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Chapter 32: Resistance and Solid-State Welding Processes

Chapter 32: Resistance and Solid-State Welding Processes. DeGarmo’s Materials and Processes in Manufacturing. 32.1 Introduction. Electrical resistance heating to form the joint. Create joints without any melting of the workpiece or filler material, know as solid –state welding process.

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Chapter 32: Resistance and Solid-State Welding Processes

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  1. Chapter 32:Resistance and Solid-State Welding Processes DeGarmo’s Materials and Processes in Manufacturing

  2. 32.1 Introduction • Electrical resistance heating to form the joint. • Create joints without any melting of the workpiece or filler material, know as solid –state welding process.

  3. 32.2 Theory of Resistance Welding • Both heat and pressure are used to induce coalescence. • Electrodes contact the material, and electrical resistance heating is used to raise the temperature of the workpiece and the interface between them. H=I2Rt H = total heat input in joules I = current in amperes R = electrical resistance in ohms t = time in seconds

  4. Basic Resistance Welding FIGURE 32-1 The basic resistance welding circuit. • Total resistance: • The bulk resistance of the electrode and workpieces. • The contact resistance between the electrode and the workpieces. • The resistance between the surfaces to be joined, known as the faying surfaces.

  5. Resistance Welding Temperature Distribution FIGURE 32-2 The desired temperature distribution across the electrodes and workpieces during resistance welding. Water cooling is usually used to keep the electrode temperature low and thereby extend their useful life.

  6. Current and Pressure for Resistance Welding FIGURE 32-3 A typical current and pressure cycle for resistance welding. This cycle includes forging and postheating operations. Applying pressure promotes a forging action, so resistance welds can be produced at lower temperatures than welds made by other processes.

  7. 32.3 Resistance Welding Processes • Resistance spot welding • Resistance seam welding • Projection welding Mass production

  8. Schematic of Resistance Spot Welding (RSW) FIGURE 32-4 The arrangement of the electrodes and workpieces in resistance spot welding.

  9. Microstructure of a Resistance Weld FIGURE 32-5 A spot-weld nugget between two sheets of 1.3-mm (0.05-in.) aluminum alloy. The nugget is not symmetrical because the radius of the upper electrode is greater than that of the lower electrode. (Courtesy Lockheed Martin Corporation, Bethesda, MD.)

  10. Tear Test FIGURE 32-6 Tear test of a satisfactory spot weld, showing how failure occurs outside of the weld.

  11. Spot-Welding Equipment FIGURE 32-7 Single-phase, air-operated, press-type resistance welder with microprocessor control. (Courtesy Sciaky Inc., Chicago, IL.) Rocker-arm machine: for light-production work where complex current-pressure cycles are not required. Press-type welder: for larger spot welds used at high production rates.

  12. Spot Welding Application Monel: Alloy of Nickel, Copper, Iron and Manganese, with antacidity

  13. Resistance Seam Welding (RSEW) FIGURE 32-8 Seam welds made with overlapping spots of varied spacing. (Courtesy Taylor-Winfield Corporation, Brookfield, OH.) • Gas- or liquid-tight welding • Resistance butt welding

  14. Schematic of Seam Welding FIGURE 32-9 Schematic representation of the seam-welding process. those

  15. Tube Welding FIGURE 32-10 Using high-Squeeze roll frequency AC current to produce a resistance seam weld in buttwelded tubing. Arrows from the contacts indicate the path of the high-frequency current

  16. Projection Welding FIGURE 32-11 Principle of projection welding (a) prior to application of current and pressure and (b) after formation of the welds. For mass-production operation, not only one spot weld at a time.

  17. 32.4 Advantages and Limitations of Resistance Welding • Advantages • Rapid • Fully automated • Conserve material, no filler metal, shielding gases, or flux • Minimal distortion • Skilled operation are not required • Dissimilar metals can be easily joined • High degree of reliability and reproducibility

  18. 32.4 Advantages and Limitations of Resistance Welding (continued) • Limitations • High initial cost • Limitation to thickness of material (less than 6mm) • Both sides of the joint require to apply the proper electrode force or pressure • Skilled maintenance on servicing the equipment • Some materials need special preparation prior to welding

  19. Process Summary for RW

  20. 32.5 Solid-State Welding Processes • Forge welding • Forge-seam welding • Cold welding • Roll welding or roll bonding • Friction welding and inertia welding • Friction stir welding • Ultrasonic welding • Diffusion welding • Explosive welding

  21. Forge Welding (FOW) • The most ancient of the welding process • Using a charcoal forge, the blacksmith heated the pieces to be welded to a practical forging temperature (by color) and then prepared the ends by hammering (hammer and anvil) so that they could be properly fitted together.

  22. Forge-Seam Welding • Still used in the manufacture of pipe – a heated strip of steel is first formed into a cylinder, and the edges are simply pressed together in either a lap or a butt configuration. • Welding is the result of pressure and deformation.

  23. Cold Welding FIGURE 32-12 Small parts joined by cold welding. (Courtesy of Koldweld Corporation, Willoughby, OH.) A variation of forge welding uses no heating but produces metallurgical bonds by means of room-temperature plastic deformation.

  24. Roll Welding or Roll-Bonding (ROW) Two or more sheets or plates of metal are joined by passing them simultaneously through a rolling mill. Perform either hot or cold and can be used to join either similar or dissimilar metals. FIGURE 32-13 Examples of roll-bonded refrigerator freezer evaporators. Note the raised channels that have been formed between the roll-bonded sheets. (Courtesy Olin Brass, East Alton, IL.)

  25. Friction Welding (FRW) FIGURE 32-14 Sequence for making a friction weld. (a) Components with square surfaces are inserted into a machine where one part is rotated and the other is held stationary. (b) The components are pushed together with a low axial pressure to clean and prepare the surfaces. (c) The pressure is increased, causing an increase in temperature, softening, and possibly some melting. (d) Rotation is stopped and the pressure is increased rapidly, creating a forged joint with external flash.

  26. Schematic for Friction Welding FIGURE 32-15 Schematic diagram of the equipment used for friction welding. (Courtesy of Materials Engineering.)

  27. Inertia Welding FIGURE 32-16 Schematic representation of the various steps in inertia welding. The rotating part is now attached to a large flywheel.

  28. Examples of Friction Welding FIGURE 32-17 Some typical friction-welded parts. (Top) Impeller made by joining a chrome–moly steel shaft to a nickel–steel casting. (Center) Stud plate with two mild steel studs joined to a square plate. (Bottom) Tube component where a turned segment is joined to medium-carbon steel tubing. (Courtesy of Newcor Bay City, Division of Newcor, Inc., Royal Oak, MI.)

  29. Friction-Stir Welding (FSW) • First performed by the Welding Institute of Great Britain in 1991 • A nonconsumable welding tool (shoulder + protruding cylindrical or tapered probe or pin) is rotated at several hundred revolutions per minute. • Most common application is the formation of butt welds, usually between plates of the lower-point metals (both wrought and cast alloys) or thermoplastic polymers.

  30. Schematic of Friction-Stir Welding FIGURE 32-18 Schematic of the friction-stir welding process. The rotating probe generates frictional heat, while the shoulder provides additional friction heating and prevents expulsion of the softened material from the joint. (Note: To provide additional forging action and confine the softened material, the tool may be tilted so the trailing edge is lower than the leading segment.)

  31. Example of Friction-Stir Welding FIGURE 32-19 (a) Top surface of a friction-stir weld joining 1.5- mm- and 1.65-mm-thick aluminum sheets with 1500-rpm pin rotation. The welding tool has traversed left-to-right and has retracted at the right of the photo. (b) Metallurgical cross section through an alloy 356 aluminum casting that has been modified by friction-stir processing.

  32. Features of Friction-Stir Welding

  33. Ultrasonic Welding (USW) • Coalescence is produced by the localized application of high-frequency (10,000 to 200,000 Hz) shear vibrations to surfaces that are held together under rather light normal pressure. • Some heating is existed at the faying surfaces, but the temperature at the interface is rarely exceeds one-half of the melting point of the material.

  34. Schematic of Ultrasonic Welding FIGURE 32-20 Diagram of the equipment used in ultrasonic welding

  35. Application of Ultrasonic Welding

  36. Diffusion Welding (DFW) • Joining surfaces are maintained in contact under sufficient pressure and time at elevated temperature. • Frequently used to join dissimilar metals and composite materials.

  37. Explosive Welding (EXW) FIGURE 32-21 (Left) Schematic of the explosive welding process. (Right) Explosive weld between mild steel and stainless steel, showing the characteristic wavy interface.

  38. Reference Problems • Review Questions • 4, 5, 9, 12, 21, 28, 32, 34, 37

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