Fusion-Welding Processes CHAPTER 7-1

General Characteristics of Fusion Welding Processes

Oxyacetylene Flames Used in Welding Figure 27.1 Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing, flame. The gas mixture in (a) is basically equal volumes of oxygen and acetylene.

Torch Used in Oxyacetylene Welding Figure 27.2 (a) General view of and (b) cross-section of a torch used in oxyacetylene welding. The acetylene valve is opened first; the gas is lit with a spark lighter or a pilot light; then the oxygen valve is opened and the flame adjusted. (c) Basic equipment used in oxyfuel-gas welding. To ensure correct connections, all threads on acetylene fittings are left-handed, whereas those for oxygen are right-handed. Oxygen regulators are usually painted green, acetylene regulators red.

Shielded Metal-Arc Welding Figure 27.4 Schematic illustration of the shielded metal-arc welding process. About 50% of all large-scale industrial welding operations use this process. Figure 27.5 Schematic illustration of the shielded metal-arc welding operations (also known as stick welding, because the electrode is in the shape of a stick).

Multiple Pass Deep Weld Figure 27.6 A deep weld showing the buildup sequence of individual weld beads.

Submerged-Arc Welding Figure 27.7 Schematic illustration of the submerged-arc welding process and equipment. The unfused flux is recovered and reused. Source: American Welding Society.

Gas Metal-Arc Welding Figure 27.8 Schematic illustration of the gas metal-arc welding process, formerly known as MIG (for metal inert gas) welding.

Equipment Used in Gas Metal-Arc Welding Figure 27.9 Basic equipment used in gas metal-arc welding operations. Source: American Welding Society.

Flux-Cored Arc-Welding Figure 27.10 Schematic illustration of the flux-cored arc-welding process. This operation is similar to gas metal-arc welding, showing in Fig. 27.8.

Equipment for Electroslag Welding Figure 27.12 Equipment used for electroslag welding operations. Source: American Welding Society.

Designations for Mild Steel Coated Electrodes

Gas Tungsten-Arc Welding Figure 27.13 The gas tungsten-arc welding process, formerly known as TIG (for tungsten inert gas) welding. Figure 27.14 Equipment for gas tungsten-arc welding operations. Source: American Welding Society.

Plasma-Arc Welding Figure 27.15 Two types of plasma-arc welding processes: (a) transferred, (b) nontransferred. Deep and narrow welds can be made by this process at high welding speeds.

Comparison of Laser-Beam and Tungsten-Arc Welding Figure 27.16 Comparison of the size of weld beads in (a) electron-beam or laser-beam welding to that in (b) conventional (tungsten-arc) welding. Source: American Welding Society, Welding Handbook (8th ed.), 1991.

Example of Laser Welding Figure 27.17 Laser welding of razor blades.

Flame Cutting and Drag Lines Figure 27.18 (a) Flame cutting of steel plate with an oxyacetylene torch, and a cross-section of the torch nozzle. (b) Cross-section of a flame-cut plate showing drag lines.

Summary metal-arc welding Shielded metal-arc welding B Electrode Molten metal A B Electrode Extruded coating flux Molten metal Gas shielding A B Electrode Molten metal Granulated Powder metal-arc welding Shielded metal-arc welding Submerged arc welding A B Consumable Electrode (filler) Molten metal Inert gas Filler A B Oxygen gas Acetylene gas Gas flow control taps Inner cone Outer envelope Fig 6.3 Gas welding using Oxyacetylene torch. TIG A B Non-consumable Electrode Filler wire Inert gas TIG

(b) Welding applications. Simple butt joint Simple butt joint (Thick plate) Single “V” joint Single “V” joint (thick plate 4-30mm) Double “V” joint Double “V” joint (thick plate 20-25mm) Single “U” joint Single “J” joint (thick plate >25mm) (b) (a) (a) Welding joints (b) Welding applications.

Where, K: constant less than 1 related to heat losses. I : Current. R: Resistance of ionized air gap. t : Welding time.