Experimental Determination of the Residual Torque Range in a Plastic Connector of the Fuel Pump Module at End of Life

<div class="section abstract"><div class="htmlview paragraph">The study of residual torque is necessary in various fields to ensure the safety and reliability of bolted joints.</div><div class="htmlview paragraph">The present study aims to determine, experimentally, the decrease in torque applied to a nut used in the assembly of two polymeric components (POM - Polyoxymethylene). These components are part of the fuel supply module, responsible for supplying fuel from the tank to the engine. This reduction in torque initially applied is mapped to the end-of-life of the components and is used as an approval criteria in the audit procedures of the Robert Bosch company. The first component features an overmolded metallic screw, injected into POM. The mating part is also injection molded from POM and is assembled onto the first part, secured by tightening a metal nut. Due to the plastic-to-metal interface, it’s expected that there will be a reduction in the initially applied torque required to fasten the pieces together.</div><div class="htmlview paragraph">The study was based on 5 steps:</div><div class="htmlview paragraph"><ol class="list nostyle"><li class="list-item"><span class="li-label">1</span><div class="htmlview paragraph">Theoretical study on residual torque at the plastic-to-metal interface;</div></li><li class="list-item"><span class="li-label">2</span><div class="htmlview paragraph">Verification of plastic component deformation due to applied torque;</div></li><li class="list-item"><span class="li-label">3</span><div class="htmlview paragraph">Assembly of samples for practical tests;</div></li><li class="list-item"><span class="li-label">4</span><div class="htmlview paragraph">Mapping of torque decrease in samples by time. In this case, a digital torque wrench was used;</div></li><li class="list-item"><span class="li-label">5</span><div class="htmlview paragraph">Analysis of the data and determination of the residual torque range at the end of the product’s life.</div></li></ol></div><div class="htmlview paragraph">After the study was completed, it was determined a minimum residual torque, for the end of the product’s life, in this application. This criterion enables more accurate control in field part verification, improves product quality, and optimizes failures identification.</div></div>