On the lubricating efficiency of high-performance powder metallurgy lubricants

Abstract

Frictional characteristics of an iron-based mixture were studied using a specifically designed friction test bench allowing (after prior compaction) the measurement of the friction coefficient during the sliding of a compact on a slab simulating the die surface. Temperature and sliding velocity were controlled. An experimental campaign was conducted with four high-performance lubricants and a conventional EBS wax, based on a single FL-4400 mix formulation. The experimental parameters included: mix temperatures from 40 to 80 °C; density of 7.20 g ⋅ cm −3 ; normal pressure of 244 MPa; sliding distance 80 mm; sliding velocity 20 mm ⋅ s −1 . The analyses focused on the evolution of the friction coefficient and the compact’s surface degradation. Two methods were compared: single testing with slab cleaning between each test, and repeated testing. After multiple repetitions, a steady state was established with a sliding distance beyond which degradation became critical. The degradation depended on the lubricant and experimental conditions. The difference between lubricants became more obvious, some of them proving an enhanced ability to create long-range lubrication. This study aims at better understanding how the friction coefficient evolves during the ejection of a production part. • High-performance lubricants increase the sliding distance before surface degradation. • The maximum sliding distance before degradation was estimated using a friction test. • Repeated testing improves the quality and repeatability of friction measurements. • Lubrication properties evolve with the number of compaction cycles.