Henrob Self Piercing Rivets (HSPR)
HENROB - Self Pierce Riveting
Innovative Joining Solutions
Rivets set to stick around
Henrob Self-Pierce Riveting (HSPR)
By Zoe Fielding
ASTON Martin chose adhesives to join key components in its DB9 luxury coupe’s aluminium body, while Honda used laser welding in the construction of its 2005 Odyssey, but as Jaguar tools up its Castle Bromwich factory for production of the XK150 in 2006, its specification of self-piercing rivets seems to prove mechanical fasteners are not being entirely superseded. Manufacturers, particularly in the automotive and aerospace sectors, are exploring new techniques to join materials often with excellent results, but Henrob managing director, Stuart Blacket, warns that each technique has disadvantages which may preclude its use in other situations. Blacket told Manufacturers ’ Monthly adhesives are rarely used alone at present because their performance can be unpredictable and secondary fastening methods are generally needed to hold product geometry as the adhesive cures. Adhesives can also be messy and a fair degree of control is required in their application. “In some cases it’s not a convenient method for high volume production,” Blacket said.
A research and development scientist with Dow Automotive, which supplied specialist adhesives for Aston Martin’s DB9, admitted adhesives extended the production time for the vehicle, but as it is largely hand-built, bonding does not need to happen as quickly as if the cars were produced on an assembly line. According to Blacket, welding technologies which do not require consumables are the main technological threat to the mechanical fasteners market. “The downside for some of the welding technologies is that they are very specialised,” he said. Laser welders for example must be isolated for safety.
“That becomes a major impediment to its mass use in a factory. “It’s also a very sophisticated technology which requires very high levels of maintenance...In production lines you really want low maintenance technology that people on the ground understand and can be fixed within minutes,” he said. One welding process Blacket says is showing promise is friction stir welding. Mazda has used this process on the aluminium rear doors and hood of its 2004 RX-8. In friction stir welding, a tool rotates at very high speeds, under intense pressure to create enough friction to melt the metal being joined. No filler metals or shield gases are needed, but Blacket says the process requires significant energy and force to work “so it has its limitations”. Blacket acknowledges there is a place in industry for all emerging technologies, and he expects to see greater segmentation of the joining and fastening market in future. He says product shape will to a large extent define the fastening method used. “An example might be that you have an aluminium or magnesium casting being joined to a piece of extrusion.
The method of joining would be welding because that’s the most practical and convenient way.” Self-pierce rivets are being used in place of spot welding for difficult to weld materials such as aluminium, high strength steels and dissimilar metals. Rivets can also be used to join metals to plastics, which is not possible with welding, and can be difficult with adhesives. Although the process is initially costly to set up, Blacket says riveting is often preferred once established. Audi, for example, adopted riveting as part of its vehicle assembly process in the early 1990s and is still specifying it as a preferred joining method in new models. Blacket said automation was also making riveting a more viable option for manufacturers. “We now have riveting equipment in robotic production lines that are working two or three shifts...we can achieve the sorts of throughputs that were achieved with spot welding and with the one big advantage that it’s a cleaner working environment,” he said.
A tough climate Despite promising signs for the future of mechanical fasteners, rivet manufacturers accept their market is no longer expanding, and they are also under threat from Australia’s tough manufacturing climate. Textron Fastening Systems national marketing and business development manager, Ross Douglas told Manufacturers ’ Monthly fastener suppliers are searching for other ways to expand their businesses. Improving fastening processes is one key opportunity Douglas says his company is pursuing. “We look at how they are moving their product through operation to the point of use and try to add value there,” he said.
That could involve delivering to the point of use on the line, changing the packaging, or conducting quality checks and procurement automatically. Douglas added designs could also be reviewed, minimising the number and type of fasteners used. New types of rivets are also being introduced. Douglas said notable advanced include plastic rivets, which are said to be lighter and stronger than standard metal rivets, and so-called intelligent fasteners. Intelligent fasteners have microchips attached which can monitor conditions such as stress and temperature. “The intelligent fastener is really a product you’re not going to see on the vacuum cleaner at home. It is an expensive product and at this stage it is specific to very key value added applications.” Douglas said intelligent fasteners would find applications in the aerospace industry and on vehicle airbags for instance where the benefit of the fastener would out weigh the cost.
8 April 2005