Development of a method for the prediction of the tightening torques of plastic nuts

The utilisation of plastic nuts constitutes a procedure which is increasingly frequently being used for the joining of components in automobile construction. In order to preventany overtightening of these injection-moulded plastic nuts in the tightening process, the tightening torque must be determined depending on the insertion and over tightening torques. One previous investigation shows that the following influencing quantities exert significant influences not only on the insertion and over tightening torques to be expected but also on the corresponding tightening torques: glassfibre content, conditioning humidity, screwing temperature, glass transition temperature and screwing-in depth. Building upon a mathematical regressionmodel, a method for the determination of a suitable tightening torque is presented in this paper. The developed method supplies high coefficients of determination taking account of case differentiation depending on the glass transition temperature. Moreover, the transferability to another nut geometryis shown successfully.