Lubricant 4.0: digitally enhanced lubricant development for metal forming applications

Abstract

Tribological behaviours at the tool-workpiece interface are important in determining material flow and surface quality of products in the metal forming process, where lubricant is usually applied to separate and protect the contacting surfaces which reduces the required forming load and prolongs the tooling life. If the lubricant was not selected properly, premature breakdown phenomenon would occur during the forming process which would deteriorate the formed surface quality and cause damage to the working face of the tooling. The selection of lubricant for a specific forming process, however, is usually experience-oriented and based on general evaluation results obtained by simplified lab-scale friction tests, which cannot fully represent the contact conditions experienced in actual forming processes. In recent years, smart manufacturing has been introduced into the metal forming industry and the digital transformation has demonstrated a prominent potential in accelerating production and technology development, which also attracts the attention of lubricant developers. Inspired by this digital trend, this work proposes a novel technique for digitally enhanced lubricant development specifically for metal forming applications. First, the digital characteristics of a metal forming process, e.g. pressure, speed, temperature etc., were generated and demonstrated by the 2D data mapping and 3D dynamic visualisation to show the evolutionary and complex features of tribological contact conditions. This presented an integral overview of the forming process variables and provided a data-driven guidance on the subsequent friction testing procedure. Friction tests were subsequently conducted to investigate friction evolution and lubricant behaviours following the data-driven approach by an automated friction testing system, Tribo-Mate, which enabled advanced testing under complex loading conditions and in-situ data processing and friction modelling. Based on the analysis of friction testing results, a mechanism-based interactive friction model was established to describe the friction evolution and transient lubricant behaviours as a function of the instantaneous contact condition and the sliding distance. Finally, a lubricant limit diagram (LLD) was proposed as an intuitive and holistic graphic description of the process-specific lubricant performance. Lubricant evaluation and improvement were performed based on LLDs to provide insightful and detailed recommendations to the lubricant developers for improving its lubricity in a specific forming process from a digital perspective.