Snap-Fits Evaluation for Minimizing the Squeak & Rattle in Automotives

The world of plastic products has been growing due to its versatile properties and has become an intrinsic and fundamental part of engineering for 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 optimal 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 evaluating the snap stiffness that alters in thickness and width along with capturing the material modulus variation. The different connection methodologies for modelling snaps and their variation in the results in this manner, change the probability of the occurrence of squeak & rattle. The FE results give a measure of confidence to the approximations made from analytical calculations and the method suggested, proves as an effective tool for capturing the snap stiffness thereby leading to early prediction of S&R issues.