The flow-drill screw for high-strength joints in sheet metals
Due to its good processing and performance characteristics, steel is still the most significant material in the sheet-metal industry. However, it faces increasing competition from lighter materials, such as aluminium. To combat this competition, the steel industry has recently developed a new range of materials, such as ultra-high-strength steels, which are used for structural and safety components in the automotive industry. These materials exhibit very high strengths while also having good formability.In order to meet the high demands of sustainability, reducing the vehicle weight is a key strategy towards a significant decrease of CO2 emissions. This push has made the automotive industry a key driver for the development of innovative lightweight materials. Nowadays, this lightweight strategy is integrated into almost all components of future vehicles. In particular, multi-material body design has shown to be a significant contributor to weight reduction.
This dissimilar material mix can meet the highest demands of stability and torsion resistance of the car body. The chosen joining technology can ensure these goals are met. These different materials must be connected in a long-lasting and reliable way and of course able to withstand high loads. In addition to one-sided accessibility, the removability of the fastener is also very important, especially with regard to recyclability. These complex conditions are an ideal case for using the EJOT FDS® screw (Flow Drill Screw). Additional processing steps such as pre-drilling, stamping or thread-cutting are no longer necessary. Thanks to the increased thread engagement of the FDS® screw in the formed extrusion, a high-strength screw joint without any chips is created. This screw joint can withstand high pull-out as well as shear forces. The extruded workpiece material contracts around the screw after the fastening process, which guarantees a high dynamic safety. Thus, additional safety elements such as an adhesive locking feature is not necessary.
With the FDS® screw, EJOT has developed an alternative from the common practice of pre-drilling the components to be joined. Through modification of the under-head geometry and adjustment of process parameters, joining of a space frame structure can be carried out completely without pre-drilling the clamping parts. As a result, the displaced material, which was previously taken up in the pilot hole of the clamping part, can be contained in the under-head groove.
Flow Drill Screws require screwdriving machines with high spindle speeds and axial force capabilities. These machines are available from various manufacturers with optimization of the process performed as a collaboration between the equipment manufacturer and EJOT. Suitable process parameters can be determined through full joint assembly and analysis at EJOT’s application laboratory APPLITEC.
As an additional service, EJOT offers an online tool for the FDS® screw technology (FDS® APPLICATION CHECK). Through this software tool, the user can determine the appropriate fastening values by simply entering the materials and sheet thicknesses wished to be joined. These values, amongst others, are the required axial force, the screwdriver rotational speed, the necessary screw length and a recommended tightening torque, considerate of different screw coatings.
EJOT FDS® at a glance:
- One-sided accessibility
- Removable and high-quality screw joints, without part preparations such as pre-drilling or punching
- No hole overlap problems for through holes and insertion holes
- No material waste during flow drilling / no chips during thread forming
- High loosening torque and vibration resistance, no need for additional safety elements
- Easy removal and recycling
