 Hello friends, myself Dr. Narendra Kartikar, Assistant Professor, Department of Mechanical Engineering, Valachandra Institute of Technology, Solapur. Now, we are going to see the discussion on study of resistance welding. At the end of this lecture or session, student will be able to understand the elements in resistance welding setup, process and also know where to apply it. The content for this particular discussion, comparison, introduction, introduction to joining processes, advantages and disadvantages of welding, resistance welding, spot type, setup and description, advantage, disadvantage and applications of resistance spot welding. In the introduction, let us see as we know to produce any single element or an assembly you require to go with any basic manufacturing processes. Out of these four processes like casting, metal forming, joining process, metal cutting and so on. But the whenever the question comes, the task comes for the permanent kind of joints of more than two elements, then only one option that is the joining processes. The rather the welding process which carried out an assembly can go with some of the parameters like heat energy, filler material, flux material and pressure. Out of these four, few of them may be used combiningly as per the requirement and type of welding process. Why to go with welding? The answer is here that is the advantages of welding processes. Welding provides a permanent joint. It is the economical way to join the components in terms of material usage and fabrication cost. Other methods of assembly requires, for example drilling of holes, usage of rivets, bolts, nuts, screws, etc., which will produce a heavier structure itself. A good weld is as strong as the base metal. General welding equipment is not very costly as well as the portable welding equipment are possible to avail the same to fulfill the task as per the requirement. Some of the further more advantages of welding are most efficient way to join the metal, lowest cost joining method, it joins all almost commercial metals together and also it provides the design flexibility itself. Some of the disadvantages or limitations of welding processes are there which restricts it for particularly application of welding. It gives out the harmful radiation in the form of light, fumes and also spatters the hot spot molten material. A skilled welder is much to produce a good welding job. The welding heat produces some of the metallurgical changes in the base metal itself. So with due restriction of particularly some of these disadvantages of welding even though we are going to use the welding joining process for making the assembly with a wide varieties and types of welding process. Some of the further disadvantages whatever the manually applied particularly welding processes. So that is why it is required a high labor cost. It is particularly producing the defects which are very difficult to go with the its remedies. At this stage of this session are you able to recall or share some of the parts where different geometries are welded with any type of welding process unless such welded parts which you had seen earlier anywhere in real time. Just enlist here we go. I hope that you had enlisted the parts or assembly which can be joined together with the means of welding process. Let us see the introduction of resistance welding itself. Resistance welding is a welding process in which work pieces are welded due to a combination of pressure applied to them and a localized heat generated by a high electric current flowing through the contact area of the weld. Here one of the type of resistance welding conceptual figure is shown over there. The electrodes of two numbers as well as the work piece is the part of electric circuit normally AC power supply of course to fulfill the particular task you required to go with the pressure parameter itself. Principle of resistance welding heat produced by the current is sufficient for local melting of the work piece at the contact point and formation of small weld pull called as nugget. The molten metal is then solidified under a pressure and joins the pieces AC electric current up to the 1 lakh ampere is supplied through the copper electrode connected to the secondary coil of welding transformer. The following metals may be welded by resistance welding, low carbon steel, aluminum alloys, medium carbon steel, high carbon steel and some other types alloy steels also. Some of the types of resistance welding, spot welding, seam welding, projection welding, resistance butt welding, flash butt welding, percussion welding, high frequency resistance welding, high frequency induction welding. Let us go to understand one of the type of resistance welding that is spot welding. Here the setup of spot welding is there. You can see the setup consists of one electric circuit may be called as resistance welding circuit where the source of electricity is there which is controlled or flow through the transformer. Another two movable, further two electrodes are there. One is fixed in the movable arm, another is fixed in the fixed arm. These particular electrodes normally a water cooled and off copper material the job can be held together under the pressurized condition of two electrode itself. You can see the regulator is there which controls the AC current supply. In this process overlapping sheets are joined by a local fusion at one or more spots by the concentration of current flowing between two electrodes. This is the most widely used resistance welding process. It essentially consists of two electrodes out of which one is fixed. The other electrode is fixed to a rocker arm to provide mechanical advantage for transmitting the mechanical force from a pneumatic cylinder itself. The other possibility is that of pneumatic or hydraulic cylinder being directly connected to the electrode without any rocker arm for welding large assembly such as car bodies, portable spot welding machines can be used. Here the electrode holders and the pneumatic pressurizing system are present in the form of portable assembly which is taken to the place where the spot is to be made. The electric current compressed air and the cooling water needed for the electrode is supplied through the cable and hoses from the main welding machine to the portable unit. In spot welding a satisfactory weld is obtained when a proper currently density is maintained the current density depends on the contact area between the electrode and the workpiece. With the continuous use if the tip becomes upset and the contact area increases the current density will be lowered and consequently the weld is obtained over a large area. This would not be able to melt the metal and hence there would be no proper fusion. Resistance spot welding setup few of the figures are here. Resistance spot welding setup multiple spot welding setup advantages of resistance welding delivers the following advantages like high welding rates low fumes almost no fumes cost effectiveness easy automation no filler material are required at all low distortion almost no distortion is there. These are the advantages of resistance spot welding as compared to the other welding processes that is gas welding and arc welding. Some of the disadvantages of resistance gas welding application of resistance gas advantages of resistance spot weldings are as follows high welding rates low fumes rather no fumes at all itself it is a cost effective cost effectiveness is the most important advantage of the resistance spot welding. It can be easily atomized no filler material is required at all it delivers very low distortion in some of the cases no distortion at all some of the disadvantages of resistance spot welding high equipment cost low strength of discontinuous welds thickness of weld sheet is limited that is it can go with the 6 millimeter rather 1 fourth inch itself. Application of resistance spot welding it has applications in automobile and aircraft industries the attachment of braces brackets pads or clips to form sheet metal parts such as cases covers or trays is another application of spot welding spot welding up to 12.5 millimeter thick steel plates has been done satisfactorily as a replacement for riveting many assemblies up to or more sheet metal stampings that do not require gas tight or liquid tight joints can be more economically joined by spot welding than by mechanical methods containers and boxes frequently are spot welded itself. Some of the references for this discussion come presentation introduction to basic manufacturing process and workshop technology by Rajendra Singh a textbook of workshop technology and manufacturing processes Khurmigopta NPTEL study material and so on. Thank you.