Press fit design : force and torque testing of steel dowel pins in brass and nylon samples

Abstract

An experimental study was conducted to determine the accuracy of current press fit theory when applied to press fit design. Brass and nylon hex samples were press fitted with hardened steel dowel pins. Press fit force and torque required to induce slipping were measured experimentally. Sample dimensions and material properties were utilized to predict expected force and torque levels, which were then measured experimentally. Brass press fit forces proved difficult to predict due to plowing effects in tight interference press fits where material yielding was observed. However, once vertical force was removed, torque was applied to each sample. The observed torque values matched press fit theory well suggesting that the interface pressure of the press fit can be accurately predicted by theory. The brass torque samples matched theory well once material yield conditions were taken into account. The creep sensitivity of the nylon samples made predictions over the testing period unreliable. Results show the need for further testing with specific attention to precision in sample machining and measurements. Other considerations include press fit interface roughness and plowing effects during press fitting.