Jaguar Cars and Henrob are teaming up to develop a new generation of self-piercing rivet systems.
Self-piercing riveting (SPR) is an automated joining process which can join dissimilar metals without any holes being drilled.
Self-piercing riveting provides static strength which is at least equal to that provided by spot welding. As it is a cold process, SPR requires no water cooling, and its power consumption is about one-tenth that of spot welding.
The major application of SPR has been up and running at Castle Bromwich since December 2002, where it is being used in the manufacture of aluminium bodies for Jaguar's new XJ saloon.
Meanwhile, a next generation SPR machine is being tested out for Jaguar's S-Type saloon at Castle Bromwich. Under this system, low feed rivet-setting tools are used to assemble the mixed-metal front bumper that had previously been a bolted unit.
However, Jaguar's plans to use aluminium in other vehicles means the pressure is on for even more advanced joining systems that are even faster, lighter, more compact and cheaper.
Under the SPR system currently in use on the XJ, hydraulic or electric servo riveting guns use either tape-feed (with spools containing 2,500 to 10,000 rivets) or cassettes (with 200 rivets), to apply the rivet to the joints. But blow feed delivery, which is now being tested on the S-Type line, looks perfect to be the next step.
The XJ saloon's new aluminium body is a big single high-volume application of Henrob's SPR technology.
Around 3,180 rivets are used in the body with advanced aerospace adhesives, around 30% of which are applied using 55 manual rivet setting tools.
There are another 148 robotic and automatic riveting tools. Each body contains 16 different types of rivet; together the rivets in each car body weigh 4.5kg.
Developments in the SPR system will focus on producing lightweight carbon fibre C-frame riveting tools to allow for faster robot acceleration and shorter total cycle time.
In addition, these would make it easier to specify smaller, cheaper robots.
Another focus for development will be on producing lighter weight guns which use blow feeders to deliver rivets to the tool head. These, too, would reduce inertia and hence faster operation, significantly cutting cycle times.
Blow feed rivets can be used with both hydraulic and electric servo riveting systems. Hydraulic systems tend to be cheaper. They are used mainly for manual production of prototypes.
Electric servo riveting tools provide fast cycle times and low energy consumption; they are also simpler to mount on robots. Many of Jaguar's riveting guns use tape-fed rivets, although blow feed rivets are cheaper.
Mark White, manager body structures at Jaguar's Whitley, Coventry engineering centre, says SPR is still an immature technology.
"There has probably only been about 10 years of SPR technology compared with some 30 years of robot technology. So there is still some way to go."
The fact that SPR can be used to join dissimilar metals has proved very useful to Jaguar, as it uses seven material types in its XJ body: five different grades of aluminium and two steel types.
There are also 31 different material grade and thickness variants. Multi-sheet joints can comprise two-sheet, three-sheet and four-sheet materials. Indeed, Jaguar has a four-thickness production joint (one 1.5mm-thick and three 2mm-thick sheets of Al 5754 aluminium material using servo riveting technology).
Henrob began testing sheet material joints in April 1998 working with Ford and Alcan on the carmaker's aluminium intensive vehicle (AIV) and P2000 car programmes.
Special aspects of the XJ work included increased use of Robcad to determine optimum rivet setter size and shape; and the need to control rivet direction with increased automation.
The fact that each rivet setter can apply only one type of rivet required increased use of handling robots, greater robot carrying capacities, more emphasis on planning ergonomics and generally a higher level of SPR equipment than would be found with spot welding equipment.
The use of SPR technology and adhesive bonding (known as riv-bonding) gives high levels of joint pull strength and resistance to vibration fatigue.