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Ultrasound-assisted water-confined laser micromachining: A novel machining process
Accepted Manuscript Letters Ultrasound-assisted Water-Confined Laser Micromachining: a Novel Machining Process Ze Liu, Yibo Gao, Benxin Wu, Ninggang Shen, Hongtao Ding PII: DOI: Reference:
S2213-8463(14)00013-3 http://dx.doi.org/10.1016/j.mfglet.2014.06.001 MFGLET 40
To appear in: Received Date: Accepted Date:
23 April 2014 1 June 2014
Please cite this article as: Z. Liu, Y. Gao, B. Wu, N. Shen, H. Ding, Ultrasound-assisted Water-Confined Laser Micromachining: a Novel Machining Process, (2014), doi: http://dx.doi.org/10.1016/j.mfglet.2014.06.001
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Ultrasound-assisted Water-Confined Laser Micromachining: a Novel Machining Process Ze Liu*, Yibo Gao*, Benxin Wu*1, Ninggang Shen**, and Hongtao Ding** *Department of Mechanical, Materials and Aerospace Engineering, Illinois Institute of Technology, Chicago, IL 60616 **Department of Mechanical and Industrial Engineering, The University of Iowa, Iowa City, Iowa 52242 Abstract: A novel machining process, called ultrasound assisted water-confined laser micromachining (UWLM) and proposed by the corresponding author, is introduced. In UWLM, in-situ ultrasound is delivered to the water-immersed workpiece surface region that is being ablated by a laser beam. The ultrasound in water may generate one or more effects among the cleaning, cooling enhancement, and peening effects. The effect(s) have a great potential to reduce one or more of the major defects of current laser machining processes. Some preliminary experimental results on UWLM have been given and discussed, and lots of future work on UWLM is still needed.
Introduction Laser machining has several advantages such as non-contact (where laser beam, as the major machining tool, does not have mechanical contact with the workpiece surface like a mechanical cutting tool), high spatial resolution (laser beam can be focused to a very small, micro-scale size), and good flexibility (laser spot machining trajectory can be easily controlled, programmed, and varied). Therefore, laser machining has many competitive industrial applications [1-2]. However, laser machining may often generate defects, which may include the deposition of the workpiece material debris, and laser-induced harmful thermal residual effects (which may include surface oxidation layer, recast layer, heat affected zone, and tensile surface residual stress, etc.) [1, 3-6]. These defects may turn out to be difficult 1
Corresponding author: Department of Mechanical, Materials and Aerospace Engineering, Illinois Institute of Technology, 10 W. 32nd Street, Engineering 1 Building, Room 207A, Chicago, IL 60616. Phone: 312.567.3451, Fax: 312.567.7230, E-mail: [email protected]
1
and/or time-consuming to completely remove through post-machining processing, and it is certainly desirable to minimize them during laser machining. In this paper, an ultrasound-assisted water-confined laser micromachining (UWLM) process will be introduced, which is a novel machining process (to the authors’ best knowledge) proposed by the corresponding author (a relevant non-provisional patent application has been filed [7]). It has a great potential to decrease or minimize one or more of the defects mentioned above, while it still inherits the major aforementioned advantages of the existing laser machining processes. The basic concept of UWLM is to apply in-situ ultrasound (ultrasonic wave) to the water-immersed workpiece surface region that is being ablated by a laser beam during laser machining, and the details will be introduced next.
UWLM Setup There are multiple possible and potential UWLM setups, which have been proposed by the corresponding author and given in [7]. In this paper, due to the space limit, only one example is given in Fig. 1. In Fig.1, the workpiece surface is immersed in water, and a laser beam with sufficiently high intensity is delivered through relevant optics to the workpiece top surface facing the laser beam, to perform laser ablation on the top surface. During laser machining, in-situ ultrasonic wave is also delivered to the workpiece surface through an ultrasonically vibrating horn. The ultrasonic wave may lead to the cavitation process in water, where the bubble generation, growth, and collapse (implosion) may occur [8]. The ultrasound will energize the water and the bubble implosion may yield very high pressures [8]. Due to the ultrasound, one or more effects,
2
among the cleaning, cooling enhancement, and peening effects [8-11], may be produced on the workpiece surface region that is being machined. The effect(s) have a great potential to decrease debris deposition and/or laser-induced harmful thermal residual effect(s). Although water is mentioned here, other types of liquid may also be used.
Results and Discussions Figures 2 and 3 have shown some preliminary experimental results. In the experiments, a nanosecond laser (Spectra-Physics Quanta-Ray GCR-170) has been used, which is operated at the 532 nm wavelength. The laser beam is delivered to the workpiece surface through a lens with a focal length of 150 mm. In UWLM, the ultrasound in water is generated through a horn driven by an ultrasonic processor (Q125, Qsonica LLC; frequency: 20 KHz). High-purity copper workpieces have been used in the experiments. The laser-ablated workpieces are characterized using a scanning electron microscope (SEM) and a confocal microscope. The holes shown in Figs. 2 and 3 are drilled using ~50 laser pulses. Figure 2a, 2b and 2c show the SEM images of holes drilled through laser ablation in air, laser ablation in water without ultrasound, and UWLM, respectively, with similar incoming pulse energies from the laser. It can be seen that the surface morphology of the holes is very different. For the hole produced through laser ablation in air (shown in Fig. 2a), significant debris deposition can be clearly observed on the workpiece top surface around the hole boundary and on the internal sidewall surface of the hole. Here, the word “debris” also includes the workpiece material that has melted, moved, re-solidified onto the surface, and changed the surface morphology. For the hole produced through laser
3
ablation in water without ultrasound (Fig. 2b), the debris deposition is less than that in Fig. 2a, but is still obviously observable. The hole produced through UWLM (Fig. 2c) clearly has less debris deposition than the hole in Fig. 2a and 2b, and one major reason is expected to be the effect of in-situ ultrasound in water during UWLM. Under the investigated conditions, it has been found that ultrasonic cleaning (with ultrasound conditions, such as intensity and frequency, similar to those in the UWLM process for Fig. 2c) in water after laser ablation is very difficult to significantly decrease the deposited debris for the holes drilled through laser ablation in air or water without ultrasound. This implies that the effect of in-situ ultrasound in water during UWLM is different from the post-process ultrasonic treatment in water after laser ablation. Figure 3a, 3b and 3c shows the profiles of the holes drilled through laser ablation in air, laser ablation in water without ultrasound, and UWLM, respectively, under similar incoming pulse energies from the laser. The profiles are measured using a confocal microscope. Comparing Fig. 3b and 3c, it can be clearly seen that, under similar incoming pulse energies from the laser, the hole drilled through laser ablation in water without ultrasound is much shallower than the hole drilled through UWLM. Also, it has been found that under the studied conditions, the depth of the hole drilled through laser ablation in water without ultrasound is very difficult to be significantly increased (if increased at all) through ultrasonic cleaning (with ultrasound conditions, such as intensity and frequency, similar to those in the UWLM process for Fig. 3c) in water after laser ablation. The results show that under the studied conditions, due to the effect of the insitu ultrasound during UWLM, material removal rate per laser pulse has been significantly increased as compared with laser ablation in water without ultrasound, and
4
the effect of the in-situ ultrasound during UWLM is different from the ultrasonic treatment in water after laser ablation,
Conclusion In summary, a novel UWLM process proposed by the corresponding author has been introduced. The preliminary experimental results have shown that, under the investigated conditions, UWLM has yielded obviously less debris deposition than laser ablation in air or water without ultrasound for holes drilled under similar incoming pulse energies from the laser, and UWLM has a much higher material removal rate per laser pulse than laser ablation in water without ultrasound. One major reason for these beneficial differences is expected to be the effect of the in-situ ultrasound during UWLM, which is different from the effect of ultrasonic treatment in water (with ultrasound conditions, such as intensity and frequency, similar to those in the compared UWLM processes) after laser ablation. Lots of future work is still needed on UWLM. It should be noted that UWLM is a general term that includes all the machining processes, where material removal occurs from the workpiece surface facing towards the incoming laser beam, and in-situ ultrasound is delivered to the liquid-immersed workpiece surface region that is being ablated by a laser beam, regardless of the laser or ultrasound conditions, immersing liquid types, specific equipment setups, workpiece material types or machined feature shapes or sizes, or other process setups, conditions or parameters. In particular, although the word “micromachining” is used, UWLM also includes the machining processes to create or modify features with sizes outside the micro-scale range.
5
Acknowledgement This material is based upon work supported by the National Science Foundation under Grant No. CMMI 1055805. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
6
References 1. Dubey, A. K., and Yadava, V., “Laser beam machining-A review”, International Journal of Machine Tools & Manufacture, 2008; 48: 609-628. 2. Meijer, J., “Laser beam machining (LBM), state of the art and new opportunities”, Journal of Materials Processing Technology, 2004; 149: 2-17. 3. Chien, W., and Hou, S., “Investigating the recast layer formed during the laser trepan drilling of Inconel 718 using the Taguchi method”, International Journal of Advanced Manufacturing Technology, 2007; 33: 308-316. 4. Matsumura, T., Kazama, A., and Yagi T., “Generation of debris in the femtosecond laser machining of a silicon substrate”, Applied Physics A: Materials Science & Processing, 2005; 81: 1393-1398. 5. Campbell, B. R., Palmer, J. A., and Semak, V. V., “Peculiarity of metal drilling with a commercial femtosecond laser”, Applied Surface Science, 2007; 253: 6334-6338. 6. Peyre, P., Chaieb, I., and Braham, C., “FEM calculation of residual stresses induced by laser shock processing in stainless steels”, Modelling and Simulation in Materials Science and Engineering, 2007; 15: 205-221. 7. U.S. Non-Provisional Patent Application, Title: Ultrasound-assisted Water-confined Laser Micromachining, Inventor: Benxin Wu, Filing Date: March 14, 2014, Application number: 14/212,876. 8. Sriraman, M. R. and Vasudevan, R., “Influence of ultrasonic cavitation on surface residual stresses in AISI 304 stainless steel”, Journal of Materials Science, 1998; 33: 2899-2904. 9. Niemczewski, B., “Observations of water cavitation intensity under practical ultrasonic cleaning conditions”, Ultrasonics Sonochemistry, 2007; 14: 13-18. 10. Kim, H. Y., Kim, Y. G., and Kang, B. H., “Enhancement of natural convection and pool boiling heat transfer via ultrasonic vibration”, International Journal of Heat and Mass Transfer, 2004; 47: 2831-2840. 11. Kim, H. J., and Jeong, J. H., “Numerical analysis of experimental observations for heat transfer augmentation by ultrasonic vibration”, Heat Transfer Engineering, 2006; 27: 14-22.
7
Laser beam Ultrasonically vibrating horn
water workpiece
Figure 1. Schematic diagram of one UWLM setup utilizing an ultrasonically vibrating horn (not drawn to scale or exactly based on the actual shape; other possible and potential setups are given in [7]).
8
(a)
(b)
(c) Figure 2. SEM images of a hole drilled by: (a) laser ablation in air, (b) laser ablation in water without ultrasound, and (c) UWLM
9
(a)
(b)
(c) Figure 3. The profiles of a hole drilled by: (a) laser ablation in air, (b) laser ablation in water without ultrasound, and (c) UWLM, measured using a confocal microscope.
10
S2213-8463(14)00013-3 http://dx.doi.org/10.1016/j.mfglet.2014.06.001 MFGLET 40
To appear in: Received Date: Accepted Date:
23 April 2014 1 June 2014
Please cite this article as: Z. Liu, Y. Gao, B. Wu, N. Shen, H. Ding, Ultrasound-assisted Water-Confined Laser Micromachining: a Novel Machining Process, (2014), doi: http://dx.doi.org/10.1016/j.mfglet.2014.06.001
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Ultrasound-assisted Water-Confined Laser Micromachining: a Novel Machining Process Ze Liu*, Yibo Gao*, Benxin Wu*1, Ninggang Shen**, and Hongtao Ding** *Department of Mechanical, Materials and Aerospace Engineering, Illinois Institute of Technology, Chicago, IL 60616 **Department of Mechanical and Industrial Engineering, The University of Iowa, Iowa City, Iowa 52242 Abstract: A novel machining process, called ultrasound assisted water-confined laser micromachining (UWLM) and proposed by the corresponding author, is introduced. In UWLM, in-situ ultrasound is delivered to the water-immersed workpiece surface region that is being ablated by a laser beam. The ultrasound in water may generate one or more effects among the cleaning, cooling enhancement, and peening effects. The effect(s) have a great potential to reduce one or more of the major defects of current laser machining processes. Some preliminary experimental results on UWLM have been given and discussed, and lots of future work on UWLM is still needed.
Introduction Laser machining has several advantages such as non-contact (where laser beam, as the major machining tool, does not have mechanical contact with the workpiece surface like a mechanical cutting tool), high spatial resolution (laser beam can be focused to a very small, micro-scale size), and good flexibility (laser spot machining trajectory can be easily controlled, programmed, and varied). Therefore, laser machining has many competitive industrial applications [1-2]. However, laser machining may often generate defects, which may include the deposition of the workpiece material debris, and laser-induced harmful thermal residual effects (which may include surface oxidation layer, recast layer, heat affected zone, and tensile surface residual stress, etc.) [1, 3-6]. These defects may turn out to be difficult 1
Corresponding author: Department of Mechanical, Materials and Aerospace Engineering, Illinois Institute of Technology, 10 W. 32nd Street, Engineering 1 Building, Room 207A, Chicago, IL 60616. Phone: 312.567.3451, Fax: 312.567.7230, E-mail: [email protected]
1
and/or time-consuming to completely remove through post-machining processing, and it is certainly desirable to minimize them during laser machining. In this paper, an ultrasound-assisted water-confined laser micromachining (UWLM) process will be introduced, which is a novel machining process (to the authors’ best knowledge) proposed by the corresponding author (a relevant non-provisional patent application has been filed [7]). It has a great potential to decrease or minimize one or more of the defects mentioned above, while it still inherits the major aforementioned advantages of the existing laser machining processes. The basic concept of UWLM is to apply in-situ ultrasound (ultrasonic wave) to the water-immersed workpiece surface region that is being ablated by a laser beam during laser machining, and the details will be introduced next.
UWLM Setup There are multiple possible and potential UWLM setups, which have been proposed by the corresponding author and given in [7]. In this paper, due to the space limit, only one example is given in Fig. 1. In Fig.1, the workpiece surface is immersed in water, and a laser beam with sufficiently high intensity is delivered through relevant optics to the workpiece top surface facing the laser beam, to perform laser ablation on the top surface. During laser machining, in-situ ultrasonic wave is also delivered to the workpiece surface through an ultrasonically vibrating horn. The ultrasonic wave may lead to the cavitation process in water, where the bubble generation, growth, and collapse (implosion) may occur [8]. The ultrasound will energize the water and the bubble implosion may yield very high pressures [8]. Due to the ultrasound, one or more effects,
2
among the cleaning, cooling enhancement, and peening effects [8-11], may be produced on the workpiece surface region that is being machined. The effect(s) have a great potential to decrease debris deposition and/or laser-induced harmful thermal residual effect(s). Although water is mentioned here, other types of liquid may also be used.
Results and Discussions Figures 2 and 3 have shown some preliminary experimental results. In the experiments, a nanosecond laser (Spectra-Physics Quanta-Ray GCR-170) has been used, which is operated at the 532 nm wavelength. The laser beam is delivered to the workpiece surface through a lens with a focal length of 150 mm. In UWLM, the ultrasound in water is generated through a horn driven by an ultrasonic processor (Q125, Qsonica LLC; frequency: 20 KHz). High-purity copper workpieces have been used in the experiments. The laser-ablated workpieces are characterized using a scanning electron microscope (SEM) and a confocal microscope. The holes shown in Figs. 2 and 3 are drilled using ~50 laser pulses. Figure 2a, 2b and 2c show the SEM images of holes drilled through laser ablation in air, laser ablation in water without ultrasound, and UWLM, respectively, with similar incoming pulse energies from the laser. It can be seen that the surface morphology of the holes is very different. For the hole produced through laser ablation in air (shown in Fig. 2a), significant debris deposition can be clearly observed on the workpiece top surface around the hole boundary and on the internal sidewall surface of the hole. Here, the word “debris” also includes the workpiece material that has melted, moved, re-solidified onto the surface, and changed the surface morphology. For the hole produced through laser
3
ablation in water without ultrasound (Fig. 2b), the debris deposition is less than that in Fig. 2a, but is still obviously observable. The hole produced through UWLM (Fig. 2c) clearly has less debris deposition than the hole in Fig. 2a and 2b, and one major reason is expected to be the effect of in-situ ultrasound in water during UWLM. Under the investigated conditions, it has been found that ultrasonic cleaning (with ultrasound conditions, such as intensity and frequency, similar to those in the UWLM process for Fig. 2c) in water after laser ablation is very difficult to significantly decrease the deposited debris for the holes drilled through laser ablation in air or water without ultrasound. This implies that the effect of in-situ ultrasound in water during UWLM is different from the post-process ultrasonic treatment in water after laser ablation. Figure 3a, 3b and 3c shows the profiles of the holes drilled through laser ablation in air, laser ablation in water without ultrasound, and UWLM, respectively, under similar incoming pulse energies from the laser. The profiles are measured using a confocal microscope. Comparing Fig. 3b and 3c, it can be clearly seen that, under similar incoming pulse energies from the laser, the hole drilled through laser ablation in water without ultrasound is much shallower than the hole drilled through UWLM. Also, it has been found that under the studied conditions, the depth of the hole drilled through laser ablation in water without ultrasound is very difficult to be significantly increased (if increased at all) through ultrasonic cleaning (with ultrasound conditions, such as intensity and frequency, similar to those in the UWLM process for Fig. 3c) in water after laser ablation. The results show that under the studied conditions, due to the effect of the insitu ultrasound during UWLM, material removal rate per laser pulse has been significantly increased as compared with laser ablation in water without ultrasound, and
4
the effect of the in-situ ultrasound during UWLM is different from the ultrasonic treatment in water after laser ablation,
Conclusion In summary, a novel UWLM process proposed by the corresponding author has been introduced. The preliminary experimental results have shown that, under the investigated conditions, UWLM has yielded obviously less debris deposition than laser ablation in air or water without ultrasound for holes drilled under similar incoming pulse energies from the laser, and UWLM has a much higher material removal rate per laser pulse than laser ablation in water without ultrasound. One major reason for these beneficial differences is expected to be the effect of the in-situ ultrasound during UWLM, which is different from the effect of ultrasonic treatment in water (with ultrasound conditions, such as intensity and frequency, similar to those in the compared UWLM processes) after laser ablation. Lots of future work is still needed on UWLM. It should be noted that UWLM is a general term that includes all the machining processes, where material removal occurs from the workpiece surface facing towards the incoming laser beam, and in-situ ultrasound is delivered to the liquid-immersed workpiece surface region that is being ablated by a laser beam, regardless of the laser or ultrasound conditions, immersing liquid types, specific equipment setups, workpiece material types or machined feature shapes or sizes, or other process setups, conditions or parameters. In particular, although the word “micromachining” is used, UWLM also includes the machining processes to create or modify features with sizes outside the micro-scale range.
5
Acknowledgement This material is based upon work supported by the National Science Foundation under Grant No. CMMI 1055805. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
6
References 1. Dubey, A. K., and Yadava, V., “Laser beam machining-A review”, International Journal of Machine Tools & Manufacture, 2008; 48: 609-628. 2. Meijer, J., “Laser beam machining (LBM), state of the art and new opportunities”, Journal of Materials Processing Technology, 2004; 149: 2-17. 3. Chien, W., and Hou, S., “Investigating the recast layer formed during the laser trepan drilling of Inconel 718 using the Taguchi method”, International Journal of Advanced Manufacturing Technology, 2007; 33: 308-316. 4. Matsumura, T., Kazama, A., and Yagi T., “Generation of debris in the femtosecond laser machining of a silicon substrate”, Applied Physics A: Materials Science & Processing, 2005; 81: 1393-1398. 5. Campbell, B. R., Palmer, J. A., and Semak, V. V., “Peculiarity of metal drilling with a commercial femtosecond laser”, Applied Surface Science, 2007; 253: 6334-6338. 6. Peyre, P., Chaieb, I., and Braham, C., “FEM calculation of residual stresses induced by laser shock processing in stainless steels”, Modelling and Simulation in Materials Science and Engineering, 2007; 15: 205-221. 7. U.S. Non-Provisional Patent Application, Title: Ultrasound-assisted Water-confined Laser Micromachining, Inventor: Benxin Wu, Filing Date: March 14, 2014, Application number: 14/212,876. 8. Sriraman, M. R. and Vasudevan, R., “Influence of ultrasonic cavitation on surface residual stresses in AISI 304 stainless steel”, Journal of Materials Science, 1998; 33: 2899-2904. 9. Niemczewski, B., “Observations of water cavitation intensity under practical ultrasonic cleaning conditions”, Ultrasonics Sonochemistry, 2007; 14: 13-18. 10. Kim, H. Y., Kim, Y. G., and Kang, B. H., “Enhancement of natural convection and pool boiling heat transfer via ultrasonic vibration”, International Journal of Heat and Mass Transfer, 2004; 47: 2831-2840. 11. Kim, H. J., and Jeong, J. H., “Numerical analysis of experimental observations for heat transfer augmentation by ultrasonic vibration”, Heat Transfer Engineering, 2006; 27: 14-22.
7
Laser beam Ultrasonically vibrating horn
water workpiece
Figure 1. Schematic diagram of one UWLM setup utilizing an ultrasonically vibrating horn (not drawn to scale or exactly based on the actual shape; other possible and potential setups are given in [7]).
8
(a)
(b)
(c) Figure 2. SEM images of a hole drilled by: (a) laser ablation in air, (b) laser ablation in water without ultrasound, and (c) UWLM
9
(a)
(b)
(c) Figure 3. The profiles of a hole drilled by: (a) laser ablation in air, (b) laser ablation in water without ultrasound, and (c) UWLM, measured using a confocal microscope.
10