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Cutting performance of a binder-less sintered cubic boron nitride tool in the high-speed milling of gray cast iron
Journal of Materials Processing Technology 127 (2002) 217–221
Cutting performance of a binder-less sintered cubic boron nitride tool in the high-speed milling of gray cast iron Hideharu Katoa,*, Kazuhiro Shintania, Hitoshi Sumiyab a
Department of Mechanical Engineering, Kanazawa Institute of Technology, 7-1 Ohgigaoka, Nonoichi, Ishikawa 921-8501, Japan b Itami Research Laboratories, Sumitomo Electric Industries, Ltd., 1-1-1 Koya-kita, Itami, Hyogo 664-0016, Japan
Abstract In the present investigation, the improvement of processing efficiency in the high-speed milling of gray cast iron is explored. The cutting performance and wear mechanism of a binder-less PcBN tool in practical milling is investigated. The tool life of the binder-less PcBN tool at a cutting speed of 33.3 m/s is improved remarkably as compared with that of the usual PcBN tool. Although the occurrence of the thermal strain crack was confirmed after a short cutting length with the usual PcBN tool, a thermal crack of the binder-less PcBN tool could not be observed at 60 km. It was clarified that the binder-less PcBN tool can improve tool life in high-speed milling. Also, the edge shape of the binder-less PcBN tool remains sharp in comparison with that of the usual PcBN tool, and an excellent low degree of roughness of the machined surface was obtained. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Binder-less PcBN tool; Gray cast iron; High-speed milling; Thermal strain cracks
1. Introduction High-speed machining is considered to be an effective means of enhancing productivity because it does not require a large machine size or great space. However, high-speed cutting is related to high temperature of tool tips, thereby countering efforts to prolong tool life [1]. In the investigation of high-speed machining of gray cast iron (FC300), it has been reported that the sintered cubic boron nitride (PcBN) tool is effective in both prolonging tool life and removing material at a higher rate [2–5]. In addition, it has been clarified that adhesion on flank faces is composed of aluminum oxide at a cutting speed of 25.0 m/s, and that the working of aluminum oxide as a protective film on a flank face reduces the flank wear rate [5]. However, the extension of tool life in a continuous cutting condition cannot be expected, even with it the usual PcBN tool, which combines the binding phases with the c-BN particle, is applied under intermittent conditions. In the case of interrupted cutting, such as milling, a number of thermal strain cracks extending perpendicular to the cutting edge were noticed, and the width of the thermal strain cracks increased, damaging the flank face [6]. Therefore, the application of the PcBN tool to the face mill in high-speed conditions seems not to be a sufficient solution so far. * Corresponding author. E-mail address: [email protected] (H. Kato).
In this study, a binder-less PcBN tool is produced experimentally by the direct conversion sintering method using a high purity h-BN particle in order to improve the heat characteristics of the usual PcBN tool. The cutting performance and wear mechanism of this tool are investigated in a high-speed milling operation.
2. Experimental procedure The workpiece material is gray cast iron (JIS-FC300, tensile strength: 300 N/mm2). Table 1 shows the chemical composition and hardness of the workpiece material. The shape and geometry of the workpiece are represented by the rectangular parallel-pipe shape of 100 mm 48 mm 70 mm. The tool materials were polycrystalline cubic boron nitride (PcBN) compacts. Two PcBN tools were tested and are shown in Table 2. As shown in the table, the BW80 tool was composed of a CoWB þ Al compound-based binder and c-BN particles. The c-BN particle size of this tool was about 3 mm. The RcBN tool (binder-less PcBN tool) is synthesized by the direct conversion sintering method from hexagonal BN under high pressure and high temperature. The c-BN particle size of binder-less PcBN compacts was smaller than about 1 mm. The thermal property of this material exhibited higher thermal conductivity as compared with the BW80 tool. Fig. 1 shows the tool geometry. The tool edge has a 458 negative
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H. Kato et al. / Journal of Materials Processing Technology 127 (2002) 217–221
Table 1 Chemical composition and hardness of the workpiece material Workpiece material FC300
Chemical composition (mass%) C
Si
Mn
S
Al
Cr
Fe
3.07
1.81
0.87
0.14
0.01
0.058
Balance
Brinell hardness (HB) 206
Table 2 Materials and thermal characteristics of the tools used Tool type
RcBN BW80
Content ratio of c-BN grain (%)
c-BN grain size
>99.9 80.0
<1 1–3
Material of binding phase
Thermal conductivity (W/m K)
Vickers hardness (HV) RT
1273 (K)
None CoWB þ Al compounds
400–500 100–150
5000 3500
2000 1200
Fig. 1. Schematic illustration of the tool geometry (dimensions: mm).
land and the diameter extent of the honing is 0.02 mm. These tips were attached to a face milling cutter body with the specifications of 100 mm, A:R: þ 8 , R:R: þ 2 . In the milling experiments, fine cutting conditions were used as follows—feed rate Sz: 0.15 mm/tooth, depth of cut t: 0.5 mm and cutting speed V: 16.7, 25.0, 33.3, 50.0 m/s. The tool life was determined by the development rate of the thermal cracks (Rc) or the width of the flank wear land (VB). The Rc value shows the ratio of the width of the thermal cracks to the length of the cutting edge, the limiting value to determine the life being set at 20%. VB was determined by measuring the mean distance between the initial cutting edge and the front of a worn portion.
condition. Although the width of the flank wear land is approximately 0.1 mm at cutting lengths exceeding 10 km, the tool life was rather short as compared to the tool life with continuous turning [5]. Solid marks shows the variation of the ratio of the width of thermal cracks. The ratio of the width of thermal cracks to cutting length when the cutting speed is 33.0 m/s is relatively low compared to that for the other two conditions. Fig. 3 shows the observations of damage to a typical tool edge following the progress of the cutting length. Although it is clear that the flank wear is relatively small, several thermal strain cracks have developed with the progress of the cutting length. Microcracks at the cutting edge are observed at a cutting length of 4 km (Fig. 3(b)). Finally, a number of thermal strain cracks extending perpendicular to the cutting edge were noticed. In addition, at this stage the width of the thermal strain cracks enlarges, resulting in damage to the flank wear face (Fig. 3(c)). The SEM micrograph of the flank wear land and
3. Experimental results and discussion 3.1. Cutting characteristics of the usual PcBN tool in high-speed milling The effect of cutting speed on tool life was investigated using a commercial PcBN tool (BW80 tool). Fig. 2 shows the correlation between the cutting length of both the width of flank wear land (VB) and the ratio of the width of thermal cracks to (Rc) obtained in the milling experiments. The cutting speed was selected according to the improvement in the material removal rate. The wear development rate, as shown by open marks, is similar among the various speeds, and no big differences in wear were observed in each
Fig. 2. The relation between the cutting length and both the width of the flank wear land and the development rate of thermal strain cracks with BW80 tool at several cutting speeds.
H. Kato et al. / Journal of Materials Processing Technology 127 (2002) 217–221
219
Fig. 4. SEM image of the flank wear land and the results analyses with BW80 tool: (a) SEM image; (b) EDS analysis of flank wear face; and (c) unworn portion.
Fig. 3. SEM image of tool edge with BW80 tool following the process of cutting length: (a) 0.1 km; (b) 4 km; and (c) 16 km.
the results of analyses of both the flank wear face and the unworn portion are shown in Fig. 4. Fig. 4(a) shows that the tool edge is clearly covered with thin adhesion and thermal strain cracks. According to the results of analysis, the unworn portion strongly suggests the presence of elements Al, N, and B, which comprise the tool materials (Fig. 4(c)), while Al and O were detected in the neighborhood of the cutting edge (Fig. 4(b)). From these test results and the observations, it is clear that the growth of thermal strain cracks prevents the formation of a stable protective coating. Therefore, a sufficient tool life has not been obtained. It is considered that the differences in thermal expansion coefficients in the tool material has a large effect on the tension field, because the tool material used is a composite of the binder and c-BN particle.
on tool wear. In order to improve the tool life in a high-speed milling operation, a binder-less PcBN (RcBN) tool composed of the single composition of the c-BN particle was produced, and the cutting performance of the RcBN tool was investigated. Fig. 5 shows the variation of the width of the flank wear land and the ratio of the width of thermal strain cracks to the length of the cutting edge, with an increase in cutting length using both the RcBN tool and the conventional PcBN (BW80) tool. As seen in this figure, it is clear that the RcBN tool is superior to the BW80 tool in wear
3.2. Application of the binder-less PcBN tool to high-speed milling As mentioned in the previous section, the thermal strain crack on the cutting edge was thought to have a major effect
Fig. 5. The relation between the cutting length for both the width of the flank wear land and the development rate of thermal strain cracks using both the RcBN tool and BW80 tools.
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H. Kato et al. / Journal of Materials Processing Technology 127 (2002) 217–221
Fig. 6. Comparison of the wear mode of the cutting edge for both of the tools: (a) BW80 tool at 16 km; (b) finished edge of (a); (c) RcBN tool at 60 km; and (d) cutting edge of (c).
resistance and has about six times the tool life. In the case of the BW80 tool, the thermal strain crack begins to arise early in the cutting length. The tool life has been determined by the thermal strain crack. In the other tool, the origin of the thermal strain cracks is not recognized, even if the RcBN tool reaches 60 km at the cutting length. Fig. 6 compares the wear mode for both tools. The cutting edge of the RcBN tool remains sharp after the cutting length progresses of 60 km (Fig. 6(c) and (d)). At a cutting length of 16 km, the tool’s
cutting edge has already become rounded, and has sustained major damage from thermal strain crack. In addition, a thermal strain crack is observed in the finishing edge, which forms the machined surface (Fig. 6(b)). Fig. 7 shows the SEM micrograph of the flank wear land and the results of analyses of the flank wear face. As seen in this figure, the flank wear face of the RcBN tool is covered with thin adhesion (Fig. 7(a)). Although in the unworn portion, B and N of the tool material component are detected (Fig. 7(c)), Al, O, and Si were detected in the adhesion of the worn part (Fig. 7(b)). It is considered that the prolonged tool life mechanism [5] effectively functions in high-speed milling using the RcBN tool. On the other hand, Fig. 8 shows the SEM micrographs of the machined surface and the profile of surface roughness with the BW80 and RcBN tools. In the case of using the BW80, a cyclic striped pattern is clearly observed and this pattern is thought to be the damage to the finishing edge. In the case of using the RcBN tool, the same patterns are hardly observed. These observations are reflected in the finished surface roughness measurement as shown in Fig. 9. With the RcBN tool, the surface roughness is constant and its level is low compared to the level of roughness with the BW80 tool. From these tests and the observations, it can be concluded that the RcBN tool is very much more effective in preventing thermal strain crack at the cutting edge. It was clarified also that improved processing efficiency and accuracy can be achieved by applying the RcBN tool to the high-speed milling of gray cast iron.
Fig. 7. SEM image of the flank wear land and the results of analyses with RcBN tool: (a) SEM image; (b) EDS analysis of the flank wear face; and (c) unworn portion.
H. Kato et al. / Journal of Materials Processing Technology 127 (2002) 217–221
221
Fig. 8. Comparison of the profile of the surface roughness and the machined surface using both tools: (a) RcBN tool; and (b) BW80 tool.
4. The origin of the thermal strain cracks is not recognized, even if the RcBN tool reaches 60 km at the cutting length. The prolonged tool life mechanism effectively functions in high-speed milling using the RcBN tool. 5. In using the RcBN tool, the level of surface roughness is constant and its value is low compared to that of the BW80 tool.
Acknowledgements
Fig. 9. The relation between cutting length and average roughness height using both the RcBN tool and BW80 tool.
The authors would like to thank Mr. S. Idezu for the supply of the test piece. In addition, Osawa Scientific Studies Grants Foundation, which partially supported this research, is gratefully acknowledged.
References 4. Conclusion In the high-speed machining of gray cast iron using the experimental PcBN tool, the cutting performance and wear mechanism of the tool life in a practical milling application was investigated. The results obtained are summarized as follows: 1. In using the usual PcBN (BW80) tool, which is a composite of the binder and c-BN particles, many thermal cracks extending perpendicular from the cutting edge were noticed, and the width of thermal strain cracks enlarged, resulting in damage to the flank wear face. 2. The formation of a stable protective coating is prevented by the growth of thermal strain cracks. 3. The binder-less PcBN (RcBN) tool is superior to the BW80 tool in wear resistance, and its length exceeds that of the BW80 tool about six times.
[1] K. Shintani, N. Suzuki, Wear mechanism of CBN tool by hightemperature cutting condition in ADI machining, JSPE 61 (6) (1995) 804–809 in Japanese. [2] K. Becker, High-speed fine turning of lamellar gray cast iron, Z. Wirtsch Fert. Autom. 88 (10) (1993) 447–450. [3] T.J. Broskea, High speed machining of gray cast iron with polycrystalline cubic boron nitride tool, in: Proceedings of the Conference on Advances in Tool Materials for Use in High Speed Machining, 1987, pp. 39–47. [4] M. Deming, B. Young, D. Ratlff, PCBN turns gray cast iron, Cutting Tool Eng. 46 (6) (1994) 84–92. [5] K. Shintani, H. Kato, H. Sugita, N. Suzuki, Wear mechanism of PcBN tool in high speed machining of gray cast iron, JSPE 64 (2) (1998) 261–265 in Japanese. [6] H. Kato, K. Shintani, H. Sugita, Cutting performance of sintered cubic boron nitride tool in high speed machining of gray cast iron—the application of prolonged tool life mechanism to the milling operation: Proceedings of the International Seminar on Improving Machine Tool Performance, Vol. I, July 6–8, 1998, San Sebastian, Spain, pp. 209–218.
Cutting performance of a binder-less sintered cubic boron nitride tool in the high-speed milling of gray cast iron Hideharu Katoa,*, Kazuhiro Shintania, Hitoshi Sumiyab a
Department of Mechanical Engineering, Kanazawa Institute of Technology, 7-1 Ohgigaoka, Nonoichi, Ishikawa 921-8501, Japan b Itami Research Laboratories, Sumitomo Electric Industries, Ltd., 1-1-1 Koya-kita, Itami, Hyogo 664-0016, Japan
Abstract In the present investigation, the improvement of processing efficiency in the high-speed milling of gray cast iron is explored. The cutting performance and wear mechanism of a binder-less PcBN tool in practical milling is investigated. The tool life of the binder-less PcBN tool at a cutting speed of 33.3 m/s is improved remarkably as compared with that of the usual PcBN tool. Although the occurrence of the thermal strain crack was confirmed after a short cutting length with the usual PcBN tool, a thermal crack of the binder-less PcBN tool could not be observed at 60 km. It was clarified that the binder-less PcBN tool can improve tool life in high-speed milling. Also, the edge shape of the binder-less PcBN tool remains sharp in comparison with that of the usual PcBN tool, and an excellent low degree of roughness of the machined surface was obtained. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Binder-less PcBN tool; Gray cast iron; High-speed milling; Thermal strain cracks
1. Introduction High-speed machining is considered to be an effective means of enhancing productivity because it does not require a large machine size or great space. However, high-speed cutting is related to high temperature of tool tips, thereby countering efforts to prolong tool life [1]. In the investigation of high-speed machining of gray cast iron (FC300), it has been reported that the sintered cubic boron nitride (PcBN) tool is effective in both prolonging tool life and removing material at a higher rate [2–5]. In addition, it has been clarified that adhesion on flank faces is composed of aluminum oxide at a cutting speed of 25.0 m/s, and that the working of aluminum oxide as a protective film on a flank face reduces the flank wear rate [5]. However, the extension of tool life in a continuous cutting condition cannot be expected, even with it the usual PcBN tool, which combines the binding phases with the c-BN particle, is applied under intermittent conditions. In the case of interrupted cutting, such as milling, a number of thermal strain cracks extending perpendicular to the cutting edge were noticed, and the width of the thermal strain cracks increased, damaging the flank face [6]. Therefore, the application of the PcBN tool to the face mill in high-speed conditions seems not to be a sufficient solution so far. * Corresponding author. E-mail address: [email protected] (H. Kato).
In this study, a binder-less PcBN tool is produced experimentally by the direct conversion sintering method using a high purity h-BN particle in order to improve the heat characteristics of the usual PcBN tool. The cutting performance and wear mechanism of this tool are investigated in a high-speed milling operation.
2. Experimental procedure The workpiece material is gray cast iron (JIS-FC300, tensile strength: 300 N/mm2). Table 1 shows the chemical composition and hardness of the workpiece material. The shape and geometry of the workpiece are represented by the rectangular parallel-pipe shape of 100 mm 48 mm 70 mm. The tool materials were polycrystalline cubic boron nitride (PcBN) compacts. Two PcBN tools were tested and are shown in Table 2. As shown in the table, the BW80 tool was composed of a CoWB þ Al compound-based binder and c-BN particles. The c-BN particle size of this tool was about 3 mm. The RcBN tool (binder-less PcBN tool) is synthesized by the direct conversion sintering method from hexagonal BN under high pressure and high temperature. The c-BN particle size of binder-less PcBN compacts was smaller than about 1 mm. The thermal property of this material exhibited higher thermal conductivity as compared with the BW80 tool. Fig. 1 shows the tool geometry. The tool edge has a 458 negative
0924-0136/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 4 - 0 1 3 6 ( 0 2 ) 0 0 1 4 5 - 0
218
H. Kato et al. / Journal of Materials Processing Technology 127 (2002) 217–221
Table 1 Chemical composition and hardness of the workpiece material Workpiece material FC300
Chemical composition (mass%) C
Si
Mn
S
Al
Cr
Fe
3.07
1.81
0.87
0.14
0.01
0.058
Balance
Brinell hardness (HB) 206
Table 2 Materials and thermal characteristics of the tools used Tool type
RcBN BW80
Content ratio of c-BN grain (%)
c-BN grain size
>99.9 80.0
<1 1–3
Material of binding phase
Thermal conductivity (W/m K)
Vickers hardness (HV) RT
1273 (K)
None CoWB þ Al compounds
400–500 100–150
5000 3500
2000 1200
Fig. 1. Schematic illustration of the tool geometry (dimensions: mm).
land and the diameter extent of the honing is 0.02 mm. These tips were attached to a face milling cutter body with the specifications of 100 mm, A:R: þ 8 , R:R: þ 2 . In the milling experiments, fine cutting conditions were used as follows—feed rate Sz: 0.15 mm/tooth, depth of cut t: 0.5 mm and cutting speed V: 16.7, 25.0, 33.3, 50.0 m/s. The tool life was determined by the development rate of the thermal cracks (Rc) or the width of the flank wear land (VB). The Rc value shows the ratio of the width of the thermal cracks to the length of the cutting edge, the limiting value to determine the life being set at 20%. VB was determined by measuring the mean distance between the initial cutting edge and the front of a worn portion.
condition. Although the width of the flank wear land is approximately 0.1 mm at cutting lengths exceeding 10 km, the tool life was rather short as compared to the tool life with continuous turning [5]. Solid marks shows the variation of the ratio of the width of thermal cracks. The ratio of the width of thermal cracks to cutting length when the cutting speed is 33.0 m/s is relatively low compared to that for the other two conditions. Fig. 3 shows the observations of damage to a typical tool edge following the progress of the cutting length. Although it is clear that the flank wear is relatively small, several thermal strain cracks have developed with the progress of the cutting length. Microcracks at the cutting edge are observed at a cutting length of 4 km (Fig. 3(b)). Finally, a number of thermal strain cracks extending perpendicular to the cutting edge were noticed. In addition, at this stage the width of the thermal strain cracks enlarges, resulting in damage to the flank wear face (Fig. 3(c)). The SEM micrograph of the flank wear land and
3. Experimental results and discussion 3.1. Cutting characteristics of the usual PcBN tool in high-speed milling The effect of cutting speed on tool life was investigated using a commercial PcBN tool (BW80 tool). Fig. 2 shows the correlation between the cutting length of both the width of flank wear land (VB) and the ratio of the width of thermal cracks to (Rc) obtained in the milling experiments. The cutting speed was selected according to the improvement in the material removal rate. The wear development rate, as shown by open marks, is similar among the various speeds, and no big differences in wear were observed in each
Fig. 2. The relation between the cutting length and both the width of the flank wear land and the development rate of thermal strain cracks with BW80 tool at several cutting speeds.
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219
Fig. 4. SEM image of the flank wear land and the results analyses with BW80 tool: (a) SEM image; (b) EDS analysis of flank wear face; and (c) unworn portion.
Fig. 3. SEM image of tool edge with BW80 tool following the process of cutting length: (a) 0.1 km; (b) 4 km; and (c) 16 km.
the results of analyses of both the flank wear face and the unworn portion are shown in Fig. 4. Fig. 4(a) shows that the tool edge is clearly covered with thin adhesion and thermal strain cracks. According to the results of analysis, the unworn portion strongly suggests the presence of elements Al, N, and B, which comprise the tool materials (Fig. 4(c)), while Al and O were detected in the neighborhood of the cutting edge (Fig. 4(b)). From these test results and the observations, it is clear that the growth of thermal strain cracks prevents the formation of a stable protective coating. Therefore, a sufficient tool life has not been obtained. It is considered that the differences in thermal expansion coefficients in the tool material has a large effect on the tension field, because the tool material used is a composite of the binder and c-BN particle.
on tool wear. In order to improve the tool life in a high-speed milling operation, a binder-less PcBN (RcBN) tool composed of the single composition of the c-BN particle was produced, and the cutting performance of the RcBN tool was investigated. Fig. 5 shows the variation of the width of the flank wear land and the ratio of the width of thermal strain cracks to the length of the cutting edge, with an increase in cutting length using both the RcBN tool and the conventional PcBN (BW80) tool. As seen in this figure, it is clear that the RcBN tool is superior to the BW80 tool in wear
3.2. Application of the binder-less PcBN tool to high-speed milling As mentioned in the previous section, the thermal strain crack on the cutting edge was thought to have a major effect
Fig. 5. The relation between the cutting length for both the width of the flank wear land and the development rate of thermal strain cracks using both the RcBN tool and BW80 tools.
220
H. Kato et al. / Journal of Materials Processing Technology 127 (2002) 217–221
Fig. 6. Comparison of the wear mode of the cutting edge for both of the tools: (a) BW80 tool at 16 km; (b) finished edge of (a); (c) RcBN tool at 60 km; and (d) cutting edge of (c).
resistance and has about six times the tool life. In the case of the BW80 tool, the thermal strain crack begins to arise early in the cutting length. The tool life has been determined by the thermal strain crack. In the other tool, the origin of the thermal strain cracks is not recognized, even if the RcBN tool reaches 60 km at the cutting length. Fig. 6 compares the wear mode for both tools. The cutting edge of the RcBN tool remains sharp after the cutting length progresses of 60 km (Fig. 6(c) and (d)). At a cutting length of 16 km, the tool’s
cutting edge has already become rounded, and has sustained major damage from thermal strain crack. In addition, a thermal strain crack is observed in the finishing edge, which forms the machined surface (Fig. 6(b)). Fig. 7 shows the SEM micrograph of the flank wear land and the results of analyses of the flank wear face. As seen in this figure, the flank wear face of the RcBN tool is covered with thin adhesion (Fig. 7(a)). Although in the unworn portion, B and N of the tool material component are detected (Fig. 7(c)), Al, O, and Si were detected in the adhesion of the worn part (Fig. 7(b)). It is considered that the prolonged tool life mechanism [5] effectively functions in high-speed milling using the RcBN tool. On the other hand, Fig. 8 shows the SEM micrographs of the machined surface and the profile of surface roughness with the BW80 and RcBN tools. In the case of using the BW80, a cyclic striped pattern is clearly observed and this pattern is thought to be the damage to the finishing edge. In the case of using the RcBN tool, the same patterns are hardly observed. These observations are reflected in the finished surface roughness measurement as shown in Fig. 9. With the RcBN tool, the surface roughness is constant and its level is low compared to the level of roughness with the BW80 tool. From these tests and the observations, it can be concluded that the RcBN tool is very much more effective in preventing thermal strain crack at the cutting edge. It was clarified also that improved processing efficiency and accuracy can be achieved by applying the RcBN tool to the high-speed milling of gray cast iron.
Fig. 7. SEM image of the flank wear land and the results of analyses with RcBN tool: (a) SEM image; (b) EDS analysis of the flank wear face; and (c) unworn portion.
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Fig. 8. Comparison of the profile of the surface roughness and the machined surface using both tools: (a) RcBN tool; and (b) BW80 tool.
4. The origin of the thermal strain cracks is not recognized, even if the RcBN tool reaches 60 km at the cutting length. The prolonged tool life mechanism effectively functions in high-speed milling using the RcBN tool. 5. In using the RcBN tool, the level of surface roughness is constant and its value is low compared to that of the BW80 tool.
Acknowledgements
Fig. 9. The relation between cutting length and average roughness height using both the RcBN tool and BW80 tool.
The authors would like to thank Mr. S. Idezu for the supply of the test piece. In addition, Osawa Scientific Studies Grants Foundation, which partially supported this research, is gratefully acknowledged.
References 4. Conclusion In the high-speed machining of gray cast iron using the experimental PcBN tool, the cutting performance and wear mechanism of the tool life in a practical milling application was investigated. The results obtained are summarized as follows: 1. In using the usual PcBN (BW80) tool, which is a composite of the binder and c-BN particles, many thermal cracks extending perpendicular from the cutting edge were noticed, and the width of thermal strain cracks enlarged, resulting in damage to the flank wear face. 2. The formation of a stable protective coating is prevented by the growth of thermal strain cracks. 3. The binder-less PcBN (RcBN) tool is superior to the BW80 tool in wear resistance, and its length exceeds that of the BW80 tool about six times.
[1] K. Shintani, N. Suzuki, Wear mechanism of CBN tool by hightemperature cutting condition in ADI machining, JSPE 61 (6) (1995) 804–809 in Japanese. [2] K. Becker, High-speed fine turning of lamellar gray cast iron, Z. Wirtsch Fert. Autom. 88 (10) (1993) 447–450. [3] T.J. Broskea, High speed machining of gray cast iron with polycrystalline cubic boron nitride tool, in: Proceedings of the Conference on Advances in Tool Materials for Use in High Speed Machining, 1987, pp. 39–47. [4] M. Deming, B. Young, D. Ratlff, PCBN turns gray cast iron, Cutting Tool Eng. 46 (6) (1994) 84–92. [5] K. Shintani, H. Kato, H. Sugita, N. Suzuki, Wear mechanism of PcBN tool in high speed machining of gray cast iron, JSPE 64 (2) (1998) 261–265 in Japanese. [6] H. Kato, K. Shintani, H. Sugita, Cutting performance of sintered cubic boron nitride tool in high speed machining of gray cast iron—the application of prolonged tool life mechanism to the milling operation: Proceedings of the International Seminar on Improving Machine Tool Performance, Vol. I, July 6–8, 1998, San Sebastian, Spain, pp. 209–218.