 We have seen the overview of the different casting process. Now, we will see the remaining process. Next we will learn about the evaporative pattern casting. What is this evaporative pattern casting? In this process we use an expendable pattern that is why this is also known as the expendable pattern casting. It is also known as the last foam casting. Here the pattern is made up of the poly strain, it is also the styrofoam. It is dipped in the gas permeable refractory slurry, what is a shell is created. Then while the pattern is still present inside the shell, the molten metal is poured. As the molten metal is entering into the shell, where there is the pattern, the pattern will be evaporated and in the place of the pattern, the molten metal will be occupying. Because the pattern is evaporating, that is why it is known as the evaporative pattern casting. Here we can see, yes this is the pattern, this is what is a cast component we require. In a similar way, we have made the pattern, poly strain pattern and here we have made a cup and sprue, made up of the foam and here you see this whole thing is the foam pattern. Now a refractory slurry is spread around this pattern and it is what is a repeatedly done so that what is a moderately thick shell is created around this foam pattern. Now this foam pattern is kept inside a molding box, molding box, only single molding box, no cope, no drag, only one molding box. In this molding box, the sand is packed around this pattern, the sand is packed around this pattern. Remember that around the pattern, we have already made a what is a moderately thick shell by means of a refractory slurry. Now after packing the sand around this pattern, now let us come here, what is happening? We will melt the metal and we will pour the molten metal into this pattern. The most surprising thing is here, the pattern is not removed, pattern means the model of the component which we are going to manufacture. Here the pattern is still present and we are pouring the molten metal inside. What happens? Because of the evaporative nature of the pattern, the pattern will be keeps on evaporating and makes a space inside. As it is evaporating, as it is creating a hollow space inside the what is a cavity inside the mold, the molten metal will be occupying that place and this process continues. Still more and more pattern evaporates and more and more molten metal occupies that. The molten metal continues to occupy that place till the entire pattern is evaporated. Now after sometime we what is a solidification takes place and after solidification, yes we can take that out of the what is a molding sand box, molding box and we can break that shell and we will get a casting. So this is the simple principle of the evaporative pattern casting because the pattern is evaporating while pouring we call it as the evaporative pattern casting. So these are the advantages of evaporative pattern casting. Here we use only one use, one flask. So one piece flask that is why it is less expensive and also less laborious. In the case of the sand molding process, we use generally two molding flasks, one the lower molding box that is the we call it as the drag and the upper molding box which we call it as the cope. So we have to assemble them carefully otherwise there will be some displacement between these two boxes. Here such problem won't arise, only one piece flask. Next one used for precision castings of ferrous and nonferrous metals, both ferrous and nonferrous metals can be cast and that too we get a very good precision and we get a next one we get the high dimensional accuracy. Next one thin sections can be cast. Next one complex shapes can be cast because if it is the wooden pattern, once we make a complex wooden pattern and removal or the vitroil of that complex pattern from the mold is very difficult. Here we can make the pattern of any complexity, then what happens while the pattern is still inside the shell we pour the molten metal. So whether it is the shape is complex or simple, it does not matter. As we keep pouring the molten metal, the pattern evaporates and escapes out of the box. That is why it is very easy to make the complex shapes with this process. Next one few air steps are involved compared to the sand casting. In the case of the sand casting there are so many process, we have to prepare the molding sand and this molding sand has to be prepared very carefully. Next one we have to prepare the core sand and we have to what say make the pattern and we have to mold it. Then we have to put the what say runner pin and the sprue pin and the patterns should be withdrawn very carefully. If these are not withdrawn the mold cavities will be breaking and we may not get the what say desired casting. So these are all the problems with the sand casting whereas here few air steps no question of vitroil of the pattern that is the greatest advantage of this process because the pattern is continuously evaporating and no need to mix binders or the other editors. In the case of the what say sand molding we what say of no doubt we use the base sand like silicon sand, zircon sand, chromium sand then we add the binder like clay bentonite. Then we have also add the editors then we add the water then these are this all these ingredients are to be mixed very carefully and this takes lot of time and it also causes the pollution problem but here there is no need to mix the binders just take the sand and pack it around the pattern power which actually is created the process is that simple and here we can see an important application. This is an engine block which is manufactured by the evaporative pattern casting. So you can see this here initially this is the one piece flask this yellow colored one is the one piece flask inside there is the pattern around which what say moderately thick shell is created and inside the pattern is still present while the pattern is still present we are pouring the molten metal it is a robotic pouring. So as we keep pouring the molten metal the pattern evaporates and escapes out of the what say box. So this is a what say very important application of the evaporative pattern casting. Next one let us see the ceramic shell molding. Now remember that we are learning about the special casting process and we have already covered all this now we are learning about the ceramic shell molding. This ceramic shell molding is almost similar to the investment casting but there is a little difference. The common pattern material is the expanded poly strain it is also known as EPS and most important thing is its weight is very less 90 percent less than a wax pattern. So that is the one good what say advantage of this process. So these are the advantages of the ceramic shell molding surface finish and dimensional tolerance are close to investment cast parts. We know that we have seen that in the investment casting process we use the wax as the pattern material and we get a very good surface finish and also we get a very good dimensional accuracy and in the ceramic shell molding also we get dimensional tolerance close to the investment casting process. Next one the expanded poly strain patterns typically weigh 90 percent less than the wax pattern. So handling of the wax patterns would be sorry not the wax patterns these EPS patterns would be easier because their weight is 90 percent less compared to the wax patterns. Similarly we have to create a shell in this process also around the what say poly strain pattern. These shells also weigh 30 to 50 percent less than the investment casting ceramic shells so handling them would be easier. Next one these shells can be stored for future use they can be made well in advance. One thing is when we want to what say cast the component these shells should be preheated then we can pour the molten metal. So these are the advantages of the ceramic shell molding. So these are the limitations the process is expensive again this what say poly strain pattern is expensive and the process is slow again and these shells should be baked. So this costs extra time and also extra power it consumes extra power. So these are the limitations of the ceramic shell molding. Next let us see the slush casting this one. Now this is another what say important and interesting casting process where we can create what say castings with hollow cavities without any cores whereas in the case of the sand casting process we have to use cores. Cores means what say some kind of pieces which are generally made up of sand and these pieces are kept inside the mold so that we can get hollow castings. So that the molten metal flows around these what say sand piece and thereby there will be a hollow cavity inside the casting. Here we get the hollow cavities without placing the cores. So that is the interesting feature of the slush casting. So here we can see this is the what say molding box. So this is the cavity mold cavity is already created so this is ready for pouring. Now here let us see what is happening the liquid metal from the interior of the casting is poured and before it solidifies then what happens it is made upside down means the solidification starts from the mold wall and slowly the what say solidification increases and once the solidification reaches what say thickness of a maybe few mm inside still the molten metal is there then we make the molding box upside down. Then the molten metal is present inside that flows out that will be draining out. So here the liquid metal is dropping down so this will be corrected in a container. Now around say close to the mold box here we can see there is a shell which has already solidified in the beginning. Now we can break this sand and we can take the casting outside so the casting has a hollow cavity inside without any use of any cores. So these are the advantages of the slush casting no cores are required as I already told in the beginning no cores are required for making the hollow castings. These are the limitations of the slush casting low volume production next one thickness cannot be controlled accurately. So just now we have seen that the solidification starts from the mold wall. So slowly the what say thickness of the solidified shell keeps on increasing. So we do not know at what time how much thickness what say has solidified. So what say without what say much understanding and we have to what say make the box upside down sometimes the thickness will be more sometimes the thickness will be less. So the thickness cannot be controlled accurately. Next one it is not preferred for the engineering applications it is used for the art applications art castings. Next one in this process skilled workers are required applicable only for relatively pure metals because allies do not form strong solid skin very quickly whereas the pure metals they quickly form the what say strong solid skin near the mold walls and inside there will be liquid metal and that we can drain out by tilting the molding box. So this is what say typical application of the slush casting. So this is a decorative stand this is made by the slush casting. Finally we will see the steel casting. So this steel casting has been developed very recently and this is offering comparatively more advantages. This steel casting is a liquid state method of composite materials fabrication. Composites means metal mixed with the ceramic. So these offer better properties than the common alloys and the metals. A dispersed phase ceramic particles are the short fibres they are mixed with the molten metal matrix by means of mechanical stirring. So we melt the metal into the metal we add ceramic powder or the what say fibres and we stir it by mechanical stirring. The steel casting is the simplest and most cost effective method of the liquid state fabrication. The liquid composite material is then cast by conventional casting methods. Then once we mix this what say ceramic particles or the fibres then we can make the casting by the any of the conventional casting methods. One thing is instead of pouring a what say pure metal or an alloy we are pouring the what say composite what say metal means metal mixed with the ceramic particles or the fibres. So here we can see so this is the typical setup of the steel casting process and this is the what say molten bath this is the crucible and here the molten metal is present and here we can see the powdered ceramic particles are continuously added to the molten metal and here we can see a stirrer which is driven by a DC motor. So this has got a blade and as it is continuously rotating this mixture or this melt is continuously stirred and after sometime so this is the what say bath of the molten aluminium. So after sometime this bath of the molten aluminium this melt will be taken and it will be poured into most of the what say poured into the most of the what say conventional moulding methods. Now these are the applications of the steel casting. Steel casting is used for making the composite castings. Remember that composite means metal mixed with the ceramic friends till now we have seen the what say classification and overview of different casting process. We are going to learn in detail about all these casting process in the subsequent lectures we have seen the overview of the conventional moulding process. We have seen the overview of the chemicals and moulding process, we have seen the overview of the permanent moulding process. And next we have seen these special casting process and again we are going to learn all these process in detail in the subsequent lectures. Next our next topic is the selection of the casting process. Which process to use to make a particular casting? We have several casting process now, right. So for a particular process, which process would be more what say economical or more what say which one would give the best what say surface finish or the dimensional accuracy. So this we need to study. Let us see the sand casting. Sand casting it is suitable for most types of the metals and alloys except titanium alloys. Next one, it has got the moderate or the simple complexity, right. Very complex castings it is not possible to make with the sand castings and what about the size? Small, medium or large castings can be made. Less than what say of a kg to 5 tons can be made by sand casting. Quantities in the large, medium or what say small ranges can be manufactured. Maybe if you want 5 castings, yes you can make 5 castings or 50 casting or even 1000 castings can be made. So the flexibility with the quantity is there, flexibility with the weight is there with the sand casting process and it has got the surface finish is 120 to 350 rms. So this is the what say 4 surface roughness. Next one, we need to give a draft to the pattern that is 0.25 to 5 degrees. Draft is to be given so that the pattern can be withdrawn from the mould and what say moderate to low casting lead times. The lead time will be moderate to low. Next one, moderate to low casting cost. The casting cost is not very high, it is moderate to low. Next one, the finishing cost is moderate to high or because we get a what say rough surface finish we need to machine it. So it will cost us, right, it is moderate to high. Next one, the gravity die casting. It is suitable for aluminium, copper base, magnesium and zinc alloys, all the non ferrous alloys and it is used for the simple complexity and these small to medium casting sizes can be made 0.5 kgs to 50 kgs and what about the quantity, quantity is medium to large ranges because these what say moulds are made up of special steels and making a cavity in these metallic moulds would be a difficult task and having made this metallic mould with much effort and if we have to make only a few castings then it would not be economical. These are the features, surface finish between 150 to 250 or mesh better than the sand casting process. Draft of 2 to 4 degrees is required. Next one, moderate tooling cost. Next one, low to moderate casting cost. Next one, moderate finishing cost whereas in the sand casting process the finishing cost is high whereas here the finishing cost is moderate. Next one, the pressure die casting. It is suitable for aluminium, magnesium and zinc alloys. So there is a difference between the gravity die casting and the pressure die casting. In the case of the gravity die casting the molten metal flows into the metallic mould by means of the gravity. Here in the pressure die casting we apply external pressure because of this external pressure even if the what say mould cavity contains some complex features the molten metal will be forced into these complex features that is how even complex shapes can be made by this pressure die casting. Next one, simple to moderate complexity. Next very small to medium casting sizes and quantities medium to very large range. Once we make what say these dies so if we have to make only a few castings so it would not be economical. The quantity should be quantity of production should be either medium or it should be large or very large then only the cost would be economical. So these are the features surface roughness between 30 to 90 rms. So this is better than the sand casting process and also the gravity die casting process. Draft 0.5 to 3 degrees. Next one, high touring cost, low casting cost and low finishing cost. Next one, the investment casting. It is suitable for iron, steel, aluminium, copper base alloys, high alloy steels, magnesium steels, magnesium and titanium alloys. In fact most of the cast alloys can be made using the investment casting process. Moderate to high complexity because the pattern is made up of wax any complex feature can be made and around that we create the cement shell. So the complexity is moderate to high. Next one, very small to medium casting sizes. Very large castings cannot be made, very small castings can be made, small castings can be made and also medium size castings. Quantity is from small to medium range. Very large production is not possible because the process is very slow. The pattern has to be made around that pattern. We have to give a ceramic slurry coating. This is ceramic slurry preparation itself takes lot of time. It has to be dried then it has to be baked. So this process of making the ceramic shell takes about 8 hours prior to, I mean after making the ceramic slurry. So this process is slow that is why large production is not possible. Next one, these are the features, surface roughness is between 63 to 125 rms. Next one, thickness of this section is 0.75 mm means thin sections as thin as 0.75 mm can be cast. Next one, moderate to high tooling cost, low to high casting cost and moderate to high finishing cost. Next one, centrifugal casting. This is suitable for steel, aluminum, high alloy steels, copper base alloys. It offers the simple complexity and the components must be exisymmetrical, small to large casting sizes and quantities in the medium range. Very large production may not be possible and these are the features, surface roughness is between 100 to 300 rms, draft is 0 to 1 degree, moderate tooling cost, moderate casting cost, low to moderate finishing cost. So these are the features of the centrifugal casting. Next one, the plaster molding. This is suitable for aluminum, copper, magnesium and zinc alloys. Simple to moderate complexity, medium or small size castings can be made say 1 kg to 100 kgs, quantities in small or medium range. So these are the features, surface roughness is between 63 to 125 rms. Again we need to give a draft of 0.5 to 2 degrees, low tooling lead times and low moderate tooling cost, low to moderate casting cost and moderate finishing cost. Next one, let us see the last foam casting that is the expendable pattern casting or also it is also known as the evaporative pattern casting. So this is suitable for iron and aluminum alloys. Simple to moderate complexity, small to medium casting sizes, 1 to 500 kgs, quantities in the small to medium range. Very large production is very difficult because the process is very slow. So these are the features, surface roughness between 100 to 300 rms, draft of 1 degree to be given, moderate to high tooling cost, low to moderate casting cost and low to moderate finishing cost. So these are the features of the evaporative pattern casting. Now let us see the comparison of the different casting methods. So these are the, we have taken sand casting, die casting, sand shell and the investment casting. Now so these are all the comparative features. So tool costs, unit costs, maximum casting weight, thin X section possible, typical dimensional tolerance, relative surface finish, relative mechanical properties, relative ease of casting complex designs, relative ease of changing design in production, metal options. So these are the different what say features. Coming to the sand casting, the unit cost is average, maximum casting weight over 1 ton. So generally these, but nowadays even up to 5 tons people are making with the sand casting process. Next one, thinnest section possible is 2.5 mm, below that it is not possible with the sand casting process. Next one, typical dimensional tolerance is 0.3 mm, relative surface finish, fair to good, relative mechanical properties good, relative ease of casting complex designs, it is fair to good. Next one, relative ease of changing design in production is best. Next one, metal options, most of the metals can be cast. And coming to the die casting, the tool costs are very high because the machine is very costly and the metallic modes we have to make. So this what say machining, these metallic modes would be very very difficult and we have to use very sophisticated machines for that. That way the tool costs are very high. Next one, unit costs are low, maximum casting weight say 30 kgs, very large castings cannot be made by die casting. Now the thinnest section possible is 0.8 mm, very thin section as thin as 0.8 mm can be made by die casting. Typical dimensional tolerance is 0.25, this is the variation 0.25 mm. Next one, relative surface finish, this is the best among the all casting process. You can see the remaining process, the sand casting process fair to good and what say sand shell, it is good and unit surface casting very good whereas die casting offers the best surface finish. Next one, relative mechanical properties very good. Next one, what say ease of what say making complex shapes good. Next one, relative ease of changing design in the process is purest because we make the metallic modes. These metallic modes are made up of very hard steels and we machine them. We create the cavity using sophisticated machines. All of a sudden after making 10 castings, some 10 casting someone says no no no change the casting design, this what say feature needs some modification, it is very difficult. So that is why change of design during the process is the purest. Next one, metal options what say it is low. Next one, sand shell process means the chemical what say sand casting process, the shell molding. Next one, the tool costs are average, unit costs are average, maximum cast weight is casting weight is 100 kgs, thinnest section possible is 2.5 mm. Real dimensional tolerance it is 0.25 mm. So this much can vary after we make the casting. Relative surface finish good, relative mechanical properties good, relative ease of casting complex designs is good, relative what say ease of changing the design is fair. Next one, metal options average means not the all the what say alloys and what say average number of alloys can be manufactured using this shell molding process. Finally, let us see the investment casting process, the unit costs are the tool costs are the average, unit costs are very high you see because we have to make the wax pattern. Sometimes we use several waxes and make the blend. So these wax patterns are very costly, these wax are very costly. Next one and next we have to make the ceramic shell or slurry then we have to apply a coating around the wax pattern. So this the ingredients of the ceramic shell are very costly that way the unit cost is high. Next one, maximum casting weight is say this is the typical weight 45 kgs but nowadays even people are making about 300 kgs, 300 kgs to 400 kgs in some special cases. Now the thinnest section possible is 1.6 mm, typical dimensional tolerance 0.25 mm. This much variation will be there after we make the final casting. Relative surface finish very good, the surface finish that is obtained in the investment casting is next to the surface finish which is obtained in the die casting. Relative mechanical properties are fair, relative ease of casting complex designs is best. Next one relative ease of changing design during the production is fair, next metal options is very high. As I already told in the beginning, most of the engineering gullois can be made by investment castings. Next one let us see the economics of the casting process. These are the what say cost components, one is the molds. So what say in the case of the sand casting process it would be extreme, sorry in the case of the sand casting process it would be low, mold cost whereas if it is the die casting process the mold cost is very high. So this is one component of the cost. Next one melting and pouring, so this is costly melting and what say it consumes lot of power. Next one heat treatment, so this also involves cost, next one cleaning, inspection and finally the labor charges. So these are all the what say cost components and the total cost is dependent on all these factors. So this is the cost equation. We can see here C is equal to C m plus C c divided by n plus C l divided by n where C is the cost per part, C m is the material cost, C c is the capital cost, C l is the labor cost, n is the number produced means this number and this n the second n is the production rate. So this is the cost equation. Now so this we can say see the what say comparison of important casting process by this graph. So this x axis shows the number of components whereas the y axis shows the relative cost per component, relative cost per component. Now let us see what is happening with the sand casting process. So in the beginning if you make only say less than 10 castings the cost is very high, not very high moderately high and as you keep increasing the components it is little what say less and it continues to be the same even if we make say 1 lakh components. Whereas let us say this one permanent mould process if we say because the what say dies are moulds are made up of the metallic ones and here if we make say less than say 100 components or 10 components the cost would be very high. But the same moulds without breaking can be used for making 100s and 1000s of components. So as we keep increasing the components the cost would come down, the cost per component would come down. Now this is the pressure die casting, the pressure die casting that mission is very costly because most of again this pressure die casting is cold chamber pressure die casting and hot chamber pressure die casting. In the hot chamber pressure die casting the melting furnace is integral part of the machine whereas in the cold chamber die casting machine the melting furnace will be outside. So if we consider the hot chamber die casting process the melting furnace is inside that mission is very very costly. Now if such a machine if we buy and if we make only 100 components cost would be very high. On the other hand if we make say 1 lakh components the same moulds can be used the same machine can be used the moulds need not be broken after the solidification that is how the speed of production would be very high and the cost per component drastically comes down. It comes down drastically is that if the cost of the production would be even lesser than the cost of the sand casting process. Here we can see this is the die casting you see in the beginning it is very high but as you increase the number of what is a component it is coming down and the cost involved part is less than the cost of the sand casting process. So what we can conclude sand casting is economical for the lower volumes whereas high production rates in die casting can justify the high cost of dies and the machinery and once we go for the high production rate in the die casting the pressure die casting the cost would be much lesser lesser than the cost of the sand casting process. Next one important considerations for the casting alloys. So these are the important considerations when we are making the cast alloys casting characteristics are important. Next one missionable casting characteristics means the surface finish the dimensional accuracy the ability of making some complex features or the thin sections. So these are the casting characteristics. Next one missionability most of the cast components after we make the casting they need the machining to get the required surface finish. So the cast alloy should have the good machinability. Next one sometimes the cast components will be welded to some other cast components or some other components then they should have the good weldability. So these are the again important considerations. These are the typical applications of the cast alloys and the characteristics. Now let us see this aluminium. So these are the typical applications we can make pistons, clutch housings our right intake manifolds right. The castability is excellent, E means excellent, G means good, F means fair, VP means very poor, D means difficulty. For the aluminium alloys the weldability is fair and the machinability is good to excellent. Next one copper alloys it is used for making pumps, valves, gear blanks, marine propellers. The castability is fair to good, weldability is fair and the machinability is fair to good. Next one let us see the ductile iron. This is the typical applications are the crank shafts, heavy duty gears, the castability is good, weldability is difficult and machinability is good. Next let us see the grey iron. These are the typical applications, gears, brake discs and drums, machine bases these are manufactured by grey iron or the grey cast iron. The castability is excellent, weldability is difficult and machinability is good. Next one malleable cast iron, these are the typical applications form and construction machinery, heavy duty bearings, railroad rolling stock these are manufactured by malleable iron and the castability is good, weldability is difficult, machinability is good. Next one white cast iron, in the white cast iron in all the cast irons carbon is present in the white cast iron carbon is present in the form of the cementite. So because of the presence of this cementite the white cast iron becomes very hard. So these are the typical applications this is used for making mill liners, railroad break shoes. So these are the very hard components, in fact these components require a high hardness and crushers, pulverizers. So these are all manufactured by white cast iron and castability is good, weldability is very poor, machinability is very poor, yes because of the presence of the cementite the machinability would be very very poor. Next let us see the steel carbon alloys. These are the typical applications, die blocks, heavy duty gear blanks, aircraft undercarriage members these are the typical applications and the castability is fair, weldability is excellent, machinability is fair. Next one steel high alloy steels. So these are the typical applications gas turbine housings, pump and valve parts, rock crusher jaws and castability is fair, weldability is excellent, machinability is fair. Next one the magnesium alloys, these are the typical applications crankcase transmission housings the castability is good to excellent, weldability is good and the machinability is excellent. Next let us see the remaining alloys these are the zinc alloys and the nickel alloys. Coming to the zinc alloys these are the typical applications door handles and radiator grills. These are manufactured by zinc alloys the castability is excellent, weldability is difficult and the machinability is again excellent. These are the nickel alloys, these are the typical applications gas turbine blades, pump and valve components for chemical plants these are manufactured by nickel alloys. What about castability fair, what about weldability fair and machinability is also fair. Friends with this lecture we have seen the what is a concept of the casting process the principle of the casting process and we have seen how the casting process has developed and how it has changed in the what is a past to history and different casting process have been developed and we have seen the classification of these different casting process. We have also seen the overview of the all these casting process and their what is a comparison and the economics of these casting process we have seen and the typical applications also we have seen. And in the next classes and we will be concentrating on the what is a each and every casting process in detail we will be learning thank you.