D3. joint assembly methods - Assembly methods for parts to be adhesively bonded parallel those for the assembly of parts to be fastened by other methods. The methods discussed below in section F are applicable. Adhesive dispensing usually is part of the assembly operation. Dispensing is facilitated by equipment that is operated manually, with a foot pedal, or with some degree of automation. For the kinds of adhesives that require some curing step such as the application of heat, radiation energy, or placement of the assembly in an oven, the operation and control of such apparatus is usually part of the assembly operation. It sometimes is necessary to hold the parts to be bonded during curing, and the fixtures to do this are manipulated as necessary by the assembly operator. When the assembly is automated to some degree, with robots or dedicated equipment, the dispensing and curing steps are similarly automated. Robots are capable of being set to spray, dispense, or otherwise apply an adhesive, and then assemble the adhesive-coated part to other parts, or to a fixture. Dedicated mechanical equipment often provides for dispensing and curing of adhesive as well as mechanical assembly operations.

D4. curing methods - All adhesives (except pressure sensitive types) require some physical or chemical change after application and assembly in order to achieve holding power. Curing normally involves a change from the liquid or semi-liquid state to the solid state. The change is brought about by one of several mechanisms: cooling, evaporation of solvents, or polymerization. Polymerization, as exemplified by epoxy and silicone adhesives, is usually brought about by heating, but with the proper catalysts, it can take place at room temperature.

In other situations, with thermosetting adhesives, polymerization is initiated by some other factor: Anaerobic adhesives polymerize at room temperature in the absence of air (oxygen). Contact with some metals yields metallic ions that act as catalysts for rapid curing. (These adhesives are used frequently by machinists to lock metal screw fasteners in place, or lock pulleys or gears to shafts).

Other adhesives, (acrylics), polymerize when exposed to ultraviolet (UV) light. One application is for dental fillings, particularly those that are visible and must match the tooth color. These can be cured in a short time at body temperature with a directed exposure to UV light. Another adhesive, a modified acrylic, cures at room temperature when an activator is applied to one of the bonding surfaces and the adhesive is applied to the other surface. No mixing is required. Other radiation sources that may be used for some adhesives are visible light, infra red light, electron-beam or microwave. The cyanoacrylate adhesives (“super glues”) are single component liquids that start to polymerize in only a few seconds from ambient humidity in the air or moisture on the adherend surface. Almost any surface has sufficient moisture to initiate polymerization. The cure takes place at room temperature. These adhesives cure more quickly if the workpiece surfaces are slightly alkaline. They are applied sparingly to only one surface of the joint. They are most useful for bonding small assemblies and are employed in adhering plastic parts.

Silicone and urethane adhesives and sealants polymerize from reaction with ambient moisture. They are used when flexibility is required in the joint. Silicone is particularly advantageous when sealing is required in wet environments subject to temperature changes.

Hot melt adhesives change from solid to liquid or semi-liquid when heated. They then flow to wet the surfaces of the joint and, when cooled, change to solids and gain sufficient holding strength.

Adhesives that harden from evaporation are often either water emulsions such as polyvinyl acetate (white glue) or hydrocarbon-solvent-based (rubber cement and household glue). Phenolics, and polyurethanes can also be solvent-based. Porous substrates such as paper or wood aid in evaporation of the solvent.