Cutting performance of textured polycrystalline diamond tools with composite lyophilic/lyophobic wettabilities

Abstract

This paper develops a new technology to improve the anti-friction performance of cutting tools by constructing textured surface with composite lyophilic/lyophobic wettabilities and this method is applied to polycrystalline diamond (PCD) tools. Lyophobic micro/nano structures and lyophilic grooves were successively fabricated on the tool surface by a pulsed fiber laser using different processing parameters. Then the influence of un-textured PCD tools, microgrooved tools and textured tools with lyophilic/lyophobic wettabilities on cutting performance and tool wear were investigated during turning of Ti6Al4V titanium alloy bar under minimum quantity lubrication (MQL) environment. The results indicated that textured PCD tools with lyophilic/lyophobic wettabilities reduced the cutting force, average friction coefficient and cutting tool wear in comparison of un-textured tools and microgrooved tools. Furthermore, the anti-friction mechanism of textured tools with lyophilic/lyophobic wettabilities was discussed from the aspects of drag reduction and the regulation of movement of cutting liquid to the impact tool-chip interface. This new technology provides a new way for textured tools to further enhance cutting performance and mitigate tool wear.

Introduction

In modern industry, titanium alloy, owing to its exceptional comprehensive characteristics, such as excellent corrosion resistance, high strength to weight ratio, super corrosion resistance abilities and lower density, is widely applied in defense, aviation and aerospace industry and even in the medical sector. However, in the cutting process of titanium alloy, because of serious conditions of tool-chip interface caused by high temperature and pressure, rapid tool wear occurs frequently. In view of the problem, several ways, such as super-hard tools, coated tools, new lubrication methods, have been proposed to alleviate the tool wear and increase tool life. However, the usage of super-hard tools is limited by its inherent characteristics, such as low impact toughness. The development of new coating materials is difficult, and it usually takes very long time from research to application. Moreover, some of the operating equipment of lubricants are not easy to operate and the prices are expensive. Due to the excellent anti-friction performance of textured surface in tribology, many scholars have introduced this technology to cutting tools. Surface textured tools play a favorable role in the cutting processes. In the past, researchers validated the performance of textured cutting tools through theoretical analysis as well as conducting extensive experiments.

The most research done on surface textured tools mainly focus on micro-grooves tools and micro-pits tools. Xing et al. (2016) found that micro-grooves tools improved the cutting performance and anti-adhesion in the aluminum alloy cutting. Lei et al. (2009) performed experiments and simulation analysis on machining of Mild steel. The authors succeeded to reduce the cutting force, contact length of chip-tool and coefficient of friction using micro-pool cutting tools. Sugihara and Toshiyuki (2017) fabricated micro pits and microgrooves on the cemented carbide cutting tools by fiber laser and carried out comparative cutting experiments for machining of Ti6Al4V. The results revealed that all textured tools showed better cutting performance than un-textured tools, this better performance was due to the storage of cutting fluid and chip. In another study by (Silva et al., 2013), comparison of experimental results revealed that anti-friction performance of micro-grooves textured tools was better than micro-pits textured tools. Moreover, microgrooves with perpendicular direction to chip flow showed better performance than that of microgrooves with other lay directions. Vasumathy and Meena (2017) fabricated micro-grooves with different lay directions to chip flow on cemented carbide tools and carried out cutting experiments of AISI316 austenitic stainless steel. Comparison of the results shown that all textured tools reduced the cutting tool wear and force. Using PA inserts, maximum of 7.7% reduction in cutting forces were noted and less cutting tool wear was observed using cutting tools with micro-grooves perpendicular to chip flow. Moreover, authors explained that fewer contact length between cutting tool and chip led lowering of the forces for the microgrooves perpendicular to chip flow. Based on micro-grooves or micro-pits textured tools, some researchers developed new textured tools to further improve the cutting performance by combining many other anti-friction technologies. For example, Deng et al. (2013) fabricated self-lubrication textured tools by laser and solid lubricant. The self-lubrication texture with nano structures played an important role for chip storage during dry cutting, further improving lubricating performance and reducing pollution compared to popular textured tools and conventional tools. Sharma and Pandey (2016) chose cemented carbide cutting tools to fabricate micro grooves and pits to form hybrid-textured tools. The hybrid-textured tools improved the cutting performance and machining quality compared to single-textured tools, which primarily caused by the collective supply as micropools for sustained lubricant complement between grooves and pits.

Su et al. (2014) analyzed the influence of laser parameters on dimensions of microstructures for the PCD cutting tools, which introduced the fabrication of micro-grooves PCD tools. Kawasegi et al. (2017) made use of focused ion beam to produce micro and nanotexture on diamond tools. The authors noted that the cutting temperature, forces and average friction coefficient were reduced during machining of Aluminum alloy. Moreover, the machined surface quality of workpiece was also improved.

From the above, surface textured tools, including micro/nano textured tools and other newly developed tools can partially improve cutting performance by decreasing the contact length, storing partial cutting liquid and chip. However, the anti-friction of textured tools is limited and the lubrication condition is still a serious issue at the tool-chip interface of textured tools because surface texture cannot control the movement of cutting liquid into the compact tool-chip interface.

Chen et al. (2016) prepared superhydrophobic surfaces on 316L stainless steel by laser texturing and fluorination. Then, the Y and S-shaped grooves with hydrophilic properties were prepared by laser ablation of part of hydrophobic materials. Through droplet experiments, they noted that droplets could move along the hydrophilic grooves though the grooves were not in straight geometry. The FEM simulations by Guo et al. (2016) analyzed the movement of a droplet on the junction of the superhydrophobic and superhydrophilic region, it was found that driven by surface tension, the droplet rapidly turned to the hydrophilic region, and the experimental results verified the simulation results. Therefore, controlling the movement of cutting liquid into the tool-chip interface is possible when cutting tools possess wettability contrast surfaces.

In this paper, a reliable method combining surface texture with composite lyophilic/lyophobic wettabilities was developed on polycrystalline diamond cutting tools for the further improvement of cutting tool performance. In order to make an investigation on the influence of the textures and wettability on the cutting tool wear and cutting performance, a comparative study of Ti6Al4V titanium alloy under minimum quantity lubrication (MQL) was conducted with un-textured tools, microgrooved tools and textured tools with lyophilic/lyophobic wetting properties.