Weld-bonding process

Some processes employ conditions subsequent to adhesive assembly which may be detrimental to the adhesive itself. High impact staking is one example, welding another. However, it should be noted that some toughened epoxides have been specially developed for use in conjunction with spot-welding — the weld-bonding process. 

Transition joints are used to join dissimilar metals where flanged, screwed, or threaded connections are not practical. They are used when fusion welding of two dissimilar metals forms interfaces that are deficient in mechanical strength and the ability to keep the system leak-tight. Transition joints consist of a bimetallic composite, a stainless steel, and a particular kind of aluminum bonded together by some proprietary process. Some of the types in use throughout the cryogenic industry are friction- or inertia-welded bond, roll-bonded joint, explosion-bonded joint, and braze-bonded joint. 

Darwish, S. M. H., and Ghanya, A., Critical Assessment of Weld-Bonded Technologies, Journal of Materials Processing Technology, vol. 105, 2000, pp. 221-229. 

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... 

Film adhesives have been found by some workers to be impractical because spot-welds could not be made consistently, due to the carrier.On the other hand, film adhesives have been found to provide substantial benefits because they improve workmanship in the production facility. The first requirement for any adhesive for the weld-through process of weldbonding is that the adhesives have the capability of being moved under pressure of the welding electrodes in order for metal-to-metal contact to occur at the joint interface. The second requirement is that the heat resulting from the spot weld cause only limited detrimental effect on the strength of the bond. ... 

Polycarbonate parts having thickness of at least 40 mils can be successfully hot gas welded. Bond strengths in excess of 70 percent of the parent resin have been achieved. Equipment should be used capable of providing gas temperature of 315 to 648°C. As prescribed for the heated tool process, it is important to adequately predry (120°C) both the polycarbonate parts and welding rods. The bonding process should occur within minutes of removing the parts from the predrying oven. 

In contrast to the aerospace industry (see Aerospace applications), conditions prevailing in automobile manufacture dictate that pre-treatments (see Pre-treatment of aluminium) should have short process times and be tolerant of production variables. The surfaces produced should retain adequate bonding properties during extended storage under poorly controlled conditions. The surface may need to be sufficiently conductive to permit weld-bonding techniques. Pre-treatments applied at the coil stage must be compatible with mill oils and press lubricants, and withstand mechanical deformation in the press. 

One of the fastest methods of bonding ABS and acetal thermoplastics is induction welding. This process usually takes 3 to 10 s, but can be done in as little as 1 s. During welding, a constant pressure of at least 100 Ih/in should be applied on the joint to minimize the development of bubbles this pressure should be maintained until the joint has sufficiently cooled. When used, metal inserts should be 0.02 to 0.04 in thick. Joints should be designed to enclose the metal insert completely. Inserts made of carbon steel require less power for heating althougdi other types of metal can be used. The insert should be located... 

---