 Hello friends, myself Sanjeev B and I, working as assistant professor in Department of Mechanical Engineering, WALCHER Institute of Technology, Solapor. In this video I am explaining welded joints. At the end of the session, students will be able to classify welded joints and they will also be able to select the proper joint according to the application. Welding is a process of joining metallic parts by heating to suitable temperature with or without the application of pressure. Welding is a very economical and efficient method for obtaining a permanent joint of metallic parts. Not all the other methods to obtain permanent joint is riveted joint but which is more cumbersome than this method. So welding is the most economical and efficient method for obtaining the permanent joint. Welding can be obtained by two processes. One is the fusion welding in which the parts to be joined are held in position and molten metal is supplied to the joint. The molten metal can come either from the parts themselves called the parent metal or it can be supplied by a filler metal. After solidification of the joint the two parts fuse into a single unit. Pause the video for a while and just recall galactic arc welding and gas welding. The another process of welding is the forge welding in which the parts are heated to reach the plastic stage and the joint is produced by impact force. The impact force is produced either by a hand hammer or a press. Rot iron or low carbon steel can be forged welded. However, this process has got very limited use in present times. It is used in the fabrication of rot iron pipes. The welded joints are broadly classified into two groups that is the butt joints and fillet joints. So this is the butt joint in which the two parts are lying in the same plane and they are connected at the end by a fillet butt weld as shown over here and symbolically it is shown by this figure. So this is the butt joint which is produced to connect two parts at the ends by preparing the ends as a groove here over here and molten metal is supplied to the joint and joint is prepared. So this is the butt joint. The various types of the butt joints which are used in practice are shown over here a square butt joint, v butt joint, u butt joint, double v butt joint, etc. The application of these joints are depending upon the plate thickness as shown over here. Square butt joint is used when the thickness is less than 5 mm, v butt joint is used when the thickness is between 5 to 25 mm, u butt joint is used when thickness is greater than 20 mm and double v butt joint is used when thickness is greater than 30 mm. So according to the plate thickness and the reliability requirement v butt joints are commonly used for pressure vessels as they are more reliable. Another type of joint is fillet weld. So in this case the two overlapping plates are joined by fillet weld at the corner which is a triangular in section as shown over here and symbolically it is been represented like this. So further it is classified as a transverse fillet weld as shown over here and it is a parallel fillet weld shown over here. In transverse fillet weld the weld section is perpendicular to the load acting on the joint as shown over here. So it is a single transverse fillet weld whereas one more transverse fillet weld if it has this side then it becomes a double transverse fillet weld. In case of parallel fillet weld the weld section is parallel to the load acting on the joint. So here is a joint where the load is acting parallel to the weld section and there are two fillets. So it is a double parallel fillet weld which is used in practice. So another types of fillet welds are T joint in which two perpendicular plates are connected like this resembling the T letter as such. So it is called the T joint and corner joint is provided for plates to join which are perpendicular to each other at the corner fillet weld is produced and in edge joint two overlapping parts are connected at the edge as shown over here. So these are some other types of fillet joints used in the practice. Welded joints offer a lot of advantages over riveted joints. So these are lighter than riveted joints. In case of riveted joints we require additional elements called rivets which are number of rivets to be used along the length of the joint and that is why the overall weight of the riveted joint is higher compared to the welded joints. So welded joints are lighter compared to riveted joints. These are less costly. Alterations and additions are easily possible. This is another advantage of welded joints. So additions are easily done in existing structure by welding. The welded structure has smooth and pleasant appearance. This is another advantage of the welded joint that it gives a smooth and pleasant appearance. In case of riveted and bolted joints the additional projections are there on the surfaces whereas in this case such projections will not be there and one can match the smoothness of the surface as per the requirement and that is why it has got pleasant appearance. The strength of the welded joint is high because the parent metals are normally fused together to get a welded joint. So strength is also higher. Welded assemblies are tight and leak proof that is additional important advantage of this welded joint as compared with riveted assemblies and that is why they are extensively used in pressure vessels. The production time is less for welded assemblies so manufacturing is at faster rate in case of welded assemblies. When two parts are joined by the riveted method the holes are required to be drilled in the parts to accommodate the rivets and that reduces the cross-sectional area as well it results in stress concentration. Such requirement is not there in case of welded joint. There is no such problem in welded connection. However there are certain disadvantages of welded joint. The important disadvantage is a thermal distortion or warping of the parts. As in welding localized heating and the joint is important and because of that unequal cooling of the parts near the vicinity may occur and that leads further distortion or warping of the parts as an disadvantage. Vibration dampening is also poor that is resistance to vibration or vibration absorption capacity is very less in case of welded joints and that is why they cannot be used as a structural element or structural requirement in case of vibrations are present or expected. The quality and strength of the welded joints depends upon the skill of the welder. So welding is a process required to be carried out by a skilled worker called a welder so that the strength and quality can be obtained. The inspection of the welded joint is more specialized and costly because by naked eye many times the cracks in the weld section may not be detected and that is why some special techniques called as X-ray techniques or X-ray machine is used to detect the cracks particularly in pressure vessels where the reliability of the joint is very important in such case the 100% inspection is required for the weld section and in such case the X-rays machines are used or technique is used which is costly. Welded joints have got lot of applications particularly in steel structures so we find that almost all steel structures majority is fabrication work in which we use the welded joints and we find the application as connections between metal plates, angles, pipes and other structural elements are frequently made by welding. Imagine a huge ship structure it is also been a welded structure pressure vessels particularly tanks of the boilers and tanks these are been obtained by welded joints particularly butt welded joints and other steel structures like welding bridges, shades, automobile bodies, railway wagons, machine cramps etc. or even in furniture we use the welded joints. So application of welded joints is very large as an industrial application so they are most popular type of permanent joints used in the industries. These are my references. Thank you.