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Constant clamp force despite fluctuating tightening torques

At the MOTEK 2016: Processing reliability in screwdriving assembly / Adaptive screwdriving procedure DEPRAG Clamp Force Control

(PresseBox) (Amberg, ) Screwdriving technology is the most widely used joining technology. Ever more complex assembly tasks, increased demand for processing reliability and higher quality standards require sophisticated procedures which are clever enough to cope with these complicated requirements. Aluminium and other lightweight metals and synthetics are increasingly being used in the automotive industry, for example, for lightweight construction. Housings for pumps, airbags or interior components – all these products are usually assembled using thread-forming or thread-cutting screws.

Strongly contrasting tightening torques are generally required in these types of screw assemblies. The use of a torque controlled tightening procedure can cause wide variations in the resulting clamp force even with excellent shut-off accuracy. The new adaptive screwdriving procedure DEPRAG Clamp Force Control (CFC) works to counter this by eliminating all frictional influences up until the point of head seating. This thereby enables a significantly improved constancy of the clamp force.

The entire screw assembly consists of the screwdriving template seating recognition and an assembly to differential torque or assembly to angle. The main part is the seating recognition: mathematical evaluation functions are continuously built up on the basis of the torque process. Seating is recognised once this function exceeds a specified limit value.

The calculation procedure combines two fundamental advantages: The calculation rule is robust in relation to coincidental fluctuations or increases during the torque procedure which do not occur as a consequence of the actual head seating. Furthermore, the algorithm is universal so the user does not have to set any relevant parameters for the calculation. There is therefore no need for extensive preliminary tests and parameterisation.    

The procedure for an EC-Servo screwdriver in combination with sequencing controller AST40 is mainly used for direct screw assemblies in metal or plastics. The occurring fluctuating tightening torques are caused for example by alterations in the screw or hole geometries or in the structure of the component material, varying surface characteristics of the screw thread and flexible elements or seating conditions.

DEPRAG SCHULZ GMBH u. CO. based in Amberg, Germany have earned their position as one of the leading companies in screwdriving technology with their outstanding product and service spectrum. The specialists, with 600 employees in over 50 countries, are consistently bringing new innovations onto the market. The full service providers are presenting their latest product developments from 10th to 13th October 2016 at the MOTEK in Stuttgart: Hall 5, Stand 5310.

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