 Hello everyone, I am Chandrakant Rathod working as an assistant professor in Mechanical Engineering Department, Walsh and the Institute of Technology, Solapur. Today we are going to start a new topic that is called pattern. At the end of today's lecture, you are able to understand what is pattern, different types of pattern, different types of pattern material, functions of pattern, different types of pattern allowances. The following topics will be discussed in this video lecture, definition of patterns, functions of patterns, pattern material and pattern allowances. What is mean by pattern? The pattern is defined as the mold forming tool, which is the replica of the casting. It is also defined as the replica of a finished product or a finished component. It is essential to form a mold cavity in which molten metal is poured. A pattern is used to form many mold cavity and hence casting. A pattern is required even if one object has to be cast. Pattern is slightly larger in size as compared to the casting because we have to give the some allowances, shrinkage allowance, machining allowance, draft allowance, etc. Then coming to the next topic that is called functions of patterns. So there are different types of or functions of patterns are there. The main functions of pattern is to produce the mold cavity. So in which we have to fill the molten metal into the cavity. To make successful mold, the pattern has to perform certain functions which are as follow. First one to provide the gating system. Gating system provides the channels and feeders to main molding cavity. The second one is to establish the parting line. It is very easy to locate the parting line with flat pattern plate, but when the pattern is curved the pattern should have a parting line on it to locate the parting line in the mold. Third one is to provide for core print. When cores are used in mold, pattern should provide proper core prints in the mold cavity. Next to establish the locating points. Locating points on the casting are essential to check the casting dimensions after casting for machining and this is done using patterns. Next one is to minimize the casting defect. A good pattern should produce a defect free mold hence a good casting. This is achieved by use of clean and properly designed pattern. Next is the pattern material. So this is very important that we have to select the pattern materials. There are many different types of pattern materials are there like metal, plastics of paris, then wood, wax, etc. So we are going to discuss one by one. The quality and finish of the casting depends mainly on the types of material used for pattern. Some factors to be considered while selecting a pattern material is as follow. So number of casting to be produced, size and shape of the casting, durability of the pattern and degree of mold accuracy and surface finish required. So coming to the first material that is called wood, wood is the most commonly used pattern material. To obtain the best result, properly seasoned wood is used. Seasoning makes the wood strong, moisture free and smooth for machining. Using for seasoned wood gives a long service with a minimum or negligible shrinkage. Different types of woods are used to make the pattern such as t-coat, mahogany, deodor, season, etc. So coming to the next material that is called metal. So cast or machined metallic patterns are widely used in making the patterns. Metallic patterns are suitable for producing casting in large quantity and repetitive production. They give good surface finish, they are dimensionally more suitable. The different metal used are cast, iron, aluminum, steel, brass and other alloys. So coming to the next material that is plastic, thermosetting and thermoplastics are used as a pattern material, thermosets are used for making durable and long run patterns and thermostatics are used for short run. The commonly used thermosets are epoxy and polystyrene resins. Plastic is in lightness, good surface finish and wear resistance. So next is the plaster. So this pattern is made up of gypsum or plasters of paris with suitable additives is strong light and gives good surface finish. They are suitable for small casting only. So coming to the next topic that is called pattern allowances. A pattern is always larger in size as compared to the final casting. There is this is because it carries a certain allowances due to metallurgical and mechanical reasons. First one is the shrinkage allowance, it is also called as a contraction allowance. It is a correction provided on the patterns to compensate the solidification shrinkage and contraction of the casting during cooling to a room temperature. The patterns are made larger in size than the required casting size. The patterns allowances required differ from metal to metal. Sometime double allowances are provided if pattern is made up of wood. This is because the metal pattern cast also shrinkage shrinks which is also been compensated. So coming to the next allowances that is called machine finish allowance or it is also called as machining allowance. So machine finish allowance is the excess dimensions on a pattern so as to obtain additional material on the casting. This allowance is very necessary to provide stock for machining, this is also provided over and above the shrinkage allowance. The amount of machining allowance depends on the type of metals to be cast, design and method of casting and cleaning requirement. Generally, we are provided 3 mm machining to the cast. So coming to the next allowance that is draft allowance, it is also called as a taper allowance. So draft allowance is the taper provided on the pattern surface to allow its withdrawal without affecting or damaging the mould surface. If the pattern surface straight, it is difficult to withdraw pattern from the mould so there is a high chance of moulding surface damage due to friction between the mould and the pattern. Mould damage is more severe at the corner of the mould at the parting surface. Hence the draft is provided on the vertical surface of the pattern. For hand drawing patterns about 10 to 20 mm draft per meter is provided. For machining drawn pattern about 1 degree is provided. Next is the distortion allowance. This allowance is provided on the pattern whose casting tends to distort on the cooling. Similarly it is required for flat, long, V and U shaped casting. To obtain the proper casting pattern itself is distort which yields a casting of required shape. So next is the wrapping or shaking allowance. So when the pattern is wrapped for easy withdrawal the mould cavity gets enlarged. To take care of this pattern size is reduced. This allowance is very important in case of recession casting. So these are the some references of foundry technology by OP Khanna, manufacturing technology by PNRA, manufacturing process 1 by AC Niranjan. Thank you.