Young-Nam Ahn

CO2 laser-micro plasma arc hybrid welding for galvanized steel sheets

A laser lap welding process for zinc-coated steel has a well-known unsolved problem-porosity formation. The boiling temperature of coated zinc is lower than the melting temperature of the base metal, which is steel. In the autogenous laser welding, the zinc vapor generates from the lapped surfaces expels the molten pool and the expulsion causes numerous weld defects, such as spatters and blow holes on the weld surface and porosity inside the welds. The laser-arc hybrid welding was suggested as an alternative method for the laser lap welding because the arc can preheat or post-heat the weldment according to the arrangement of the laser beam and the arc. CO2 laser-micro plasma hybrid welding was applied to the lap welding of zinc-coated steel with zero-gap. The relationships among the weld quality and process parameters of the laser-arc arrangement, and the laser-arc interspacing distance and arc current were investigated using a full-factorial experimental design. The effect of laser-arc arrangement is dominant because the leading plasma arc partially melts the upper steel sheets and vaporizes or oxidizes the coated zinc on the lapped surfaces. Compared with the result from the laser-TIG hybrid welding, the heat input from arc can be reduced by 40%.

High-deposition-rate position welding of Al 5083 alloy for spherical-type liquefied natural gas tank

High-deposition-rate welding is used in the fabrication of liquefied natural gas tanks from thick aluminium plates because the weld defect generally increases and the productivity decreases with increasing number of passes. In this study, high-deposition-rate gas metal arc welding was implemented in vertical-up and horizontal positions. High deposition was achieved in the vertical-up position by pulse welding using 2.4-mm single wire and 1.6-mm twin wires and in the horizontal position by electromagnetic lifting of the weld pool. The arc stabilities for the applied processes were examined and welding procedures for thick plates were developed. A total of 14 welding passes were required for the vertical-up welding of a 70-mm thick plate by using the conventional 1.6-mm single-wire process, and the fully penetrated welds could be achieved with 8 welding passes by using twin-wire welding. Also, 10 welding passes were required for the horizontal welding of a 35-mm-thick plate by the conventional approach, and 6-pass full-penetration welding was successfully implemented by applying an external electromagnetic field.

Porosity Reduction during Gas Tungsten Arc-Gas Metal Arc Hybrid Welding of Zinc Coated Steel Sheets (II) - Hybrid Welding Results

The use of Zn coated steel has increased in the automotive industry due to its excellent corrosion resistance. Conventionally the BIW(body-in-white) structure and the hang-on parts have been made of Zn coated steel and more recently Zn coated steel began to be applied in the chassis parts. During gas metal arc (GMA) welding of the chassis part, lap fillet joint used to be adopted but spatter generation and porosities are most important concerns. In the industrial applications, an intentional joint gap was made to avoid the weld defects but it is not easy to control the size of joint gap. In this research, gas tungsten arc (GTA) is combined with GMA welding where GTA precedes GMA. As pulsed arc was adopted as GMA, GTA was oscillated along the longitudinal direction by pulsing GMA, but the arc oscillation did not disturb the molten droplet transfer of GMA welding. By increasing the distance between GTA and GMA, the length of weld pool increased and porosity could be reduced. Moreover porosity in the welds was fully removed when the distance between two arcs was 15 mm.

Comparison of Powder Feeding and Wire Feeding in Laser Cladding

Abst ract In this research, laser cladding characteristics were investigated for various filler metal feeding methods such as powder, cold wire, and hot wire feeding. Appropriate parameter window, deposition rate, material efficiency and dilution for each filler feeding method were evaluated with same laser power and cladding speed range. Laser powder cladding has wider process parameter window but higher material efficiency and lower dilution were achieved by laser wire cladding. Among these feeding methods, laser hot-wire cladding showed best efficiency in material usage and deposition rate.

Laser Welding of Automotive Aluminum Alloys

Si Fe Cu Mn Mg Cr Zn Ti5052 0.25 0.40 0.10 0.102.2~2.80.15~0.350.10 -5J32 0.25 0.040.1~0.50.205.0~6.00.20 0.20 0.106K21*1.00.130.010.070.540.010.010.016K320.8~0.150.400.5~0.70.150.4~0.70.20 0.10 0.1560050.6~0.90.35 0.10 0.100.4~0.60.10 0.10 0.107021 0.25 0.40 0.25 0.101.2~1.80.055.0~6.00.10* Mill sheet상의 성분조성

Porosity Reduction during Gas Tungsten Arc-Gas Metal Arc Hybrid Welding of Zinc Coated Steel Sheets (I) - Effect of Preceding Gas Tungsten Arc

The Zn coating on automotive galvanized steel sheets can improve corrosion resistance. However, the boiling temperature of Zn is lower than the melting temperature of steel and it causes well-known spatter and porosity problem. One of most prominent solutions is a pretreatment of Zn coating by an additional welding arc prior to the main welding process. In this research, GTA and GMA are selected as heat sources for pretreatment and main welding processes, respectively. The authors suggested three possible mechanisms to reduce weld defects by the GTA pretreatment: (1) Formation of gap between the sheets; (2) Evaporation of Zn layer; (3) Oxidation of Zn layer. Among them, Zn Oxidation is the most important mechanism to reduce weld defects in the GTA-GMA hybrid process.

Laser Welding of Automotive Transmission Components

Abstract In this research, laser welding of automotive transmission components was investigated to replace electronbeam welding which is normally conducted under vacuum condition. Fiber laser welding was applied to the automotive transmission components - hub clutch and annulus gear. In the component welding, the laser welding parameters were optimized to eliminate spatters and the end crater. By applying laser weldingto the transmission parts, the process time could be reduced up to 70% compared with the current electron beam welding process.Key Words : Automotive transmission, Laser, Welding, Electron beam welding, Parameter optimization (a) Annulus gear (b) Hub clutch assembly Fig. 1 Powertrain components 1. 서 론 레이저 용접은 고밀도 에너지빔을 이용하는 용접방법으로 레이저 빔을 재료표면에 조사하면 매우 빠른 시간 내에 에너지가 재료에 흡수되고 용융열로 변환되어 용융과 응고가 매우 빠르게 진행되는 고품위 용접방법이다. 자동차의 변속기는 엔진의 발생동력을 전달하는 부품으로 변속기의 효율 향상만으로도 10%이상의 연비향상이 가능한 고연비 자동차개발의 핵심부품이다. 자동차 변속기 부품의 경우 아직 국내에서 전자빔용접이 주로 이용되고 있으나 생산성이 높은 레이저 용접을 적용하려는 시도가 활발하다

Process Evaluation of Plasma-GMA Welding for Al 5052 and 6061 Alloy

In this study, the bead-on-plate welding were conducted by using GMA welding and plasma-GMA welding on Al 5052 and, Al 6061 plates. For these processes, the maximum welding speeds for full penetration were compared, and various weld qualities such as bead appearance, cross-section, cracks and porosities were examined. Faster welding speed, cleaner bead surface and more stable drop transfer could be achieved by plasma-GMA welding, compared with GMA welding.

Crack Susceptibility Reduction and Weld Strength Improvement for Al Alloy 5J32-T4 by using Laser Weaving Method

사용한 사다리꼴 시험편의 형상을 나타내고 있으며 용접은 좁은 면에서 넓은 면으로 진행된다. 이때 균열은 용접시작점에서 시작되며 용접방향으로 균열이 진전된다. 레이저 용접 속도는 50mm/s로 고정하였으며, 레이저출력, 위빙 폭, 위빙 주파수를 변화시켜 용접을 수행하였으며, 용접공정변수는 Table 2와 같다. 발생한 균열의 길이는 X-ray 시험을 통해 측정하였다. 전단인장강도는 겹치기 용접을 수행한 시편을 이용하여 평가하였으며, 가로길이, 세로길이, 두께가 각각 100mm, 50mm, 1mm인 박판재를 이용하여 Fig. 3와 같이 시험편을 제작하였다. 이 때, 레이저 용접속도는 50mm/s로 고정하였으며, 레이저 출력, 위빙 폭, 위빙 주파수를 변화시켜 겹치기 용접을 수행하였으며, Table 3은 각 실험에 사용한 용접공정변수를 나타낸다.

A Study to Improve Weld Strength of Al 6k21-T4 Alloy by using Laser Weaving Method

For Al 6k21-T4 alloy, linear laser welding produced the lower shear-tensile strength than the base metal. This study improved the shear-tensile strength by using the weaving laser at the optimized welding condition, i.e., 2mm weaving width and 25Hz frequency. The large weaving width increased the weld width, therefore improving the joint strength. For the specimen of low strength, the porosity was distributed continuously along the intersection between the plates and fusion line. However, for the optimized welding condition, large oval-shaped porosities were located only in the advancing track of the concave part. Regardless of the welding condition, solidification cracking was initiated at the intersection and propagated through small porosities in the weld part. furthermore, the concave part had more significant porosity in the weld and HAZ, respectively than the convex part. The continuity of porosities played a key role to determine the strength. And, the weaving width was an important parameter to control the strength.