Hybrid joining is the combination of two or more joining techniques to produce joints with properties additional to those obtained from a single technique. The most common types of hybrid joint are used for joining sheet materials and involve an adhesive in conjunction with a point joint such as a fastener (rivet or threaded device), a clinched joint or a resistance spot weld.
Other examples of hybrid joints include a combination of two different fusion processes (e.g. MIG/MAG augmented laser welding) or a combination of two different types of adhesive (e.g. tape combined with paste).
Adhesive in conjunction with point joints
The main advantages of combining a point joining method with an adhesive are:
- continuous, leak-tight joint
- higher strength (generally)
- increased joint stiffness
- improved peel and impact resistance (point joint arrests crack growth in adhesive bond)
In general, adhesive is applied to the surfaces to be joined prior to assembly and fixing with point joints. The most widely used hybrid joining methods are:
- conventional fasteners plus adhesives/sealants
- resistance spot welding in combination with adhesives - is one of the most common hybrid joining technologies used in the high volume automotive sector. Use with structural adhesives, rather than low strength adhesives or sealants, is on the increase. The weld-bonding process is often fully automated and utilises robotic dispensing systems.
- rivets (including self-piercing types) in combination with adhesives - is increasingly used within the automotive sector. Riv-bonding can in many instances provide similar peak loading strengths to weld-bonding but has the advantage that it is a cold joining technology and can therefore be employed on a wider range of substrates including pre-painted materials.
In this variant, point joints are produced using clinching
technology. Clinch joints are not as strong as riveted or spot welded joints. Clinch-bonding, like riv-bonding, has the advantage of being a cold joining process but, with this technique, the only consumable is the adhesive. Clinch-bonding is used for niche applications in the automotive industry, e.g. window apertures involving steel to aluminium joints.
Conventional fasteners plus adhesives/sealants
Hybrid joining with conventional fastening systems is used extensively in many industries: from building and construction (attaching composite panels and glass), to the aerospace sector where the combination of fasteners and sealants is the main joining method for aircraft wing fabrication.
Invented by TWI, AdhFAST® is a hybrid joining technology which differs from the above methods in that the adhesive is introduced into the joint after
the structure has been assembled using fasteners.
Adhesive is injected into the joint through the specially designed AdhFAST® fasteners. The fasteners incorporate a means of controlling the spacing between the top and bottom substrates. This gives greater control of bond-line thickness and, therefore, improved process reliability and joint quality.
Comeld TM involves the use of a proprietary surface treatment technique in the joining of metals and composite materials. A Comeld joint combines adhesive bonding and mechanical interlocking to produce a joint with enhanced mechanical performance.
Comparison of static properties of point and hybrid joints in steel sheets. This PDF file (4.16MB) is only available to TWI Industrial Members.