#4 | 2020
SYN] Magazin
11/21

When things get tight – self-pierce riveting for narrow flanges

Typically in body-in-white production, vehicle flanges must be wide enough to allow for joining methods to ensure a stable joint. However, as a result of lightweight approaches and modern vehicle design, manufacturers are looking to narrow these flanges. With the new self-pierce riveting systems from Atlas Copco, this no longer presents a problem.

Typically in body-in-white production, vehicle flanges must be wide enough to allow for joining methods to ensure a stable joint. However, as a result of lightweight approaches and modern vehicle design, manufacturers are looking to narrow these flanges. With the new self-pierce riveting systems from Atlas Copco, this no longer presents a problem. 

In body-in-white production, car manufacturers design aluminum and steel parts in such a way that the edges are initially bent to form a flange. The parts are then joined firmly together using self-pierce riveting or other joining procedures. Over the past few years, the growing use of aluminum has resulted in these flanges widening to accommodate aluminum’s higher bending radius than that of steel.  

Maintaining the rigidity and strength of these supporting structural elements is a key vehicle requirement. Self-pierce riveting is one of the most important mechanical joining technologies used for body-in-white production. However, a self-piercing rivet retains the highest joint strength when it is positioned at a sufficient distance from the edge of the material. The further the centerline of the rivet is located from the edge of the flange, the higher is its sheer and peel strength. If the flange is too narrow, the rivet may be positioned too close to the edge for sufficient stability.  

The positioning of the set rivet is in part determined by the size of the nose in the setting equipment; a wide nose limits how deeply a joint can be made in a flange. 

Narrow flanges are increasingly popular 

Manufacturers are increasingly designing vehicles with narrower flanges in order to improve accessibility to the interior and to make the entrances to the vehicle larger. Narrow flanges also have the advantage that glazed areas and window frames can be made larger, facilitating modern vehicle design as well as improved passenger visibility and safety. The reduction of flange widths can also contribute to the continued strategy of improving vehicle fuel-efficiency via lightweighting. Decreasing a flange by even a few millimeters over the span of the whole car body can have a significant impact on reducing overall vehicle weight in addition to reducing material costs in manufacturing. 





The solution: smaller rivet setting noses

The nose of rivet setting systems must be able to fit adequately on the flange, therefore the nose width is an important factor in determining the required flange width. The noses of conventional SPR setters are fitted with silicone compression pads and ball bearings that support the head of the rivet as it is inserted. The nose must have sufficient thickness to house these components. It is this nose size that often limits the minimum flange width that can be joined.  

For this reason, Atlas Copco has developed a new nose design especially for narrow flanges. Able to set the same size rivet, the outer diameter of the nose is reduced while continuing to provide effective support for the rivet and ensuring robust joining. Due to the patent-pending design with an arrangement of a hemispherical ball cage assembly made of spring steel, the overall structure of the nose piece is more compact overall.  

As a result, self-pierce riveting can be carried out in a secure process on flanges which are more than 20 percent narrower. The smaller nose diameters allow customers to maintain build and trim tolerances on narrower flanges by placing the rivet closer to the flange root, improving peel performance and consistency.