Chapter-1 Introduction Introduction:- One of the main functions of the Engineering Works is joining of the parts. Collectively this joining is called Fastening. Fastening is generally two type are- 1. Temporary Fastening: In this process of fastening, the parts are ready to separation. Ex-Nut and Bolts, Nut and screws, Nuts and studs are all temporary fastenings. 2. Permanent Fastening: In this process of fastening the parts not likely to require separate. Ex-Welding. 3. Semi-permanent Fastening: In this process of fastening the parts are semi separable. 4. Ex-Soldering, Brazing and Riveting. 1 Chapter-2 2.1 Definition:- The welding is a process of joining two similar or dissimilar metals by fusion or without fusion, with or without the application of pressure and with or without filler metal. [3] During fusion a solid union or a compact mass is formed. If filler material is similar with the base material then this type of welding is called homogenous welding and if filler material is different from base material then it is heterogenous welding, where filler material is given should have low melting temperature. 2.2. Types of welding:- The overall welding process shown in chart below 2 The welding is broadly divided into the two groups: I. Pressure welding or diffusion welding: this welding process is done under pressure without additional filler metals. It is classified as- a) Hot pressure welding and b) cold pressure welding 2nd state 1st state 2nd 4 II. Fusion or non-pressure welding: This process is done with additional filler metals. It is classified as a) Gas welding, b) Thermit welding, c) Electroslage welding, d) Electron beam welding, e) Laser beam welding and f) Arc welding. Chapter-3 Cold pressure welding 3 3.1 Cold pressure welding Cold or contact welding is a solid-state welding process in which joining takes place without fusion/heating at the interface of the two parts to be welded. Unlike in the fusion-welding processes, no liquid or molten phase is present in the joint. Cold pressure welding is the establishment of an atom-to-atom bond between the two pieces to be joined through intimate contact between oxide-free areas achieved under pressure and without the formation of liquid phase. In order to develop this bond, surface films have to be removed or at least reduced in amount. Cold pressure welding is used for joining of aluminium cables, joining wires and rods, various kitchen furniture, communication lines, and application of joining different materials nowadays. ADVANTAGE Cold pressure welding of metals has the following advantages: There is no softening of a work hardened or heat-treated metal since the process is carried out at room temperature. This welding is suitable for electronic parts, which may be broken by heating When dissimilar metals are welded, a brittle intercrystalline layer is not formed which is observed in the conventional heat welding at the interface of the metals. Then, welding cannot be achieved by just pressing two metals together since the surface of the metal is generally covered with oxide layer, absorbed vapor layer and stained layer such as oil. Cold pressure welding is accomplished with intimate contact of virgin metals, which appear owing to the breakdown of the surface layers, by plastic deformation of the base metals. PRESEDURE Cold pressure welding can be characterized by the large number of possible metal combinations. 1. Surface Preparing In order to reduce surface films, all the specimens were first degreased in acetone and then wire brushed using a motor driven wire brush. 2. Deformation Amount in Lap Welding In this welding method, deformation amount is an important parameter and named with deformation result with the joined surface. In order to obtain bonding joint, plastic deformation of the two metals is necessary, supposing that 4 a basic parameter in cold pressure welding is the degree of deformation normally expressed as the reduction R. For lap welding is given by where h0 is the original thickness of sheet and h1 is the instantaneous thickness at deformation R. 3. Surface Roughness The fact that initially rough surfaces are required for welding suggests that bringing oxide free metals into contact does not result in welding unless there is also some shear displacement as the two surfaces come into contact. 2.4. The Bond Formation Wire brushing at mechanical surface preparation forms a hard and brittle surface film at metal surface. This layer is called as cover layer. The observations on researches show that bond formation is realized by means of the stages given below. The stages are given in 5 Figure 1 shows schematically the mechanism of bonding. Deformation has not been yet occurred in figure 1.a., and the cover layers are intact. Figure 1.b shows that a small deformation has been resulted in fracture of the two cover layers as one layer. In figure 1.c, the surface expansion has further increased, and extrusion of virgin material through the cracks is initiated. Real contact and bonding have been established between the rough end surfaces of the extruded metals as shown in figure 1.d. 2.5. Welding Dies and Welding 6 Schematic welding dies designed for lap welding is given figure 2.In space After surface preparation, the specimens are immediately set in the welding die and then the pressure was applied. At the beginning of the experiments, the pressure is applied at very slow rate and then at a much higher rate. It is found that the rate of applying the pressure does not have a marked effect on either the welding deformation or the weld strength. The welding time (time of applying and releasing the pressure) is then set to be 1 min in all the experiments were carried out at room temperature. 3.2 Hot pressure welding Hot-pressure-welding is a solid state process that produces joints between the faying surfaces of two bodies. It is done by application of heat and pressure. Fusion temperature is not reached, filler metal is not needed, substantial plastic deformation is generated.Heat is generally applied by flames of oxyfuel torches directed on the end surfaces of solid bars or hollow sections to be joined. Alternatively, heat can be generated by eddy currents caused by electrical induction from a suitable inductor coil. As soon as the two bodies facing ends reach the correct temperature, the torches are suddenly removed, not to stand in the way. The bodies are brought to contact and upset together under pressure, usually by hydraulic equipment. This variant is properly called the open joint process. If the parts are making contact under pressure before heat application from the outside, it is called the closed joint process. In either case flash material is expelled and a bulge is formed at the joint. Hot-pressure-welding is similar in a way to both friction welding (see Friction Welding Processes) and flash welding (see Flash Welding Process), although the source of heating is different. For obtaining the best results the surfaces should be machined square and clean. Some beveling can be used to control the amount of upset. The process as described is performed as a manual operation. 7 The materials to be welded must exhibit hot ductility or forgeability. Therefore cast iron cannot be Hot-pressure-welded. The materials commonly joined by Hot-pressure-welding are carbon steels, low alloy steels, and certain nonferrous metals. Certain dissimilar materials combinations are weldable by Hot-pressure-welding. Materials that immediately form on the surface adherent oxides upon heating cannot be easily welded in air by this process. Typically among them aluminum alloys and stainless steels. Tests were performed in a vacuum chamber. Advantages • Simple process • Simple joint preparation • Relatively low cost equipment • Quick weld production • High quality joints • No filler metal needed • Minimally skilled operators required Limitations • Not all metals are weldable • Not easily automated • Length of cycle dependent on time for heating • Removal of flash and bulge required after welding. • Only simple sections readily butt weldable. The most important parameter is the pressure sequence cycle, possibly being developed by trial and error. Pressure in the range of 40 to 70 MPa (6 to 10 ksi) must be available. Typical application reported, refer to butt Hot-pressure-welding of railroad rails sections and steel reinforcing bars, especially in Japan. For use in the production of weldments for the aerospace industry with delicate materials Hot-pressure-welding can be carried out in closed chambers with vacuum or a shielding medium. Mechanical properties tend to be near those of the base materials, but depend upon materials composition, cooling rate and quality. Hot- pressure-welding can be an economic and successful process for performing butt joints of simple shapes if the materials are easily weldable. Hot pressure welding is further sub devided as- 1. Gass pressure welding 2. Electric resistance welding 3. Forge welding 4. Ultrasonic welding 8 5. Friction welding 6. Explosion welding 7. Blacksmiths forge welding 3.2.1 Gass pressure welding It is welding method directly of raw material itself to press under the condition which is before heat melting(1,200°C ~1,300°C) for junction part with oxy- acetylene gas to fix on both side rebars to connect in carrying out of rebar concrete structure building. Also, it is economic splice method than folded tying (lap splice), mechanical spiral tying (mechanical splice) and also the strength of junction part is stronger than raw material. 3.2.1.1 Composition of gas pressure welding equipment Welding units 1. Oxygen pressure controller 2. Acetylene pressure controller 3. Acetylene outlet hose 4. Oxygen outlet hose 5.