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Temperature measurement in a solid body heated by laser beam
International Journal of Machine Tools & Manufacture 44 (2004) 927–931 www.elsevier.com/locate/ijmactool
Temperature measurement in a solid body heated by laser beam Takao Kato a,, Hiroshi Fujii b a
Department of Material Science and Technology, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan b Faculty of Engineering, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan Received 17 July 2003; received in revised form 13 January 2004; accepted 21 January 2004
Abstract A new technique, call the PVD film method, was developed for measuring the temperature inside a solid body. This technique involves physically depositing thin films on the specimen’s surface to act as thermal sensors. The solid body was quickly heated with laser irradiation and the proposed technique was used to measure the internal temperature. The experimentally determined isotherm configurations were then compared with those calculated using FEM analysis, and the analytical and experimental results coincided well. This suggests that the proposed method could prove useful in measuring the temperature of a solid body in a quasi-steady state, such as the tool and workpiece in machining processes. # 2004 Elsevier Ltd. All rights reserved. Keywords: Temperature measurement; PVD film method; Machining
1. Introduction Heat generation is nearly inevitable in almost all traditional and non-traditional manufacturing processes. It is well known that the heat generated during processing not only affects the performance and service life of cutting and forming tools, but also influences the finished surface’s integrity and dimensional accuracy. The heat that is generated by friction in rubbing components, such as gears, cams, and brakes, significantly influences the friction, wear, and lubrication of the parts. The altered behavior of these tribological characteristics can induce premature part failure because the majority of the frictional energy is transformed into heat and dissipated in the vicinity of real contact area. The rubbing surface temperature has been shown to be the decisive factor in part performance [1]. When lasers and electron beams are used for localized welding or heat treatments, the focused heat quickly spreads. The temperature distribution in the solid and the melting and solidification rates affect the metal’s stress distribution and recrystallization process, Corresponding author. Tel.: +81-58-293-2511; fax: +81-58-2301892. E-mail address: [email protected] (T. Kato).
0890-6955/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmachtools.2004.01.014
which in turn determines the strength of the specimen. An appropriate cooling rate is essential for obtaining good results [2]. Therefore, the ability to predict and measure accurately the temperature inside solid bodies as a function of time is essential for coping with a variety of thermal problems in welding processes. Many experimental techniques for measuring surface and near-surface temperatures of solid bodies subjected to dynamic heat sources have been developed with varying degrees of success. These techniques have included the use of thermocouples and infrared radiation detection [3–6]. A previous paper [7] described a newly developed technique, called the PVD film method, that measures the internal temperature of a solid body during operation, such as cutting tools during machining. Several kinds of materials were physically-vapor-deposited on the cutting tool’s split surface. The films can be used as thermal sensors in determining the temperature distribution near the cutting edge because each of the film materials melts at its specific melting temperature. A calibration test demonstrated that the temperature at the boundary between the melted and unmelted film is equal to the melting point of the thin film material. The results of the test suggested that the temperature distribution at carbide
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T. Kato, H. Fujii / International Journal of Machine Tools & Manufacture 44 (2004) 927–931
and ceramic tools’ cutting edges could be successfully measured with this method. The calibration test cited in the previous paper [7], however, was conducted under quasi-steady conditions because of the calibration apparatus’ limitations. Therefore, the method’s transient response was not fully investigated. This study uses the proposed temperature measurement process to investigate the rapid heating transient response of a solid body exposed to a laser-based heat input.
2. Experimental method Fig. 1 depicts a schematic of the experimental setup. In this study, a laser beam machining apparatus (Mitsubishi ML-15S), which is commercially available for metal cutting and welding, was used to rapidly heat the solid surface. The specimen was heated by laser irradiation using a continuous-wave CO2 laser with a wavelength of 10.6 lm and a power of 0.2 kW. The solid surface was irradiated for less than one second in order to heat, but not melt, the specimen. The unfocused beam’s diameter at the top surface of specimen was set to 5 mm by adjusting the distance between the probe and the specimen’s surface. The average heat flux was fixed at 10.2 W/mm2 and the beam produced a near-Gaussian energy distribution on the surface. The top surface was finished by grinding before it was
Fig. 1.
Laser beam heating experimental set up.
irradiated by the laser beam. And, in order to eliminate the possibility of laser beam reflection, the ground surface was coated with colloidal graphite, an irradiationabsorbing agent. Two square plates of the specimen were prepared from carbon steel (S55C) stock. The plates measured 50 mm wide, 50 mm long, and 5 mm thick. One surface of each plate was ground and lapped to a mirror finish with several different diamond slurries. A material with a known melting point was physically-vapor-deposited on the finished surface using a conventional vacuum deposition apparatus. After the two plates were prepared, they were fixed together in a vice. The laser probe was positioned so that the center of the beam exactly hit the boundary between the two plates by adjusting the table’s position, as shown in Fig. 1. Then, the constant power laser beam irradiated the specimen’s surface for a predetermined length of time, from 0.1–1.0 s. After the irradiation was complete, the plates were removed from the vice and the film material was examined with a microscope. Fig. 2 shows a photograph of v a bismuth film (melting point: 273 C) after a 0.5-s laser irradiation. A boundary, which is clearly apparent on the PVD film, denotes the separation between the melted film zone and the unmelted film zone. In the melted film zone, the irradiation melted the deposited material and then the material condensed and solidified during the cooling process. This melting/solidification process resulted in a slightly rougher area than the original surface, while the unmelted film zone remained unchanged. During irradiation, the temperature in the melted film zone is above the film’s melting point, while the temperature in the unmelted film zone is below the melting point. It follows that the temperature at the boundary is equal to the melting point of the deposited film. Therefore, the boundary is equivalent to the film’s melting point isotherm. The temperature distribution in the plate can be obtained by repeating the above process using the same irradiation time, but with different PVD films that have different melting points. This procedure is called the PVD film method. The main advantage of using a thin film sensor is that the thin film has an extremely small mass. This is advantageous because the thin film should only have a slight impact on the body’s heat transfer characteristics and the influence of the film’s physical characteristics on the internal temperature will be negligible. The PVD film materials consisted of four pure metals and one alloy. The alloy was composed of bismuth, lead and tin. The melting points and purity of the film materials are listed in Table 1. The alloy’s melting point determined experimentally.
T. Kato, H. Fujii / International Journal of Machine Tools & Manufacture 44 (2004) 927–931
Fig. 2.
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Photograph of the bismuth film after laser irradiation.
Table 1 Melting point and purity of the PVD films PVD film material
Symbol
Melting point v C
Purity %
Tellurium Lead Bismuth Indium Alloya
Te Pb Bi In Alloy
450 328 271 157 96.6
99.999 99.999 99.999 99.999 99.99
a
Composition (wt %) Bi : Pb : Sn ¼ 50 : 28 : 22.
3. Experimental results The location of the boundary observed on the film was determined with a digital micrometer mounted on a tool microscope. The results for the tellurium and the alloy film are shown in Fig. 3 after an irradiating time of 0.6 s. The results from several experimental runs using the same irradiating conditions are plotted in the figure. The isotherms appear nearly axisymmetric
Fig. 4.
Five kinds of isotherms after 0.8 s of laser irradiation.
about the laser beam’s centerline, with only a minimal amount of scatter. Fig. 4 displays a temperature map of the specimen obtained by using several different films and an irradiation time of 0.8 s. As can be seen in the figure, the isotherms are distinctly evident. 4. Finite element modeling of rapid heating 4.1. Isotherms under a transient condition
Fig. 3. Isotherms obtained from the tellurium and alloy films.
A numerical analysis of the specimen’s transient temperature distribution during the stationary heating process was conducted using a finite element method. The program used for the analysis was ANSYS 5.7. Heat was introduced to a circular area located at the center of specimen’s top surface. It was assumed that the laser beams’ energy distribution, or heat flux, was Gaussian and that 95% of the total energy flowed into the specimen. The total power of the beam was 200 W.
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T. Kato, H. Fujii / International Journal of Machine Tools & Manufacture 44 (2004) 927–931
Table 2 Thermal properties of the specimen 7850 kg/m3 473 J/(kgK) 51.5 W/(mK)
Density Specific heat Thermal conductivity
The irradiation diameter on the specimen’s surface was set to 5 mm. The density, the specific heat, and the thermal conductivity of the specimen were assumed to be constant and independent of temperature. The heat loss due to convection and radiation on the specimen’s surface was neglected. Table 2 lists the thermal properties of the specimen material. 4.2. Comparison of FEM analysis with experimental results The isotherms for the alloy film materials obtained through analysis were compared with the experimental data after 0.3 s of irradiation in Fig. 5. The experimental results and the FEM analysis results coincide well for the irradiation time. Two parameters, the isotherm’s depth at the center of the irradiation and the diameter of isotherm on the specimen’s surface, can be used to describe the shape of the isotherms. Fig. 6a,b shows the comparisons between the FEM analysis and the experimental results with irradiation times ranging from 0.1 to 1 s for lead and alloy film, respectively. Although some scatter exists, the agreement between the measured and the computed results are satisfactory for all of the conditions. The PVD film proved to respond fast by providing measurable results even after only 0.1 s of irradiation. This agreement verifies that the proposed PVD film method can be successfully employed to measure the tool’s and the work’s transient temperature distribution during manufacturing processes. The knowledge that can be obtained with this method will allow for thermal conditions to be measured, such
v
Fig. 5. 96.6 C isotherm after 0.3 s of irradiation.
v
Fig. 6. (a) Change in the 328 C isotherm over irradiation time. (b) v Change in the 96.6 C isotherm over irradiation time.
as the energy partition at a sliding contact surface or a grinding zone. These measurements are critical for fully understanding the various types of thermal damage encountered in engineering environments.
5. Conclusion The PVD film method, which involves physicallyvapor-depositing a thin film on a surface, was used as a thermal sensor determined the temperature distribution in a specimen rapidly heated by a laser. The experimental results were then compared to those obtained through FEM analysis. The PVD film method allows for transient temperature distributions in rapidly heated solid bodies to be measured with reasonable levels of accuracy. Therefore, this method can be applied to a variety of situations in which the temperature rises abruptly when the process starts, such as in a cutting tool during a machining process. The PVD film method is also a promising technique for measuring the quasi-steady temperature inside a solid body, which could prove useful in a variety of engineering applications. The data obtained through these experiments will provide a greater understanding
T. Kato, H. Fujii / International Journal of Machine Tools & Manufacture 44 (2004) 927–931
of the thermal phenomena involved in manufacturing processes. Acknowledgements The authors gratefully acknowledge the help of Mr. Yoshiaki Masuo at the Nagoya Municipal Industrial Research Institute for conducting the experimental work. The support provided for this work by Noritake Company Limited is also greatly appreciated. References [1] F.E. Kennedy, Thermal and thermomechanical effects in dry sliding, Wear 100 (1984) 453–476.
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[2] Y.N. Liu, E. Kannatey-Asibu Jr., Laser beam welding with simultaneous gausssian laser preheating, Transactions of the ASME, Journal of Heat Transfer 115 (1993) 34–41. [3] W.E. Littmann, J. Wulff, The influence of the grinding process on the structure of hardened steel, Transactions of the ASME 47 (1955) 692–714. [4] F.E. Kennedy, S.C. Cullen, J.M. Leroy, Contact temperature and its effects in an oscillatory sliding contact, Transactions of the ASME, Journal of Tribology 111 (1989) 63–69. [5] X. Tian, F.E. Kennedy, J.J. Deacutis, A.K. Henning, The development and use of thin film thermocouples for contact temperature measurement, Tribology Transactions 35 (1992) 491–499. [6] R.R. Hebbar, S. Chandrasekar, T.N. Farris, Ceramic grinding temperatures, Journal of the American Ceramic Society 75 (1992) 2742–2748. [7] T. Kato, H. Fujii, PVD film method for measuring the temperature distribution in cutting tools, Transactions of the ASME, Journal of Engineering for Industry 118 (1996) 117–122.
Temperature measurement in a solid body heated by laser beam Takao Kato a,, Hiroshi Fujii b a
Department of Material Science and Technology, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan b Faculty of Engineering, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan Received 17 July 2003; received in revised form 13 January 2004; accepted 21 January 2004
Abstract A new technique, call the PVD film method, was developed for measuring the temperature inside a solid body. This technique involves physically depositing thin films on the specimen’s surface to act as thermal sensors. The solid body was quickly heated with laser irradiation and the proposed technique was used to measure the internal temperature. The experimentally determined isotherm configurations were then compared with those calculated using FEM analysis, and the analytical and experimental results coincided well. This suggests that the proposed method could prove useful in measuring the temperature of a solid body in a quasi-steady state, such as the tool and workpiece in machining processes. # 2004 Elsevier Ltd. All rights reserved. Keywords: Temperature measurement; PVD film method; Machining
1. Introduction Heat generation is nearly inevitable in almost all traditional and non-traditional manufacturing processes. It is well known that the heat generated during processing not only affects the performance and service life of cutting and forming tools, but also influences the finished surface’s integrity and dimensional accuracy. The heat that is generated by friction in rubbing components, such as gears, cams, and brakes, significantly influences the friction, wear, and lubrication of the parts. The altered behavior of these tribological characteristics can induce premature part failure because the majority of the frictional energy is transformed into heat and dissipated in the vicinity of real contact area. The rubbing surface temperature has been shown to be the decisive factor in part performance [1]. When lasers and electron beams are used for localized welding or heat treatments, the focused heat quickly spreads. The temperature distribution in the solid and the melting and solidification rates affect the metal’s stress distribution and recrystallization process, Corresponding author. Tel.: +81-58-293-2511; fax: +81-58-2301892. E-mail address: [email protected] (T. Kato).
0890-6955/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmachtools.2004.01.014
which in turn determines the strength of the specimen. An appropriate cooling rate is essential for obtaining good results [2]. Therefore, the ability to predict and measure accurately the temperature inside solid bodies as a function of time is essential for coping with a variety of thermal problems in welding processes. Many experimental techniques for measuring surface and near-surface temperatures of solid bodies subjected to dynamic heat sources have been developed with varying degrees of success. These techniques have included the use of thermocouples and infrared radiation detection [3–6]. A previous paper [7] described a newly developed technique, called the PVD film method, that measures the internal temperature of a solid body during operation, such as cutting tools during machining. Several kinds of materials were physically-vapor-deposited on the cutting tool’s split surface. The films can be used as thermal sensors in determining the temperature distribution near the cutting edge because each of the film materials melts at its specific melting temperature. A calibration test demonstrated that the temperature at the boundary between the melted and unmelted film is equal to the melting point of the thin film material. The results of the test suggested that the temperature distribution at carbide
928
T. Kato, H. Fujii / International Journal of Machine Tools & Manufacture 44 (2004) 927–931
and ceramic tools’ cutting edges could be successfully measured with this method. The calibration test cited in the previous paper [7], however, was conducted under quasi-steady conditions because of the calibration apparatus’ limitations. Therefore, the method’s transient response was not fully investigated. This study uses the proposed temperature measurement process to investigate the rapid heating transient response of a solid body exposed to a laser-based heat input.
2. Experimental method Fig. 1 depicts a schematic of the experimental setup. In this study, a laser beam machining apparatus (Mitsubishi ML-15S), which is commercially available for metal cutting and welding, was used to rapidly heat the solid surface. The specimen was heated by laser irradiation using a continuous-wave CO2 laser with a wavelength of 10.6 lm and a power of 0.2 kW. The solid surface was irradiated for less than one second in order to heat, but not melt, the specimen. The unfocused beam’s diameter at the top surface of specimen was set to 5 mm by adjusting the distance between the probe and the specimen’s surface. The average heat flux was fixed at 10.2 W/mm2 and the beam produced a near-Gaussian energy distribution on the surface. The top surface was finished by grinding before it was
Fig. 1.
Laser beam heating experimental set up.
irradiated by the laser beam. And, in order to eliminate the possibility of laser beam reflection, the ground surface was coated with colloidal graphite, an irradiationabsorbing agent. Two square plates of the specimen were prepared from carbon steel (S55C) stock. The plates measured 50 mm wide, 50 mm long, and 5 mm thick. One surface of each plate was ground and lapped to a mirror finish with several different diamond slurries. A material with a known melting point was physically-vapor-deposited on the finished surface using a conventional vacuum deposition apparatus. After the two plates were prepared, they were fixed together in a vice. The laser probe was positioned so that the center of the beam exactly hit the boundary between the two plates by adjusting the table’s position, as shown in Fig. 1. Then, the constant power laser beam irradiated the specimen’s surface for a predetermined length of time, from 0.1–1.0 s. After the irradiation was complete, the plates were removed from the vice and the film material was examined with a microscope. Fig. 2 shows a photograph of v a bismuth film (melting point: 273 C) after a 0.5-s laser irradiation. A boundary, which is clearly apparent on the PVD film, denotes the separation between the melted film zone and the unmelted film zone. In the melted film zone, the irradiation melted the deposited material and then the material condensed and solidified during the cooling process. This melting/solidification process resulted in a slightly rougher area than the original surface, while the unmelted film zone remained unchanged. During irradiation, the temperature in the melted film zone is above the film’s melting point, while the temperature in the unmelted film zone is below the melting point. It follows that the temperature at the boundary is equal to the melting point of the deposited film. Therefore, the boundary is equivalent to the film’s melting point isotherm. The temperature distribution in the plate can be obtained by repeating the above process using the same irradiation time, but with different PVD films that have different melting points. This procedure is called the PVD film method. The main advantage of using a thin film sensor is that the thin film has an extremely small mass. This is advantageous because the thin film should only have a slight impact on the body’s heat transfer characteristics and the influence of the film’s physical characteristics on the internal temperature will be negligible. The PVD film materials consisted of four pure metals and one alloy. The alloy was composed of bismuth, lead and tin. The melting points and purity of the film materials are listed in Table 1. The alloy’s melting point determined experimentally.
T. Kato, H. Fujii / International Journal of Machine Tools & Manufacture 44 (2004) 927–931
Fig. 2.
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Photograph of the bismuth film after laser irradiation.
Table 1 Melting point and purity of the PVD films PVD film material
Symbol
Melting point v C
Purity %
Tellurium Lead Bismuth Indium Alloya
Te Pb Bi In Alloy
450 328 271 157 96.6
99.999 99.999 99.999 99.999 99.99
a
Composition (wt %) Bi : Pb : Sn ¼ 50 : 28 : 22.
3. Experimental results The location of the boundary observed on the film was determined with a digital micrometer mounted on a tool microscope. The results for the tellurium and the alloy film are shown in Fig. 3 after an irradiating time of 0.6 s. The results from several experimental runs using the same irradiating conditions are plotted in the figure. The isotherms appear nearly axisymmetric
Fig. 4.
Five kinds of isotherms after 0.8 s of laser irradiation.
about the laser beam’s centerline, with only a minimal amount of scatter. Fig. 4 displays a temperature map of the specimen obtained by using several different films and an irradiation time of 0.8 s. As can be seen in the figure, the isotherms are distinctly evident. 4. Finite element modeling of rapid heating 4.1. Isotherms under a transient condition
Fig. 3. Isotherms obtained from the tellurium and alloy films.
A numerical analysis of the specimen’s transient temperature distribution during the stationary heating process was conducted using a finite element method. The program used for the analysis was ANSYS 5.7. Heat was introduced to a circular area located at the center of specimen’s top surface. It was assumed that the laser beams’ energy distribution, or heat flux, was Gaussian and that 95% of the total energy flowed into the specimen. The total power of the beam was 200 W.
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T. Kato, H. Fujii / International Journal of Machine Tools & Manufacture 44 (2004) 927–931
Table 2 Thermal properties of the specimen 7850 kg/m3 473 J/(kgK) 51.5 W/(mK)
Density Specific heat Thermal conductivity
The irradiation diameter on the specimen’s surface was set to 5 mm. The density, the specific heat, and the thermal conductivity of the specimen were assumed to be constant and independent of temperature. The heat loss due to convection and radiation on the specimen’s surface was neglected. Table 2 lists the thermal properties of the specimen material. 4.2. Comparison of FEM analysis with experimental results The isotherms for the alloy film materials obtained through analysis were compared with the experimental data after 0.3 s of irradiation in Fig. 5. The experimental results and the FEM analysis results coincide well for the irradiation time. Two parameters, the isotherm’s depth at the center of the irradiation and the diameter of isotherm on the specimen’s surface, can be used to describe the shape of the isotherms. Fig. 6a,b shows the comparisons between the FEM analysis and the experimental results with irradiation times ranging from 0.1 to 1 s for lead and alloy film, respectively. Although some scatter exists, the agreement between the measured and the computed results are satisfactory for all of the conditions. The PVD film proved to respond fast by providing measurable results even after only 0.1 s of irradiation. This agreement verifies that the proposed PVD film method can be successfully employed to measure the tool’s and the work’s transient temperature distribution during manufacturing processes. The knowledge that can be obtained with this method will allow for thermal conditions to be measured, such
v
Fig. 5. 96.6 C isotherm after 0.3 s of irradiation.
v
Fig. 6. (a) Change in the 328 C isotherm over irradiation time. (b) v Change in the 96.6 C isotherm over irradiation time.
as the energy partition at a sliding contact surface or a grinding zone. These measurements are critical for fully understanding the various types of thermal damage encountered in engineering environments.
5. Conclusion The PVD film method, which involves physicallyvapor-depositing a thin film on a surface, was used as a thermal sensor determined the temperature distribution in a specimen rapidly heated by a laser. The experimental results were then compared to those obtained through FEM analysis. The PVD film method allows for transient temperature distributions in rapidly heated solid bodies to be measured with reasonable levels of accuracy. Therefore, this method can be applied to a variety of situations in which the temperature rises abruptly when the process starts, such as in a cutting tool during a machining process. The PVD film method is also a promising technique for measuring the quasi-steady temperature inside a solid body, which could prove useful in a variety of engineering applications. The data obtained through these experiments will provide a greater understanding
T. Kato, H. Fujii / International Journal of Machine Tools & Manufacture 44 (2004) 927–931
of the thermal phenomena involved in manufacturing processes. Acknowledgements The authors gratefully acknowledge the help of Mr. Yoshiaki Masuo at the Nagoya Municipal Industrial Research Institute for conducting the experimental work. The support provided for this work by Noritake Company Limited is also greatly appreciated. References [1] F.E. Kennedy, Thermal and thermomechanical effects in dry sliding, Wear 100 (1984) 453–476.
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[2] Y.N. Liu, E. Kannatey-Asibu Jr., Laser beam welding with simultaneous gausssian laser preheating, Transactions of the ASME, Journal of Heat Transfer 115 (1993) 34–41. [3] W.E. Littmann, J. Wulff, The influence of the grinding process on the structure of hardened steel, Transactions of the ASME 47 (1955) 692–714. [4] F.E. Kennedy, S.C. Cullen, J.M. Leroy, Contact temperature and its effects in an oscillatory sliding contact, Transactions of the ASME, Journal of Tribology 111 (1989) 63–69. [5] X. Tian, F.E. Kennedy, J.J. Deacutis, A.K. Henning, The development and use of thin film thermocouples for contact temperature measurement, Tribology Transactions 35 (1992) 491–499. [6] R.R. Hebbar, S. Chandrasekar, T.N. Farris, Ceramic grinding temperatures, Journal of the American Ceramic Society 75 (1992) 2742–2748. [7] T. Kato, H. Fujii, PVD film method for measuring the temperature distribution in cutting tools, Transactions of the ASME, Journal of Engineering for Industry 118 (1996) 117–122.