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An experimental technique for the measurement of temperature on CBN tool face in end milling
ARTICLE IN PRESS
International Journal of Machine Tools & Manufacture 47 (2007) 2071–2076 www.elsevier.com/locate/ijmactool
An experimental technique for the measurement of temperature on CBN tool face in end milling Masahiko Satoa,, Takashi Uedab, Hisataka Tanakaa a b
Department of Mechanical Engineering, Tottori University, Koyamacho-minami 4-101, Tottori 680-8552, Japan Department of Mechanical Systems Engineering, Kanazawa University, Kakumatyo, Kanazawa 920-1192, Japan Received 28 February 2007; received in revised form 18 May 2007; accepted 25 May 2007 Available online 7 June 2007
Abstract An infrared radiation pyrometer with two optical fibers connected by a fiber coupler was developed and applied to the measurement of tool–chip interface temperature in end milling with a binderless CBN tool. The infrared rays radiated from the tool–chip interface and transmitted through the binderless CBN are accepted by the optical fiber inserted in the tool and are then sent to the pyrometer. A combination of the two fibers and the fiber coupler makes it possible to transmit the accepted rays to the pyrometer, which is set up outside of the machine tool. This method is very practical in end milling for measuring the temperature history at tool–chip interface during chip formation. The maximum tool–chip interface temperature in up milling of a 0.55% carbon steel is 480 1C when the cutting speed is 2.2 m/s and 560 1C at 4.4 m/s, and in the down milling, 500 1C at 2.2 m/s and 600 1C at 4.4 m/s. r 2007 Elsevier Ltd. All rights reserved. Keywords: Temperature measurement; End milling; CBN tool
1. Introduction End milling is widely used as a machining process in the manufacture of mechanical components that requires high geometric accuracy and smooth surfaces. In the machining of high-speed steel, stainless steel, high-temperature alloys, and so on, cubic boron nitride (CBN) is often used as a milling tool tip material because of its physical and chemical stability at high temperatures, and its low affinity for ferrous metals which is difficult for the diamond tools to make effective cutting. When a work material is machined, most of the power consumed is converted into heat. The heat generated increases the temperature of the cutting tool and the workpiece and it causes various thermal damages such as tool wear, thermal expansion, and the degradation of dimensional tolerance. Tool wear especially causes deterioration of surface integrity, increase of cutting forces, and Corresponding author. Tel.: +81 857 31 5195; fax: +81 857 31 5195.
E-mail address: [email protected] (M. Sato). 0890-6955/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmachtools.2007.05.006
occurrence of chatter vibration. In order to avoid these undesirable problems and choose appropriate machining conditions, it is necessary to acquire accurate information about milling temperatures. McFeron and Chao [1] developed a procedure and necessary equations for the computation of the average, transient tool–chip interface temperature in plain peripheral milling, and measured the average tool–chip interface temperature using a tool–work thermocoupling technique. Since they used a mercury bath to make electrical contact, the peripheral speed was limited to a relatively low speed. Schmidt [2] determined the maximum temperature occurring in or near the surface of a workpiece while it was being milled. He took temperatures at several different depths in the workpiece using thermocouple embedded in the workpiece. Stephenson and Ali [3] theoretically and experimentally investigated the tool temperatures in interrupted cutting. Theoretically, the temperature in a semi-infinite rectangular corner heated by a time-varying heat flux with various spatial distributions was used to investigate the general nature of tool temperature distribution. They
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compared the results of this analysis with the cutting temperature measured by infrared and tool–chip thermocouple technique. An infrared video image system was used in the end turning of a slotted tube to simulate interrupted cutting. Lazoglu and Altintas [4] presented a numerical model based on the finite difference method to predict tool and chip temperature fields in continuous machining and time-varying milling process. They showed that the results of the simulation are in satisfactory agreement with experimental temperature measurements reported in the literature. Ueda et al. [5] measured the temperature of the flank face of a cutting tool in high speed milling using a two-color pyrometer with an optical fiber. The fiber was inserted into a fine hole drilled in the workpiece and accepted infrared energy that was radiated from the flank face of the cutting tool when it passed above the hole. Although these previous investigations into milling temperatures provided valuable information, very little work has been done on the measurement of tool face temperatures during chip formation in end milling with a CBN tool. This is because the contact area between the tool and the chip is very small and the chip is produced intermittently in a very short time. The thermocouple technique is the most promising method but cannot be applied to CBN tool because CBN is an electrical insulator. Also, a conventional thermal radiation pyrometer cannot be applied to measure the rake face temperature, since the rake face cannot be seen from the outside during chip formation. Generally, CBN tool is produced by sintering a CBN powder mixed with a binder material such as TiC and TiN. Recently, a new technology has been developed making it possible to sinter the CBN tool without binder materials. The binderless CBN tools have many advantages, such as high thermal conductivity, high resistance to thermal shock and oxidation, and good transmittance for infrared rays. The translucent characteristic of binderless CBN tools makes it possible to measure the tool–chip interface temperature in end milling. In tribological applications, using translucent heads or disks, the temperatures of microscopic areas in a sliding contact were measured [6,7]. In precision turning, Ueda et al. [8] measured the temperature on the rake face of a singlecrystal diamond tool using infrared pyrometer. In the present study, we develop an infrared radiation pyrometer with two optical fibers connected by a fiber coupler and measure the tool–chip interface temperature in end milling with a binderless CBN tool while a chip is producing. The infrared rays radiated from the tool–chip interface and transmitted through the binderless CBN are accepted by one optical fiber, which is inserted into the tool and fixed in the main spindle of machine tool. Then the infrared energy is sent to the other fiber, which is fixed at the column of machine tool and led to the two-color pyrometer. The fiber coupler makes it possible to connect two optical fibers without touching each other.
Fig. 1. Pyrometer’s schematic illustration.
2. Pyrometer 2.1. Fundamental structure Fig. 1 shows a schematic illustration of an infrared radiation pyrometer with optical fibers. Two optical fibers, fiber-A and fiber-B, are used and a fiber coupler is used to connect fiber-A with fiber-B without touching each other. Fiber-A can be rotated upon an axis at high speed. On the other hand, fiber-B is fixed in the coupler and is in a stationary stage. The infrared rays radiated from the object are accepted and transmitted by fiber-A. The infrared rays emitted from the other end face of fiber-A are accepted and transmitted by fiber-B and focused on the infrared detectors using a condenser. The output signals of the detectors are amplified and then recorded. This system makes it possible to transmit the rays from the rotating shaft of the machine tool to the pyrometer on the outside of the machine tool. 2.2. Components The pyrometer is characterized by the composition of all components. The use of an optical fiber facilitates the detection of energy radiated from a very small object, even if the target is in an intricate part of the object. We used a multimode step index fluoride glass optical fiber in this study. The fiber has a fluoride core and a fluoride cladding with a lower refractive index. The diameters of core and cladding of fibers-A are 195 and 215 mm, respectively, and those of fiber-B are 430 and 477 mm, respectively. The numerical aperture of both fibers is 0.22. The fluoride glass fiber transmits light with wavelength from 0.5 to 4 mm. In other words, the wavelength of the light transmission using the fluoride fiber is longer than that using a quartz fiber. The end faces of the optical fiber are created using a sharp blade and the faces are observed by a microscope. We then checked whether the output voltage of the pyrometer with the optical fiber reaches a standard value under constant illumination.
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Fig. 2. Frequency characteristics of amplifier.
Two-color detector, which is used in this experiment, is composed of two kinds of photocells: an indium arsenic (InAs) cell and an indium antimonide (InSb) cell. The InAs cell is mounted in a sandwich configuration over the InSb cell. The InAs cell detects the radiation at wavelength from about 1 to 3 mm. The InSb cell detects the radiation at wavelength from about 3 to 6 mm, which transmits through the InAs cell. Temperature can be measured by taking the ratio of the signals from each photocell. The photocells are maintained at 77 K using liquid nitrogen in order to decrease thermal noise and achieve high sensitivity. Calcium fluoride (CaF2) lens is used as a condenser. It offers a constant transmission of more than 90% in wavelength from about 0.5 to 10 mm. The electric current signals, which are derived from these photocells when they are exposed to the infrared radiation, were converted into voltage signals and then amplified. Fig. 2 shows the frequency characteristics of the amplifier for a rectangular wave, which clearly indicates that the amplifier has a flat response from 10 Hz to 100 kHz. Since the response time of the photocells is approximately 1 ms, the frequency characteristics of the pyrometer are the same as the amplifier. 2.3. Influence of fiber deviation and eccentricity at the coupler In this study, as Fig. 1 shows, the infrared energy radiated from the object is accepted by fiber-A, which is rotating upon its center axis and transmitted to fiber-B using the fiber coupler, and led to the pyrometer. Fig. 3 shows the fiber deviation ‘‘a’’ between the rotational center axis and fiber-B and the eccentricity ‘‘e’’ between the fiberA and the rotational center axis in the fiber coupler. Fig. 3(a) is the ideal case when both center axes of fiber-A and fiber-B coincide with the rotational center axis and the radiation energy transmitted from fiber-A to fiber-B reaches maximum. However, in practice, there is a slight difference in position among these three axes, so that three cases of the position of axis can be considered as shown in Fig. 3(b)–(d). In Fig. 3(b), the center axis of fiber-A coincides with the rotational center axis but there is a slight deviation between the two fiber axes. In Fig. 3(c), the center
Fig. 3. Deviation and eccentricity between fibers.
axis of fiber-B coincides with the rotational center axis but there is a little eccentricity between the center axis of fiberA and the rotational center axis. In Fig. 3(d), these three axes do not coincide with each other, so that there is a fiber deviation and an eccentricity, simultaneously. The deviation and the eccentricity cause the cyclical variation in the transmission energy between these two optical fibers. Two-color pyrometer compensates for the measurement errors ascribed to the cyclical variation. Since the variation of incident infrared radiation energy to each photocell caused by deviation and eccentricity are exactly the same, their effects are cancelled in the process of taking the output ratio of InAs- and InSb-pyrometers. This means that the two-color pyrometer is independent of deviation and eccentricity between the fibers. 3. Experimental arrangement and conditions The experimental arrangement is illustrated schematically in Fig. 4, and the experimental conditions are summarized in Table 1. We used a single point end milling cutter. The tool insert was made by bonding the binderless CBN of 0.65 mm thickness to a cemented carbide substrate. Fig. 5 shows the shape of the tool insert and the details of the hole position in the insert. A small hole was drilled into the tool insert from underneath until the bottom of the hole reached the surface of CBN tip. The hole is 1.7 mm from the tool top and has a tilt of 151 in order to target on the tool–chip contact area in the chip formation. Fig. 6 shows the spectral transmittance of the 0.65-mm-thick binderless CBN used in this study. In the milling experiment, the optical fiber was inserted into the hole until the incident face of the fiber reached the bottom surface of the CBN. The diameter of the fiber’s target area on the rake face is about 0.5 mm. The target area is shown in Fig. 5. During the chip formation, the infrared rays, radiated from the tool–chip interface and transmitted through the
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Fig. 6. Spectral transmittance of 0.65-mm-thick binderless CBN.
Fig. 4. Experimental arrangement. Table 1 Cutting conditions
Fig. 7. Calibration set-up.
Tool tip material Workpiece Cutting speed (m/s) Feed rate (mm/s) Feed per tooth (mm) Axial depth of cut (mm) Radial depth of cut (mm) Radial rake angle (deg) Axial rake angle (deg) Diameter of cutter (mm) Cutting fluid
Binderless CBN 0.55% carbon steel 2.2–4.4 2.7–5.3 0.2 2 3 3 0 52 None
coupler without touching. The coupler makes it possible to transmit the infrared rays accepted by fiber-A to fiber-B. The infrared energy transmitted to fiber-B is led to the photocells and converted into electric signals. The signals are stored in a data acquisition board and analyzed using a personal computer. The workpiece used is 0.55% carbon steel and is mounted on the piezoelectric dynamometer. Cutting tests are performed in both up milling and down milling under the conditions in Table 1. 4. Experimental results 4.1. Calibration We calibrated the pyrometer by sighting on a radiating target that has a known temperature, as shown in Fig. 7. A mechanical chopper is used to modulate the radiation from the target. For the target, we used the same work material as used in the experiment. A thermocouple is embedded in the target to monitor its temperature. Fig. 8 shows the resulting calibration curve for carbon steel. Using this curve, the output ratio of the photocells is converted into the temperature. 4.2. Tool temperatures
Fig. 5. Details of tool insert.
CBN, were accepted and transmitted by the inserted optical fiber-A. Fiber-A runs through the inside of the machine tool spindle and connects to fiber-B using the fiber
Fig. 9 shows the cutting forces and cutting temperature in up milling. In Fig. 9(a), Fx is a principal cutting force and Fy is a normal cutting force, as shown in Fig. 4. Fig. 9(b) shows the tool–chip interface temperature history during chip formation, which is obtained by taking the
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Fig. 8. Calibration curve.
Fig. 10. Output waves in down milling: V ¼ 3.3 m/s.
Fig. 9. Output waves in up milling: V ¼ 3.3 m/s.
ratio of the output signals of the InAs- and InSbpyrometers in up milling. The cutting length is about 12.9 mm, and the maximum depth of cut is about 0.093 mm. The cutting force increases with the cutting operation as shown in the figure. In Fig. 9(b), the temperature on the rake face increases very quickly at the beginning of the cutting and reaches a constant temperature, and the temperature of 500 1C is constantly maintained during the cutting. From the characteristics of radiation pyrometer, the temperature measured is approximate to the maximum temperature on the target area [8]. Fig. 10(a) and (b) shows the cutting forces and the tool–chip interface temperature in down milling, respectively. During chip formation, the cutting force decreases as the cutting proceeds. The temperature increases quickly at the beginning of cutting, and then the temperature tends to decrease as the cutting proceeds. Fig. 11 shows the variation in the maximum cutting temperatures at the tool–chip interface, which are mea-
Fig. 11. The relation between cutting speed and maximum tool tip temperature measured during cutting.
sured during chip formation. The tool temperature increases with the increase of cutting speed. In up milling, the temperature is 480 1C at cutting speed of 2.2 m/s and 560 1C at 4.4 m/s, and in down cutting, 500 1C at 2.2 m/s and 600 1C at 4.4 m/s. It is found that the maximum tool temperature in down milling is about 50 1C higher than that in up milling and the temperature difference at rake face is about 90 1C when the cutting speed is doubled. Ueda et al. [9] measured the temperature of a cutting edge of CBN tool flank in turning of 0.45% carbon steel by using a two-color pyrometer. A CBN sintered with TiN binder was used and the volumetric percent of CBN was approximately 60%. In the test, cutting speed, depth of cut and feed were 2.5–3.8 m/s, 0.8 mm and 0.15 mm/tooth, respectively. The cross-sectional area of the uncut chip was 0.12 mm2. The experimental tests were performed by continuous cutting and the measured temperatures of the
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cutting edge for these cutting conditions were found to be 640–720 1C. In our end milling test, the maximum cross-sectional area of the uncut chip is 0.186 mm2 and the measured temperature is 480 1C when cutting speed is 2.2 m/s and 560 1C at 4.4 m/s. The temperatures in the end milling test are lower than those in the turnig test in nearly the same cutting conditions. In end milling process, since the tool is subjected to cyclic heating and cooling as it passes in and out of the workpiece [3], the temperature is lower than that in continuous cutting. In addition, the use of binderless CBN inserts, which have high heat conductivity than CBN with binder contents, reduces temperatures, because the heat is more readily conducted away through the tool. 5. Conclusions The infrared radiation pyrometer with two optical fibers connected by the fiber coupler was developed and the binderless CBN tool–chip interface temperature in end milling was measured using the pyrometer. The infrared rays radiated from the tool–chip interface and transmitted through the binderless CBN were accepted by an optical fiber inserted in the tool insert. These rays were then led to the InAs- and InSb-pyrometer connected by the fiber coupler that transmits the rays outside the machine tool. The two-color pyrometer compensates for measuring errors ascribed to deviation and eccentricity between fibers at the fiber coupler. This method is very practical for measuring the tool–chip interface temperature in end milling. The tool–chip interface temperature in up milling of the 0.55% carbon steel is 480 1C at cutting speed 2.2 m/s and 560 1C at 4.4 m/s and in down milling 500 1C at 2.2 m/s and 600 1C at 4.4 m/s. It is found that the maximum tool
temperature in down milling is about 50 1C higher than that in up milling and the temperature difference at rake face is about 90 1C when the cutting speed is doubled. Acknowledgment The authors would like to thank Sumitomo Electric Hardmetal Corp. for providing the binderless CBN tool insert. References [1] D.E. McFeron, B.T. Chao, Transient interface temperatures in plain peripheral milling, Transactions of the ASME, Journal of Engineering for Industry 80 (1958) 321–329. [2] A.O. Schmidt, Workpiece and surface temperature in milling, Transactions of the ASME, Journal of Engineering for Industry (1953) 883–890. [3] D.A. Stephenson, A. Ali, Tool temperatures in interrupted metal cutting, Transactions of the ASME, Journal of Engineering for Industry 114 (1992) 127–136. [4] I. Lazoglu, Y. Altintas, Prediction of tool and chip temperature in continuous and interrupted machining, International Journal of Machine Tools and Manufacture 42 (2002) 1011–1022. [5] T. Ueda, A. Hosokawa, K. Oda, K. Yamada, Temperature on flank face of cutting tool in high speed milling, Annals of the CIRP 50 (1) (2001) 37–40. [6] S. Suzuki, F.E. Kennedy, The detection of flash temperatures in a sliding contact by the method of tribo-induced thermoluminescence, Transactions of the ASME, Journal of Tribology 113 (1991) 120–127. [7] B.L. Weick, M.J. Furey, B. Vick, Surface temperatures generated with ceramic materials in oscillating/fretting contact, Transactions of the ASME, Journal of Tribology 116 (1994) 260–267. [8] T. Ueda, M. Sato, K. Nakayama, The temperature of a single crystal diamond tool in turning, Annals of the CIRP 47 (1) (1998) 41–44. [9] T. Ueda, M.A. Huda, K. Yamada, K. Nakayama, Temperature measurement of CBN tool in turning of high hardness steel, Annals of the CIRP 48 (1) (1999) 63–66.
International Journal of Machine Tools & Manufacture 47 (2007) 2071–2076 www.elsevier.com/locate/ijmactool
An experimental technique for the measurement of temperature on CBN tool face in end milling Masahiko Satoa,, Takashi Uedab, Hisataka Tanakaa a b
Department of Mechanical Engineering, Tottori University, Koyamacho-minami 4-101, Tottori 680-8552, Japan Department of Mechanical Systems Engineering, Kanazawa University, Kakumatyo, Kanazawa 920-1192, Japan Received 28 February 2007; received in revised form 18 May 2007; accepted 25 May 2007 Available online 7 June 2007
Abstract An infrared radiation pyrometer with two optical fibers connected by a fiber coupler was developed and applied to the measurement of tool–chip interface temperature in end milling with a binderless CBN tool. The infrared rays radiated from the tool–chip interface and transmitted through the binderless CBN are accepted by the optical fiber inserted in the tool and are then sent to the pyrometer. A combination of the two fibers and the fiber coupler makes it possible to transmit the accepted rays to the pyrometer, which is set up outside of the machine tool. This method is very practical in end milling for measuring the temperature history at tool–chip interface during chip formation. The maximum tool–chip interface temperature in up milling of a 0.55% carbon steel is 480 1C when the cutting speed is 2.2 m/s and 560 1C at 4.4 m/s, and in the down milling, 500 1C at 2.2 m/s and 600 1C at 4.4 m/s. r 2007 Elsevier Ltd. All rights reserved. Keywords: Temperature measurement; End milling; CBN tool
1. Introduction End milling is widely used as a machining process in the manufacture of mechanical components that requires high geometric accuracy and smooth surfaces. In the machining of high-speed steel, stainless steel, high-temperature alloys, and so on, cubic boron nitride (CBN) is often used as a milling tool tip material because of its physical and chemical stability at high temperatures, and its low affinity for ferrous metals which is difficult for the diamond tools to make effective cutting. When a work material is machined, most of the power consumed is converted into heat. The heat generated increases the temperature of the cutting tool and the workpiece and it causes various thermal damages such as tool wear, thermal expansion, and the degradation of dimensional tolerance. Tool wear especially causes deterioration of surface integrity, increase of cutting forces, and Corresponding author. Tel.: +81 857 31 5195; fax: +81 857 31 5195.
E-mail address: [email protected] (M. Sato). 0890-6955/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmachtools.2007.05.006
occurrence of chatter vibration. In order to avoid these undesirable problems and choose appropriate machining conditions, it is necessary to acquire accurate information about milling temperatures. McFeron and Chao [1] developed a procedure and necessary equations for the computation of the average, transient tool–chip interface temperature in plain peripheral milling, and measured the average tool–chip interface temperature using a tool–work thermocoupling technique. Since they used a mercury bath to make electrical contact, the peripheral speed was limited to a relatively low speed. Schmidt [2] determined the maximum temperature occurring in or near the surface of a workpiece while it was being milled. He took temperatures at several different depths in the workpiece using thermocouple embedded in the workpiece. Stephenson and Ali [3] theoretically and experimentally investigated the tool temperatures in interrupted cutting. Theoretically, the temperature in a semi-infinite rectangular corner heated by a time-varying heat flux with various spatial distributions was used to investigate the general nature of tool temperature distribution. They
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compared the results of this analysis with the cutting temperature measured by infrared and tool–chip thermocouple technique. An infrared video image system was used in the end turning of a slotted tube to simulate interrupted cutting. Lazoglu and Altintas [4] presented a numerical model based on the finite difference method to predict tool and chip temperature fields in continuous machining and time-varying milling process. They showed that the results of the simulation are in satisfactory agreement with experimental temperature measurements reported in the literature. Ueda et al. [5] measured the temperature of the flank face of a cutting tool in high speed milling using a two-color pyrometer with an optical fiber. The fiber was inserted into a fine hole drilled in the workpiece and accepted infrared energy that was radiated from the flank face of the cutting tool when it passed above the hole. Although these previous investigations into milling temperatures provided valuable information, very little work has been done on the measurement of tool face temperatures during chip formation in end milling with a CBN tool. This is because the contact area between the tool and the chip is very small and the chip is produced intermittently in a very short time. The thermocouple technique is the most promising method but cannot be applied to CBN tool because CBN is an electrical insulator. Also, a conventional thermal radiation pyrometer cannot be applied to measure the rake face temperature, since the rake face cannot be seen from the outside during chip formation. Generally, CBN tool is produced by sintering a CBN powder mixed with a binder material such as TiC and TiN. Recently, a new technology has been developed making it possible to sinter the CBN tool without binder materials. The binderless CBN tools have many advantages, such as high thermal conductivity, high resistance to thermal shock and oxidation, and good transmittance for infrared rays. The translucent characteristic of binderless CBN tools makes it possible to measure the tool–chip interface temperature in end milling. In tribological applications, using translucent heads or disks, the temperatures of microscopic areas in a sliding contact were measured [6,7]. In precision turning, Ueda et al. [8] measured the temperature on the rake face of a singlecrystal diamond tool using infrared pyrometer. In the present study, we develop an infrared radiation pyrometer with two optical fibers connected by a fiber coupler and measure the tool–chip interface temperature in end milling with a binderless CBN tool while a chip is producing. The infrared rays radiated from the tool–chip interface and transmitted through the binderless CBN are accepted by one optical fiber, which is inserted into the tool and fixed in the main spindle of machine tool. Then the infrared energy is sent to the other fiber, which is fixed at the column of machine tool and led to the two-color pyrometer. The fiber coupler makes it possible to connect two optical fibers without touching each other.
Fig. 1. Pyrometer’s schematic illustration.
2. Pyrometer 2.1. Fundamental structure Fig. 1 shows a schematic illustration of an infrared radiation pyrometer with optical fibers. Two optical fibers, fiber-A and fiber-B, are used and a fiber coupler is used to connect fiber-A with fiber-B without touching each other. Fiber-A can be rotated upon an axis at high speed. On the other hand, fiber-B is fixed in the coupler and is in a stationary stage. The infrared rays radiated from the object are accepted and transmitted by fiber-A. The infrared rays emitted from the other end face of fiber-A are accepted and transmitted by fiber-B and focused on the infrared detectors using a condenser. The output signals of the detectors are amplified and then recorded. This system makes it possible to transmit the rays from the rotating shaft of the machine tool to the pyrometer on the outside of the machine tool. 2.2. Components The pyrometer is characterized by the composition of all components. The use of an optical fiber facilitates the detection of energy radiated from a very small object, even if the target is in an intricate part of the object. We used a multimode step index fluoride glass optical fiber in this study. The fiber has a fluoride core and a fluoride cladding with a lower refractive index. The diameters of core and cladding of fibers-A are 195 and 215 mm, respectively, and those of fiber-B are 430 and 477 mm, respectively. The numerical aperture of both fibers is 0.22. The fluoride glass fiber transmits light with wavelength from 0.5 to 4 mm. In other words, the wavelength of the light transmission using the fluoride fiber is longer than that using a quartz fiber. The end faces of the optical fiber are created using a sharp blade and the faces are observed by a microscope. We then checked whether the output voltage of the pyrometer with the optical fiber reaches a standard value under constant illumination.
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Fig. 2. Frequency characteristics of amplifier.
Two-color detector, which is used in this experiment, is composed of two kinds of photocells: an indium arsenic (InAs) cell and an indium antimonide (InSb) cell. The InAs cell is mounted in a sandwich configuration over the InSb cell. The InAs cell detects the radiation at wavelength from about 1 to 3 mm. The InSb cell detects the radiation at wavelength from about 3 to 6 mm, which transmits through the InAs cell. Temperature can be measured by taking the ratio of the signals from each photocell. The photocells are maintained at 77 K using liquid nitrogen in order to decrease thermal noise and achieve high sensitivity. Calcium fluoride (CaF2) lens is used as a condenser. It offers a constant transmission of more than 90% in wavelength from about 0.5 to 10 mm. The electric current signals, which are derived from these photocells when they are exposed to the infrared radiation, were converted into voltage signals and then amplified. Fig. 2 shows the frequency characteristics of the amplifier for a rectangular wave, which clearly indicates that the amplifier has a flat response from 10 Hz to 100 kHz. Since the response time of the photocells is approximately 1 ms, the frequency characteristics of the pyrometer are the same as the amplifier. 2.3. Influence of fiber deviation and eccentricity at the coupler In this study, as Fig. 1 shows, the infrared energy radiated from the object is accepted by fiber-A, which is rotating upon its center axis and transmitted to fiber-B using the fiber coupler, and led to the pyrometer. Fig. 3 shows the fiber deviation ‘‘a’’ between the rotational center axis and fiber-B and the eccentricity ‘‘e’’ between the fiberA and the rotational center axis in the fiber coupler. Fig. 3(a) is the ideal case when both center axes of fiber-A and fiber-B coincide with the rotational center axis and the radiation energy transmitted from fiber-A to fiber-B reaches maximum. However, in practice, there is a slight difference in position among these three axes, so that three cases of the position of axis can be considered as shown in Fig. 3(b)–(d). In Fig. 3(b), the center axis of fiber-A coincides with the rotational center axis but there is a slight deviation between the two fiber axes. In Fig. 3(c), the center
Fig. 3. Deviation and eccentricity between fibers.
axis of fiber-B coincides with the rotational center axis but there is a little eccentricity between the center axis of fiberA and the rotational center axis. In Fig. 3(d), these three axes do not coincide with each other, so that there is a fiber deviation and an eccentricity, simultaneously. The deviation and the eccentricity cause the cyclical variation in the transmission energy between these two optical fibers. Two-color pyrometer compensates for the measurement errors ascribed to the cyclical variation. Since the variation of incident infrared radiation energy to each photocell caused by deviation and eccentricity are exactly the same, their effects are cancelled in the process of taking the output ratio of InAs- and InSb-pyrometers. This means that the two-color pyrometer is independent of deviation and eccentricity between the fibers. 3. Experimental arrangement and conditions The experimental arrangement is illustrated schematically in Fig. 4, and the experimental conditions are summarized in Table 1. We used a single point end milling cutter. The tool insert was made by bonding the binderless CBN of 0.65 mm thickness to a cemented carbide substrate. Fig. 5 shows the shape of the tool insert and the details of the hole position in the insert. A small hole was drilled into the tool insert from underneath until the bottom of the hole reached the surface of CBN tip. The hole is 1.7 mm from the tool top and has a tilt of 151 in order to target on the tool–chip contact area in the chip formation. Fig. 6 shows the spectral transmittance of the 0.65-mm-thick binderless CBN used in this study. In the milling experiment, the optical fiber was inserted into the hole until the incident face of the fiber reached the bottom surface of the CBN. The diameter of the fiber’s target area on the rake face is about 0.5 mm. The target area is shown in Fig. 5. During the chip formation, the infrared rays, radiated from the tool–chip interface and transmitted through the
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Fig. 6. Spectral transmittance of 0.65-mm-thick binderless CBN.
Fig. 4. Experimental arrangement. Table 1 Cutting conditions
Fig. 7. Calibration set-up.
Tool tip material Workpiece Cutting speed (m/s) Feed rate (mm/s) Feed per tooth (mm) Axial depth of cut (mm) Radial depth of cut (mm) Radial rake angle (deg) Axial rake angle (deg) Diameter of cutter (mm) Cutting fluid
Binderless CBN 0.55% carbon steel 2.2–4.4 2.7–5.3 0.2 2 3 3 0 52 None
coupler without touching. The coupler makes it possible to transmit the infrared rays accepted by fiber-A to fiber-B. The infrared energy transmitted to fiber-B is led to the photocells and converted into electric signals. The signals are stored in a data acquisition board and analyzed using a personal computer. The workpiece used is 0.55% carbon steel and is mounted on the piezoelectric dynamometer. Cutting tests are performed in both up milling and down milling under the conditions in Table 1. 4. Experimental results 4.1. Calibration We calibrated the pyrometer by sighting on a radiating target that has a known temperature, as shown in Fig. 7. A mechanical chopper is used to modulate the radiation from the target. For the target, we used the same work material as used in the experiment. A thermocouple is embedded in the target to monitor its temperature. Fig. 8 shows the resulting calibration curve for carbon steel. Using this curve, the output ratio of the photocells is converted into the temperature. 4.2. Tool temperatures
Fig. 5. Details of tool insert.
CBN, were accepted and transmitted by the inserted optical fiber-A. Fiber-A runs through the inside of the machine tool spindle and connects to fiber-B using the fiber
Fig. 9 shows the cutting forces and cutting temperature in up milling. In Fig. 9(a), Fx is a principal cutting force and Fy is a normal cutting force, as shown in Fig. 4. Fig. 9(b) shows the tool–chip interface temperature history during chip formation, which is obtained by taking the
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Fig. 8. Calibration curve.
Fig. 10. Output waves in down milling: V ¼ 3.3 m/s.
Fig. 9. Output waves in up milling: V ¼ 3.3 m/s.
ratio of the output signals of the InAs- and InSbpyrometers in up milling. The cutting length is about 12.9 mm, and the maximum depth of cut is about 0.093 mm. The cutting force increases with the cutting operation as shown in the figure. In Fig. 9(b), the temperature on the rake face increases very quickly at the beginning of the cutting and reaches a constant temperature, and the temperature of 500 1C is constantly maintained during the cutting. From the characteristics of radiation pyrometer, the temperature measured is approximate to the maximum temperature on the target area [8]. Fig. 10(a) and (b) shows the cutting forces and the tool–chip interface temperature in down milling, respectively. During chip formation, the cutting force decreases as the cutting proceeds. The temperature increases quickly at the beginning of cutting, and then the temperature tends to decrease as the cutting proceeds. Fig. 11 shows the variation in the maximum cutting temperatures at the tool–chip interface, which are mea-
Fig. 11. The relation between cutting speed and maximum tool tip temperature measured during cutting.
sured during chip formation. The tool temperature increases with the increase of cutting speed. In up milling, the temperature is 480 1C at cutting speed of 2.2 m/s and 560 1C at 4.4 m/s, and in down cutting, 500 1C at 2.2 m/s and 600 1C at 4.4 m/s. It is found that the maximum tool temperature in down milling is about 50 1C higher than that in up milling and the temperature difference at rake face is about 90 1C when the cutting speed is doubled. Ueda et al. [9] measured the temperature of a cutting edge of CBN tool flank in turning of 0.45% carbon steel by using a two-color pyrometer. A CBN sintered with TiN binder was used and the volumetric percent of CBN was approximately 60%. In the test, cutting speed, depth of cut and feed were 2.5–3.8 m/s, 0.8 mm and 0.15 mm/tooth, respectively. The cross-sectional area of the uncut chip was 0.12 mm2. The experimental tests were performed by continuous cutting and the measured temperatures of the
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cutting edge for these cutting conditions were found to be 640–720 1C. In our end milling test, the maximum cross-sectional area of the uncut chip is 0.186 mm2 and the measured temperature is 480 1C when cutting speed is 2.2 m/s and 560 1C at 4.4 m/s. The temperatures in the end milling test are lower than those in the turnig test in nearly the same cutting conditions. In end milling process, since the tool is subjected to cyclic heating and cooling as it passes in and out of the workpiece [3], the temperature is lower than that in continuous cutting. In addition, the use of binderless CBN inserts, which have high heat conductivity than CBN with binder contents, reduces temperatures, because the heat is more readily conducted away through the tool. 5. Conclusions The infrared radiation pyrometer with two optical fibers connected by the fiber coupler was developed and the binderless CBN tool–chip interface temperature in end milling was measured using the pyrometer. The infrared rays radiated from the tool–chip interface and transmitted through the binderless CBN were accepted by an optical fiber inserted in the tool insert. These rays were then led to the InAs- and InSb-pyrometer connected by the fiber coupler that transmits the rays outside the machine tool. The two-color pyrometer compensates for measuring errors ascribed to deviation and eccentricity between fibers at the fiber coupler. This method is very practical for measuring the tool–chip interface temperature in end milling. The tool–chip interface temperature in up milling of the 0.55% carbon steel is 480 1C at cutting speed 2.2 m/s and 560 1C at 4.4 m/s and in down milling 500 1C at 2.2 m/s and 600 1C at 4.4 m/s. It is found that the maximum tool
temperature in down milling is about 50 1C higher than that in up milling and the temperature difference at rake face is about 90 1C when the cutting speed is doubled. Acknowledgment The authors would like to thank Sumitomo Electric Hardmetal Corp. for providing the binderless CBN tool insert. References [1] D.E. McFeron, B.T. Chao, Transient interface temperatures in plain peripheral milling, Transactions of the ASME, Journal of Engineering for Industry 80 (1958) 321–329. [2] A.O. Schmidt, Workpiece and surface temperature in milling, Transactions of the ASME, Journal of Engineering for Industry (1953) 883–890. [3] D.A. Stephenson, A. Ali, Tool temperatures in interrupted metal cutting, Transactions of the ASME, Journal of Engineering for Industry 114 (1992) 127–136. [4] I. Lazoglu, Y. Altintas, Prediction of tool and chip temperature in continuous and interrupted machining, International Journal of Machine Tools and Manufacture 42 (2002) 1011–1022. [5] T. Ueda, A. Hosokawa, K. Oda, K. Yamada, Temperature on flank face of cutting tool in high speed milling, Annals of the CIRP 50 (1) (2001) 37–40. [6] S. Suzuki, F.E. Kennedy, The detection of flash temperatures in a sliding contact by the method of tribo-induced thermoluminescence, Transactions of the ASME, Journal of Tribology 113 (1991) 120–127. [7] B.L. Weick, M.J. Furey, B. Vick, Surface temperatures generated with ceramic materials in oscillating/fretting contact, Transactions of the ASME, Journal of Tribology 116 (1994) 260–267. [8] T. Ueda, M. Sato, K. Nakayama, The temperature of a single crystal diamond tool in turning, Annals of the CIRP 47 (1) (1998) 41–44. [9] T. Ueda, M.A. Huda, K. Yamada, K. Nakayama, Temperature measurement of CBN tool in turning of high hardness steel, Annals of the CIRP 48 (1) (1999) 63–66.