cutting tool geometry will definitely affect the surface finish on the work piece. And then the combination of work piece material and tool material and their mechanical properties will also affect the finish of the work piece. And what type of machine tool we use? Very robust and well built machine tool if we use, naturally we get a good finish. And then the use of auxiliary tooling like work trace and then proper loading of the work piece between centers and the use of coolant, those things will also definitely affect the finish what we get. So vibrations between work piece, machine tool and cutting tool, this is also very important factor which will definitely affect the finish. If we reduce these aspects then we get good finish. And then this diagram will show the relative production cost or time necessary to produce surface finish by different processes. We can see here x axis is, it shows the rj value in micrometers. The range is 0.025 micrometer to 50 micrometer and in the y axis we have 1 to 24 that is, it is relative production time or relative production cost. In this picture we have considered various machining operations like the cylindrical grinding, surface grinding and then reaming operation, end milling, turning, peripheral milling operation, shaping and planing operation and very commonly used the machining operations. Now we can understand that whenever we want very fine surfaces naturally we go for grinding and then polishing operations. Now here we have cylindrical grinding and surface grinding which are able to give very fine surfaces with surface finish of less than 0.4 micrometer rj. So naturally the production time is more and production cost is more compared to the other processes. Now whenever we want a roughness value of 0.8 micrometer rj, we can see this is possible to produce by various machining operations. If it is a hole making operation we can use drilling operation. I can see 0.8 micrometer rj value can be obtained by many operations like drilling. If it is a hole making we can get it by drilling operation and then shaping planing also will also give 0.8 micrometer rj value and then peripheral milling operation and it is also possible to have this finish by turning operation by proper usage of machining parameters and end milling also we can use and then reaming also will produce this 0.8 micrometer rj. Now we can compare the relative production time and relative production cost. So when we want 0.8 micrometer rj finish then the cylindrical grinding will easily give that finish and the production time will be very rapidly they will be able to produce that fine finish. Now when compared to the surface grinding and cylindrical grinding other surface other machining operations become very they consume more time. So since grinding machines are basically meant for finishing operations it is better to use cylindrical grinding or surface grinding whenever we require very fine surfaces. Whereas if we require fine finishes lesser than 0.4 micrometer rj and naturally we have to go for the grinding operations. Now this picture shows surface roughness values for common production processes and these are roughness average or rj value in terms of micrometers you can see range is 0.025 micrometer to 50 micrometer rj value and these this row shows the iso grades n1 grade n2 grade up to n12 grade the n1 n2 n3 they are fine they provide fine finishes and then we use n10 n11 n12 grades whenever we want to specify rough surfaces. We have considered the various production processes like sand casting, hot rolling and an extruding operation, planing, drilling, EDM process, milling so and then fine finishing operations like grinding, honing, electro polishing. Now I can see here these finishing processes like grinding, honing, lapping, super finishing they are able to give very fine finishes. I can see here the range is from 0.05 up to 0.8 micrometer rj super finishing can provide even the finer finish of up to 0.025 micrometer rj. Now depending upon the availability whether which facility is available we can appropriately select the machining operation and then for rough surfaces we can always go for these the milling, drilling, planing operations which are able to provide the finish in the range of 0.8 to 6.3 micrometer rj. Now you can see this is sand cast process in the case of sand cast surface the finish will be very rough like 12.5 to 25 micrometer rj. So if machining is required then if finer finish is required because of the movement of other sliding surfaces then we can go for machining operations to produce required finish. Now recently some newer machining processes have come up and one such thing is plain glass cutting by hot air jet. The hot air jet was used to cut the glass plain glass plates. So there are other methods like laser cutting, water jet cutting and then diamond cutting is most commonly used but they provide very rough surface whereas this hot air jet cutting is able to give very fine finish of some 0.3 micrometer rj to 0.8 micrometer rj. Now after understanding these the basics of surface finish and how to produce the finish we will understand how the finish surface texture is indicated on the technical drawings. Now you can see here this we have two lines separated by 60 degree one longer line and one shorter line. This is the basic symbol which is used to indicate the surface roughness on technical drawings and you can see the lines are unequal and they are separated by 60 degree and the symbol must be represented by thin line. This is the basic symbol used to indicate the roughness on the technical drawings. If it is required to machine the surface, if the surface is to be made by some machining operation or by some removal of material then you can see here a bar is added. So this indicates that machining is required that means we have to remove the material by machining operation like maybe turning operation or milling operation or the shaping operation something like that. Now if removal of material is not permitted then a circle is added bar is removed and circle is added. So this indicates that no removal is permitted. It should be left as like cast surface. So no further machining is to be made and then when special surface characteristic are to be indicated for example maybe electroplating or the surface should be electroplating or painting then a bar is added here to the longer line and then what is the how that special characteristic is to be produced should be written on this horizontal line. Now sometimes we specify what is the roughness that is needed. Now you can see here we have three symbols here. So A indicates the surface roughness value. So if no parameter is specified then it is understood that the value represents RA value in terms of micrometer. If other parameters are required then RT value or RP value or max value then that should be clearly mentioned. Now here the symbol number one roughness A is obtained by production some production process which is not mentioned which production method is not mentioned. Like maybe it is cast surface or a forged surface or extruded surface and in the symbol two we have a bar is added it indicates that some machining operation has been done and the symbol three has a circle here it indicates that surface is obtained without the removal of material. Now sometimes it is necessary to mention the two values upper limit of the roughness and then lower limit of the roughness. In that case we use this symbol wherein we have used A1 and A2. A1 indicates the maximum surface finish and A2 indicates the minimum surface finish. You can see here we have used this basic symbol this is the surface on which the symbol is mentioned and then here we have two RA values are mentioned this is a maximum RA value that is A1 and then minimum RA value so 125 and 63. So it is in microns RA value is 125 microns and R it varies from 63 micrometer to 125 micrometer and then you can see there is another symbol mentioned here inverted T. So this is to indicate the lay. So now this is the surface okay surface under question and then now we have used this symbol this indicates that some machining operation is required and it also shows the lay direction that means to the surface that is mentioned to this particular surface lay is perpendicular that means perpendicular to the direction of lay we have to measure the surface roughness and this shows that the lay is it is both angle it is angle lay angular in both directions okay to if the surface is like this then we use x shape here and we can also see on the horizontal line we have mentioned maximum waviness height okay like so distance between peak to valley what is the maximum waviness height that is mentioned here so it is 0.002 micrometer or 0.002 millimeter or 2 micrometer and maximum waviness width is also mentioned here it is 2 millimeter that means so this gap is 2 millimeter and then roughness width cutoff is also mentioned here we will learn about this cutoff in greater detail after sometime and maximum roughness width this is maximum roughness width 0.005 millimeter. Now you can see here if it is required to produce the surface with a particular production method like shaping operation or turning operation or grinding operation then that is mentioned on the horizontal line so you can see here the symbol we have a bar here it indicates that surface is to be machined by some operation what is that operation is mentioned here turning operation and what is the roughness value that is also mentioned here and sometimes what is the allowance machining allowance that is provided on the workpiece is also indicated in the symbol okay this is 5 millimeter machining allowance is provided on the workpiece and these are the some other types of indication as per the ANSI standards so you can see here the removal of material by machining is optional we can remove by machining or otherwise and here it is obligatory since we have this bar and then the machining preparation of the surface is required by machining operation so here grade is mentioned and here the roughness value is mentioned since no parameter is mentioned understood that it is RA value in micrometer and here no machining is required we need N8 grade or 3.2 micrometer surface finish RA without the removal of material and here the limits are mentioned maximum roughness and minimum roughness values are mentioned now these are various kinds of surface texture symbols now you can see here if inverted T is used then the lay is perpendicular to the direction in which the measurement is made and here the cross hatch type texture is there and lay is multidirectional then we say M and if the lay is parallel to the measurement of surface finish and then we use this particular symbol parallel and then if the surface texture is concentric like this then we use this particular symbol this happens when we turn the workpiece in the face turning operation and then we have a particulate non-directional texture then we use this P3 and then when the have the texture like this radial relate to the center of the surface then we use this particular symbol R. Now you can see here these diagrams show how the surface texture of surface finish is indicated on drawings now I can see here we have a hole here machined hole you can see the symbol here so we have this symbol with bar it indicates that the surface is to be produced by machining operation normally drilling operation you can see here drilling operation can provide us with roughness varying from 1.6 to 6.3 1.6 micrometer R8 to 6.3 so here we have mentioned 3.2 micrometer R8 so this hole can be produced by drilling operation and here it is a 3.2 micrometer RA now if required we can go for rimming operation so rimming can provide us the finish of 0.8 to 3.2 micrometer RA so if better drilled hole is required better finish the hole is required then we can go for rimming and here we can see the grades are used this is single triangle and double triangles are used now from this diagram we can understand single triangle means it is a very rough surface maybe it is as cast surface is as cast and no machining is needed and here we have a hole in which two grades as a two triangle grade is used so two triangle grade means we can use machining operations like milling, drilling operation, cleaning operation so such machining operations can be used to produce a two triangle finish okay so like this we can indicate the surface finish on technical drawings now these pictures show some roughness profile when they actually use some measuring instrument and when they measure the surface finish we get the surface profiles like this we should understand that the see this is the workpiece surface and say we have a stylus like this so this stylus is moved so because of the roughness, waviness and form error the stylus will move up and down when we draw the stylus on the surface because of these variations the stylus will move up and down so this up and down movement is amplified and then we get the roughness profiles like this so normally these peaks and valleys high asperity heights are very small in terms of microns so very large magnification is used to amplify this vertical movement and the horizontal magnification is normally less so horizontal magnification may be some 100 times or 200 times whereas the vertical magnification will be a few thousands may be like 1000, 5000, 10,000 so if it is very fine surface produced by grinding, lapping, supermining process then we have to use very high magnification like 50,000 or 1 lakh if it is very surface produced by turning operation or shaping operation or planing operation in that case it will be very rough surface will be very rough and we can use the lesser magnification like 1000, 2000, 3000. Now let us try to understand what are the various parameters used to specify the surface finish so we should understand some of the terminologies like mean line so this is a straight line that is generated on the profile resulting in equal areas above and below the line for example we say we have a profile like this now we have to draw a line a straight line like this such that equal areas above and below the line we get equally so we have area here area above the mean line and then area below the mean line so we should draw the straight line may be by trial and error method so that area above the area between the straight line and the profile above the mean line and area below the mean line they are equal or we can always use some software to establish this straight line so this mean line is also known as center line and then profile we understood it is a combination of form error and then waviness and roughness and roughness parameters non periodic finer irregularities in the surface structure which are inherent in the production process because of various reasons so these are a measure of vertical characteristic of the surface and then we should understand what is the meaning of sampling length this is the area selected or the length selected for assessment and evaluation of roughness parameter having the cutoff wavelength any surface irregularities based further apart than the sampling length are considered as waviness so the sampling length is also known as cutoff length it is something let us say we have some wavy profile like this so we consider we take a small portion of this and then we enlarge this to get the roughness profile so this length that is selected is known as cutoff length so this cutoff length selection depends upon what is the machining process used and yeah depending upon the process that is used a machining process that is used we select the sampling length now this shows a surface profile measurement length so this is the total length which is known as traversing length which traversed by the stylus of the instrument out of this so initially we have some run-up length and then over travel length which is not considered to evaluate the length the surface and this distance is known as evaluation length L and normally the it consists of 5 sampling lengths so evaluation length is divided into 5 lengths each length is called sampling length or cutoff length which is indicated by small L now let me conclude this lecture in this lecture we discussed about the basic aspects of surface roughness we try to understand what is wavyness what is roughness what is form error and what is the meaning of profile and what are the various production processes and what type of the roughness value they are able to give and then what is the meaning of central line mean line and what is the meaning of sampling length cutoff length those things we studied and also we studied how to indicate the surface roughness on technical drawings so with this we will conclude this lecture in the next class we will continue the discussion on measurement of surface finish thank you.