B4. Induction brazing (IB) - is the same process described above in paragraph A2h but applied to brazing alloys rather than solders. It is used when the assembly has a shape to lend itself to placement of induction coils and when high-strength, heat-resistant joints are needed. The technique is widely used in brazing and is well adapted to brazing alloys except those that are in the high range of melting temperatures. Filler metal can be fed by the operator but is more commonly prepositioned before the induction heating operation. Flux is normally required though some induction brazing is done in a protective atmosphere. The process has the same advantages for brazed joints as for soldered joints: localized heating, fast process time, accurate control of heat, and uniform results with less need for operator skill. However, unique coils are usually needed for each assembly and development of the right coupling between the coil and workpiece may take some development. Induction brazing is used for aerospace components, appliance assemblies, industrial equipment, hand and machine tools, and hose and tubing fittings. Fig. 7A2h is also illustrative of brazing applications.

B5. dip brazing - similar to dip soldering. The assembly or the joint is immersed in molten filler metal, which is covered by a layer of molten flux. Filler metal flows into the joint but also will coat other portions of the workpieces immersed in the bath. Primarily for this reason, the process is not widely used. The method normally is restricted to small assemblies and only some brazing alloys.

B6. salt bath brazing - The parts to be brazed are immersed in a bath of molten salt that is maintained at a temperature slightly above the melting temperature of the filler metal. The method has a number of advantages: heating is rapid but overheating can be avoided; the bath provides protection against oxidation. Because of this, fluxing is often not required. However, fluxing agents may also be part of the salt bath. The salt bath also prevents decarburization of the workpiece (though it can occur after the workpiece is removed from the salt bath). Preheating is advisable to prevent the salt from freezing around the joint area of a cold workpiece. Multiple joints can be salt-bath brazed in one operation. The process is also useful for hidden joints. Carburizing and cyaniding can be performed in the same salt bath. Parts must be held in fixtures or held together by other means and the filler metal must be assembled to the joint beforehand. The brazed assembly is washed afterward to remove the salts, since trapped salts cause corrosion. Salt bath brazing is used with aluminum, copper, and ferrous alloys but is especially suited to aluminum.

B7. Resistance brazing (RB) - uses resistance to electrical current in both the workpieces and the electrodes that contact them to provide the heat necessary to melt the brazing filler alloys. The parts are pressed together between two electrodes and the current flows through both the electrodes and the parts. The parts heat up and additional heat is conducted from the electrodes to the parts. The method is best adapted for lower-melting-temperature silverbrazing alloys. Carbon electrodes are often used. Regular resistance welding machines can be utilized for the operation. As with other brazing operations, a flux is needed. The method can provide very rapid brazing with precise, repeatable, high quality results. Equipment is economical. However, the process is best suited for small workpieces or small joints in larger assemblies. It is used for electrical components such as cable connectors and contacts. It is not suitable for large or complex assemblies. Fig. 7B7 illustrates the process.

Fig. 7B7 Resistance brazing.

B8. diffusion brazing - is a variation of brazing in which the filler metal not only wets the surfaces to be joined but actually diffuses into them. The term diffusion bonding is sometimes used, although that term applies to diffusion welding also, when there is no filler metal. The process is the similar to diffusion welding as described in paragraph C13g but a foil of different material (a brazing alloy) is placed between the two surfaces of the joint. The brazing alloy melts and, under prolonged heating, diffuses extensively into the base metal. Diffusionbrazing is most common when dissimilar metals are to be joined, and in the aerospace industry where it is used to bond titanium, nickel, cobalt, and aluminum alloy components. The furnace processing cycle can require from 1 / 2 to 80 hours or more 1 . Fig. 7B8 illustrates the progression of a diffusion-brazed joint where the diffusion is extensive enough that the identity of the original joint is lost.

Fig. 7B8 Diffusionbrazing with extensive diffusion of the brazing alloy: a) The brazing alloy is placed between two base-metal workpieces. b) Heat causes the brazing alloy to melt. c) Further heating causes the brazing alloy to diffuse into the base metals. d) After prolonged heating, the brazing alloy is fully diffused and the original junction of the two workpieces is no longer visible.