Improvement in the Machining Processes by Micro-Textured Tools during the Turning Process ^†

Abstract

The cutting fluid’s lubrication affects a workpiece’s surface finish and cutting tool lifespan during turning. To optimize machine performance, appropriate lubrication is needed. Empirical experiments examined how machining factors affected a redesigned single-point cutting tool. Texturing the tool’s rake surface without altering its physical qualities was achieved utilizing super-drilling and laser engraving technologies. The goal was to build a surface junction that would keep cutting fluid in contact with the tool longer, improving lubrication and cooling. Both standard and customized tools were used to compare cutting force, temperature, power usage, and surface polish. Magnified pictures from the scanning electron microscope were utilized to analyze tool wear in different places. The improved tool dramatically lowered mean cutting force, heat output, and power consumption in experiments. The textured tool produced continuous chips instead of discontinuous/burnt chips due to increased friction at the tool–chip interface. The updated tool improved lubrication and cooling with cutting fluid.

1. Introduction

Metals are removed from the work material to generate chips in the classic machining process. During the machining process of dry turning, aside from tool wear, a rise in temperature can cause distortion of the machined surface and a deterioration in overall machining quality [1]. Researchers have been investigating the use of various cutting fluids and lubricants, as well as innovative strategies for applying and utilizing them throughout the machining process, to address these problems. The use of minimum quantity lubrication (MQL), which includes administering a small amount of lubricant directly to the cutting zone via a nozzle or similar device, is one option. This approach can provide adequate cooling and lubrication while using less fluid and lowering the risk of environmental contamination. Another option is to use cryogenic cooling, which involves cooling the cutting zone with a stream of liquid nitrogen or another cryogenic fluid. This approach can dramatically reduce the temperature at the tool–chip interface, reducing tool wear and enhancing surface quality. To increase the tribological qualities of the tool surface, advanced machining procedures such as electrical discharge machining (EDM) and laser-assisted machining (LAM) can be used. These approaches can form microstructures on the tool surface, which can increase lubricant retention and reduce friction and wear during the machining process.

To summarize, producing high-quality workpieces with low heat creation during the machining process is a major difficulty in the manufacturing industry. To solve this issue, researchers are investigating new cutting fluids, lubricants, and application procedures, as well as sophisticated machining processes for enhancing tool surface qualities. These efforts are aimed at improving the quality of the machined surface, reducing tool wear, and increasing overall machining efficiency.

Surface texturing has previously been studied in mechanical seals, rings, and bearings to improve lubrication [2,3,4]. Perforation was made on its surface, and it performed better as a result. Based on this, it is well established that perforation improves tribological characteristics and greatly lowers sliding wear. To establish a viable reduction in tool wear and friction, the surface texturing on the tools and its behavior throughout the machining process were explored. Lei [5] empirically evaluated a comparison of tools with and without roughness during mild steel machining. There was a 30% reduction in cutting force and chip tool contact, as well as an overall improvement in the machining process. The finite element approach was used, and the results showed that the temperature and stress caused on the tooltip of the textured tool were reduced. Kawasegi [6] conducted similar research on aluminum samples to suggest improvements in the machining process. Microgrooves parallel to the machined surface outperformed other textures in terms of machining performance. When textured tools were compared to standard tools, they demonstrated increased cutting force and better tool-to-workpiece adhesion. Obikawa [7] explored the effect of cutting aluminum alloys with a cemented carbide texturing tool. The texture of the parallel-type tool improved during the machining process due to improved lubrication conditions. In contrast, publications citing aerial textures [8,9], dimple textures [10], and channel textures [11] aid in reducing the cutting process and tool wear. Several researchers [9,11,12] discovered that cutting instruments with microholes has a favorable effect. As a result, there is a need for a thorough grasp of the effective usage of other types of textures to optimize the machining process.

The purpose of this research is to look at the texture parameters when the machining force varies. The work material for the study was normal stainless steel. The effect of increasing the depth of cut on the machining process was thoroughly explored. The effects of changing the cutting speed on the machining parameters were also explored.

2. Experimental Details

For the process, steel was utilized as a cutting tool of Miranda S400 make. The toolbar was properly ground to achieve the tool geometry graphically modeled and depicted in Figure 1. In addition, tiny holes were marked over the rake surface and micro-drilled near the tooltip, as seen in Figure 2. A laser system can easily create these textures. The laser drilling machining (50 W Fiber Laser Deep Engraving Machine) process involves the use of a high-energy laser beam to create precise holes or features in a material. The process involves directing the laser beam onto the material’s surface, causing it to undergo vaporization, which results in the formation of microholes. A 0.5 mm hole was drilled near the tooltip, followed by two and three holes in succession away from the tooltip. In addition, a 1 mm hole was drilled after the third row and away from the tooltip, as illustrated in Figure 2a. The hole and groove depths were both fixed at 3 mm. The wider hole may aid in keeping the lubricant for a longer period, and as it progressively advances towards the tooltip, this will increase the heat transfer created by friction. A tiny channel was created on the other tool (Figure 2b), which will aid in the retention of the lubricant at the tooltip for a longer amount of time.

The cutting test was carried out on a conventional lathe machine for dry cutting and wet cutting with un-textured and textured tools. The AlSI 1014 mild steel (Ø25 × 150 mm length) was placed rigidly in the tailstock and spun at 330 and 500 rpm for all the experiments. The constant feed rate of 0.143 mm/rev and depth of cut of 1.0 and 0.75 mm were selected as parameters for the experiments. The cutting force that was generated was measured by a précised lathe tool dynamometer (CONTECH make; precision 0.2 N).

3. Results and Discussions

Several cutting parameters were selected for an in-depth understanding of the machining process. The detailed selected parameters are shown in

Table 1. Selected parameters for the processes.

Group	Cutting Speed (mm/min)	Depth of Cut (in mm)	Feed Rate (mm/rev)
E1	39	1.00	0.143
E2	39	0.75	0.143
E3	26	1.00	0.143
E4	26	0.75	0.143

. The various processes carried out were grouped with a suitable name and tabulated in

Table 2. Cutting process and the process number defined.

P1	Dry Turning Process (without Perforation tool)
P2	Wet Turning Process (without Perforation tool)
P3	Wet Turning Process (with microhole texturing tool)
P4	Wet Turning Process (with microchannel texturing tool)

.

3.1. Effect of Cutting Force and Tooltip Temperature

During the machining process, a considerable amount of mechanical energy was transformed into heat. The majority of the heat transfer was generated in the shear zone, while the rest of the heat was developed in the tooltip (rake surface and clearance side). The quantity of heat generated depends on the magnitude of the cutting force, rotating speed, and the condition of the friction generated at the tooltip. The determination of the temperature at the tool–workpiece interface is complex. The following simplified empirical equation was used to determine the temperature at the tool–workpiece interface [13]:

$$∆\mathrm{Tc}=\frac{{\mathrm{P}}_{\mathrm{u}}}{\mathrm{Mc} {\mathrm{C}}_{\mathrm{s}}}$$

(1)

where P_u is the friction power generated at the tooltip (in N), Mc is the metal removal rate (in kg/s), and C_s is the specific coefficient of the heat of the workpiece (Nm/kg °C). Figure 3a exhibits a variation in the cutting force with respect to the process using different cutting tools. In comparison, a maximum cutting force was recorded for the dry turning operation and a minimum value for the process with a channel-type cutting tool. According to the experiment, it was observed that the perforated tools facilitate easy chip removal from the machining zone. The presence of the liquid film over the rake surface reduces the frictional effort and, in turn, reduces the tooltip temperature. The cutting force primarily depends on the cutting environment due to the availability of lubrication during machining. In the case of the P1 and P2 processes, the generation of high friction creates a hardening of the workpiece. A larger cutting force is thus required to shear off the chips from the workpiece [14]. A lower cutting speed results in some difficulties in tool penetration through the workpiece, primarily due to some wobbling. Hence, a lower cutting force was observed because of the repeated tool striking on the workpiece. Figure 3b represents the tooltip temperature for the various cutting conditions. Improper contact and repeated loading on the tooltip may lead to a decrease in the tooltip temperature and is observed during the process. The lower viscous cutting fluid aids in an easier machining process, and thus, lower cutting force and temperature levels are observed during the P2 process. The tooltip temperature was further reduced by tool texturing over the rake surface due to the improved availability of lubricant at the tooltip.

3.2. Effect of Power and Surface Roughness

Figure 4a depicts the power distribution for the different turning processes considered. The maximum drop in cutting power to around 35% was observed when compared with the dry turning and cutting processes that used the microchannel tools. An increase in the power for the higher rotation speed is observed due to the generation of more friction during the turning process. The drop in power generation is mainly attributed due to the retention of liquid over the tooltip over some time. This results in the presence of viscosity properties that aid in reducing friction and power [15,16]. A margin deposit in the lubrication layer is formed at the tooltip junction during the turning process when using the perforated tools. This aids in a reduction in the friction between the surfaces. Figure 4b shows the formation of surface roughness for the various process conditions. During the dry turning process, the generation of heat due to friction at the mating surface modifies the tooltip geometry. The higher friction leads to the thermal softening of the tooltip, thus reducing the tool’s strength. Here, an aggressive cutting atmosphere is created with a higher level of cutting friction, power, and tool wear. This can be minimized by applying the lubricant between the mating surfaces, wherein the cutting power and surface finish were reduced by around 20% and 34%, respectively. A better surface finish was observed when the textured tools were used. A better lubrication in the microchannel texturing tool was noticed with reduced power and an improved surface finish.

3.3. Effect of Chip Formation and Tool Wear

The various turning processes exhibit different chip formations and tool wear, which are influenced by the dynamics of the machining process. Figure 5 provides a visual representation of the chip morphology for these processes. By analyzing the chip formation, the cutting forces and the machinability of the process can be better understood. At lower turning speeds, thick chips with irregular wavy patterns are commonly observed due to the fluctuation of contact at the tooltip junction during machining. The repeated changes in the shear angle caused by the tool’s wobbling lead to the formation of such chips. The chips formed during this process have a rough surface on one side and a smooth surface on the other, which is likely caused by plastic deformation of the chip edge rubbing against the tool rake surface. However, the use of textured tools can result in continuous chips with reduced waviness due to the presence of a liquid film that reduces friction over the machined surface. Moreover, an increase in the depth of the cut leads to proportional increases in chip formation, which are not wrecked during the process. When cutting speed is increased, the textured tool process results in a decrease in chip thickness, leading to a rising shear angle and indicating a more stable and efficient machining process [17]. The chips were smaller in the textured tools when analyzed from the non-textured tools. Continuous even edges on both sides of the chips were formed.

The tool wear for different cutting tools under specific conditions was analyzed, and the results were presented in Figure 6. The experiments were conducted using a 1 mm depth of cut and a spindle speed of 500 rpm. The flank wear was observed for all the tools due to the rubbing action of the flank face against the hard particles that formed on the machined surface. The flank wear decreased when the tools were changed from non-textured to textured counterparts, with the channel type showing the least flank wear. The dry turning process caused rapid tool wear. The microchannel textured tool showed lower flank wear depth due to the improved tribological properties and reduced heat generation. The uncoated tool suffered from improper adhesion and high attrition with the workpiece, resulting in significant tool wear. Both flank and crater wear were observed, with the latter being the dominant mechanism. The use of lubricants on the tool surface reduced the intensity of both wear mechanisms gradually. Tool wear due to abrasion, wherein the lubricants carried away microburr particles, was also reduced during the process. The textured tools experienced considerably less attrition and abrasion during the machining process, resulting in significantly reduced flank wear. Among the two textured tools, the microchannel textured tool showed better performance by considerably reducing tool wear.

3.4. Overall Discussion

The cutting force was analyzed to compare the performance of non-textured and textured cutting tools during machining. The results showed a significant reduction in cutting force when microchannel cutting tools were used, compared to other tools. The cutting force was reduced by approximately 30% in dry cutting and around 22% in wet-turning processes. The smaller cutting force with textured tools suggests a reduction in friction between the rake surface of the tool and the workpiece. Additionally, the microchannels in the tool helped in improving the contact area at the tooltip by forming a thin film of lubricating oil, thus reducing the friction force. Overall, the reduced cutting force and stress formation can enhance the machining process’s performance and tool life.

The power utilization during the machining process does not depend on the stability of the machine tool itself. There are other factors such as cutting parameters, workpiece materials, type of lubrication used, and other changes in the power value [18]. During the turning process, the machine tool operations contribute to more than 50% of the total power for its utilization. The changes in the positioning of the tool have an adverse effect on the power consumption and machined quality. The repeated fatigue load acting on the tooltip leads to an increase in power consumption. An increase in power due to the aforementioned reasons was observed in the case of the dry turning process. A larger inertia force was formed during the dry turning and showed a large power profile during rotation. The inertia force and fatigue load gradually reduced in the wet turning process and were further reduced during machining with the textured tools. An improved bonding between the tool and the workpiece aided in improving the machining process, and consequently, power consumption was reduced. When further compared to the surface roughness, the microchannel tool performed a better surface finish when compared with the other tools. In the case of a high rotational speed and 1 mm depth of cut, there was an improvement of 98% in the surface finish when compared to the machining process between the microchannel tools and the wet turning process.

By comparison of the process between the textured and non-textured tools, the formation of carbides, oxides, and other nonmetallic inclusions present in the work material requires more shear force to become detached [19]. Here, a large amount of heat and stress was generated at the tooltip, which resulted in abrasion during the process. Also, the cutting temperature becomes insufficient for easy removal of the chip, which causes a serration with irregularities on the chip edge during the process [20]. Thus, a long build-up edge (BUE) was seen for all the processes when rotated at lower cutting speeds. However, BUE is seen much more during the dry turning process, which is in line with the work carried out by Surjeet Singh [21]. In the case of severe sliding action at a higher rotating speed, the attrition wear of the micro-welded chips was seen in the case of the dry turning process. With the use of a coolant, the formation of BUE is not seen much in the wet turning process due to the reduced friction and temperature level. In the case of textured tools, the attrition wear was considerably reduced.

A fairly accurate tool wear width on the rake surface was considered by observing an image in a high-end image analyzer. The present tooltip contact length from the original tooltip measured and analyzed the tool wear. The tooltip contact lengths from the non-textured to the textured tool of 0.62, 0.54., 0.52, and 0.49 were found. The increase in the tool wear along its length resulted in the tool hardening at the tooltip, which resulted in a higher cutting force and power, hence a poor machining process. In the case of the microhardness tool, the desired hardness and improved contact area helped in strong adhesion at the tooltip junction. Hence, the micro-textured tool, which aids in improving the lubrication process over the rake surface, substantially improved machining conditions.

4. Conclusions

An empirical investigation was carried out using four different tools during the dry turning operation, wet turning operation, and machining process, with two independent textured tools. By using the micro-textured tool, a profound influence over the machining operation was seen when comparisons were made in terms of cutting force, power, and surface roughness. The micro-textured tool helps to reduce friction, or technically, coefficient of friction and reduces the energy loss during metal cutting. The textured tool demonstrated superior performance when compared with non-textured tools. A significant improvement in the contact area between the tooltip and the workpiece was seen during the process. A continuous chip was formed in the textured tools when the machining process was carried out at higher speeds. In the case of lower speeds, BUE was observed due to poor adhesion during the process. Larger crater and flank wear were observed for the dry turning process, and these wears were gradually reduced when using textured tools.