• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2000년도 특별강연 및 추계학술발표대회 개요집
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• pp.170-172
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• 2000

In this research, newly proposed heat source equations were calculated to predict micro distortion of small structure in laser welding and compared with experimental results which were measured using laser speckle metrology. A finite element code, ABAQUS is used for the heat transfer analysis with a three-dimensional plane assumption. The results suggest that weld distortion is varied according to the heat source of the. laser beam.

• Journal of Welding and Joining
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• 제32권2호
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• pp.63-69
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• 2014

Dual laser heat sources were used for polymer based material joining. An infrared camera and thermocouple DAQ system were used to correlate the temperature distribution to computer simulation. A 50 degree tilted pre-heating laser source was acting as a heating source to promote the temperature to minimize thermal shock by the following a welding heat source. Based on the experimental result, the skin depth was empirically estimated for computer simulation. The offsets of 3mm, 5mm and 10mm split by weld and preheat were effectively used to control the temperature distribution for the optimal laser joining process. The closer offset resulted in an excessive melting or burning caused by sudden temperature rising. The laser power was split by 50%, 75% and 100% of the weld power, and the best results were found at 50% of preheating. To accurately simulate the physical laser beam absorption and joining optical properties were experimentally measured for the computer FEM simulation. The simulation results showed close correlation between theoretical and experimental results. The developed dual laser process is expected to increase productivity and minimize the cost for the final products.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1560-1565
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• 2005

Laser beam welding is increasingly being used in welding of structural steels. The laser welding process is one of the most advanced manufacturing technologies owing to its high speed and deep penetration. The thermal cycles associated with laser welding are generally much faster than those involved in conventional arc welding processes, leading to a rather small weld zone. Experiments are performed for 304 stainless steel plates changing several process parameters such as laser power, welding speed, shielding gas flow rate, presence of surface pollution, with fixed or variable gap and misalignment between the similar and dissimilar plates, etc. The following conclusions can be drawn that laser power and welding speed have a pronounced effect on size and shape of the fusion zone. Increase in welding speed resulted in an increase in weld depth/ aspect ratio and hence a decrease in the fusion zone size. The penetration depth increased with the increase in laser power.

• International Journal of Precision Engineering and Manufacturing
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• 제6권3호
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• pp.19-23
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• 2005

To minimize the weld defect in manufacturing of the welded tube by using $CO_2$ laser, the monitoring of the welding quality and the seam tracking along the butt-joint lengthwise to the tube axis are studied. The longitudinal butt-joint is shaped from $60kgf/mm^2$ grade steel sheet by 2 roll bending method, and welded by the $CO_2$ laser welding system equipped with the seam tracker and plasma sensor. The laser welded tube has the thickness of 1.5mm, diameter of 105.4mm and length of 2000mm. The precise positioning of the laser beam on the butt-joint to be assembled is obtained within $200{\mu}m$ by the laser vision sensor. The artificial defects in the butt-joint are well observed by the signal of plasma intensity measured from the plasma sensor of UV wavelength range within 400nm. The developed $CO_2$ laser tube welding system has the function of the precision seam tracking and the real-time monitoring of the welding quality. In conclusion, the laser welded tube can be used for manufacturing of automobile chassis and components after hydro-forming.

• 한국정밀공학회지
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• 제27권2호
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• pp.40-49
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• 2010

The Purpose of this paper is to weld a rapid palatal expander using a continuous wave Nd:YAG laser. The rapid palatal expander has become a useful treatment method for severe maxillary transverse deficiencies and posterior crossbites. Rapid maxillary expansion is a well-established method to correct transverse maxillary deficiency and arch length discrepancy. The major process parameters studied in the present laser welding experiment were the positions of focus, laser power and travel speed of laser beam. We measured the fusion zone size and its shape using an optical microscope for the observation of cross-sectional area and tension stress of a rapid palatal expander welded. Through the experimental investigation, the optimum speeds and power of laser without deficiencies of weld cross-sectional area were obtained.

• Journal of Welding and Joining
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• 제28권3호
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• pp.42-48
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• 2010

Polycarbonate (PC) and Acrylonitrile Butadiene Styrene (ABS) were welded by a combination of a diode laser and a CNC machining center. Laser beam delivered through the transparent PC and was absorbed in an opaque ABS. Polymers were melted and joined by absorbed and conducted heat. Experiments were carried out by varying working distance from 44mm to 50mm for the focus spot diameter control, laser input power from 10W to 25W, and scanning speed from 100 to 400mm/min. The weld bead and cross-section were analyzed for weld quality, and tensile results were presented through the joint force measurement. With focus distance at 48mm, laser power with 20W, and welding speed at 300mm/min, experimental results showed the best welding quality which bead size was measured to be 3.75mm. The shear strength at the given condition was $22.8N/mm^2$. Considering tensile strength of ABS is $43N/mm^2$, shear strength was sufficient to hold two materials. A single process was possible in a CNC machining system, surface processing, hole machining and welding. As a result, the process cycle time was reduced to 25%. Compared to a typical process, specimens were fabricated in a single process, with high precision.

• 한국정밀공학회지
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• 제30권6호
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• pp.638-643
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• 2013

Laser beam machining (LBM) is fast, contactless and able to machine various materials. So it is used to cut metal, drill holes, weld or pattern the imprinted surface. However, after LBM, there still leave burrs and recast layers around the machined area. In order to remove these unwanted parts, LBM process often uses electrochemical etching (ECE). But, the total thickness of workpiece is reduced because the etching process removes not only burrs and recast layers, but also the entire surface. In this paper, surface coating was performed using enamel after LBM on metal. The recast layer can be selectively removed without decreasing total thickness. Comparing with LBM process only, the surface quality of enamel coating process was better than that. And edge shape was also maintained after ECE.

• Journal of Welding and Joining
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• 제31권4호
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• pp.17-22
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• 2013

The excellent beam quality of high power fiber lasers are commonly used for remote welding applications in body job applications. The Welding speed and productivity is unmatched with any other welding technology including resistance spot welding or traditional laser welding. High tooling cost for clamping and bulky safety enclosures are obstacles which are limiting the use. With the newly developed Laser stitch welding gun we have an integrated clamping in the process tool and the laser welding is shielded in a way that no external enclosure is needed. Operation of this laser welding gun is comparable with resistance spot welding but 2-times faster. Laser stitch welding is faster than spot welding and slower than remote welding. It is a laser welding tool with all the laser benefits like welding of short flanges, weld ability of Ultra High Strength steel, 3 layers welding and Aluminium welding. Together with low energy consumption and minimum operation cost of IPG fiber laser it is a new and sharp tool for economic car body assembly.

• 한국레이저가공학회지
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• 제7권3호
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• pp.25-36
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• 2004

This study was performed to clarification of the formation of weld discontinuities in the dissimilar laser fusion zone. Welding parameters were beam power of 1300, 1430, 1560, and 1700 W and travel speed of 1, 1.3, and 1.7 m/min. Most cavities in the fusion zone were observed near the tip. Cavities in the fusion zone observed to be formed and grown from pores in the tip. More cavities were formed as the beam position moves to the tip side. Small cavities were decreased but large cavities were increased when the energy input increased. W content in the fusion zone was increased with heat input and as the beam position close to the tip. In the fusion zone, W content in the dendrite boundary was increased with heat input. Considering the propagation path and fracture morphology, cracks were solidification cracking, and were initiated and propagated along the dendrite boundaries. The formation of cracks might be related with the W rich ${\mu}$ phase which was formed in the grain boundaries and dendrite boundaries.

• 한국레이저가공학회지
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• 제4권3호
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• pp.30-39
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• 2001

This work was tamed out to apply a laser welding technique in joining between a Zn coated low carbon steel plate(SECC) and a free cutting carbon steel shaft(SUM24L) with or without W coating. Experiments were carried out and analysed by applying the FD(factorial design)method to obtain the optimum Laser welding condition. Optical microscopy, SEM, TEM and XRD analyses were performed in order to observe the microstructures in the fusion zone and the HAZ. Mechanical properties of the welded specimens were examined by microhardness test, tensile test and twist test. There was no flawed Zn in the fusion zone by EDS analysis. This means that during the welding process, Zn gas could be eliminated by appropriate shielding gas flow rate and butt welding gap. Ni coating itself did not influence on the tensile strength and hardness. However, twist bending strength and the weld depth of the Ni-coated free cutting carbon steel were lower as compared with those of the uncoated free cutting carbon steel. It was attributed to a lower absorbance of laser beam to the shin Ni surface. According to the results of the factorial design tests, the twist bending strength of welded specimens was primarily affected by pulse width, laser power, frequency and speed.