The structure design and cutting performance research about the groove of the indexable inserts for machining stainless steel

Stainless steel is a notoriously difficult-to-machine material, with challenges such as hard-to-break chips and severe tool wear. To address these issues, a finishing indexable insert has been designed and developed specifically for stainless steel. This tool, named HMF, was compared to commercial tools (NF4, BF) in terms of its curved groove structure and cutting performance using SEM (scanning electron microscope Sigma500), 3D scanning (KEYENCE-VR 5000) and a profiler (Mitutoyo C-200). The HMF tool utilizes a curved edge with a curved chip breaker, and a chip-breaking bump on the tool nose. The groove parameters of the HMF insert are as follows: cutting edge angle of 12°, chip breaker groove width of 1.89 mm, back wall height of 0.095 mm, and anti-chip angle of 4°49’. 3D scanning of the chip break site reveals that the HMF chip break has a higher bump and a more pronounced chip rolling effect. HMF tool chip-breaking experiments show that it has ideal chip-breaking performance in the finishing range of ap = 0.6–1.0 mm, and f = 0.1–0.25 mm r−1. Chip analysis shows that the HMF chip curl frequency increases and the chip curl is tighter as the feed rate increases, and the curl radius gradually decreases when the feed rate is greater than 0.15 mm r−1. The results of the wear performance study are as follows: all three tools show rake face crater wear when cutting stainless steel. A small amount of built-up edge appears on the HMF cutting edge. The wear life of HMF is close to NF4 and better than BF; the wear of BF is faster in the later stages of wear.


Introduction
Stainless steel is a notoriously difficult material to work with due to its high ductility, easy work hardening, and low thermal coefficient [1][2][3].To effectively machine stainless steel, it's crucial to have better control over the chip.Poor chip control can lead to chip entanglement in the workpiece, which reduces machining efficiency as shown in figure 1.Long chips are also a serious problem in continuous turning, posing a safety hazard to workers and tools, as well as negatively impacting workpiece quality and tool life [4].Therefore, the development of tools with excellent chip-breaking properties is necessary for effective machining of stainless steel.
The maximum strain value (ε max ) of the chip must not exceed the ultimate strain value (ε b ) of the workpiece material, otherwise the chip will fracture [5].Chip fracture can occur in three ways: the chip can break at the contact point with the chip breaking bump, it can be naturally thrown off, or it can hit the workpiece and break [6].To break chips into an ideal 'C' shape, a curved chip breaker and chip breaking bump are used.Henriksen has developed an efficient chip breaking bump that improves chip breaking by optimizing the feed rate and chip flow curl radius [7].Jialu Xu and Fuzeng Wang, among others, conducted extensive experiments on the chip breakability of different indexable inserts under low feed conditions and found that the N123G5-0300-0001-CF indexable inserts had the best chip breakability [8].Libo Wu and Jiyu Liu used finite element software to simulate SANDVIK'S EM groove tools under different machining parameters, and compared the results with experimental data, proposing new designs for complex curved chip breakers [9].Jawahir studied the effect of groove parameters on curved chip breaker positive tools with a 5°clearance angle, using a high-speed camera and extensive experiments.The results showed that the chip breaking performance of different groove types exhibited cyclical changes during machining, and that the chip curl radius varied depending on the utilization of the chip breaking groove [10].
The machinability of a tool is not only dependent on its chip breaking ability, but also on its wear resistance.I S Jawahir investigated the effect of chip flow on tool wear in complex groove tools and identified forms of wear such as crater wear, flank wear, and notch wear.It has been found that the chip side flow angle and restricted contact length during machining significantly affect tool wear, including wear on the cutting edge, chip breaker groove bottom, and chip breaker bump, as shown in figure 2 [11].X D Fang and I S Jawahir concluded that tool wear affects chip breaking performance, and that the chip breaking capacity varies with the degree of tool wear, particularly with crater and flank wear [12].Tool failure is usually determined by critical back face wear (VB) and crater wear (KT) values at the point of failure [13].According to ISO standards, VB = 0.2 mm is considered minor wear, 0.35 mm is regular wear, and 0.5 mm is heavy wear [14].
Cemented carbide indexable inserts are widely used in stainless steel processing due to its high hardness and stability, which enhances the overall performance of the tool.This study focuses on designing and manufacturing a curved chip breaker indexable tool based on existing research.The process of designing and developing curved chip breakers will be summarized, and the effect of different groove parameters on cutting  performance will be explored.The developed groove tools will be compared to commercial indexable inserts in terms of cutting performance to provide a reference for the efficient application of curved chip breaker tools.

Curved chip breaker design
2.1.Groove design process 2.1.1.Chip fracture condition Before the chip contact portion slips from the bottom of the tool, the strain on the chip surface reaches the maximum elongation of the chip material, then the chip with a radius of curvature R0 will fracture [15].
The strain at fracture of the workpiece material, ε, is mainly determined by the material being cut.The chip thickness, t 2 , on the other hand, is determined by cutting parameters such as feed and cutting speed.Meanwhile, R L refers to the maximum radius of curvature when the chip curl touches the back face of the tool, while R 0 is closely linked to the radius of curvature of the chip breaker chip flow.These four parameters have a direct impact on chip curl fracture.For this study, the grooved tool base design criteria adhere to the design benchmark established by Prof. Jawahir and Fang [16].The curved chip breaker indexable tool studied here is specifically intended for use in the finishing field of austenitic stainless steel, and is designed to break chips in the range of f = 0.1-0.25 mm rev −1 and ap = 0.4-1.0mm.

Determine the basic profile type of the groove
Based on available studies, groove tools with the same restricted contact length are categorized into four types based on their back wall heights, as illustrated in figure 3.In practice, a tool with identical back wall form can be divided into four types based on the shape of the cutting edge, as depicted in figure 4. The profile shape of the chip breaker encompasses the shape of the tool nose cutting edge and major cutting edge, including the margin and rake angle parameters.

Determination of groove type parameters
The chip-breaker tool utilizes the chip breaker groove to guide the chips to flow back into the groove.Once the chip curl strength is reached, the chips break and chip-breaking are achieved.The form of chip breakage depends on the relationship between the tool band width lc and the limiting contact length at different depths of cut, as illustrated in figure 5.If the chip limiting contact length is lower than the tool band width lc, it enhances the chip flow into the groove, increases the chip flow angle, and improves the groove utilization [17,18].The groove shape is influenced by several parameters including tool band width lc, rake angle γ, groove depth d, groove width W n , and the height of the back wall H.The tool band width lc and rake angle γ determine the sharpness of the cutting edge and cutting force.Additionally, the values of tool band width lc, groove width W n , and rake angle γ affect the minimum chip break feed (f min ), but have a minor impact on the minimum depth of cut.The minimum chip break feed (f min ) increases as the tool band width lc or groove width W n increases in the same manner.However, the minimum chip break feed (f min ) gradually decreases as the rake angle γ increases [19,20].The height of the back wall H has no bearing on chip breakage.Instead, the width-depth ratio W n /H affects the minimum chip breakage feed (f min ), and that decreases gradually as the width-depth ratio W n /H increases [21].The common machining dosage and tool parameters for stainless steel are shown in table 1, and the data are taken from the technical manual shared by Sandvik Coromant.

Determination of tool shape
Each tool shape has its own unique strengths and limitations.For example, increasing the included angle of a tool will improve its cutting-edge strength, but it will also increase cutting force and vibration.Meanwhile, higher feed rates during machining can be achieved by using tools with larger included angles, but the profiling of the tool will be more difficult to access.Therefore, selecting the best tool for a particular application requires careful consideration of not only tool shape, but also corner radius.The value of the corner radius is often determined by the minimum depth of cut required; for example, a tool with a corner radius of 0.4 mm should be selected if the minimum depth of cut required is 0.3 mm in order to achieve better chip-breaking.There are seven main types of tool shapes commonly used, which are denoted by letters R, S, C, W, T, D, and V (as shown in table 2).

Determine the production process
There are two primary methods for manufacturing the groove pattern on turning tools: grinding and pressing.Figure 6 shows representative groove patterns created using each of these methods.

• Pressed sintered tools
Pressed sintered inserts are crafted by pressing tungsten carbide powder into a mold to create a blank, which is then sintered into a finished tool.These tools can be designed with more complex curved grooves and edge shapes than their ground counterparts, and their smoother joints reduce stress concentrations during use.Additionally, pressed sintered inserts can be sharpened with a finishing edge, which can increase the feed rate and thus cutting efficiency while also improving surface quality.One common type of pressed sintered insert is the symmetric groove type (SGT) tool, such as the one shown in figure 6(a).
• Sharpening type tools Sharpening type tools are created by grinding diamond wheels on the tool substrate to produce a simpler groove type, such as the common asymmetric groove type (AGT) seen in figure 6(b).These tools feature simple grooves, low production cost, and can be easily modified in terms of groove parameters.However, the application range and chip-breaking effect of sharpened tools are not as good as those of pressed sintered tools.

Selection of groove type parameters
In this study, the tool design features a groove chip breaker with a back wall elevation of d1 (as shown in figure 3(a)) and a rake angle edge structure (as seen in figure 4(b)) to ensure effective chip-breaking and edge sharpness during finishing of stainless steel.Additionally, the tools are designed to have a very small chip limiting contact length and an appropriate rake angle in order to further promote finishing sharpness.Specific parameters of the tool design also include a rounded transition design at the rear of the major cutting edge with a radius of 0.6 mm to ensure sufficient strength, and a 6°cutting edge inclination starting from a point 1.6 mm

5
(greater than the designed cutting depth of 1.0 mm) from the corner area to reduce the local cutting force on the cutting edge.Available research literature [22] suggests that a groove width of W n = 1.5 mm can be used for a feed rate of f = 0.05-0.25 mm rev −1 .The groove indexable inserts feature a limiting contact length l, as given by the following equation [23]: r is the radius of the tool corner radius.x is the cutting-edge angle k r .λ is approach angle.γ is rake angle.Use η s to further determine the value of the tool-chip contact length l c : The radius of the chip outflow circle R c can be calculated [25]: Equations ( 7) and (8) can be used to calculate the effect of groove type on chip curling.Once the extrusion strength reaches the fracture strength of the stainless-steel material, the tool can achieve effective chip breaking action.
The tool design used in this study features a triangular model TNMG160404 with an external turning indexable insert.The main offset angle is k r = 90°and λ = 0°, while the tool rake angle is γ = 14°, the corner radius is r = 0.4 mm, and the groove width is W n = 1.5 mm.
Additionally, pressed sintering is used to manufacture the pressed sintered type tools with the HMF tool shape.

Preparation of groove tools
The tool material used in this study is tungsten carbide cobalt, and one of the tools, TNMG160404-HMF, features the HMF groove indexable insert specifically designed for this study.Additionally, TNMG160404-BF and TNMG160404-NF4 are commercial carbide indexable inserts designed for stainless steel machining.In the following discussion, these three tools will be referred to by their respective groove type names: HMF, BF, and NF4.Relevant tool information is provided in table 3 below.The preparation of the HMF tool involves six basic steps: mould making, tool blank pressing, blank sintering, coating pre-treatment, PVD coating, and coating post-treatment, as illustrated in figure 7. The first step is to create a 3D data model in order to manufacture the mould.In the second step, the blank is pressed in a metal-powder press (OSTERWALDER SP 160, Switzerland) with pressing parameters set at 35KN and 10 g.The blank is then sintered in a low pressure sintering furnace (XDDY, Xiangtan City, China) with sintering parameters set to a heating rate of 5 °C min −1 , a sintering temperature of 1350 °C, a holding time of 2 h, and a cooling rate of 30 °C min −1 .In the fourth step, a TiN coating substrate with TiSiN as a hard layer of composite coating is applied to the finished blank using a physical coating furnace (ICS-800PRO, Italy).Details of the pretreatment and post-treatment of the coating are not provided.Finally, the HMF experimental sample is prepared, as shown in figure 7.

Experimental method 3.2.1. Chip breaking experiment
In this study, experiments were conducted using the CY-K6150B/1000 (Guang Zhou, China) CNC lathe to machine stainless steel 304 material using groove tools in order to study chip breaking action.The cutting parameters utilized in the experiments are presented in table 4, and they were sequentially modified in order to cut and collect the chips generated during the process.The three tools (HMF, BF, and NF4) were tested alternately in order to reduce the influence of the workpiece material during the experiments.
Due to the rich alloying elements, stainless steel material has excellent corrosion resistance and alloy strength; however, its turning performance deteriorates, especially in terms of chip breaking.The chemical composition of the stainless steel 304 workpiece material can be found in table 5.

Wear performance experiments
The wear experiments described in this study involved the continuous cutting of stainless steel 304 using a CY-K6150B/1000 CNC lathe manufactured in Guang Zhou, China.External turning was used, with a turning time of 10 min The samples were further analysed through SEM using a Sigma 500 microscope from Germany, with the specific machining parameters listed in table 6.The tool life experiment involved the use of three tools for alternate external round turning, with specific machining parameters as outlined in table 6.The wear values of the rear tool face were measured using a KEYENCE-VHX2000 depth-of-field microscope from Osaka, Japan at intervals of three minutes.Three sets of experiments were carried out, and the average wear values were recorded in a table to create a life curve.

Analysis of tool groove type parameters
The groove profile of the sintered tool was mapped using a Mitutoyo C-200 machine in Shanghai, China.The HMF groove tools, designed in this study, were compared to the commercially available finished tools BF and NF4 to analyse groove parameters and contours.The groove section located at a distance of 1.0 mm from the tool corner was selected and depicted in figure 8.The comparison revealed that the BF tool had the largest groove width of 0.904 mm, resulting in a large chip curl radius at a depth of cut of 1.0 mm.Furthermore, all three tools had similar groove depths of approximately 0.12 mm, but the groove widths of NF4 and HMF were smaller at 0.7 mm.This reduced the space for chip curling, causing severe chip extrusion.As a result, the chips of both HMF and NF4 were broken into ideal 'C' chips at a depth of cut of 1.0 mm.
The tool corner groove profile parameters, in figure 9.The BF corner part has a groove depth of 0.212 mm and a larger groove width that provides sufficient space for effective chip curling.However, its anti-chip angle of 6°17′ is greater compared to the HMF tool.The rake angle is 13°24′, as shown in figure 9(a).On the other hand, the HMF tool has a groove depth of 0.125 mm, a corner part H of 0.095 mm, an anti-chip angle of 4°49′, and a rake angle of 12°11′, as seen in figure 9(b).The NF4 tool corner part has a groove depth of 0.144 mm, an antichip angle of 5°12′, and a rake angle of 15°38′, as shown in figure 9(c).Compared to the BF and HMF tools, the NF4 has a smaller depth and width of groove but a greater rake angle, resulting in better sharpness.The BF tool's larger anti-chip angle may cause more intense wear of the chip breaker than the HMF tool.When comparing the HMF and NF4 tools, it can be observed that they have similar groove widths and anti-chip angles.However, the HMF tool has a higher back wall height of 0.095 mm with a shallower groove depth of 0.125 mm, while the NF4 has a greater rake angle of 15°38′, resulting in better sharpness.Additionally, the HMF tool uses a circular transition cutting edge, which provides a natural transition at the connection of the circular edge, avoiding stress concentration.

Tool groove structure analysis
The 3D shape of the three tools was scanned using the KEYENCE-VR 5000 equipment, where the depth is represented by blue and the height is represented by orange and red colors, as shown in figure 10.The HMF tool has a wider chip breaker cross-section compared to the BF and commercial tools, and the BF has a narrower chip breaker cross-section, with a turning groove arc highlighted by blue around the deeper chip pits of its chip breaker.The HMF chip breaking bump is more orange-red in color, with a higher chip breaking device and a more pronounced chip rolling action, as seen in figure 10(a1) and (c1).
Comparing the chip breaking parts of HMF and NF4 tools, the chip breaking bump and corner of the HMF tool are shallower.Therefore, the NF4 tool has a more obvious chip curling effect, with a smaller curl radius and an upward chip curling effect, as shown in figures 10(b1) and (c1).The shape of all three tools is characterized by a gradual, curved chip breaker with a sharp cutting edge in the corner and a larger rake angle, along with an inclined edge angle.The overall main cutting edge is curved instead of being traditionally straight.A platform for easy toolholder clamping is added to the middle part of the edge, as depicted in figures 10(a2), (b2), and (c2).
The vertical profile structure of the curved chip breaker groove varies at each position, forming a typical three-dimensional curved chip breaker groove.This design increases the random collision of rolled chips and provides better chip-breaking performance than a linear through-groove tool.

Analysis of chip breaking performance of groove type 4.3.1. Chip breaking range
Chip breakage experiments were conducted on the three tools to determine their chip breakage range when machining SUS304 material, which can also serve as a reference for similar materials, as depicted in figure 11.     machining parameters.When comparing figures 11(b) and (c), it can be observed that the HMF has fewer C-shaped chip connections while the NF4 has more than one C-shaped chip connection, indicating varied chip breaking performance.The BF groove tool exhibited poor chip-breaking performance for external turning of SUS304 material, while both the HMF and NF4 tools demonstrated good chip-breaking performance, resulting in smoother cutting during machining and better chip handling without winding the workpiece, which ideally accounts for a larger proportion of C chips.The three tools perform well in high feed and depth of cut (ap>0.8mm, f>0.2mm r −1 ) operation with good chip-breaking capabilities.

Chip analysis
The machining parameters used were a cutting speed of 250 m min −1 , a depth of cut of 0.4 mm, and a feed of 0.25 mm r −1 , with the chip cutting process of the three tools shown in figure 12.The BF chip curling process is not uniform, with the curl radius varying from large to small due to the longer chips remaining unbroken, which are then thrown off by gravity, resulting in a larger local curl radius as depicted in figure 11(a).The HMF chip curl radius is smaller, with uniform curl and shorter chips, as shown in figure 12(b).In contrast, the chip curl of NF4 was uniform, but the chips overall were longer, as shown in figure 12(c).
The measurement of chip curl was further performed by counting the chip curls under the above machining parameters, as shown in figure 13.The number of curls (Nc) of a 50 mm chip length was measured, and the frequency of chip curl (Rc) was calculated using equation (10).N c is number of curls.R c is rate of chip curls.A higher frequency in chip curl indicates that the curl is tighter, reflecting the randomness of chip curl and the unsatisfactory chip breaking effect of the tool.As feed increases, the chip curl frequency of HMF and NF4 tools gradually increases because the thicker chips are harder to curl and eventually reach a point where gravity causes them to throw off or crash off, as displayed in figure 13(a).The chip curl frequency of the BF tool varies more overall.The overall chip curl frequency of the HMF tool is higher than that of the NF4 tool, with the HMF chip curl being tighter, as demonstrated in figure 13(a).
When the feed amount reaches 0.15 mm r −1 , the curl radius of the HMF and NF4 tools gradually decreases with increasing feed amount, and the chips curl tighter and finer, as depicted in figure 13(b).The curl radius of the BF tool is unstable and changes abruptly when the feed amount is larger, with a larger chip curl radius due to more space for chip curling available in the chip breaker of the BF tool, as shown in figure 13(b).The curl radius of the NF4 and HMF tools are close to each other at higher feeds.

Tool chip morphology
The chips collected from HMF tools at various cutting dosages were morphologically analysed using SEM scanning electron microscopy, as depicted in figure 14.The free surface of the chips was shaped into serrations due to the extrusion of the tool during cutting.At low cutting depths, the chips exhibited a linear shape with a significant number of shear bands, and the chip curl was not particularly strong, as illustrated in figure 14(a).However, as the cutting depth increased, the squeezing and cracking action became more intense, leading to coarser serrations and more prominent curling, as demonstrated in figure 14(b).The chips became wider and thicker with larger depths of cut and feed rates.When the anti-chip device of the tool 'squeezed' the chip, it broke easily, leading to fewer serrations and less pressure on the chip's free surface, as illustrated in figure 14(c).The impact of cutting depth on chip curl was much more noticeable, as shown in both figure 14 15 illustrates the SEM wear morphology of the rake and flank faces of three tools with the same parameters and long-term continuous turning of SUS304.The rake face of the tools mainly showed crater wear and abrasive wear, whereas the flank face showed groove wear and built-up edge.All three tools exhibited varying degrees of crater wear marks on their rake faces, as shown in figure 15.After long-term turning, the NF4 tool's rake surface marks were small, and its cutting edge exhibited chipping and grooving due to the large rake angle of 20°, which resulted in reduced cutting-edge strength, as demonstrated in figure 15(a).
The main cutting edge of the HMF tool featured built-up edge, which is easily produced in the hightemperature and high-pressure environment during stainless steel turning, as depicted in figure 15(b).The BF tool, with the smallest rake angle of 14°and the largest groove width, had the weakest chip curl and did not display built-up edge or chipping on the main cutting edge.The tool's rake face had a long crescent depression, while the flank face showed irregular abrasive wear scratches, as depicted in figure 15(c).

Wear life analysis
The three tools were utilized for alternate cylindrical turning of SUS304 material with 3 min intervals, and the wear values of the flank face were measured using KEYENCE-VHX2000 (Osaka in Japan).The wear life curve was created by taking the average value of the three experiments, as shown in figure 16.All three tools displayed three stages of wear (Severe Stage-Stable Stage-Severe stage), in accordance with the Taylor life model [26,27].During the initial stage of wear, the irregular surface of the blade edge, which is sharp, causes rapid surface material loss, leading to an increase in wear rate [28].After a period of wear, which is the mid-term wear stage, the blade surface becomes more uniform, and the wear begins to stabilize gradually, resulting in a decrease in wear rate [29].In the later stage of wear, surface coating damage and temperature accumulation result in a large amount of protective coating shedding off, causing further deterioration of the wear environment and increasing the wear rate [30].The wear value of the HMF tool before 9 min of cutting was larger, with a fast wear rate.All three tools exhibited slow wear during the period between 9 min and 15 min The wear rate of the BF tool gradually increased, resulting in an increase in wear value.Between 15 and 18 min of previous wear, the wear value increased due to the loss of the coating.The rake angle affects the degree of sharpness, which, to some extent, affects the tool's wear.The wear performance of NF4 was better than HMF, whereas the BF tool exhibited poor wear performance.

Conclusion
This study is focused on developing a groove indexable tool specifically designed for the finishing of difficult-tomachine stainless steel materials.The newly developed tool is compared with two commercially available tools, NF4 and BF, in terms of their turning performance.
(1) The newly designed groove tool, developed specifically for the finishing of difficult-to-machine stainless steel materials, is given the model's name TNMG160404.The tool corner parameters include a cutting-edge angle of 12°, a chip breaker groove width of 1.89 mm, a 0.095 mm height of the back wall, and an anti-chip angle of 4°49′.The curved chip breaker structure includes a gradual curve edge with a three-dimensional groove and a chip break bump located at the tool's corner.
(2) The HMF tool has been compared with commercial tools BF and NF4 in terms of their chip breaking performance.The results indicate that HMF's chip breaking range is comparable to that of NF4, making it suitable for finishing applications in the range of ap = 0.6-1.0mm and f = 0.1-0.25 mm r −1 .BF's chip breaking range, on the other hand, is smaller.A chip analysis shows that the frequency of chip curl increases with HMF tools as the feed increases, and the curl radius gradually decreases when the feed exceeds 0.15 mm r −1 .An analysis of the chip morphology generated by different machining ranges of HMF tools shows an increase in chip thickness and width as the machining parameters increase.Additionally, the shear deformation on the free surface decreases and the tool's extrusion strengthens, resulting in fewer sawtooth shapes on the chip free surface.
(3) The cutting wear experiments yielded results indicating that all three tools displayed crater wear on the rake face.However, the NF4, which has a larger rake angle, experienced chipping on the flank face while the HMF, which has a smaller rake angle, had built-up edge on the cutting edge.Further analysis of the wear life revealed that all three tools went through three different wear stages, namely severe stage, stable stage, and severe stage again.The HMF demonstrated the second-highest wear life after the NF4, with the BF wearing faster in the later stages of wear.

Figure 1 .
Figure 1.Main forms of tool wear.

Figure 2 .
Figure 2. Hazards of long chips during machining.

Figure 5 .
Figure 5. (a) Schematic diagram of groove structure parameters, (b) cutting under different restricted contact lengths.

Figure 7 .
Figure 7.The experimental sample preparation process of HMF groove cutter was designed.

Table 4 .
Experimental parameters for chip breaking.

Figure 8 .
Figure 8.(a) Shows the 1.0 mm groove profile of BF tool, (b) shows the 1.0 mm groove profile of HMF tool, (c) shows the 1.0 mm groove profile of NF4 tool.

Figure 9 .
Figure 9. (a) Shows the BF tool corner groove profile parameters, (b) shows the HMF tool corner groove profile parameters, (c) shows the NF4 tool corner groove profile parameters.

Figure 10 .
Figure 10.(a) Shows the 3D morphology of the BF tool, (b) shows the 3D morphology of the NF4 tool, (c) shows the 3D morphology of the HMF tool.

Figure 11 .
Figure 11.(a) Chip breaking range of BF groove tool, (b) Chip breaking range of HMF groove tool, (c) Chip breaking range of NF4 groove tool.

Figure 12 .
Figure 12.(a) Chip shape of BF tool, (b) chip shape of HMF tool, (c) chip shape of NF4 tool.

Figure 13 .
Figure 13.(a) Variation of chip curl frequency with feed for three tools, (b) Variation of chip curl radius with feed.

Figure 15 .
Figure 15.(a) Wear morphology of the rake and flank tool face of NF4, (b) Wear morphology of the rake and flank tool face of HMF, (C) Wear morphology of the rake and flank tool face of BF.

Table 2 .
Common tool shape information.

Table 3 .
Parameter information of the experimental sample tool.

Table 6 .
Wear comparison experimental parameters.