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Experimental Investigation of Varying Laser Pass on Micro-channel Characteristics of Thick PMMA by Laser Transmission Micro-machining
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 18 (2019) 3514–3520
www.materialstoday.com/proceedings
ICMPC-2019
Experimental Investigation of Varying Laser Pass on Micro-channel Characteristics of Thick PMMA by Laser Transmission Micromachining S. Biswas a*, N. Roy a, R. Biswas b, A.S. Kuar a
b
a Department of Production Engineering, Jadavpur University, Kolkata, 700032, India Department of Mechanical Engineering, MCKV Institute of Engineering, Howrah, 711204, India
Abstract Depth of fabrication is an essential characteristic of micro-channels. The laser beam machining process is one of the most suitable processes to fabricate micro-channels. This process has an excellent potential for the fabrication of microfluidic devices which are instrumental for various biomedical applications such as electrophoresis, chromatography, blood protein studies, DNA analysis, etc. In this research work, an attempt has been made to fabricate micro-channels on a thick Polymethyl methacrylate (PMMA) plate at submerged condition by utilizing laser transmission micro-machining process. The laser transmission micromachining operation is conducted here at submerged condition to reduce the adverse thermal effect during machining. Nanosecond pulsed Nd: YAG laser with wavelength in near infrared region has been used here. The depth of micro-channel and heat affected zone (HAZ) width has been taken into account as machining responses. Total 3 sets of experiments which contain 31 experiments in each set have been conducted for three different laser beam pass with the aid of response surface methodology (RSM). The effects of varying laser beam pass on the depth and HAZ width has been studied. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019 Keywords: Nd: YAG laser; laser transmission machining; micro-channeling; PMMA.
1. Introduction Laser beam machining (LBM) is one of the advanced machining processes which are used for a wide range of engineering materials. The laser beam machining is carried out for channelling, drilling, marking, welding, sintering, etc. [1]. Laser beam micro-machining is most commonly used thermal energy process which utilized in the micromachining applications for its clean machining operation along with the ability to machine different critical shapes in a wide variety of engineering materials like polymers, metals, ceramics, semiconductors, etc. [2]. Ageev (1975) * Corresponding author. Tel.: +918617232080. E-mail address: [email protected] 2214-7853© 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019
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has been carried out the first underwater laser machining operation and observed the material ablation during emission spectroscopy. Underwater laser beam machining procedure is a unique invention to produce clean, clogfree micro-features on materials by utilizing local cooling effect as well as reducing the redeposition of ablated material on the surface [3]. A micro-machining on silicon in both open air and underwater condition using excimer lasers has been carried out by Choo et al., (2004). A vast thermal damage has been observed in open air machining operation, while the underwater procedure has resulted with the absence of thermal damage. Underwater laser processing has also been proved to be very helpful in through cutting operation [4]. Incident laser beam travelled through the thick transparent PMMA plate with no or minimal absorption which is inadequate to perform any kind of machining on the said plate. Whenever an absorbent is added at the bottom surface of the workpiece, that absorbed the thermal energy from the laser beam and heated up the adjacent zone of the workpiece by conduction as well as by transmission method. The temperature of the adjacent zone increased with more absorption and the machining takes place. This laser machining process is generally known as laser transmission process or laser backside etching. In absence of adequate literature on laser transmission machining of thick PMMA an experimental investigation on laser transmission machining on thick PMMA has been carried out. Laser working power, pulse frequency, pulse width and cutting speed are taken as input parameters as constant whereas depth of micro-channel and heat affected zone (HAZ) width are chosen as machining responses. Passes are varying for this experiment during the machining operation to find out the changes of the output responses. Response surface methodology has been used to perform the micro-channelling operations. Three set of experiment (i.e., 31 experiments for each set) has been carried out to look out the changes. Final results are analyzed and described in this paper.
2. Experimental Procedures The CNC controlled pulsed Nd: YAG laser machine (model no. SLT-SP-2000) manufactured by M/s Sahajanand Laser Technology (India), has been used to carry out the transmission micro-machining operation. Workpiece material is selected as thick transparent Polymethyl methacrylate (PMMA) plate. The thickness of the PMMA plate has measured at different sections throughout the workpiece using a digital vernier calliper, having a resolution of 0.0001 mm. An absorbent material is chosen regarding the machining operation which is affixed at the bottom surface of the PMMA plate. This absorbent coated sample is kept in a specially designed workpiece holding unit to carry out the laser transmission micro-machining operation at the partially submerged condition. The schematic diagram of the workpiece holding unit is given below in figure1.The workpiece is partially submerged in 6 mm height of water column. The height of the water column is measured from the height of the sleeve gauge and kept it constant throughout the experiments by pouring the water externally. The parametric ranges have chosen based on the extensive trial experiments one factor at a time approach and listed in table1. Also, a high and low range of the parameters is given in the table1. Numbers of passes are varying for each set of present experimentations. The schematic picture of laser transmission operation is given in figure 2.
Fig. 1.Workpiece holding unit for underwater laser transmission machining [5]
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S. Biswas et al./ Materials Today: Proceedings 18 (2019) 3514–3520 Table 1.Range for Input Parameters of Laser Beam Transmission Micro-Channelling Process Parameters & Low High Symbol Working Power (watt) (A) 9 11 Pulse frequency (kHz) (B) 25 45 Pulse width (%) 90 98 (C) Cutting speed (mm/sec) (D) 1 2
The Olympus-STM-6, optical microscope has been used to capture the images of the output responses. Depth and heat affected zone (HAZ) width for all the experiments have been measured at three different locations along the micro-channel and the average is taken for further analysis.
Fig. 2.Schematic diagram of laser transmission micro-machining of transparent PMMA coated with black sellotape [6]
3. Experimental Result and Discussion The experimental values of depth of cut and HAZ width with varying laser passes are documented in table no.2. Table 2.Experimental results of single pass, double pass and triple pass for depth and HAZ width of the micro-channels Single Pass Double Pass Triple Pass Exp. Depth HAZ HAZ width HAZ width No Depth (µm) Depth (µm) (µm) width(µm) (µm) (µm) 1 58.37 133.81 65.83 149.96 70.57 81.78 2 53.2 151.57 92.77 142.325 65.23 111.6 3 54.73 161.92 89.63 111.89 89.07 111.44 4 58.8 192.64 98.63 117.755 89.53 116.61 5 44.57 118.22 89.67 130.87 85.17 100.92 6 52.6 156.27 100.5 125.03 89.87 122.82 7 36.73 122.02 107.87 131.64 93.23 130.29 8 58.17 161.82 105.67 134.765 96.37 121.18 9 51.5 83.67 109.3 122.82 89.27 88.02 10 40.53 58.13 130.27 141.255 98.43 114.27 11 50.9 114.48 122.83 83.03 101.6 93.01 12 44.5 116.76 123.47 113.925 116.2 95.28 13 23.4 100.74 125.83 84.58 98.73 98.67 14 27.37 103.04 132.07 109.225 116.5 112.01 15 17.57 116.28 124.53 93.765 100.17 100.05 16 29.43 137.23 116.7 127.88 118.13 90.85 17 24.7 110.97 146.23 85.84 101.53 86 18 31.4 138.035 156.05 112.24 109.8 113.64 19 19.93 96.42 124.13 118.11 98.03 97.05 20 20.37 141.68 129.83 103.13 117.17 97.29 21 94.8 149.27 69.67 142.34 85.3 89.01 22 62.27 147.06 82.13 129.72 101.4 110.55 23 87.9 158.42 52.23 154.6 56.33 139.66 24 54.23 76.4 106.43 116.38 93.13 105.04 25 66.13 116.35 35.27 131.375 99.83 140.1 26 65.33 111.49 32.8 130.45 103.33 140.32
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3.1 For Depth Fig. 3, fig. 4, fig. 5 and fig. 6 shows the influence of working power, pulse frequency, pulse width and cutting speed on the depth of cut at three different laser pass. Depth (1), depth (2) and depth (3) represents single pass, double pass, and triple pass respectively. Figures (3, 4, 5 and 6) demonstrate the variation of depth of cut with number of passes.
Fig. 3.Working power vs depth (1), depth (2) and depth (3)
Fig. 4.Pulse frequency vs depth (1), depth (2) and depth (3)
Fig. 5.Pulse width vs depth (1), depth (2) and depth (3)
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Fig. 6.Cutting speed vs depth (1), depth (2) and depth (3)
It is found from the fig. 3 that the micro-channel depth is increased upto double pass and after that, it decreases with increase in laser pass along with varying laser working power. From the fig. (4, 5, 6) it is also noticed, when passes are varying with respective parameters (i.e., pulse frequency, pulse width and cutting speed respectably), depth of cut also changing in the same way. In all the above cases, after double passes the depth of cut decreases. It is observed that at higher laser power with more number of laser passes, comparatively more thermal energy is absorbed and transmitted to the targeted region which helps to get more depth of cut. But it is also observed that depth of cut is comparatively less after 3rd consecutive pass than the experiments conduct with two laser passes. Presence of debris at machining zone in submerged condition and cumulative time factor may affect the material removal for which this kind of phenomenon may observed. The presence of debris in the water not only affects the material removal by affecting the surface tension force acting on the machining zone but also vary the rate of absorption which may also affects the adequacy of thermal energy required to conduct the transmission machining procedure. 3.2 For HAZ width Fig. 7, fig. 8, fig. 9 and fig. 10 show the influence of laser working power, pulse frequency, pulse width and cutting speed on HAZ width. HAZ width (1), HAZ width (2) and HAZ width (3) represents the measured HAZ width at single pass, double pass, and triple pass respectively.
Fig.7.Working power vs HAZ width (1), HAZ width (2) and HAZ width (3)
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Fig. 8.Pulse frequency vs HAZ width (1), HAZ width (2) and HAZ width (3)
Fig.9.Pulse width vs HAZ width (1), HAZ width (2) and HAZ width (3)
Fig. 10.Cutting speed vs HAZ width (1), HAZ width (2) and HAZ width (3)
Thermal energy density on the machining zone is comparatively more at higher laser working power and higher pulse frequency which helps to get more HAZ width and vice versa. From the figures (8, 9, 10) it is also noticed, when number of passes are varying with respected parameters (i.e., pulse frequency, pulse width and cutting speed
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respectably), HAZ width also varying in the similar way. It is also observed that with the increase in passes the HAZ width decreases significantly. Reason behind this phenomenon may be the cumulative time factor and the presence of water at machining zone. Presence of water in the machining zone helps to restrict the thermal affects on the neighbouring zone by rapid cooling. Formation and collapse of the bubbles after two passes, in and around the machining zone not only carry out the debris from machining zone but also make a turbulence on the machining zone which carry out the heat and cool down the machining zone. Thus this kid of phenomenon is observed. 4. Conclusions Laser transmission micro-machining technique is successes fully employed in this study. Laser passes are varying for each set of experiment to observe and analysis the process outcome. It is found that the experimental results are significantly changed with the varying laser passes. From the figures 3-10, it can be concluded that the depth of cut changes significantly with the changes of passes at a certain limit, i.e., after double pass, there are no significant changes are observed. The significant change is found out at 28 amps of working power, pulse frequency at 35 kHz, 94% pulse width and at 1.5mm/sec of cutting speed. It is shown from the figures (7, 8, 9 and 10) that the passes are taking a vital role in HAZ width. The most significant change is found out at working power of 24 amps, pulse frequency at 25 kHz, 90% pulse width and cutting speed at 2 mm/sec respectably. From the study it is observed that within the specific parametric range, number of laser pass is a dominant factor along with all the other process variable upto a certain limit. It is also observed that increase in number of laser pass during each experiment from two to three have a good effect on HAZ width but adverse effect on depth of cut. Acknowledgements The authors gratefully acknowledge the financial support from CAS Ph IV (UGC) programme of production engineering department of Jadavpur University, Kolkata, India for technical equipment support. References [1] A.K. Dubey, V. Yadava, Laser beam machining: a review. International Journal of Machine Tools and Manufacture. 48(6) (2008) 609–628. [2] I.A. Choudhury, S. Shirley, Laser cutting of polymeric materials: An experimental investigation, Optics and Laser Technology. 42(3) (2010) 503-508. [3] V.A. Ageev, Investigation of optical erosion of metals in liquids, Joural of Applied Sprectoscopy. 23 (1) (1975) 903-906. [4] K.L. Choo, Y. Ogawa, G. Kanbargi, V. Otra, L.M. Raff, R. Komanduri, Micromachining of silicon by short-pulse laser ablation in air and under water, Materials Science and Engineering: A. 372 (1-2)(2004) 145–162. [5] N. Roy, A. S. Kuar, S. Mitra, A. Das, Submerged Pulsed Nd:YAG Laser Beam Cutting on Inconel 625 Superalloy: Experimental Investigation. Lasers in Engineering. 35 (1-4) (2016) 151-171. [6] S. Biswas, N. Roy, R. Biswas, A.S. Kuar, Experimental Investigation on Underwater Laser Transmission Micro-channeling on PMMA. Proceedings of 6th International & 27th All India Manufacturing Technology, Design and Research Conference (AIMTDR-2016), Pune. (2016), ISBN: 978-93-86256-27-0.
ScienceDirect Materials Today: Proceedings 18 (2019) 3514–3520
www.materialstoday.com/proceedings
ICMPC-2019
Experimental Investigation of Varying Laser Pass on Micro-channel Characteristics of Thick PMMA by Laser Transmission Micromachining S. Biswas a*, N. Roy a, R. Biswas b, A.S. Kuar a
b
a Department of Production Engineering, Jadavpur University, Kolkata, 700032, India Department of Mechanical Engineering, MCKV Institute of Engineering, Howrah, 711204, India
Abstract Depth of fabrication is an essential characteristic of micro-channels. The laser beam machining process is one of the most suitable processes to fabricate micro-channels. This process has an excellent potential for the fabrication of microfluidic devices which are instrumental for various biomedical applications such as electrophoresis, chromatography, blood protein studies, DNA analysis, etc. In this research work, an attempt has been made to fabricate micro-channels on a thick Polymethyl methacrylate (PMMA) plate at submerged condition by utilizing laser transmission micro-machining process. The laser transmission micromachining operation is conducted here at submerged condition to reduce the adverse thermal effect during machining. Nanosecond pulsed Nd: YAG laser with wavelength in near infrared region has been used here. The depth of micro-channel and heat affected zone (HAZ) width has been taken into account as machining responses. Total 3 sets of experiments which contain 31 experiments in each set have been conducted for three different laser beam pass with the aid of response surface methodology (RSM). The effects of varying laser beam pass on the depth and HAZ width has been studied. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019 Keywords: Nd: YAG laser; laser transmission machining; micro-channeling; PMMA.
1. Introduction Laser beam machining (LBM) is one of the advanced machining processes which are used for a wide range of engineering materials. The laser beam machining is carried out for channelling, drilling, marking, welding, sintering, etc. [1]. Laser beam micro-machining is most commonly used thermal energy process which utilized in the micromachining applications for its clean machining operation along with the ability to machine different critical shapes in a wide variety of engineering materials like polymers, metals, ceramics, semiconductors, etc. [2]. Ageev (1975) * Corresponding author. Tel.: +918617232080. E-mail address: [email protected] 2214-7853© 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019
S. Biswas et al./ Materials Today: Proceedings 18 (2019) 3514–3520
3515
has been carried out the first underwater laser machining operation and observed the material ablation during emission spectroscopy. Underwater laser beam machining procedure is a unique invention to produce clean, clogfree micro-features on materials by utilizing local cooling effect as well as reducing the redeposition of ablated material on the surface [3]. A micro-machining on silicon in both open air and underwater condition using excimer lasers has been carried out by Choo et al., (2004). A vast thermal damage has been observed in open air machining operation, while the underwater procedure has resulted with the absence of thermal damage. Underwater laser processing has also been proved to be very helpful in through cutting operation [4]. Incident laser beam travelled through the thick transparent PMMA plate with no or minimal absorption which is inadequate to perform any kind of machining on the said plate. Whenever an absorbent is added at the bottom surface of the workpiece, that absorbed the thermal energy from the laser beam and heated up the adjacent zone of the workpiece by conduction as well as by transmission method. The temperature of the adjacent zone increased with more absorption and the machining takes place. This laser machining process is generally known as laser transmission process or laser backside etching. In absence of adequate literature on laser transmission machining of thick PMMA an experimental investigation on laser transmission machining on thick PMMA has been carried out. Laser working power, pulse frequency, pulse width and cutting speed are taken as input parameters as constant whereas depth of micro-channel and heat affected zone (HAZ) width are chosen as machining responses. Passes are varying for this experiment during the machining operation to find out the changes of the output responses. Response surface methodology has been used to perform the micro-channelling operations. Three set of experiment (i.e., 31 experiments for each set) has been carried out to look out the changes. Final results are analyzed and described in this paper.
2. Experimental Procedures The CNC controlled pulsed Nd: YAG laser machine (model no. SLT-SP-2000) manufactured by M/s Sahajanand Laser Technology (India), has been used to carry out the transmission micro-machining operation. Workpiece material is selected as thick transparent Polymethyl methacrylate (PMMA) plate. The thickness of the PMMA plate has measured at different sections throughout the workpiece using a digital vernier calliper, having a resolution of 0.0001 mm. An absorbent material is chosen regarding the machining operation which is affixed at the bottom surface of the PMMA plate. This absorbent coated sample is kept in a specially designed workpiece holding unit to carry out the laser transmission micro-machining operation at the partially submerged condition. The schematic diagram of the workpiece holding unit is given below in figure1.The workpiece is partially submerged in 6 mm height of water column. The height of the water column is measured from the height of the sleeve gauge and kept it constant throughout the experiments by pouring the water externally. The parametric ranges have chosen based on the extensive trial experiments one factor at a time approach and listed in table1. Also, a high and low range of the parameters is given in the table1. Numbers of passes are varying for each set of present experimentations. The schematic picture of laser transmission operation is given in figure 2.
Fig. 1.Workpiece holding unit for underwater laser transmission machining [5]
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S. Biswas et al./ Materials Today: Proceedings 18 (2019) 3514–3520 Table 1.Range for Input Parameters of Laser Beam Transmission Micro-Channelling Process Parameters & Low High Symbol Working Power (watt) (A) 9 11 Pulse frequency (kHz) (B) 25 45 Pulse width (%) 90 98 (C) Cutting speed (mm/sec) (D) 1 2
The Olympus-STM-6, optical microscope has been used to capture the images of the output responses. Depth and heat affected zone (HAZ) width for all the experiments have been measured at three different locations along the micro-channel and the average is taken for further analysis.
Fig. 2.Schematic diagram of laser transmission micro-machining of transparent PMMA coated with black sellotape [6]
3. Experimental Result and Discussion The experimental values of depth of cut and HAZ width with varying laser passes are documented in table no.2. Table 2.Experimental results of single pass, double pass and triple pass for depth and HAZ width of the micro-channels Single Pass Double Pass Triple Pass Exp. Depth HAZ HAZ width HAZ width No Depth (µm) Depth (µm) (µm) width(µm) (µm) (µm) 1 58.37 133.81 65.83 149.96 70.57 81.78 2 53.2 151.57 92.77 142.325 65.23 111.6 3 54.73 161.92 89.63 111.89 89.07 111.44 4 58.8 192.64 98.63 117.755 89.53 116.61 5 44.57 118.22 89.67 130.87 85.17 100.92 6 52.6 156.27 100.5 125.03 89.87 122.82 7 36.73 122.02 107.87 131.64 93.23 130.29 8 58.17 161.82 105.67 134.765 96.37 121.18 9 51.5 83.67 109.3 122.82 89.27 88.02 10 40.53 58.13 130.27 141.255 98.43 114.27 11 50.9 114.48 122.83 83.03 101.6 93.01 12 44.5 116.76 123.47 113.925 116.2 95.28 13 23.4 100.74 125.83 84.58 98.73 98.67 14 27.37 103.04 132.07 109.225 116.5 112.01 15 17.57 116.28 124.53 93.765 100.17 100.05 16 29.43 137.23 116.7 127.88 118.13 90.85 17 24.7 110.97 146.23 85.84 101.53 86 18 31.4 138.035 156.05 112.24 109.8 113.64 19 19.93 96.42 124.13 118.11 98.03 97.05 20 20.37 141.68 129.83 103.13 117.17 97.29 21 94.8 149.27 69.67 142.34 85.3 89.01 22 62.27 147.06 82.13 129.72 101.4 110.55 23 87.9 158.42 52.23 154.6 56.33 139.66 24 54.23 76.4 106.43 116.38 93.13 105.04 25 66.13 116.35 35.27 131.375 99.83 140.1 26 65.33 111.49 32.8 130.45 103.33 140.32
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3.1 For Depth Fig. 3, fig. 4, fig. 5 and fig. 6 shows the influence of working power, pulse frequency, pulse width and cutting speed on the depth of cut at three different laser pass. Depth (1), depth (2) and depth (3) represents single pass, double pass, and triple pass respectively. Figures (3, 4, 5 and 6) demonstrate the variation of depth of cut with number of passes.
Fig. 3.Working power vs depth (1), depth (2) and depth (3)
Fig. 4.Pulse frequency vs depth (1), depth (2) and depth (3)
Fig. 5.Pulse width vs depth (1), depth (2) and depth (3)
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Fig. 6.Cutting speed vs depth (1), depth (2) and depth (3)
It is found from the fig. 3 that the micro-channel depth is increased upto double pass and after that, it decreases with increase in laser pass along with varying laser working power. From the fig. (4, 5, 6) it is also noticed, when passes are varying with respective parameters (i.e., pulse frequency, pulse width and cutting speed respectably), depth of cut also changing in the same way. In all the above cases, after double passes the depth of cut decreases. It is observed that at higher laser power with more number of laser passes, comparatively more thermal energy is absorbed and transmitted to the targeted region which helps to get more depth of cut. But it is also observed that depth of cut is comparatively less after 3rd consecutive pass than the experiments conduct with two laser passes. Presence of debris at machining zone in submerged condition and cumulative time factor may affect the material removal for which this kind of phenomenon may observed. The presence of debris in the water not only affects the material removal by affecting the surface tension force acting on the machining zone but also vary the rate of absorption which may also affects the adequacy of thermal energy required to conduct the transmission machining procedure. 3.2 For HAZ width Fig. 7, fig. 8, fig. 9 and fig. 10 show the influence of laser working power, pulse frequency, pulse width and cutting speed on HAZ width. HAZ width (1), HAZ width (2) and HAZ width (3) represents the measured HAZ width at single pass, double pass, and triple pass respectively.
Fig.7.Working power vs HAZ width (1), HAZ width (2) and HAZ width (3)
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Fig. 8.Pulse frequency vs HAZ width (1), HAZ width (2) and HAZ width (3)
Fig.9.Pulse width vs HAZ width (1), HAZ width (2) and HAZ width (3)
Fig. 10.Cutting speed vs HAZ width (1), HAZ width (2) and HAZ width (3)
Thermal energy density on the machining zone is comparatively more at higher laser working power and higher pulse frequency which helps to get more HAZ width and vice versa. From the figures (8, 9, 10) it is also noticed, when number of passes are varying with respected parameters (i.e., pulse frequency, pulse width and cutting speed
3520
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respectably), HAZ width also varying in the similar way. It is also observed that with the increase in passes the HAZ width decreases significantly. Reason behind this phenomenon may be the cumulative time factor and the presence of water at machining zone. Presence of water in the machining zone helps to restrict the thermal affects on the neighbouring zone by rapid cooling. Formation and collapse of the bubbles after two passes, in and around the machining zone not only carry out the debris from machining zone but also make a turbulence on the machining zone which carry out the heat and cool down the machining zone. Thus this kid of phenomenon is observed. 4. Conclusions Laser transmission micro-machining technique is successes fully employed in this study. Laser passes are varying for each set of experiment to observe and analysis the process outcome. It is found that the experimental results are significantly changed with the varying laser passes. From the figures 3-10, it can be concluded that the depth of cut changes significantly with the changes of passes at a certain limit, i.e., after double pass, there are no significant changes are observed. The significant change is found out at 28 amps of working power, pulse frequency at 35 kHz, 94% pulse width and at 1.5mm/sec of cutting speed. It is shown from the figures (7, 8, 9 and 10) that the passes are taking a vital role in HAZ width. The most significant change is found out at working power of 24 amps, pulse frequency at 25 kHz, 90% pulse width and cutting speed at 2 mm/sec respectably. From the study it is observed that within the specific parametric range, number of laser pass is a dominant factor along with all the other process variable upto a certain limit. It is also observed that increase in number of laser pass during each experiment from two to three have a good effect on HAZ width but adverse effect on depth of cut. Acknowledgements The authors gratefully acknowledge the financial support from CAS Ph IV (UGC) programme of production engineering department of Jadavpur University, Kolkata, India for technical equipment support. References [1] A.K. Dubey, V. Yadava, Laser beam machining: a review. International Journal of Machine Tools and Manufacture. 48(6) (2008) 609–628. [2] I.A. Choudhury, S. Shirley, Laser cutting of polymeric materials: An experimental investigation, Optics and Laser Technology. 42(3) (2010) 503-508. [3] V.A. Ageev, Investigation of optical erosion of metals in liquids, Joural of Applied Sprectoscopy. 23 (1) (1975) 903-906. [4] K.L. Choo, Y. Ogawa, G. Kanbargi, V. Otra, L.M. Raff, R. Komanduri, Micromachining of silicon by short-pulse laser ablation in air and under water, Materials Science and Engineering: A. 372 (1-2)(2004) 145–162. [5] N. Roy, A. S. Kuar, S. Mitra, A. Das, Submerged Pulsed Nd:YAG Laser Beam Cutting on Inconel 625 Superalloy: Experimental Investigation. Lasers in Engineering. 35 (1-4) (2016) 151-171. [6] S. Biswas, N. Roy, R. Biswas, A.S. Kuar, Experimental Investigation on Underwater Laser Transmission Micro-channeling on PMMA. Proceedings of 6th International & 27th All India Manufacturing Technology, Design and Research Conference (AIMTDR-2016), Pune. (2016), ISBN: 978-93-86256-27-0.