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ABSTRACT 13

제1장 서론 16

1.1. 연구배경 16

1.2. 연구동향 20

가. 레이저 용접 22

나. 레이저 절단 28

1.3. 목적 및 내용 32

가. 파이버 레이저에 의한 기어부품 용접 32

나. 시트레일 부품의 파이버 레이저 용접 33

다. 구조용 압연 소재 SS400의 파이버 레이저 절단 34

제2장 이론적 배경 36

2.1. 고출력 파이버 레이저의 발진 원리 및 특성 36

2.1.1. 파이버 레이저 개발배경 36

2.1.2. 파이버 레이저 발진원리 41

2.1.3. 파이버 레이저 특성 45

2.2. 파이버 레이저 용접 54

2.3. 파이버 레이저 절단 65

제3장 실험 장치 및 방법 71

3.1. 실험 장치 71

3.1.1. 파이버 레이저 용접 장치 73

3.1.2. 파이버 레이저 절단 장치 80

3.2. 실험 재료 84

3.2.1. 레이저 용접 84

3.2.2. 레이저 절단 86

3.3. 실험 방법 87

3.3.1. 기어부품용 소재 IF강의 파이버 레이저 용접 87

3.3.2. 시트레일부품용 소재 SAPH강의 파이버 레이저 용접 89

3.3.3. 구조용 압연 소재 SS400의 파이버 레이저 절단 91

3.4. 가공시편 및 분석 장치 92

가. 기어부품 시편 92

나. 기어부품 시편 93

다. 용접 후 시료 분석 96

라. 광학 및 전자현미경 분석 97

마. 경도분포 측정 98

바. 비파괴 X-Ray 분석 99

제4장 결과 및 고찰 100

4.1. 기어부품용 소재 IF강의 파이버 레이저 용접 100

4.1.1. 비드 온 플레이트 (Bead-on-plate) 용접특성 100

4.1.2. 용접 후 미세조직 특성 106

4.1.3. 전자빔 용접과 레이저 용접성 비교 111

4.2. 시트레일부품용 소재 SAPH강의 파이버 레이저 T형상 용접 118

4.2.1. 레이저 가공공정변수에 따른 용접특성 118

4.2.2. T 형상 Gap에 따른 용접특성 126

4.2.3. 비파괴 분석에 의한 전자빔 및 레이저 용접부 비교 128

4.2.4. 용접부 인장강도 특성 130

4.3. 구조용 압연강 SS400의 파이버 레이저 절단 134

4.3.1. 레이저 출력 변화에 따른 절단 특성 134

4.3.2. SS400 박판 레이저 절단 특성 137

4.3.3. SS400 후판 레이저 절단 특성 140

4.3.4. CO₂레이저와 파이버 레이저 절단 속도 비교 143

제5장 결론 145

가. 기어부품용 소재 IF강의 파이버 레이저 용접 145

나. Seat rail 부품의 T형상 파이버 레이저 용접 146

다. 구조용 압연강 SS440의 파이버 레이저 절단 147

참고문헌 148

관련 논문실적 159

List of Tables

Table 1-1. A recent research of automobile parts welding by laser 25

Table 1-2. A recent research of dissimilar metal cutting by laser 30

Table 2-1. Weldability of dissimilar metal 63

Table 3-1. Chemical compositions of IF steel 85

Table 3-2. Chemical compositions of SAPH440 85

Table 3-3. Mechanical properties of SAPH440 85

Table 3-4. Chemical composition of SS400 86

Table 3-5. Mechanical properties of SS400 86

Table 3-6. Parameters of laser welding for gear parts 88

Table 3-7. Parameters of T-joint laser welding 90

Table 3-8. Parameters of SS400 fiber laser cutting 91

Table 4-1. Result of tensile test 132

List of Figures

Fig. 2-1. Schematic diagram of a CO₂Laser 37

Fig. 2-2. Schematic diagram of a YAG Laser 38

Fig. 2-3. Illustration of thermal lens effect of rod type laser 40

Fig. 2-4. Schematic laser resonator change concept 40

Fig. 2-5. Schematic fiber laser system to structures 42

Fig. 2-6. Design of a fiber spacial coupler 42

Fig. 2-7. Design of a double clad fiber of light pumping : laser active fiber 43

Fig. 2-8. Schematic of fiber laser module 46

Fig. 2-9. Fiber laser beam profile 47

Fig. 2-10. Compared to the high power CW laser efficient 49

Fig. 2-11. Absorption rate of light to metal 50

Fig. 2-12. Schematic fiber laser system of optical beam transmission 52

Fig. 2-13. Structure of optical fiber cable 53

Fig. 2-14. Banding radius of optical fiber cable 53

Fig. 2-15. Variation in power density and interaction time with process of laser 55

Fig. 2-16. Schematic illustration of laser keyhole welding bubble 56

Fig. 2-17. Schematic illustration of laser keyhole welding 58

Fig. 2-18. Schematic illustration of laser conduction welding 59

Fig. 2-19. Laser welding geometry overview 64

Fig. 2-20. Schematic illustration of laser cutting 66

Fig. 2-21. Quality defects of laser cutting edges 68

Fig. 2-22. Schematic illustration of laser cutting gas jet 70

Fig. 3-1. Schematic of fiber laser processing system 72

Fig. 3-2. Schematic of gear welding laser focusing optic head & beam profile 75

Fig. 3-3. Rotary clamp centering jig for gear parts 76

Fig. 3-4. Schematic of laser welding system for gear parts 76

Fig. 3-5. Tilting centering jig for T-joint welding 79

Fig. 3-6. Principle of distance measurement from nozzle to cutting material 83

Fig. 3-7. Classification of laser cutting nozzle 83

Fig. 3-8. Car seat frame and modeling of upper rail parts assembly 90

Fig. 3-9. Mechanical drawings of upper rail parts for fiber laser welding 94

Fig. 3-10. Dimension of seat rail welding test sample 95

Fig. 3-11. Dimension of tensile strength test sample 95

Fig. 4-1. Variation of penetration depth according to laser powers and welding speeds 101

Fig. 4-2. Cross sectional area of welding zone according to the welding speeds 104

Fig. 4-3. Variation of heat input according to laser powers and welding speeds 105

Fig. 4-4. Photographs of melting zone after bead on plate welding (Heat input 21.23 x 10³J/㎠) 108

Fig. 4-5. Photographs of melting zone after bead on plate welding (Heat input 7.96 x 10³J/㎠) 109

Fig. 4-6. Surface hardness measurement of bead on plate welding seam 110

Fig. 4-7. Micrographs of melting zone with laser welding 112

Fig. 4-8. Concept for key hole and cooling with laser conner welding 113

Fig. 4-9. Comparison of laser welding with E-beam welding 115

Fig. 4-10. Perspective of CT for melting zone after E-beam of gear part 116

Fig. 4-11. Perspective of CT for melting zone after laser beam of gear part 117

Fig. 4-12. Cross section of T-joint laser welding 119

Fig. 4-13. T-joint welding laser condition 121

Fig. 4-14. Cross section of T-joint laser welding 124

Fig. 4-15. Cross section of T-joint laser 2-step welding 125

Fig. 4-16. Cross section of T-joint laser welding gap 127

Fig. 4-17. X-Ray 3D Image of T-joint laser welding 129

Fig. 4-18. Tensile strength curves of T-joint laser welding gap 133

Fig. 4-19. Classification of laser cutting quality 136

Fig. 4-20. Influence of cutting speed according to the fiber laser power in SS400. 136

Fig. 4-21. The best cutting area according to cutting parameters (thickness; 2.3 ㎜) 138

Fig. 4-22. The best cutting area according to cutting parameters (thickness; 3.2 ㎜) 139

Fig. 4-23. Fiber laser dual cutting nozzle 141

Fig. 4-24. The best cutting area according to cutting parameters (thickness; 16 ㎜) 141

Fig. 4-25. The best cutting area according to cutting parameters (thickness; 20 ㎜) 142

Fig. 4-26. Comparison of cutting speeds with fiber laser and CO₂ laser 144

List of Photographs

Photo 2-1. Optical fiber cable 52

Photo 3-1. 5㎾ fiber laser and gear parts welding experiment equipment 74

Photo 3-2. 5㎾ fiber laser and T-joint welding experiment equipment 78

Photo 3-3. 2㎾ fiber laser oscillator and 2D cutting experiment equipment 82

Photo 3-4. Fiber laser welding for gear parts 88

Photo 3-5. Picking of gear welding specimen after laser welding 92

Photo 3-6. Hot mounting press 96

Photo 3-7. Automatic grinder / polisher 96

Photo 3-8. Metallurgical microscope 97

Photo 3-9. Micro vickers hardness tester 98

Photo 3-10. 3D micro X-Ray CT 99

Photo 4-1. Image tensile test of T-joint welding 132

초록보기

 As science and technology progress, lasers have been developed rapidly as the material processing device for advanced core components that require high precision. Laser manufacturing is a high energy density processing technology that is most frequently applied in industrial fields. It provides state of the art core component processing with high speed and precision.

In particular, laser welding and cutting technology in the automotive industry is high value-added processing technology to achieve automotive weight reduction, crash stability, quality improvement, and productivity. New alternative technical approaches are actively being developed.

In this study laser welding and cutting characteristics have been examined experimentally to obtain an optimal processing condition for improved productivity and flexibility in manufacturing automobile steel parts.

For this purpose, first, using a continuous-wave high power fiber laser, comparative analysis was conducted for the continuous wave fiber laser welding of the IF (interstitial-atom free) steel automotive gear parts in order to examine its substitution possibility of the conventional electron beam welding process. The experimental conditions were 3~5 kW laser power and 30~110 mm/sec welding speed.

To compare welding quality between electron-beam welded gear parts in industrial fields and gear parts laser-welded in our experiments, X-Ray CT non-destructive inspection was conducted. To achieve the optimal welding conditions, the depth of fusion in the present laser welding experiments was prepared with the same as for the electron-beam-welded specimens. The experimental conditions were 3 kW laser power and 30 mm/sec welding speed, and the heat input was 2.123 × 104 J/㎠.

Second, the fiber laser T-joint welding process for the seat-upper-rail parts made out of SAPH (Steel Automobile Press Hot) 440 steel was examined in its mechanical properties and compared with the conventional bolt-locking process of the same parts.

T-shape welding characteristics, which are the main factors of experiment procedures, were examined for the laser beam irradiation angle of 15, 30 and 45 degrees. Laser power and welding speed were 2~3 kW and 40~120 mm/sec, respectively. Gap gauges of 0.1 mm and of 0.4 mm were used to measure the acceptable distance of weld zones when gaps were present between weld zones.

Tension tests of weld zones were performed for the stability of laser-weld zones and mechanical properties of T-shape zones and were compared with the test results for the bolt-locking process. X-ray non-destructive test results showed that the dynamic drive of key holes was repeated in the interval of 5mm, which confirmed that collapse and regeneration of key holes progress at 100 mm/sec welding speed, in 50 ms with a frequency of 20 Hz.

Finally, fiber laser cutting of SS400 steel used for automotive frame parts was examined to obtain the optimal processing conditions in order to facilitate a 2D fiber laser cutting machine.

For the key factor to determine the laser processing quality is the spot size on the surface of specimens, the optimal cutting quality conditions for different focal lenses were obtained. The focal length of the cutting lenses was 5.0, 7.5, and 10 inch. 3 types of cutting nozzle were employed in the present study and each nozzle type was selected for material thickness.

This study was based only on one axis cutting in order not to consider corner parts that affect acceleration and deceleration in the X/Y stage of laser cutters. Cutting quality was classified as high, middle and low, and subsequently, the best cutting area for each specimen was determined.

When a general spherical nozzle was used with a laser power of 2 kW, for cutting thick plates, good cutting performance was achieved up to 12 mm thickness. When a dual-shape nozzle was used, good cutting quality was achieved up to 20 mm. The beam focal size on the surface of specimens was 254 ㎛ and the heat input range for cutting 20 mm thick plates was 44,900~46,300 J/㎠.

참고문헌 (104건) : 자료제공( 네이버학술정보 )

참고문헌 목록에 대한 테이블로 번호, 참고문헌, 국회도서관 소장유무로 구성되어 있습니다.
번호 참고문헌 국회도서관 소장유무
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98 "Laser processing heads for Fiber lasers Recent Developments for 10kW Laser power and Diffraction limited Beam Quality" 2nd lnternational workshop on Fiber laser, July. 2006. 미소장
99 "Effects of an Auto-tracking of the Focal Distance on the Quality of the Cut Part in the Laser Cutting of a Low Carbon Sheet," The Journal of Manufacturing Engineering & Technology, Vol. 16, pp. 101-107, 2007 미소장
100 Heiniger Modelling of Supersonic gas flow of Nozzles for laser cutting systems. 미소장
101 "brochure for Japanese market", 2006. 미소장
102 "The Strength Analysis of Passenger Car Seat Frame",KSAE, Vol.11, No.6, pp. 205-212, 2003. 미소장
103 "A Study on the Optimization of Aluminum Seat Slider Rail", KSAE, pp. 962-966, 2004. 미소장
104 ROFIN-SINAR Laser GmbH, "The Slab Principle, A Fact Book for the Most Advanced CO2 Laser in the World," 2007. 미소장

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