Suitability, Compatibility, and Capability Critical When Using Adhesives in Assembly Operations

Posted on 11/23/2021 10:09:25 AM By ASC

When manufacturers are looking to use adhesives in an assembly operation, three steps must enter into the decision process: suitability, compatibility, and capability.

Suitability means there has been discernment that an adhesive is either necessary or desirable. When welding either metals or thermoplastics, the two materials to be joined must be metallurgically or polymerically compatible. That is frequently not the case when joining dissimilar metals, and it is almost always the case when joining dissimilar polymers. Even metals within the same general class (e.g., steels, aluminum) may not be metallurgically compatible, and polymers within the same class (e.g., polyethylene) may not weld to each other.

Mechanical fastening requires holes or some form of crimp/puncture, which results in poor stress distribution and the need for increased material thickness since all the load is borne by point contacts. This is often overcome by including adhesives with mechanical fasteners, which results in more even load distribution with attendant weight and material savings. It also enables the joining of dissimilar materials. In the absence of welding or fastening, adhesive bonding is the suitable choice.

Compatibility refers to an adhesive’s ability to bond to both surfaces. This can be an issue when joining dissimilar materials because the surface adhesion characteristics differ. Examples include joining a polymer or composite to a metal or joining different metals. Different adhesive types have differing abilities to bond to different materials.

Epoxy adhesives have been the traditional choice for bonding ceramics or metals, as well as composites. However, they are less frequently used for bonding polymers. Acrylic adhesives work well on most types of materials and are used for metals, composites, and polymers. They have lower strength and temperature resistance than epoxies.