Shin Ichi Nakashiba

Welding characteristics of aluminum alloy by pulsed nd: Yag laser with pre-and post-irradiation of superposed continuous diode laser

Authors developed the high-performance micro-welding of aluminum alloy, in which the superposition of continuous diode laser of wavelength 808nm and pulsed Nd:YAG laser of wavelength 1064nm could perform the high-processing speed, the deeper penetration depth and the wider bead width. However, the penetration depth at the beginning of laser scanning was insufficient, and the evaluation of cracks wasnot cleared yet. Therefore, in this study, the effects of pre-and post-heating with continuous diodelaser on welding phenomena of aluminum alloy were experimentally and numerically investigated. Thecombination of continuous diode laser and pre-heating pulse of Nd:YAG laser without melting of specimensurface could keep the high surface temperature, which led to the stable deeper penetration and widerbead width with smooth surface integrity even at the beginning of laser scanning. Moreover, it was confirmed that the superposition of continuous diode laser was effective to improve a welding quality of aluminum alloy, since the superposition of continuous diode laser prevented rapid heating and cooling of aluminum alloy. The post-heating with continuous diode laser kept the gentle temperature gradient at the laser spot, and the generation of crack could be decreased by appropriate power and irradiation time of continuous diode laser.Authors developed the high-performance micro-welding of aluminum alloy, in which the superposition of continuous diode laser of wavelength 808nm and pulsed Nd:YAG laser of wavelength 1064nm could perform the high-processing speed, the deeper penetration depth and the wider bead width. However, the penetration depth at the beginning of laser scanning was insufficient, and the evaluation of cracks wasnot cleared yet. Therefore, in this study, the effects of pre-and post-heating with continuous diodelaser on welding phenomena of aluminum alloy were experimentally and numerically investigated. Thecombination of continuous diode laser and pre-heating pulse of Nd:YAG laser without melting of specimensurface could keep the high surface temperature, which led to the stable deeper penetration and widerbead width with smooth surface integrity even at the beginning of laser scanning. Moreover, it was confirmed that the superposition of continuous diode laser was effective to improve a welding quality of aluminum all...

Investigation on Micro-Machining Characteristics and Phenomenon of Semiconductor Materials by Harmonics of Nd:YAG Laser

Precision micro-machining without crack and heat affected zones is required in order to use high-performance materials such as silicon and silicon carbide, and it is expected that the higher harmonics of the Nd:YAG laser can perform precision micro-machining due to its high photon energy. However, even by using the harmonics of the Nd:YAG laser, a heat affected zone is inevitable due to the plasma generation. In order to reduce the influence of plasma on the processing results, it is important to understand the generation mechanism of plasma. Therefore, the laser induced plasma in micro-drilling of silicon carbide was observed by a high-speed shutter camera, and the influence of laser wavelength and surrounding conditions on the machining characteristics were experimentally investigated. The removal depth increased with decreasing wavelength and the surrounding gas pressure. The surface integrity was improved by the combination of shorter wavelength and reduced pressure conditions. The behavior of laser induced plasma was different from the wavelength of the laser beam and the surrounding gas pressure. Under atmospheric pressure conditions, the plasma grew greatly and affected the wider surface around the drilled hole with increasing wavelength. Under reduced pressure conditions, there was little difference in plasma size by wavelength, and the affected zone around the drilled hole became relatively smaller. It became clear that a low surrounding gas pressure and shorter wavelength were important to obtain better surface integrity and highly efficient processing.

Evaluation of damaged region at the groove edge of TCO film in pulsed fiber laser processing

Nonosecond pulsed fiber laser has been widely used for the removal of TCO film, because of its compact oscillator with the flexible processing head. However, the wide bandwidth of wavelength from the fiber laser would deteriorate the edge quality of groove such as cracks and burrs at the resolidified region due to the chromatic aberration. Therefore, the edge quality of scribed groove was experimentally investigated in the removal process of TCO film by the nanosecond pulsed fiber laser of 1060nm in wavelength. The damaged region such as cracks and burrs at the edge of groove could be improved by using achromatic focusing lenses. The singlet lens for focusing optics led to the large damaged region at the edge of groove, and the cracks and burrs appeared remarkably with increasing the pulse energy. The combination of singlet focusing lens and a circle mask to trim the laser beam made it possible to become the damaged region smaller, since the intensity distribution of laser beam could be sharpen at the edge by using the mask with an appropriate diameter hole.Nonosecond pulsed fiber laser has been widely used for the removal of TCO film, because of its compact oscillator with the flexible processing head. However, the wide bandwidth of wavelength from the fiber laser would deteriorate the edge quality of groove such as cracks and burrs at the resolidified region due to the chromatic aberration. Therefore, the edge quality of scribed groove was experimentally investigated in the removal process of TCO film by the nanosecond pulsed fiber laser of 1060nm in wavelength. The damaged region such as cracks and burrs at the edge of groove could be improved by using achromatic focusing lenses. The singlet lens for focusing optics led to the large damaged region at the edge of groove, and the cracks and burrs appeared remarkably with increasing the pulse energy. The combination of singlet focusing lens and a circle mask to trim the laser beam made it possible to become the damaged region smaller, since the intensity distribution of laser beam could be sharpen at the edg...

Influence of surrounding gas type and pressure condition on micro-drilling of silicon carbide by harmonics of Nd: YAG laser

Micro-drilling characteristics of silicon carbide by fundamental wavelength and three kinds of harmonic of Nd:YAG laser were experimentally investigated in the viewpoints of surrounding gas type and the pressure condition. Moreover, its characteristics were discussed by the observation of plasma behaviour, flow filed and debris behaviour on the specimen surface with a high-speed camera. The cracks were observed around drilled hole under the argon surrounding gas condition due to the generation of high intensity plasma. On the other hand, the helium surrounding gas kept the plasma in the vicinity region on the top surface of specimen, and the surrounding area of drilled hole was remarkably roughened. The better surface integrity could be obtained under the appropriate combination of surrounding gas type and the reduced pressure conditions.Micro-drilling characteristics of silicon carbide by fundamental wavelength and three kinds of harmonic of Nd:YAG laser were experimentally investigated in the viewpoints of surrounding gas type and the pressure condition. Moreover, its characteristics were discussed by the observation of plasma behaviour, flow filed and debris behaviour on the specimen surface with a high-speed camera. The cracks were observed around drilled hole under the argon surrounding gas condition due to the generation of high intensity plasma. On the other hand, the helium surrounding gas kept the plasma in the vicinity region on the top surface of specimen, and the surrounding area of drilled hole was remarkably roughened. The better surface integrity could be obtained under the appropriate combination of surrounding gas type and the reduced pressure conditions.

High efficiency and high quality welding of aluminum alloy by hybrid system combined Nd: YAG laser and diode laser

Recently, the welding of aluminum alloy has been strongly required for lightening the electronic products, automobiles and so on. Then, hybrid laser system was newly developed in order to perform the high efficiency and high quality welding of aluminum alloy. We have developed the hybrid system which is consisted of a continuous diode laser and a pulsed Nd:YAG laser. In this system, high electric-optical conversion efficiency was achieved by the newly developed diode laser pumping system, and it can deliver two laser beams by using only one fiber. Higher absorption of laser energy to the aluminum alloy can be expected under the continuous irradiation of diode laser (wavelength: 808nm), since the absorption of light to aluminum alloy shows the maximum at 850nm. When the pulse waveform took the highest peak at the first period, the suitable bead width and depth could be obtained with better surface integrity. The bead width and depth increased with increasing the power of continuous diode laser, which led to overlapping welding even under the high speed condition. Numerical calculation made it clear that the surface temperature of aluminum alloy with diode laser could keep 300K higher than that without diode laser before the next laser shot. Therefore, it could be expected that pulsed Nd:YAG laser would be absorbed more effectively because of higher surface temperature of aluminum alloy, and high efficiency processing would be performed. Moreover, the high efficiency and the high quality welding of aluminum battery case could be accomplished by this hybrid system, in which the suitable pulse energy and the peak power could be given even under the high pulse repetition rate.Recently, the welding of aluminum alloy has been strongly required for lightening the electronic products, automobiles and so on. Then, hybrid laser system was newly developed in order to perform the high efficiency and high quality welding of aluminum alloy. We have developed the hybrid system which is consisted of a continuous diode laser and a pulsed Nd:YAG laser. In this system, high electric-optical conversion efficiency was achieved by the newly developed diode laser pumping system, and it can deliver two laser beams by using only one fiber. Higher absorption of laser energy to the aluminum alloy can be expected under the continuous irradiation of diode laser (wavelength: 808nm), since the absorption of light to aluminum alloy shows the maximum at 850nm. When the pulse waveform took the highest peak at the first period, the suitable bead width and depth could be obtained with better surface integrity. The bead width and depth increased with increasing the power of continuous diode laser, which led t...