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Riveting

A rivet is a fastener that has a head and a shank and is made of a deformable material. It is used to join several parts by placing the shank into holes through the several parts and creating another head by upsetting or deforming the projecting shank. During World War II, Rosie the Riveter was a popular cartoon character in the United States. No better image can illustrate the advantages of riveted joints. These are
1. Low cost
2. Fast automatic or repetitive assembly
3. Permanent joints
4. Usable for joints of unlike materials such as metals and plastics
5. Wide range of rivet shapes and materials
6. Large selection of riveting methods, tools, and machines
Riveted joints, however, are not as strong under tension loading as are bolted joints, and the joints may loosen under the action of vibratory tensile or shear forces acting on the members of the joint. Unlike with welded joints, special sealing methods must be used when riveted joints are to resist the leakage of gas or
fluids.
Rivets are made from malleable materials and depend on deformation to fasten and hold components in place. They may be closed either in the red-hot or cold condition depending on the materials to be joined, their thickness and the rivet material. Some techniques for making riveted joints.
(Basic Manufacturing,(Third edition), Roger Timings,p 190)

Electron Beam Welding (EBW)

In EBW process, the heat is generated when the electron beam impinges on work piece. As the high velocity electron beam strikes the surfaces to be welded, their kinetic energy changes to thermal energy and hence causes the workpiece metal to melt and fuse.This process employs an electron gun in which the cathode in form of hot filament of tungsten or tantalum is the source of a stream of electrons. The electrons emitted from filament by thermionic emission are accelerated to a high velocity to the anode because of the large potential difference that exists between them. The potential differences that are used are of the order of 30 kV to 175 kV. The higher the potential difference, higher would be the acceleration. The current levels are low ranging between 50 mA to 1000 mA. The electron beam is focused by a magnetic lens system on the workpieces to be welded. The depth of penetration of the weld depends on the electron speed which in turn is dependent upon the accelerating voltage. When the high velocity electron beam strikes the work-piece all the kinetic energy is converted to heat. As these electrons penetrate the metal, the material that is directly in the path is melted which when solidifies form the joint. Electron beam welding has several advantages which may not be found in other welding processes. The penetration of the beam is high. The depth to width ratios lies between 10:1 to 30:1 can be easily realized with electron beam welding. It is also possible to closely control this penetration by controlling the accelerating voltage, beam current, and beam focus. The process can be used at higher welding speeds typically between 125 and 200 mm/sec. No filler metal or flux needs to be used in this process. The heat liberated is low and also is in a narrow zone, thus the heat affected zone is minimal as well as weld distortions are virtually eliminated. It is possible to carry out the electron beam welding in open atmosphere. For welding in vacuum, the work-piece is enclosed in a box in which the vacuum is created. When electron beam moves in the normal atmosphere, the electrons would be impinging with the gas molecules in the atmosphere and would thus be scattered. This scattering increases the spot size of the electron beam and consequently there is lower penetration. As the vacuum increases, the scattering effect of the electron beam decreases and hence, penetration increases. The other advantage of using vacuum is that the weld metal is not contaminated.
(Introduction to Basic Manufacturing Processes and Workshop Technology,Rajender Singh,p336-337)

Thermit Welding (TW)

It may be of forge or fusion kind of welding. Fusion welding requires no pressure. Thermit welding process is depicted in Fig. 17.29. It is a process which uses a mixture of iron oxide and granular aluminium. This mixture in superheat liquid state is poured around the parts to be joined. The joint is equipped with the refractory mold structure all around. In case of thermit pressure welding, only the heat of thermit reaction is utilized to bring the surface of metal to be welded in plastic state and pressure is the applied to complete the weld. The temperature produced in the thermit reaction is of the order of 3000°C. Thermit welding is used for welding pipes, cables, conductors, shafts, and broken machinery frames, rails and repair of large gear tooth.
(Introduction to Basic Manufacturing Processes and Workshop Technology,Rajender Singh,p335)

Laser Beam Welding (LBW)

Laser beam welding is a fusion welding process. Through the laser beam, the laser produces the energy necessary for welding. It is led to the focusing lens system by mirrors or optical fibers. The lens system then focuses the laser beam on the joint. Depending on the intensity generated there, different processes of beam–material interaction will take place. When the intensity is low, most of the radiation will be reflected by the workpiece, and only a very small part
will be absorbed by the metal in a thin layer (< 1μm) at the surface and transformed into heat. The energy input into the workpiece is achieved by heat conduction.With increasing intensity, the workpiece is locally heated by the laser radiation that is absorbed. When the melting temperature is reached, a molten puddle forms as the time of influence is increased. If the parameters are chosen so as to maintain a stationary state, the process is described as thermal conduction welding.
If, however, the intensity is further increased so that more energy is absorbed than can be dissipated by heat conduction, then the enormous energy density of the laser beam in the focus will cause the metal to vaporize. The pressure of the metal vapor that flows off creates a steam passage in the melt, the so-called keyhole. Typically, the diameter of such a capillary steam tube shows the magnitude of the beam diameter (0.1 to 1 mm). Characteristic threshold intensities for capillary formation lie in the range of 106W/cm2.
In laser beam penetration welding, the system of capillary steam tube and surrounding molten bath is led along the assembly line. The molten bath flows around the capillary on both sides, comes together behind it, and, when solidifying, forms a joint.
(Springer Handbook of Mechanical Engineering, Grote, Antonsson (Eds.),part B, p668-669)

Copolymers

In copolymers the polymer chain is composed of two or more types of monomers. The monomers can be arranged randomly, alternating, or as blocks (short molecule chains, consisting of the same monomer units). Another version is that blocks built from one type of monomer are fixed as side chains onto a backbone built from another monomer type. Common copolymers are polystyrene-butadiene-rubber (SBR) and acrylonitrilebutadiene- styrene (ABS).

(Springer Handbook of Mechanical Engineering, Grote, Antonsson (Eds.),part B, p2079)

Continuous Chip(in Metal Machining)

Continuous chips coming out during machining in machine shop. These types of chips are obtained while machining ductile material such as mild steel and copper. A continuous chip comes from the cutting edge of a cutting tool as a single one piece, and it will remain as one piece unless purposely broken for safety or for convenience in handling. Formation of very lengthy chip is hazardous to the machining process and the machine operators. It may wrap up on the cutting tool, work piece and interrupt in the cutting operation. Thus, it becomes necessary to deform or break long continuous chips into small pieces. It is done by using chip breakers. Chip breaker can be an integral part of the tool design or a separate device.
(Introduction to Basic Manufacturing Processes and Workshop Technology,Rajender Singh,p 402)