Materially joining process

Adhesive-bonding is assigned to the materially joined processes. Bonding processes serve the production of joints of materials of the same kind or of material combinations. The term materially joined process , which also includes welding and soldering, derives from the fact that the bond occurs by a separately added material, that is... 

Glass has a very low thermal expansion coefficient the materials joined with glass have to be similar in expansion or must be duetile, while staying vacuum tight. Even with best-matched materials skilled craftsmanship is asked for the joining process. 

In any brazing/soldering process, a molten alloy comes in contact with a surface of solid, which may be an alloy, a ceramic, or a composite material (see Ceramics Composite materials). For a molten alloy to advance over the soHd surface a special relationship has to exist between surface energies of the hquid—gas, soHd—gas, and Hquid—soHd interfaces. The same relationships should, in principle, hold in joining processes where a molten alloy has to fill the gaps existing between surfaces of the parts to be joined. In general, the molten alloy should have a lower surface tension than that of the base material. 

Thermojunctions may be formed by welding, soldering or pressing the materials together. Such junctions give identical emfs (by law (iii)), but may well produce different currents as the contact resistance will differ depending on the joining process utilised. Whilst many materials exhibit thermoelectric effects, only a small number are employed in practice. The characteristics of the more common thermocouple materials are listed in Table 6.4. 

Sometimes conventional welding or a mechanical joining process is just not possible. Substrate materials may be incompatible for metallurgical welding due to their thermal expansion coefficients, chemistry, or heat resistance. The end product may not be able to accept the bulk or shape required by mechanical fasteners. 

This chapter certainly does not consider all possible substrates. However, the guidance that is offered should be sufficient for the user to select candidate joining processes and epoxy adhesive materials, no matter what substrate or combination of substrates is involved. 

A. Passerone and M.L. Muolo, Metal-ceramic interfaces wetting and joining processes. International Journal of Materials and Product Technology, 20(5-6), 420-439 (2004). 

In spite of the promise of this joining technique, very little information exists on actual material behavior under FSW conditions. The vast differences in the pin tool geometry and materials used in the various experimental and modeling studies have made it difficult to correlate the processing parameters with the microstructure development. However, some important aspects of FSW formation mechanisms have been illuminated that provide an effective framework for more focused investigations into some of the fundamentals of the joining process. 

Despite the successes to date, more work is needed for a complete understanding of FSW of titanium alloys. Development of new tool materials/designs is needed to increase tool life to a point where FSW of titanium alloys is cost-competitive with other joining processes. Moreover, an explanation for tool/workpiece material interactions is required. Better designs for FSW machines purpose-built for processing of titanium and higher-flow-stress/higher-temperature materials that can accommodate the heat lost to the tool holder are probably necessary. 

As human beings developed tools and weapons, sharp stones had to be fastened to handles to make axes and spears. Some of these were bound with vines, fibers, pieces of animal skin, or tendons or other body parts, and some had natural self-adhering properties to supplement the use of knots. To enhance the joining process, observing users soon smeared on sticky materials found locally. 

Potential adverse effects adhesion to hot metal surface, bubbling, increased mold cleaning frequency, lack of adhesion in joining processes, residue on the product surface, transfer to a material in contact, welding impairment... 

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