#2 | 2019
SYN] Magazine
16/21

Powerful but sensitive

Flow drill fastening joins different materials fast and securely. The technology is becoming increasingly important especially in automotive body-in-white production. A complex interaction of forces.

Lightweight design, multi-material design and e-mobility are increasingly calling for the joining of several different materials such as aluminium, ultra-high-strength steels, castings, carbon fibre and plastics. Frequently, adhesive bonding is combined with other mechanical joining procedures to increase the dynamic strength and corrosion resistance of a joint. Mechanical procedures such as clinching or self-pierce riveting always require access to the joint from both sides to generate counter-pressure. Especially in the case of complex vehicle bodies, this poses a challenge.

A flowing process

The solution is flow drill fastening – a technology that can join several layers of different materials in a one-shot process without preliminary drilling and with access from only one side. The term “flow drill fastening” is not particularly apt, as a precise look at the joining process will show. A special joining element, the flow drill fastener, is positioned on the workpiece and then rotated at a high speed. The material is heated in the process. The joining tool then presses the fastener through the material layers at high rotation speed and force – and the fastener shapes a thread. The joining element is only tightened in the final stage of the process. The entire fastening operation is completed in only 1.5 to 2 seconds.

Finely balanced interaction

Rotation speeds up to 9,000 rpm and process forces up to 3,000 N as well as a clamping force of up to 1,400 N give an indication of the high forces in operation during flow drill fastening. The key factor is finely balanced interaction. The parameters must be precisely defined for the material combination to be joined and the conditions on site. High-strength steel requires a lower rotation speed and a higher joining force so that the material is not heated too severely. Aluminium is more ductile and therefore calls for higher speeds but less force. Welding spots beside the joint or adhesive applications also have an impact on the process and need to be taken into consideration. Considerable experience and sensitivity are therefore required for joining materials by flow drill fastening in a secure process. If these conditions are met, the technology is a real problem solver for the mass production of car bodies. It is also increasingly used for battery assembly, for the joining of the cover to the battery tray. The joint not only ensures electrical insulation but is also disconnectable, which is a significant benefit for maintenance.

K-Flow: concentrated joining skills

The advanced joining systems in Atlas Copco’s K-Flow product line are designed for the high standards of mass production in the automotive industry. We ensure that the joining technology, the fasteners and the materials are perfectly harmonized and that the process is fast and reliable. With the comprehensive know-how of our joining and process experts, we develop the ideal process parameters for your individual requirements and material combinations and test the process thoroughly. 

Learn more about our solutions for flow drill fastening