Snap-fits evaluation for minimizing the Squeak & Rattle in Automotives

The world of plastic products has been growing due to its versatile properties, which have become an intrinsic and fundamental part of the engineering of new products. The most important aspects contributing to this spectacular growth are the design and assembly, making sure that plastic parts are designed optimally. The safety requirements have been increased due to the safety ratings and thus interior parts must provide more absorption and protection to occupants. The main connection types used in the plastic parts are heat stakes and snap fits. The purpose of a good snap fit is not only to have a high retention effort but also to present ergonomic characteristics with low insertion and extraction effort because each part requires a different function. With the time-dependent loading the material will redistribute its internal energy thereby performing a time-related flow leading to reduced pretension thus decreasing stiffness. This paper presents an analytical and numerical method for the evaluation of the snap stiffness that alters in thickness and width along with capturing the material modulus variation. The different connection methodology for modelling the snaps and the variation in the results in this manner, change the probability of occurrence of squeak & rattle. The FE results give confidence to the approximations made from analytical calculations and the method suggested, proving an effective tool for capturing the snap stiffness, leading to early prediction of S&R issues.