Improvement of Frictional Property of AISI D2 Tool Steel Surface against JIS SPFC 980Y Advanced High-Strength Steel by Using Laser Texturing Process

Surface friction in metal forming processes can be reduced by creating lubricant reservoirs
at the interface between surfaces in contact, and a laser texturing process can be employed to
produce the micro-dimples that act as the reservoirs on the surfaces. However, the role of the
laser texturing parameters in the friction reduction of tool steel surfaces has still received very little
attention. Therefore, this study aims to reduce the friction of the AISI D2 tool steel surface on which
a nanosecond pulse laser was applied to create an array of micro-lubricant pockets for trapping
lubricant. The effects of laser power, irradiation duration, and spacing distance between pockets on
the pocket diameter, size of the heat-affected zone, surface friction, and wettability were investigated
in this work. The average laser power in the range from 5 to 10 W and laser irradiation duration
of 0.02 to 0.10 s were applied. The results showed that the increase in laser power and irradiation
duration enlarged the pocket diameter and heat-affected zone. The largest pocket diameter of 40 m
was achievable by using 10 W laser power together with 0.10 s irradiation time. The pin-on-disc
method was employed to determine the friction coefficient of the tool steel, where JIS SPFC 980Y
advanced high-strength steel was used as a disc. The friction coefficient of laser-textured with
different spacing distances of 150, 200, and 250 m versus untextured surfaces was compared and
found to vary depending on the applied normal load. The laser-textured surface having a pocket
spacing distance of 150 m and pocket density of 5.6%, offered the lowest friction coefficient of 0.097
on average for all tested loads, whereas the average friction coefficient of the untextured surface
was 0.117. In addition, the wettability of textured surfaces was insignificantly changed compared
to that of untextured ones, so the micro-lubricant pockets did not cause oleophobicity affecting the
performance of lubrication. Well-defined micro-pockets using the most appropriate laser parameters,
i.e., 10 W laser power with 0.10 s irradiation duration and 150 m spacing distance, successfully
reduced the sliding friction of contacting couples between the laser-textured tool steel and advanced
high-strength steel surfaces. The low surface friction induced by the laser-fabricated micro-lubricant
pockets has been feasible for the forming tool and die applications where the energy consumed in
their operations can be minimized.