02.03.2010
Under the name of RIVTAC®, the Böllhoff Group presents a new joining method for diverse industrial sectors
Welding, screw-fastening, riveting, joining? Questions that are increasingly difficult to answer − also in automotive engineering. This is because new materials and material combinations ask for innovative fastening technologies. The Böllhoff Group in Bielefeld, Germany, has now enriched its range of technologies with a worldwide unprecedented future-oriented innovation. The name: RIVTAC®. The technology: High-speed joining
Nothing is more constant than change. This is particularly true for body construction in the automotive industry. Increased comfort, vehicle dynamics and safety, reduced weight and consumption − all at lower manufacturing and production costs. Requirements which over the last years have considerably changed the material combinations in cars. Steel, light metals and plastics continue to be the most important materials. Within these material groups, however, there is a great number of new compositions − and of mutual substitutions. Requirements for the fastening technology are correspondingly complex and demanding.
"Innovative ability and customer orientation have become crucial competitive factors," knows Dr Torsten Draht, Project Manager at the Research & Development department of the Böllhoff Group. The family business has always regarded that dynamics of the market as a driving force. This is how, on the long term, our "think tank" is always able to convert new material and construction principles on the side of the user into new products and solutions. The youngest offspring of the future-oriented product range is called RIVTAC® and is a type of high-speed joining. With this technology, Böllhoff was basically able to apply compressed-air nailing common in the craft sector to an industrial-quality technology for small wall thicknesses.
In the innovative mechanical joining process, a nail-like auxiliary joining part is accelerated to high speed and driven into the not pre-punched joining parts. The pointed tack displaces the material without forming punchings. Important conditions for joining: The joining parts must be sufficiently stiff. This ensures that they can sustain the penetration impulse of the tack without major deformation.
This development was − as so often − initiated in the automotive engineering sector. That is because in body construction, the proportion of closed profiles with small wall thicknesses is increasing. Challenge for the fastening technology: On the one hand shall profiles, which are often heat-treated, be joined in a low-heat process so that material characteristics are maintained. On the other hand are these parts often parts with only one-sided accessibility. And − last but not least − do engineers aspire to have only one production step without pre-punching to reduce costs.
In case of one-sided accessibility, traditional state-of-the-art methods soon reach their limits. The only alternatives may then be direct screw-fitting and blind riveting. Common disadvantage: Both technologies usually require pre-punching of at least one joining part and a great positioning effort to insert the fasteners. That is expensive and therefore widely avoided in large-series production.
Not so for high-speed joining. Böllhoff explains that also high-strength parts and profiles with a strength above 1,000 MPa as well as multiple-layer joints can be joined without loss of performance. And with particularly good strength characteristics. This was proven by comparison with the widespread resistance spot welding for the employment of high-speed joining in the "ScaLight" body study (lightweight steel construction concept of the two German companies Salzgitter AG and Wilhelm Karmann GmbH). It resulted that the impact of the stress direction on the joint stability is lower than upon resistance spot welding and that overall strength characteristics are equal. The high dynamic strength is also visible in the course of the S-N curve. Under identical material conditions, the k value for high-speed joining is 4.96 whereas the k value for resistance spot welding is only 3.23.
The method does therefore fulfil the high requirements for safety-relevant joints and can also be perfectly combined with adhesion technology. The high speed at which the tack penetrates the materials avoids that the adhesive disperses uncontrollably. According to Dr Torsten Draht, this results from the short joining time which is well below one second. Thus, the process is three times as fast as e.g. direct screwing. Impressive cycle times − with the corresponding attractive potential of cost reduction. Convenient additional benefit for the user logistics: The fastener can almost be universally used. That means that, almost independently of the materials to be joined, the geometry of each "nail" is the same.
Even if the way to series production with this new technology may still be long, does not only the automotive industry already show a great interest in the process. "With high-speed joining, we have taken a great step forward and strongly emphasised the innovative capacity of our company," sums up Dr Torsten Draht.
This is high technology at its best. The specific challenges were the geometry of the tack on the one hand and the material composition of the fastener on the other hand. Furthermore, the tack also had to reach the required acceleration speeds. The result of intensive research effort "will meet future requirements, particularly in the body construction sector," is Dr Torsten Draht convinced.
The most important stop on the way to practical use is the certified Böllhoff laboratory. The central institution for an unconditional quality management was already certified according to EN ISO EIC 17025:2000 in 1999. There, up-to-date methods for mechanical and physical tests as well as for chemical material analysis are employed.
"We always strive to be a step ahead," says Dr Torsten Draht. That made RIVTAC® an investment in the future of the company and in the partnership with the automotive industry as Böllhoff's important performer.
As usual for Böllhoff, for high-speed joining, joining element and joining tool come from a single source. Optimal conditions for maximum joint quality. The portable hand tools, which will soon be available under the name of RIVTAC® Portable, have a piston that is accelerated with compressed air between 4 and 8 bar and drives the tack into the components to be joined. At the same time, fully-automatic high-speed joining systems are already being developed in the Böllhoff development laboratory. With respect to those systems, the engineers also show creativity when it comes to the joining elements. The aim is clear: intelligent solutions for the markets of tomorrow.
That is because lightweight construction and new materials result in ever increasing requirements for the joining technology. "With our RIVTAC® invention we take on new fields of application where common methods reach their technical and economical limits," is Dr Torsten Draht convinced. He does therefore not accept fears that Böllhoff could compete with its own departments: "We enhance our expertise, close a gap in the portfolio and strengthen our market position." Optimal conditions to also in the future distinguish themselves as a solution specialist for innovative industries ready to take on the challenges of the future.
Plus:
Benefits of high-speed joining:
- Joining in case of one-sided accessibility
- Joining without pre-punching
- Joining of high-strength materials
- Joining of multiple-layer joints
- Short cycle times of less than one second
- High strengths
- Optimal possibility of combination with adhesion technology
© Böllhoff Group, Bielefeld 2010
Reprint authorised.
Responsible authors
Dr.-Ing. Torsten Draht
Project Manager Research & Development
of the Böllhoff Group
Archimedesstr. 1-4
D–33649 Bielefeld
Phone +49 (0)5 21 44 82-01
Fax +49 (0)5 21 44 93 64
Please send sample copy to:
Böllhoff Gruppe
Wolfgang Sönel
Archimedesstr. 1-4
D–33649 Bielefeld
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