Characteristics of Cutting Surface According to Cutting Direction and Laser Output During Laser-Oxygen Hybrid Cutting for Nuclear Power Plant Dismantling Application

DoYeong Mun,SunIl Kim,MinGyu Choi,DongHyun Kim,IlWoo Moon 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2

Thermal cutting processes that can be applied to dismantling nuclear power plants include oxygen cutting, plasma cutting, and laser cutting. According to the global trend, research projects are being carried out in various countries to upgrade laser cutting, and many studies are also being conducted in Korea with plans to apply laser cutting processes when dismantling nuclear power plants. However, with the current technology level of the laser cutting process, the maximum thickness that can be cut is limited to 250 mm. Therefore, in this study, a laser-oxygen hybrid cutting process was implemented by adding a laser heat source to the oxygen cutting process that can cut carbon steel with a thickness of 250 mm or more (RV, beam, column, beam, etc.) when dismantling the nuclear power plant. This has the advantage of improving the cutting speed and reducing the cutting width Kerf compared to conventional oxygen cutting. In this research, the laser-oxygen hybrid cutting process consisted of laser cutting to which Raycus’ 8 kW Fiber Laser power source was applied and oxygen cutting to which hydrogen was applied with Fuel Gas. The oxygen torch was placed perpendicular to the test piece, and the laser head was irradiated by tilting 35° to 70°. The effects of cutting directions on quality and performance were studied, and cutting paths were selected by comparing cutting results. Thereafter, it was confirmed that there is an optimal laser output power according to the cutting thickness by studying the effect on the cutting surface quality by changing only the laser output power under the same cutting conditions. The results of this study are expected to be helpful in the remote cutting process using laser-oxygen hybrid cutting when dismantling domestic nuclear power plants in the future.

LED 모듈의 초고속 레이저 절단을 위한 연구

최원용,좌성훈,Choi, Won Yong,Choa, Sung-Hoon 한국마이크로전자및패키징학회 2017 마이크로전자 및 패키징학회지 Vol.24 No.1

최근 레이저를 이용하여 전자 소자 및 모듈을 절단하기 위한 많은 연구가 진행되고 있다. 본 연구에서는 레이저를 이용하여 LED 모듈을 초고속 절단하기 위한 기초 연구를 수행하였다. 특히 기존의 다이싱(dicing) saw의 절단 속도를 훨씬 능가하는 100 mm/s의 초고속 레이저 절단의 가능성을 검토하였다. 이를 위하여 LED 모듈의 구성 재료인 copper/ceramic 및 silicone/ceramic 이종 복합 기판을 제작하여 레이저 절단 후, 절단면의 표면 특성, 표면조도, 굽힘 강도를 다이싱 saw를 이용하여 절단한 샘플과 비교하였다. 복합 기판에 대한 최적의 레이저 절단 조건을 찾기 위하여, 세라믹 및 구리 단일 기판의 레이저 절단을 통하여 다양한 레이저 공정 조건들에 대한 영향 검토하였다. 절단면의 표면 특성이 가장 좋은 최적의 레이저 절단 조건은 Ar 보조 가스의 사용, 높은 레이저 파워 및 높은 보조 가스의 압력이었다. Copper/ceramic 및 silicone/ceramic 이종 복합 기판에 대하여 레이저 절단과 다이싱 saw로 절단한 기판의 절단면을 비교한 결과, 레이저로 절단된 기판이 다이싱 saw 절단에 비하여 표면이 거칠고 표면 특성이 약간 나쁘다. 레이저 절단면의 평균 표면조도는 약 $9{\mu}m$ 이며, 다이싱 saw로 절단된 절단면의 표면조도는 약 $4{\mu}m$ 이었다. 그러나 다이싱 절단의 절단 속도(3 mm/s)를 고려하면 레이저 절단면의 표면 morphology가 비교적 균일하고, 표면조도도 다이싱 절단의 경우와 큰 차이가 없기 때문에 어느 정도 만족할 만한 결과를 얻었다고 판단된다. 또한 레이저 절단된 기판의 굽힘 강도가 다이싱으로 절단된 기판의 굽힘 강도보다 동등하거나 약간 열세이었다. 그러나 향후 레이저의 절단 조건이 좀 더 최적화된다면 LED 모듈의 초고속 레이저 절단이 가능할 것으로 판단된다. In this study, we conducted the preliminary research for high speed laser cutting of LED module. In particular, the feasibility of ultra-high speed laser cutting of 100 mm/s which exceeds the cutting speed of conventional dicing saw was examined. For this, copper/ceramic and silicone/ceramic hybrid substrates, which are the components of the LED module, were fabricated, and the surface morphology, surface roughness and flexural strength of the laser-cut samples were investigate and compared with the dicing-cut samples. To investigate optimal laser cutting conditions for hybrid substrates, the effects of various laser cutting conditions on cutting surface characteristics were studied using single ceramic and copper substrate. Optimal laser cutting conditions of the hybrid substrates were the use of Ar assist gas, high laser power and high assist gas pressure. Comparing the cutting surface of the hybrid substrates, the surface characteristics of the laser-cut samples are slightly inferior to those of the dicing-cut samples. The average surface roughness of the laser-cut samples was about $9{\mu}m$, and that of the dicing-cut samples was about $4{\mu}m$. However, considering very low cutting speed (3 mm/s) of the dicing saw, the surface morphology of the laser-cut sample was relatively uniform, and the surface roughness was not much different from that of the dicing-cut sample. The flexural strength of the laser-cut samples was equivalent to or slightly inferior to the flexural strength of dicing-cut samples. However, if the laser processing conditions are sufficiently optimized, the ultra-high speed laser cutting of the LED module will be possible.

Safety Study on Residual Power Transmitted From Laser-cut Object for Nuclear Decommissioning Application

Jae Sung Shin,Ki-Hee Song,Seong Y. Oh,Seung-Kyu Park 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.2

Laser cutting has been attracting attention as a next-generation tool in application for nuclear decommissioning. It enables high-speed cutting of thick metal objects, and its narrow kerf width greatly reduces the amount of secondary waste compared to other cutting methods. In addition, it only requires the relatively small cutting head without any complicated equipment, and long-distance cutting apart from a laser generator is possible using beam delivery through optical fiber. And there is almost no reaction force because it is non-contact thermal cutting. For these reasons, the laser cutting is very advantageous for remote cutting. In laser cutting, the irradiated laser power is absorbed and consumed to melt the material of the cutting target. When the applied laser power is greater than the power consumed for melting, the residual power is transmitted to the back of the cut object. This residual power may unintentionally cut or damage undesired objects located behind the cutting target. In order to prevent this, it is necessary to adjust the laser power for each thickness of the target object to be cut, or to increase the distance between the cut target and the surrounding structures so that the transmitted power density can be sufficiently lowered. In this work, safety study on residual power that penetrates laser-cut objects was conducted. Experimental studies were performed to find safe conditions for irradiation power density that does not cause surface damage to the stainless steel by adjusting the laser power and stand-off distance from the target.

Underwater Laser Cutting of Thick Stainless Steel in Various Cutting Directions for Application to Nuclear Decommissioning

Shin, Jae Sung,Oh, Seong Y.,Park, Seung-Kyu,Kim, Taek-Soo,Park, Hyunmin,Lee, Jonghwan Korean Radioactive Waste Society 2021 방사성폐기물학회지 Vol.19 No.3

For application in nuclear decommissioning, underwater laser cutting studies were conducted on thick stainless-steel plates for various cutting directions using a 6 kW fiber laser. For cutting along the horizontal direction with horizontal laser irradiation, the maximum cutting speed was 110 mm·min^-1 for a 48 mm thick stainless-steel plate. For cutting along the vertical direction with horizontal laser irradiation, a maximum speed of 120 mm·min^-1 was obtained for the same thickness, which confirmed that the cutting performance was similar but slightly better. Moreover, when cutting with vertically downward laser irradiation, the maximum cutting speed was 120 mm·min^-1 for a plate of the same thickness. Thus, the cutting performance for vertical irradiation was nearly identical to that for horizontal irradiation. In conclusion, it was possible to cut thick stainless-steel plates regardless of the laser irradiation and cutting directions, although the assist gas rose up due to buoyancy. These observations are expected to benefit laser cutting procedures during the actual dismantling of nuclear facilities.

고출력 Nd:YAG UV레이저를 이용한 polyimide층과 Cu-metal층의 가공상태에 대한 실험적 고찰

최경진,이용현,Choi, Kyung-Jin,Lee, Young-Hyun 한국반도체디스플레이기술학회 2009 반도체디스플레이기술학회지 Vol.8 No.4

In this paper, the laser cutting characteristics of the flexible PCB using high power Nd:YAG UV laser were investigated. A specific FPCB model was selected for the experiment. Test sheets were made, which had equal materials and layer structure to those of the outline (OL) region and the contact pad (CP) region in the FPCB. The experiment is made up of two stages. In the first stage of the experiment, the laser cutting fluence was found, which is the threshold fluence to cut the test sheets completely. The laser cutting fluence of the OL sheet is $1781.26{\sim}1970.16\;J/cm^2$ and that of the CP sheet is $2109.34{\sim}2134.34\;J/cm^2$. In the second stage, cutting performance and its qualities were analyzed by the experiment. The laser cutting performance remained almost unchanged for all laser and process parameter sets. The average cutting width (top side/bottom side) of the OL sheet was $40.45\;{\mu}m/11.52\;{\mu}m$ and that of the CP sheet was $22.14\;{\mu}m/10.93\;{\mu}m$. However, the laser cutting qualities were different according to the parameters. The adjacent region of the cutting line on the OL sheet was carbonized as the beam speed was low and the overlap coefficient was high. The surface quality around the cutting line of the CP sheet was about the same. Carbonization and debris occurred on the surface of the cutting line. As a result of the experiment, the cutting qualities were better as the overlap coefficient was made low and beam speed high. Therefore, the overlap coefficient 2 or 3 is proper for the FPCB laser cutting.

Cutting performance of thick steel plates up to 150 mm in thickness and large size pipes with a 10-kW fiber laser for dismantling of nuclear facilities

Shin, Jae Sung,Oh, Seong Yong,Park, Hyunmin,Chung, Chin-Man,Seon, Sangwoo,Kim, Taek-Soo,Lee, Lim,Lee, Jonghwan Elsevier 2018 Annals of nuclear energy Vol.122 No.-

<P><B>Abstract</B></P> <P>The cutting performance of thick steel plates and large size pipes with a 10 kW fiber laser was studied for the dismantling of nuclear facilities. First, thick steel plates of up to 100 mm were tried to be cut at a high speed. For the thickness of 100 mm, both stainless steel and carbon steel plates were cut at maximum cutting speeds of ∼30 mm/min. And narrow kerf widths of less than 5 mm were obtained for all cutting tests. Second, a 150-mm thick stainless steel plate near the cutting thickness limit was attempted to be cut. The specimen was able to be cut even with a low cutting speed of 3 mm/min. To the best of our knowledge, this thickness is the largest among the published reports with a laser power of 10 kW. And this corresponds to a cutting capability in which most thick structures in a nuclear reactor can be cut. In addition, large size stainless steel pipes were also attempted to be cut. For a 165 mm diameter pipe, it was possible to be cut at high speed by one scan at a speed of 50 mm/min and round trip scan at a speed of 100 mm/min. This result implies that high-speed cutting was also possible for most pipe-type components inside the nuclear reactor. As a result, our 10-kW laser cutting system showed very efficient cutting performance in terms of the cutting speed and thickness. Moreover, the cuttings showed narrow kerf widths of less than 5 mm even for very thick steel of up to 150 mm in thickness. In the future, it is expected that the results of this work will contribute to cutting thick metal structures as basic research data in the dismantling of nuclear facilities using a laser. In addition, it is also expected that this work will contribute to other industrial fields requiring a thick steel cutting technique.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cutting of thick steel plates and large pipes with a 10 kW fiber laser was studied. </LI> <LI> Stainless steel and carbon steel plates of up to 100 mm were cut at a high speed. </LI> <LI> A 150-mm thick stainless steel plate was also able to be cut. </LI> <LI> A 165 mm diameter pipe was possible to be cut. </LI> <LI> Our system showed efficient cutting performance in terms of speed and thickness. </LI> </UL> </P>

Cutting thin glass by femtosecond laser ablation

Shin, Hyesung,Kim, Dongsik Elsevier 2018 Optics and laser technology Vol.102 No.-

<P><B>Abstract</B></P> <P>The femtosecond laser ablation process for cutting thin aluminoborosilicate glass sheets of thickness 100 μm was investigated with emphasis on effective cutting speed (<I>V</I> <SUB>eff</SUB>) and mechanical strength of diced samples. The process parameters including the laser fluence (<I>F</I>), overlap ratio (<I>r</I>) of the laser beam and polarization direction were varied at a fixed pulse repetition rate <I>f</I> = 1 kHz to find the optimal process condition that maximizes <I>V</I> <SUB>eff</SUB> and edge strength. A three-point bending test was performed to evaluate the front-side and back-side bending (edge) strength of the laser-cut samples. <I>V</I> <SUB>eff</SUB> was proportional to <I>F</I> unless <I>r</I> exceeded a critical value, at which excessive energy began to be delivered at the same spot. The front-side edge strength was bigger than the back-side strength because of the back-side damages such as chipping. Good edge strength, as high as ∼280 MPa (front-side) and ∼230 MPa (back-side), was obtained at <I>F</I> = 19 J/m<SUP>2</SUP>, <I>r</I> = 0.99, with laser polarization vertical to the cutting path.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Thin glass cutting process using femtosecond laser ablation is analyzed. </LI> <LI> Processing parameters are optimized to maximize the cutting speed and edge strength. </LI> <LI> Cutting speed is proportional to fluence unless the overlap ratio exceeds a critical value. </LI> <LI> High edge strength in laser-cut thin glass requires low fluence and high overlap ratio. </LI> <LI> Polarization should be vertical to cutting path for better cutting performance. </LI> </UL> </P>

Improvement of cutting performance for thick stainless steel plates by step-like cutting speed increase in high-power fiber laser cutting

Seon, Sangwoo,Shin, Jae Sung,Oh, Seong Yong,Park, Hyunmin,Chung, Chin-Man,Kim, Taek-Soo,Lee, Lim,Lee, Jonghwan Elsevier 2018 OPTICS AND LASER TECHNOLOGY Vol.103 No.-

<P><B>Abstract</B></P> <P>A study was conducted to improve the cutting performance of a 60-mm thick stainless steel plate using a 6-kW fiber laser. Two techniques for improving the initial cutting performance were evaluated by preheating the work piece with a waiting time and step-like cutting speed increase. Both techniques showed improved cutting results compared to constant speed cutting. Among them, the method with a step-like cutting speed increase showed the better result in terms of cutting performance. As a result, a 60-mm thick stainless steel plate was cut at a maximum cutting speed of 72 mm/min with a preheating cutting speed of 24 mm/min. In order to confirm the effect of preheating, an additional experiment was performed to measure the temperature variation during the cutting process. Through this experiment, preheating temperature conditions were found to allow the specimen to be cut. It is expected that the results of this work will contribute to improving the cutting performance of thick metal structures in various industrial fields, as well as the dismantling of nuclear facilities using lasers in the future.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Methods for improving the cutting performance of thick steel plates were evaluated. </LI> <LI> With a waiting time, the performance was slightly improved but very sensitive. </LI> <LI> With a step-like cutting speed increase, the performance was greatly improved. </LI> <LI> This work is expected to contribute in dismantling of nuclear facilities. </LI> </UL> </P>

Analysis of different laser cutting conditions on electrical characteristics of half-cut HJT solar cells

Otgongerel Zulmandakh,Moon Jiyeon,Jun Da Yeong,Park Godeung,Nam Hyeryeong,Kwon Oryeon,Lim Hyunsoo,Kim Sung Hyun 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.83 No.6

Nowadays, as wafer sizes continue to increase in the solar industry, the use of half-cut cells has gained attention as a means of increasing the current output by reducing resistive losses. The laser scribing technology cannot increase the output power, as the laser process can cause losses due to laser-induced damages. Therefore, laser scribing losses have a more substantial infuence on the photovoltaic electrical characteristic. It is signifcantly impacted by high-efciency solar cells such as heterojunction technology (HJT) and passivated contact solar cells. Currently, infra-red (IR) and non-destructive cutting (NDC) technology are both very useful cutting technologies for halved solar cells. IR technology has been already known conventional scribing method and has been considerably researched. However, how NDC cutting causes damage and the critical factors to reduce the damage still lack comprehensive research. Hence, in this research, we studied how diferent laser-cutting conditions afect the electrical characteristics of half-cut HJT solar cells. Firstly, IR laser scribing at the front and rear surfaces of HJT cells was demonstrated to compare surface damage dependence. Next, we exploited state-of-the-art cutting technology NDC with various cutting conditions, such as laser scribing powers and scan speeds. The results show that NDC cutting technology shows that the second laser power and scan speeds impacted output performance. Therefore, the NDC method shows a higher power efciency than conventional IR scribing technology, with improvements of 2.6% in fll factor and 0.63 W in output power.

Nd:YAG UV 레이저를 이용한 연성회로 다층기판 절단특성에 대한 연구

최경진(Kyung Jin Choi),이용현(Young-Hyun Lee) Korean Society for Precision Engineering 2010 한국정밀공학회지 Vol.27 No.3

The FPCB is used for electronic products such as LCD display. The process of manufacturing FPCB includes a cutting process, in which each single FPCB is cut and separated from the panel where a series of FPCBs are arrayed. The most-widely used cutting method is the mechanical punching, which has the problem of creating burrs and cracks. In this paper, the cutting characteristics of the FPCB have been experimented using Nd:YAG DPSS UV laser as a way of solving this problem. To maximize the industrial application of this laser cutting process, test samples of the multilayered FPCB have been chosen as it is actually needed in industry. The cutting area of the FPCB has four different types of layer structure. First, to cut the test sample, the threshold laser cut-off fluence has been found. Various combinations of laser and process parameters have been made to supply the acquired laser cut-off fluence. The cutting characteristics in terms of the variation of the parameters are analyzed. The laser and process parameters are optimized, in order to maximize the cutting speed and to reach the best quality of the cutting area. The laser system for the process automation has been also developed.