Why Do We Bond and Rivet On Modern Automobiles
Riveting of vehicle panels (especially aluminium) is becoming more of the norm nowadays but it is still mostly applicable to the more expensive vehicles. Over the last 20 years, manufacturers have developed there techniques and equipment have become more sophisticated. The first SPR was invented by Ralph Furhmeister in his garage and was picked up by Jaguar Landrover for use in its aluminium bodied vehicles.
Slowly more types of rivet have been invented such as, Flow Form, Blind and POP riveting. This has been the preferred way of joining aluminium as spot welding is very difficult in production and cannot be reproduced in aftermarket body repair full stop. You require 5 times the power to spot weld aluminium compared to steel and these sort of outputs are just not available in body repair shops.
Legislation has helped in pushing vehicles to become lighter and more C02 efficient. The introduction of the EU directive 443/2009 gave a limit to the maximum permissible values for C02. To reinforce this higher taxes would be implemented and also manufacturers fined.
This pushed manufacturers to increase energy efficiency and reduce weight. They experimented with joining aluminium, magnesium, plastics, composites, and AHSS steels together in varying degrees and this could only be performed by bonding and riveting. A typical steel vehicle has up to 6000 spot welds, a riveted shell maybe 3500 rivets. This and the use of lighter materials and fewer joints means shells could be made lighter, stronger and quicker.
Different rivets are used in different parts of the vehicle, this is critical especially in SPR. The Length of the rivet must be correct for that part of the vehicle otherwise the anvils cannot form the SPR correctly and the joint will not be strong enough. In the video, you can see the SPR is forced into the panels and the rear anvil forces the legs of the rivet to spread. They shouldn't breakthrough and the rivet face must be flush. To stop incorrect rivets being used many manufacturers produce there own rivets and these are supplied with the new panel for repair.
Many Rivets are also specially coated so that they do not corrode or cross-contaminate the panels to be joined. A zinc coating tends to be used on steel, zinc, and tin used on aluminium with a bake temperature up to 160 degrees centigrade.
There is also a special coating called Almac used on temperatures over 180 degrees Centigrade.
Blind rivets or break stem rivets are tubular fasteners with a mandrel through the centre. Blind rivets are inserted into drilled holes in the parts to be joined, and a special tool is used to draw the mandrel through the body of the rivet. The blind end expands, and the mandrel is snapped off. Unlike solid rivets, blind rivets can be installed in joints from only one side of the part—making them “blind” to the opposite side.
SPR or Self Piercing Rivets can be used with no preparation. The action of the rivets piercing the material forces it into the shaping anvil behind forcing the legs of the rivet to splay. This with the correct force applied gives the required strength.SPR rivets can be used to join dissimilar materials together as well as similar.
Flow form rivets are used when you have an existing hole.or on structural panels where there has been an existing SPR. They can be used on steel, aluminium, composites, and plastics. Flow form Rivets require higher squeeze pressures up to 9 Kn
Manufacturers use adhesive bonding and rivet bonding in aftermarket repair, there are several reasons for this but the main ones are more temperature-sensitive materials being used and corrosion resistance of the joint (many manufacturers have warranties now up to 12 years).
There will always be some welding though so getting VIN specific repair methods is critical nowadays for a correct repair.
Always ensure your bond is correct for the vehicle and the joint and also ensure its in date as some are age-sensitive. Different bonds have different preparation criteria so again always check.
As part of joint preparation for instance on aluminium some manufacturers such as Jaguar Landrover and BMW us a joint preparation system called Pyrosil Suralink 021. This makes the surfaces to be joined extra tacky and enables better adhesion.
Bonding on its own is not structural, you will always find bonding with a mechanical property. This could be a spot weld, rivet or bolt etc.
Bond peels or "zips", if you can split from the start of the joint. This zipping effect is reduced if a mechanical is incorporated.
The result is that bonding and riveting are going to be more prevalent as newer more exotic steels, aluminium and plastics need to be joined together for strength and weight saving. Welding these different materials together becomes increasingly difficult therefore we feel riveting and bonding is here to stay.