ABSTRACT

Welding is the process of uniting together of two pieces of similar metals or alloys by fusion. Intense heat is applied close to the parts to be welded, keeping the two pieces of metals together, so as to form a molten puddle at the place of weld which during cooling, unite together by metallurgical atom to atom bond. As a general rule a filler rod or an electrode is used to fill up the weld and to form the puddle Metals play a major role in the industrial and everyday life of human beings. We see hundreds of metal objects and parts which find engineering applications. Mild steel is used in transportation, industrial-structural frame work, engine parts, decorative features, doors, window frames, fittings, conductors, heat exchanger parts, packaging and different alloys of mild steel is vastly used in trucks, trains, buses and aero planes. Mild steel is used for making valves, gears, crank shafts, connecting rods, railway axles, camshafts, shits and strips for fan blades, forgings, drag lines etc. Thus it is found that the selected materials have vast uses. To make above mechanical parts welding is essential. For these reasons it is necessary to know the mechanical properties of the metal that means stress, strain & hardness. In this thesis work the mechanical properties of the selected material are analyzed and studied with the relationship of these mechanical properties before and after welding. It was seen that the stress of mild steel bar decreased after welding for any cross-section. The stress decreased due to heat treatment of metal. After welding the hardness of the mild steel increased because of rapid cooling. During experiment it was seen that the proportional limit of the specimens decreased due to effect of welding. It was also observed that the strength of the specimens decreased which means the yield strength & ultimate strength decreased but hardness increased because, after welding when it cooled the molecules of the specimen became compact Thus the property of the specimen has changed due to welding effect. In order to test stress, strain and hardness number, first it was made the specimens in the machine shop. Then the stress, strain and hardness number were tested in the metrology lab. Again the virgin specimens were made and these specimens were cut in the middle position and welded. Then the stress, strain and hardness number were tested. The data was compared with the virgin (before welding) specimen. The welding causes a percent of decrease in the yield stress & ultimate stress and increased the hardness number of the specimens.

Click Here to download full report.