An In-Situ Tribotest Method Designed for Predicting Wear Life and Frictional Performance During the Aluminum Forming Process

摘要

Quick Plastic Forming (QPF) and Superplastic Forming (SPF) are high temperature forming processes that have been designed to make a variety of aluminum automobile components at both high (QPF) and low (SPF) production volumes. These newly-developed processes operate at high temperatures in excess of 400°C to improve formability, and as a result, special solid lubricants and tool coatings are required to improve wear life and tribological performance under these hot forming conditions. The major aspect of this aluminum forming process is the tribological interaction between the aluminum blank and the forming tool. Tribological characteristics have a significant impact on the surface quality, tool wear life, and durability. The majority of the conventional tribology tests used to measure wear life and frictional performance for conventional sheet metal forming are incapable of monitoring friction behaviour and wear life in-situ. In addition, most of the bench tests used in industry do not capture the deformation state during metal forming, where the forming aluminum material is undergoing sliding and stretching at the same time, leading to transient friction behaviour and fast strain rate changes that are hard to measure in-situ by a bench test. Therefore, an in-situ tribotest is critically needed for measuring friction behaviour and predicting wear life during the quick plastic forming process, including determining the effects of solid lubricants and die coatings, and the basic mechanisms of aluminum blank/tool surface interaction. In this research paper, an in-situ tribotest method has been designed to predict the wear life and frictional performance of aluminum sheets and their lubricants during the quick plastic forming process. This tribotest machine can directly determine wear life and friction characteristics of aluminum sheets during the forming process. In addition, a new probe sensor has been designed and constructed to determine friction force, friction coefficient, and wear depth of aluminum surface contact during the forming process in-situ without any interruption or re-assembly of the metal forming system. It can be observed from in-situ experiments that this developed method and tribotest design provide several technology advantages, including a simple structure, high sensitivity, good stability, and precise measurement of wear life and frictional performance. The correlation between friction coefficient and process parameters for the aluminum forming process has also been studied. This new experimental design and in-situ tribotest method provide valuable tools for evaluation of the tribological characteristics of aluminum sheets, solid lubricants, and tool coatings during the quick plastic forming process.