• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.3
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• pp.37-45
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• 2000

The technique of laser sheet beam has been applied to optically accessible diesel engine for the quantitative measurement of soot. The results provide the information for us for reduction of soot in diesel engine. We used both LIS nad LII techniques simultaneously in this study. LIS and LII images show the quantitative distribution of the soot concentration in an optically accessible diesel engine. In this study, several results were obtained by the simultaneous measurement of LIS and LII technique. The diameter and number density of soot in combustion chamber of the test engine were obtained from ATDC 20$^{\circ}$ to 110$^{\circ}$ . The increase rate of soot diameter was about 40$^{\circ}$ between ATDC 20$^{\circ}$and 110$^{\circ}$. And the number density of soot decreased significantly between ATDC 20$^{\circ}$and 40$^{\circ}$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.238-244
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• 2002

A 5-valve(intake 3-valve) engine has been developed to increase engine performance. These engines have a high power caused by the decrease of inertia mass of an intake valve and the increase of intake effective area. In this study, in-cylinder flow patterns were visualized with laser sheet method and velocity profiles at near intake valves were inspected by using a two-color PIV. In addition, steady flow tests were performed to quantify tumble ratio of flow-fields generated by a tumble control valve(TCV). Experimental results of steady flow test show that the cure of tumble ratio in intake 3-valve engine farmed as a S shape with valve lift changes. This tendency is different from the one in intake 2-valve engine. Using laser sheet method and two color PIV method, we can find that the intake flow through upper valve increases and the velocity gradient also slightly increases as valve lift increases. From this study, the in-cylinder flow characteristics around intake valves were made clearly.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.2313-2318
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• 2003

By means of flexible forming processes in sheet metal manufacturing it is possible to produce parts of complex geometry within short manufacturing time. These procedures are suitable especially for prototyping or adjustment of deformation. Here formative procedures like laser forming are increasingly important, because they make the large-scale-like production of the prototypes with the required materials possible. High accuracy and reproducibility of the products is the precondition of the production. Due to the lack of a forming tool, complex geometries can hardly be manufactured within tolerances. To overcome this problem an automatic closed loop control system for the adjustment of deformations has been developed. An important element of the closed loop control system is the definition of a suitable irradiation strategy for laser forming. For the determination of the irradiation strategy a lot of influences must be taken into consideration from the field of material, geometry and laser. In this paper the improved closed loop control system and the development of an irradiation strategy for 4 mm deep buckles in an ALMgSi1 sheet will be represented. This system can be used e.g. in the automated adjustment of hail damage in car bodies or deformation by heat treatment.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.107-110
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• 2003

The sheet metal shearing process is normally used in the precision elements such as semi-conductor components. In precision elements, burrs usually reduce the quality of machined parts and cause interference, jamming and misalignment during assembly procedures and because of their sharpness, they can be safety hazard to personnel. Furthermore, not only burrs are hard to predict and avoid, but also deburring, the process of removing burrs, is time-consuming and costly. In order to get the burr-free parts, therefore, we developed the precise burr measuring system using the laser. Using the X-Y precious table, we used vertical measuring method. Through the laser measurement system, we gain the minute analog signal, so this signal was amplified by the electric circuit. Finally, we gained the realtime burr data using A/D converter, PC. By introducing the novel laser measuring method which employing vertical measurement mechanism, we could get fast and precious burr data. Through the experiments, the accuracy of the developed system is proved. The burr height measured during the punching process can be used for automatic deburring and in-situ aligning.

• Laser Solutions
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• v.1 no.1
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• pp.4-10
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• 1998

A basic research for tailored blank welding between mild steel and Zn-coated steel was carried out with $CO_2$ laser beam. The materials used in this work were low carbon steel sheet with a thickness of 1.2mm and Zn-coated steel sheet with the same thickness and 6.3$\mu$m Zn coating. Experiments were carried out by applying the Taguchi method in order to obtain optimized conditions for the application of tailored blank laser welding method in practical manufacturing process. Optical microscopy, XRD, SEM and TEM analysis were performed to observe microstructures and to determine the solidification mode of welded zone. Also mechanical properties were measured by microhardness test tensile test and Erichsen test in order to evaluate the formability of welded specimen. There was no trapped Zn in the fusion zone, and the phases in this region consisted of polygonal ferrite, quasi-polygonal ferrite, banitic ferrite and martensite. The elongation value of welded specimen was more than 80% of that value in the substrate and LDH value was more than 90% of that value in the substrate metal.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1317-1321
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• 2007

Aluminized steel sheet that Al coated on low carbon steel has a excellent heat resistance, thermal reflection and corrosion resistance. It has applied to fuel tank, automotive exhaust systems, etc. Laser weldability of the aluminized steel for the full penetration welding will be described in this paper. We focused on the effect of Al coating conditions on weld strength. For these objectives, aluminized steel sheets that has various thickness and coating weight were prepared for laser welding. And then, tensile-shear and hardness test were carried out. At that same time, Al content mixed in weld after laser welding was evaluated and investigated a correlation between the mixed Al and mechanical properties. Besides, as removing partially coating layer, weldability has been investigated according to position of coating layer. As a result of this study, as increasing Al content in weld, tensile-shear strength was decreased. Also it was identified that Al of coating layer caused grain growth.

• Proceedings of the KWS Conference
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• 2003.11a
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• pp.18-20
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• 2003

Optimal processing and system to produce the laser welded tube for one body formed bumper beam are studied. The calculated size of tube is a thickness of 1.4mm, diameter of 105.4mm and length of 2000mm. The tube is shaped from cool rolled high strength steel sheet(tensile strength: 60kgf/$\textrm{mm}^2$ grade). Two roll bending method is the optimal tube shaping process compared to UO-bending, bending on press brake, multi-step continuous roll forming and 3 roll bending methods. Weld quality monitoring and seam tracking along the butt-joint lengthwise to the tube axis are also studied. The longitudinal butt-joint is welded by the $CO_2$ laser welding system equipped with a seam tracker and plasma sensor. The constructed $CO_2$ laser tube welding system can be used for the precision seam tracking and the real-time monitoring of weld quality. Finally, the obtained laser welded tube can be used for one-body formed automobile bumper beam.

• Journal of Welding and Joining
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• v.16 no.1
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• pp.77-87
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• 1998

This paper deals with the effect of laser welding parameters on the weld formation. Thin steels for automotive application were prepared so as to be welded with high power carbon dioxide laser system. Major process parameters were position of focus and travel speed. The effect of shielding gas was also discussed by employing the high speed photometry. Test results showed that the optimal position of focus varied in accordance with the joint configuration; bead-on-plate, butt or lap welding. It was recommended that the position of focus for the lap welding be located at slightly inner part of the material to be welded. In this case, however, it was noticeable that the weld penetration ratio, d/t$_{0}$ dropped drastically at the critical region. Results also demonstrated that both the bead width and penetration reduced as the travel speed increased. The penetration ratio showed two distinct regions; stabilized zone at the lower range of the travel spped and sudden drop zone at the higher range of travel speed. Lower limit of the penetration for acceptable weld was proved to be about 90% of the parent metal thickness based on the physical properties of the weld. Mixed gas application for both the shielding of molten metal and laser induced plasma control was recommended as far as the penetration was concerned.d.

• Journal of Welding and Joining
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• v.26 no.5
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• pp.90-96
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• 2008

The objective of this paper is to investigate the effects of the laser power, the material thickness, comer angles, and the loop size on the formation of the comer in the cutting of Inconel 718 super-alloy sheet using high-power CW Nd: YAG laser. In order to investigate the influence of comer angles and loop sizes on the melted area and the formation of comer in the sharp comer, angular cutting tests and loop cutting tests were carried out. The results of the angular cutting tests were shown that the melted area is minimized and the melting mode is changed from nose melting in the thickness direction to the secondary melting induced by the attached dross when the comer angle is $90^{\circ}$. Through the results of loop cutting tests, the variation of the melted area and the comer shape in the sharp comer according to the loop size were examined. In addition, it was shown that a proper loop size is approximately 3 mm. The results of above experiments will be reflected on the knowledge base to generate optimal cutting path of the laser.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.2
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• pp.30-37
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• 2020

We propose a practical method for increasing formability of a sheet metal plate using laser heat treatment (LHT) and cladding process. In this work, two kinds of process such as laser-induced heat treatment and cladding were utilized to evaluate the effect on formability of SUS316 sheets with different thickness of 1 and 3 mm. By using a vertically line-patterned tensile specimen that was LHTed or cladded on its surface, the process parameters of each surface treating method were studied and optimized. Through the basic test, we knew that the laser power of 900 W and scanning speed of 500 mm/min was the best condition for increase of formability. As the treatment results, ultimate tensile strength and elongation were increased as approximately 2.1 and 7.0%, respectively. To verify the usefulness of this work in industrial cases, we conducted a bulging test using with and without LHTed SUS316 sheet metal blanks. The results show that the bulging height of LHTed sheet was increased by 73% compared to that of the original one.