Chapter 29 - Goodheart-Willcox

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Figure 29-9. Underwater welding electrode holder. Note that the holder is well insulated, with no bare metal areas exposed. (Broco, Inc.) Solid-State Welding Processes The American Welding Society lists nine processes and four subprocesses in the solid-state welding group. Refer to Figure 2-6. Solid-state welding (SSW) may be defined as a group of welding processes that produce a fusion weld by application of pressure at a welding temperature below the melting temperature of the base metal and filler metal. Solid-state welding may be done cold, warm, or hot, but never above the melting temperature of the base or filler metal. The following sections describe some of the more common solid-state welding processes. Friction Welding (FRW) When two objects are rubbed together, they generate heat. This principle is the basis of friction welding (FRW). Figure 29-10 shows the steps in a friction weld. One part is held stationary, while the other part is held in a chuck and rotated rapidly. The parts are pressed tightly together. Friction heats the two parts to their welding temperature. The welding temperature is lower than the solidus of either part, but high enough to allow fusion under pressure. When the welding temperature is reached, the rotation is stopped. The parts are then suddenly forced together under heavy pressure. After the heavy pressure is applied, the parts are held firmly until they cool. The finished weld is strong, with complete fusion over the entire joining surface. As shown in Figure 29-10, the weld is upset (enlarged) where the parts meet. Friction welds are often produced in less than 15 seconds. Friction welding has been used successfully to join some dissimilar (unlike) metals that normally cannot be welded by other processes. Friction Stir Welding (FSW) Friction stir welding (FSW) is similar to friction welding except a rotating tool, not a rotating part, creates the heat. This welding process was developed at TWI, Cambridge UK in 1991. 356 A special rotating tool, firmly pressing on the parts to be welded develops heat. The rotating tool has a wide shoulder and a probe or pin that penetrates the parts along the weld joint. Friction created by the rapidly rotating tool softens the base metals and the base metals are mixed together. Full penetration welds can be made. Figure 29-11 shows a drawing of the process and a completed butt weld. Ultrasonic Welding (USW) Sound waves can cause vibrations in objects. For example, a loud stereo can make the walls vibrate. In ultrasonic welding (USW), a very high-pitched sound is used to vibrate the surfaces of the metals to be welded. Ultrasonic welding has many advantages. Since there is literally no heat, there is no metal distortion. Fluxes and filler metal are not needed. Very thin metals can be joined easily. Ultrasonic welds are normally small welds like resistance spot welds. Seam welds can also be made. Figure 29-10. The steps in making a friction weld on two pieces of 1″ (25.4 mm) diameter carbon steel. The rod at the left is spun at a high speed. The rod at the right is then forced against it. Friction creates enough heat to produce a strong weld. Welding Technology Fundamentals A B Figure 29-11. A—A rapidly rotating tool with a large shoulder and a probe to penetrate the parts being welded softens the base metal. The base metals are welded together by stirring and mixing. B—A completed friction stir weld is shown. (TWI) Figure 29-12 shows a schematic of an ultrasonic weld in process. The parts to be joined are placed between two tips, as in resistance spot welding. An electronic device called an ultrasonic transducer causes either a wedge-reed or a lateral drive to vibrate extremely fast. This, in turn, causes a sonotrode (sound electrode) to vibrate. A slight force is applied to the parts through the sonotrode. The vibrations break up surface films, causing the parts to bond together without heat. An ultrasonic weld is completed faster than a resistance spot weld. Ultrasonic welds can be made on similar or dissimilar metals. Other Welding Processes Other welding processes are those that do not meet the definition of arc welding, oxyfuel gas welding, resistance welding, or solid state welding. These other welding processes are listed in Figure 2-6, Master Chart of Welding, Joining, and Allied Processes. The most common of these processes will be explained in the following pages. Chapter 29 Special Welding and Cutting Processes Laser Beam Welding (LBW) A laser creates a beam of light with a high energy density. This light energy is emitted from the laser beam welding (LBW) machine as energy particles called photons. The photons produce heat by striking, and having their energy absorbed by, the base metal. The most popular lasers include the Nd:YAG (neodymium-doped yttrium aluminum garnet) crystal laser and the CO 2 gas laser. A schematic view of a CO 2 laser is shown in Figure 29-13. Electrical energy is Reed Sonotrode tip Anvil Clamping force Wedge Vibration Weldment Ultrasonic transducer Figure 29-12. A schematic drawing of the wedge-reed ultrasonic welding principle. A small spot weld is made by vibrating the reed while it is in contact with the base metal. (Sonobond Ultrasonics, Inc.) Turning mirrors CO 2 laser tube Full reflecting mirror Electrodes Partially reflecting mirror Shutter Laser beam Lens Weld Workpiece Figure 29-13. A carbon dioxide (CO 2 ) laser welding machine. Mirrors reflect and aim the laser beam and a lens focuses it. The beam is released to make the weld when the shutter opens. 357
generally used to excite the lasing material in the laser source, releasing photons. Photon energy is allowed to build up in the laser or laser welding machine until the desired level is reached. The energy is then released to fuse the weld joint. Fusion occurs at the point where the laser beam strikes the weldment. Laser beams may be continuous or pulsed. They can be focused with lenses to a very small and accurate beam. Their direction can be changed through the use of mirrors. Electron Beam Welding (EBW) Figure 29-14 shows the basic parts of an electron beam welding (EBW) machine. Electrons are emitted from the electron gun. They are then focused and directed at the weld joint. The kinetic energy of the electrons creates the heat for welding. Kinetic energy is the energy of an object in motion. In this case, the objects in motion are the electrons. Electron beam welding may be done in a high vacuum, a partial vacuum, or under normal atmosphere pressure. A vacuum is a condition in which atmospheric pressure in a closed vessel has been decreased. This is done by pumping out air. Figure 29-15 shows an electron beam welder in use in industry. The beam energy is easier to direct under high vacuum conditions. Also, less energy is lost in a vacuum. 358 Column valve Optics Magnetic lens Deflection coil High vacuum 3″ 75 mm Base metal Weld joint Upper column Electron gun Vacuum chamber Figure 29-14. The basic parts of an electron beam welding machine shown in schematic form. Note that, in this machine, the weldment is mounted in a vacuum chamber. (PTR-Precision Technologies, Inc.) Advantages of Laser and Electron Beam Welding Laser and electron beam welding machines are made in a variety of energy levels. The greater the electrical energy input, the greater the energy output. Nd:YAG lasers are produced in sizes from 100W–4000W (watts). CO 2 lasers are produced in sizes from 500W–25,000W. A 600W Nd:YAG laser will penetrate steel .01″ (2.5 mm) in thickness. Electron beam welding machines are produced in sizes from 1kW–100kW (kilowatts). A 100kW EB welding machine will produce 100% penetration on steel 10″ (254 mm) thick. See Figure 29-16. Laser beam and electron beam welding offer these advantages: Figure 29-15. This electron beam welding machine comes with an optical viewing system, video, wire feed, vacuum chamber, and CNC technology. (PTR-Precision Technologies, Inc.) Figure 29-16. A cross section of an electron beam weld. Notice how thin the weld is in relation to the metal thickness. (PTR-Precision Technologies, Inc.) Welding Technology Fundamentals • Low heat input. • Controlled welding atmospheres. • The ability to weld dissimilar metals. • The ability to weld parts as thin as .001″–.002″ (.025 mm–.050 mm). • No need for filler metal. • Very precise aiming of beams to produce accurate and repeatable welds. Special Cutting Processes Special cutting processes using oxyfuel gas and oxygen arc cutting equipment have been developed for use in underwater salvaging and repairs. Other special thermal cutting processes were developed to 6 5 4 3 2 1 7 23 Chapter 29 Special Welding and Cutting Processes 8 9 25 24 10 11 26 27 12 28 permit the cutting of nonferrous metals and even concrete. These processes make it possible to cut metals that cannot be cut using regular oxyfuel gas cutting. Oxyfuel Gas Cutting (OFC) Underwater Underwater cutting is often done to repair underwater structures. It is also used to cut and salvage sunken ships. Oxyfuel gas cutting (OFC) is a process that can be done underwater, using a special torch. The torch is similar to the regular OFC torch, with two major changes. First, an air jacket is installed around the cutting tip. Second, a tube is added to carry compressed air to the air jacket, Figure 29-17. Oxygen and fuel gas are mixed in the torch and burned at the tip, as in a regular cutting torch. A cutting oxygen valve and lever directs pure oxygen through 39 40 1–Air jacket 14–H. P. valve plug 30–“O” ring (friction) 2–Lock nut 15–Valve spring 31–“O” ring (sealing) 3–Tip nut 16–Seat holder assembly 32–“O” ring retainer 4–Oxygen-hydrogen tip 17–Seat holder 33–Valve stem Sizes 2 to 7 18–Seat screw 34–Bolt for lever Oxygen acetylene 19–Seat 35–Lock washer Sizes 1 to 4 20–Oxygen connection 36–Acetylene control valve assembly 5–Gasket 21–Nut Valve stem assembly 6–Torch head 22–Tailpiece Control valve body 7–H. P. oxygen tube 23–Mixing chamber tube 37–Nut 8–H. P. oxygen tube coupling nut 24–Mixing chamber nut 38–Tailpiece 9–Ferrule 25–Spiral mixer 39–Compressed air tube 10–Lock nut 26–Acetylene tube 40–Compressed air tube coupling nut 11–Barrel 27–Inner oxygen tube 41–Oxygen valve stem assembly 12–Rear H. P. oxygen tube 28–Lever 42–Compressed air valve assembly 13–Body 29–H. P. valve “O” ring retainer assembly Valve body Valve stem assembly 30 15 13 14 16 17 Figure 29-17. A cross-sectional drawing of an underwater oxyfuel gas cutting torch. The air valve, part #42, controls the airflow to the air jacket, part #1. The air flow is shown in cross-hatched light green with red arrows. This high-pressure air keeps water away from the cutting tip. (Victor Equipment Co.) 29 31 OXY 32 41 33 18 19 34 20 21 36 35 37 22 38 42 359
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Chapter 29 - Goodheart-Willcox

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