SYN] Magazine
#3 | 2019

Facilitators for Lightweight Design and E-Mobility

Self-pierce riveting is becoming increasingly popular in the automotive industry. Joining experts Michael Bettin and Sinan Sirmagül explain the benefits of this technology and the requirements to be met for successful use.

What joining applications is self-pierce riveting suitable for?

Michael Bettin: „Self-pierce riveting has been an established technology in the automotive and components industry for many years. In addition to joints between two or more layers of a single material such as aluminum or steel, this technology is outstandingly well-suited for composite joints of aluminum, high-strength steels, cast iron, extruded sections and in some cases even composite plastics. Depending on the individual joining task, hybrid joints using rivets combined with structural adhesives have also proved to be very effective.”

Sinan Sirmagül: „These joints are mainly used in body production, for structural components and attachments. Self-pierce riveting is also becoming increasingly popular in the e-mobility sector, for example for the production of battery housings, individual modules and the installation of batteries in the car body. The battery is one of the key structural components of an electric car, which is why joining is especially important in this case.” 

What are the advantages of self-pierce riveting compared with conventional joining technologies?

Sinan Sirmagül: „Self-pierce riveting is a cold, mechanical joining technology that creates a positive, friction-locked bond. In contrast to welding, the material structure is not modified and no heat is applied to the components. This has considerable benefits, for example in the production of battery modules. Sensitive cell stacks can easily be damaged by weld spatter, a risk that is entirely avoided with self-pierce riveting. In combination with adhesives and sealants, self-pierce riveting can produce an outstandingly well-sealed battery housing. This has a positive impact on the overall service life and performance of the battery. In combination with adhesive bonding, properties such as dynamic stability, overall rigidity and energy absorption in the case of a collision as well as corrosion protection can be improved.” 

Lightweight design and e-mobility are the megatrends in the automotive industry. What does that mean for joining?

Michael Bettin: „The objective of lightweight design is to reduce weight at the same time as maintaining or improving crash safety. This means that the materials used become thinner and stronger. However, the materials have different properties. Considerable know-how is needed for the secure bonding of ultra-high-strength steels with lightweight, brittle aluminum. We can offer or develop a suitable rivet for joining almost any combination of materials and material thicknesses. In some cases, self-pierce riveting makes innovative joints possible and is a facilitator for lightweight design.”

What are the differences between the various types of rivet?

Sinan Sirmagül: „In addition to different lengths and diameters, it is the geometry of the rivet that is most important. It must be precisely adapted to the material combination to be joined. For example, our BG-Rivet has a stronger shaft with a special coating and is therefore especially well-suited for joints with ultra-high-strength steels. The A-Rivet is a short rivet with sharp edges developed especially for thin aluminum sheets. Another innovative product is the T-Rivet. This is a tubular rivet for up to 4 layers of aluminum that allows excess material to escape upwards through the rivet. We are currently developing special rivets for narrow flanges – a key area in lightweight design.”

Michael Bettin: „We offer the most comprehensive range of self-pierce rivets and produce about 4.5 billion rivets every year. Our two production locations in the USA and the UK even have a capacity of up to 10 billion units per year. We manufacture each individual rivet entirely in-house using a special wire specified by us. Our specifications cover all stages in production from cold forming through various cleaning processes and heat treatment to coating. All our rivets are 100% visually inspected and sorted using a camera system before they are packed in accordance with our customers’ requirements.” 

More and more material combinations, more and more different rivet types – how can systems keep pace?

Sinan Sirmagül: „Riveting systems must be in a position to handle a growing number of joint variants. As a general principle, Atlas Copco’s Henrob systems can process all types of rivets with a single diameter. A new rivet therefore does not necessarily mean that you need a new system. In addition, the die must be adapted to the material combination and the rivet. Our Unity is a new self-pierce riveting platform that offers our customers even greater flexibility. Unity can process different rivets and dies in a single system. This means that manufacturers are outstandingly well-prepared for new designs and materials.”

Michael Bettin: „Especially for globally active manufacturers, Unity offers considerable benefits. They can work with the same test technology and data architecture throughout the world at the same time as making market-specific adaptations. Especially as regards rivet feeding, there are considerable differences. In Europe, customers prefer loose feeding systems, either blow feeders or Poka-Yoke bottles and magazine solutions. Customers in the USA mainly use tape feeding systems. Nevertheless, the system components and data offer global compatibility – laying the foundation for Industry 4.0.″

What distinguishes Atlas Copco from other self-pierce riveting systems?

Sinan Sirmagül: „We already cooperate closely with our customers early in the design phase and not only test the appropriate rivet and die combinations for the individual application but also the optimum joining process. The individual system components such as the C-frame, setter and rivet feeder, as well as the system options are precisely designed to meet the customer’s requirements. This is extremely important for developing a secure process with high, repeatable joint quality.”

Michael Bettin: „With 16 customer centers, we have a global presence and are in a position to provide our customers with on-site support from development through to after-sales service. In addition to self-pierce riveting, we also offer adhesive bonding and flow drill fastening solutions from a single source. In the case of combinations between adhesive bonding and riveting, we develop the appropriate adhesive application pattern. We are experts in joining, irrespective of the method used.”

Learn more about Henrob self-pierce riveting systems from Atlas Copco