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Screwdriving technology is the most popular form of joining technology. More and more complex assembly tasks, increasing requirements for processing reliability and higher quality standards require sophisticated procedures which can fulfil these high specifications. In the automobile industry for example, aluminium, light metals and plastics are used more frequently due to the need for lightweight construction. Housings for pumps, ECUs (Electronic Control Units), airbags, interior components – all these products are normally assembled using self-forming or self-cutting screws. In the processing of these screws a tapping drill hole is used, the screw itself however acts as the thread forming or cutting tool. However for assemblies usually in series assembly, for self-forming or self-cutting screws tightening based on a defined end torque is the established screwdriving procedure. The torque guided screwdriving process is always the most adequate solution if the forming torque required for the screwdriving process lies at a constant value.

The actual required force for connection of these two or more components to ensure a reliable and safe connection is the pre-load force. The lack of practical methods of measuring this pre-load force means that you are usually reliant on the torque as an aiding measurement in series assembly. When assembling with pre-cut thread the applied torque is the same as the pre-load force. But for self-forming or self-cutting screws a share of the applied torque is used during the thread forming or thread cutting process. The other share of the torque generates the pre-load force.

“So long as all influencing factors are repeated accurately within an acceptable framework then the assembly result with the tightening strategy “screw assembly to torque” is also repeated accurately and reliable processing is ensured”, explains Jürgen Hierold, Sales Manager at DEPRAG SCHULZ GMBH u. CO.