Friction involved in metal-forming processes typically leads to the wear of tool and die surfaces, and in turn shortens the tool’s service life. A thriving need for reducing surface friction requires the tool surface to be modified. This paper presents the surface modification of SKH51 tool steel, on which the hexagonal array of micro-dimples is fabricated by a nanosecond pulse laser. Using the average laser power of 25 W can create decent dimples for trapping lubricant and enabling hydraulic pressure at the surfaces in contact. The effect of dimple density and sliding speed on the coefficient of friction was examined in this study through the pin-on-disc test, in which a stainless steel pin was applied against the tool steel disc with a constant load. The laser-textured tool steel surface with a dimple density of 35% had a friction coefficient of 0.087, which was lower than that of the untextured surface by 12.6% when using a sliding speed of 15 cm/s. In addition to friction reduction, there was no substantial wear found on the laser-textured surface compared to the untextured sample. The findings of this study can be a processing guideline and benefit the treatment of tool and die surfaces for friction and wear reduction in metal-forming and related processes.

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 µm 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 µm 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 µm 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 µm 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.

A TiCN-based cermet die was utilised to improve the formability in ironing of stainless steel drawn cups. By employing the cermet die, additional coating was not required because it was made of hard TiCN having low friction. As a comparison, TiC-coated WC-Co, non-coated WC-Co and tool steel dies were used. The effects of the viscosity of a lubricant and the ironing speed on the formability for the cermet die were examined. The cermet die exhibited the largest seizure resistance. The performance of the cermet die in repeated ironing was evaluated. For repeated ironing using the cermet die, the occurrence of seizure was prevented up to 100 strokes. It was found that the cermet die with low friction was effective in ironing stainless steel drawn cups

Excessive surface friction encountered during metal-forming processes typically leads to die wear and seizure in part surfaces, which consequently shortens the die’s service lifespan and lowers the surface quality of the formed parts. To minimize surface friction, tool surface modification is required. This study focuses on reducing the sliding friction of SKH51 high-speed steel by fabricating micro-grooves with various crosshatch angles using a nanosecond pulse laser. The effects of laser texturing parameters on achieving the groove aspect ratio of 0.1 were investigated. This aspect ratio facilitates lubricant retention and enhances lubrication performance on the contact surfaces. The influence of groove crosshatch angles (30°, 60°, and 90°) on the friction in the sliding contact between a textured high-speed steel disc and an AISI304 stainless steel pin was evaluated using a pin-on-disc test with a constant load. Moreover, the contact pressure distribution and stress concentration associated with each groove pattern were numerically analyzed using the finite element method. The results demonstrated that a laser power of 20 W effectively produced groove geometries with the desired aspect ratio. Among the tested patterns, the surface textured with a 60° crosshatch angle exhibited the lowest coefficient of friction of 0.111, compared to 0.148 for the untextured surface. Finite element analysis further revealed that the 60° crosshatch pattern provided the most balanced combination of load redistribution, reduced mean pressure, and average stress, which may reduce the friction under sliding conditions. These findings confirm that laser surface texturing, particularly with an optimized crosshatch angle, can significantly reduce sliding friction and enhance the tribological performance of high-speed steel tools.

Seizure during ironing negatively affects the quality of parts and die life. To prevent seizures, lubrication has to be improved. In this study, laser-textured dies with lubricant pockets were utilized to improve seizure resistance in the ironing of aluminum alloy sheets and stainless steel cups. The effects of array patterns of micro-pockets, such as grid and crossing array patterns with circular pockets, as well as a grooved array patterns on seizure resistance, were experimentally examined by strip ironing. The sheet and die materials were the A1050-O aluminum alloy and JIS SKD11 tool steel, respectively. Moreover, the underlying physics of the lubricant flow influencing the load-carrying capacity were investigated using three-dimensional computational fluid dynamics simulations. The optimum array patterns of the micro-pockets were then utilized on a tungsten carbide-cobalt (WC-Co) die surface for ironing SUS430 stainless steel cylindrical cups. The strip ironing results showed that the grid array pattern was successful in ironing sheets with a high ironing ratio. The grid array pattern increased the load-carrying capacity of the lubricant more than the crossing pattern, as demonstrated by the simulations, thereby improving the ironing limit. The subsequent ironing of stainless steel cups revealed that when using a textured die with a grid array pattern and lubricant without the extreme pressure additive in comparison to an untextured die, the ironing limit increased by 6% and the average ironing load decreased by 35%. The seizure resistance was improved because the pockets on the surface structured by laser surface texturing improved the load-carrying capacity during ironing.