Adhesives for Weldbonding

Most adhesives used for weldbonding are arbitrarily selected from adhesives that were developed for other purposes, resulting in a compromise when used for weldbonding. Adhesives specifically developed for weldbonding should have the following characteristics in addition to those mentioned above  

Viscosity should be low enough to be forced out of welding area by the pressure of the electrodes yet sufficiently high that it will not flow out of the joint during the cure cycle. For the flow-in process, the viscosity must be low enough to fill the joint via capillary pressure or with moderate vacuum or positive pressure. 

Metal fillers are often used to provide low electrical resistance between substrates. 

An adhesive layer with appropriate thickness and elastic modulus is necessary to obtain reasonable distribution of stresses in the region of a weldbond joint. A thin adhesive layer of high elastic modulus improves the fatigue properties of weldbonded joints.43 

The heat created by the spot welding process should not degrade the adhesive so as to weaken the final bond strength or create thermal decomposition products, which can contaminate and weaken the weld area. 

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