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.