Session: 02-05-01: Session #1: 7th Symposium on Fastening and Joining Research and Advanced Technology

Paper Number: 95614

95614 - Effect of Using 3D Printed Parts on the Torque-Tension Relationship of Threaded Joints 

This study investigates the effect of using additive manufacturing parts on the torque-tension relationship, the static preload relaxation (seating) and vibration loosening performance of threaded joints, as compared to that of joints with commercially available machined or extruded parts. A commercially available computer-controlled RS System is used for tightening test joints, with various control options that include torque-only, torque-angle, or torque-to-yield. The RS System uses its own built in high precision transducers and angle encoder for collecting real time data on the tightening torque, angle of turn, bolt tension/joint clamp load, versus time. The system software uses generated data to calculate the bearing and thread friction coefficients, using Motosh model for the torque- tension relationship. Three orientations are taken into account in order to evaluate the effect of building orientation on the friction coefficient in the underhead. A final group of specimens is analyzed to evaluate the effect of machining on the tribological response of the bolted joint. Different types of screws, all in the range of “high-strength” grades, are tested, thus accounting for different preload levels for a given geometry. Both dry and lubricated contacts are considered for each material/bolt grade combination. The experimental plan includes the frictional response over 5 retightening operations.

 

Respective torque components are compared for 3D printed and commercially available joint parts; namely, the thread friction, bearing friction, and pitch torque components that add up to the total amount of tightening torque. Comparison of the static preload relaxation due to seating of the material, which particularly affects the underhead contact region, is performed based on preload versus time plots, directly obtained by the RS System. Comparison of the vibration loosening performance is performed using actual and/or simulated Junker testing that measures the rate of clamp load decay per cycle, when the clamped joint is subjected to a known cyclic transverse shear load.   For the simulated Junker testing vibration loosening evaluation, the effective values for thread and bearing friction coefficients are obtained from the torque-tension data and Motosh model for the torque-tension relationship and entered, along with relevant joint system data, into BoltVibe software that calculates the rate of loosening per cycle. Results in terms of preload retention capability, friction coefficients, and nut factor are provided Data Analysis performed by means of statistical tools of ANOVA and Fisher’s test in order to evaluate the effect of each parameter on the output variables. Conclusions are useful to both design engineers and researchers to evaluate the best tightening procedure for the analyzed bolted joint.

 

Keywords: Motosh model, Junker test, Vibration loosening 

 

Presenting Author: Francesco Robusto University of Bologna

Presenting Author Biography: Will be uploaded shortly

Authors:

Francesco Robusto University of Bologna
Sayed Nassar Oakland University
Joon Ha Lee Hyundai Motor Company
Marco Gerini-Romagnoli Oakland University
Massimiliano De Agostinis Università di Bologna