Tribological behavior of tool–workpiece interface during milling of ultra-high strength steel under different cooling conditions

Abstract

Ultra-high-strength steels have been widely utilized in the aviation industry due to their superior mechanical and physical properties. However, the intense friction occurring at the tool–workpiece interface can result in significant tool wear, impacting both the machining efficiency and surface quality. Therefore, a deep understanding of the tribological behavior at the tool–workpiece interface is crucial for extending tool life. The current study proposed a novel open tribo-system to simulate the intermittent contact conditions between the tool and the workpiece during the milling process. An improved friction model was established to calculate the real friction coefficient under intermittent contact conditions. Tribological comparative experiments on ultra-high-strength steel and cemented carbide were conducted under various cooling conditions: dry, high-pressure air cooling (HPAC), air atomization of cutting fluid (AACF), and ultrasonic atomization of cutting fluid (UACF). The influences of various cooling conditions on the tribological characteristics were investigated, with a focus on the depth of the wear mark, height of the pile-up, measured force, adhesion friction coefficient, and wear morphology. The results reveal that the depth of the wear mark, height of the pile-up, and measured forces play pivotal roles in determining the adhesion friction coefficient. The synergistic action of airflow and droplets results in the formation of a liquid film, improving the friction at the interface between the ball and the workpiece. Compared with the AACF condition, the UACF condition results in a 7.7% reduction in the adhesion friction coefficient due to its excellent film-forming ability stemming from its small droplet size and uniform droplet size distribution. Abrasive wear, adhesive wear, and oxidative wear are the primary wear types for cemented carbide, regardless of the cooling conditions. The effective cooling and lubrication capability provided by the uniform liquid film in UACF contributes to improving the wear resistance of cemented carbide, offering valuable insights for mitigating tool wear.

Graphical abstract

Keywords

tribological behavior / cooling and lubrication / ultra-high-strength steel / adhesion friction coefficient / wear morphology

RIGHTS & PERMISSIONS

Higher Education Press